Abstract
Reversed plane bending fatigue tests were conducted on extruded Al-15Zn P/M (Powder Metallurgy) aluminum alloy using two types of specimens with different notch dimensions. The initiation and growth of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail.A large difference in crack initiation strength was observed between the extruded (L-C orientation) and transverse directions (C-C orientation). It was found that the strength of shallow notched specimen, when evaluated by true stress at the notch root, was lower than that of deep notched one. If the stress intensity range of inclusion at which the fatigue crack initiated was calculated, the difference in fatigue strength depending on specimen orientation and notch size could be eliminated. And also, a prediction method of fatigue strength in smooth specimen was proposed on the basis of the extreme value statistics. The macroscopic fatigue crack growth rate could be expressed by the Paris equation in terms of the maximum stress intensity factor irrespective of stress level and the notch size, and the growth rate was found faster in C-C orientation specimen than that in L-C orientation specimen.
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