In this study a review of existing recognised standards for wood mechanical testing was conducted. This review considers tensile, compressive, bending and shear test methodologies from a range of sources. In addition, values for wood mechanical properties were obtained through controlled experimentation using a universal material testing machine. Selected standard procedures were used to obtain wood strength properties both along and across the grain. These consist of a three point bending procedure used to evaluate the wood strength across the grain and a longitudinal shear procedure used to evaluate the wood

strength along the grain. Strength properties obtained through controlled experimentation are compared to values available in existing literature with little discrepancy

Hackney, Philip

Naylor, Andrew

Perera, Noel

English

Northumbria Research Link

Northumbria Research Link
Citation: Naylor, Andrew, Hackney, Philip and Perera, Noel (2012) Determination of wood strength 
properties  through  standard  test  procedures.  In:  ICMR  2012:  10th  International  Conference  on 
Manufacturing Research, 11-13 September 2012, Aston University, Birmingham, UK. 
URL: http://www1.aston.ac.uk/icmr2012/ <http://www1.aston.ac.uk/icmr2012/>
This version was downloaded from Northumbria Research Link: http://nrl.northumbria.ac.uk/9686/
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Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
372
DETERMINATION OF WOOD STRENGTH PROPERTIES THROUGH STANDARD TEST
PROCEDURES
Andrew Naylor
Philip Hackney
Noel Perera
School of Computing, Engineering and Information Sciences
Northumbria University, Ellison Building
Newcastle Upon Tyne, NE1 8ST, UK
andrew2.naylor@northumbria.ac.uk
ABSTRACT
In this study a review of existing recognised standards for wood mechanical testing was conducted. This
review considers tensile, compressive, bending and shear test methodologies from a range of sources. In
addition, values for wood mechanical properties were obtained through controlled experimentation using
a universal material testing machine. Selected standard procedures were used to obtain wood strength
properties both along and across the grain. These consist of a three point bending procedure used to
evaluate the wood strength across the grain and a longitudinal shear procedure used to evaluate the wood
strength along the grain. Strength properties obtained through controlled experimentation are compared to
values available in existing literature with little discrepancy.
Keywords: Mechanical Test Procedures, Universal Testing Machine, Wood Strength Properties
1 INTRODUCTION
Wood is anisotropic and hence some mechanical test procedures are often performed both along and
across the grain. Tension and compression tests have been successfully performed both along and across
the grain. Compression tests show that wood has much larger strength and modulus of elasticity values
along the grain rather than across (Reiterer and Stanzl-Tschegg 2001, Manríquezand Moraes 2009). The
trend for tensile tests is the same as compressive (Oh 2011, Galicki and Czech 2005) (larger values along
the grain). However, the magnitude of the compressive strengths is significantly larger than tensile,
typically ten times larger. Due to the nature of the test procedure, static bending test procedures are
mainly implemented to characterise wood strength across the wood grain. Shear test procedures have
been implemented in all three wood machining directions (Munthe and Ethington 1968) revealing that
only a true shear failure mode occurs along the wood grain.
1.1 Static Bending
Four point bending is recommended by British Standards for wood as failure occurs at the point of
maximum displacement between the two loaded anvils (British Standards 2003). This eliminates the
excessive compressive forces that would occur with the use of a single anvil and reduces likely-hood of
shear along the grain. American Standards for three point bending specifies a span to depth ratio of 1:14
(ASTM 2009). Once again this ensures that the failure mode is bending with no shear along the grain or
compressive deformation caused by the loaded anvil.
Previous research into the properties of Finnish birch (Gustafsson 2001) has evaluated both the
British and American test procedures. The findings reveal an average modulus of elasticity (MOE) of
11.2 GPa for three point bending compared to 14.9 GPa for four point bending, an increase of
approximately 25%. Comprehensive records (Bergman et al 1999) reveal an MOE value of 13 GPa in
static bending which lies between these two values, showing that results from both test procedures are
Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
373
within an appropriate range. The modulus of rupture (MOR), commonly referred to as bending strength,
is calculated to be the same regardless of the testing procedure.
Despite the discrepancy between the two test procedures for determination of MOE, evidence from
literature shows that MOE has been accurately determined using the three point method. This was used to
evaluate Green wood (Coutand et al 2004) and wood plastic composites (Wechsler and Hiziroglu 2007)
ܯ ܱܴ =
ଷி௅
ଶ௕ௗమ
, At point of fracture (1)
ܯ ܧܱ =
ி௅య
ସ௕ௗయఠ
, At elastic limit (2)
1.2 Shear
Shear occurs most commonly along the grain direction hence values in this direction are referred to as
longitudinal shear. French standards for longitudinal shear incorporate a test specimen with three separate
shear zone where failure can occur (AFNOR 1942). This standard has been used previously to determine
the modulus of rigidity for a predictive cutting force model where a tool machines wood along the grain
(Eyma et al 2004). Alternatively, American standards have developed a method for accurately measuring
the shear strength (τ) and modulus of rigidity (G) (ASTM 2009). The set-up consists of a test piece that
can fail along only one zone of shear.
߬=
ி
஺
, At point of fracture (3)
ܩ =
ఛ
ఊ
=
ி௅
஺௫
, At elastic limit (4)
A previous study on wood shear (Munthe and Ethington 1968) using spruce, applied the American
standard methodology and apparatus to all three orthogonal planes of symmetry with respect to the wood
grain direction. The results indicate that the wood is much stronger along the grain. Tests both across the
fibre direction and growth rings (end grain) yield τ values approximately 20% that of along the grain and
G values of approximately 3%. Furthermore, only true shear was observed along the wood grain. This
was illustrated by a uniform fault line propagating along the wood grain. Other failure modes were
observed: Buckling of the annual growth rings at the wood end grain and bending of the fibres across the
grain which are both referred to as “rolling shear”.
2 METHODOLOGY
A programme of work was completed using the American standard test procedures for three point
bending and longitudinal shear. These determined wood properties across and along the grain
respectively. Eight wood species including both hardwoods and softwoods were selected. The American
test standards were favoured as they were easier to implement in the universal testing machine. Hence the
question must be asked; does this more simple approach produce results comparable to results obtained
via other well established methods?
2.1 Three point Bending
All tests were performed using the American standard methodology described in sub-sections 1.1 and 1.2.
The span (L) of all of test specimens was kept at 300mm with a 20mm depth (d); this is in keeping with
the specified 14:1 minimum span to depth ratio. An additional criterion that was also specified by the
standard was a 1.3 mm/min crosshead maintained throughout testing until failure. The wood was placed
into the experimental set-up in the universal testing machine (Figure 1) where the apparatus was placed
between a moving crosshead and a 10 kN load cell. Force vs. Displacement plots were initially
Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
374
Figure 1: A) Three point bending set up in universal testing machine. B) Schematic diagram
Figure 2: A) Longitudinal shear set up in universal testing machine. B) Schematic diagram
Figure 3: Deformation zones on a typical stress vs. strain curve
Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
375
generated by the test machine data acquisition system. The linear region where Force was directly
proportional to Displacement was taken to be the elastic region where no permanent deformation occurs.
Force and Displacement measurements from this region are used to calculate MOE. The Force
measurement at the point of fracture was subsequently used to calculate MOR.
2.2 Longitudinal Shear
As with three point bending, all tests were performed using the American standard methodology. The
experimental set up also used the 10 kN load cell. All proportions for the test piece used in
experimentation are detailed (Figure 2). A 0.6 mm/min crosshead was maintained throughout testing
until failure. As the shear zone was approximately square, both the length and width were taken to be a.
Equations 3 and 4 could be modified to accommodate the standard test specimen. Once again Force vs.
Displacement plots were acquired to determine the elastic region and the point of fracture τ and G were
calculated using equations 5 and 6 respectively.
߬=
ி
௔మ
, At point of fracture (5)
ܩ =
ி௔
௔మ௫
=
ி
௔௫
, At elastic limit (6)
2.3 Toughness
Toughness was calculated as the area under the stress (σ) vs. strain (ε) curves (Figure 3) generated from
the universal testing machine force extension plots. The stress strain curve was in the form of a quadratic
polynomial. Toughness (U) was obtained by taking the definite integral of the quadratic function between
zero and the point of facture (n) (equation 7).
ܷ = ∫ (ߝ݂) = ∫ ଶߝܽ) + +ܾߝ )ܿ
଴
௡
଴
௡
(7)
3 RESULTS
In general the average strength of the wood species tested across the grain (denoted by MOR) obtained
through the three point bending tests (table 1) was measured to be over eight times greater than the
strength along the grain (denoted by τ) obtained through the longitudinal shear tests. However, the
average elasticity of the wood across the grain (denoted by MOE) was measured to be nearly 40 times
greater than along the grain (denoted by G).
3.1 Bending
For all moisture levels evaluated, values for mean MOR for the wood species evaluated range from 50-90
MPa with a linear decrease in strength observed for increased moisture content. The values for mean
MOE of the wood species evaluated ranges from 4-8 GPa with a linear decrease in elasticity also
observed for increased moisture content. The results from the force extension plots show there is no
discernible pattern to suggest that the hardwoods yield higher MOE values than the softwoods.
3.2 Shear
The average τ values range from 5-12 MPa. The highest values represent the three hardwoods tested
which have values approximately 45% greater than the softwoods. Furthermore a linear decrease in
strength is observed with an increase in moisture content. The average G values of the wood species
evaluated range from 15-230 MPa with the larger values once again representing the hardwoods. These
values are approximately 50% greater than the softwoods. G exhibits a negative linear trend with respect
to moisture content.
Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
376
Table 1: Properties obtained through mechanical testing
Species MOE MOR Ub G τ Us ρ MC
(GPa) (MPa) (J/m
2
) (MPa) (MPa) (J/m
2
) (kg/m
3
) (%)
D
R
Y
(N
O
M
IN
A
L)
Scots Pine (SW) 6.28 79.21 33250 151.47 9.53 26650 576.64 6.00
Yellow Pine (SW) 5.08 47.72 24910 286.27 6.28 17100 484.80 6.00
Douglas Fir (SW) 6.92 72.01 49000 236.51 7.58 34080 496.62 8.00
Western Red Cedar (SW) 9.15 99.28 40600 52.78 8.62 31730 671.57 6.00
Siberian Larch (SW) 7.33 65.24 49020 260.16 9.31 54000 638.46 8.00
Ash (HW) 5.75 105.57 84000 277.03 17.06 94300 912.87 6.00
Beech (HW) 8.89 127.44 61750 363.83 15.55 86400 669.00 6.00
Sapele (HW) 7.80 92.73 58050 219.11 18.17 57200 819.08 6.00
AVERAGE 7.15 86.15 50070 230.90 11.51 50180 658.63 6.50
RANGE 4.07 79.72 59090 311.05 11.89 77200 428.07 2.00
STANDARD DEVIATION 1.44 25.24 18350 94.06 4.65 28200 148.44 0.93
1
0
%
(N
O
M
IN
A
L)
Scots Pine (SW) 5.83 61.99 21000 152.64 7.97 25200 559.04 14.00
Yellow Pine (SW) 4.03 47.62 19200 91.30 5.69 16120 436.15 11.00
Douglas Fir (SW) 6.14 58.57 24750 43.32 3.97 26850 478.93 14.00
Western Red Cedar (SW) 3.95 54.60 22100 268.98 4.76 26250 460.96 11.00
Siberian Larch (SW) 6.70 88.62 28840 208.32 10.34 27280 615.38 11.00
Ash (HW) 8.23 119.09 61740 123.21 14.20 84000 850.73 10.00
Beech (HW) 11.36 95.04 47250 211.37 14.15 60750 696.65 11.00
Sapele (HW) 9.11 113.05 45500 691.02 14.31 28600 759.75 8.00
AVERAGE 6.92 79.82 33790 223.77 9.42 36880 607.20 11.25
RANGE 7.41 71.47 42540 647.70 10.34 67880 414.58 6.00
STANDARD DEVIATION 2.54 27.77 15670 202.15 4.43 23080 151.22 1.98
2
0
%
(N
O
M
IN
A
L)
Scots Pine (SW) 6.49 53.85 8750 128.55 10.85 15260 546.36 20.00
Yellow Pine (SW) 3.24 30.57 3840 46.22 2.22 11700 416.88 25.00
Douglas Fir (SW) 4.47 40.92 20470 152.23 4.85 21000 462.60 25.00
Western Red Cedar (SW) 4.69 56.63 10330 138.98 3.74 16640 434.53 25.00
Siberian Larch (SW) 4.08 48.80 22500 136.96 5.76 24080 604.35 20.00
Ash (HW) 7.76 103.94 42750 84.88 7.32 70950 714.17 24.00
Beech (HW) 5.11 78.47 42000 209.07 7.17 35500 737.15 27.00
Sapele (HW) 3.15 62.47 38740 195.14 10.64 28250 632.64 23.00
AVERAGE 4.87 59.46 23670 136.50 6.57 27920 568.59 23.63
RANGE 4.61 73.37 38910 162.85 8.63 59250 320.27 7.00
STANDARD DEVIATION 1.58 22.93 15730 53.23 3.08 18980 124.04 2.50
SA
T
(N
O
M
IN
A
L)
Scots Pine (SW) 4.41 47.00 15400 6.21 5.70 9100 530.23 32.00
Yellow Pine (SW) 2.49 26.65 10200 7.75 2.31 7100 407.70 35.00
Douglas Fir (SW) 3.66 29.69 22000 25.20 4.42 11600 448.67 35.00
Western Red Cedar (SW) 4.33 43.84 21930 19.91 3.49 11000 354.88 30.00
Siberian Larch (SW) 4.45 40.83 22800 7.71 4.71 14200 575.65 32.00
Ash (HW) 5.62 73.15 45990 18.45 6.34 40000 708.26 45.00
Beech (HW) 5.84 76.76 45600 16.20 8.35 31200 787.75 40.00
Sapele (HW) 4.78 69.15 45000 19.54 11.39 21000 595.21 31.00
AVERAGE 4.45 50.88 28610 15.12 5.84 18150 551.04 35.00
RANGE 3.35 50.11 35790 18.99 9.08 32900 432.87 15.00
STANDARD DEVIATION 1.06 19.64 14610 7.02 2.89 11760 147.96 5.13
3.3 Toughness
The average toughness values (Ub and Us) range from 18000-50000 J/m2. These values are not as
significantly affected by the grain direction as the materials strength (MOR and τ) or elasticity (MOE
and G). The mean values obtained by σ vs. ε plots in three point bending (Ub) yielded approximate values
only 10% greater than the mean values obtained by σ vs. ε plots in longitudinal shear (Us).
4 DISCUSSION
Established values in literature (Bergman et al 1999) are compared to the obtained mechanical properties
in this study (for woods of low moisture content ≈ 6-12%):
 The MOR values in this study are 5% lower than the values in literature for the hardwood and
8% lower for the softwoods.
 The MOE values are 14% lower for the hardwoods and 41% lower for the softwoods.
Proceedings of the 10th International Conference on Manufacturing Research ICMR 2012
377
 The Ub values are 28% lower for the hardwoods and 41% lower for the softwoods.
 The τ values in this study 20% higher for the hardwoods and 7% lower for the softwoods.
There were no readily available values of Us or G from literature to compare to the obtained values
documented in this study. MOE and Ub recorded values collate less well to established values in
literature than MOR and τ recorded values. Both MOE and Ub are dependent upon strain however MOR
and τ are not. The source of this discrepancy must hence originate from different measurements of strain.
A possible cause of this could be variations in the crosshead speed of the universal testing machine.
American standards (ATSM 2009) specify speeds of 1.3 mm/min and 0.6 mm/min for the bending and
shear tests respectively. Crosshead speeds in the comparable study (Bergman et al 1999) are not specified.
5 CONCLUSION
In general, the American standards for testing (ATSM 2009) were accurately able to determine strength
properties, i.e. τ and MOR (although a small percentage of error in τ was observed for the hardwood
species evaluated). A larger degree of error was however noticed for the elastic and toughness properties.
The values for the bending toughness values (Ub) and elastic modulus (MOE) documented in this study
are noticeably lower than values from literature (Bergman et al 1999). Documented values of shear
toughness (Us) and modulus of rigidity (G) were not readily available from literature to compare to the
values recorded in this study. Hence further work is warranted to investigate how values of Us and G
(obtained using the American standard) compare to values using other test methodologies.
REFERENCES
1942. AFNOR NF B51-012: Wood Shear Test, French National Organisation for Standardisation, Paris
Munthe, B.P and Ethington, R.L. 1968. Method for evaluating Shear Properties of Wood. U.S.
Department of Agriculture Forest Service, Madison, WI
Bergman, R. Cai, Z. Carll, C.G. Clausen, C.A.; Dietenberger, M.A. Falk, R.H. Frihart, C.R.; Glass, S.V.;
Hunt, C.G. Ibach, R.E. Kretschmann, E. Rammer, D.R.; Ross, R.J. Star, N.M. Wacker, J.P. Wang. X.
White, R.H, Weidenhoeft, A.C. Weimann, M.C. Zelinka, S.L. 1999. Wood Handbook, Wood as an
Engineering Material, U.S. Department of Agriculture Forest Service, Madison, WI
Gustafsson, S. I. 2001. Mechanical Properties of some Swedish hard wood species, Proceedings of the
Institution of Mechanical Engineers, 215:125-131
Reiterer, A. and Stanzl-Tschegg, S. E. 2001. Compressive behaviour of softwood under uniaxial loading
at different orientations to the grain. Mechanics of Materials, 33:705-715
2003. BS EN 408: Timber structures - Structural timber and glued laminated timber - Determination of
some physical and mechanical properties. British Standards Institute, London
Coutand, C. Jeronimidis, G. Chanson, B. and Loup, C. 2004. Comparison of mechanical properties of
tension and opposite wood in Populus, Wood Science and Technology, 38:11-24
Eyma, F. Méausoone, P.J. and Martin, P. 2004. Strains and cutting forces involved in the solid wood
rotating cutting process. Journal of Materials Processing Technology, 148:220-225
Galicki, J. and Czech, M. 2005. Tensile strength of softwood in LR orthotropy plane. Mechanics of
Materials, 37:677-686
Wechsler, A. and Hiziroglu, S. 2007. Some of the properties of wood-plastic composites. Building and
Environment, 42:2637-2644
2009. ASTM D143-09: Standard Test Methods for Small Clear Specimens of Timber. American Society
for Testing and Materials. West Conshohocken, PA
Manríquez, M. J. and Moraes, P. D. 2009. Influence of the temperature on the compression strength
parallel to grain of paricá. Constr Build Mater, 24: 99-104
Oh, S.C. 2011. Applying failure criteria to the strength evaluation of 3-ply laminated veneer lumber
according to grain direction by uniaxial tension test Constr Build Mater, 25:1480-1484



Determination of wood strength properties through standard test procedures

Northumbria University Research Portal

Citation: Naylor, Andrew, Hackney, Philip and Perera, Noel (2012) Determination of wood strength  properties  through standard test  procedures.  In:  ICMR 2012:  10th  International Conference  on  Manufacturing  Research,  11-13  September  2012,  Aston  University, Birmingham, UK. URL: http://www1.aston.ac.uk/icmr2012/ <http://www1.aston.ac.uk/icmr2012/>This  version  was  downloaded  from  Northumbria  Research  Link: http://nrl.northumbria.ac.uk/9686/Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University’s research output. Copyright © and moral rights for items on NRL are retained by the individual author(s) and/or other copyright owners.  Single copies of full items can be reproduced,  displayed or  performed,  and given to  third parties in  any format  or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided the authors, title and full bibliographic details are given, as well  as a hyperlink and/or URL to the original metadata page. The content must  not  be changed in any way. Full items must not be sold commercially in any format or medium without  formal  permission  of  the  copyright  holder.   The  full  policy  is  available  online: http://nrl.northumbria.ac.uk/policies.htmlThis document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher’s website (a subscription may be required.)Proceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012372DETERMINATION OFWOOD STRENGTH PROPERTIES THROUGH STANDARD TESTPROCEDURESAndrew NaylorPhilip HackneyNoel PereraSchool of Computing, Engineering and Information SciencesNorthumbria University, Ellison BuildingNewcastle Upon Tyne, NE1 8ST, UKandrew2.naylor@northumbria.ac.ukABSTRACTIn this study a review of existing recognised standards for wood mechanical testing was conducted. Thisreview considers tensile, compressive, bending and shear test methodologies from a range of sources. Inaddition, values for wood mechanical properties were obtained through controlled experimentation usinga universal material testing machine. Selected standard procedures were used to obtain wood strengthproperties both along and across the grain. These consist of a three point bending procedure used toevaluate the wood strength across the grain and a longitudinal shear procedure used to evaluate the woodstrength along the grain. Strength properties obtained through controlled experimentation are compared tovalues available in existing literature with little discrepancy.Keywords: Mechanical Test Procedures, Universal Testing Machine, Wood Strength Properties1 INTRODUCTIONWood is anisotropic and hence some mechanical test procedures are often performed both along andacross the grain. Tension and compression tests have been successfully performed both along and acrossthe grain. Compression tests show that wood has much larger strength and modulus of elasticity valuesalong the grain rather than across (Reiterer and Stanzl-Tschegg 2001, Manríquezand Moraes 2009). Thetrend for tensile tests is the same as compressive (Oh 2011, Galicki and Czech 2005) (larger values alongthe grain). However, the magnitude of the compressive strengths is significantly larger than tensile,typically ten times larger. Due to the nature of the test procedure, static bending test procedures aremainly implemented to characterise wood strength across the wood grain. Shear test procedures havebeen implemented in all three wood machining directions (Munthe and Ethington 1968) revealing thatonly a true shear failure mode occurs along the wood grain.1.1 Static BendingFour point bending is recommended by British Standards for wood as failure occurs at the point ofmaximum displacement between the two loaded anvils (British Standards 2003). This eliminates theexcessive compressive forces that would occur with the use of a single anvil and reduces likely-hood ofshear along the grain. American Standards for three point bending specifies a span to depth ratio of 1:14(ASTM 2009). Once again this ensures that the failure mode is bending with no shear along the grain orcompressive deformation caused by the loaded anvil.Previous research into the properties of Finnish birch (Gustafsson 2001) has evaluated both theBritish and American test procedures. The findings reveal an average modulus of elasticity (MOE) of11.2 GPa for three point bending compared to 14.9 GPa for four point bending, an increase ofapproximately 25%. Comprehensive records (Bergman et al 1999) reveal an MOE value of 13 GPa instatic bending which lies between these two values, showing that results from both test procedures areProceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012373within an appropriate range. The modulus of rupture (MOR), commonly referred to as bending strength,is calculated to be the same regardless of the testing procedure.Despite the discrepancy between the two test procedures for determination of MOE, evidence fromliterature shows that MOE has been accurately determined using the three point method. This was used toevaluate Green wood (Coutand et al 2004) and wood plastic composites (Wechsler and Hiziroglu 2007)ܯܱܴ = ଷி௅ଶ௕ௗమ, At point of fracture (1)ܯܱܧ = ி௅యସ௕ௗయఠ, At elastic limit (2)1.2 ShearShear occurs most commonly along the grain direction hence values in this direction are referred to aslongitudinal shear. French standards for longitudinal shear incorporate a test specimen with three separateshear zone where failure can occur (AFNOR 1942). This standard has been used previously to determinethe modulus of rigidity for a predictive cutting force model where a tool machines wood along the grain(Eyma et al 2004). Alternatively, American standards have developed a method for accurately measuringthe shear strength (τ) and modulus of rigidity (G) (ASTM 2009). The set-up consists of a test piece thatcan fail along only one zone of shear.߬ = ி஺ , At point of fracture (3)ܩ = ఛఊ = ி௅஺௫, At elastic limit (4)A previous study on wood shear (Munthe and Ethington 1968) using spruce, applied the Americanstandard methodology and apparatus to all three orthogonal planes of symmetry with respect to the woodgrain direction. The results indicate that the wood is much stronger along the grain. Tests both across thefibre direction and growth rings (end grain) yield τ values approximately 20% that of along the grain andG values of approximately 3%. Furthermore, only true shear was observed along the wood grain. Thiswas illustrated by a uniform fault line propagating along the wood grain. Other failure modes wereobserved: Buckling of the annual growth rings at the wood end grain and bending of the fibres across thegrain which are both referred to as “rolling shear”.2 METHODOLOGYA programme of work was completed using the American standard test procedures for three pointbending and longitudinal shear. These determined wood properties across and along the grainrespectively. Eight wood species including both hardwoods and softwoods were selected. The Americantest standards were favoured as they were easier to implement in the universal testing machine. Hence thequestion must be asked; does this more simple approach produce results comparable to results obtainedvia other well established methods?2.1 Three point BendingAll tests were performed using the American standard methodology described in sub-sections 1.1 and 1.2.The span (L) of all of test specimens was kept at 300mm with a 20mm depth (d); this is in keeping withthe specified 14:1 minimum span to depth ratio. An additional criterion that was also specified by thestandard was a 1.3 mm/min crosshead maintained throughout testing until failure. The wood was placedinto the experimental set-up in the universal testing machine (Figure 1) where the apparatus was placedbetween a moving crosshead and a 10 kN load cell. Force vs. Displacement plots were initiallyProceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012374Figure 1: A) Three point bending set up in universal testing machine. B) Schematic diagramFigure 2: A) Longitudinal shear set up in universal testing machine. B) Schematic diagramFigure 3: Deformation zones on a typical stress vs. strain curveProceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012375generated by the test machine data acquisition system. The linear region where Force was directlyproportional to Displacement was taken to be the elastic region where no permanent deformation occurs.Force and Displacement measurements from this region are used to calculate MOE. The Forcemeasurement at the point of fracture was subsequently used to calculateMOR.2.2 Longitudinal ShearAs with three point bending, all tests were performed using the American standard methodology. Theexperimental set up also used the 10 kN load cell. All proportions for the test piece used inexperimentation are detailed (Figure 2). A 0.6 mm/min crosshead was maintained throughout testinguntil failure. As the shear zone was approximately square, both the length and width were taken to be a.Equations 3 and 4 could be modified to accommodate the standard test specimen. Once again Force vs.Displacement plots were acquired to determine the elastic region and the point of fracture τ and G werecalculated using equations 5 and 6 respectively.߬ = ி௔మ, At point of fracture (5)ܩ = ி௔௔మ௫ = ி௔௫, At elastic limit (6)2.3 ToughnessToughness was calculated as the area under the stress (σ) vs. strain (ε) curves (Figure 3) generated fromthe universal testing machine force extension plots. The stress strain curve was in the form of a quadraticpolynomial. Toughness (U) was obtained by taking the definite integral of the quadratic function betweenzero and the point of facture (n) (equation 7).ܷ = ∫ ݂(ߝ) = ∫ (ܽߝଶ + ܾߝ + ܿ)଴௡଴௡ (7)3 RESULTSIn general the average strength of the wood species tested across the grain (denoted by MOR) obtainedthrough the three point bending tests (table 1) was measured to be over eight times greater than thestrength along the grain (denoted by τ) obtained through the longitudinal shear tests. However, theaverage elasticity of the wood across the grain (denoted by MOE) was measured to be nearly 40 timesgreater than along the grain (denoted by G).3.1 BendingFor all moisture levels evaluated, values for mean MOR for the wood species evaluated range from 50-90MPa with a linear decrease in strength observed for increased moisture content. The values for meanMOE of the wood species evaluated ranges from 4-8 GPa with a linear decrease in elasticity alsoobserved for increased moisture content. The results from the force extension plots show there is nodiscernible pattern to suggest that the hardwoods yield higher MOE values than the softwoods.3.2 ShearThe average τ values range from 5-12 MPa. The highest values represent the three hardwoods testedwhich have values approximately 45% greater than the softwoods. Furthermore a linear decrease instrength is observed with an increase in moisture content. The average G values of the wood speciesevaluated range from 15-230 MPa with the larger values once again representing the hardwoods. Thesevalues are approximately 50% greater than the softwoods. G exhibits a negative linear trend with respectto moisture content.Proceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012376Table 1: Properties obtained through mechanical testingSpecies MOE MOR Ub G τ Us ρ MC(GPa) (MPa) (J/m2) (MPa) (MPa) (J/m2) (kg/m3) (%)DRY(NOMINAL)Scots Pine (SW) 6.28 79.21 33250 151.47 9.53 26650 576.64 6.00Yellow Pine (SW) 5.08 47.72 24910 286.27 6.28 17100 484.80 6.00Douglas Fir (SW) 6.92 72.01 49000 236.51 7.58 34080 496.62 8.00Western Red Cedar (SW) 9.15 99.28 40600 52.78 8.62 31730 671.57 6.00Siberian Larch (SW) 7.33 65.24 49020 260.16 9.31 54000 638.46 8.00Ash (HW) 5.75 105.57 84000 277.03 17.06 94300 912.87 6.00Beech (HW) 8.89 127.44 61750 363.83 15.55 86400 669.00 6.00Sapele (HW) 7.80 92.73 58050 219.11 18.17 57200 819.08 6.00AVERAGE 7.15 86.15 50070 230.90 11.51 50180 658.63 6.50RANGE 4.07 79.72 59090 311.05 11.89 77200 428.07 2.00STANDARD DEVIATION 1.44 25.24 18350 94.06 4.65 28200 148.44 0.9310%(NOMINAL)Scots Pine (SW) 5.83 61.99 21000 152.64 7.97 25200 559.04 14.00Yellow Pine (SW) 4.03 47.62 19200 91.30 5.69 16120 436.15 11.00Douglas Fir (SW) 6.14 58.57 24750 43.32 3.97 26850 478.93 14.00Western Red Cedar (SW) 3.95 54.60 22100 268.98 4.76 26250 460.96 11.00Siberian Larch (SW) 6.70 88.62 28840 208.32 10.34 27280 615.38 11.00Ash (HW) 8.23 119.09 61740 123.21 14.20 84000 850.73 10.00Beech (HW) 11.36 95.04 47250 211.37 14.15 60750 696.65 11.00Sapele (HW) 9.11 113.05 45500 691.02 14.31 28600 759.75 8.00AVERAGE 6.92 79.82 33790 223.77 9.42 36880 607.20 11.25RANGE 7.41 71.47 42540 647.70 10.34 67880 414.58 6.00STANDARD DEVIATION 2.54 27.77 15670 202.15 4.43 23080 151.22 1.9820%(NOMINAL)Scots Pine (SW) 6.49 53.85 8750 128.55 10.85 15260 546.36 20.00Yellow Pine (SW) 3.24 30.57 3840 46.22 2.22 11700 416.88 25.00Douglas Fir (SW) 4.47 40.92 20470 152.23 4.85 21000 462.60 25.00Western Red Cedar (SW) 4.69 56.63 10330 138.98 3.74 16640 434.53 25.00Siberian Larch (SW) 4.08 48.80 22500 136.96 5.76 24080 604.35 20.00Ash (HW) 7.76 103.94 42750 84.88 7.32 70950 714.17 24.00Beech (HW) 5.11 78.47 42000 209.07 7.17 35500 737.15 27.00Sapele (HW) 3.15 62.47 38740 195.14 10.64 28250 632.64 23.00AVERAGE 4.87 59.46 23670 136.50 6.57 27920 568.59 23.63RANGE 4.61 73.37 38910 162.85 8.63 59250 320.27 7.00STANDARD DEVIATION 1.58 22.93 15730 53.23 3.08 18980 124.04 2.50SAT(NOMINAL)Scots Pine (SW) 4.41 47.00 15400 6.21 5.70 9100 530.23 32.00Yellow Pine (SW) 2.49 26.65 10200 7.75 2.31 7100 407.70 35.00Douglas Fir (SW) 3.66 29.69 22000 25.20 4.42 11600 448.67 35.00Western Red Cedar (SW) 4.33 43.84 21930 19.91 3.49 11000 354.88 30.00Siberian Larch (SW) 4.45 40.83 22800 7.71 4.71 14200 575.65 32.00Ash (HW) 5.62 73.15 45990 18.45 6.34 40000 708.26 45.00Beech (HW) 5.84 76.76 45600 16.20 8.35 31200 787.75 40.00Sapele (HW) 4.78 69.15 45000 19.54 11.39 21000 595.21 31.00AVERAGE 4.45 50.88 28610 15.12 5.84 18150 551.04 35.00RANGE 3.35 50.11 35790 18.99 9.08 32900 432.87 15.00STANDARD DEVIATION 1.06 19.64 14610 7.02 2.89 11760 147.96 5.133.3 ToughnessThe average toughness values (Ub and Us) range from 18000-50000 J/m2. These values are not assignificantly affected by the grain direction as the materials strength (MOR and τ) or elasticity (MOEand G). The mean values obtained by σ vs. ε plots in three point bending (Ub) yielded approximate valuesonly 10% greater than the mean values obtained by σ vs. ε plots in longitudinal shear (Us).4 DISCUSSIONEstablished values in literature (Bergman et al 1999) are compared to the obtained mechanical propertiesin this study (for woods of low moisture content ≈ 6-12%): The MOR values in this study are 5% lower than the values in literature for the hardwood and8% lower for the softwoods. TheMOE values are 14% lower for the hardwoods and 41% lower for the softwoods.Proceedings of the 10thInternational Conference on Manufacturing Research ICMR 2012377 The Ub values are 28% lower for the hardwoods and 41% lower for the softwoods. The τ values in this study 20% higher for the hardwoods and 7% lower for the softwoods.There were no readily available values of Us or G from literature to compare to the obtained valuesdocumented in this study. MOE and Ub recorded values collate less well to established values inliterature thanMOR and τ recorded values. BothMOE and Ub are dependent upon strain however MORand τ are not. The source of this discrepancy must hence originate from different measurements of strain.A possible cause of this could be variations in the crosshead speed of the universal testing machine.American standards (ATSM 2009) specify speeds of 1.3 mm/min and 0.6 mm/min for the bending andshear tests respectively. Crosshead speeds in the comparable study (Bergman et al 1999) are not specified.5 CONCLUSIONIn general, the American standards for testing (ATSM 2009) were accurately able to determine strengthproperties, i.e. τ and MOR (although a small percentage of error in τ was observed for the hardwoodspecies evaluated). A larger degree of error was however noticed for the elastic and toughness properties.The values for the bending toughness values (Ub) and elastic modulus (MOE) documented in this studyare noticeably lower than values from literature (Bergman et al 1999). Documented values of sheartoughness (Us) and modulus of rigidity (G) were not readily available from literature to compare to thevalues recorded in this study. Hence further work is warranted to investigate how values of Us and G(obtained using the American standard) compare to values using other test methodologies.REFERENCES1942. AFNOR NF B51-012: Wood Shear Test, French National Organisation for Standardisation, ParisMunthe, B.P and Ethington, R.L. 1968. Method for evaluating Shear Properties of Wood. U.S.Department of Agriculture Forest Service, Madison, WIBergman, R. Cai, Z. Carll, C.G. Clausen, C.A.; Dietenberger, M.A. Falk, R.H. Frihart, C.R.; Glass, S.V.;Hunt, C.G. Ibach, R.E. Kretschmann, E. Rammer, D.R.; Ross, R.J. Star, N.M. Wacker, J.P. Wang. X.White, R.H, Weidenhoeft, A.C. Weimann, M.C. Zelinka, S.L. 1999. Wood Handbook, Wood as anEngineering Material, U.S. Department of Agriculture Forest Service, Madison, WIGustafsson, S. I. 2001. Mechanical Properties of some Swedish hard wood species, Proceedings of theInstitution of Mechanical Engineers, 215:125-131Reiterer, A. and Stanzl-Tschegg, S. E. 2001. Compressive behaviour of softwood under uniaxial loadingat different orientations to the grain. Mechanics of Materials, 33:705-7152003. BS EN 408: Timber structures - Structural timber and glued laminated timber - Determination ofsome physical and mechanical properties. British Standards Institute, LondonCoutand, C. Jeronimidis, G. Chanson, B. and Loup, C. 2004. Comparison of mechanical properties oftension and opposite wood in Populus, Wood Science and Technology, 38:11-24Eyma, F. Méausoone, P.J. and Martin, P. 2004. Strains and cutting forces involved in the solid woodrotating cutting process. Journal of Materials Processing Technology, 148:220-225Galicki, J. and Czech, M. 2005. Tensile strength of softwood in LR orthotropy plane. Mechanics ofMaterials, 37:677-686Wechsler, A. and Hiziroglu, S. 2007. Some of the properties of wood-plastic composites. Building andEnvironment, 42:2637-26442009. ASTM D143-09: Standard Test Methods for Small Clear Specimens of Timber. American Societyfor Testing and Materials. West Conshohocken, PAManríquez, M. J. and Moraes, P. D. 2009. Influence of the temperature on the compression strengthparallel to grain of paricá. Constr Build Mater, 24: 99-104Oh, S.C. 2011. Applying failure criteria to the strength evaluation of 3-ply laminated veneer lumberaccording to grain direction by uniaxial tension test Constr Build Mater, 25:1480-1484

AFNOR NF B51-012: Wood Shear Test, French National Organisation for Standardisation,

Mechanical Properties of some Swedish hard wood species, Proceedings of the Institution of Mechanical Engineers,

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Determination of wood strength properties through standard test procedures

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