Interior induced fatigue of surface‐strengthened steel under constant and variable loading: Failure mechanism and damage modeling

Abstract

Pulsating tension tests with constant amplitude (CA) and variable amplitude (VA) were conducted to investigate the interior failure mechanisms of a carburized Cr steel, and a cumulative damage model with the fine granular area (FGA) formation process was proposed in this study. Such a steel represents the continuously descending S‐N (stress‐number of cycles) curve characteristics associated with inclusion‐FGA‐fisheye induced failure even under variable amplitude. Due to crack growth retardations and accelerations resulted from the interaction effect between stepwise resets of the applied stress, the crack morphology under variable amplitude loading is much rougher. The interior failure mechanism was elucidated in combination with the determination of stress intensity factor values at different crack tips. Based on proposed damage model, the agreement between the predicted and experimental results is fairly good within the factor‐of‐two range.

High‐cycle and very‐high‐cycle fatigue behavior and life prediction of Ni‐based superalloy at elevated temperature

“…[1][2][3] Especially in recent days, the concept of very-high-cycle fatigue (VHCF) with over 10 7 cycles fatigue life has been widely concerned, and a series of research results have been obtained. [4][5][6] However, most of the experimental studies are limited to room temperature, and the S-N characteristics, 7-13 failure mechanism, [14][15][16][17][18][19][20][21][22][23][24] and fatigue life evaluation methods [25][26][27][28][29][30][31][32] under elevated temperature environment in VHCF regime are not yet well understood. Therefore, in order to ensure the long-term safety of structural components, the VHCF fatigue characteristics of structural materials in elevated temperature environment still needs to be further studied.…”

Ultrasonic fatigue testing of cast steel G42CrMo4 at elevated temperatures

“…Other authors evaluated values of SIF for FGA formation from 4 up to 5 MPa√m. 12,[48][49][50][51] Li et al 52 reported a SIF threshold value of 6.5 MPa√m for the formation of an FGA. In the present study, an average value of ΔK th = 7.0 ± 2.2 MPa√m for all failed specimens was determined using the √area parameter of Murakami 18 and the polygon method to determine the defects' area.…”

A fatigue life prediction approach to interior cracking induced high cycle and very high cycle fatigue for surface‐carburized steels

“…This characteristic microstructure area can be called as “optically dark area” (ODA), 9 “granular bright facet” (GBF), 10 “rough granular area” (RGA) 11 or “fine granular area” (FGA) 12 based on different observation methods. Herein, according to previous studies, 13 the term FGA will be used in this paper. Several mechanisms have been proposed to explain the formation of FGA induced by inclusions, such as “hydrogen‐assisted crack growth”, 9 “depressive decohesion of spherical carbides”, 10 and “formation and debonding of fine granular layer” 12 .…”