Assessing local proper.es of wood within the stem from full- field measurements J. Pereira 1,2, J. Xavier 1, J. Morais 1, J. Lousada 1 1 UTAD, CITAB Research and Agro- Environmental, Vila Real, Portugal 2 ISPV, Superior Scholl of Technology and Management, DEMad, Viseu, Portugal Workshop Micro Characterisa1on of Wood Material & Proper1es October 24-26, 2011 Our Dynamic Earth, Edinburgh, Scotland
WOOD AS AN ENGINEEGING MATERIAL Wood is a hierarchical, anisotropic and heterogeneous material Meso scale lenght (m) Mo1va1on 10 10-6 10 10-4 10-6 -4 10-2 10-2 10 0 0 Cell Wall Ealywood Latewood Clear wood Log Cell wall level earlywood latewood Plank level Log level Annual ring level why transversal (RT) plane? - Lack of mechanical properues (meso scale; stem scale) - BeWer understanding of structure- properues relauonships - Importance in fracture mechanics (e.g., drying process...), wood joints (e.g., pin joints), wood machining 2
MECHANICAL TESTS: RT PLANE Mechanical test Proposed by Tensile test (onaxis) Pereira, et al; 2005 Tensile test (onaxis) Pereira, et al; 2005 Geometry Mechanical properties E R ; ν RT E T ; ν TL Mo1va1on Tensile test (offaxis) Garrido, et al; 2004 G RT Compression test Simon, et al; 2009 E R Arcan test Oliveira, et al; 2004 G RT Iosipescu test Xavier, et al; 2003 G RT 3
PROPOSED MECHANICAL TEST PROPOSED TEST Ring- oriented tensile test Mo1va1on [Q EW ] [Q LW ] Orthotropy and heterogeneity: [Q EW ], [Q LW ] q q Inverse method Full- field measurements 4
IDENTIFICATION METHODS FROM FULL- FIELD MEASUREMENTS Mo1va1on 5
OUTLINE iden1fica1on - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 6
OUTLINE iden1fica1on - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 7
ANISOTROPIC- BASED METHOD Ring- oriented tensile test iden1fica1on ConsUtuUve equauons Off- axis angle θ Digital image correlauon (DIC) Off- axis angle θ For:. : 8
VIRTUAL FIELDS METHOD ConsUtuUve equauons - Image segmentauon iden1fica1on 9
VIRTUAL FIELDS METHOD VFM base equauons iden1fica1on S EW EW: LW: - along each cross- secuon LW EW - for a given set of specimens l 10
OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 11
MATERIAL q Wood samples q Off- axis angles P. pinaster wood 50(R)x5(L)x2(T) (mm) R1 R2 R3 R4 R5 [ ] 12
OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 13
DIGITAL IMAGE CORRELATION q DIC principle q Strain reconstruc1on Point- wise local least- squares filng over a window of (2m+1)x(2m+1) subsets 14
DIGITAL IMAGE CORRELATION q Speckle paiern Polishment: Sandpaper grit 80, 120, 180 Base: White mawe acrylic spray Airbrush: Iwata CM- B (Black acrylic paint (Createx) 15
DIGITAL IMAGE CORRELATION q Op1cal system CCD sensor: 8- bit Baumer Optronic FWX20 Lens: Optronic Telecentric TC2309 Field Of View (1/1.8 ): 7.1 x 5.4 mm Working distance: 63,3 ± 2 mm Conversion factor: 4.4 μm/pixel Code: Aramis DIC- 2D GOM Acquisi:on frequency: 1.0 Hz 16
DIGITAL IMAGE CORRELATION q Measuring parameters of DIC (based on rigid- body translauon tests) Facet size: 15x15 pixels (66x66 μm) Facet step: 11x11 pixels (48.4x48.4 μm) Strain step: 7 subsets (0.339 mm) Displacement resolu:on : 10-2 Strain resolu:on : 0.01 % 17
OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 18
EXPERIMENTAL TEST METHOD q Photo- mechanical Set- up Instron tes:ng machine: 5848 MicroTester Displacement rate: 0.2 mm.min - 1 Load Cell: 2 kn 19
OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves Cost AcUon FP0802 20
STRAIN FIELDS ON MATERIAL COORDINATE SYSTEM 21
ELASTIC PROPERTIES (GLOBAL PROPERTIES) θ Fig. Stress- Strain curves on the specimen coordinate system (10 specimens). Fig. Engineering elasuc properues in the RT plate determined by the anisotropic- based method. Tab. Reference elasuc constants of P. pinastet in the RT plane E R (GPa) E T (GPa) ν RT (-) G RT (GPa) 1.5-1.9 0.8-1.4 0.68-0.71 0.255 0.280 22
IDENTIFIABILITY? Fig. Stress- Strain curves on the specimen coordinate system (10 specimens). Fig. Engineering elasuc properues in the RT plate determined by the anisotropic- based method. 23
OFF- AXIS ANGLE OPTIMISATION q Enhancing shear behaviour (Chamis and Sinclair, 1977) q Balancing out strain components (Grédiac et al 2006) 24
ELASTIC PROPERTIES (LOCAL PROPERTIES) e.g. image classificauon iden1fica1on strategy - IdenUfiability: Q 11 ( E R ) and Q 66 (G RT ) Future EW LW LW/EW EW LW LW/EW Q11 (GPa) 1.515 1.902 1.25 Q66 (GPa) 0.417 1.367 3.28 Fig. Engineering elasuc properues in the RT plate determined by the virtual fields method.
OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 26
CONCLUSIONS & PERSPECTIVES CONCLUSIONS - IdenUficaUon were proposed for evaluaung transverse elasuc properues (E R, E T, ν RT, G RT ) of P. pinaster by coupling ring- oriented tensile tests with full- field measurements provided by DIC PERSPECTIVES - Improving idenufiability (mechanical test) for extracung: (global) 4 orthotropic constants; (local) 8 orthotropic heterogeneous constants. - Assessing inter- and intra- variauon of RT elasuc properues within the stem. 27
Acknowledgment ACKNOWLEDGEMENT - COST AcUon FP0802: Short Term Scien1fic Mission STSM Topic: CharacterisaUon of local properues of wood at the meso scale by coupling full- field measurement with an inverse method Host: Stéphane Avril - Portuguese Founda1on for Science and Technology: SFRH/PROTEC/50149/2009 and Ciência 2008 program 28
Thank you 29