Issue 35

V. Shlyannikov et alii, Frattura ed Integrità Strutturale, 35 (2016) 114-124; DOI: 10.3221/IGF-ESIS.35.14 116 crack opening displacement of specimen at the gauge length, a pulley arrangement with an externally axial encoder is introduced (Fig. 2). All tests are carried out with sinusoidal loading form with load control. Two different stress ratio R f values (0.1 and 0.5) were applied several times to the specimens in order to highlight the crack front geometry during propagation: during each test, beach marks were produced on each specimen by increasing the applied stress ratio from 0.1 to 0.5 at constant value of maximum cyclic nominal stress, when the surface crack length was approximately increased to a  0.1mm. The typical beach marks on the post mortem cross section of different specimens are shown in Figs. 2 and 3 for biaxial tension and bending, respectively. From the crack front shape obtained in a) b) c) Figure 1 : Details of the (a) cruciform specimen and (b) plate geometry and (c) initial notches. Figure 2 : Test equipment for measuring COD and crack path under biaxial loading. a) b) Figure 3 : Surface crack paths under bending for initial aspect ratio (a) (a/c) 0 =1.0 and (b) (a/c) 0 =0.36 .