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**Composites Testing and Model Identification**

28-30 January 2003 – ENSAM, Châlons-en-Champagne, France A comparison of shear characterization of Pinus Pinaster Ait., with the Iosipescu and off-axis shear test methods J. Xaviera, N. Garridob, M. Oliveirab, J. Moraisa,P.Camanhoc, F. Pierrond (a) CETAV/UTAD, Vila Real, PT (b) ESTV, Viseu, PT (c) DEMEGI/FEUP, Porto, PT (d) LMPF/ENSAM, Châlons-en-Champagne, FR

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**Table of contents Introduction Data reduction Experimental work**

Finite element analyses Results and discussion Conclusions

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Introductions Wood as an orthotropic material: L R T LR LT RT

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**Stress-strain functions in the LRT coordinate system:**

sLL sRR sTT tRT tLT tLR eLL f11 f12 f13 eRR f22 f23 eTT f33 gRT f44 gLT f55 gLR f66 - Iosipescu shear test - Off-axis tensile test Identification of the shear behaviour of Pinus Pinaster Ait.:

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Data reduction Iosipescu shear test:

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**Shear modulus correction:**

Assumption: exists a uniform distribution of shear stress and strain through the thickness of the specimen; The strains measured on both faces of the specimen can be quite different due to boundary conditions effects (Pierron (1998)) Averaging the shear strains on the two faces of the specimen eliminates that effect.

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**Off-axis tensile test:**

Tsai-Hill strength criterion:

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**Experimental work Material**

Wood of maritime pine (Pinus Pinaster Ait.), of about 74 years old, from Viseu (Portugal).

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**Specimens: Iosipescu specimen: Moisture content: 10% - 12%;**

(Dimensions based on ASTM D Standard) Moisture content: 10% - 12%; Oven-dry density: – 0,655 (g/cm3); 9, 10 and 8 specimens in the LR, LT and RT planes, respectively; 0/90 rosettes (CEA WT-350);

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Off-axis specimens: Oblique end tabs were bounded for specimens in the LR and LT planes: Kambala

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**Tabless specimens were used in the RT plane:**

Moisture content: 10% - 12%; Oven-dry density: – 0,655 (g/cm3); 16, 14 and 14 specimens in the LR, LT and RT planes, respectively; 60-ded-delta rosettes (CEA UR-350);

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**Temperature of 23ºC (1ºC) e relative humidity of 40% (5%)**

Mechanical testing: Controlled displacement rate of 1 mm/mn Data acquisition system HBM SPIDER 8 INSTRON 1125 universal machine of 100 KN of capacity Temperature of 23ºC (1ºC) e relative humidity of 40% (5%)

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**Iosipescu tests: EMSE Iosipescu Fixture Attachement to test machine**

Stationary part of fixture Movable part of the fixture Parte móvel da amarra Specimen Adjustable wedges to tighten the specimen Wedge adjusting screw Fixture linear guide rod Attachement to test machine EMSE Iosipescu Fixture

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Off-axis tests: Gripping arrangement Specimen

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**Finite element analyses**

Objectives of the analyses: to acess to the stress and strain fields at the test section of the specimens; to determine the numerical corrections factors C and S. Numerical analysis of the Iosipescu and off-axis shear test were developed in ANSYS 6.0®. Wood was modeled as an linear elastic, orthotropic and homogeneous material. Elastic properties of wood Pinus Pinaster Ait.: EL (GPa) ER (GPa) ET (GPa) nLR nTL nRT GLR (GPa) GLT (GPa) GRT (GPa) 15.133 1.912 1.010 0.471 0.051 0.586 1.262 1.100 0.221

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**Iosipescu shear test models and results:**

Mesh and boundary conditions: 2-D finite element models were developed; Quadrilateral isoparametric element PLANE82, with 8 nodes; 1800 elements and 5577 nodes.

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**Normalizes stress components along the vertical line, between the V-notches:**

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**Normalizes stress components along the vertical line, between the V-notches:**

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**Normalizes stress components along the vertical line, between the V-notches:**

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**Normalizes shear strain under an area circumscribed by the strain-gage grid:**

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**Normalizes shear strain under an area circunscribed by the strain-gage grid:**

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**Normalizes shear strain under an area circunscribed by the strain-gage grid:**

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**Principal material planes C S CS LR 0.967 0.988 0.955 (4.5%) LT 0.919**

Numerical corrections factors C and S: Principal material planes C S CS LR 0.967 0.988 0.955 (4.5%) LT 0.919 0.995 0.914 (8.6%) RT 1.050 0.972 1.021 (2.1%)

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**Off-axis tensile test models and results:**

Mesh and boundary conditions: 19089 elements 16000 nodes. 3159 elements 1920 nodes. 3-D finite element models were developed; Solid isoparametric element SOLID64, with 24 DOF;

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**Uniformity of stress components in the LR plane:**

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**Uniformity of stress components in the LT plane:**

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**Uniformity of stress components in the RT plane:**

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**Principal material planes**

Numerical corrections factors C and S: Principal material planes C S CS LR 0.997 1.001 0.998 (0.2%) LT 0.978 0.961 0.940 (6.0%) RT 0.876 1.039 0.910 (9.0%)

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**Results and discussion**

Iosipescu tests: Experimental data obtained for a specimen in the LR plane:

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**Initial zone of the shear stress-strain curves, in the LR plane:**

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**The apparent shear modulus definition:**

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**Shear modulus, in the LR plane:**

Specimen 1 1,274 2 1,516 3 1,500 4 1,543 5 1,415 6 1,258 7 1,164 8 1,457 9 1,577 MEAN 1,411 CV (%) 10,31

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**Complete shear stress-strain curves, in the LR plane:**

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**Typical failure for LR principal material plane:**

Large displacement and deformations Cracks Local crushing

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**Shear modulus, in the LT plane:**

Specimen 1 1,258 2 1,287 3 1,303 4 1,420 5 1,168 6 1,091 7 1,262 8 1,160 9 1,112 10 1,144 MEAN 1,220 CV (%) 8,42

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**Complete shear stress-strain curves, in the LT plane:**

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**Typical failure for LT principal material plane:**

Large displacement and deformations Cracks Local crushing

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**Shear modulus, in the RT plane:**

Specimen 1 0,216 2 0,258 3 0,348 4 0,273 5 0,255 6 0,339 7 0,315 8 0,283 MEAN 0,286 CV (%) 15,85

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**Complete shear stress-strain curves, in the RT plane:**

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**Two typical failure for RT principal material plane:**

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Off-axis tests: Experimental data obtained for a specimen in the LR plane:

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**Complete shear stress-strain curves, in the LR plane:**

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**Typical failure for a specimen in the LR plane:**

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**Shear properties in the LR plane:**

Specimens 1 1,228 3,613 2 1,316 3,360 3 1,164 3,435 4 1,111 2,903 5 1,142 4,621 6 1,031 3,583 7 1,150 3,923 8 1,104 4,637 9 1,129 4,121 10 1,050 4,064 11 1,095 3,404 12 1,089 3,725 13 1,093 3,907 14 4,802 15 1,054 3,142 16 1,017 4,604 MEAN 1,113 3,865 CV (%) 7,00 14,88

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**Complete shear stress-strain curves, in the LT plane:**

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**Typical failure for a specimen in the LT plane:**

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**Shear properties in the LT plane:**

Specimens 1 0,980 2,875 2 0,942 4,205 3 0,951 3,659 4 0,922 3,934 5 1,108 3,883 6 1,037 3,461 7 1,161 3,565 8 0,891 4,151 9 0,916 4,596 10 1,032 4,038 11 0,955 3,953 12 0,943 4,220 13 0,977 3,338 14 0,893 3,874 MEAN 0,979 3,839 CV (%) 8,12 11,30

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**Complete shear stress-strain curves, in the RT plane:**

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**Typical failure for a specimen in the RT plane:**

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**Shear properties in the RT plane:**

Specimens 1 0,157 0,755 2 0,133 0,790 3 0,144 0,938 4 0,149 0,834 5 0,153 0,603 6 0,584 7 0,328 0,784 8 0,142 0,779 9 0,127 0,693 10 0,140 0,565 11 0,152 0,746 12 0,124 0,750 13 0,685 14 0,126 0,675 MEAN 0,155 0,727 CV (%) 32,75 14,03

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**Comparison of the shear properties obtained from both Iosipescu and off-axis shear test methods:**

Shear modulus Shear strength Iosipescu test 1.411 1,220 0,286 - Off-axis test 1,113 0,979 0,155 3,865 3,839 0,727 Difference (%) 21,12 19,75 45,80

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Conclusions The Iosipescu and off-axis shear test methods are suitable for measuring the shear moduli in all principal material planes of Pinus Pinaster Ait.; The complete shear behaviour of Pinus Pinaster Ait., including the shear strength, can not be properly determined by the Iosipescu sheat test; The off-axis tensile test is suitable for the complete identification of the shear stress-strain functions of Pinus Pinaster Ait.;

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