13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Experiments on cracks under spatial loading Hans A. Richard1,*, Alexander Eberlein1, Nils-H. Schirmeisen2 1 Institute of Applied Mechanics, University of Paderborn, 33100, Germany 2 WINDMOELLER & HOELSCHER KG, Lengerich, 49525, Germany * Corresponding author: richard@fam.upb.de Abstract The basic loading cases (Mode I, Mode II and Mode III) of cracks are generally defined by the near-field solutions for the stress distribution at the crack front. Cracks, whose stress near fields are symmetric due to geometry and/or loading of the structure, are called Mode I-cracks. In case of spatial loaded cracks the stress fields near the crack tip are unsymmetrical. The fracture mechanical treatment of such Mixed-Mode-loaded cracks is consequently more complicated as of pure Mode I-loaded cracks. For experimental investigations of 3D-Mixed-Mode-loaded cracks the CTSR-specimen (Compact-Tension- Shear-Rotation-specimen) will be proposed. The CTSR-specimen with the corresponding loading device enables the generation of pure Mode I, pure Mode II, pure Mode III and several combinations of the three basic fracture modes. In this paper the CTSR-specimen, the loading device and various experimental results for fracture and fatigue loading situations are illustrated. Furthermore these results will be compared with existing fracture criteria for 3D-Mixed-Mode-problems. Keywords 3D-Mixed-Mode, fracture, fatigue, CTSR-specimen 1. Introduction In real structures fracture processes are in many cases of a three dimensional character. Different defects, e.g. pre-cracks, which often exist in materials and structures, may experience complex loading conditions. Cracks under complex loading are subjected to a superposition of the three basic fracture modes I, II and III. In this case cracks tend to kink and/or twist, Fig. 1. Mode I+II+III pre-crack crack growth surface Figure 1. Crack screwing under combined loading For static loading the stress field near the crack front (Eq. 1) here is not only defined by the stress intensity factor KI, but also by KII and KIII. In this case the calculation of a comparative stress intensity factor KV is important (Eq. 2) [1].
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