Abstract:
This paper presents a validation of the commercially available explicit finite element code, LS-DYNA, for use in the mechanical design of spallation neutron targets. The validation is performed by comparing the code's predictions of transient stress waves in a perfectly elastic, solid cylindrical target with a closed-form analytic solution. This benchmarking process serves to verify the code's physics and numerical methods for simple loading and geometry cases, and it highlights the effects of approximations used in the analytic expressions. The study investigates two loading scenarios: an instantaneous thermal load and a ramped thermal load, both applied uniformly along the central core of the target. Through this work, the authors determined that using a poor approximation for the zeros of the first-order Bessel function in the analytic solution leads to significant errors, emphasizing the need for precise values when evaluating analytic stress components. By using the exact zeros, the computational results from LS-DYNA showed excellent correlation with the analytic solution, especially for the more physically realistic ramped thermal loading case. The study confirms that LS-DYNA is a reliable tool for simulating thermo-elastic behavior and, by extension, more complex nonlinear phenomena such as plasticity, material failure, and contact conditions that will be present in future target designs. The validated analytic solution can also be used to quickly establish an upper bound for transient loading, guiding preliminary design choices before undertaking detailed numerical analyses.
