ON THE ESTIMATION OF ELASTIC PROPERTIES OF WOOD AT THE GROWTH RING SCALE

Transcription

1 ON THE ESTIMATION OF ELASTIC PROPERTIES OF WOOD AT THE GROWTH RING SCALE J. Xavier, J. Pereira, F. Pierron, J. Morais, J. Lousada CITAB/UTAD, Vila Real, Portugal LMPF/ENSAM, Châlons-en-Champagne, France

2 OUTLINE 1 INTRODUCTION 2 EXPERIMENTAL WORK 3 RESULTS AND DISCUSSION 4 CONCLUSIONS AND PERSPECTIVES 2 / 18

3 OUTLINE 1 INTRODUCTION 2 EXPERIMENTAL WORK 3 RESULTS AND DISCUSSION 4 CONCLUSIONS AND PERSPECTIVES 3 / 18

4 PROPERTIES OF WOOD: SPATIAL VARIABILITY Massive scale (>1m) Macro scale (0.1-1 m) Meso scale (1-10 mm) Micro scale ( µm) 4 / 18

5 PROPERTIES OF WOOD: SPATIAL VARIABILITY Massive scale (>1m) Macro scale (0.1-1 m) Meso scale (1-10 mm) Micro scale ( µm) 4 / 18

6 PROPERTIES OF WOOD: SPATIAL VARIABILITY MESO SCALE: GROWTH RINGS Changes on the structure of wood through the tree growing caused by variation of external conditions: Earlywood Latewood {}}{{}}{ T R } {{ } Growth ring 4 / 18

7 PROPERTIES OF WOOD: SPATIAL VARIABILITY MESO SCALE: GROWTH RINGS Changes on the structure of wood through the tree growing caused by variation of external conditions: RELATED WORK C.S. Modén and L.A. Berglund: Holzforschung, 62: , Earlywood Latewood {}}{{}}{ T R } {{ } Growth ring 4 / 18

8 PROPERTIES OF WOOD: SPATIAL VARIABILITY MESO SCALE: GROWTH RINGS Changes on the structure of wood through the tree growing caused by variation of external conditions: Earlywood Latewood {}}{{}}{ MAIN GOAL Assessing the spatial variability of elastic properties of wood on the RT plane T R } {{ } Growth ring 4 / 18

9 OUTLINE 1 INTRODUCTION 2 EXPERIMENTAL WORK 3 RESULTS AND DISCUSSION 4 CONCLUSIONS AND PERSPECTIVES 5 / 18

10 MATERIAL AND SPECIMEN Species: P. pinaster wood Material plane: Radial-Tangential (RT ) Hierarchical scale: meso-scale (growth ring scale) Nominal dimensions: 50(R) 7(T ) 2(L) mm T R Density: g.cm 3 MECHANICAL TEST Uniaxial tensile test along the R direction Full-field measurement technique: Digital Image Correlation 6 / 18

11 MATERIAL AND SPECIMEN Species: P. pinaster wood Material plane: Radial-Tangential (RT ) Hierarchical scale: meso-scale (growth ring scale) Nominal dimensions: 50(R) 7(T ) 2(L) mm T R Density: g.cm 3 MECHANICAL TEST Uniaxial tensile test along the R direction Full-field measurement technique: Digital Image Correlation 6 / 18

12 Introduction Experimental work Results and discussion Conclusions and perspectives PHOTO - MECHANICAL SET- UP Testing machine: Instron 5848 MicroTester Displacement rate: 0.05 mm.min 1 Load cell: 2 kn CCD camera: 8-bit Baumer Optronic FWX20 ( pixels) Lens: Nikon AF Micro-Nikkor 200mm f/4d IF-ED DIC system: ARAMIS GOM ( Working distance Conversion factor Acquisition frequency Subset size Local differentiation technique over ' = = = = 400 mm 6 µm.pixel Hz pixels ( µm) 3 3 macro-pixels 7 / 18

13 Introduction Experimental work Results and discussion Conclusions and perspectives PHOTO - MECHANICAL SET- UP Testing machine: Instron 5848 MicroTester Displacement rate: 0.05 mm.min 1 Load cell: 2 kn CCD camera: 8-bit Baumer Optronic FWX20 ( pixels) Lens: Nikon AF Micro-Nikkor 200mm f/4d IF-ED DIC system: ARAMIS GOM ( Working distance Conversion factor Acquisition frequency Subset size Local differentiation technique over ' = = = = 400 mm 6 µm.pixel Hz pixels ( µm) 3 3 macro-pixels 7 / 18

14 Introduction Experimental work Results and discussion Conclusions and perspectives PHOTO - MECHANICAL SET- UP Testing machine: Instron 5848 MicroTester Displacement rate: 0.05 mm.min 1 Load cell: 2 kn CCD camera: 8-bit Baumer Optronic FWX20 ( pixels) Lens: Nikon AF Micro-Nikkor 200mm f/4d IF-ED DIC system: ARAMIS GOM ( Working distance Conversion factor Acquisition frequency Subset size Local differentiation technique over ' = = = = 400 mm 6 µm.pixel Hz pixels ( µm) 3 3 macro-pixels 7 / 18

15 SURFACE PREPARATION: TEXTURED PATTERN DIC requirement: A textured pattern from which the light intensity will vary continuously with a suitable contrast 8 / 18

16 Introduction Experimental work Results and discussion Conclusions and perspectives SURFACE PREPARATION : TEXTURED PATTERN DIC requirement: A textured pattern from which the light intensity will vary continuously with a suitable contrast NATURAL CELLULAR TEXTURE OF WOOD 7 mm 6 9 mm HH H pixels? Surface polishing using sandpaper P120:P400 8 / 18

17 MEASURING RESOLUTION: STATIC TESTS 8 / 18

18 MEASURING RESOLUTION: STATIC TESTS 8 / 18

19 OUTLINE 1 INTRODUCTION 2 EXPERIMENTAL WORK 3 RESULTS AND DISCUSSION 4 CONCLUSIONS AND PERSPECTIVES 9 / 18

20 MECHANICAL RESPONSE: GLOBAL Heterogeneous strain fields: Y X Movie: ε X field 10 / 18

21 MECHANICAL RESPONSE: GLOBAL Heterogeneous strain fields: Y X Load = 50.4 N 10 / 18

22 MECHANICAL RESPONSE: GLOBAL Heterogeneous strain fields: STRESS-STRAINS CURVES Y X Load = 50.4 N Assumption : uniaxial and plane stress approach Strain effective (average) strain X radial direction (R) Y tangential direction (T ) 10 / 18

23 SEGMENTATION: EARLYWOOD AND LATEWOOD LAYERS X-ray micro-densitometry 11 / 18

24 SEGMENTATION: EARLYWOOD AND LATEWOOD LAYERS X-ray micro-densitometry IMAGE PROCESSING Segmentation : single thresholding Morphology operations : erosion + dilation 11 / 18

25 SEGMENTATION: EARLYWOOD AND LATEWOOD LAYERS Load = 50.4 N IMAGE PROCESSING Segmentation : single thresholding Morphology operations : erosion + dilation 11 / 18

26 SEGMENTATION: EARLYWOOD AND LATEWOOD LAYERS Load = 50.4 N IMAGE PROCESSING Segmentation : single thresholding Morphology operations : erosion + dilation 11 / 18

27 MECHANICAL RESPONSE: LOCAL X STRESS X STRAIN CURVES 12 / 18

28 MECHANICAL RESPONSE: LOCAL X STRESS X STRAIN CURVES Y STRAIN X STRAIN CURVES 12 / 18

29 MECHANICAL RESPONSE: LOCAL X STRESS X STRAIN CURVES Y STRAIN X STRAIN CURVES Effective Earlywood (EW) Latewood (LW) LW/EW ρ (g.cm 3 ) (-34.97%) (39.54%) 2.1 E R (GPa) (-12.05%) 1.99 (19.72%) 1.4 ν RT (-0.14%) (0.18%) / 18

30 ELASTIC PROPERTIES OF P. PINASTER: MESO SCALE MODULUS OF ELASTICITY 13 / 18

31 ELASTIC PROPERTIES OF P. PINASTER: MESO SCALE MODULUS OF ELASTICITY Reference: J. Pereira. Mechanical behaviour of wood along its material symmetry directions. Master s thesis, UTAD, / 18

32 ELASTIC PROPERTIES OF P. PINASTER: MESO SCALE MODULUS OF ELASTICITY Reference: J. Pereira. Mechanical behaviour of wood along its material symmetry directions. Master s thesis, UTAD, Mixture law: E effective R = E earlywood E latewood R R E earlywood f R earlywood +E R latewood f latewood f latewood = 45% 13 / 18

33 ELASTIC PROPERTIES OF P. PINASTER: MESO SCALE MODULUS OF ELASTICITY POISSON S RATIO Reference: J. Pereira. Mechanical behaviour of wood along its material symmetry directions. Master s thesis, UTAD, Mixture law: E effective R = E earlywood E latewood R R E earlywood f R earlywood +E R latewood f latewood f latewood = 45% 13 / 18

34 PROPERTIES VERSUS DENSITY PROFILES 14 / 18

35 PROPERTIES VERSUS DENSITY PROFILES Load = 50.4 N 14 / 18

36 PROPERTIES VERSUS DENSITY PROFILES Load = 50.4 N 14 / 18

37 OUTLINE 1 INTRODUCTION 2 EXPERIMENTAL WORK 3 RESULTS AND DISCUSSION 4 CONCLUSIONS AND PERSPECTIVES 15 / 18

38 CONCLUSIONS FULL-FIELD MEASUREMENTS Heterogeneous strain fields associated to the earlywood and the latewood layers were measured by digital image correlation with suitable spatial resolution and accuracy. MATERIAL IDENTIFICATION Local elastic properties (E R, ν RT ) of earlywood and latewood were determined for P. pinaster wood, assuming a uniaxial and plane stress approach. 16 / 18

39 CONCLUSIONS FULL-FIELD MEASUREMENTS Heterogeneous strain fields associated to the earlywood and the latewood layers were measured by digital image correlation with suitable spatial resolution and accuracy. MATERIAL IDENTIFICATION Local elastic properties (E R, ν RT ) of earlywood and latewood were determined for P. pinaster wood, assuming a uniaxial and plane stress approach. 16 / 18

40 PERSPECTIVES INVERSE IDENTIFICATION METHODS To identify the spatial variation of the 4 RT elastic properties (E R, E T, ν RT, G RT ) by a single tensile test from full-field measurements. [1] L.O. Jernkvist and F. Thuvander: Holzforschung, 55: , [2] Xavier et al: Holzforschung, 61: , / 18

41 PERSPECTIVES INVERSE IDENTIFICATION METHODS To identify the spatial variation of the 4 RT elastic properties (E R, E T, ν RT, G RT ) by a single tensile test from full-field measurements. [1] L.O. Jernkvist and F. Thuvander: Holzforschung, 55: , [2] Xavier et al: Holzforschung, 61: , Load = 50.4 N 17 / 18

42 PERSPECTIVES INVERSE IDENTIFICATION METHODS To identify the spatial variation of the 4 RT elastic properties (E R, E T, ν RT, G RT ) by a single tensile test from full-field measurements. [1] L.O. Jernkvist and F. Thuvander: Holzforschung, 55: , [2] Xavier et al: Holzforschung, 61: , IMAGE SEGMENTATION Multi-level thresholding coupled with fuzzy logic: better definition of the continuous transition from earlywood to latewood. 17 / 18

43 PERSPECTIVES INVERSE IDENTIFICATION METHODS To identify the spatial variation of the 4 RT elastic properties (E R, E T, ν RT, G RT ) by a single tensile test from full-field measurements. [1] L.O. Jernkvist and F. Thuvander: Holzforschung, 55: , [2] Xavier et al: Holzforschung, 61: , IMAGE SEGMENTATION Multi-level thresholding coupled with fuzzy logic: better definition of the continuous transition from earlywood to latewood. STRUCTURAL-PROPERTIES RELATIONSHIPS: SPATIAL VARIATION Study of the relationships between the cellular structure of wood and its elastic properties. 17 / 18

44 Thank you for your attention! J. Xavier CITAB/UTAD Engenharias I, Apartado Vila Real Portugal web page: jmcx/ 18 / 18