Selecting Material Properties for Maximizing Gun Firing Power

The design of gun barrels aims at maximizing its firing power determined by its SMP — the maximal allowed firing pressure, which is considerably enhanced by inducing a favorable residual stress field through the barrel’s wall commonly by the autofrettage process. Presently, there are two distinct processes: hydrostatic and swage autofrettage. In both processes the barrel’s material is fully or partially plastically deformed. Recently, a 3-D code was developed, which finally enables a realistic simulation of both swage and hydraulic autofrettage, using the experimentally measured stress-strain curve, and incorporating the Bauschinger effect. This code enables a detailed analysis of all the factors involving the final SMP of a barrel, and it can be used to establish the optimal process for any gun barrel design. A major outcome of this analysis was the fact that the SMP of an autofrettaged barrel is dictated by the detailed plastic characteristics on the barrel’s material. The main five plastic parameters of the material that have been identified are: the exact (zero offset) value of the yield stress, the universal plastic curve in tension and in compression, the Bauschinger Effect Factor (BEF) curve, and the Elastic-Plastic Transition Range (EPTR). A detailed analysis of these three materials points to the fact that the major parameter determining the barrel’s SMP is the yield stress of the material and that the best way to determine it is by the newly developed “zero offset” method. All these four parameters have a greater influence on the SMP of an hydraulically autofrettaged barrel than on a swaged one.