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To improve the firing dispersion of the tank, the influences of random factors on firing dispersion are analyzed quantitatively. Based on the six-degree-of-freedom rigid-body ballistic equation, considering the influences of processing and assembly errors, initial disturbances and the wind on flight, using the Sobol’ global sensitivity analysis method, the weights of affecting factor are obtained. The analysis results show that, under the current manufacturing and measuring conditions, the initial disturbance of projectile is the premier factor that takes effect on the firing dispersion of the straight shooting weapon (such as a tank) with small elevation angle.

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Rails are subjected to repeated stresses due to wheel-rail contact during train service. Rails under stress conditions undergo microstructural changes, and these cause degradations of the structural integrity and lifetime of rails. In this study, three different rails (newly-manufactured rail, newly-manufactured headhardened rail, and worn (used) rail) were compared to examine the effects of heat treatment and repeated wheel-rail contact stress on the microstructure and mechanical behavior of continuous welded rail. The crystal structure, constituent phase distribution, tensile property, and hardness were investigated at various locations along a cross section of the rails. All three rails consisted of a mixture of BCC and FCC crystal structures as a majority phase with a very small amount of cementite (Fe 3 C) as a minor phase. Rietveld analysis revealed that the weighted fractions of the BCC crystal structure were approximately 74%, 64%, and 85% for the new rail, head-hardened rail, and worn rail, respectively. While the web and foot areas of the three rails showed no significant differences in mechanical properties, the railheads of the three rails revealed much higher yield strength, tensile strength, and hardness. The highest tensile strength and hardness were measured at the railhead in the head-hardened rail, and were attributed to the evolution of the bainite phase, generated by additional heat treatment. The higher mechanical strength of the railhead of the worn rail is thought to have resulted from a combination of work hardening and smaller lamellar spacing of the pearlite phase, induced by repeated wear processes during train operation.