Impact of Imperfect Kolsky Bar Experiments Across Different Scales Assessed Using Finite Elements

Typical Kolsky bars are 10-20mm in diameter with lengths of each main bar being on the scale of meters. To push 104+ strain rates, smaller systems are needed. As the diameter and mass decreases the precision in the alignment must increase to maintain the same relative tolerance, and the potential impacts of gravity and friction change. Finite Element models are typically generated assuming a perfect experiment with exact alignment and no gravity. Additionally, these simulations tend to take advantage of the radial symmetry of an ideal experiment which removes any potential for modeling non-symmetric effects, but has the benefit of reducing computational load. In this work we discuss results from these fast-running symmetry models to establish a baseline and demonstrate their first-order use case. We then take advantage of high-performance computing techniques to generate half symmetry simulations using Abaqu to model gravity and misalignment. The imperfection is initially modeled using a static general step followed by a dynamic explicit step to simulate the impact events. This multi-step simulation structure can properly investigate the impact of these real-world, non-axis symmetric effects. These simulations explore the impacts of these experimental realities and are described in detail to allow other researchers to implement a similar FE modeling structure to aid in experimentation and diagnostic efforts. It is shown that of the two sizes evaluated, the smaller 3.16mm system is more sensitive than the larger 12.7mm system to such imperfections