Mechanism of effects of warm prestressing (WPS) on apparent toughness of notched steel specimens Part II: Calculations and analyses

Abstract

Based on the experimental results of Part I of present work, this paper describes results of FEM calculations and analyses in details which identified that the effect of tensile-warm pre-stressing (WPS) on improvement of the apparent toughness of notched specimens results from three factors i.e. the residual compressive stress, macroscopic blunting of the original notch, and prestrain-deactivating cleavage initiation. The effects of three factors are separated and is effective for each at various extents of prestressing specified with a prestress-ratio, P₀/P_gy, defining the prestressing load P₀ as a fraction of general yield load P_gy. For values of prestress-ratio lower than 1.0, the residual compressive stress acts as the main factor. Between 1.0 to 1.5 of prestress-ratio values, in addition to the residual compressive stress the macroscopic blunting plays increasing role. The effect of the prestrain-deactivating cleavage initiation presents at the prestress-ratio P₀/P_gy≥1.2. In the case of compressive-warm prestressing, the apparent toughness is deteriorated due to the residual tensile stress. The effects of complex cycles of WPS, with various steps of loading and unloading different in signs, are determined mainly by the loading step just before the fracturing step.