Abstract and Figures

In this paper, we present a new and innovative sheet material folding technology and the associated advances in folding different patterns using continuous manufacturing techniques. A novel approach is developed for the continuous folding process where sheet material is progressively folded in two dimensions, through a set of rollers, followed by a configured roller for the final folding in the third dimension. The final roller can be designed for longitudinal folding, cross-folding and angular folding to produce the desired folded pattern. This process is more economical than traditional forming processes. An application of this process to the production of impact energy absorption structure is presented.
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1
A Continuous Folding Process for Sheet Materials
E. A. Elsayed and Basily B. Basily
Department of Industrial and Systems Engineering
Rutgers University
96 Frelinghuysen Road
Piscataway, NJ 08854-8018
ABSTRACT
In this paper, we present a new and innovative sheet material folding technology and the associated
advances in folding different patterns using continuous manufacturing techniques. A novel approach is
developed for the continuous folding process where sheet material is progressively folded in two
dimensions, through a set of rollers, followed by a configured roller for the final folding in the third
dimension. The final roller can be designed for longitudinal folding, cross-folding and angular folding to
produce the desired folded pattern. This process is more economical than traditional forming processes.
An application of this process to the production of impact energy absorption structure is presented.
Keywords: folding technology; rollers; Kraft paper; folded sheet; energy absorption; Chevron pattern
structures; lamination; tessellations.
1. INTRODUCTION
A novel technique for continuous sheet material folding is developed in which the sheet material is
progressively folded in the two dimensions normal to feeding direction through a set of rollers, followed by
a configured roller for the final folding in the third dimension, the two dimensional pre-folded sheet
transforms into the final three dimensional folded shape, as it passes through the configured main roller.
Figure 1. Folded Chevron Pattern From a Flat Sheet
Figure 1 shows what we refer to as a Chevron pattern, made of paper, which is generated through a
sequence of folding steps. This pattern can also be produced by folding different sheet materials, such as
aluminum, copper, stainless steel, Kraft paper, composites and plastics.
It should be emphasized that folding technology for sheet material, is one of the most efficient shape and
structural forming processes. Other production methods such as stretch-drawing, forging, pressing and
fabrication [1] may produce costly three-dimensional patterns that appear similar, but the mechanical
properties of the resultant patterns are significantly different. This is particularly so in the case of folding
thin sheet materials where variations in sheet thickness and/or mechanical properties are unacceptable.
2
Additionally the developed continuous sheet folding technique is capable of producing very intricate
structures that can be economically produced at high-speed from rolled stock through the use of single
manufacturing process; namely folding.
2. BASIC SHEET FOLDING CONCEPT/THEORY
Given a pair of points on a surface, measurement of the length of the shortest path that can be drawn on that
surface connecting them is called the intrinsic geometry of the two points [2, 3]. Folding preserves the
intrinsic geometry, since any curve drawn on a sheet will have the same length before and after folding.
This holds as long as the sheet thickness is relatively small. Of course, thicker sheets will experience
deformation and stretching when the bending is significant. In this paper, we consider the former case
only, i.e., no extensions in the sheet.
Theoretically such surfaces are not stretched in any direction and hence, folded structure can be readily
unfolded back to flat surfaces without any variation in sheet thickness or dimensions.
One of the important properties of folded structures, also referred to as developables by Duncan and
Duncan [4], is that the tangent plane at a point makes contact with the surface along the entire length of a
straight line in the surface. This line is called a generator of the surface. An element of folded structure is
constructed by having the generators of two surfaces coincide. Thus the two surfaces will only meet at one
line.
In folding a flat sheet of material into a three-dimensional folded structure, it is important to ensure the
following conditions in order to guarantee that the sheet can indeed be folded in the specified pattern:
1. Tessellations (normally polygons) made of identical polygons as shown in Figure3 are considered
a set of 2D polygons lying on a common plane (the flat sheet). These polygons must be convex.
Every polygon in the 3D folded structure has a corresponding face in the 2D polygons. The shape
of each face is the parallel projection of the corresponding polygon onto a plane a plane
perpendicular to that polygon. No face may overlap with any other, Bangay (5).
2. Each vertex in a folded structure must have the angles meeting there from the adjacent faces
totaling 2p as a limiting condition for the vertex to unfold flat [6, 7].
Therefore, not any set of 2D polygons on a flat sheet is foldable. Indeed, Bern and Hayes [2] show that it is
NP-hard to determine whether a crease pattern (2D polygons) is flat foldable. Hull [8] and Kawasaki [9]
focus on necessary and sufficient conditions on overlap orders, resulting in a characterization of flat
foldability for general crease patterns. Lang [10] describes an algorithm to construct uniaxial” bases,
which can be folded into arbitrarily complex models.
Folded patterns also have one or more elementary flat surface, each of which has a specific geometrical
shape which forms the basic building elements of the folded pattern. Additionally, a combination or
multiplication of these elementary flat surfaces of a specific geometrical shape constitutes the basic
building cell of a folded pattern, as it is repeated in two dimensions, creating the three-dimensional folded
shape.
In the case of Chevron folded pattern, as an example, the basic building element is a flat surface polyhedron
defined by its length a, width b, and the included angle
f
, shown in Figure 2 where both a and b are of
arbitrary lengths with typical included angle
f
=60
o
, however
f
could theoretically assume any value in
the range of 0
/2
f p
££ .
3
The basic building cell of the Chevron pattern consists of four identical polyhedron [A, B, C, and D] each
of length a, width b and an included angle
60
o
f
= . The cell is arranged laying flat prior to folding as
shown in Figure. 3. Also the repetition of the cell m times in the direction of the arrow along the X axis
provides the unfolded length of the tessellated sheet, while the cell repetition n times in the direction of
the arrow along the Y axis provides the unfolded width of the tessellated sheet.
Figure 2. Basic Element Of The Chevron Pattern
Creation of three dimensional folded Chevron structures from a sheet tessellated with the basic building
cell is achieved by inducing a permenant edge bending in particular directions between these four
polyhedron elements and along all the edges of these four basic elements. This generates the basic building
block which is a three dimensional structure with block length
q
, block width
W
q
and block heigh
h
q
,
the building block of the Chevron pattern is shown in Figure 4. Reptition of the building block in the X
and Y directions forms the entire folded Chevron structure shown in Figure5.
Figure 3. Basic Building Cell of Tessellated Chevron Pattern Sheet
4
A
Figure 4. Basic Building Block of Tessellated Chevron Pattern Sheet
Figure 5. Three Dimensional Chevron Structure
During any folding stage, the geometrical dimensions and angles of the folded structure can be determined
in terms of the three parameters of the basic building cell. For example, consider a Chevron pattern with
the following parametes (refer to Figure 6):
a basic element length
b basic element width
f
basic element angle
For an inclined angle
q
(also called folding angle) with respect to X-Y plane, where
q
varies from 0
corresponding to flat unfolded cell to
/2
qp
=
, corresponding to fully folded block, The geometrical
parameters of the basic folded block, corresponding to that inclined angle
q
, which refers to a given
state of folding are given by
sin
ca
f
=
sinsin
ha
fq
=
sin
gb
f
=
1
sin(sinsin)
gfq
-
=
1
sin(tan/tan)
agf
-
=
1
1
tan()
tancos
y
fq
-
=
5
cos
ub
y
=
cos
va
g
=
Figure 6. Geometrical Parameters of the Basic Building Block of Chevron Pattern
For a folded Chevron pattern with m tessellations of the basic building element of its flat surface
polyhedron in the X direction and n tessellations in the Y direction of same basic building element of flat
surface polyhedron, the unfolded sheet of thickness t would have an initial length, width, and thickness
volume given by
o
Lma
=
cos
o
Wnb
f
=
cos
o
Vmntab
f
=
When the above tessellated sheet is folded to an inclined angle
q
, the corresponding fold dimensions
(length, width, thickness and volume) are given by
cos
Lma
q
g
=
cos
Wnb
q
y
=
sinsin
hat
q
fq
=+
2
.sinsincoscos
VLWhmnab
qqqq
fqgy
=
Where
,,
LWh
qqq
and
V
q
are the fold length, width, height and volume respectively.
Since the structure is initially folded from a flat sheet of material with length
L
o
, width
o
W
, sheet
thickness t and materialdensity
z
, therefore the fold apparent density is determined as
o
V
V
q
q
z
z
=
The relative density ratio is then given by:
6
[1/((coscos)((sinsin)1))]
a
t
q
z
gyfq
z
=+
which indicates that the apparent density of the folded structure varies with the folding angle
q
with the
fold apparent densities equal to the unfolded sheet at
0
q
=
and
/2
qp
=
. This also indicates that there is
a fold minimum apparent density at about
45
o
q
=
as shown in Figure 7 for a constant a/t ratio.
0 10 20 30 40 50 60 70 80 90
0
10
20
30
40
50
60
70
80
90
Fold Inclination angle (Theta)
Fold correlated angular parameters
gamma
psi
alpha
Volume ratio
Figure 7. Variation of Fold Geometry
,,and
agy
and Density Ratio With Folding angle
q
3. ADVANTAGES OF SHEET FOLDED STRUCTURES AND APPLICATIONS
The folded sheet configuration may be adapted by changing scale, parameters of the element geometry and
material composition to suit a given application with specific mechanical properties, such as compressive
and shear strength and impact energy absorbing capacity.
Typical applications in packaging may include Kraft paper cores for laminated panels that would out-
perform corrugated cardboard or multi-layer folded blocks that could replace Styrofoam in space filling and
shock absorbing applications. Folded patterns may also be used as decorative packages such as trays and
boxes for displaying cosmetics and similar products.
In the aerospace industry, light-weightcores folded from aluminum and composites could improve the
performance of such cores and expand its use in airframes, fuselage, floors, wings, and tails. Additionally
folded structures can be generated with customized stress/strain characteristics in predetermined
values/directions designed to fit surfaces with any curvature.
In civil engineering infrastructures, Applications could include aluminum and steel laminated folded
structures as panels for warehouse roofs. Interior walls made from particle wood could be replaced by light-
weight wood-pulp paneling materials with folded cores. Likewise, stainless steel decorative folded designs
for building facades, interiors of elevators and floor decks can be made of folded patterns with pre-
specified geometries and properties. Heavier gauges of high-strength steel sheets can be folded for
applications in buildings and steel structures, bridges, and replacements of concrete decks.
In the transportation industry, aluminum and steel laminated panels may be used in light-weight sturdy
trailer beds, automobile body structures to provide frames of higher strength, rigidity, and vibration
dampening. The light-weight/high-strength ratio and high impact energy absorbing properties make folded
structures most suited for bumpers, hoods, crash protecting car doors and highways crash barriers.
7
Other applications include construction of filters and heat exchangers. This can be also designed from folds
with specific shape flow channels, which would provide controlled flow rate and large surface area. The
use of silicon carbide/ceramics, fabricated from UV photo-curable pre-ceramic polymers of SiC and
Si
3
N
4
/SiC, with higher than 85% ceramic yield in foldable paper form, and optimizing the fold geometry,
would produce a uniquely folded ceramic particulate filter with high tortuosity [6], strength and
temperature oxidation resistance. UV cross-linkable pre-ceramic polymers can also be used to fabricate
uniquely folded ceramic, carbon and polymer PEM fuel cells.
In military applications, Kraft paper folded pads, designed for impact energy absorption out performed
current structures used in high-velocity air drop. This is due to the unique energy absorbing capability of
the folded structures in three dimensions, compared to the unilateral energy absorbing ability of other
commercially available cushioning pads. The design of these energy-absorbing pads can be tailored to
provide predetermined load deceleration, and impact energy absorbing capacity compatible to the fragility
of the package content.
Folded patterns from sheet materials exhibit superior crush resistance and energy absorption characteristics.
Since the technology applies to paper, plastic, sheet metal, composites, cloths and other foldable sheet
materials, the commercial applications for this technology are numerous.
4. SHEET FOLDING PROCESS
The folding process uses minimal energy in forming since the material does not entirely stretch or
undergoes large scale yielding conditions to acquire the final shape. The work is done in a localized scale in
the form of plastic bending of the edges of the facets only. Therefore, extremely lower forces and energies
are required in the folding process when compared with typical metal forming process such as pressing,
stamping or stretch forming [7].
The plastic bending force and energy required to permanently fold these elements to produce a given
pattern is derived from the plastic work involved in the bending these flat elements around the element
edges to a given permanent angle that corresponded to initial folding angle of the sheet, hence, for bending
a sheet of thickness t to a radius of curvature
r
the strain at a distance y from the neutral plane is given by
(see Figure 8):
Figure 8. Variation of Folded Angle With Bending
y
e
r
=
where
1
r
is the curvature of the elastic curve of the deflected sheet., the bending moment at this
cross section of the sheet is given by:
8
Myldy
s
=
ò
Assuming elastic-perfectly plastic sheet material, then the bending moment, M on an element edge of a
length l is given by:
/2/2
/20
y
y
y
tt
ty
Mlydyydyydy
ss
+
-
==+
òòò
where
y
y
y
e
= is limiting elastic strain
Since the stress in the elastic portion of the bent cross sections is given by
Ey
s
r
= , where E is the material Young’s modulus, then,
2
32
4
2
()
34
yyy
t
E
Mlyly
s
r
=+-
since
y
y
y
E
r
s
= then
22
3
2
1
43
yy
lt
Ml
E
r
ss
=-
and the bend curvature is given by
3
2
2
1
1
3
1
4
y
y
l
E
ltM
s
r
s
=
-
When the moment M is removed after plastic yielding of bent edge, the material will spring back,
decreasing the initial bent angle and the resulting final curvature that the bent edge retains is given by:
3
2
3
2
1
112
3
1
4
y
res
y
l
M
E
Etl
ltM
s
r
s
=-
-
This spring back is due to the residual stresses in the plastically bent edge resulted from the elastic strains
being locked in position by yielding of the external layers along the cross section of the sheet material. The
distribution of these residual stresses is shown in Figure 9 with maximum values of:
'
2
6
resy
M
lt
ss
=- at the outer surface of the cross section, and
"
3
12
y
resy
My
lt
ss
=- at the height of
y
from the cross section neutral axis.
9
Figure 9. Distribution of Residual Stresses in a Plastically Bent Cross Section
In the case of the folded Chevron pattern, each basic element of the flat surface polyhedron defined by its
length a, width b, and the included angle
f
, is plastically bent all along its edges, with respect to the
adjacent elements, however, at any given stage of folding, the bent angle along the element edge a given by
angle
a
is related to bent angle of the other element edge b given by angle
q
by the above geometrical
relations of the building block, shown in Figure.3. Hence the bending moment required to fold a Chevron
pattern of
mn
´
flat surface of polyhedrons, of length a and width b and included angle
f
folded from
sheet metal of thickness t and mean yield strength
y
s
is given by
1
2
sin
4
1
sin
LW
oo
a
tab
oy
M
p
WL
oo
b
ba
sf
f
æö
æö
æö
-
ç÷
ç÷
ç÷
æö
èø
èø
ç÷
ç÷
=
ç÷
ç÷
æö
ç÷
æö
ç÷
èø
+-
ç÷
ç÷
ç÷
èø
èø
èø
(1)
The plastic work required to fold the pattern to a given angle
q
Which is function of the bend angles
and
qa
of the edges of the flat surface of the polyhedron of length a and width b and included angle
f
where
0/2
qp
<<
and
0/3
ap
<<
, that is between the initially flat unfolded surface cells
(
0
qa
==
) and the fully folded Chevron block ( ,
23
pp
qa
==
) is given by
2
1
sin
4
1
sin
oo
oy
p
oo
LW
a
abt
W
WL
b
ba
a
fs
q
f
ìü
æö
æö
-+
ïï
ç÷
ç÷
æö
èø
ïèøï
ç÷
=
íý
ç÷
æö
æö
ïï
èø
-
ç÷
ç÷
ïï
èø
èø
îþ
(2)
where
,and
ooo
LWt
are initial sheet material length, width, and thickness respectively.
The edges of the facets of a surface produced by the folding process have no discontinuity because the
original connectedness of the sheet is preserved across each fold along the element. Moreover, each of the
flat surfaces of polyhedron element is not subjected to any stretching, thinning, or forming and the
generation of the folded structure, is achieved by creating localized plastic deformations only along the
edges of the folded elements. In this way folding is an optimal construction technique for fiber composites,
which are manufactured by conforming a piece of composite to fit a mold.
10
Therefore, sheet folding presents a new technology for manufacturing core materials for light-weight
structures with built-in high-strength to weight ratio and high impact energy absorbing characteristics. This
makes it a competitor for existing light structures, used in aerospace industry, such as honeycomb.
However, production of such folded sheet patterns and structures on an industrial scale is a challenging
task. since each small facet of the folded sheet material must fit into a predetermined three-dimensional
contracting movement relative to the next adjacent element.
We have developed several processes for sheet material folding including discrete parts folding and
continuous folding processes; we focus this presentation on the continuous sheet folding process.
5. CONTINUOUS SHEET FOLDING PROCESS
Continuous folding of sheet material from rolled material feedstock is rather a complicated process. This is
due to the fact that the sheet material requires to be continuously reduced in dimensions in both the normal
and longitudinal flow directions simultaneously while it is being folded. Since the sheet material cannot be
stretched, then the difficulty stems from the fact that the sheet, which is fed through a series of mating
rollers, is required to slip a predetermined distance normal to rollers axis throughout the entire series of
rollers. Each roller has one or more edges with Vee-grooved having an included angle.
This slippage is practically difficult because the fold creases formed by the Vee-grooved edges may result
in shredding the material as it progresses from one roller to another. The problem is further aggravated by
the fact that sheet material is also required to slip in the direction parallel to the roller axis in order to
achieve the contraction in the other dimension. Hence production of a continuous folding machine is not a
straightforward process, as it seems.
6. DESIGN AND DEVELOPMENT OF A CONTINUOUS SHEET FOLDIN MACHINE
The machine for continuous production of folded patterns has been designed and constructed. It
successfully folded patterns of different geometry from different sheet materials. This was achieved by
implementing a novel technique, in which, sheet material is pre-folded through a set of sequential and
circumferentially grooved rollers, followed by final set of cross folding rollers engraved with specific
patterns
(Patent is applied for by Rutgers University).
In this pre-folding technique, Figure 10, the first set of linear folding rollers, has only one mating Vee-
grooving, that indent a linear fold positioned at the center of the sheet. As the material advances further
through the second set of rollers, which is fitted with three V-grooves, the sheet material will be registered,
by the initial central linear fold, previously formed by the first set of rollers, but indented with further two
linear folds, one on each side of the central fold. Similarly the third set of rollers, which has five grooves,
will result in adding two further linear folds to the material, as the process proceeds, further longitudinal
folds are made in an arithmetical sequence of 1-3-5-7--- until the desired amount of sheet contraction is
achieved in the normal direction of the sheet advance.
11
Figure10. Schematic Drawing of the Pre-Folding Technique
A schematic drawing of the continuous folding machine is shown in Figure 11.
Figure 11. Schematic Drawing of the Continuous Sheet Folding Process
Shredding is eliminated since the sheet material edges are free to slip inward towards the center of the
roller, overcoming only two friction effects in each folding step, while totally eliminate the material of
being locked between roller grooves. Final folding is then achieved by the master final pair of folding
rollers, that directly follows the pre-folding sets of rollers. The machine uses only one set of these patterned
rollers to perform the final folding process. As the cross section of the sheet material entering these final set
of rollers is not a straight line anymore, but a linearly folded in an approximate zigzag shape.
This technique reduces the work of folding process to be performed by the final set of rollers, to only
folding the incoming sheet with the remaining contraction in the longitudinal rolling direction. The
technique enables handling the sheet reduction in two consecutive stages, which reduces the difficulty from
a two dimension slippage problem along the surface of the rollers to linear slipping problem occurring at
each tooth of the final folding set of rollers.
12
Figure 12. Photograph of the Continuous Sheet Folding Machine
The machine for continuous folding was built with great design experimental flexibility to include means of
varying, folding loads, rollers driving torque and speed, rollers pitch diameters, rollers folding gap, and
rollers relative speeds, where all these parameters could be varied without losing relative synchronization
during fold process. Photograph of the machine sheet folding rolling sequence is shown in Figures 12 14.
Figure 13 Photograph of sheet folding rolling sequence
The machine is successfully able to fold thin sheets of paper, copper, aluminum and stainless steel sheet
material using this novel pre-folding technique. The rollers with engraved Chevron pattern (shown in
Figure 14) are machined using 4-axies CNC milling machine.
13
Figure 14. Photograph of the Continuous Sheet Folding Machine
7. DESIGN AND DEVELOPMENT OF IMPACT ENERGY ABSORBING PADS
A recent industrial application of folded structures involves the design and construction of high energy
absorbing pads for high speed airdrop. Typical air delivery systems use a parachute for a load descends
speed of 14 mile/hr. The goal is to increase the descending speed up to 50 mile/hr while mitigating the
destructive impact with a drogue parachute and high energy-absorbing cushioning pads. The cushioning
materials should absorb the majority of the shock so that the supplies are delivered undamaged. The
primary advantage of such rapid descent is the reduction in delivery location error and enemy detection.
Replacement of existing paper honeycomb structures by cushioning pads produced from sheet folding of
Kraft paper, Figure 16, enables absorption of same impact energy per unit volume at half the impact load.
This reduction in impact stress (load), Figure 22, would allow airdrop of same cargo at higher speeds, or
successful delivery of a fragile cargo at existing speeds. Kraft paper is extremely well suited in this
application because of its low production cost using the developed continuous folding process. Moreover,
Kraft paper is easily disposable which minimizes the risk of enemy detection and the impact on the
environment.
8. CONSTRUCTION OF THE IMPACT ENERGY ABSORBING FOLDEDPAD
The impact energy absorbing pads are constructed from multiple layers of laminated cores of folded Kraft
paper sheet material. The folded core is initially compacted to a specific ratio, which corresponds to a given
fold angle
q
(see Figure 4). The core is then laminated by a sheet of the same Kraft paper on one side only,
since consecutive lamination will build up the structure with alternative layers of cores and laminated sheet
respectively. Elm paper adhesive is used in gluing the structured pads which are then cured at
200
o
F
for
24 hours before conducting the impact testing.
Impact testing at speeds ranging from 25 to 40 ft/sec is conducted using the INSTRON impact testing
machine (machine impact head is shown in Figure 15). The test pads are trimmed to 5.5”
´
5.5 in cross
section and 3 in height, which corresponds to the height of the standard honeycomb structure material
already used in commercial applications for comparison. A typical Kraft paper energy absorbing pad is
shown in Figure 16.
14
Figure 15. Head of the INSTRON Impact Testing Machine With Added Weight Compartment
9. TESTING OF IMPACT ENERGYABSORBING FOLDED PADS
Tests are conducted on Kraft paper honeycomb samples and on folded structures samples using three
orientations of folded structures, namely; flat orientation as shown in Figure 16, side orientation as shown
in Figure 17, and vertical orientation as shown in Figure 18. The orientation of folded structure is related to
direction of folded pattern and lamination and the direction of the applied impact force as shown clearly in
these figures.
Figure 16. Flat Orientation of Folded Chevron Pad With Arrow Showing Direction of the Impacted Force
15
Figure 17. Side Orientation of Folded Chevron Pad With Arrow Showing Direction of the Impacted Force
Figure 18. Vertical Orientation of Folded Chevron Pad With Arrow Showing Direction of the Impacted
Force
All test samples are subjected to the same impact speed of 30 ft/sec at a constant weight of the impact head
at 21 lbs, which corresponds to a total impact energy of about 300 lb-ft.
Multi-layers of the 3 standard height of the honeycomb samples are glued to achieve heights (6, 9 and
12) equivalent to those of the Chevron samples.
10. RESULTS AND CONCLUSIONS
Variation of both impact load and absorbed impact energy with crushed displacement for the folded
samples, impacted on the three orientations of the folded samples are shown in Figures 19-22.
Results show that the laminated Chevron folded pads are capable of absorbing energy in all the three
directional orientations. The vertical orientation sample of the folded Chevron pad is capable of absorbing
the maximum impact energy when compared with both honeycomb samples and samples tested at other
orientations as shown in Figure 21.
16
Kraft paper folded pads absorbed higher impact energy per unit volume compared with honeycomb pads as
shown in Figure 22. These samples are able to absorb impact energy in the three direction of orientations
compared to only vertical-axial direction of the Honeycomb samples.
Kraft paper folded pads outperform honeycomb samples in energy absorbing capacity due to the uniform
crushing pattern shown in Figure 23 when compared with the honeycomb shown in Figure 24.
Additionally the ability of folded structure to absorb energy in the three direction of orientation, and the
low cost of production, make the folded pads ideal for energy absorbing applications.
Figure19. Impact Force and Energy Capacity VS Displacement for Flat Orientation Pads
Figure 20. Impact Force and Energy Capacity VS Displacement for Side Orientation Pads
17
Figure 21. Impact Force and Energy Capacity VS Displacement for Vertical Orientation Pads
Figure 22. Impact Force and Energy Capacity Vs Displacement for Honeycomb and Vertical Orientation
Samples
Figure 23. Folded Sample Before and After Impact
18
Figure 24. Honeycomb samples before and after impact
11. ACKNOWLEDGEMENTS
This work was supported by the National Science Foundation, Grant No. NSF DMI 015440.and the Naval
Facilities Engineering Command, Port Hueneme, contract No. N47408-01-C-7230. The authors would like
to thank Ms. Jessica Hiraoka of the Naval Facilities Engineering Service Center for her help and
suggestions during the course of this research.
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th
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19
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st
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[12] Basily, B. B., Elsayed, E. A., and Kling, D Manufacturing Process for Folded Sheet Material
Proc., National Science Foundation Conference, NSF Conf., Birmingham, Alabama., Jan., 6-10, 2003.
... Herein, Miura-ori core, as a novel generation of core for sandwich applications, is supposed to be a promising substitution to traditional honeycomb core in the aerospace industry. On the one hand, the existing forming processes for Miura-ori core are based on the ancient origami art, i.e. folding a planar material to three-dimensional structure along the creases [12,13]. In this case, no further cutting or machining steps are essential, which is much important for carbonfiber-reinforced composites. ...
... Though some manufacturing approaches [12,13] have been performed to fabricate Miura-ori core with different parent materials, that for carbon-fiber-reinforced Miuraori core is still a challenge till date. In this paper, a hot-press molding and twice curing technique was adopted to fabricate carbon-fiber-reinforced MSPs. ...
... To fabricate Miura-ori cores, two plies of prepregs with a stacking sequence of [0°] 2 were folded and pressed into the mould gradually by hands. Note that through an origami-like manner [12,13], the fiber orientation of prepregs remains constant during the folding and mold-pressing procedure. It means that 0° represents the fiber is arranged along the side b, as shown in in Fig. 1. ...
Article
Full-text available
Sandwich structures with Miura-ori core are supposed to be a promising substitution to traditional sandwich structures with honeycomb core in the aerospace industry. To reveal the failure mechanism of carbon-fiber-reinforced Miura-ori core sandwich panels subjected to in-plane compressive load, a multi-failure theory considering five potential failure modes, including bending and shear global buckling, face local buckling, face debonding and face crushing, is proposed. The critical failure loads of specific geometrical configurations are predicted and failure mechanism map is deduced to figure out the optimizing route for lightweight design. Three groups of the specimens with different face sheet thickness are designed and fabricated by adopting a hot-press molding and twice curing technique. Two typical failure modes including face local buckling and face debonding are revealed by the in-plane compressive tests, and the analytical results are in a reasonable agreement with the tested. Compared to corrugated core sandwich panels with the same dimension, Miura-ori core sandwich panels possess a higher anti-local-buckling capacity thanks to the stronger constraint of Miura-ori core to the face sheet. It is expected that this work can provide a significant guideline for the practical application and design of such kind of sandwich structures.
... Fig. 1a) A foldcore (Fig. 1b) is a core made from a flat sheet of any material that has been folded into a desired pattern. Foldcores can be made of carbon fiber reinforced plastics (CFRP), aluminum, aramids, papers, and plastics [1][2][3][4][5][6][7]. The foldcore concept emerged in the 1970s [1] as a possible alternative to legacy cores. ...
... Discontinuous manufacturing processes are common among researchers when making foldcore test coupons [5,6]. The up-front material and time costs for discontinuous folding processes are much cheaper than up-front continuous folding processes costs, but the size and number of foldcore samples are limited [7]. ...
Conference Paper
Full-text available
A foldcore is a novel core made from a flat sheet of any material folded into a desired pattern. A foldcore sandwich composite (FSC) provides highly tailorable structural performance over conventional sandwich composites made with honeycomb or synthetic polymer foam cores. Foldcore design can be optimized to accommodate complex shapes and unit cell geometries suitable for protective shielding structures. This work aims to characterize hypervelocity impact (> 2000 m/s, HVI) response and corresponding damage morphologies of carbon fiber reinforced polymer (CFRP) FSCs. A series of normal (0° impact angle) and oblique (45° impact angle) HVI (~3km/s nominal projectile velocity) impact tests were performed on CFRP FSC targets to understand the effects of projectile impact on redirected debris formation, and variable debris cloud expansion. HVI damage in FSC targets were assessed using visual inspection and high-speed imaging analysis. The results from the present study indicate that debris cloud propagation and expansion are strongly influenced by foldcore impact location/angle and open-channel direction. This work serves as a baseline study to understand HVI response of FSC targets and to identify critical FSC design parameters to optimize HVI mitigation performance.
... The flatwise compression and transverse shear tests were carried out on all the foldcore sandwiches. The low and high velocity impact tests were performed only on the types with greater energy absorption capability, i.e. type C and D, where the damages were assessed with the ultrasonic C-scans and Micro-CT scan images.High-Rate Dynamic Compression Tests were performed inElsayed and Basily 2004;Kazemahvazi, Kiele et al. 2010). Through quasi-static and dynamic compression tests, the out-of-plane impact properties of corrugated carbon fibre composite cores have been investigated in(Kazemahvazi, Kiele et al. 2010). ...
... Through quasi-static and dynamic compression tests, the out-of-plane impact properties of corrugated carbon fibre composite cores have been investigated in(Kazemahvazi, Kiele et al. 2010). Utilising a drop tower, the dynamic compression testing of laminated block of foldcore in out-of-plane direction and both in-plane directions has been documented inElsayed and Basily 2004). The tests indicated the laminated block of foldcore, made from the Kraft paper, can surpass the honeycomb cores in energy absorption despite being made of the same material. ...
Thesis
A special family of origami, rigid origami is when each paper facet surrounded with crease lines neither stretches nor bends during folding. In recent years, deployable structures and patterned sheets inspired by rigid origami have gained popularity among researchers in the fields of both mathematics and engineering. The focus of this thesis is on the kinematic modeling of the deployable structures, the mechanical behaviour and the mechanics of the Miura-ori patterned sheets. The first part of this thesis is devoted to kinematic modeling of deployable surfaces. A kinematic model of mobile assemblies has been proposed based on the closed adjacent assembly of four spherical 4R linkages. To ensure the assemblies have a mobility of one, the kinematic compatibility conditions of the model have been obtained. The solutions to the compatibility conditions cover the existing one degree of freedom mobile assemblies, as well as twelve novel ones. In total, eighteen types of mobile assemblies have been devised. Based on the solutions, relationships between kinematic variables, hybrid assemblies, networks and rigid origami patterns for flat surfaces have been studied. The second part of the thesis focuses on the kinematic modeling of the deployable prismatic structures. A kinematic model has been introduced based on closed opposite assembly of spherical 4R linkages. The kinematic compatibility conditions of these mobile assemblies have then been derived. Two groups of even-sided deployable prismatic structures have been obtained. For the 4-sided case, one structure incorporates a kite-shaped intersection, whereas the other incorporates a parallelogram. Unit variations have been discussed. Straight and curvy multi-layer prisms have been obtained by changing the dihedral angles between the intersecting planes. A general method to design even-sided multi-layer deployable prismatic structures has been proposed using the geometric conditions of the origami patterns. All the deployable structures constructed using this method can be deployed and folded along the central axis with a single degree of freedom; this makes them usable for a wide range of engineering applications. An investigation of deformations in patterned sheets forms the final part of this thesis. A Miura-ori patterned sheet was made from copolymer Elvaloy by compression molding and its deformation behavior was investigated experimentally and using finite element analysis. Mechanical tests have been performed on the material and patterned sheet. FE simulations using ABAQUS/Explicit have been carried out to analyse deformations on the patterned sheet. Based on the simulation results, the deformation patterns on the patterned sheet under different loading conditions were examined, as well as their energy absorption capacities. Theoretical analyses based on the deformation patterns predicted the mechanical behaviour of the patterned sheet. Therefore, the geometry and material of the patterned sheet can be designed to meet the requirements of a certain application.
... An interesting concept for continuous sheet folding was introduced by (Elsayed, 2004). It proposed a complex set of 8 consecutive rollers, which gradually fold continuous sheet of material supplied off a drum. ...
Article
Foldcore sandwich structures have aroused considerable research interest in recent years. While foldcores made of metal or composite have been studied extensively, paper-based foldcore are relatively rare. In this paper, we focus on the flat-wise compression properties of foldcore sandwich paperboard with the Miura-ori pattern in the field of packaging and logistics engineering. The flat-wise compression properties and affecting factors of foldcore sandwich paperboard are identified experimentally. Among these factors, the side length ratio (a/b) of the Miura-ori unit significantly influences the deformation mode of the foldcore sandwich paperboard, thus affecting the load-carrying performance and energy-absorption properties. Moreover, the foldcore sandwich paperboard is compared with the conventional corrugated paperboard. The results indicated that although the specific peak stress of foldcore sandwich paperboard and conventional B-flute corrugated paperboard are approximately equal at the same profile angle, the specific energy absorption of the former was 2.06 times higher than the latter. What is more, the specific peak stress and specific energy absorption of the foldcore sandwich paperboard are 1.93 times and 3.24 times higher than those of B-flute corrugated paperboard by merely increasing the sector angle from 60° to 75°. These findings may provide the potential for practical application of paper-based foldcore sandwich panels, thus facilitating the structural design of multilayered cushioning paper pads.
Article
Hybrid composites offer an effective method of improving toughness and impact properties while reducing the cost of an advanced composite material. This paper aims at experimentally investigating the influences of impact energy, impact position and ply combination on the low-velocity impact responses of carbon/glass hybrid S-shaped foldcore sandwich structures. Carbon/glass hybrid S-shaped foldcore sandwich structures were manufactured using plain weave carbon fabrics and satin weave glass fabrics with epoxy resin. Low-velocity impact tests were carried out to study the impact behavior. The results show that the damage mode of the sandwich panel gradually changed from the local damage of the top face sheet and the foldcore to the complete penetration damage of the sandwich panel with the increase of the impact energy. And the node position has higher load carrying capacity, energy absorption capacity, and resistance to deformation compared with the base position. Although the initial load carrying capacity of carbon/glass hybrid sandwich panels is lower than that of the carbon fiber reinforced plastic (CFRP) sandwich panels, the addition of glass fabrics can improve energy absorption capacity and perforation threshold of CFRP sandwich panels.
Article
The added bonding platform of the M-shaped folded core is expected to address the issue of facesheet-core interface debonding in sandwich plates. A two-dimensional reduced-order plate model based on variational asymptotic method is proposed to investigate the effective performance of the original composite sandwich plate with an M-shaped folded core (CSP-MFC). The effective plate properties of CSP-MFC are obtained by constitutive modeling over the unit cell, and inputted into the two-dimensional reduced-order plate model (2D-REM) for global and local analysis. The novelties of cell tailoring and local field recovery within the unit cell are very important features compared to traditional finite element models and significantly facilitate the engineering analysis of CSP-MFC. By comparing the global and local responses of the 2D-REM with those of the three-dimensional refined plate model (3D-RPM) under various boundary conditions, the accuracy and efficacy of the 2D-REM were validated. In addition, a comprehensive investigation of the structural responses to various parameters, including the layup configuration and core geometric parameters (e.g., opening angle, core height, side length, wall thickness, and form of the folded core), was also performed. It was determined that the CSP-MFC with a layup of ±45°/0°/90°s, a larger opening angle and width of the bonding platform, as well as a smaller side length and core height had the most balanced performance.
Article
The sandwich structure with foldcore is a new type of structural material with light weight, high specific strength, high specific rigidity and multi-functional potential, which is connected with each other in core space, this kind of three dimensional structures can be formed by folding based on two dimensional materials. The main research achievements and characteristics of sandwich structure with foldcore in recent years are summarized and analyzed according to the lightweight and multi-functional requirements of aircraft structure in this paper. The configuration optimization scheme and fabrication process of the sandwich structure with foldcore are described. Moreover, the research status of multi-function of the sandwich structure with foldcore are summarized, including sound insulation, thermal protection, stealth performance of the structure, etc.
Article
The composite sandwich folded plate (CSFP) not only has excellent mechanical properties but is multi-functional, owing to the internal transparent design. To investigate its effective performance, the original CSFP is reduced to constitutive modeling over the unit cell (providing the orthotropic elastic constants) and global analysis over the two-dimensional reduced-order plate model (2D-RPM) based on the variational asymptotic method, and transformed to a Reissner–Mindlin model for practical application. The accuracy and effectiveness of 2D-RPM is verified by comparison with the static and dynamic results of three-dimensional direct numerical simulation (3D-DNS) under different boundary conditions. Furthermore, a parameter study is carried out to investigate the effects of layup configurations and core structural parameters (opening angle, core height, wall thickness, and forms of folded core) on the effective performance of the CSFP. It is concluded that the CSFP has the best balanced performance with a layup of ±45°/0°/90°s and larger opening angle and wall thickness of the folded core, as well as a smaller Z-line length and height.
Article
Sandwich structures with Miura-ori cores have been studied especially in aerospace industry. However, by removing the face sheets one can obtain esthetical, multifunctional, self-supporting structures for various applications, such as packaging. This study focuses on the mechanical performance of planar, self-supporting Miura-ori structures under compressive loads. Through systematic variations of both origami geometry and base material orientation, this study performs linear stress and stability analyses by utilizing the finite element method. The results reveal the effects of the geometric parameters and the material orthotropy on the structural performance, finally resulting in parameter ranges forming a basis for structural design.
Article
Full-text available
Origami is the art of folding pieces of paper into works of sculpture without the aid of scissors or glue. Modern advancements in the complexity of origami (e.g., the work of Montroll and Maekawa) reveal a rich geometric structure governing the possibilities of paperfolding. In this paper we initiate a mathematical study of this "origami geometry" and explore the possibilities of a graph theoretic model. In particular, we study the properties of origami models which fold flat (i.e., can be pressed in a book without crumpling). Necessary and sufficient conditions are given for an origami model to locally fold flat, and the problems encountered in trying to extend these results globally are discussed. 1 Introduction Origami is the art of folding paper, without the aid of scissors or glue, into pieces of sculpture. Even when we restrict ourselves to folding a single square of paper, the possible results offer rich variety and complexity (see [3], [8], [10], or [11]). Things expl...
Article
A plane, inextensible sheet may be folded or creased along a curved line to produce two connected but distinct developable surfaces. Various theorems applying to this folding process are identified and two special cases investigated. In one, the fold line remains a plane curve during deformation and in the other the dihedral angle at the fold is constant along the curve. Curved-line folding occurs naturally in the collapse of thin-sheet-metal structures composed of developable surfaces. The theorems presented identify the kinematic constraint existing between pairs of developable surfaces connected by curved-line folds and permit the design of sheet-metal products that use these surfaces. This expands considerably the range of engineering products that can be made by folding and bending a single inextensible sheet.