Fatigue crack closure over the range of stress ratios from −1 to 0.8 down to stress intensity threshold level in HT80 steel and SUS304 stainless steel

Stress ratio effect on crack growth behavior of dissimilar friction stir welded butt joint between AA6061 and AA7075 alloys

“…This may be due to the reasons described above, and a significant rough surface was observed for R = −0.5 as compared to R > 0. This type of observation is also reported by Ohta et al 72 The present observation is similar to Kemper et al 73 who concluded that the roughness of the fracture surfaces was dependent on microstructure and deformation characteristics and the fracture surfaces were not smooth when high compressive loads were applied.…”

“…0. This type of observation is also reported by Ohta et al 72 The present observation is similar to Kemper et al 73 who concluded that the roughness of the fracture surfaces was dependent on microstructure and deformation characteristics and the fracture surfaces were not smooth when high compressive loads were applied. The pictorial view of the crack path for different stress ratio is presented in Figure 11.…”

“…Thus, the new surface ahead of the crack tip depends on the applied loading, deformation, and microstructure. It has been reported by Ohta et al 72 that fatigue damage occurs at a negative stress ratio even when the crack is closed. When the stress ratio R < 0, the crack closure stress is above the minimum applied load.…”

“…It was shown that all compressive loads do not collapse the crack surfaces but some of it is dissipated in reducing and even reversing the residual stresses in the vicinity of the crack tip. 72 This means that the residual stresses at the crack tip may substantially reduce or even eliminate the compressive portion of the load cycle, and thus, directly influencing the crack front surfaces. In welded components due to higher residual stress, the compressive portion of the stress cycle helps in damage.…”