High-Cycle Fatigue Properties of Automobile Cold-Rolled Steel Sheet with Stress Variation

Abstract

Since many components in the automotive body and chassis are produced by various manufacturing processes, have different chemical compositions, and are subjected to complex loading cycles, it is important to understand their loading mechanisms and susceptibility to damage. This research examined the mechanical properties of cold-rolled steel sheets and evaluated the effects of stress variations on fatigue behavior. Specifically, a series of load-controlled high-cycle fatigue tests were conducted by varying the stress levels of SPCC and SPRC340 sheet materials. The results showed that fatigue life and the fatigue limit increased with higher tensile and yield strengths. In addition, testing results indicated that the fatigue limit was higher than the monotonic yield strength due to cyclic hardening with plastic deformation during fatigue cycling. Regarding tensile properties upon pre-deformation, the yield strength increased with a higher amount of pre-deformation and was greater than the fatigue limit after deformation. Based on these experimental results, two types of fracture modes were observed under the applied stress range. General fatigue fracture mode, which denotes failure by crack initiation, propagation and final rupture at low stress amplitude, was observed with fatigue lives larger than 4 © 10 5 cycles. On the other hand, constrained fracture mode occurred at stress levels higher than 0.89 times the tensile strength and exhibited a fracture surface without fatigue crack initiation or propagation.

Research of the Ball Burnishing Impact over Cold-Rolled Sheets of AISI 304 Steel Fatigue Life Considering Their Anisotropy

“…Some authors [7,8] studied the effects of prestraining and different manufacturing processes on the fatigue properties of rolled specimens. Chang-Yeol Jeong et al reported a fatigue limit higher than the monolithic yield strength (YS) of low carbon steel sheets faces, using a modification of the classical BB process, called "vibratory ball burnishing" (VBB) [31,32].…”

Precipitation dependence of thermal properties for Al–Si–Mg–Cu–(Ti) alloy with various heat treatment

“…AleSi alloys with Cu and Mg are widely used in automotive engine applications [1,2] and they have been steadily replacing many conventional ferrous alloys. Cu and Mg additions in the AleSi system are known to promote the precipitation of secondary phases by a simple heat treatment and thereby improve mechanical properties [1,3,4].…”

“…Even though, during the initial stages of aging, there may be a subsequent decrease in conductivity, attributed to Guinier-Preston zone formation and its related phenomena, in general, the thermal conductivity of agehardening aluminum alloys is known to increase with exposure time and temperature [6]. The increase in conductivity is primarily due to the decrease of solute in solid solution associated with the precipitation and the growth of various phases [2,4]. It is known from our former studies [1,7,8] that the thermal conductivity and the thermal diffusivity of Al-based alloys depend on their thermal history.…”