Issue 37

A. Eberlein et alii, Frattura ed Integrità Strutturale, 37 (2016) 1-7; DOI: 10.3221/IGF-ESIS.37.01 3 Figure 3 : Crack growth retardation after changing the loading direction from mode I to mixed-mode I + III. On the one hand the retardation effects are caused by the new crack growth direction due to mode III-loading part. Hereby the crack twists at an angle ψ 0 out of its previous orientation. Additionally the crack separates in many facets, which influence the crack growth rate too. Characteristic fractured surfaces with facet formation after changing the loading direction from mode I-loading to mixed-mode I + III-loading are pictured in Fig. 4. This row on fractured surfaces shows the facet formation depending on mode III-part on the total stress intensity factor K III /( K I + K III ). The figures indicate that facet formation begins at a specific mode III-part on the total stress intensity factor of K III /( K I + K III ) = 0.37. Within this experimental research no facets were observed below that ratio. The first fractured surface on the left hand side of Fig. 4, captured by mode III-part on the total stress intensity factor of K III /( K I + K III ) = 0.26, shows that the crack continuously and smoothly without any facet initiation changes its direction. Furthermore, the crack front is still coherent. With increasing mode III-part on the mixed-mode I + III-loading the facets’ shape changes clearly. Figure 4 : Facet formation with increasing mode III-part.