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A comparison of shear characterization of Pinus Pinaster Ait., with the Iosipescu and off-axis shear test methods J. Xavier a, N. Garrido b, M. Oliveira b, J. Morais a,P.Camanho c, F. Pierron d (a) CETAV/UTAD, Vila Real, PT (b) ESTV, Viseu, PT (c) DEMEGI/FEUP, Porto, PT (d) LMPF/ENSAM, Châlons-en-Champagne, FR Composites Testing and Model Identification January 2003 – ENSAM, Châlons-en-Champagne, France

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Table of contents Introduction Data reduction Experimental work Finite element analyses Results and discussion Conclusions

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

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Stress-strain functions in the LRT coordinate system: LL RR TT RT LT LR LL f 11 f 12 f 13 RR f 12 f 22 f 23 TT f 13 f 23 f 33 RT f 44 LT f 55 LR f 66 - 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: (Dimensions based on ASTM D Standard) 9, 10 and 8 specimens in the LR, LT and RT planes, respectively; 0/90 rosettes (CEA WT-350); Moisture content: 10% - 12%; Oven-dry density: – 0,655 (g/cm 3 );

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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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16, 14 and 14 specimens in the LR, LT and RT planes, respectively; 60-ded-delta rosettes (CEA UR-350); Tabless specimens were used in the RT plane: Moisture content: 10% - 12%; Oven-dry density: – 0,655 (g/cm 3 );

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

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Iosipescu tests: 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: Specimen Gripping arrangement

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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. Wood was modeled as an linear elastic, orthotropic and homogeneous material. Elastic properties of wood Pinus Pinaster Ait.: E L (GPa) E R (GPa) E T (GPa) LR TL RT G LR (GPa) G LT (GPa) G RT (GPa) Numerical analysis of the Iosipescu and off-axis shear test were developed in ANSYS 6.0 ®.

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

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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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Numerical corrections factors C and S: Principal material planes CSCS LR (4.5%) LT (8.6%) RT (2.1%)

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19089 elements nodes elements 1920 nodes. Mesh and boundary conditions: 3-D finite element models were developed; Solid isoparametric element SOLID64, with 24 DOF; Off-axis tensile test models and results:

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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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Numerical corrections factors C and S: Principal material planes CSCS LR (0.2%) LT (6.0%) RT (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 11,274 21,516 31,500 41,543 51,415 61,258 71,164 81,457 91,577 MEAN1,411 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: Local crushing Large displacement and deformations Cracks

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Specimen 11,258 21,287 31,303 41,420 51,168 61,091 71,262 81,160 91, ,144 MEAN1,220 CV (%)8,42 Shear modulus, in the LT plane:

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

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Typical failure for LT principal material plane: Local crushing Large displacement and deformations Cracks

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Shear modulus, in the RT plane: Specimen 10,216 20,258 30,348 40,273 50,255 60,339 70,315 80,283 MEAN0,286 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 11,2283,613 21,3163,360 31,1643,435 41,1112,903 51,1424,621 61,0313,583 71,1503,923 81,1044,637 91,1294, ,0504, ,0953, ,0893, ,0933, ,0314, ,0543, ,0174,604 MEAN1,1133,865 CV (%)7,0014,88

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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 10,9802,875 20,9424,205 30,9513,659 40,9223,934 51,1083,883 61,0373,461 71,1613,565 80,8914,151 90,9164, ,0324, ,9553, ,9434, ,9773, ,8933,874 MEAN0,9793,839 CV (%)8,1211,30

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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 10,1570,755 20,1330,790 30,1440,938 40,1490,834 50,1530,603 60,1570,584 70,3280,784 80,1420,779 90,1270, ,1400, ,1520, ,1240, ,1420, ,1260,675 MEAN0,1550,727 CV (%)32,7514,03

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Comparison of the shear properties obtained from both Iosipescu and off-axis shear test methods: Shear modulusShear strength Iosipescu test1.4111,2200, Off-axis test1,1130,9790,1553,8653,8390,727 Difference (%)21,1219,7545,80---

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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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