38 5 2016 10 1) 2) ( 116024)..... TU366.2 A doi 10.6052/1000-0879-15-069 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 116024, 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].. 2015 03 23 1 2015 05 01. 1) (51108055) (DUT13LK44). 2). E-mail: bohanxu@dlut.edu.cn,,.., 2016, 38(5): 493-500 Xu Bohan, Wang Yaxun, Zhao Yanhua. State-of-the-art of wood fracture toughness along the grain. Mechanics in Engineering, 2016, 38(5): 493-500
494 2016 38. [4] 10. [5]. [6]... [7].. 1 1.1 10 30 [1].. 3 L R T ( 1) 3. 120 MPa 150 MPa 2 3 1/30 1/40 [8]. 1.2 [9]. [10].. [11]. 1.3 6 TL, RL, LR, LT, RT TR 1 2 ( 2). TL RL. 2 6 [12]. 2 1 3 G K
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..... 2.1.1 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.
496 2016 38 [19] [20]. 2.1.2 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]. 2.2.1 K IC K IC ( 6) ( 7). [26] ( 8) TL TR -- K IC TL TR TL TR.
5 497 6 7 8 [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. 2.2.2 K IIC K IIC ( 9). [36] TL G IIC K IIC -- G IIC 0.7 0.85 K IIC K IIC.
498 2016 38 9 [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.. 2.4. K. [42] -- G IC G IC. [43] G IC G IC. [44] G IC 1.79. [45-46] G IIC 0.35. G II G IIC.
5 499 [47] G IC. 3.. -- G C.. 3 [48] Y K... [28,49] [50]. [51] [52]... [44]. 1,.. :, 2009 2. ( )., 2012, 26(1): 7-10 3 Smith I, Landis E, Gong M. Fracture and Fatigue in Wood. New Jersey: John Wiley and Sons 2003 4 King MJ, Sutherland IJ, Le-ngoc L. Fracture toughness of wet and dry pinus radiate. Holz als Roh-und Werkstoff, 1999, 57(4): 235-240 5,,. LT., 2002, 24(2): 59-61 6,,.., 2003, 39(1): 119-125 7.. : 2006 8.. :, 1998 9.., 2002, 24(4): 49-51 10 Wu EM. Application of fracture mechanics to anisotropic plates. Journal of Applied Mechanics, 1967, 34(4): 967-974 11,.., 1997, 19(3): 85-92 12.. [ ]. :, 2009 13 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, 1993 14,,.., 2001, 37(2): 112-116 15 Yoshihara H, Kawamura T. Mode I fracture toughness estimation of wood by DCB test. Composites Part A: Applied Science and Manufacturing, 2006, 37(11): 2105-2113 16 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): 335-346 17 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): 2537-2549 18 DE Moura M, Morais JJL, Dourado N. A new data reduction scheme for mode I wood fracture characterization
500 2016 38 using the double cantilever beam test. Engineering Fracture Mechanics, 2008, 75(13): 3852-3865 19 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): 23-42 20 Morel S, Bouchaud E, Schmittbuhl J, et al. R-curve behavior and roughness development of fracture surfaces. International Journal of Fracture, 2002, 114(4): 307-325 21 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): 8-12 22 Yoshihara H. Mode II initiation fracture toughness analysis for wood obtained by 3-ENF test. Composites Science and Technology, 2005, 65(14): 2198-2207 23 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): 1334-1344 24 Silva MAL, Morais JJL, DE Moura M, et al. Mode II wood fracture characterization using the ELS test. Engineering Fracture Mechanics, 2007, 74(14): 2133-2147 25 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): 231-240 26 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): 371-376 27 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): 1189-1205 28.. [ ]. :, 2008 29 Reiterer A, Tschegg S. The influence of moisture content on the mode I fracture behaviour of sprucewood. Journal of Materials Science, 2002, 37(20): 4487-4491 30,,.., 2002, 16(2): 26-28 31,,..,, 2006 32 Schachner H, Reiterer A, Stanzl-Tschegg SE. Orthotropic fracture toughness of wood. Journal of Materials Science Letters, 2000, 19(20): 1783-1785 33 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): 935-940 34 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): 29-36 35 Stanzl-Tschegg SE. Microstructure and fracture mechanical response of wood. International Journal of Fracture, 2006, 139(3-4): 495-508 36 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): 4727-4739 37 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): 2775-2788 38 Planas J, Guinea GV, Elices M. Generalied size effect equation for quasi-brittle Materials. Materials and Sructures, 1997, 20(5): 671-687 39 Boatright SWJ, Garrrentt GG. The effect of microstructure and stress state on fracture behaviour of wood. Journal of Materials Sciencd, 1983, 18: 2181-2199 40 Stanzl-Tschegg SE, Tan DM, Tschegg EK. New splitting method for wood fracture characterization. Wood Science Technology, 1995, 29: 31-50 41 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): 510-520 42 Conrad MPC, Smith GD, Fernlund G. Fracture of discontinuous wood-adhesive bonds. International Journal of Adhesion and Adhesives, 2003, 23(1): 39-47 43 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): 1227-1237 44 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): 3-10 45 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): 1865-1884 46 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): 875-897 47 Wang VZ, Ginger JD, Narayan K. Intralaminar and interlaminar fracture characterization in glued-laminated timber members using image analysis. Engineering Fracture Mechanics, 2012, 82: 73-84 48.. :, 1993 49.. [ ]. :, 2009 50.. [ ]. :, 2013 51 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): 3548-3555 52.. [ ]., 2008 ( : )