Fatigue performance of ultra-high-strength steel laser cut notches under variable amplitude loading

Experimental fatigue tests with variable amplitude (VA) load were conducted for notched uncoated and hot-dip galvanized (HDG) notched laser cut components made of S960 ultra-high-strength steel (UHSS). Tests were conducted with low (constant minimum) and high (constant maximum) mean stresses and major differences between fatigue lives with the tests on identical equivalent stress were found. A multiparametric 4R method application, in conjunction with the theory of critical distances (TCD) to obtain fatigue-effective stresses at notch, was utilized on the mean stress correction and fatigue strength assessment. The introduced 4R method was proven to be highly efficient to consider different mean stress levels based on the experimental results and different loading and specimen types could be evaluated with single FAT class.