Finite element model to simulate impact on a soft tissue simulant

Abstract

A finite element model of an impact test on a soft tissue simulant, used as part of a shoulder surrogate, was developed in Ansys© LS-DYNA®. The surrogate consisted of a metal hemicylindrical core, with a diameter of 75 mm, covered with a 15 mm thick relaxed muscle simulant. The muscle simulant consisted of a 14 mm thick layer of silicone covered with 1 mm thick chamois leather to represent skin. The material properties of the silicone were obtained via quasi-static compression testing (curve fit with hyperelastic models) and compressive stress relaxation testing (curve fit with a Prony series). Outputs of the finite element models were compared against experimental data from impact tests on the shoulder surrogate at energies of 4.9, 9.8 and 14.7 J. The accuracy of the finite element models was assessed using four parameters: peak impact force, maximum deformation, impact duration and impulse. A 5-parameter Mooney-Rivlin material model combined with a 2-term Prony series was found to be suitable for modelling the soft tissue simulant of the shoulder surrogate. This model had under 10% overall mean deviation from the experimental values for the four assessment parameters across the three impact energies. Overall, the model provided a repeatable test method that can be adapted to help predict injuries to skin tissue and the performance/efficacy of personal protective equipment.

A finite element model for predicting impact-induced damage to a skin simulant

“…To support the development of an FE model of a stud impact on the shoulder surrogate of Imam et al 12 , in terms of gaining experimental data for validation, the skin stamping test was adapted from the World Rugby™ Studs and Outsoles Specification 23 : Test B-Skin Stamping Test. The skin stamping test method was chosen as it provides a scenario (stud and skin contact) like those that may occur and cause a cut, during rugby.…”

“…The effective total mechanical energy of a foot strike during walking or running has been reported as 0.24–6 J 25 – 30 . To simulate a stud impact on the soft tissue simulant the impact test setup from Imam et al 12 , 31 was modified by replacing the flat-faced impactor with an aluminium stud (18 mm Stud Set-Carta Sport, ~ 12 g). Following this modification to the test setup, the mass of the impactor was 3.65 kg, which is closer to the effective mass (0.5–2.9 kg) reported by Oudshoorn et al 24 for a foot strike (during a simulated rugby stamping event) than the 8.5 kg mass stated in the Studs and Outsoles Specification: Test B-Skin Stamping Test.…”

“…These simulants can degrade with repeated impacts 10 , 11 and a new sample is often required after the one being tested is damaged, e.g., following a test that mimics a cut or abrasion. To overcome such limitations of physical testing, Imam et al 12 developed a Finite Element (FE) model for simulating impact on a soft tissue simulant, using the commercial software Ansys© LS-DYNA. Developing such a model to simulate impact-induced damage to the skin simulant would allow prediction of the ability of padding to protect against such injuries.…”

“…With such material models, an element in the mesh is removed if the assigned failure criteria are met, simulating damage. Most of the material models with fracture prediction capabilities are either ductile (metallic), having a defined plastic phase before fracture, or brittle (such as wood or ceramic), where the fracture may occur at low strain 12 , 20 . Skin tissue simulants are usually elastomeric, with comparatively smaller plastic regions and large strains before fracture.…”

“…The aim of this study was to develop and validate the FE model of the soft tissue simulant of Imam et al 12 to predict the onset of impact-induced damage to the outer surface of the simulant (i.e., skin damage) 12 .…”