Mode II fracture testing method for highly orthotropic materials like wood

Abstract

In this paper a mode II fracture testing method has been developed for wood from analytical, experimental and numerical investigations. Analytical results obtained by other researchers showed that the specimen geometry and loading type used for the proposed mode II testing method results in only mode II stress intensity and no mode I stress intensity at the crack tip. Experiments have been carried out to determine mode II fracture toughness/';'nc and fracture energy GHF from the test data collected from both spruce (picea abies) and poplar (populus nigra) specimens. It was found that there existed a very good relation between fracture toughness KHc and fracture energy GUF when the influence of orthotropic stiffness Eli in mode II was taken into account. It verified that for this mode II testing method the formula of LEFM can be employed for calculating mode II fracture toughness even for highly orthotropic materials like wood. In the numerical studies for the tested spruce specimen, the crack propagation process, stress and strain fields in front of crack tips and the stress distributions along the ligament have been investigated in detail. It can be seen that the simulated crack propagating process along the ligament is a typical shear cracking pattern and the development of cracks along the ligament is due to shear stress concentrations at the crack tips of the specimen. It has been shown that this mode II fracture testing method is suitable for measuring mode II fracture toughness Ki~c for highly orthotropic materials like wood.

Experimental determination of KIIC of normal strength concrete

“…However, more research is needed until GHF can be determined on concrete experimentally. It should be noted that previous tests on wood have allowed to determine GFI I [28] and that numerical simulation of tests on high strength concrete was able to produce acceptable values OfGFi I [29].…”

“…For finite specimen sites, it has been shown [28,30] that Tada's formula applies ifh _> 2a and w _> r~ a. Ifh _> 2a and w _< rt a the geometry can be regarded as an infinite strip and the following formula [28] applies:…”

“…A new specimen geometry and loading arrangement has been proposed and as already been applied to wood. For this highly anisotropic material, it was possible to determine KII c and GII F in the direction normal to the grain [28]. Furthermore, the new method has proven its applicability to high strength concrete, to generate a shear fracture and to determine KII c [29].…”

Fracture characterization of concrete/epoxy interface affected by moisture

“…Mode II fracture block specimen with dimensions of 200 mm (width, 2w) Â 200 mm (height, 2h) Â 100 mm (thickness) and a through thickness double-edged notch with a depth 50 mm (see Fig. 2) based on recommendation from prior research studies (Xu et al, 1995;Reinhardt et al, 1997) were tested under mode II fracture condition.…”

A short-beam shear fracture approach to measure the mode II fracture toughness of materials with preferred interfaces

“…A similar analysis to determine the fracture toughness of composite materials is conducted. First, the effective plane elastic modulus of the composite materials is calculated by using the formula presented below (Sih et al 1965;Xu et al 1996)…”