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An experimental method is presented that enables stress intensity factors due to residual stress to be determined directly, without prior determination of the residual stress. The method is based on the crack compliance method, where a narrow cut is introduced progressively into the considered component, and the resulting strain change is measured by a strain gage. The required mathematical relations to determine stress intensity factors from strain measurements are established by means of some basic relations of linear elastic fracture mechanics. They are derived explicitly for two exemplary geometrical systems, which allowed for analytical treatment. Experimental data obtained in the case of a steel roller are presented and discussed.

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Before a dry snow slab avalanche is released, a shear failure along a weak layer or an interface has to take place. This shear failure disconnects the overlaying slab from the weak layer. A better understanding of this fracture mechanical process, which is a key process in slab avalanche release, is essential for more accurate snow slope stability models. The purpose of this work was to design and to test an experimental set-up for a mode II fracture test with layered snow samples and to find a method to evaluate the interfacial fracture toughness or alternatively the energy release rate in mode II. Beam-shaped specimens were cut out of the layered snow cover, so that they consisted of two homogeneous snow layers separated by a well defined interface. In the cold laboratory 27 specimens were tested using a simple cantilever beam test. The test method proved to be applicable in the laboratory, although the handling of layered samples was delicate. An energy release rate for snow in mode II was calculated numerically with a finite element (FE) model and analytically using an approach for a deeply cracked cantilever beam. An analytical bilayer approach was not suitable. The critical energy release rate G c was found to be 0.04 ± 0.02 J m −2 . It was primarily a material property of the weak layer and did not depend on the elastic properties of the two adjacent snow layers. The mixed mode interfacial fracture toughness for a shear fracture along a weak layer estimated from the critical energy release rate was substantially lower than the mode I fracture toughness found for snow of similar density.

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The cut compliance method was developed to measure residual stress profiles. Its idea is to release them by introducing progressively a cut into the considered body. From the strain change due to progressive cutting it is possible to calculate the distribution of the released stresses. Since the method uses fracture mechanics principles the stress intensity factor due to residual stresses is delivered as well. Being a special type of residual stresses, the distribution of the contact stresses of fatigue crack closure and the corresponding closure stress intensity factors can be suitably determined by this method. Furthermore, it enables the residual stresses in front of the crack tip to be determined, which in crack retardation play a role as important as the closure effects. The basic theoretical relations for some frequently used fatigue specimens are analytically derived. They also can serve to evaluate the contact stresses from the commonly used unloading compliance technique, which is often used to identify crack closure effects. Some preliminary examples demonstrate the capability of the suggested method.