Incremental cyclic fracture behaviour of 20MnMoNi55 steel at room temperature

Fracture behavior of low alloy steel 20MnMoNi55 has been evaluated under cyclic loading condition. Effect of unloading extent and degree of cycling on fracture resistance has been evaluated by varying load ratio (R)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(R)$$\end{document} and incremental plastic displacement (ΔV)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$(\varDelta V)$$\end{document}. It is observed that the initiation fracture toughness and tearing modulus decreased significantly with more negative R\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R$$\end{document} ratio and decrease in incremental plastic displacement. Examination of interrupted cyclic fracture test specimens revealed considerable crack tip re-sharpening and suppression of void growth and this is thought to be the reason for the reduction in fracture resistance under cyclic loading.