ROAD SAFETY RESEARCH REPORT
CR 193
2000
The Development of a Protective Headband
for Car Occupants
Robert W G Anderson
Kirsten White
A Jack McLean
Road Accident Research Unit
University of Adelaide
Department of Transport and Regional Services
Australian Transport Safety Bureau
The Development of a Protective
Headband for Car Occupants
Robert W G Anderson, Kirsten White and A Jack McLean
Road Accident Research Unit
University of Adelaide
iii
AUSTRALIAN TRANSPORT SAFETY BUREAU
DOCUMENT RETRIEVAL INFORMATION
Report No. Date Pages ISBN ISSN
CR 193 January 2000 54 0 642 25502 4 0810-770X
Title and Subtitle
The Development of a Protective Headband for Car Occupants
Authors
Anderson RWG, White K and McLean AJ
Performing Organisation
Road Accident Research Unit
University of Adelaide
South Australia 5005
Sponsored by / Available from
Australian Transport Safety Bureau
PO Box 967
CIVIC SQUARE ACT 2608
Project Officer: John Goldsworthy
Abstract
This report addresses the development of a protective headband for car occupants. It
focuses on the investigation of suitable materials for the headband by examining their
impact absorbing properties. Tests consisted of: a series of impacts where material was
interposed between a steel slab and the headform dropped from a height; a series a of
drop tests where prototype headbands were attached to a headform and dropped
against standard helmet testing anvils; and a series of tests with the most promising
prototypes in which the headband was attached to the headform and then fired against
an internal structure of a passenger car. Two prototype concepts appear worthy of
further investigation: a headband constructed of polyurethane foam and a headband
consisting of a cardboard honeycomb liner encased in a hard shell both significantly
reduced the severity of impacts with the car structures. However, further investigation
into optimising the selection of materials for their impact absorbing qualities and their
comfort and durability in normal use is warranted. These tests demonstrate that a
headband for car occupants could significantly reduce the severity of certain head
impacts in a crash. The best prototype headband reduced the HIC and peak
acceleration values by over 60 percent in a standard test with the interior of the car.
The reduced impact was approximately equivalent in severity to an unprotected impact
with the structure at half the speed.
Keywords
HEADBAND, HELMET, OCCUPANT PROTECTION, HEAD INJURY, PADDING,
IMPACT
NOTES:
(1) This report is disseminated in the interests of information exchange.
(2) The views expressed are those of the author(s) and do not necessarily represent those of the
Commonwealth. Reproduction of this page is authorised
v
Executive summary
In 1997 McLean et al. (1997) demonstrated that energy absorbing headwear for car
occupants might be effective in reducing the numbers of head injuries sustained by car
occupants. The estimated benefits were greater than the estimated benefits of padding of the
upper interior of vehicles to the requirements of the US Federal Motor Vehicle Safety
Standard 201. This report investigates the suitability of selected materials for head
protection, in the form of a headband that could be worn by car occupants.
The study is divided into three phases. Phase 1 surveys materials with a range of properties
and impact behaviours. Impact tests provided the data by which assessments were made of
the materials’ effectiveness. The tests in this phase showed that a range of materials were
able to attenuate the severity of the impact to a reasonable degree.
The materials identified in Phase 1 were tested further in Phase 2. Prototype headbands
were constructed and attached to instrumented headforms which were dropped onto
standard helmet testing anvils. The purpose of these tests was to examine the prototypes’
response to concentrated loading. Several prototypes showed themselves to be unable to
perform adequately in these tests; the anvils split or shattered the headband. Several
prototype designs did perform well in Phase 2. These designs were tested in simulated head
strikes with vehicle structures in Phase 3.
Phase 3 consisted of a series of preliminary tests in which a headform, protected by the
prototype headband, was fired toward an interior structure that commonly causes head
injury to car occupants in crashes.
Two prototype concepts appear worthy of further investigation. A headband constructed of
polyurethane foam and a headband consisting of a cardboard honeycomb liner encased in a
hard shell both significantly reduced the severity of impacts with the car structures.
However, further investigation into optimising the selection of materials for their impact
absorbing qualities and their comfort and durability in normal use is warranted.
These tests demonstrate that a headband for car occupants could significantly reduce the
severity of certain head impacts in a crash. The best prototype headband reduced the HIC
and peak acceleration values by over 60 percent in a standard test with the interior of the
car. The reduced impact was approximately equivalent in severity to an unprotected impact
with the structure at half the speed.
_______________________________
Robert Anderson, Principal Investigator
vii
Contents
Executive summary...............................................................................................................................................................1
Contents .............................................................................................................................................................................vii
List of tables.........................................................................................................................................................................ix
List of figures........................................................................................................................................................................x
1. Introduction..............................................................................................................................................................1
1.1. Background.....................................................................................................................................................1
1.1.1. The requirements of FMVSS 201.......................................................................................................2
1.1.2. Characteristics of padding..................................................................................................................2
1.1.3. Padding for injury prevention............................................................................................................3
1.1.4. Selection of padding for head protection.........................................................................................3
1.2. Aims of this Project........................................................................................................................................4
1.3. Methodology..................................................................................................................................................5
Phase 1.......................................................................................................................................................................5
Phase 2.......................................................................................................................................................................5
Phase 3.......................................................................................................................................................................5
2. Phase 1.......................................................................................................................................................................7
2.1. Method............................................................................................................................................................7
2.2. Candidate Materials .......................................................................................................................................9
2.2.1. Closed Cell Polyolefin Foams .............................................................................................................9
2.2.2. ViscoElastic Foams ..............................................................................................................................9
2.2.3. Honeycomb cardboard ........................................................................................................................9
2.2.4. Polyurethane Foams ..........................................................................................................................10
2.2.5. Polystyrene Foams .............................................................................................................................10
2.3. Results ...........................................................................................................................................................11
2.3.1. Baseline results...................................................................................................................................11
2.3.2. Closed cell polyolefin foams.............................................................................................................12
2.3.3. ViscoElastic Foams ............................................................................................................................13
2.3.4. Honeycomb cardboard ......................................................................................................................19
2.3.5. Polyurethane Foams ..........................................................................................................................22
2.3.6. Polystyrene Foams .............................................................................................................................24
2.4. Summary ........................................................................................................................................................25
3. Phase 2 testing .......................................................................................................................................................29
3.1. Method..........................................................................................................................................................29
3.2. Candidate Materials .....................................................................................................................................31
3.3. Results ...........................................................................................................................................................32
3.3.1. Hemispherical Anvil Tests................................................................................................................32
3.3.2. Sharp Anvil tests................................................................................................................................33
3.4. Discussion.....................................................................................................................................................35
4. Phase 3 testing .......................................................................................................................................................37
4.1. Method..........................................................................................................................................................37
4.2. Candidate Materials .....................................................................................................................................38
4.3. Results ...........................................................................................................................................................39
4.3.1. B-pillar..................................................................................................................................................39
4.4. Discussion.....................................................................................................................................................40
5. Conclusions and recommendations....................................................................................................................41
6. References...............................................................................................................................................................43
ix
List of tables
Table 1. Materials tested in Phase 1 of the study ..............................................................................................11
Table 2. Results for closed cell polyolefin foams, drop height 1.0 m..............................................................12
Table 3. Results comparing two grades of Confor foam...................................................................................13
Table 4. Results for Confor foam from two drop heights ..................................................................................14
Table 5. Effect of thickness of viscoelastic foam at various drop heights and temperatures .....................16
Table 6. Results showing the effect of temperature on Confor foam..............................................................18
Table 7. Phase 1 results for honeycomb cardboard ...........................................................................................21
Table 8. Phase 1 results for polyurethane foams................................................................................................22
Table 9. Phase 1 results for polystyrene foams ..................................................................................................25
Table 10. Drop Height 1.0 m, velocity 16.0 km/h, and material thickness 25 mm ...........................................26
Table 11. Drop Height 1.45 m, velocity 19.2 km/h, and material thickness 25 mm .........................................27
Table 12. Materials tested in Phase 2...................................................................................................................31
Table 13. Results of headband tests on the hemispherical anvil (drop height 1.385 m, velocity 18.8 km/h)
.........................................................................................................................................................................32
Table 14. Results of tests on the sharp anvil......................................................................................................34
Table 15. Prototypes tested in Phase 3................................................................................................................39
Table 16. Results from Phase 3 - Tests at 23 km/h horizontally against the B-pillar of a 1977 Toyota
Corolla station wagon..................................................................................................................................39
List of figures
Figure 1 Head impact locations recorded in McLean et al. (1997).....................................................................2
Figure 2. Force/deflection characteristics of rigid materials and semi-rigid materials .....................................3
Figure 3. Approximate relationship between padding stiffness and impact speed for HIC<1000, assuming
a head mass of 4.7 kg .....................................................................................................................................4
Figure 4. The EEVC WG10 headform used in the study......................................................................................8
Figure 5. The test setup used in Phase 1...............................................................................................................8
Figure 6. Photograph of the cells in the honeycomb cardboard ......................................................................10
Figure 7. The force/displacement characteristics of the EEVC headform in a drop test onto the steel slab
from a height of 1.0 m...................................................................................................................................12
Figure 8. Effect of type of 25mm Confor foam, drop height 1.0 m....................................................................14
Figure 9. Effect of drop height on 25 mm CF45100 at 15° C...............................................................................15
Figure 10. Effect of drop height on 25 mm CF45100 at 25° C.............................................................................15
Figure 11. Effect of thickness on the effectiveness of CF45100 at elevated temperatures, drop height 1.0
m......................................................................................................................................................................16
Figure 12. Effect of thickness on the effectiveness of CF45100 at lower temperatures, drop height 1.45 m
.........................................................................................................................................................................17
Figure 13. Effect of thickness on the effectiveness of CF47100 at lower temperatures, drop height 1.0 m17
Figure 14. Effect of thickness on the effectiveness of CF47100 at elevated temperatures, drop height 1.0
m......................................................................................................................................................................18
Figure 15. Effect of Temperature on the effectiveness of 25 mm CF45100, drop height 1.0 m.....................19
Figure 16. Typical Force Displacement Curve for 45 mm thick Honeycomb cardboard...............................21
Figure 17. Force/displacement characteristics measured in tests on the polyurethane foams from a drop
height of 1.0 m. ..............................................................................................................................................22
Figure 18. Force/displacement characteristics measured in tests on the polyurethane foams from a drop
height of 1.45 m.............................................................................................................................................23
Figure 19. Durability of Polyurethane Foams, drop height 1.0 m.....................................................................24
Figure 20. Durability of Polyurethane Foams, drop height 1.45 m...................................................................24
Figure 21. Force/deflection curves for polystyrene foams of varying thickness, drop height 1.0 m.........25
Figure 22. Force/deflection curves of various materials, 25 mm thick, drop height 1.0 m............................27
Figure 23. Force/deflection curves of various materials, 25 mm thick, drop height 1.45 m..........................28
Figure 24. Sharp anvil for helmet testing from the Australian Standard "Helmets for horse riding and
horse related activities" (AS/NZS3838:1998) ...........................................................................................30
xi
Figure 25. Hemispherical anvil for helmet testing from the Australian Standard "Determination of impact
energy attenuation - helmet drop test" (AS2512.3.1)..............................................................................30
Figure 26. Phase 2 drop testing setup..................................................................................................................31
Figure 27. Hemispherical anvil drop test results.................................................................................................33
Figure 28. Sharp anvil drop test results ...............................................................................................................35
Figure 29. The aluminium headform used in Phase 3 tests ...............................................................................37
Figure 30. Test setup for B-pillar test...................................................................................................................38
Figure 31. Phase 3, B-pillar Test Results..............................................................................................................39
Figure 32. Force defelection curve and work done by the headband in test 17069901................................40
1. Introduction
1.1. Background
Car crashes remain a significant source of head injury in the community. Car occupants have
an annual hospital admission rate of around 90 per 100,000 population. Of drivers who are
admitted to hospital, the most serious injury is usually to the head (O'Conner and Trembath,
1994).
In a previous study, McLean et al. (1997) estimated the benefits that are likely to accrue to
Australia from the use of padding of the upper interior of the passenger compartment. This
study specifically examined the effects of the ammendment to the United States Federal
Motor Vehicle Safety Standard 201 (FMVSS 201) in which passenger cars have to pass
head impact tests with the upper interior. That report estimated the total annual reduction in
harm to the Australian community to be around $123 million. But more impressive were the
estimates of introducing protective headwear for car occupants. The authors of the report
estimated that the annual reduction in harm would be in the order of $380 million. The
benefit of padding the head is that the head is protected from strikes with unpadded
automotive components, exterior objects and in vehicles that predate any eventual
introduction of padded interiors.
The same report examined the distribution of impacts to the head of occupants who
sustained a head injury. The data were drawn from a sample of crashes that occurred in
South Australia and had been investigated by members of the Road Accident Research
Unit. Impacts tended to be distributed about the cranium of the head rather than to the face,
and significant proportions of impacts occurred about the side and front of the head (see
Figure 1). In 44 per cent of these cases, the impact was to a region of the head that could
have been covered by some sort of protective headband.
2
The development of a protective headband for car occupants
Figure 1 Head impact locations recorded in McLean et al. (1997) are displayed as
dots. The ‘RARU headband’ is superimposed. It covers 44% of the recorded
impacts (from McLean et al. 1997)
1.1.1. THE REQUIREMENTS OF FMVSS 201
FMVSS 201 requires vehicles to pass a test in which a 15 pound (6.7 kg) headform is fired
at upper interior structures of the passenger compartment at 15 mph (24.15 km/h). The
design requirement is that the headform acceleration should not exceed 80 g for more than 3
ms.
1.1.2. CHARACTERISTICS OF PADDING
Padding materials commonly used in applications where crash protection is required can be
broadly classified as rigid or semi-rigid. Rigid foams used in crash protection are stiffer
than semi-rigid foams and deform primarily in a plastic (non-recoverable) manner. Semi-
rigid foams generally recover their shape after deformation and deform in a more elastic or
viscoelastic manner than rigid foams. Lockett et al. (1981) tested the characteristics of a
series of materials commonly used in crash padding. They found that rigid materials exhibited
characteristically different force/deflection behaviour than semi-rigid materials. The
differences in their behaviour are illustrated in Figure 2, which shows dynamic
force/deflection curves for rigid and semi-rigid materials. Rigid materials (Figure 2, left) are
stiff up to their yield strength and so they resist deformation. Beyond this yield strength, they
deform with little change in resistive force. During the unloading phase, the force rapidly
drops to zero, and very little energy is returned to the system. This is due to the plastic
Introduction
3
nature of the yielding phase. Semi-rigid materials (Figure 2, right) may show some yielding
behaviour during their loading phase, but behave in a more elastic manner, with the load
increasing with deformation more or less constantly. These materials may return more energy
to the system than a rigid material during the unloading phase.
Figure 2. Force/deflection characteristics of rigid materials (left) and semi-rigid
materials (right)
In addition to these variations in behaviour, the characteristics of many materials are also
rate sensitive. This means that the exact nature of their force/deflection curve is dependent
upon the initial velocity of the object striking the material. The characteristics of rate sensitive
materials are often described in terms of viscoelasticity.
1.1.3. PADDING FOR INJURY PREVENTION
Padding protects the body by absorbing some of the energy of impact and by reducing the
peak loads applied to the part of the body being struck by spreading the change in velocity
of the body over a longer period. Padding may also protect the body by spreading the load
over a larger contact area.
The selection of padding is linked to the design criteria used to assess the risk of injury. For
the prevention of head injuries, the requirement may be to minimise the peak acceleration of
a testing headform, the level of the Head Injury Criterion (HIC) or the peak 3 ms
acceleration of the headform. It has been widely reported that these types of measures may
not sufficiently describe the risk of head injury for a given impact; the measures say nothing
of any localised loading, which may increase the risk of skull fracture, and they ignore the
angular acceleration imparted to the head. Angular acceleration is hypothesised to be a
significant mechanism of diffuse type brain injuries. Nevertheless, these measures probably
bear some relation to the risk of some forms of head injury and minimising these measures is
likely to reduce the risk posed by other mechanisms of injury.
1.1.4. SELECTION OF PADDING FOR HEAD PROTECTION
There is published research on the selection of crash padding materials based on particular
design applications for minimising the risk of head injury in an impact. The work of Monk
and Sullivan (1986) is relevant to preventing injuries from head impacts with the upper
interior of the passenger compartment. They reported a methodology for the selection of
F
o
r
c
e
deflection deflection
Force
loading
unloading
loading
unloading
4
The development of a protective headband for car occupants
padding materials for protecting the head in strikes with the A-pillar of vehicles. The
methodology starts with an analytical representation of a head impact and an approximation
function for the Head Injury Criterion (HIC). From the analysis, they were able to construct
a curve that describes the maximum allowable stiffness of a material that would produce a
HIC value of 1000 (the maximum allowable), for impacts with a 4.7 kg headform, over a
range of impact velocities. That curve is reproduced in Figure 3. The notable feature of the
curve is that the stiffness requirements of effective crash padding materials is not constant for
all impact speeds.
10 20 30 40 50 60
0
200
400
600
800
1000
1200
impact speed (km/h)
maximum allowable stiffness (kN/m)
HIC>1000
HICŠ1000
Figure 3. Approximate relationship between padding stiffness and impact speed for
HIC<1000, assuming a head mass of 4.7 kg (Monk and Sullivan, 1986)
Monk and Sullivan went on to conduct a series of static and dynamic tests to discern the
stiffness and energy absorbing characteristics of a range of crash padding materials. The
padding material was placed against a rigid surface for the tests so that only the stiffness of
the material (and not its supporting structure) was measured. They used the results and the
analytical techniques they had developed to estimate the characteristics of desirable foams
and to aid their selection of materials for the next stage of the testing. A headform was fired
at a simulated A-pillar and the candidate materials that had been identified from the previous
testing were interposed between the headform and the A-pillar. All padding samples were
one inch thick and they all significantly reduced the severity of the impact. Based on their
research they concluded that one inch of padding could significantly reduce the severity of
the impact between the head and A-pillar at 25 mph (40 km/h).
1.2. Aims of this Project
The work cited above indicates that some form of protective headwear might reduce the
severity of impacts and resulting injuries to car occupants in crashes. This report examines
Introduction
5
the technical feasibility of such headwear by measuring the characteristics of candidate
materials and the performance of such headwear in simulated crash situations. Specifically,
the aims of the study are to:
• test the characteristics of materials suitable for use in a headband, and to
• test prototype headbands to evaluate their effectiveness in reducing the severity of
headform impacts with vehicle structures in simulated crash situations.
1.3. Methodology
Candidate materials were assessed using three methods as outlined below.
PHASE 1
A headform simulating the mass of a human head was dropped onto candidate materials at
different velocities. The materials were placed on a rigid and massive steel slab, so the test
measured the impact characteristics of the material only. The design of the test accounted for
the temperature of the material, the thickness of the material and the durability of the material
where appropriate.
PHASE 2
Prototype headbands were constructed from the materials that performed well in Phase 1.
The headform, with the headband attached, was dropped onto standard helmet testing anvils
to see how the performance of the headbands compared to standard measures of helmet
performance. Two anvils were used; a hemispherical anvil, and a sharp edged anvil.
PHASE 3
The better performing prototype headbands were attached to a headform and fired at
various internal structures of a vehicle. The impact severity was compared to tests in which
no padding was attached to the headform.
2. Phase 1
2.1. Method
The tool used for testing the performance of the materials in Phase 1 was the 'adult'
headform proposed by Working Group 10 of the European Experimental Vehicles
Committee for the assessment of pedestrian head protection1. This headform consists of a
sphere of phenolic resin with a diameter of 165 mm. The sphere is covered with a silicon
rubber skin to simulate the compliance of the scalp and bone of a human head. A steel insert
in the sphere is used to adjust the weight of the headform to 4.8 kg and to house a tri-axial
accelerometer to measure the acceleration of the headform on impact. The headform is
illustrated in Figure 4.
Each material was tested by placing it on a massive steel slab. Some materials were tested at
elevated temperatures by heating for several minutes in a stream of hot air prior to the test.
The temperature of the material was measured immediately following the test. The headform
was suspended above the material and dropped from a predetermined height. The resulting
impact acceleration was recorded using a high-speed data acquisition system (50 kHz) after
being passed through a 10 kHz analogue filter. The resulting acceleration data was then
filtered according to SAE CFC 1000. The test setup is illustrated in Figure 5.
The peak acceleration was noted and the Head Injury Criterion (HIC) was calculated for
each test. The HIC is the criterion most commonly used for head injury risk assessment. It is
calculated according to the formula
HIC =(t2−t1)adt
t1
t2
∫t2−t1
2
.
5
where t2 and t1 are chosen so that the function is maximised. Impacts that produce HIC
values of more than 1000 are considered to be unacceptably severe.
1 The headform will be referred hereafter as the EEVC WG10 headform
8
The development of a protective headband for car occupants
Figure 4. The EEVC WG10 headform used in the study
Figure 5. The test setup used in Phase 1
The force experienced by the headform was calculated and plotted against the displacement
of the material in each test. The displacement was calculated by identifying the beginning and
end of the acceleration and integrating the acceleration twice within those bounds. In some
tests the beginning of the pulse is difficult to identify and so there may be some error in the
maximum displacement calculated in each experiment. The force was calculated by
multiplying the acceleration experienced by the headform by the mass of the headform.
EEVC WG10
headform
Test
material
Steel
slab
Phase 1 Tests
9
2.2. Candidate Materials
2.2.1. CLOSED CELL POLYOLEFIN FOAMS
Five samples of cross-linked closed cell polyolefin foams were obtained from Pilon Plastics
Pty Ltd. According to the suppliers, the foams have been used for impact protection in
cricket helmet linings, rugby headgear and jockey vests. The samples varied in thickness
from 2 mm to 17 mm. The supplier suggested that a certain combination of materials may
work well, and this combination was tested along with the individual materials. The last two
materials are examples from the Pilon "Playground Softfall Underlay" range. These materials
are designed to absorb impacts in playground falls.
The materials tested were:
• SPS2515 Beige, 15 mm thick
• E3015 White, 15 mm thick
• S1002 Black, 2 mm thick
• S3004/Weave/S3008 Black, 12 mm thick
• S1002/Weave/E3015 Yellow/Grey, 17 mm thick
2.2.2. VISCOELASTIC FOAMS
Confor Foam exhibits viscoelastic behaviour. If it is struck slowly it is relatively soft, but it is
stiffer if struck at a higher velocity. At higher velocities, the foam becomes stiffer, maximising
the energy absorbed over the crush depth of the material. Confor foam is often used to
represent human flesh on crash test dummies, as its dynamic behaviour is similar to that of
flesh.
Two grades of Confor Foam were tested; CF45100 Blue, and CF47100 Green, both
obtained in 25 mm thick sheets.
2.2.3. HONEYCOMB CARDBOARD
Honeycomb cardboard is made of kraft paper that is glued together in a honeycomb
pattern, then sandwiched between two sheets of kraft paper, so that the cells of the
honeycomb run perpendicular to the surface of the sheet. In an impact normal to the surface
of the sheet the paper cells buckle and crush, absorbing the energy of the impact.
Honeycomb cardboard is used for packaging, and the samples tested were sourced from
the packaging of automotive parts.
Two grades of honeycomb cardboard were tested, at various thicknesses. The fine grade
had cells approximately 12.5 mm in size, and the coarse grade had cells approximately 18
mm in size. Figure 6 shows the structure of the cells after the outer sheet of kraft paper has
been removed. The sample on the left is the fine grade, the sample on the right is the coarse
grade.
10
The development of a protective headband for car occupants
Figure 6. Photograph of the cells in the honeycomb cardboard
2.2.4. POLYURETHANE FOAMS
Polyurethane foams exhibit a range of material behaviours; they can be designed to behave
in flexible, semi-rigid or rigid manners.
Several semi-rigid polyurethane foams were obtained from the Woodbridge Group, an
American automotive materials developer and manufacturer. An Australian company, Orica
supplied several equivalent (and Australian made) automotive polyurethane foams. Several
of the grades of polyurethane that were tested are being promoted by their producers as
appropriate foams to pad the upper interiors of vehicles, in response to FMVSS 201.
2.2.5. POLYSTYRENE FOAMS
Polystyrene is the primary material used for the energy absorbing liner of bicycle and
motorcycle helmets in Australia. Polystyrene is an obvious candidate material for head
protection for car occupants. The grade of polystyrene tested in this study is one used in
helmet manufacture. Samples 6 mm to 25 mm thick were tested.
Table 1 lists the materials surveyed in Phase 1 of the study.
Phase 1 Tests
11
Table 1. Materials tested in Phase 1 of the study
Material name Supplier Category Thickness tested
SPS251 Pilon Plastics Pty Ltd. Closed cell foam 15 mm
E3015 Pilon Plastics Pty Ltd. Closed cell foam 15 mm
S1002 Pilon Plastics Pty Ltd. Closed cell foam 2 mm
S3004/Weave/S3008 Pilon Plastics Pty Ltd. Closed cell foam 12 mm
S1002/Weave/E3015 Pilon Plastics Pty Ltd. Closed cell foam 17 mm
CF45100 E-A-R Specialty
Composites Viscoelastic foam 25 mm, 50 mm
CF47100 E-A-R Specialty
Composites Viscoelastic foam 25 mm
Honeycomb cardboard
12 mm cell Unknown* Honeycomb
cardboard 15 mm, 30 mm
Honeycomb cardboard
18 mm cell Unknown* Honeycomb
cardboard 45 mm, 70 mm
E175 Woodbridge Group Automotive EA
polyurethane foam 25 mm
E900, 5.6 pcf Woodbridge Group Automotive EA
polyurethane foam 25 mm
E900, 6.0 pcf Woodbridge Group Automotive EA
polyurethane foam 25 mm
BB-38 Woodbridge Group Automotive EA
polyurethane foam 25 mm
Polystyrene foam Lactec Foam Products Polystyrene Foam 6 mm. 10 mm, 15 mm,
20 mm, 25 mm
*Sourced from packaging material for automotive body panels
2.3. Results
2.3.1. BASELINE RESULTS
For comparison with the results of tests in this report, Figure 7 shows the force/deflection
characteristics of the unprotected EEVC WG10 headform, in a drop test onto the steel slab
from a height of 1.0 m. This test produced a peak acceleration of 650 g and a
corresponding HIC value of 4640.
12
The development of a protective headband for car occupants
00.005 0.01 0.015 0.02 0.025 0.03 0.035
0
0.5
1
1.5
2
2.5
3x 10
4Force/displacement curve in z axis - test14089811
displacement (m)
Figure 7. The force/displacement characteristics of the EEVC headform in a drop
test onto the steel slab from a height of 1.0 m
2.3.2. CLOSED CELL POLYOLEFIN FOAMS
Five samples of closed cell polyolefin foams were tested alone, and in combination, as
suggested by the supplier. The foams were initially tested from a drop height of 1.0 m, and it
was intended that all foams be retested from a larger drop height, but as the closed cell
foams did not perform as well as other materials, it was decided that no further tests should
be done. A summary of the results for the closed cell foams is given in Table 2.
Table 2. Results for closed cell polyolefin foams, drop height 1.0 m
Material type Thickness
(mm) Peak acceleration
(g) HIC Test number
#5 yellow side up 17 323 1720 24089801
#5 grey side up 17 290 1440 24089802
32 205 900 24089804
32 214 970 24089805
32 223 1050 24089806
32 237 1130 24089808
32 234 1100 24089809
Combination of #1, #2 and
#3 (repeat tests)
32 229 1090 24089810
#3 on #2 17 322 1870 24089807
#4 12 352 2020 24089811
Phase 1 Tests
13
Material type Thickness
(mm) Peak acceleration
(g) HIC Test number
#5 yellow side up on #2 32 183 800 24089812
#1 15 425 2920 24089813
#2 15 379 2080 24089814
#1 on #2 30 263 1320 24089815
1. SPS2515 Beige, 15 mm thick
2. E3015 White, 15 mm thick
3. S1002 Black, 2 mm thick
4. S3004/Weave/S3008 Black, 12 mm thick
5. S1002/Weave/E3015 Yellow/Grey, 17 mm thick
The average HIC value for 32 mm of closed cell foam, made up of a combination of foams
1, 2 and 3 was 1040, and the average HIC for 17 mm of closed cell foam was 1680. These
results were judged poor by comparison with the results of tests using alternative materials.
2.3.3. VISCOELASTIC FOAMS
Two types of viscoelastic foam were tested, both forms of Confor foam. They were
CF45100 and CF47100. The materials were compared in a test where the headform was
dropped onto the material from a height of 1 m. The results are shown in Table 3, and
illustrated in Figure 8. CF45100 and CF47100 performed similarly, with resultant HIC and
peak acceleration within 10%. CF47100 is slightly stiffer however (as indicated by the
steeper slope of the force displacement curve).
Table 3. Results comparing two grades of Confor foam
Material
type Drop
height
(m)
Velocity
(km/hr) Thickness
(mm) Temp.
(°C) Peak
acceleration
(g)
HIC Test
number
CF-45100 1.00 16.0 25 17 102 300 14089810
CF-47100 1.00 16.0 25 16.5 91 270 27089812
14
The development of a protective headband for car occupants
Figure 8. Effect of type of 25mm Confor foam, drop height 1.0 m
Confor foam CF-45100 was also tested from a drop height of 1.45 m. The results of tests
at the two drop heights and two temperatures are presented in Table 4. The results show
that increasing drop height from 1.0 m to 1.45 m (an increase in velocity from 16 to 19.2
km/h, and a 45% increase in impact energy) caused HIC to more than double, and
increased the peak accelerations by between 50 to 100%. The force displacement curves
for the first pair of tests at 15° C, in Table 4 are shown in Figure 9. The figure shows that
the increase in impact severity was due to the material bottoming out; i.e. the material crush
depth was fully utilised before the headform’s energy had been absorbed by the material.
Figure 10 shows the force displacement curves for the pair of tests performed at 25 ° C
(see Table 4). Both Figure 9 and Figure 10 show that the peak force increases with drop
height, and that the initial stiffness of the CF45100 (indicated by the slope of the curve) was
not affected by the increase in impact velocity from 16 to 19.2 km/hr.
Table 4. Results for Confor foam from two drop heights
Material
type Drop
height
(m)
Velocity
(km/hr) Thickness
(mm) Temp.
(°C) Peak
acceleration
(g)
HIC Test
number
CF-45100 1.0 16.0 25 17 102 300 14089810
1.45 19.2 25 15 204 880 14089802
1.0 16.0 25 27 191 660 27089812
1.45 19.2 25 25 282 1490 14089808
Phase 1 Tests
15
Figure 9. Effect of drop height on 25 mm CF45100 at 15° C
Figure 10. Effect of drop height on 25 mm CF45100 at 25° C
The effect of doubling the thickness of the foam is shown in Table 5. In these tests the foam
was tested at a low temperature and at an elevated temperature and at drop heights of 1 m
and 1.45 m.
16
The development of a protective headband for car occupants
Table 5. Effect of thickness of viscoelastic foam at various drop heights and
temperatures
Material
type Drop
height
(m)
Velocity
(km/hr) Thickness
(mm) Temp.
(°C) Peak
acceleration
(g)
HIC Test
number
CF-45100 1.0 16.0 25 42 262 1120 27089808
50 50 114 330 27089809
1.45 19.2 25 15 204 880 14089802
50 15 78 280 14089803
CF-47100 1.0 16.0 25 16.5 91 270 14099801
50 16.5 67 180 14099802
25 41 270 1190 14099805
50 37 64 140 14099804
When the thickness of the Confor Foam was doubled, the resulting HIC was reduced by
between 30 and 88%. The most dramatic reductions in HIC were obtained when the foam
was hot (the first and last pair of tests shown in Table 5); the addition of a second layer
prevented the test from bottoming out,. The effect of doubling the thickness of foam when
testing the material at an elevated temperature is illustrated in Figure 11 and Figure 14. Even
at the lower temperature of 15° C, there was a significant reduction in impact severity. The
effects of foam thickness at this temperature are illustrated in Figure 12 and Figure 13.
25mm of CF45100 at 42ÞC
50mm of CF45100 at 50ÞC
0 10 20 30 40 50 60 70
0
5
10
15
displacement(mm)
Figure 11. Effect of thickness on the effectiveness of CF45100 at elevated
temperatures, drop height 1.0 m
Phase 1 Tests
17
Figure 12. Effect of thickness on the effectiveness of CF45100 at lower
temperatures, drop height 1.45 m
Figure 13. Effect of thickness on the effectiveness of CF47100 at lower
temperatures, drop height 1.0 m
18
The development of a protective headband for car occupants
Figure 14. Effect of thickness on the effectiveness of CF47100 at elevated
temperatures, drop height 1.0 m
At low temperatures, Confor foam performed well, absorbing energy and reducing the
impact severity. But at temperatures approaching that of the human body (30°C and above)
the foam became very compliant. Its ability to reduce the severity of an impact became
compromised. A summary of the effect of temperature on Confor Foam is given in Table 6
which shows that increasing the temperature of CF45100 from 17° C to 27° C increases the
HIC result from 300 to 660. Increasing the temperature to 42° C produced a HIC of 1120.
Similar results are obtained in tests performed with a drop height of 1.45 m. CF47100
behaves similarly at elevated temperatures.
Table 6. Results showing the effect of temperature on Confor foam
Material
type Drop
height
(m)
Velocity
(km/hr) Thickness
(mm) Temp.
(°C) Peak
acceleration
(g)
HIC Test
number
CF-45100 1.00 16.0 25 17 102 300 14089810
27 191 660 27089812
42 262 1120 27089808
CF-45100 1.45 19.2 25 15 204 880 14089802
25 282 1490 14089808
CF-47100 1.00 16.0 25 16.5 90.6 270 14099801
31 219 800 14099803
41 270 1190 14099805
Phase 1 Tests
19
Figure 15 shows the force/displacement curves for the first three tests shown in Table 6. It
illustrates the effect of temperature on the performance of Confor foam in these tests. At low
temperatures, the Confor foam exhibits near ideal impact absorption properties; the force is
almost constant during the second half of the displacement. At higher temperature, the foam
softens. With softening, the foam is no longer as effective in absorbing energy so the material
bottoms out. This causes a sharp increase in the peak load applied to the headform.
Figure 15. Effect of Temperature on the effectiveness of 25 mm CF45100, drop
height 1.0 m
2.3.4. HONEYCOMB CARDBOARD
Two grades of honeycomb cardboard (12.5 mm and 18 mm cell size) were tested. Different
thicknesses were tested at two drop heights. A summary of the results for the honeycomb
cardboard is given in
20
The development of a protective headband for car occupants
Table 7.
The honeycomb cardboard performed well in Phase 1 tests. It had the lowest HIC of any
material tested at the 1.0 m drop height. This low HIC is achieved because of the
mechanism by which the cardboard absorbs energy under impact loading. In an impact
normal to the surface of the sheet, the paper walls of the cells in the honeycomb buckle and
crush under the load, absorbing energy, without returning any energy to the headform in the
unloading phase.
Selecting an appropriate combination of cell size, paper thickness, and paper strength
controls the crushing strength of the honeycomb. In Figure 16, the force during the impact
reaches a maximum of about 2000 N at 20 mm displacement, and remains nearly constant
for the remaining displacement. This represents near ideal energy absorption behaviour; the
load reaches its maximum relatively quickly, then stays almost constant until all the impact
energy is absorbed.
Phase 1 Tests
21
Table 7. Phase 1 results for honeycomb cardboard
Test
number Drop
height
(m)
Velocity
(km/hr) Material type Thickness
(mm) Temp.
(°C) Peak
acceleration
(g)
HIC
26059905 1.00 15.9 Small celled
honeycomb
cardboard
15 16.0 285 1190
17129820 1.435 19.1 Small celled
honeycomb
cardboard
2x15 25.5 104 440
17129801 1.43 19.1 Large celled
honeycomb
cardboard
45 25.5 51 140
17129821 1.405 18.9 Large celled
honeycomb
cardboard
70 25.5 66 210
00.01 0.02 0.03 0.04 0.05 0.06 0.07
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000 Force/displacement curve in z axis - test17129801
displacement (m)
Figure 16. Typical Force Displacement Curve for 45 mm thick Honeycomb
cardboard
There may be several disadvantages with using honeycomb cardboard as headband
material. Being made of paper, it is sensitive to moisture. The presence of moisture (from
perspiration, for example) may cause the performance of the headband to deteriorate. Also,
the cardboard may not be durable in use, storage, and misuse. However, honeycombs made
of alternative materials such as aluminium, polymers, or polymer-coated paper may
overcome some of these problems. If so, honeycomb made from an alternative material may
be a promising material for the headband.
22
The development of a protective headband for car occupants
2.3.5. POLYURETHANE FOAMS
Four types of Automotive Energy Absorbing (EA) Polyurethane foam were tested at 25 mm
thickness, and two different drop heights. A summary of the results is given in Table 8.
Figure 17 and Figure 18 show the force/displacement curves for the materials at each drop
height. All the polyurethane foams that were tested performed similarly at the lower drop
height. At the greater drop height, larger differences between the materials emerged.
Table 8. Phase 1 results for polyurethane foams
Drop
height
(m)
Velocity
(km/hr) Thickness
(mm) Temp.
(°C) Material type Peak
acceleration
(g)
HIC Test
number
1.00 15.9 25 25 BB-38 140 560 15129801
E175 129 450 15129805
E900, 5.6 pcf 129 460 15129809
E900, 6.0 pcf 135 490 15129813
1.45 19.2 25 25.5 BB-38 208 1119 17129804
E175 198 962 17129808
E900, 5.6 pcf 260 1532 17129813
E900, 6.0 pcf 227 1234 17129816
Figure 17. Force/displacement characteristics measured in tests on the
polyurethane foams from a drop height of 1.0 m.
Phase 1 Tests
23
Figure 18. Force/displacement characteristics measured in tests on the
polyurethane foams from a drop height of 1.45 m
Some of the materials appeared crushable when handled, and so tests were conducted to
examine the durability of the foams. Each sample of material was tested four times at the one
impact site at each drop height. A low level of durability is indicated by an increase in the
peak acceleration recorded for subsequent tests. Figure 19 and Figure 20 illustrate the
durability of the four foams.
Figure 19 shows that at drop height 1.0 m, BB-38 is relatively durable, with an increase in
maximum acceleration of approximately 10 g (9% increase), whereas E900 5.6 pcf is less
durable, with an increase in maximum acceleration of approximately 50 g (39% increase).
Figure 20 shows that at drop height 1.45 m, BB-38 is relatively durable, with an increase in
maximum acceleration of approximately 20 g (9% increase), whereas E900 6.0 pcf is less
durable, with an increase in maximum acceleration of approximately 90 g (40% increase).
For both drop heights, BB-38 was the most durable polyurethane foam.
24
The development of a protective headband for car occupants
Figure 19. Durability of Polyurethane Foams, drop height 1.0 m
Figure 20. Durability of Polyurethane Foams, drop height 1.45 m
2.3.6. POLYSTYRENE FOAMS
Polystyrene foam was obtained in sheets of five different thicknesses, and tested at 1.0 m
drop height. The two thickest samples were then tested at 1.45 m drop height. The thinner
samples were not tested at the higher drop height, as their performances in the initial tests
were poor. A summary of the results for polystyrene foams is given in Table 9 below, and is
illustrated in Figure 21.
Phase 1 Tests
25
Table 9. Phase 1 results for polystyrene foams
Drop
height
(m)
Velocity
(km/hr) Temp. (°C) Thickness
(mm) Peak
acceleration
(g)
HIC Test number
1.00 15.9 20.5 6420 2580 27089801
10 380 2170 27089802
15 290 1410 27089803
20 194 760 27089804
25 127 440 27089805
6 + 6 300 1410 27089806
10 + 15 118 410 27089807
1.45 19.2 25.5 25 232 1089 17129802
20 344 1929 17129803
Figure 21. Force/deflection curves for polystyrene foams of varying thickness, drop
height 1.0 m
Figure 21 illustrates that the material bottoming out dominated the tests with the thinner
sheets of polystyrene. In every test, the displacement of the headform was at least the
thickness of the material. The thicker samples showed less of the effects of bottoming, and
gave results that were as good as the polyurethane foams.
2.4. Summary
A summary of the results for the tests performed in Phase 1 is given in Table 10 and Table
11. The corresponding force displacement curves are compared in Figure 22 and Figure 23.
26
The development of a protective headband for car occupants
These results indicate that the most promising materials at the end of phase 1 were the
polystyrene, the polyurethanes and the cardboard honeycomb. Note that the 30 mm sample
of honeycomb cardboard was not tested from a drop height of 1.0 m, as it performed well
at 1.45 m drop height (see Table 11). The HIC obtained for the 30 mm sample of
honeycomb cardboard is less than half that of the next best material (E175) at a drop height
of 1.45 metres. Figure 22 clearly shows that the closed cell foam, and Confor foams at
raised temperatures, had significantly higher peak loads when tested from a drop height of
1.0 m than the other materials. The results were more evenly spread (apart from the
honeycomb cardboard) in tests performed from a drop height of 1.45 m (Figure 23). It
should be noted however that materials that performed poorly at 1.0 m were not necessarily
tested from a height of 1.45 m.
Although Confor foam performed well at low temperatures, its variations in properties with
changes in temperature exclude it as a suitable material for padding which is likely to see a
wide range of temperatures. As a result, the Confor foams along with the closed cell
polyolefin foams were excluded from Phase II of the study.
Table 10. Drop Height 1.0 m, velocity 16.0 km/h, and material thickness 25 mm
Material type Temp.
(°C) Peak
acceleration
(g)
HIC Test number
Polystyrene 20.5 127 440 27089805
BB-38 25 140 560 15129801
E175 25 129 450 15129805
E900, 5.6 pcf 25 129 460 15129809
E900, 6.0 pcf 25 135 490 15129813
15 mm small celled
honeycomb cardboard 16 285 1190 26059905
CF-45100 42 262 1120 27089808
CF-47100 41 270 1190 14099805
32 mm closed cell
polyolefin foams 17 223 1050 24089806
Phase 1 Tests
27
Table 11. Drop Height 1.45 m, velocity 19.2 km/h, and material thickness 25 mm
Material type Temp.
(°C) Peak
acceleration
(g)
HIC Test number
Polystyrene 25.5 232 1090 17129802
BB-38 25.5 208 1120 17129804
E175 25.5 198 960 17129808
E900, 5.6 pcf 25.5 260 1530 17129813
E900, 6.0 pcf 25.5 227 1230 17129816
30 mm small celled
honeycomb cardboard 25.5 104 440 17129816
CF-45100 25 282 1490 14089808
Figure 22. Force/deflection curves of various materials, 25 mm thick, drop height
1.0 m
28
The development of a protective headband for car occupants
Figure 23. Force/deflection curves of various materials, 25 mm thick, drop height
1.45 m
3. Phase 2 testing
3.1. Method
Anvils are commonly stipulated by standards that govern the performance requirements of protective
helmets. The helmets, attached to a standard headform, are dropped onto the anvils to test for the
effects of concentrated loading. Under this type of loading, the energy absorption of the helmet will
differ from that in an impact with a flat surface.
Phase 2 of this study used two standard helmet anvils; a sharp edged anvil, and a hemispherical anvil.
The sharp anvil was constructed according to the Australian Standard "Helmets for horse riding and
horse related activities" (AS/NZS3838:1998), and is illustrated in Figure 24. The hemispherical anvil
was constructed according to the Australian Standard for methods of testing protective helmets
"Determination of impact energy attenuation - helmet drop test" (AS2512.3.1), and is illustrated in
Figure 25. Each anvil was mounted to the steel slab that was used for the phase 1 tests. A prototype
headband was attached to the headform which was then dropped onto the anvil. The drop height
was 1.3 m for the sharp anvil and 1.385 m for the hemispherical anvil, as specified in the relevant
standard.
The criteria for the helmet standards is that the peak acceleration should be less than 300 g, and that
the cumulative duration of acceleration should not exceed 3 ms for accelerations greater than 200 g
and 6 ms for accelerations greater than 150 g. In this study, we have used the peak acceleration, the
HIC value and the force/displacement curve as assessments of impact severity, to maintain
consistency with the Phase 1 results. All data acquisition and signal processing was the same as in
Phase 1 of this study. The drop testing setup is shown in Figure 26.
Figure 24. Sharp anvil for helmet testing from the Australian Standard "Helmets for horse
riding and horse related activities" (AS/NZS3838:1998)
Figure 25. Hemispherical anvil for helmet testing from the Australian Standard
"Determination of impact energy attenuation - helmet drop test" (AS2512.3.1)
Figure 26. Phase 2 drop testing setup
3.2. Candidate Materials
From the analysis of the Phase 1 results, polystyrene foam, honeycomb cardboard and the
polyurethane foams emerged as the most suitable materials for testing in Phase 2. The closed cell
foams and viscoelastic foams were rejected from further testing as they did not perform well enough
in the Phase 1 tests (see previous section). The materials tested in phase 2 are shown in Table 12.
These materials were used to construct prototype headbands that could be attached to the EEVC
WG10 headform.
Table 12. Materials tested in Phase 2
Material name Supplier Category Thicknesses tested
Honeycomb cardboard
12 mm cell Unknown* Honeycomb
Cardboard 15 mm, 30 mm
E175 Woodbridge Group Automotive EA
polyurethane foam 25 mm
E900, 5.6 pcf Woodbridge Group Automotive EA
polyurethane foam 25 mm
E900, 6.0 pcf Woodbridge Group Automotive EA
polyurethane foam 25 mm
BB-38 Woodbridge Group Automotive EA
polyurethane foam 25 mm
Polystyrene foam Lactec Foam Products Polystyrene Foam 25 mm
* Sourced from packaging material for automotive body panels
3.3. Results
3.3.1. HEMISPHERICAL ANVIL TESTS
The hemispherical anvil test is derived from the Australian Standard "Determination of impact energy
attenuation - helmet drop test" (AS2512.3.1). The drop height specified in this standard (1.385m)
was used in these tests. Table 13 summarises the results of tests that used this anvil to test the
prototype headbands.
The results show that the best material was the 30 mm honeycomb cardboard with a hard shell, as it
had the lowest HIC, at 260. This result is less than a third that of the next best performing material,
BB-38, with a HIC of 860. Interestingly, the honeycomb cardboard without the hard shell
performed similarly to the BB-38, with a HIC of 970. The remainder of the materials tested all had
poor results in comparison with the BB-38 and the honeycomb cardboard, with HIC values
between 1410 and 1740. The polystyrene sample shattered completely during the impact, which
suggests that it is not suitable for a headband material without additional support (such as a hard
shell).
Table 13. Results of headband tests on the hemispherical anvil (drop height 1.385 m,
velocity 18.8 km/h)
Prototype description Peak acceleration
(g) HIC Test number Damage to prototype
30 mm honeycomb cardboard 241 970 02069901 none
15 mm honeycomb cardboard
in 4 mm PVC shell 290 1410 02069903 none
25 mm E175, polyurethane
foam 286 1470 02069904 none
25 mm E900, 5.6 pcf,
polyurethane foam 289 1520 02069905 none
25 mm E900, 6.0 pcf,
polyurethane foam 320 1740 02069906 none
25 mm BB-38, polyurethane
foam 185 860 02069907 none
25 mm polystyrene foam 348 1650 02069908 shattered
30 mm honeycomb cardboard
in 4 mm PVC shell 87 260 09069910 none
The results of the hemispherical anvil test are shown in Figure 27. The 30 mm thick honeycomb
cardboard with the hard PVC shell is clearly the best material in this test. The peak force is
significantly lower than for the other materials. The next best material is the BB-38 polyurethane
foam. All the other materials show about the same peak force.
Figure 27. Hemispherical anvil drop test results
3.3.2. SHARP ANVIL TESTS
The purpose of the sharp anvil test was to ascertain the penetration resistance of the headband. It is
derived from the Australian Standard "Helmets for horse riding and horse related activities"
(AS/NZS3838: 1998). In that standard, the drop height is specified as 1.3 m. Tests were first
performed at drop height 0.65 m, half the drop height given in the standard. This was so that the
performance of the materials could be compared without risking damage to the headform. It was
predicted that the sharp anvil might penetrate some of the test materials from the higher drop height.
The results from the tests performed from a drop height of 0.65 m are given in Table 14. The HIC
results for all materials tested were very similar, ranging from 130 for the 30 mm honeycomb
cardboard in a 4 mm PVC shell, up to 230 for 25 mm E900, 5.6 pcf. A better indicator of
penetration resistance for this test is the condition of the material after the test. The headband made
from 25 mm thick E900 (5.6 pcf) was cut halfway through by the sharp anvil, indicating a poor
resistance to penetration. The polystyrene also performed poorly, shattering on impact with the sharp
anvil. The BB-38 and honeycomb cardboard in the hard shell suffered no permanent damage from
the test. The remaining polyurethanes (E175 and E900, 6.0 pcf) had a visible dent where the impact
with the sharp anvil occurred.
Because of their good results in the tests performed from 0.65 m, the headbands made from 30 mm
thick honeycomb cardboard (with a hard shell) and from 25 mm thick BB-38 polyurethane foam
were tested from the full drop height specified by the standard. The intention was also to test, from
this height, those headbands that suffered only denting at the lower drop height. However, only one
of these tests was performed. The results from the tests at drop height 1.3 m are given in the second
half of Table 14. The honeycomb cardboard with hard shell produced the lowest HIC, at 260. The
BB-38 had the highest HIC, at 730. The 25 mm thick E900 polyurethane foam produced a HIC of
620, but was cut through completely by the sharp anvil. This headband provided little protection for
the headform from the anvil; the headform sustained such damage that further tests on the sharp anvil
at 1.3 m drop height were abandoned.
Table 14. Results of tests on the sharp anvil
Prototype description Drop
Height
(m)
Velocity
(km/hr) Peak
acceleration
(g)
HIC Test
number Damage to
prototype
headband
25 mm E175,
polyurethane foam 0.65 12.9 86 190 09069900 Dent
25 mm E900, 5.6 pcf,
polyurethane foam 97 230 09069901 Cut halfway
through
material
25 mm E900, 6.0 pcf,
polyurethane foam 92 210 09069902 Dent
25 mm BB-38,
polyurethane foam 77 180 09069903 None
25 mm polystyrene
foam 111 220 09069904 Shattered
completely
15 mm honeycomb
cardboard in 4 mm
PVC shell
92 210 09069905 None
30 mm honeycomb
cardboard in 4 mm
PVC shell
53 130 09069906 None
30 mm honeycomb
cardboard in 4 mm
PVC shell
1.3 18.2 71 260 09069907 None
25 mm BB-38,
polyurethane foam 170 730 09069908 Dent
25 mm E900, 6.0 pcf,
polyurethane foam 148 620 09069909 Cut through
completely,
and damage to
headform
Figure 28. Sharp anvil drop test results
3.4. Discussion
The results presented in the previous two sections clearly show that the best performing headbands
in these two tests involving concentrated impacts are the 30 mm honeycomb cardboard with the
hard shell, and the 25 mm BB-38. Figure 28 shows that the honeycomb cardboard headbands are
stiff in the initial phase of their deformation. The force is limited, however, by the crushing strength of
the material, and it is only when it bottoms out that the force increases. It is noteworthy that the
headband constructed from 15 mm of honeycomb had almost identical characteristics to the
headband constructed from 30 mm of the material. Only when the displacement of the material
approached 15 mm do the characteristics diverge. This suggests that the crushing strength of the
honeycomb is not dependent on the thickness of the material.
Some of the poylurethanes are not suitable as headband materials on their own, due to a lack of
penetration resistance. The polystyrene in the configuration tested (a simple 25 mm sheet) completely
disintegrated in both tests. The results from the hemispherical anvil tests show that BB-38
polyurethane foam has good load spreading capabilities on its own, with out the need for a hard
shell. The ease of manufacture that this would seem to imply indicates that this grade of polyurethane
is also worthy of further investigation.
4. Phase 3 testing
4.1. Method
In phase 3, prototype headbands were constructed from the most promising materials identified in
phase 2. These headbands were attached to an aluminium headform. The headform was fired at
various internal structures of a vehicle to see how the headband reduced the severity of the impact.
The EEVC WG10 headform could not be used in these tests because at the test speed (24 km/h)
the guidance system did not prevent the headform from rotating before the impact. The aluminium
headform did not suffer this problem at the test speed because it used an different guidance system.
The aluminium headform was designed by the Road Accident Research Unit for use in the
reconstruction of pedestrian/car collisions. The headform has a spherical contact surface of 165 mm
diameter, but is cylindrical about its long axis (Figure 29). This headform, which has a mass of 4.8
kg, is fired from a launcher at any angle between vertical (toward the ground), and horizontal. The
machine is not currently configured to fire the headform at angles higher than horizontal.
8 2 .50 mm
160 mm
Figure 29. The aluminium headform used in Phase 3 tests
A 1977 Toyota Corolla station wagon was used for phase 3 testing. The site for testing was chosen
based on three criteria: a) its involvement in impacts causing severe head injury in real life, b) its
ability to sustain repeated tests without damage and c) the ability of the launcher to access the impact
location. Unfortunately, this precluded sites where we felt that the headband should also be
evaluated; the windscreen, front header rail, side rail, roof and door could not be tested as they were
inaccessible to the launcher. The instrument panel, steering wheel rim and the D-ring assembly of the
seatbelt were not tested as they were judged to be sites where tests would not be repeatable on one
vehicle.
The site that was tested was the driver's side B-pillar. The tests were performed horizontally. We
also attempted to test the hub of the steering wheel, and the A-pillar, but initial tests showed that the
hub was deformed by each test and the impact angle for the A-pillar test was problematic, producing
inconsistent results.
The tests were performed at a nominal speed of 24 km/h (15 mph), which is the speed stipulated by
FMVSS 201. The criterion in FMVSS 201 is that the maximum acceleration in the impact should
not exceed 80 g for more than 3 ms. However, the peak acceleration, the HIC value and the force
deflection curves were used to assess each impact, to remain consistent with earlier phases of this
study. The test setup is illustrated in Figure 30.
Figure 30. Test setup for B-pillar test. The photo was taken immediately after a test (Note
that the RARU headform was used in the tests reported on in this report, not the EEVC WG10 headform as
shown).
4.2. Candidate Materials
Phase 2 showed that the best prototype headbands were the ones constructed from the BB-38
grade of polyurethane and the one constructed from 30 mm of honeycomb cardboard with a hard
PVC shell. Prototypes were constructed and attached to the aluminium headform (Table 15).
Table 15. Prototypes tested in Phase 3
Material name Supplier Category Thickness tested
Honeycomb cardboard 12 mm cell,
with a 200 mm diameter PVC shell Unknown* Honeycomb
Cardboard 30 mm, with 4 mm
PVC shell
BB-38 polyurethane Woodbridge
Group Automotive EA
polyurethane foam 25 mm
* Sourced from packaging material for automotive body panels
4.3. Results
4.3.1. B-PILLAR
A summary of results for B-pillar tests using the aluminium headform is given in Table 16. The
force/displacement characteristics for these four tests are presented in Figure 31.
Table 16. Results from Phase 3 - Tests at 23 km/h horizontally against the B-pillar of a
1977 Toyota Corolla station wagon
Prototype description Velocity
(km/hr) Peak acceleration
(g) HIC Test number
30 mm honeycomb cardboard
in a 4 mm PVC shell 22.8 78 280 17069901
25 mm BB-38 polyurethane 22.5 130 600 17069902
25 mm BB-38, repeat test 22.7 137 640 17069903
No headband 23.0 193 850 17069905
Figure 31. Phase 3, B-pillar Test Results
4.4. Discussion
Figure 31 clearly shows the headband’s protective effect. The result of the test with no headband
shows that the force rose sharply during the initial contact. The maximum displacement of the
headform during this impact was around 20 mm. From the shape of the force/displacment curve it
can be concluded that the deflection in this test is largely due to the dynamic deformation of the B-
pillar structure.
In each of the headband tests, the contact between the headform and the B-pillar is less stiff than the
contact between the headform and B-pillar with no headband. In each case, the peak acceleration
and the HIC value were significantly reduced. BB-38 polyurethane reduced the peak acceleration by
29 percent and the HIC value by 25 percent. The honeycomb cardboard headband was even better
at reducing the severity of the impact; the peak acceleration was reduced by 62 percent and the HIC
by 67 percent. The peak force in this test was limited to between 2 and 3 kN, until the effects of
bottoming out became apparent. This limiting value of the force was consistent for the honeycomb
cardboard through all phases of the study.
By integrating the force/deflection curve, the work done in crushing the honeycomb can be
calculated. The initial energy of the headform in test 17069901 was 96 Joules (calculated as 1/2mv2).
By plotting the work done by the headband, against the displacement during the impact, it is
apparent that approximately 70 Joules of work had been done by the headband before the
honeycomb began to bottom out (Figure 32). This left the headform with approximately 27 percent
of its initial energy at this point in the impact event. This is equivalent to the energy in an impact at
about half the test speed (which would have 25 percent of the energy).
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
work
force
00.01 0.02 0.03 0.04 0.05 0.06 0.07
0
10
20
30
40
50
60
70
80
90
100
displacement (m)
Figure 32. Force defelection curve and work done by the headband in test 17069901. The
vertical line indicates the displacment at which the headband begins to bottom out. At this displacement, around
70 Joules of work had been done.
Limit of crush
5. Conclusions and recommendations
The results from Phase 3 indicate that a headband can greatly reduce the severity of an impact to the
head. HIC was reduced by 25 percent with the use of 25 mm of BB-38 polyurethane, and 67
percent with the honeycomb cardboard prototype, when compared with an impact with no
headband. It is also noteworthy that the peak force produced in the test using the honeycomb
headband was less than half the force produced by the headform alone. The honeycomb cardboard
absorbed around three quarters of the impact energy before it began to bottom out.
The tests indicate that a crushable material, such as honeycomb, has the most effective
characteristics for a headband. The ideal material would be one which
• Limits the peak force applied to the head
• Does so at a constant level from the initiation of the deformation
• Returns little energy to the head
• Does not bottom out
Practical considerations limit the thickness of the headband, so the challenge is to absorb the
maximum amount of energy while limiting the peak loads transferred to the head of the wearer. In
this way, the maximum amount of energy can be absorbed before the material bottoms out.
Honeycomb is stiff initially when loaded, compared to polymer foams, but the peak load is limited by
its inherent properties. The material stores little elastic energy, so the head of the wearer would be
unlikely to rebound as severely as with some other materials.
One concern we had with the honeycomb cardboard is its durability. The material may deteriorate
dut to environmental factors. There are several alternatives to paper, however, for the construction
of a honeycomb structure. These include aluminium, polymers, and coated paper. These materials
would give the same benefits as the honeycomb cardboard: energy absorption, force limiting
characteristics, lightweight structure, but with the benefits of water resistance, and durability, in
storage and handling.
The polyurethane headband also performed reasonably well in all phases of the tests. The BB-38
grade was the best performer of the polyurethanes. It may be possible to formulate a polyurethane
with improved properties. However, at this time we have not seen a polyurethane which can match
the honeycomb material in its behaviour.
We recommend that further investigation is made into materials of a honeycomb structure to find a
material of the correct crushing strength and durability. We also recommend that prototypes be
developed further to be included in a testing program that would include other vehicle structures
tested over a range of velocities.
6. References
McLean, A. J., Fildes, B. N., Kloeden, C. N., Digges, K. H., Anderson, R. W. G, Moore, V. M. and
Simpson, D. A. 1997, 'Prevention of Head Injuries to Car Occupants: An Investigation of Interior
Padding Options', Report CR 160, Federal Office of Road Safety, Commonwealth Department of
Transport and Regional Development, 92 pages.
Monk, M.W. and Sullivan, L.K. 1986, 'Energy absorption material selection methodology for head/A-
pillar', Thertieth Stapp Car Crash Conference, San Diego, California, Paper 861887, Society of
Automotive Engineers, pp. 185-198.
O'Conner P.J. and Trembath R.F. 1994, 'Road Injury in Australia, 1991', Raod Injury Information Program
No. 4, National Injury Surveillance Unit, Adelaide Australia
- CitationsCitations2
- ReferencesReferences3
- "When the effects of the age of Australia's car fleet is considered, the development of some sort of head protection that might be worn by car occupants becomes compelling. To this end, the Australian Transport Safety Bureau commissioned a series of reports detailing the technical feasibility of some sort of protective headwear, specifically designed for car occupants (Anderson, White and McLean, 2000; Anderson et al., 2001, Anderson et al., 2002). These reports covered the selection and testing of energy absorbing materials through to the construction and testing of production prototypes. "
[Show abstract] [Hide abstract] ABSTRACT: McLean et al. (1997) demonstrated that energy absorbing headwear for car occupants might be effective in reducing the numbers of head injuries sustained by car occupants. They estimated that the benefits were greater than the estimated benefits of padding of the upper interior of vehicles to the requirements of the US Federal Motor Vehicle Safety Standard 201. This paper will describe the development of head protection for car occupants (the RARU Headband) that would protect the head of an occupant in a crash. The development process included the testing of candidate materials, the construction of prototypes and ultimately the evaluation of the prototypes according to test methods outlined in FMVSS 201. The evaluation was made by attaching the headband to a free motion headform, and firing the headform at 24 km/h at an unpadded beam that had similar characteristics to a vehicle A-pillar, simulating a frontal collision. Three beams of varying stiffness were used to examine the protective effect of the headband over a range of impact severities. The protective effect was measured by comparing the impact severity between impacts with and without the headband present. Results showed that the headband produced marked reductions in the Head Injury Criterion value compared to the unprotected headform. In beams that produced severe impacts with the unprotected headform, that exceeded the threshold set by FMVSS 201, the headband reduced the severity to safe levels. This study showed that head impact severities can be markedly reduced for car occupants by the use of moderate amounts of head protection in frontal impacts. Further evaluation is required for other impact directions. This study was completed for the Australian Transport Safety Bureau.- [Show abstract] [Hide abstract] ABSTRACT: Protective helmets are typically required to absorb energy in order to reduce head injury risk during blunt impact events. The energy-absorbing mechanism must be robust enough to reduce the impact energy to a low-injury probability level throughout a realistic range of impact velocities and environmental temperatures, regardless of the helmet impact site. The Advanced Combat Helmet (ACH) is configured with fitting pads that possess the capability to attenuate limited blunt head impact forces. Prior combat helmets were not required by their governing specifications to provide any tested levels of blunt impact protection. to obtain further information, a series of blunt impact tests were conducted with the ACH and the paratrooper and infantry versions of the PASGT helmet. The helmets were tested at two impact velocities, three environmental temperatures, and seven impact sites with two successive impacts. The performance of each was characterized by the transmitted acceleration measured within a standard head form and compared against the recommended threshold for mean and maximum acceleration.
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