Fatigue Damage Formation And Microstructure
Of Ultrafine Grained Copper Under Two-step
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Author(s)
M. Goto, S. Z. Han, K. Euh, N. Teshima, T. Yakushiji
& N. Kawagoishi
Abstract
In order to study the effect of stress change on the surface damage formation of
ultrafine grained copper, two step fatigue stress tests were conducted. The
microstructural evolution and crack growth direction of ultrafine-grained copper
fatigued under constant stressing depends on the magnitude of the applied stress
amplitude. The growth direction occurred perpendicular to the loading axis at
low stresses, and changed to 45° to the loading axis at high stresses. In the case
of high-to-low block stressing, the 45° inclined growth direction under high
stress changed to the perpendicular direction under subsequent low stress. In
low-to-high block stressing, although the growth direction perpendicular to the
loading axis at low stresses was still retained at subsequent high stress,
the degree of zigzag behaviour in the crack growth drastically increased after the
stress change. The sizes and topographies of evolved microstructures, which
have a great effect on the crack path formation, depended on stress histories
(order, cycle number and magnitude of the applied stress). The formation
behaviour of the fatigue damage under high- and low-stress amplitudes and the
effect of pre-stressing on crack growth direction are discussed from the
viewpoints of the microstructural evolution under different stress histories.
Keywords: ultrafine grain, copper, fatigue, two-step loading, surface damage.
Keywords
Keywords: ultrafine grain, copper, fatigue, two-step loading, surface damage.
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