Issue 38

A. Eberlein et alii, Frattura ed Integrità Strutturale, 38 (2016) 351-358; DOI: 10.3221/IGF-ESIS.38.45 356 of interspersed mode I-mode II-block loads on mode II-base load are shown in Fig. 8. Here a pure mode II-block load causes the greatest retardation effect on the crack growth in mode II-base load. Figure 7 : Crack growth retardation due to interspersed mode I-mode III-block loads in mode I-base load. Figure 8 : Crack growth retardation due to interspersed mode I-mode II-block loads in mode II-base load. Indeed, the displacement according to amount of the crack flanks increases in y-direction with increasing mode I- component of the mode I-mode-II-block load and enlarges the plastic zone at the crack front, but the residual compressive stresses does not retard the crack growth in mode II-base load. The reason for that is the displacement of the crack flanks in mode II-base load, which takes place parallel to the crack growth direction. In comparison to the crack growth in mode I- and mode II-base load the crack growth in mode III-base load due to interspersed mode I-, mode III- as well as mode I-mode III-block load combinations shows varyingly strong retardations (see Fig. 9). Indeed, it can be observed that the retardation effect decreases with increasing K I / K III -ratio, nevertheless the influence of the mode I-component in the mode I-mode III-block loads on a mode III-loaded crack is still existing. A part of typical fractured surfaces developed within the experiments are presented in Fig. 10. The fractured surfaces show for interspersed mode I-mode II-block loads in mode II-base load expected characteristics. Due to a pure mode I-block load a significant step on the fractured surface arises (Fig. 10 a)). Concerning the crack growth direction a crack kinking angle φ 0 of ca. 63° was measured before as well as after interspersing the block load. The fractured surfaces resulting from interspersed mode I-mode III-block loads in mode III-base load, shown in Fig. 10 b), reveal several facets and are relatively jagged. In conclusion, it can be registered that the greatest retardation effects respectively the greatest advantages