The autofrettage and shrink-fit processes are used to increase the load bearing capacity and fatigue life of the pressure vessels under thermomechanical loads. In this paper, a design optimization methodology has been proposed to identify optimal configurations of a two-layer cylinder subjected to different combinations of shrink-fit and autofrettage processes. The objective is to find the optimal thickness of each layer, autofrettage pressure and radial interference for each shrink-fit, and autofrettage combination in order to increase the fatigue life of the compound cylinder by maximizing the beneficial and minimizing the detrimental residual stresses induced by these processes. A finite element model has been developed in ANSYS environment to accurately evaluate the tangential stress profile through the thickness of the cylinder. The finite element model is then utilized in combination with design of experiment (DOE) and the response surface method (RSM) to develop a smooth response function which can be effectively used in the design optimization formulation. Finally, genetic algorithm (GA) combined with sequential quadratic programming (SQP) has been used to find global optimum configuration for each combination of autofrettage and shrink-fit processes. The residual stress distributions and the mechanical fatigue life based on the ASME code for high pressure vessels have been calculated for the optimal configurations and then compared. It is found that the combination of shrink-fitting of two base layers then performing double autofrettage (exterior autofrettage prior to interior autofrettage) on the whole assembly can provide higher fatigue life time for both inner and outer layers of the cylinder.

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Muzzle brakes (MBs) have a great effect on reducing the recoil force of weapons during firing. In this paper, optimum MB efficiency, MB force and recoil force for (12,7 x 99 mm) sniper rifle have been studied. The objective is to obtain the optimum area of side openings, inclination angle and number of chambers for the MB in order to increase the MB efficiency and MB force and thereby to decrease their coil force of the weapon. An analytical model for calculating MB efficiency, MB force and weapon recoil force for MBs of two, three and four chambers has been established. This Model is then utilised in combination with design of experiment (DOE) and Response Surface Method (RSM) statistical techniques to develop a smooth response function which can be efficiently used in optimisation formulation. Finally, multi objectives generic algorithm (MOGA) optimisation method has been employed to find the optimum MB design parameters. The optimisation results show that the three or four chambers MBs have no significant effect on reducing the weapon recoil force compared with the two chamber MB for this sniper rifle.

The autofrettage and shrink-fit processes are used to enhance the load carrying capacity and fatigue life of the pressure vessels. Previous works were mainly concerned with increasing the compressive residual stress at the near bore area of the compound cylinders, ignoring the harmful high tensile residual stress developed at the outer part of the cylinder. Also, the idea of multiple or re-autofrettage had been only used at the inner surface of the cylinder to increase the magnitude of compressive residual stress at the near bore area. In this study, a new design approach is proposed by applying an autofrettage cycle on the external surface of the cylinder prior to an autofrettage cycle on the internal surface of the cylinder. It is shown that this double autofrettage cycle not only increases the magnitude of compressive residual stress at the near bore area but also decreases the tensile residual stress at the near outer surface area. Moreover, the proposed double autofrettage process has been combined with shrink-fit and standard inner surface autofrettage processes to produce new combinations of a two-layer compound cylinder. The fatigue life for these new combinations has been evaluated to verify the improvement while using the double autofrettage process.

In this paper, a modified analytical solution for time-dependent one dimension heat diffusion equation in cylindrical coordinate had been mathematically solved to calculate the temperature distribution through thick-walled weapon barrel subjected to successive shots. The analytical solution has been compared with experimental measurements for the temperature at the outer surface of the barrel at two different positions. The General Purpose Machine Gun (GPMG) 7.62X51 mm was considered as the case of study. The results show a good agreement between the analytical model and the experimental work with a difference less than 3 %. The main difference between them mainly as a result of the very short time of the heating phenomena as it takes about 6 (ms) only, although the used Data Acquisition System was able to take a high sampling rate and a high sensitive thermocouple type k with only 0.5 mm thickness had been used.