Issue 37

H.A. Richard et alii, Frattura ed Integrità Strutturale, 37 (2016) 80-86; DOI: 10.3221/IGF-ESIS.37.11 80 Focussed on Multiaxial Fatigue and Fracture 3D-mixed-mode-loading: material characteristic values and criteria’s validity H. A. Richard, A. Eberlein University of Paderborn, Institute of Applied Mechanics, Pohlweg 47-49, 33098 Paderborn, Germany , , A BSTRACT . In many structures and components cracks, which are exposed to a 3D-mixed-mode-loading, occur due to multiaxial loading situation. A reliable evaluation of those components requires fracture mechanical criteria validated by experimental investigations. Within this article 3D-mixed-mode criteria for static as well as cyclic loadings will be presented. Experiments for pure mode I-loading, pure mode II-loading, pure mode III- loading and 2D- as well as 3D-mixed-mode-loading combinations are performed using specially developed specimens and loading devices. By comparing the experimental results with criteria a widely validity of criteria and a generally conservative behaviour are revealed. K EYWORDS . 3D-mixed-mode Criteria; Threshold Values; Fracture Toughness; CTSR-specimen. I NTRODUCTION n many practical cases crack growth leads to fatigue fracture or abrupt failure of components and structures. For reasons of a reliable quantification of the endangerment due to sudden fracture of a component it is of huge importance to know the limiting values (fracture toughness) for the beginning of instable crack growth as well as the threshold values for the fatigue crack growth. This contribution deals with the complex problem of crack growth under mixed-mode-loading. It will present a comparison between concepts, which characterises the superposition of mode I and mode II (2D-mixed-mode) as well as the superposition of all three modes (mode I, mode II and mode III) for spatial loading conditions, and experimental results for stable and unstable crack growth. M ULTIAXIAL STRESS FIELD AND FRACTURE MODES n linear-elastic fracture mechanics the characterisation of the loading situation at the crack front and in its neighbourhood is based on stresses and displacements. Generally, a crack can be loaded by a multiaxial stress field consisting of six stress components. As Fig. 1 exemplary shows on a boarder crack with the length a in a volume cube, different stresses causes various crack loadings (fracture modes). σ y induces a crack opening (mode I). A mode I- loaded crack grows perpendicular to the normal stress σ y . Due to the shear stress τ xy the crack kinks out of its previous direction in shear stress plane. In this case a mode II-loading on crack is present. The shear stress τ yz effects an anti-plane shear loading (mode III) at the crack, which leads to a crack twisting. Furthermore the initial crack separates in multiple daughter crack segments. I I