A study has been made of fatigue crack propagation in a low alloy steel which is subject to temper embrittlement. Effects of mean stress on the growth rate have been examined and comparisons between temper embrittled and unembrittled conditions have been made. Whereas fatigue crack propagation rates were found to be insensitive to mean stress in the unembrittled steel, growth rates in the embrittled condition were significantly faster and were strongly influenced by the level of mean stress.
The effects observed are ascribed to the presence of “static” modes of fracture which occur in association with classical fatigue striations. It is shown that similar static modes can account for effects of mean stress and for the enhanced growth rates observed in a variety of materials of low fracture toughness.
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