Fatigue Crack Growth of the Gun Tube Steel under Spectrum Loading

An analysis of linear elastic fracture mechanics fatigue life prediction models was conducted on specified gun tube load spectrums. Comparison was made with experimental results of specimen fatigue lives. Load interaction effects were evaluated for gun tube steel. Due to various internal pressures generated by different classes of ammunition, the service loads of a gun tube are variable in nature. Previous investigations into the service lives of gun tubes have shown that fatigue lives are often shorter than the bore wear lives; hence, accurate prediction of gun tubes fatigue lives is important. Several fatigue crack growth models for variable amplitude loading exist. This study compares three models, a no-load-interaction model, a Modified Wheeler model and a Generalized Willenborg model, for four variable amplitude load histories. Predicted fatigue crack growth lives were compared with actual test lives and good correlation was achieved for all models. The Generalized Willenborg model yields the best overall load spectrum life prediction but all three models predicted lives within a factor of 2.0 of the experimental lives.