Issue 37

A. Eberlein et alii, Frattura ed Integrità Strutturale, 37 (2016) 1-7; DOI: 10.3221/IGF-ESIS.37.01 2 CTSR (Compact Tension Shear Rotation) -specimen Referring to the AFM-specimen a new specimen, so-called CTSR-specimen (Fig. 1) has been developed [4]. Relevant specimen’s dimensions are listed in the chart on the right hand side of Fig. 1. Hereby the specimen thickness t is a compromise between a thick specimen with a high torsional stiffness and high testing load levels. The appropriate loading device is shown in Fig. 2. In combination with the new specimen this loading device enables any combination of mixed- mode-loading including pure mode I-, pure mode II- and pure mode III-loading. A detailed explanation and illustration of adjusting the mixed-mode-loading can be found in [4, 5, 6]. specimen length l 103 mm specimen width w 55 mm initial crack length a 0 27.5 mm specimen thickness t 15.5 mm Figure 1 : CTSR-specimen with characteristic dimensions. Experimental Procedure under combined Mode I-Mode III-loading For the creation of facets crack growth experiments with changing loading directions were performed. After a crack growth of a crack length a = 3.5 mm under mode I-loading condition with a constant cyclic comparative stress intensity factor Δ K V the loading direction by turning the loading device and rotating the specimen was changed into mixed- mode I + III-loading with Δ K I ≠ 0 and Δ K III ≠ 0 (Fig. 2). Figure 2 : Mixed-mode I + III-loading by shifting the loading device. Then the tests started again under constant cyclic load range Δ F set so, that the cyclic comparative stress intensity factor Δ K V before and after the loading direction was identically. Crack length-Cycle Curves and Fractured Surfaces Typical a - N -curves resulting from such experiments with changing loading directions are shown in Fig. 3. The mixed- mode I + III-loading was adjusted by varying both loading angles α and β . A crack length a of 3.5 mm under mode I- loading, due to that high cyclic stress intensity factor Δ K V = Δ K I , is reached after ca. N = 70,000 cycles. Afterwards changing the loading direction the crack growth delays. Significant crack growth retardations were noticed by stress intensity factor ratios 1 < K III / K I < ∞.