4 Discussion
This work made use of experimentally-determined and derived JC strength model parameters. Similar studies into Fe-Ni and Psyche-analogous materials have used JC input parameters for Armco Iron (e.g., Raducan et al., 2020 and Ogawa et al., 2021). Given that Marchi et al. (2020) reported that target temperature has measurable effects on strength, where cooled targets are up to 20% stronger than room temperature targets, we emphasize that measuring the strength and finding the JC parameters at a cold temperature (77 K) is necessary to include the temperature dependence portion of the JC strength model in cases where the target reference temperature is greater than the target surface temperature. Figure 5 illustrates the distinct effect temperature has on the strength of a material in the JC strength model.
Unlike silicates, which are brittle under compression, metals typically undergo ductile deformation, meaning they permanently deform by bending or flowing without becoming weaker, breaking, or failing. Analysis of our tensile tests has shown an equivalent plastic strain to failure,\(\epsilon_{f},\)of up to 1.8 (or 180%) for Fe-Ni ingots as well as the Gibeon meteorite. Yet, extensive cracking and fracturing — indicative of brittle deformation — were observed in some of the targets in the impact experiments. There is no current damage model for metals in iSALE, a major limitation in modeling the observed cracking. Although CTH is less widely used in the planetary science community, it proves to be a valid and useful tool in simulating impacts into metal. The CTH suite includes both a Johnson and Cook strength model (Johnson and Cook, 1983) and a Johnson and Cook fracture model (Johnson and Cook, 1985), which we plan to explore the implementation of in the JC fracture model into iSALE in future work.