Topology optimization of auxiliary frame of a vehicle-mounted howitzer using variable density method

The finite element model (FEM) of main carriage, auxiliary frame and support legs of a vehicle-mounted howitzer are established. The meshes are generated by hand to enhance numerical accuracy. The basal structure of auxiliary frame is meshed with 8-node isoparametric hexahedral elements, and main carriage and support legs are meshed with isoparametric quadrilateral elements. During the optimization, the constraint conditions are the displacement at the centre point of the lower seat ring and the maximal stress of the auxiliary frame. And the objective function is minimizing volume fraction of the basal structure. The fictitious density of each finite element is chosen as the design variable and its relationship with Young's modulus is expressed by an empirical formula. After 30 design iterations, the material layout under six load cases is obtained. It concludes from the analysis results by comparing the optimization model with the original model that the maximal stress of the auxiliary frame is decreased by 23.87%, the displacement of the centre is reduced by 28.90%, the mass of the auxiliary frame is decreased by 12.32%, and the lowest natural frequency was increased by 8.18%. In addition, the difference of the maximal stress and displacement under six load cases are smaller than the original ones, and the utilization of the material is more reasonable. It's available for the method to improve the stiffness and to cut down the volume of the model.