Assessing local proper.es of wood within the stem from full- field measurements

Transcription

1 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

2 WOOD AS AN ENGINEEGING MATERIAL Wood is a hierarchical, anisotropic and heterogeneous material Meso scale lenght (m) Mo1va1on 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

3 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

4 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

5 IDENTIFICATION METHODS FROM FULL- FIELD MEASUREMENTS Mo1va1on 5

6 OUTLINE iden1fica1on - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 6

7 OUTLINE iden1fica1on - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 7

8 ANISOTROPIC- BASED METHOD Ring- oriented tensile test iden1fica1on ConsUtuUve equauons Off- axis angle θ Digital image correlauon (DIC) Off- axis angle θ For:. : 8

9 VIRTUAL FIELDS METHOD ConsUtuUve equauons - Image segmentauon iden1fica1on 9

10 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

11 OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 11

12 MATERIAL q Wood samples q Off- axis angles P. pinaster wood 50(R)x5(L)x2(T) (mm) R1 R2 R3 R4 R5 [ ] 12

13 OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 13

14 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

15 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

16 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

17 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

18 OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 18

19 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

20 OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves Cost AcUon FP

21 STRAIN FIELDS ON MATERIAL COORDINATE SYSTEM 21

22 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)

23 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

24 OFF- AXIS ANGLE OPTIMISATION q Enhancing shear behaviour (Chamis and Sinclair, 1977) q Balancing out strain components (Grédiac et al 2006) 24

25 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) Q66 (GPa) Fig. Engineering elasuc properues in the RT plate determined by the virtual fields method.

26 OUTLINE - Anisotropic- based method - Virtual fields method - Material - Digital image correlauon - Ring- oriented tensile tests perspecuves 26

27 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

28 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

29 Thank you 29