Weight and shape optimization of armored amphibious vehicle suspension system lower control arm

The control arms are one of the main sub-parts of the wheeled vehicle's suspension system. Within the scope of this study, the lower control arm, one of the main parts of double wishbone system, which is also widely used in the armored wheeled vehicles, is discussed. The crucial factor to be considered is to keep the vehicle weight at a minimum especially for the amphibious vehicles which are able to operate in both the land and water. For this reason, size, shape and weight optimization studies are performed for the parts with a large volume and mass such as the control arm. Also, within the scope of this study, after the validation of the finite element analysis of suspension lower control arm with on-vehicle tests, weight optimization study is performed by using surrogate models. For the optimization study that is carried out a couple of steps, finite element model is prepared initially. In order to verify the created model, strain values are collected with strain-gauge from the lower control arm of the 8x8 wheeled vehicle and the similar boundary conditions are applied to the related part on ANSYS Workbench. The ANSYS analysis results and experimental test data are compared and the created FE model are validated by acceptable deviations. Subsequently, the solution step of the optimization problem is initiated with determination of four design variables. In order to complete this step, the surrogate models which are able to examine several variable at a time, low computational cost and high reliability, are used. Two different design of experiments are used in training data generation for surrogate models: central composite design (CCD) and Latin hypercube sampling (LHS) design. The optimization process are performed and the results are obtained for the both models. In the consequence of the compared results, it has been observed that the part weight can be reduced more by using the surrogate model creating with CCD. When the selected candidate point is applied to the part, the initial weight value which is 25,2 kg, is reduced to 21,8 kg with decreasing the ratio of %13,3. This means that 27 kg weight reduction in total approximately for a 8x8 vehicle. In the last step, two quasi-static load scenarios which may be exposed on the suspension while the vehicle is in motion and preferred by vehicle manufacturers, are selected. These are longitudinal impact (pothole strike) and lateral impact (pavement crushing). In addition to these, wheel change scenario by using lifting jack is added as a third validation step. Optimized lower control arm is analysed under the related forces in the ANSYS Workbench. It has been observed that obtained stress values are below the yield strength of the material and it is verified with the safety factor of 1,46 for pothole strike scenario, 1,08 for pavement crushing and 3,17 for the wheel change scenario.