Abstract
With comprehensive application of the theories of coating shear failure mechanism and fatigue cumulative damage, a life prediction method of a gun barrel is proposed based on the shear fatigue damage accumulation at the coating-substrate interface. The life of a small-caliber gun barrel is predicted by use of constant tensile strength at normal temperature and temperature-dependent tensile strength, respectively. The influence of the two kinds of tensile strength on barrel life prediction results is analyzed. Life test proves that the prediction method proposed here is credible and practical. The research results show that the reduction of interface tensile strength due to temperature rise in the firing process is an important inducement of interface damage and gun barrel failure. When the temperature-dependent tensile strength is considered in life prediction model, the prediction results are smaller than that predicted by use of constant tensile strength and well matched with the life test results. Therefore, the temperature-dependent tensile strength should be incorporated in the model of gun barrel life prediction.
Highlights
With comprehensive application of the theories of coating shear failure mechanism and fatigue cumulative damage, a life prediction method of a gun barrel is proposed based on the shear fatigue damage accumulation at the coating-substrate interface
When the temperature-dependent tensile strength is considered in life prediction model, the prediction results are smaller than that predicted by use of constant tensile strength and well matched with the life test results. erefore, the temperature-dependent tensile strength should be incorporated in the model of gun barrel life prediction
Various research works have been conducted by scholars on the failure mechanism, the influence factors on barrel life, and its prediction. rough comparing three likely failure mechanisms of coating segment, Underwood believes that the shear stress near the coating-substrate interface is the main driving force which causes coating interface failure, and the interface shear failure is the most likely coating failure mechanism [2]
Summary
It is reasonable to believe that the interface failure of coating in a gun barrel is a damage accumulation process, and the coating desquamation is fatigue behavior under the effect of cyclic thermal shock. E applied stress caused by chamber pressure can be obtained by the renown Lame formula based on the assumption that cracks at coating surface do not influence the distribution of applied stress; it is tensile in circumference and can be written as SP p1. Considering that the stress in the gun barrel is mainly thermal stress during firing, the sign of compressive stress is set as positive, and the sign of tensile stress is set as negative here for convenience of calculation and expression; according to equations (1)∼(4), the shear stress along the base of coating segment can be expressed as. Assume that the loading history consists of various levels of stress, which are δ1, δ2, . . ., δl. e fatigue life under each stress level isN1, N2, . . ., Nl, respectively; the loading cycle of each stress level is n1, n2, . . ., nl, respectively; l is the number of stress levels. en the fatigue life of a gun barrel can be expressed as [13]
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