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Physical and Mechanical Properties of
Hard Maple (Acer saccharum) and
Yellow Poplar (Liriodendron tulipifera)
Marly Gabriela Carmona Uzcategui
Roy Daniel Seale
Frederico Jose
´Nistal Franc¸a
Abstract
Maple and poplar are common names of species that grow in the eastern United States. Physical and mechanical properties
were evaluated from small clear wood specimens of hard maple (Acer saccharum) and yellow poplar (Liriodendron
tulipifera). Specific gravity, static bending strength and modulus of elasticity, compression parallel and perpendicular to
grain, and Janka hardness were tested. The experiments were carried out on defect-free specimens extracted from boards
supplied by members of the Staircase Manufacturers Association. The material was donated by companies located in the
eastern United States. On the basis of the findings, it can be stated that mechanical properties for maple and yellow poplar
have not changed substantially because the average values remain in a range that is very close to the values published in
previous studies.
Hardwood timber is a resource that is strong,
sustainable, and aesthetically attractive. Hardwoods are
used in numerous structural applications, such as furniture
parts, stairs, tool handles, bowling pins, baseball bats,
parallel bars, stairs and stair railings, highway guardrail
posts, and pallets. Although they are usually used for small-
scale structures and non–load-bearing applications, there is
a growing interest in combining structural performance with
aesthetic design.
Hard maple (in some cases also called sugar maple [Acer
saccharum]) is a wide-ranging species that grows in the
eastern United States (mainly the mid-Atlantic region) and
the Great Lakes states of the upper Midwest. The sapwood
is creamy white with a slight reddish-brown tint, and the
heartwood varies from light reddish brown to dark brown.
Maple wood is hard and heavy, with straight grain and good
strength properties (Wiemann 2010). Some uses include
flooring, furniture, paneling, cabinets, millwork, stairs,
handrails, doors, woodenware, and sporting goods (Hard-
wood Manufacturers Association 2019).
Yellow poplar (Liriodendron tulipifera) grows in the
eastern United States. Its wood is medium density with low
bending, shock resistance, stiffness, and compression
values. The sapwood is usually white. The heartwood is
yellowish brown and sometimes has parts that are purple,
green, black, blue, or red. The presence of these colors does
not affect its physical properties. It is used for lumber,
veneer, pulpwood, light construction, furniture, kitchen
cabinets, doors, paneling, moulding and millwork, edge-
glued panels, turnings, musical instruments, and carvings
(Koch 1985, Wiemann 2010, Hardwood Manufacturers
Association 2019).
In the stairway industry, hardwoods have been identified
as some of the species with the greatest economic impact
due to their historically excellent performance. However,
unlike other materials, the hardwoods used for kiln-dried
appearance grade in stairs lack information on tests that
confirm the design values necessary for the creation of
products that meet the standards (Cooper 2014). Initial
information about the mechanical properties of hardwoods
comes from studies conducted nearly 100 years ago (Newlin
and Wilson 1917, Markwardt and Wilson 1935). The most
recent and accepted values for these properties are the ones
published in the Wood Handbook (Kretschmann 2010).
However, some of these data were generated in the early
1900s. For this reason, performing mechanical tests to verify
The authors are, respectively, Graduate Research Assistant,
Warren S. Thompson Professor, and Assistant Research Professor,
Dept. of Sustainable Bioproducts, Mississippi State Univ., Starkville
(mgc273@msstate.edu, rds9@msstate.edu, fn90@msstate.edu [cor-
responding author]). This paper was received for publication in
February 2020. Article no. 20-00005.
ÓForest Products Society 2020.
Forest Prod. J. 70(3):326–334.
doi:10.13073/FPJ-D-20-00005
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the properties of these species is important in maintaining
current information that fulfills regulations and building
codes.
The mechanical and physical properties of wood are
influenced by a variety of factors, such as weather, moisture,
geography, soil, silvicultural practices, and harvesting
decisions. These properties vary according to the axis of
measurement (longitudinal, radial, or tangential) due to the
anisotropic nature of wood. Mechanical properties are the
basis of design values, which estimate the structural
performance of specific material sizes and qualities. Some
of the most common mechanical properties measured
through structural test procedures are modulus of elasticity
(MOE), modulus of rupture (MOR), maximum stress in
compression parallel to grain, compression perpendicular to
grain, shear strength parallel to grain, tension parallel to
grain, hardness, and specific gravity (SG; Kretschmann
2010).
MOE and MOR are important properties used to
determine the use of wood. MOE helps to describe stiffness
and is a good overall indicator of wood strength (Franc¸a et
al. 2018). MOR, on the other hand, is a measure that
indicates the bending strength of a board or structural
member. MOR represents the maximum load that a wooden
specimen can withstand in bending before rupture (Kretsch-
mann 2010).
Mechanical testing is important when trying to under-
stand the behavior of wood. Previous studies, such as those
by Newlin and Wilson (1917), Markwardt and Wilson
(1935), and Kretschmann (2010), have characterized
physical properties, such as growth ring count (GRC),
moisture content (MC), percentage of latewood (LW), SG,
and the strength properties, such as MOE, bending strength
(MOR), compression, and hardness, of hard maple and
yellow poplar.
Variation in the values is associated with factors such as
the modernization of the technology used to perform the
tests, the temperature conditions or MC at the time of the
test, the methods of data collection, the characteristics of
some forests that change over time, and even the variability
from each tree and from where the test specimens were
obtained (Kretschmann 2010).
The lumber industry is aware of the uncertainty
associated with the average values of the mechanical
properties of wood species, which is why it invests large
amounts of money carrying out continuous tests that later
help to obtain the most accurate and reliable design values
(Southern Forest Products Association 2013). As part of the
contribution to maintaining the validity and reliability of
these values, the Staircase Manufacturers Association, in
conjunction with US Department of Agriculture Forest
Service, Forest Products Laboratory, has funded tests to
evaluate the mechanical properties of the most important
species for the staircase industry.
Despite what is known about the physical and mechanical
properties of these species, there is still uncertainty
associated with the average values of the properties of hard
maple and yellow poplar, and ongoing resource monitoring
is needed to evaluate changes in these properties over time.
This study will provide useful information to staircase
manufacturers, allowing them to perform future calculations
or adjustments to published strength values. This study will
also provide information on the quality of the raw material
and possibilities for its end use.
In this sense, the purpose of this study was to investigate
the physical and mechanical properties of hard maple and
yellow poplar to supplement available information on these
species. Specific objectives were to determine the growth
characteristics (GRC and LW), and test the physical
properties (MC and SG) and mechanical properties of small
clear wood specimens (static bending, compression parallel
and perpendicular to grain, and Janka hardness) and then to
compare the results from both species with the published
values in earlier studies.
Materials and Methods
Sample preparation
The material was obtained from the Northeast, upper
Midwest, Southeast, mid-South, Appalachian, and Southeast
United States. No species verification was performed
because the objective of this study was to evaluate the
material commercially utilized by the US wood industry.
Kiln-dried, defect-free, straight-grained hard maple and
yellow poplar boards with dimensions of 2.54 by 5 by 38 cm
were donated by staircase manufacturers. Boards were kept
in a controlled environment (218C at 65 percent relative
humidity) for several weeks before initial testing.
Prior to data collection and testing, each board was
labeled with the initial of the species name and a sequential
number to identify and organize boards and samples. GRC
and percentage of LW were collected from each end of the
boards. Manufacturer location, MC, and temperature were
collected from 92 hard maple and 92 yellow poplar boards.
Specimens for SG (SG
12%
), static bending, Janka
hardness, and compression (parallel and perpendicular to
grain) tests were cut in accordance with the ‘‘secondary
method’’ explained in Section 8.1 of ASTM D 143 (ASTM
International 2014). The secondary method was selected by
default because the boards were 2.54 cm thick. From each
board, six samples were cut as follows: one SG, two for
static bending (one radial and one tangential), one Janka
hardness, and two compression (one parallel and one
perpendicular; Fig. 1).
Each specimen was weighed and measured before testing.
All machines were equipped with Bluehill 3 software
(Instron, Norwood, Massachusetts) to control testing
operations. The generated data were recorded directly into
a Structured Query Language database. The MC of the test
specimens was also measured during the SG procedure.
Growth characteristics
GRC was calculated by counting the number of the rings
and dividing by the thickness or the width, depending on the
grain orientation of the piece (radial or tangential).
Percentage of LW was determined using a 2.54 by 2.54-
cm dot grid by dividing the number of dots that fell on LW
by the total number of dots in the grid. Both measurement
techniques followed the standard grading rules of the
Southern Pine Inspection Bureau (2014). Even though both
species are diffuse porous, it was possible to delineate the
transition from earlywood to LW. This boundary was made
on the basis of the difference in colors. The earlywood
region is where the vessels maintain their greatest water
transport function during the first growth season, resulting in
a lighter color compared to the LW region (Bond and
Hamner 2002; see Fig. 2).
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Board density, SG, and MC
Board density was determined using bulk weight and bulk
volume. SG
12%
followed the specifications of ASTM D
2395 (ASTM International 2017). MC was determined using
a Model MMC 220 moisture meter (Wagner Meters, Rogue
River, Oregon).
SG
12%
values were determined on 2.54 by 5.08 by 5.08-
cm test specimens. For calculation, dimensions of each
specimen were collected before and after being oven-dried
at 1038C628C. Ovendried weight of the specimens was
recorded after the mass was stabilized (see Fig. 3).
Static bending test
The static bending, compression parallel and perpendic-
ular to grain, and hardness tests were performed on a Model
5566 universal testing machine (Instron) following ASTM
D 143 (ASTM International 2014).
Static bending tests were performed on specimens with
dimensions of 2.54 by 2.54 by 40.64 cm
3
. Load was applied
at the center point with a test speed of 0.127 cm/min (Fig.
4a). The load span was 35.6 cm. As indicated in Figure 1,
for this test, two samples of static bending were labeled A
and B to generate a group of samples to be loaded in the
radial face and another group to be loaded in the tangential
face (Fig. 4b). MOE was calculated as
MOE ¼DPL3
4Dfbh3ð1Þ
where MOE is the bending MOE (MPa), DPis the loading
increase (N), Lis the span length (m), Dfis the deflection
increase (m), bis the width (m), and his the depth of the
specimen (m). MOR was calculated as
MOR ¼3PL
2bh2ð2Þ
where MOR is the bending MOR (MPa), Pis the maximum
force (N) at the mid-span, Lis the span length (m), bis the
width (m), and his the depth (m).
Compression parallel to grain
Specimen dimensions for the compression parallel to
grain test were 2.54 by 2.54 by 10.16 cm
3
. The load was
Figure 1.—Cutting scheme of small clear wood specimens from the boards. SG
¼
specific gravity.
Figure 2.—Transition from earlywood/latewood in (a) hard maple and (b) yellow poplar. Source: The Wood Database (2019a,
2019b).
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applied at a rate of 0.00762 cm/cm of nominal specimen
length per minute. The type of deformation was recorded for
each specimen. Figure 5a shows the testing setup.
Compression perpendicular to grain
Dimensions for each test specimen were 2.54 by 2.54 by
15.24 cm
3
. The load was applied through a bearing plate
5.08 cm wide, placed at the top of the specimen to be in
contact with its radial surface. The speed rate of loading was
0.305 mm/min. The setup for this test is shown in Figure 5b.
Janka side hardness
Hardness values of defect-free hard maple and yellow
poplar samples were determined by embedding a steel
0.444-in. (1.13-cm)-diameter steel ball at a rate of 0.6 cm/
min. The ball penetrated the tangential and radial surfaces
with a speed of 6 mm/min. The test continued until the ball
penetrated to one-half of the ball’s diameter as determined
by the calibrated extensometer. The dimensions for each
sample were 25.4 by 50.8 by 152.4 mm
3
(ASTM
International 2014). The Janka test setup is shown in Figure
5c.
Results and Discussion
Table 1 exhibits a summary of the growth characteristics
and physical properties of hard maple and yellow poplar
specimens obtained from the conducted tests. The average
MC of hard maple boards ranged from 8.6 to 15.3 percent
with a mean of 12.21 percent and a coefficient of variation
of 14.36 percent, whereas the MC yellow poplar boards
ranged from 5.2 to 13.5 percent with an average value of
9.53 percent and a coefficient of variation of 23.46 percent.
GRC for hard maple ranged from 1.07 to 65.63 with a mean
of 19.39 and a coefficient of variation of 71.14 percent. For
yellow poplar, GRC ranged from 0.58 to 15.91 with a mean
of 5.26 and a coefficient of variation of 51.88 percent.
The average percentage of LW of hard maple ranged
from 12.5 to 73.5 percent with a mean of 49.22 percent.
Density for hard maple boards ranged from 416 to 797 kg/
m
3
with a mean of 703 kg/m
3
and a coefficient of variation
Figure 3.—Yellow poplar ovendried samples.
Figure 4.—Bending test: (a) test setup and (b) radial and tangential bending specimens.
Figure 5.—Minor properties test: (a) compression perpendicular to grain, (b) compression parallel to grain, and (c) Janka ball side
hardness.
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of 6.43 percent. The mean SG of hard maple was found to
be 0.65 with a coefficient of variation of 4.97 percent.
Minimum and maximum values were 0.57 and 0.79,
respectively.
Percentage of LW of yellow poplar ranged from 7.81 to
62.5 percent with a mean of 31.19 percent and a coefficient
of variation of 35.49 percent. Board density ranged from
394 to 659 kg/m
3
with a mean of 508 kg/m
3
and a
coefficient of variation of 10.43 percent. The SG mean was
found to be 0.46 with a minimum of 0.36 and a maximum of
0.60 and a coefficient of variation of 11.14 percent.
MOE and MOR average values for hard maple are higher
than those for yellow poplar. In Table 2, average values as
well as the range of variation and coefficient of variation
obtained from testing in the radial and tangential directions
are listed. Hard maple average values for MOE and MOR
were 12,417 and 123.6 MPa, respectively. Yellow poplar
average values for MOE and MOR were 9,611 and 83.4
MPa, respectively. In general, for both species, MOE and
MOR results in the tangential direction are slightly higher
than the ones obtained in the radial direction.
Compression parallel and perpendicular to grain results
for hard maple and yellow poplar are listed in Table 3. For
both species, tested samples in compression parallel to grain
are higher than the ones obtained from tests perpendicular to
grain. Hard maple’s compression parallel to grain values
ranged from 45.2 to 83.1 MPa with a mean of 61.7 MPa and
a coefficient of variation of 10.78 percent. Yellow poplar’s
compression parallel to grain values ranged from 30.4 to
56.3 MPa with a mean of 43.7 MPa and a coefficient of
variation of 12.17 percent.
For compression perpendicular to grain, hard maple
values ranged from 15.5 to 32.7 MPa with a mean of 21.0
MPa and a coefficient of variation of 13.71 percent. For
Table 1.—Moisture content (MC), growth ring count (GRC), percentage of latewood (LW), and specific gravity (SG) values for hard
maple and yellow poplar.
Species NProperties Mean Min Max SD CV
a
(%)
Hard maple 90 MC (%) 12.21 8.6 15.3 1.75 14.36
92 GRC 19.39 1.07 65.63 13.79 71.14
92 LW (%) 49.22 12.5 73.5 21.22 43.11
92 Board density 703 416 797 45 6.43
91 SG
12%
0.65 0.57 0.79 0.03 4.97
Yellow poplar 92 MC (%) 9.53 5.2 13.5 1.80 18.89
90 GRC 5.26 0.58 15.91 2.73 51.88
92 LW 31.19 7.81 62.5 11.07 35.49
92 Board density 508 394 659 53 10.43
89 SG
12%
0.46 0.36 0.60 0.05 11.14
a
CV ¼coefficient of variation.
Table 2.—Static bending modulus of elasticity (MOE) and modulus of rupture (MOR) values in radial and tangential directions for
hard maple and yellow poplar.
Species N
Static bending (MPa)
Direction Variable Mean Min Max CV
a
(%)
Hard maple 92 Radial MOE 12,162 7,384 15,720 13.51
MOR 128.6 78.9 167.2 12.19
92 Tangential MOE 12,679 7,267 15,796 11.60
MOR 118.6 67.3 165.4 14.83
184 Average MOE 12,417 7,267 15,796 12.69
MOR 123.6 67.3 167.2 14.03
Yellow poplar 92 Radial MOE 9,349 7,074 11,514 10.96
MOR 82.7 54.5 108.6 14.00
91 Tangential MOE 9,880 7,612 12,259 10.91
MOR 83.9 49.4 108.6 14.06
183 Average MOE 9,611 7,067 12,259 11.26
MOR 83.4 49.4 108.6 14.02
a
CV ¼coefficient of variation.
Table 3.—Compression parallel and perpendicular to grain values for hard maple and yellow poplar.
Species Direction
Compression (MPa)
NMean Min Max CV
a
(%)
Hard maple Parallel 91 61.7 45.2 83.1 10.78
Perpendicular 91 21.0 15.5 32.7 13.71
Yellow poplar Parallel 93 43.7 30.4 56.3 12.17
Perpendicular 93 9.9 5.1 18.5 26.13
a
CV ¼coefficient of variation.
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yellow poplar, compression perpendicular values ranged
from 5.1 to 18.5 MPa with a mean of 9.9 MPa and a
coefficient of variation of 26.13 percent.
Janka hardness results for hard maple and yellow poplar
are listed in Table 4. For hard maple, Janka hardness values
in the radial direction ranged from 4.5 to 10.5 kN with a
mean of 6.3 kN and a coefficient of variation of 14.33
percent. In the tangential direction, hard maple hardness
values ranged from 4.8 to 10.5 kN with a mean of 7.0 and a
coefficient of variation of 12.53 percent. The average
hardness for hard maple ranged from 4.5 to 10.5 kN with a
mean of 6.7 kN and a coefficient of variation of 14.49
percent.
For yellow poplar, Janka hardness values in the radial
direction ranged from 1.6 to 5.4 kN with a mean of 2.9 kN
and a coefficient of variation of 26.75 percent. In the
tangential direction, yellow poplar values ranged from 1.8 to
6.2 kN with a mean of 3.2 kN and a coefficient of variation
of 26.58 percent. The average hardness for yellow poplar
ranged from 1.6 to 6.2 with a mean of 3.1 kN and a
coefficient of variation of 27.16 percent.
Comparisons with previous studies
Table 5 shows a summary of sample sizes and methods
used in previous studies. Comparisons of the properties’
values obtained from different studies and the current study
were done to identify possible variations in the physical and
mechanical properties of hard maple and yellow poplar.
Some of these values were absent in the literature; thus,
comparisons in some cases were limited to the information
available. A comparison of the present study with previous
studies for GRC and LW for hard maple and yellow poplar
is shown in Table 6.
A study was conducted by Newlin and Wilson (1917) to
determine the physical and mechanical properties of wood
species grown in the United States. This study observed an
average of 21 GRC for hard maple and 14 GRC for yellow
poplar. Markwardt and Wilson (1935) found an average of
18 GRC. Duchesne et al. (2016) studied mechanical
properties and discolored heartwood proportions in hard
maple from New Brunswick, Canada. The study found an
average of 45.7 GRC with a range of 22.9 to 83.8. Yelle and
Table 4.—Janka hardness values in radial and tangential directions for hard maple and yellow poplar.
Species Direction
Janka hardness (kN)
NMean Min Max CV
a
(%)
Hard maple Radial 184 6.3 4.5 10.5 14.33
Tangential 182 7.0 4.8 10.5 12.53
Average 368 6.7 4.5 10.5 14.49
Yellow poplar Radial 184 2.9 1.6 5.4 26.75
Tangential 184 3.2 1.8 6.2 26.58
Average 368 3.1 1.6 6.2 27.16
a
CV ¼coefficient of variation.
Table 5.—Summary information of literature cited for specific gravity and mechanical properties: sample size, moisture content
(MC), and method used.
Literature
Specific gravity Mechanical properties
NMC (%) Method NMC (%) Standard
Hard maple
Newlin and Wilson (1917) 22
a
Green
b
Clear samples 22
a
Green
b
Clear samples
Markwardt and Wilson (1935) 22
a
Green
b
Clear samples 5
a
Green
b
ASTM D 143
Zhang et al. (2006) — 8 Unknown — — —
Kretschmann (2010) — 12 Unknown — 12 ASTM D 143
Duchesne et al. (2016) 122
a
12 ASTM D 143
Yelle and Stirgus (2016) 30 12 ASTM D 143 30 12 ASTM D 143
Duchesne et al. (2016) — — — 92 12 ASTM D 143
Hindman (2017) — — — 90 12 Schmidt and MacKay (1997)
Fu et al. (2018) 8 12 X-ray — — —
Fortin-Smith et al. (2018) — — — 54 ASTM D 6110-10
Yellow poplar
Newlin and Wilson (1917) 22
a
Green
b
Clear samples 22
a
Green
b
Clear samples
Markwardt and Wilson (1935) 22
a
Green
b
Clear samples 11
a
Green
b
ASTM D 143
Faust et al. (1990) — — — 240 12 ASTM D 143
Stern (1944) — — — 480 9 ASTM D 143
Green et al. (2006) — — — 10 12 ASTM D 143
Kretschmann and Green (2008) — — — 160 12 ASTM D 143
Kretschmann (2010) — 12 Unknown — 12 ASTM D 143
Ulker et al. (2018) — — — 80 12 Ulker and Hiziroglu (2017)
a
Number of trees tested.
b
Above fiber saturation point.
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Stirgus (2016) found an average of 10.2 GRC with a range
of 4.2 to 16.2.
From Table 6, it can be seen that the average GRC
obtained in the present study is similar to that obtained by
Newlin and Wilson (1917) and Markwardt and Wilson
(1935). For yellow poplar, on the other hand, results show
lower average GRC.
A comparison of the present study and other studies for
SG of hard maple and yellow poplar is shown in Table 7.
The results of this study are similar to those of other studies.
For hard maple, wood samples tested by Newlin and
Wilson (1917) showed an average SG of 0.62. Markwardt
and Wilson (1935) found that SG for hard maple was 0.68.
A study conducted by Fu et al. (2018) to determine the
properties of hard maple reported an average SG value of
0.69 with a range of 0.68 to 0.71. Hindman (2017) described
an average SG of 0.66 with 0.51 as a minimum and 0.81 as a
maximum. In a study conducted by Zhang et al. (2006), the
authors found an average SG of 0.70. Yelle and Stirgus
(2016) found an average SG of 0.67 with a range varying
from 0.64 to 0.70. Kretschmann (2010) listed an average SG
of 0.63 for hard maple.
For yellow poplar, Newlin and Wilson (1917) found an
average value of 0.41 for SG, and Markwardt and Wilson
(1935) found a value of 0.40. Stern (1944) evaluated the SG
of yellow poplar from Virginia. For small specimens, the
author found that the average SG was 0.43, varying from
0.41 to 0.44. Kretschmann and Green (2008) determined an
average SG of 0.51 with a range of 0.42 to 0.64.
Kretschmann (2010) reported an average of 0.42.
A comparison of the present study with previous studies
for bending MOE and MOR for hard maple and yellow
poplar is shown in Table 8. Even though MOE for yellow
poplar was found to be slightly lower in general, the average
MOE values found in this study for hard maple and yellow
poplar are similar to the results found by other studies.
For hard maple, the average MOR value was found to be
slightly higher when compared with other studies. For
yellow poplar, MOR was found to be similar to the results
obtained by Newlin and Wilson (1917) and higher than the
results obtained by the other studies.
For hard maple, Newlin and Wilson (1917) reported
average MOE and MOR values of 12,548 and 108.9 MPa,
respectively. Markwardt and Wilson (1935) found MOE and
MOR values for hard maple of 12,617 and 108.9 MPa,
respectively. Duchesne et al. (2016) found the mechanical
properties of small clear wood of sugar maple varying from
5,434 to 15,008 MPa for MOE with an average of 10,684
MPa and an average of 113.2 for MOR with a range of 65.4
to 144.6 MPa. Zhang et al. (2006) reported an average MOE
of 12,600 MPa with a range of 10,500 to 14,700 MPa.
Kretschmann (2010) listed the average values for hard
maple as 12,617 MPa for MOE and 108.9 MPa for MOR.
Yellow poplar static bending values described by Newlin
and Wilson (1917) were 11,100 MPa for MOE and 81.35
MPa for MOR. Markwardt and Wilson (1935) determined
average MOE and MOR values for yellow poplar of 10,342
and 63.43 MPa, respectively. Faust et al. (1990) studied the
strength and stiffness properties of yellow poplar structural
lumber. In the study, the authors found an average MOE
value of 11,032 MPa. For MOR, the authors reported an
average value of 41.56 MPa, varying from 33.7 to 49.4.
Stern (1944) found an average MOE of 10,928 MPa with a
range of 11,611 to 12,480 MPa. Kretschmann (2010) listed
average MOE and MOR values of 10,893 and 69.63 MPa,
respectively.
A comparison of the present study with other studies for
compression parallel and perpendicular to grain for hard
maple and yellow poplar is shown in Table 9. The results of
the present study are in accordance with previous studies.
Newlin and Wilson (1917), studying hard maple com-
pression properties, found average values of 59 and 11.16
MPa for compression parallel and perpendicular to grain,
respectively. Markwardt and Wilson (1935) reported for
hard maple an average value of 54 MPa for compression
parallel to grain and 12.47 MPa for compression perpen-
dicular to grain. Fortin-Smith et al. (2018) found an average
of 77.4 and 14.5 MPa, respectively. Kretschmann (2010)
listed the average for compression parallel to grain as 54 and
10.13 MPa for compression parallel and perpendicular to
grain, respectively.
For yellow poplar, Newlin and Wilson (1917) found
values of 51.6 MPa for compression parallel to grain and 5.1
MPa for compression perpendicular to grain. Markwardt
and Wilson (1935) reported average values of 36.5 and 3.9
MPa, respectively. Kretschmann (2010) reported average
values of 38.2 and 3.4 MPa for compression parallel to grain
Table 6.—Comparison of the present study with previous
studies for growth ring count (GRC) and percentage of
latewood (LW) for hard maple and yellow poplar.
Literature
GRC, mean
(range)
%LW, mean
(range)
Hard maple
Newlin and Wilson (1917) 21 (—) 49 (—)
Markwardt and Wilson (1935) 18 (—) —
Duchesne et al. (2016) 45.7 (22.86–83.82) —
Yelle and Stirgus (2016) 10.2 (4.2–16.2) —
Present study 19.39 (1.07–65.63) 49.22 (12.5–73.5)
Yellow poplar
Newlin and Wilson (1917) 14 (—) —
Markwardt and Wilson (1935) 14 (—) —
Present study 5.26 (0.58–15.91) 31.17 (7.81–62.5)
Table 7.—Comparison of the present study with other studies
for specific gravity for hard maple and yellow poplar.
Literature Mean (range)
Hard maple
Newlin and Wilson (1917) 0.62 (—)
Markwardt and Wilson (1935) 0.68 (—)
Zhang et al. (2006) 0.70 (—)
Kretschmann (2010) 0.63 (—)
Duchesne et al. (2016) 0.60 (0.52–0.65)
Yelle and Stirgus (2016) 0.67 (0.64–0.70)
Hindman (2017) 0.66 (0.51–0.81)
Fu et al. (2018) 0.69 (0.68–0.71)
Present study 0.70 (0.42–0.80)
Yellow poplar
Newlin and Wilson (1917) 0.41
Markwardt and Wilson (1935) 0.40
Stern (1944) 0.43 (0.41–0.44)
Kretschmann and Green (2008) 0.51 (0.42–0.64)
Kretschmann (2010) 0.42 (—)
Present study 0.46 (0.36–0.60)
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and compression perpendicular to grain, respectively. Stern
(1944) found average values of 43.6 and 8.6 MPa for
compression perpendicular to the grain and compression
parallel to grain, respectively. Faust et al. (1990) reported an
average value of 40.2 for compression parallel to grain.
Overall, hard maple compression values in both direc-
tions are higher than those reported for yellow poplar. It is
also noticeable that values of compression parallel to grain
are higher than those obtained in the other direction for both
species. From the literature review, for hard maple, values
for compression parallel to grain are similar those obtained
in the present study. However, values for compression
perpendicular to grain were found to be higher than those of
other studies.
For yellow poplar, compression parallel to grain was
found to be within the range of values listed in the other
studies. The current results are very similar to those
obtained by Stern (1944), Faust et al. (1990), and
Kretschmann and Green (2008). For compression perpen-
dicular to grain, the results are similar to those of Stern
(1944) and higher than those of the other studies. These
findings show that over time, there was no significant
change for compression parallel to grain for both species
tested.
A comparison of the present study with other studies for
Janka hardness for hard maple and yellow poplar is shown
in Table 10. The results found in the present study are
similar to those found in the other studies. For hard maple,
Newlin and Wilson (1917) reported an average Janka
hardness of 6.3 kN. Markwardt and Wilson (1935) found an
average value of 6.4 kN. Kretschmann reported values
similar to those of the two previous studies.
Newlin and Wilson (1917), studying yellow poplar Janka
hardness, found an average value of 2.0 kN. The same value
was reported by Markwardt and Wilson (1935). Ulker et al.
(2018) evaluated the properties of thermally treated yellow
poplar. The authors reported an average hardness value of
5.7 kN with a range of 5.1 to 6.3 kN. Green et al. (2006)
determined the Janka hardness using nonstandard speci-
mens. The authors found an average hardness of 2.44 kN
with a range of 1.36 to 4.55 kN. Kretschmann (2010)
reported an average hardness of 2.40 kN for yellow poplar.
Stern (1944) found an average side hardness of 4.08 kN.
Conclusions
Through this research, it was possible to obtain updated
information on the characteristics of the mechanical
properties of hard maple and yellow poplar lumber and to
compare the findings of the current study with those of past
Table 9.—Comparison of the present study with other studies
for compression parallel and perpendicular to grain for hard
maple and yellow poplar.
Literature
Compression
Parallel (MPa) Perpendicular (MPa)
Hard maple
Newlin and Wilson (1917) 59 11.16
Markwardt and Wilson (1935) 54 12.47
Fortin-Smith et al. (2018) 77.4 14.5
Kretschmann (2010) 54 10.13
Present study 62 21
Yellow poplar
Newlin and Wilson (1917) 51.6 5.1
Markwardt and Wilson (1935) 36.5 3.9
Faust et al. (1990) 40.2 —
Stern (1944) 43.6 8.6
Kretschmann and Green (2008) 42.1 5.7
Table 10.—Comparison of the present study with other studies
for Janka hardness for hard maple and yellow poplar.
Literature Mean (range), kN
Hard maple
Newlin and Wilson (1917) 6.3 (—)
Markwardt and Wilson (1935) 6.4 (—)
Kretschmann (2010) 6.4 (—)
Present study 6.7 (4.5–10.5)
Yellow poplar
Newlin and Wilson (1917) 2.00 (—)
Markwardt and Wilson (1935) 2.00 (—)
Stern (1944) 4.08
Green et al. (2006) 2.44 (1.36–4.55)
Kretschmann (2010) 2.40 (—)
Ulker et al. (2018) 5.7 (5.1–6.3)
Present study 3.1 (1.6–6.2)
Table 8.—Comparison of the present study with previous studies for bending modulus of elasticity (MOE) and modulus of rupture
(MOR) for hard maple and yellow poplar.
Literature MOE (MPa) Range MOR (MPa) Range
Hard maple
Newlin and Wilson (1917) 12,548 — 108.9 —
Markwardt and Wilson (1935) 12,617 — 108.9 —
Zhang et al. (2006) 12,600 10,500–14,700 — —
Kretschmann (2010) 12,617 — 108.9 —
Duchesne et al. (2016) 10,684 5,434–15,008 113.2 65.4–144.6
Present study 12,417 7,267–15,796 123.6 67–167.2
Yellow poplar
Newlin and Wilson (1917) 11,100 81.35 —
Markwardt and Wilson (1935) 10,342 63.43 —
Faust et al. (1990) 11,032 11,030–11,033 41.56 33.7–49.4
Stern (1944) 10,928 11,611–12,480 — —
Kretschmann (2010) 10,893 69.63 —
Present study 9,611 7,067–12,259 83.4 49.4–108.6
FOREST PRODUCTS JOURNAL Vol. 70, No. 3 333
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studies. It is economically important for the hardwood
industry to confirm the accuracy and reliability of
mechanical property values to develop design values that
are up to date with building codes and regulations.
The staircase industry will be able to use this information
to calculate the strength of wood members and establish safe
working stresses of the studied species. These findings
reinforce the need for ongoing sampling of raw material to
assess possible resource changes over time. More specifi-
cally, the results of this study show the following:
The mechanical properties of hard maple and yellow
poplar have not changed substantially because the
average values remain in a range that is very close to
those of previous studies.
GRC decreased for yellow poplar when compared with
past studies. GRC for hard maple remained similar to that
of previous studies.
The percentage of LW for hard maple was found to be
very similar to that reported in the literature review.
The values found in the literature can still be used for
engineering purposes.
MOE and MOR values for hard maple and yellow poplar
were found to be similar to those of previous studies.
For hard maple, compression parallel to grain values
found in the literature review showed similar values when
compared with the present study. However, the values for
compression perpendicular to grain were found to be
slightly higher.
For yellow poplar, compression strength values are
similar to those used for comparison.
SG and hardness values are similar to those found in
previous studies.
Acknowledgments
This research was funded by a grant from the USDA
Forest Service. This publication is a contribution and is
approved as journal article SB 982 of the Forest and
Wildlife Research Center, Mississippi State University. The
authors are also thankful for the technical assistance
provided by Franklin Quin and Edward Entsminger to carry
out the above work.
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