鋳造アルミニウム合金AC4CHの疲労挙動に及ぼす温度の影響

概要

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Fully reversed axial fatigue tests were conducted using plate specimens of a cast aluminium alloy, AC4CH, at three different temperatures of room temperature (R.T.), 150℃ (423K) and 250℃ (523K), and crack initiation and small crack growth were studied in detail by means of replication technique. At 150℃ and 250℃, fatigue strength was nearly the same as, or significantly lower than, at R.T., respectively. The fatigue strength characterized in terms of fatigue ratio, σ/σB, was the same at all temperatures in high stress region, but slightly lower at 250℃ in low stress region. Cracks invariably initiated from a casting porosity at R.T., while crack initiation due to slip deformation became dominant at elevated temperatures. At 250℃, a number of cracks were initiated due to slip deformation and the coalescence of the main crack and other cracks occurred very frequently, particularly in low stress region. At a fixed maximum stress intensity factor, K_<max>, small crack growth rates were faster with increasing test temperature. When characterized in terms of K_<max>/E (E: Elastic modulus), crack growth rates became similar at R.T. and 150℃, but still faster at 250℃. It was indicated that such enhanced crack growth at 250℃ was attributed to most frequent coalescence of the main crack and other cracks, resulting in the lowest fatigue strength at this temperature.
2006-02-15