STATE-OF-THE-ART of WOOD FRACTURE TOUGHNESS ALONG THE GRAIN 1)

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1 ) 2) ( )..... TU366.2 A doi / STATE-OF-THE-ART of WOOD FRACTURE TOUGHNESS ALONG THE GRAIN 1) XU Bohan 2) WANG Yaxun ZHAO Yanhua (State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian , Liaoning, China) Abstract Defects may lead to wood fracture under low stress state. In this paper we summarize the state-ofthe-art of wood fracture toughness along the grain, which is an important mechanical parameter of wood. We introduce main fracture toughness test methods, and analyze the advantages and disadvantages of different test methods and data processing methods. We focus on the related influence factors of the fracture toughness, such as wood species, density, moisture content, wood fiber bridging effect, specimen span/depth ratio, and so on. Moreover, we summarize the research results of the fracture toughness s size effect. Considering the wide usage of engineered wood products in practice, the research sate of wood adhesive bonds fracture is also introduced. Key words wood, fracture toughness, fracture along the grain, size effect, wood adhesive bonds fracture [1]. [2].. [3] ) ( ) (DUT13LK44). 2). bohanxu@dlut.edu.cn,,.., 2016, 38(5): Xu Bohan, Wang Yaxun, Zhao Yanhua. State-of-the-art of wood fracture toughness along the grain. Mechanics in Engineering, 2016, 38(5):

2 [4] 10. [5]. [6]... [7] [1].. 3 L R T ( 1) MPa 150 MPa 2 3 1/30 1/40 [8]. 1.2 [9]. [10].. [11] TL, RL, LR, LT, RT TR 1 2 ( 2). TL RL. 2 6 [12] G K

3 5 495 G = K2 E (1) E. [13] 1 E = 1 E x E x 2E y E x E y + E x 2G xy µ yx E x E y (2) x y E x E y G xy µ yx. G C K C. G K G G C K K C (3) 2.1 G C G C G C = P 2 C 2B C a = a C (4) a P C B C a a C. G C G C G IC G IC ( 3). [12,14]. 3. [15] TL G IC G IC. G IC [16]. TL [17] ( 4). 4 [17] [18] RL G IC -- G IC.

4 [19] [20] G IIC G IIC ( 5). G IIC [21] 8 (5) (6) G IIC E x (5) C (6). (6) G IIC 12. G IIC = G IIC = 9P 2 C a2 16E x B 2 H 3 (5) 9CP 2 C a2 2B(2L 3 + 3a 3 ) 5 (6). [16] [22] TL G IIC 3 G IIC. [23] 2 G IIC G IIC G IIC. [17] ( 4) TL.. [24] RL. 2.2 K C K C K = Y σ πa (7), K σ a Y ( ). K C G C (1). [25] K IC K IC ( 6) ( 7). [26] ( 8) TL TR -- K IC TL TR TL TR.

5 [16] [27] K IC K IC K IC. [28] TL RL K IC P C. [29] TL K IC 7% 12%( ) K IC 12%( ) 55%( ) K IC. [30-31] 17% K IC 17% 6% K IC. [32] 1/4 K IC. RL LR. [33] RL K IC TL K IC. [34] [35] K IC RL K IC TL K IC K IIC K IIC ( 9). [36] TL G IIC K IIC -- G IIC K IIC K IIC.

6 [37] TL K IIC K IIC K IIC,. 2.3 [38]. [39] 1 mm 50 mm 9 10 mm K IC. [40] 70 mm 30 mm K IC. [41] 6 K IC. [9,12] 6 TL 10 mm 45 mm 10 mm K IC. [28] 3 K IC. [16] 5 G C G C K. [42] -- G IC G IC. [43] G IC G IC. [44] G IC [45-46] G IIC G II G IIC.

7 5 499 [47] G IC G C.. 3 [48] Y K... [28,49] [50]. [51] [52]... [44]. 1,.. :, ( )., 2012, 26(1): Smith I, Landis E, Gong M. Fracture and Fatigue in Wood. New Jersey: John Wiley and Sons King MJ, Sutherland IJ, Le-ngoc L. Fracture toughness of wet and dry pinus radiate. Holz als Roh-und Werkstoff, 1999, 57(4): ,,. LT., 2002, 24(2): ,,.., 2003, 39(1): : :, , 2002, 24(4): Wu EM. Application of fracture mechanics to anisotropic plates. Journal of Applied Mechanics, 1967, 34(4): ,.., 1997, 19(3): [ ]. :, Gustafsson P. Fracture mechanics models for strength analysis of timber beams with a hole or a notch: a report of RILEM TC-133: mean stress approach and initial crack approach (paper in report). Vol Report TVSM-7134, Lund University, Sweden, ,,.., 2001, 37(2): Yoshihara H, Kawamura T. Mode I fracture toughness estimation of wood by DCB test. Composites Part A: Applied Science and Manufacturing, 2006, 37(11): Yoshihara H, Satoh A. Shear and crack tip deformation correction for the double cantilever beam and three-point end-notched flexure specimens for mode I and mode II fracture toughness measurement of wood. Engineering Fracture Mechanics, 2009, 76(3): Yoshihara H. Mode I and mode II initiation fracture toughness and resistance curve of medium density fiberboard measured by double cantilever beam and three-point bend end-notched flexure tests. Engineering Fracture Mechanics, 2010, 77(13): DE Moura M, Morais JJL, Dourado N. A new data reduction scheme for mode I wood fracture characterization

8 using the double cantilever beam test. Engineering Fracture Mechanics, 2008, 75(13): Morel S, Mourot G, Schmittbuhl J. Influence of the specimen geometry on R-curve behavior and roughening of fracture surfaces. International Journal of Fracture, 2003, 121(1-2): Morel S, Bouchaud E, Schmittbuhl J, et al. R-curve behavior and roughness development of fracture surfaces. International Journal of Fracture, 2002, 114(4): Yoshihara H. Influence of span/depth ratio on the measurement of mode II fracture toughness of wood by end-notched flexure test. Journal of Wood Science, 2001, 47(1): Yoshihara H. Mode II initiation fracture toughness analysis for wood obtained by 3-ENF test. Composites Science and Technology, 2005, 65(14): Silva MAL, DE Moura M, Morais JJL. Numerical analysis of the ENF test for mode II wood fracture. Composites Part A: Applied Science and Manufacturing, 2006, 37(9): Silva MAL, Morais JJL, DE Moura M, et al. Mode II wood fracture characterization using the ELS test. Engineering Fracture Mechanics, 2007, 74(14): Wang QZ. A sandwich three-point bend specimen for testing mode-i interlaminar fracture toughness for fiberreinforced composite materials. International Journal of Fracture, 1997, 85(3): Watanabe K, Shida S, Ohta M. Evaluation of end-check propagation based on mode I fracture toughness of sugi (Cryptomeria japonica). Journal of Wood Science, 2011, 57(5): Ardalany M, Deam B, Fragiacomo M. Experimental results of fracture energy and fracture toughness of Radiata Pine laminated veneer lumber (LVL) in mode I (opening). Materials and Structures, 2012, 45(8): [ ]. :, Reiterer A, Tschegg S. The influence of moisture content on the mode I fracture behaviour of sprucewood. Journal of Materials Science, 2002, 37(20): ,,.., 2002, 16(2): ,,..,, Schachner H, Reiterer A, Stanzl-Tschegg SE. Orthotropic fracture toughness of wood. Journal of Materials Science Letters, 2000, 19(20): Reiterer A, Burgert I, Sinn G, et al. The radial reinforcement of the wood structure and its implication on mechanical and fracture mechanical properties a comparison between two tree species. Journal of Materials Science, 2002, 37(5): Reiterer A, Sinn G, Stanzl-Tschegg SE. Fracture characteristics of different wood species under mode I loading perpendicular to the grain. Materials Science and Engineering: A, 2002, 332(1): Stanzl-Tschegg SE. Microstructure and fracture mechanical response of wood. International Journal of Fracture, 2006, 139(3-4): Yoshihara H. Mode II fracture mechanics properties of wood measured by the asymmetric four-point bending test using a single-edge-notched specimen. Engineering Fracture Mechanics, 2008, 75(16): Susanti CME, Nakao T, Yoshihara H. Examination of the Mode II fracture behaviour of wood with a short crack in an asymmetric four-point bending test. Engineering Fracture Mechanics, 2011, 78(16): Planas J, Guinea GV, Elices M. Generalied size effect equation for quasi-brittle Materials. Materials and Sructures, 1997, 20(5): Boatright SWJ, Garrrentt GG. The effect of microstructure and stress state on fracture behaviour of wood. Journal of Materials Sciencd, 1983, 18: Stanzl-Tschegg SE, Tan DM, Tschegg EK. New splitting method for wood fracture characterization. Wood Science Technology, 1995, 29: DE Moura M, Dourado N, Morais JJL. Crack equivalent based method applied to wood fracture characterization using the single edge notched-three point bending test. Engineering Fracture Mechanics, 2010, 77(3): Conrad MPC, Smith GD, Fernlund G. Fracture of discontinuous wood-adhesive bonds. International Journal of Adhesion and Adhesives, 2003, 23(1): Veigel S, Müller U, Keckes J, et al. Cellulose nanofibrils as filler for adhesives: effect on specific fracture energy of solid wood-adhesive bonds. Cellulose, 2011, 18(5): Veigel S, Follrich J, Gindl-Altmutter W, et al. Comparison of fracture energy testing by means of double cantilever beam-(dcb)-specimens and lap joint testing method for the characterization of adhesively bonded wood. European Journal of Wood and Wood Products, 2012, 70(1-3): Qiao PZ, Wang JL, Davalos JF. Analysis of tapered ENF specimen and characterization of bonded interface fracture under Mode-II loading. International Journal of Solids and Structures, 2003, 40(8): Wang JL, Qiao PZ. Fracture toughness of wood wood and wood FRP bonded interfaces under mode-ii loading. Journal of Composite Materials, 2003, 37(10): Wang VZ, Ginger JD, Narayan K. Intralaminar and interlaminar fracture characterization in glued-laminated timber members using image analysis. Engineering Fracture Mechanics, 2012, 82: :, [ ]. :, [ ]. :, Moutou Pitti R, Dubois F, Pop O, et al. A finite element analysis for the mixed mode crack growth in a viscoelastic and orthotropic medium. International Journal of Solids and Structures, 2009, 46(20): [ ]., 2008 ( : )

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