Crack Shape Control using Cold Rolling

ABSTRACT. The effect of cold rolling on crack shape evolution was investigated by experimentation. A recently developed technique termed stitch rolling, which applies differing intensities of surface compressive residual stress at specific regions in an engineering structure, was adopted to introduce compressive residual stress onto test specimens to control both the rate and shape of crack propagation. Three BS 7191 Grade 275A mild steel plates having undergone different cold rolling procedures were subjected to medium cycle fatigue tests under bending. Fatigue crack growth was periodically monitored using crack sizing non-destructive testing methods and results are presented in terms of crack shape evolution. The different cold rolling procedures were seen to have a significant influence on the crack initiation, crack propagation path and the overall fatigue life of the specimens. The fatigue lives of stitch rolled specimens were significantly improved. In addition, cold rolling was observed to have caused crack arrest and retardation. Comparisons with an analytical fracture mechanics solution is also presented