Issue34

S. Henkel et alii, Frattura ed Integrità Strutturale, 34 (2015) 466-475; DOI: 10.3221/IGF-ESIS.34.52 468 made with radii, which reduce the load carrying area of the loading arms. Therefore, the measurement area is reduced in thickness to get higher stresses there. The notch was induced by electro discharge machining. For small crack sizes the behavior of the specimen is near to the infinite plate. Loading only the Y-axis, the specimen with the crack configuration shown in Fig. 2a is quite comparable to the center crack tension (CCT) specimen. A negative T-stress is resulting [15]. An additional tensile loading in X-direction results in a shift of the T-stress to positive direction. Fig. 2b shows the T-stress based biaxiality ratios  versus the normalized crack size a/W for different standard specimen geometries [2] and the principle possible variation within the cruciform specimen. a) b) Figure 1 : a) Microstructure of the tested aluminum alloy 6061 T651: Precipitates arranged in lines parallel to the rolling direction. b) Crack growth curves for different load ratios R =  min /  max measured on SENB specimens. a) b) Figure 2 : a) Cruciform specimen with slotted arms and thinned inner measurement area together with the loading directions F X and F Y (dimensions in mm). b) Biaxiality ratio  depending on crack length to ligament ratio for different standard specimens [2] and the cruciform specimen with variation of F X .