New splitting method for wood fracture characterization

Abstract

Summary A testing procedure with a new and simple specimen shape is presented which is appropriate to characterize fracturing of inhomogeneous and complex materials like wood. With this, the fracture energy of spruce wood is determined in the TL and RL direction. The "size effect", i.e. influences of specimen dimensions on K~c and Gf (specific fracture energy) are investigated. Stress and deformation distribution in the newly developed specimens are analysed with FE methods. The measured load-displacement curves are approximated by bilinear softening diagrams and FE analysis. Based on these results, it is tried to interpret typical deviations from LEFM's behaviour by mechanisms like microcracking, crack branching or crack tip bridging.

Experimental Investigation of Mode-I Fracture Properties of Parallel Strand Bamboo Composite

“…It can be observed that the critical stress intensity factor, KIc, measured for categories A-1 to A-4, were almost equal, whereas the results of A-5 deviated greatly from the mean value of the others. Together, considering the experimental results and Tschegg's (1995) suggestion, a crack depth ratio of 0.30 was assigned to the second group (Group-B) of samples, while all other dimensions were the same as Group-A (Fig. 3).…”

“…The first group, labeled A, was comprised of 15 specimens with different prefabricated crack lengths that were divided into 5 categories according to the crack depth ratio. Specimens were designed according to the instructions of Tschegg et al (1995) and ASTM E 399. The ligament lengths of the test specimens were determined in such a way that the initial crack depth ratio, / aW   varied from 0.20 to 0.40 increments of 0.05 while the prefabricated crack length, a, remained constant.…”

“…During testing, the wedge produces both opening forces perpendicular to the crack face, driving crack propagation, and vertical forces parallel to the crack direction, stabilizing crack growth. This method has some outstanding advantages (Stanzl-Tschegg et al 1995). First, it is a very stable test approach and the specimen is compact.…”

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

“…The crack simulation by finite element modeling (FEM) in the present study is based on description of a cohesive crack model for wood. It is a mode I fracture model, which is verified by fracture tests of wood (Stanzl-Tschegg et al 1994, 1995Vasic and Smith 2002;Coureau et al 2006). The tangential fracture parameters used here are based on experimental studies presented in the literature (Valentin et al 1991;Reiterer and Sinn 2002;Gustafsson 2003;Smith and Vasic 2003;Vasic and StranzlTschegg 2007;Dourado 2008;Dourado et al 2008).…”

Modeling crack propagation in wood and wood composites. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

“…Stanzl-Tschegg et al (1995) developed a wedge-splitting test procedure along with a finite element analysis of the crack tip to separate ''microcracking'' from ''crack bridging'' contributions to fracture energy. An important finding was that the bridging component in the RL direction was significantly higher than that in the TL direction due to the presence of ray cells normal to the crack plane.…”