13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Table 1: Test conditions Material 7075 T651 S355 steel Test n° CCP7a CCP7Na CCP5a CCP2a CCP2Na Environment air NaCl air air NaCl Range of apparent ΔKI (Mpa√m) 7-18 7-18 9-20 18-35 18-35 Stress range (MPa) 34 34 40 100 100 Cycles for crack initiation 30000 10000 15000 35000 27000 Cycles of crack growth until fracture 202440 110260 59000 157730 138730 Fracture surface topographies were reconstructed using a digital optical microscope. The results were obtained as (x, y, z) triplets, where x denotes the distance from the notch root, y, the position in depth, and z the height from the notch plane. Transverse height profiles, z(y) were derived. Polynomial expressions were fitted to these profiles and used to compute the local twist angle as arctang (dz/dy). The shear lips width, denoted by ts, was deduced from these height profiles. 3. Experimental results Salt water reduced the number of cycles for crack initiation by a factor of 3 in the aluminium alloy and 1.3 in steel. Crack growth was significantly accelerated in the aluminium alloy, but not in steel. Figure 1 shows examples of crack transverse profiles, z(y), and twist angle profiles at different stages of crack growth. Fig 1: Topographic reconstructions of fracture surfaces. a) transverse profiles and b) twist angles for specimen CCP5a. c) transverse profiles and d) twist angles for specimen CCP2a. y z
RkJQdWJsaXNoZXIy MjM0NDE=