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Low-cycle Fatigue Behaviors of Small Cracks of Glidcop Al-15

Y. YIN, H.B. CHEN, W.L. XIAO

Abstract


Glidcop Al-15, a dispersion strengthened copper alloy containing 0.15% of submicroscopic alumina particles, is a particularly attractive material for high temperature components because of its excellent thermal conductivity, strength retention and micro-structural stability at elevated temperatures [1-3]. As fatigue damage requires to be expressed in terms of a crack, observations are made on Glidcop Al-15 that relate to the initiation zones and the propagation of small cracks subjected to low cycle fatigue and these observations are based on surface replica studies [4, 5]. On the other hand, the effect of prior fatigue history on the growth rate of a small crack is investigated systematically using special specimens containing an artificial small hole of various diameters, i.e. 40, 100 and 200 μm at three different load levels equivalent to cyclic stress levels separately. Similar experiments for a medium carbon steel NO.45 are also operated for comparison with the results of Glidcop Al-15 [6]. Hour-glass shaped specimens which have a minimum diameter of 8 mm at the central cross-section are used in the fatigue tests. These specimens are called ‘plain specimens’. To simulate a defect or an inclusion, a very small hole was drilled on the periphery of the central portion of a plain specimen. The diameter d of the hole and its depth were identical, as indicated in Figure 1. Three hole diameters were used, with d equal to 40, 100 or 200 μm. These specimens are called ‘holed specimens’.

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