Plywood , modulus of elasticity, tension, bending, shear Testing

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RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1 103
BIRCH PLYWOOD SAMPLE TENSION AND BENDING PROPERTY INVESTIGATION
AND VALIDATION IN SOLIDWORKS ENVIRONMENT
Agris Zalcmanis1
, Kaspars Zudrags1
, Guntis Japiņš2
1
AS “Latvijas Finieris”, Latvia
2
Riga Technical University, Latvia
agris.zalcmanis@finieris.lv
Abstract
Birch plywood has proved itself to be one of the most rational ways of wood processing. Growing demand of high
performance birch plywood products requires a complex numerical analysis based on Finite Element Method (FEM),
instead of using simple analytical assumptions, which prevent optimization of plywood construction (lay-up). In the
research samples of birch plywood of several thicknesses, both sanded and non-sanded, with fiber direction of external
veneer both in the longitudinal and transverse directions were tested. An extensometer and optical strain gauge were
used for strain measurement. The FEM analysis, using commercial software SolidWorks Simulation Premium (SW),
versus experimental bending and tension testing according to LVS EN 789 was carried out in this paper.
The analysis of results indicates that there is a high correlation between the results of the experiments and the FEM.
Particularly for in tension loaded specimens one can be tested up to the maximum ply strength (100 MPa); meanwhile,
in bending up to 71MPa – the average stress in load bearing ply at the proportionality limit. Due to software restrictions,
shear stresses cannot be evaluated. Future studies are considered to investigate terms for designing plywood with
dynamic properties of strength and stiffness to be taken into account.
Key words: plywood, modulus of elasticity, tension, bending, shear.
Introduction
Birch (Betula sp.) is species of wood typically
found in Eurasia and a second widespread breed
in Latvia, reaching 30.9% (Latvian Forest Sector,
2017). Birch is considered as hardwood and has
excellent mechanical properties due to which it has
a huge economical potential. Nowadays birch is also
one of the main species (38%) used for afforestation
of former agricultural lands (Jansons et al., 2011).
Furthermore, the gain of birch plantations might be
substantially improved by breeding (Zeltiņš et al.,
2018) to satisfy a growing demand for birch products
like lumber, sawn timber and plywood.
Plywood is considered a layered cross-ply
unidirectional fiber reinforced composite produced
from veneers with a fiber direction perpendicular
to each other. A typical usage of birch plywood is
found in automotive (trailer floors, wall linings) and
construction industry (concrete formworks). Plywood
is also used for yacht building, as insulation panels
in liquid natural gas tankers, furniture, builders’
carpentry and joinery and many others. In automotive,
yacht building and sea transport industry analytical
calculations of plywood load bearing capacity and
stiffness must be carried out.
Common praxis is to use simple analytical
assumptions in design of plywood or plywood
constructions. Unfortunately, the use of such a method
restricts application of plywood as a contemporary
construction material, prevents optimization of its
construction (lay-up) and evaluation of stresses
in the material at complex stress states. Computer
simulations based on the finite element method (FEM)
are now fundamental design practices in a number
of high performance industries like aerospace and
aviation. Meanwhile, other industries are beginning
to evaluate the benefits of FEM analysis and use it to
develop innovative solutions.
To develop a reliable design method using FEM,
it is necessary to determine characteristics of plywood
experimentally and validate FEM design guidelines.
In the research samples of birch plywood of several
thicknesses, sanded and non-sanded, with the fiber
direction of external veneer in the longitudinal and
transverse directions were tested. Tensile and bending
tests were conducted according to LVS EN 789. Both
the extensometer and optical strain gauge were used
for strain measurement. The shear modulus and the
global elastic modulus in bending were calculated in
accordance with LVS EN 408. Analysis and validation
of the obtained data indicate that there is a correlation
between the results of the experiments and the FEM.
This paper presents validation of FEM design
method versus experimental bending and tension
testing for birch plywood in commercial software
SolidWorks.
Materials and Methods
In order to elaborate the FEM design method, the
analysis was performed for all panel thicknesses in the
range from 4 to 50 mm manufactured from birch and
glued with phenol formaldehyde resin. Restrictions
for thickness analysis:
• All veneers including outer plies before sanding
must be of the same thickness;
• Thickness of plywood made from virtual plies must
be as close as possible to the average thickness of
actual product in a range as wide as possible.
FORESTRY AND WOOD PROCESSING DOI: 10.22616/rrd.24.2018.016
104 RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1
The following assumptions are made:
• Mechanical properties of layers in same direction
are identical;
• A glue layer between plies is omitted;
• Sanding is symmetric from both sides;
• Only variable to comprehend actual thickness for
particular specimen is sanding depth.
Modeling plywood with a different ply thickness
and sanding depth showed that the ply thickness 1.43
mm and sanding depth 0.4 mm from each side show
the most adequate correlation between actual and
virtual models in the widest range. Table 1 shows
thicknesses and lay-ups of test specimens used in the
FEM method validation.
Table 1
Lay-up and average thickness of specimens
Designation Lay-up
Thickness
for virtual
testing
(sanded)
(mm)
Thickness for
virtual testing
(non-sanded)
(mm)
12-0 I-I-I-I-I 12.07 12.87
12-90 -I-I-I-I- 12.07 12.87
18-0 I-I-I-I-I-I-I 17.79 18.59
18-90 -I-I-I-I-I-I- 17.79 18.59
SolidWorks Premium (Service pack 4.1; Dassault
Systemes, 2017) with Simulation Premium package
(2017) was used for virtual testing. Plywood is
modeled as solid consisting of bodies which represent
mechanical properties of ply (table 2) (Labans et
al., 2017). The material is linear elastic orthotropic,
contact type between plies is ‘bonded’- no slippage or
delamination, entities behave as if they were welded
(‘Bonded contact’, 2017). Solid mesh is ‘compatible’-
the program merges coincident nodes along the
interface (‘Compatible’, 2017).
Table 2
Mechanical properties of birch ply
Property Value
Longitudinal modulus 17 GPa
Transverse modulus 0.5 GPa
Shear modulus 0.7 GPa
Poisson’s ration 0.35
Poisson’s ration 0.01
Longitudinal strength 100 MPa
Transverse strength 4 MPa
Eighty eight (8 groups, 11 specimen in series)
tensile test and forty eight (8 groups, 6 specimen in
series) bending test specimens from birch plywood
were manufactured. Samples were cut from various
panels. Specimens cut from the same panel were
marked. Tensile and bending tests were conducted
according to LVS EN 789. A contact extensometer
was used in tensile tests to measure displacement
of both outer layers, measuring the span 100 mm,
an extensometer was placed symmetrically in the
middle. During the test outer plies of specimen are
clamped with hydraulic jaws. Authors are concerned
that especially for plywood with load bearing outer
plies direct contact with jaws could cause inaccuracy
in measurements and furthermore in calculations of
modulus of elasticity. Hypothesis is put forward that
outer plies deform more than core plies. Figure 1
shows a possible distribution of displacement through
thickness. Optical strain gauge with tracking points
on core plies was used in order to estimate difference
between ply displacements along the thickness of the
sample.
DOI: 10.22616/rrd.24.2018.016
 A glue layer between plies is omitted;
 Sanding is symmetric from both sides;
 Only variable to comprehend actual thickness
for particular specimen is sanding depth.
Modeling plywood with a different ply thickness and
sanding depth showed that the ply thickness 1.43 mm
and sanding depth 0.4 mm from each side show the
most adequate correlation between actual and virtual
models in the widest range. Table 1 shows thicknesses
and lay-ups of test specimens used in the FEM method
validation.
Table 1
Lay-up and average thickness of specimens
Design
ation
Lay-up Thickness
for virtual
testing
(sanded)
(mm)
Thickness
for virtual
testing
(nonsanded)
(mm)
12-0 I-I-I-I-I 12.07 12.87
12-90 -I-I-I-I- 12.07 12.87
18-0 I-I-I-I-I-I-I 17.79 18.59
18-90 -I-I-I-I-I-I- 17.79 18.59
SolidWorks Premium (Service pack 4.1;
Dassault Systemes, 2017) with Simulation Premium
package (2017) was used for virtual testing. Plywood is
modeled as solid consisting of bodies which represent
mechanical properties of ply (table 2) (Labans et al.,
2017). The material is linear elastic orthotropic, contact
type between plies is ‘bonded’- no slippage or
delamination, entities behave as if they were welded
(‘Bonded contact’, 2017). Solid mesh is ‘compatible’-
the program merges coincident nodes along the
interface (‘Compatible’, 2017).
Table 2
Mechanical properties of birch ply
Property Value
Longitudinal modulus 𝐸𝐸𝑥𝑥 17 GPa
Transverse modulus 𝐸𝐸𝑦𝑦,𝑧𝑧 0.5 GPa
Shear modulus 𝐺𝐺𝑥𝑥𝑥𝑥,𝑦𝑦𝑦𝑦,𝑥𝑥𝑥𝑥 0.7 GPa
Poisson’s ration 𝑃𝑃𝑥𝑥𝑥𝑥,𝑥𝑥𝑥𝑥 0.35
Poisson’s ration 𝑃𝑃𝑦𝑦𝑦𝑦 0.01
Longitudinal strength 𝜎𝜎𝑥𝑥 100 MPa
Transverse strength 𝜎𝜎𝑦𝑦 4 MPa
Eighty eight (8 groups, 11 specimen in series)
tensile test and forty eight (8 groups, 6 specimen in
series) bending test specimens from birch plywood
were manufactured. Samples were cut from various
panels. Specimens cut from the same panel were
marked. Tensile and bending tests were conducted
according to LVS EN 789. A contact extensometer was
used in tensile tests to measure displacement of both
outer layers, measuring the span 100 mm, an
extensometer was placed symmetrically in the middle.
During the test outer plies of specimen are clamped
with hydraulic jaws. Authors are concerned that
especially for plywood with load bearing outer plies
direct contact with jaws could cause inaccuracy in
measurements and furthermore in calculations of
modulus of elasticity. Hypothesis is put forward that
outer plies deform more than core plies. Figure 1 shows
a possible distribution of displacement through
thickness. Optical strain gauge with tracking points on
core plies was used in order to estimate difference
between ply displacements along the thickness of the
sample.
Figure 1. Distribution of displacement through
thickness in tensile test.
(1 – jaws; 2 – test specimen).
In four-point bending test specimen
dimensions are dependent on thickness. The span
length is calculated according to the nominal thickness
regardless of the surface condition. For samples with
the nominal thickness 12 mm span length is 684 mm
and the overall sample length is 884 mm, for samples
with the nominal thickness 18 mm – 876 mm and 1,076
mm. The distance between loading points is 300 mm.
During the test the local deflection on the
compression side of panel (top) and the global
deflection on the tension side of panel (bottom) of
bending was measured with two high precision plunger
type extensometers located in the middle of the span.
The local modulus of elasticity in bending was
calculated according to LVS EN 789. The global
modulus of elasticity in bending was calculated
according to LVS EN 408. Values calculated according
to LVS EN 408 cannot be used for calculations of
characteristic values. Shear deformation of the layers in
the vicinity of the support was measured according to
LVS EN 408 shear field test method as it allows
collecting all the necessary data together with the
determination of the bending strength and global
modulus of elasticity. LVS EN 789, in contrast,
requires special specimens and loading equipment.
Optical strain gauge with four tracking points forming
Figure 1. Distribution of displacement through
thickness in tensile test.
(1 – jaws; 2 – test specimen).
In four-point bending test specimen dimensions are
dependent on thickness. The span length is calculated
according to the nominal thickness regardless of the
surface condition. For samples with the nominal
thickness 12 mm span length is 684 mm and the
overall sample length is 884 mm, for samples with the
nominal thickness 18 mm – 876 mm and 1,076 mm.
The distance between loading points is 300 mm.
During the test the local deflection on the
compression side of panel (top) and the global
deflection on the tension side of panel (bottom)
of bending was measured with two high precision
plunger type extensometers located in the middle of
Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT
RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1 105
the span. The local modulus of elasticity in bending
was calculated according to LVS EN 789. The global
modulus of elasticity in bending was calculated
according to LVS EN 408. Values calculated according
to LVS EN 408 cannot be used for calculations of
characteristic values. Shear deformation of the layers
in the vicinity of the support was measured according
to LVS EN 408 shear field test method as it allows
collecting all the necessary data together with the
determination of the bending strength and global
modulus of elasticity. LVS EN 789, in contrast,
requires special specimens and loading equipment.
Optical strain gauge with four tracking points
forming a square was used for the shear deformation
measurement (Figure 2).
DOI: 10.22616/rrd.24.2018.016
a square was used for the shear deformation
measurement (Figure 2).
Figure 2. Four-point bending test arrangement with shear deformation measuring. (1 – test specimen; 2 – loading bars; 3 – optical strain gauge; 4 – vision field of camera; 5 – support bars; 6 – tracking points). Attempts were made to measure the permanent deformation to determine the limit of elasticity. An optical strain gauge with one tracking point in the middle of the span was used to obtain a deflection-force curve during relief of the specimen. Statistical processing of obtained data was performed, the modulus of elasticity in tension and bending was calculated as well as a planar shear modulus in bending. A virtual testing of specimens with the same geometric parameters was carried out. Strainstress curves were plotted to validate numerical results with experimental. Results and Discussion Obtained numerical calculations and experimental results are in a good agreement confirming that input values for the ply thickness and mechanical properties describe birch plywood under bending and tensile loads relatively well. The rupture in tension for almost all specimens regardless of fiber orientation in the outer ply happened along the line where a fillet started. A minor part of specimens ruptured in the uniform stress zone. The rupture near jaws or in the fillet zone was not observed. The stress concentrator in exactly the same place can be seen in FEM model (Figure 3). 12mm-0- unsanded maximum stress in ply reaches 125 MPa, while the average stress across the cross section of ply is 103 MPa. The average stress in the vicinity of fillet is equal with the average stress in the uniform stress zone. Figure 3. Stress distribution in FEM model. (1 – non load bearing veneer; 2 – load bearing veneer; 3 – fillet starting zone). Strain measurement parameters used in the experiment were reproduced in a virtual test with tracking points on outer surfaces. LVS EN 1058 allows using mean values of modulus of elasticity from series as a characteristic value. The mean thickness of plywood will be used for the FEM method validation. Figure 4 shows an example of the load-deflection curve obtained from the test and virtual test. It is clearly visible that the load-elongation curve is linear up to the rupture. Summary of test results for all specimen groups are shown in Table 3 and Table 4. Figure 4. Load-elongation curve for 12mm-0-unsanded plywood. Figure 2. Four-point bending test arrangement with shear deformation measuring. (1 – test specimen; 2 – loading bars; 3 – optical strain gauge; 4 – vision field of camera; 5 – support bars; 6 – tracking points). Attempts were made to measure the permanent deformation to determine the limit of elasticity. An optical strain gauge with one tracking point in the middle of the span was used to obtain a deflectionforce curve during relief of the specimen. Statistical processing of obtained data was performed, the modulus of elasticity in tension and bending was calculated as well as a planar shear modulus in bending. A virtual testing of specimens with the same geometric parameters was carried out. Strain-stress curves were plotted to validate numerical results with experimental. Results and Discussion Obtained numerical calculations and experimental results are in a good agreement confirming that input values for the ply thickness and mechanical properties describe birch plywood under bending and tensile loads relatively well. The rupture in tension for almost all specimens regardless of fiber orientation in the outer ply happened along the line where a fillet started. A minor part of specimens ruptured in the uniform stress zone. The rupture near jaws or in the fillet zone was not observed. The stress concentrator in exactly the same place can be seen in FEM model (Figure 3). 12mm0-unsanded maximum stress in ply reaches 125 MPa, while the average stress across the cross section of ply is 103 MPa. The average stress in the vicinity of fillet is equal with the average stress in the uniform stress zone. DOI: 10.22616/rrd.24.2018.016 a square was used for the shear deformation measurement (Figure 2).
Figure 2. Four-point bending test arrangement with
shear deformation measuring.
(1 – test specimen; 2 – loading bars; 3 –
optical strain gauge; 4 – vision field of
camera; 5 – support bars; 6 – tracking
points).
Attempts were made to measure the permanent
deformation to determine the limit of elasticity. An
optical strain gauge with one tracking point in the
middle of the span was used to obtain a deflection-force
curve during relief of the specimen.
Statistical processing of obtained data was
performed, the modulus of elasticity in tension and
bending was calculated as well as a planar shear
modulus in bending. A virtual testing of specimens with
the same geometric parameters was carried out. Strainstress curves were plotted to validate numerical results
with experimental.
Results and Discussion
Obtained numerical calculations and
experimental results are in a good agreement
confirming that input values for the ply thickness and
mechanical properties describe birch plywood under
bending and tensile loads relatively well.
The rupture in tension for almost all
specimens regardless of fiber orientation in the outer
ply happened along the line where a fillet started. A
minor part of specimens ruptured in the uniform stress
zone. The rupture near jaws or in the fillet zone was not
observed. The stress concentrator in exactly the same
place can be seen in FEM model (Figure 3). 12mm-0-
unsanded maximum stress in ply reaches 125 MPa,
while the average stress across the cross section of ply
is 103 MPa. The average stress in the vicinity of fillet
is equal with the average stress in the uniform stress
zone.
Figure 3. Stress distribution in FEM model.
(1 – non load bearing veneer; 2 – load bearing
veneer; 3 – fillet starting zone).
Strain measurement parameters used in the experiment
were reproduced in a virtual test with tracking points on
outer surfaces. LVS EN 1058 allows using mean values
of modulus of elasticity from series as a characteristic
value. The mean thickness of plywood will be used for
the FEM method validation. Figure 4 shows an example
of the load-deflection curve obtained from the test and
virtual test. It is clearly visible that the load-elongation
curve is linear up to the rupture. Summary of test results
for all specimen groups are shown in Table 3 and Table
4.
Figure 4. Load-elongation curve for 12mm-0-unsanded plywood.
Figure 3. Stress distribution in FEM model.
(1 – non load bearing veneer; 2 – load bearing veneer; 3 –
fillet starting zone).
Strain measurement parameters used in the
experiment were reproduced in a virtual test with
tracking points on outer surfaces. LVS EN 1058 allows
using mean values of modulus of elasticity from
series as a characteristic value. The mean thickness of
plywood will be used for the FEM method validation.
Figure 4 shows an example of the load-deflection
curve obtained from the test and virtual test. It is
clearly visible that the load-elongation curve is linear
up to the rupture. Summary of test results for all
specimen groups are shown in Table 3 and Table 4.
Capturing of individual ply displacement is
continued up to the rupture. Regardless of the surface
condition of outer ply – sanded or non-sanded, with
fiber direction parallel or perpendicular, it deforms
more than core plies. The hypothesis is partly
confirmed. There is a noticeable difference between
strains among plies. The summary of results for
specimen groups is shown in Table 5.
Results indicate that thicker panels are having
bigger differences in the outer and core ply strain. 12
mm panels regardless of surface condition of the outer
ply – sanded or non-sanded, with a fiber direction
Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT
106 RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1
Figure 4. Load-elongation curve for 12mm-0-unsanded plywood.
Table 3
Results of tensile test
Specimen
designation
Average
stress
DOI: 10.22616/rrd.24.2018.016
Table 3
Results of tensile test
Specimen
designation
Average
stress
𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Standard
deviation
𝑠𝑠
(MPa)
CV
(%)
Min
stress
(MPa)
Allowable
design stress
𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠
(MPa)
Tension
strength
(Plywood
Handbook,
2017)
(MPa)
Average
stress in
load
bearing
ply from
SW
(MPa)
Max
stress in
load
bearing
ply
from
SW
(MPa)
12mm-0-
unsanded
58.7 5.6 9.5 50.5 47.6 43.3 103 125
12mm-90-
unsanded
53.3 5.0 9.4 45.7 43.3 34.7 115 136
12mm-0-
sanded
50.5 8.5 16.8 40.3 33.5 41.6 93.5 113
12mm-90-
sanded*
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) Standard deviation DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) CV (%) Min stress (MPa) Allowable design stress DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. Due to restrains in testing equipment and large deflections of specimen, it was impossible to evaluate the bending failure strength. Therefore, specimens were tested only up to the maximum deflection possible in the testing set-up. The global and local modulus of elasticity in bending was calculated. Permanent deformation was observed. Four out of six specimens in series were used to evaluate shear modulus in the shear field (LVS, 2011), two were used for the measurement of permanent deformation. Results shown in Table 6 prove that the shear field test method developed for structural and laminated timber can be used for the shear deformation measurement also for wooden cross-ply – plywood. Unfortunately, interlaminar shear stress components do not apply for bodies defined as orthotropic materials (‘Composite Laminate’, 2017) for current SolidWorks Simulation Professional license, values obtained from the ply relative displacement Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš BIRCH PLYWOOD SAMPLE TENSION AND BENDING PROPERTY INVESTIGATION AND VALIDATION IN SOLIDWORKS ENVIRONMENT RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1 107 test in tension and shear field test in bending cannot be validated. Lack of shear deformation will cause an inaccuracy in measurements for thick plywood panels. Figure 5 shows an example of load-deflection curve obtained from the test. It is clearly visible that a load-elongation curve is linear up to the proportional limit, followed by the non-linear stiffness decrease. Linear approximation is used to approximate elastic modulus in bending after the proportional limit. Elastic deformation is calculated according to formula: DOI: 10.22616/rrd.24.2018.016 Due to restrains in testing equipment and large deflections of specimen, it was impossible to evaluate the bending failure strength. Therefore, specimens were tested only up to the maximum deflection possible in the testing set-up. The global and local modulus of elasticity in bending was calculated. Permanent deformation was observed. Four out of six specimens in series were used to evaluate shear modulus in the shear field (LVS, 2011), two were used for the measurement of permanent deformation. Table 5 Strain at rupture among plies Specimen designation Average strain of core ply Average strain of outer ply Average strain SW 12mm-0- unsanded 0.0062 0.0067 0.0064 12mm-90- unsanded 0.0069 0.0075 0.0068 12mm-0- sanded 0.0057 0.0062 0.0055 12mm-90- sanded

– 0.0069
18mm-0-
unsanded
0.0054 0.0066 0.0062
18mm-90-
unsanded*
– 0.0054
18mm-0-
sanded
0.0050 0.0059 0.0063
18mm-90-
sanded
0.0056 0.0069 0.0059
Results shown in Table 6 prove that the shear
field test method developed for structural and
laminated timber can be used for the shear deformation
measurement also for wooden cross-ply – plywood.
Unfortunately, interlaminar shear stress
components do not apply for bodies defined as
orthotropic materials (‘Composite Laminate’, 2017) for
current SolidWorks Simulation Professional license,
values obtained from the ply relative displacement test
in tension and shear field test in bending cannot be
validated. Lack of shear deformation will cause an
inaccuracy in measurements for thick plywood panels.
Table 6
Planar shear modulus
Specimen
designation
Planar shear
modulus
𝐺𝐺𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠 (MPa)
Planar shear
modulus
(Plywood
Handbook, 2017)
(MPa)
12mm-0-
unsanded
240 192
12mm-90-
unsanded
198 149
12mm-0-
sanded
140 190
12mm-90-
sanded
171 156
18mm-0-
unsanded
184 192
18mm-90-
unsanded
242 162
18mm-0-
sanded
174 189
18mm-90-
sanded
182 168
Figure 5 shows an example of load-deflection
curve obtained from the test. It is clearly visible that a
load-elongation curve is linear up to the proportional
limit, followed by the non-linear stiffness decrease.
Linear approximation is used to approximate elastic
modulus in bending after the proportional limit. Elastic
deformation is calculated according to formula:
𝑤𝑤𝑒𝑒 = 𝑤𝑤𝑡𝑡𝑡𝑡𝑡𝑡 − 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝, (1)
Where: 𝑤𝑤𝑡𝑡𝑡𝑡𝑡𝑡 – total deflection (mm), 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 –
permanent deformation.
Figure 5. Load-deflection curve for the 12mm-0-unsanded plywood.
, (1)
where: – total deflection (mm), – permanent
deformation.
Table 4
Results of tensile test
Specimen
designation
Average
modulus of
elasticity
DOI: 10.22616/rrd.24.2018.016
Table 3
Results of tensile test
Specimen
designation
Average
stress
𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Standard
deviation
𝑠𝑠
(MPa)
CV
(%)
Min
stress
(MPa)
Allowable
design stress
𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠
(MPa)
Tension
strength
(Plywood
Handbook,
2017)
(MPa)
Average
stress in
load
bearing
ply from
SW
(MPa)
Max
stress in
load
bearing
ply
from
SW
(MPa)
12mm-0-
unsanded
58.7 5.6 9.5 50.5 47.6 43.3 103 125
12mm-90-
unsanded
53.3 5.0 9.4 45.7 43.3 34.7 115 136
12mm-0-
sanded
50.5 8.5 16.8 40.3 33.5 41.6 93.5 113
12mm-90-
sanded*
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) Min modulus of elasticity DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) Max modulus of elasticity DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) Elastic modulus from SW DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (MPa) DOI: 10.22616/rrd.24.2018.016 Table 3 Results of tensile test Specimen designation Average stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Standard deviation 𝑠𝑠 (MPa) CV (%) Min stress (MPa) Allowable design stress 𝜎𝜎𝑎𝑎𝑎𝑎𝑎𝑎 − 2 ∗ 𝑠𝑠 (MPa) Tension strength (Plywood Handbook, 2017) (MPa) Average stress in load bearing ply from SW (MPa) Max stress in load bearing ply from SW (MPa) 12mm-0- unsanded 58.7 5.6 9.5 50.5 47.6 43.3 103 125 12mm-90- unsanded 53.3 5.0 9.4 45.7 43.3 34.7 115 136 12mm-0- sanded 50.5 8.5 16.8 40.3 33.5 41.6 93.5 113 12mm-90- sanded
57.6 1.5 2.6 56.6 54.6 36.4 117 139
18mm-0-
unsanded
55.8 5.1 9.2 48.5 45.5 42.0 106 129
18mm-90-
unsanded*
44.0 0.9 2.0 43.0 42.2 36.0 92 109
18mm-0-
sanded
57.3 3.9 6.9 52.2 49.4 40.8 107 130
18mm-90-
sanded
49.9 5.0 10.0 41.6 39.9 37.2 100 119
Samples taken out of stress analysis due to errors. Remaining samples are from the same panel. Table 4 Results of tensile test Specimen designation Average modulus of elasticity 𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎 (MPa) Min modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Max modulus of elasticity 𝐸𝐸𝑡𝑡;𝑚𝑚𝑚𝑚𝑚𝑚 (MPa) Elastic modulus from SW 𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆 (MPa) (𝐸𝐸𝑡𝑡;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑡𝑡;𝑎𝑎𝑎𝑎𝑎𝑎) − 1 (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0- unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90- unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0- unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90- unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Capturing of individual ply displacement is continued up to the rupture. Regardless of the surface condition of outer ply – sanded or non-sanded, with fiber direction parallel or perpendicular, it deforms more than core plies. The hypothesis is partly confirmed. There is a noticeable difference between strains among plies. The summary of results for specimen groups is shown in Table 5. Results indicate that thicker panels are having bigger differences in the outer and core ply strain. 12 mm panels regardless of surface condition of the outer ply – sanded or non-sanded, with a fiber direction parallel or perpendicular got the average disparity of 0.0005 mm/mm, meanwhile 18 mm panels 0.0011 mm/mm. The difference of plywood panels thickness used in tests is 1.5 times, but the difference of average disparity – 2.2. (%) Elastic modulus in tension (Plywood Handbook, 2017) (MPa) 12mm-0-unsanded 10615 9699 11250 9712 -8.5 10000 12mm-90-unsanded 8881 7777 10639 7838 -11.7 8000 12mm-0-sanded 9108 7625 10113 9182 0.8 9600 12mm-90-sanded 8168 6788 10193 8342 2.2 8400 18mm-0-unsanded 9789 9231 10326 9000 -8.1 9692 18mm-90-unsanded 8753 7919 10163 8148 -6.9 8308 18mm-0-sanded 10554 9416 12260 9095 -13.8 9409 18mm-90-sanded 8846 8058 10163 8458 -4.4 8591 Table 5 Strain at rupture among plies Specimen designation Average strain of core ply Average strain of outer ply Average strain SW 12mm-0-unsanded 0.0062 0.0067 0.0064 12mm-90-unsanded 0.0069 0.0075 0.0068 12mm-0-sanded 0.0057 0.0062 0.0055 12mm-90-sanded – – 0.0069
18mm-0-unsanded 0.0054 0.0066 0.0062
18mm-90-unsanded* – – 0.0054
18mm-0-sanded 0.0050 0.0059 0.0063
18mm-90-sanded 0.0056 0.0069 0.0059
Table 6
Planar shear modulus
Specimen designation Planar shear modulus
DOI: 10.22616/rrd.24.2018.016
Due to restrains in testing equipment and large
deflections of specimen, it was impossible to evaluate
the bending failure strength. Therefore, specimens were
tested only up to the maximum deflection possible in
the testing set-up. The global and local modulus of
elasticity in bending was calculated. Permanent
deformation was observed. Four out of six specimens
in series were used to evaluate shear modulus in the
shear field (LVS, 2011), two were used for the
measurement of permanent deformation.
Table 5
Strain at rupture among plies
Specimen
designation
Average
strain of
core ply
Average
strain of
outer ply
Average
strain
SW
12mm-0-
unsanded
0.0062 0.0067 0.0064
12mm-90-
unsanded
0.0069 0.0075 0.0068
12mm-0-
sanded
0.0057 0.0062 0.0055
12mm-90-
sanded*
– 0.0069
18mm-0-
unsanded
0.0054 0.0066 0.0062
18mm-90-
unsanded*
– 0.0054
18mm-0-
sanded
0.0050 0.0059 0.0063
18mm-90-
sanded
0.0056 0.0069 0.0059
Results shown in Table 6 prove that the shear
field test method developed for structural and
laminated timber can be used for the shear deformation
measurement also for wooden cross-ply – plywood.
Unfortunately, interlaminar shear stress
components do not apply for bodies defined as
orthotropic materials (‘Composite Laminate’, 2017) for
current SolidWorks Simulation Professional license,
values obtained from the ply relative displacement test
in tension and shear field test in bending cannot be
validated. Lack of shear deformation will cause an
inaccuracy in measurements for thick plywood panels.
Table 6
Planar shear modulus
Specimen
designation
Planar shear
modulus
𝐺𝐺𝑡𝑡𝑡𝑡𝑡𝑡,𝑠𝑠 (MPa)
Planar shear
modulus
(Plywood
Handbook, 2017)
(MPa)
12mm-0-
unsanded
240 192
12mm-90-
unsanded
198 149
12mm-0-
sanded
140 190
12mm-90-
sanded
171 156
18mm-0-
unsanded
184 192
18mm-90-
unsanded
242 162
18mm-0-
sanded
174 189
18mm-90-
sanded
182 168
Figure 5 shows an example of load-deflection
curve obtained from the test. It is clearly visible that a
load-elongation curve is linear up to the proportional
limit, followed by the non-linear stiffness decrease.
Linear approximation is used to approximate elastic
modulus in bending after the proportional limit. Elastic
deformation is calculated according to formula:
𝑤𝑤𝑒𝑒 = 𝑤𝑤𝑡𝑡𝑡𝑡𝑡𝑡 − 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝, (1)
Where: 𝑤𝑤𝑡𝑡𝑡𝑡𝑡𝑡 – total deflection (mm), 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 –
permanent deformation.
Figure 5. Load-deflection curve for the 12mm-0-unsanded plywood.
(MPa)
Planar shear modulus
(Plywood Handbook, 2017) (MPa)
12mm-0-unsanded 240 192
12mm-90-unsanded 198 149
12mm-0-sanded 140 190
12mm-90-sanded 171 156
18mm-0-unsanded 184 192
18mm-90-unsanded 242 162
18mm-0-sanded 174 189
18mm-90-sanded 182 168
Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT
108 RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1
Figure 5. Load-deflection curve for the 12mm-0-unsanded plywood.
Table 7
Results of four-point bending test
Specimen
designation
Average modulus
of elasticity up to
proportional limit
DOI: 10.22616/rrd.24.2018.016
Table 7
Results of four-point bending test
Specimen
designation
Average
modulus of
elasticity up to
proportional
limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Average modulus
of elasticity up to
proportional limit
with shear
𝐸𝐸𝑏𝑏,𝑔𝑔;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Elastic
modulus
from SW
𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆
(MPa)
(𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
Elastic modulus
in bending
(Plywood
Handbook,
2017) (MPa)
12mm-0-
unsanded
11762 12072 11444 -2.7 11975
12mm-90-
unsanded
6340 6464 6093 -3.9 6025
12mm-0-sanded 10423 10874 10426 0.0 11026
12mm-90-
sanded
8372 8496 7280 -13.0 6974
18mm-0-
unsanded
10888 11692 10332 -5.1 11069
18mm-90-
unsanded
7276 7375 6648 -8.6 6931
18mm-0-sanded 10097 10454 9470 -6.2 10335
18mm-90-
sanded
8156 8472 7532 -7.6 7665
Table 8
Results of four-point bending test
Specimen
designation
Average modulus of elasticity
after proportional limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′
(MPa)
Average stress in outer load
bearing ply at proportional
limit from SW
(MPa)
(𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′ ⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
12mm-0-unsanded 7265 74.4 -38.2
12mm-90-unsanded 3655 75.2 -42.3
12mm-0-sanded 6303 70.4 -39.5
12mm-90-sanded 5057 74.0 -39.6
18mm-0-unsanded 5542 72.3 -49.1
18mm-90-unsanded 3791 67.8 -47.9
18mm-0-sanded 6026 68.3 -40.3
18mm-90-sanded 3751 64.2 -54.0

From the relief curve it is visible that if it
cannot be approximated with the line parallel to loading
up to the proportional limit, bending has caused a
damage in the material. Stiffness degradation has
happened. The summary of test results for all specimen
groups are shown in Table 7 and Table 8. As there are
no shear deformations in SolidWorks, global modulus
of elasticity in bending for the FEM method validation
will be calculated with the infinite shear modulus (LVS,
2011). Deflection measurement parameters used in the
experiment were reproduced in the virtual test with
tracking points on outer surfaces. Figure 6 shows the
stress distribution in test specimen. As expected, there
is an equal and truly uniform stress zone between lines
where the load is applied on a tension and compression
side. Modulus of elasticity is strongly dependent on the
thickness because in calculations it is in third order. For
this reason virtual tests were carried out for every
particular specimen, with adapted sanding depth to
match thickness with corresponding test sample, only
then mean values were calculated.
Figure 6. Stress distribution in bending for 12mm-0-
unsanded plywood.
Results of tensile and bending tests show that elastic
modulus obtained from SW is 6.1% smaller than the
(%)
Elastic modulus in
bending (Plywood
Handbook, 2017)
(MPa)
12mm-0-unsanded 11762 12072 11444 -2.7 11975
12mm-90-unsanded 6340 6464 6093 -3.9 6025
12mm-0-sanded 10423 10874 10426 0.0 11026
12mm-90-sanded 8372 8496 7280 -13.0 6974
18mm-0-unsanded 10888 11692 10332 -5.1 11069
18mm-90-unsanded 7276 7375 6648 -8.6 6931
18mm-0-sanded 10097 10454 9470 -6.2 10335
18mm-90-sanded 8156 8472 7532 -7.6 7665
Table 8
Results of four-point bending test
Specimen
designation
Average modulus of elasticity
after proportional limit
DOI: 10.22616/rrd.24.2018.016
Table 7
Results of four-point bending test
Specimen
designation
Average
modulus of
elasticity up to
proportional
limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Average modulus
of elasticity up to
proportional limit
with shear
𝐸𝐸𝑏𝑏,𝑔𝑔;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Elastic
modulus
from SW
𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆
(MPa)
(𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
Elastic modulus
in bending
(Plywood
Handbook,
2017) (MPa)
12mm-0-
unsanded
11762 12072 11444 -2.7 11975
12mm-90-
unsanded
6340 6464 6093 -3.9 6025
12mm-0-sanded 10423 10874 10426 0.0 11026
12mm-90-
sanded
8372 8496 7280 -13.0 6974
18mm-0-
unsanded
10888 11692 10332 -5.1 11069
18mm-90-
unsanded
7276 7375 6648 -8.6 6931
18mm-0-sanded 10097 10454 9470 -6.2 10335
18mm-90-
sanded
8156 8472 7532 -7.6 7665
Table 8
Results of four-point bending test
Specimen
designation
Average modulus of elasticity
after proportional limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′
(MPa)
Average stress in outer load
bearing ply at proportional
limit from SW
(MPa)
(𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′ ⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
12mm-0-unsanded 7265 74.4 -38.2
12mm-90-unsanded 3655 75.2 -42.3
12mm-0-sanded 6303 70.4 -39.5
12mm-90-sanded 5057 74.0 -39.6
18mm-0-unsanded 5542 72.3 -49.1
18mm-90-unsanded 3791 67.8 -47.9
18mm-0-sanded 6026 68.3 -40.3
18mm-90-sanded 3751 64.2 -54.0

From the relief curve it is visible that if it
cannot be approximated with the line parallel to loading
up to the proportional limit, bending has caused a
damage in the material. Stiffness degradation has
happened. The summary of test results for all specimen
groups are shown in Table 7 and Table 8. As there are
no shear deformations in SolidWorks, global modulus
of elasticity in bending for the FEM method validation
will be calculated with the infinite shear modulus (LVS,
2011). Deflection measurement parameters used in the
experiment were reproduced in the virtual test with
tracking points on outer surfaces. Figure 6 shows the
stress distribution in test specimen. As expected, there
is an equal and truly uniform stress zone between lines
where the load is applied on a tension and compression
side. Modulus of elasticity is strongly dependent on the
thickness because in calculations it is in third order. For
this reason virtual tests were carried out for every
particular specimen, with adapted sanding depth to
match thickness with corresponding test sample, only
then mean values were calculated.
Figure 6. Stress distribution in bending for 12mm-0-
unsanded plywood.
Results of tensile and bending tests show that elastic
modulus obtained from SW is 6.1% smaller than the
(%)
12mm-0-unsanded 7265 74.4 -38.2
12mm-90-unsanded 3655 75.2 -42.3
12mm-0-sanded 6303 70.4 -39.5
12mm-90-sanded 5057 74.0 -39.6
18mm-0-unsanded 5542 72.3 -49.1
18mm-90-unsanded 3791 67.8 -47.9
18mm-0-sanded 6026 68.3 -40.3
18mm-90-sanded 3751 64.2 -54.0
Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT
RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1 109
From the relief curve it is visible that if it cannot
be approximated with the line parallel to loading up to
the proportional limit, bending has caused a damage
in the material. Stiffness degradation has happened.
The summary of test results for all specimen groups
are shown in Table 7 and Table 8. As there are no
shear deformations in SolidWorks, global modulus of
elasticity in bending for the FEM method validation
will be calculated with the infinite shear modulus
(LVS, 2011). Deflection measurement parameters
used in the experiment were reproduced in the virtual
test with tracking points on outer surfaces. Figure 6
shows the stress distribution in test specimen. As
expected, there is an equal and truly uniform stress
zone between lines where the load is applied on a
tension and compression side. Modulus of elasticity
is strongly dependent on the thickness because in
calculations it is in third order. For this reason virtual
tests were carried out for every particular specimen,
with adapted sanding depth to match thickness with
corresponding test sample, only then mean values
were calculated.
DOI: 10.22616/rrd.24.2018.016
Table 7
Results of four-point bending test
Specimen
designation
Average
modulus of
elasticity up to
proportional
limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Average modulus
of elasticity up to
proportional limit
with shear
𝐸𝐸𝑏𝑏,𝑔𝑔;𝑎𝑎𝑎𝑎𝑎𝑎
(MPa)
Elastic
modulus
from SW
𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆
(MPa)
(𝐸𝐸𝑏𝑏;𝑆𝑆𝑆𝑆⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
Elastic modulus
in bending
(Plywood
Handbook,
2017) (MPa)
12mm-0-
unsanded
11762 12072 11444 -2.7 11975
12mm-90-
unsanded
6340 6464 6093 -3.9 6025
12mm-0-sanded 10423 10874 10426 0.0 11026
12mm-90-
sanded
8372 8496 7280 -13.0 6974
18mm-0-
unsanded
10888 11692 10332 -5.1 11069
18mm-90-
unsanded
7276 7375 6648 -8.6 6931
18mm-0-sanded 10097 10454 9470 -6.2 10335
18mm-90-
sanded
8156 8472 7532 -7.6 7665
Table 8
Results of four-point bending test
Specimen
designation
Average modulus of elasticity
after proportional limit 𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′
(MPa)
Average stress in outer load
bearing ply at proportional
limit from SW
(MPa)
(𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎
′ ⁄𝐸𝐸𝑏𝑏;𝑎𝑎𝑎𝑎𝑎𝑎) − 1
(%)
12mm-0-unsanded 7265 74.4 -38.2
12mm-90-unsanded 3655 75.2 -42.3
12mm-0-sanded 6303 70.4 -39.5
12mm-90-sanded 5057 74.0 -39.6
18mm-0-unsanded 5542 72.3 -49.1
18mm-90-unsanded 3791 67.8 -47.9
18mm-0-sanded 6026 68.3 -40.3
18mm-90-sanded 3751 64.2 -54.0

The FEM design method elaborated and validated
in this paper can be used for virtual testing of birch
plywood in SW environment ( in bending tests, in
tension tests), although for bending tests model
used here is valid only for linearly elastic region
up to the proportionality limit.
More tests need to be performed to evaluate
modulus of elasticity in tension with through pins
and optical strain gauge. Bending experiments
from proportional limit up to the rupture need
to be conducted, as well as the appearance of
stiffness degradation in the elastic region must be
investigated. A decrease of stiffness and strength
must be evaluated with cyclic loading tests.
Simple analytical assumptions can be used for
basic calculations, but when stress concentrators,
large displacements and complex stress states arise,
the FEM design method must be used instead.
Acknowledgements
In accordance with the contract No.
1.2.1.1/16/A/009 between “Forest Sector Competence
Centre” Ltd. and the Central Finance and Contracting
Agency, concluded on 13th of October, 2016, the study
has been conducted by the JSC Latvijas Finieris with
support from the European Regional Development
Fund (ERDF) within the framework of the project
“Forest Sector Competence Centre”.
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Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT
110 RESEARCH FOR RURAL DEVELOPMENT 2018, VOLUME 1
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Agris Zalcmanis, Kaspars Zudrags, Guntis Japiņš
BIRCH PLYWOOD SAMPLE TENSION AND
BENDING PROPERTY INVESTIGATION AND
VALIDATION IN SOLIDWORKS ENVIRONMENT

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