Fatigue Behavior of the Single Spot Welded Joint of Zinc Galvanized Steel Sheets

J. Ocean Eng. Technol. 1992;6(2):21-34.

아연도금 강판의 점용접재의 피로균형에 관한 연구

서창민,강성수,오상표

부산대학교 기계공학과,부산대학교 기계공학과,국방과학연구소

Keywords: Spot Welding, Fatigue Crack, High Strength Steel, Monogalvanized Steel, Nnugget, Stress Intensity Factor

핵심용어: 점용접, 피로구렬, 고장역강, 아연도금강, 너깃, 응력광대계수

Abstract

The behavior of fatigue crack growth in the single spot welded joint of zinc galvanized steel sheets was studied experimentally and analytically based on fracture mechanics. Axial tension fatigue tests were carried out with the BSxGAB specimen that the bare plane(GAB) of monogalvanized steel sheet was spot welded to the double thickness bare steel sheet(BS), and with the GAxGAB specimen that the galvanized plane (GA) was spot welded to the equal thickness bare plane (GAB) 1. The relation between maximum stress intensity factor, K sub(max) and the number of cycles to failure, N sub(f) has shown a linear relation on log-log plot in the spot weld of the zinc galvanized steel sheet. 2. The fatigue strength of BSxGAB specimens is about 23% higher than that of GAxGAB specimens at the fatigue strength of $1 imes10^6$ cycles. And the fatigue life of BSxGAB specimens at the same load range increases 6~9 times higher than that of GAxGAB specimens. 3. The general tendency at the angle of bending($ heta$) in an applied load has changed rapidly at the initial 20% of its life. After then, it has changed slowly. The change at the angle of bending has increased linearly as the load range increases. 4. It has shown a linear relation between the location ratio of initiation ${gamma}$ and fatigue life $N_f$ on the semi-log graph paper. Here $gamma$ means that the crack distance between main crack and sub-crack, 2L is divided by the nugget diameter, 2r. $gamma=a{cdot}log N_f+n$ (where a and n are material constant.)