Analysing Efficacy of Padded Clothing in Rugby using Finite Element Analysis

Imam, Syed (2021) Analysing Efficacy of Padded Clothing in Rugby using Finite Element Analysis. Doctoral thesis (PhD), Manchester Metropolitan University in collaboration with World Rugby.

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Abstract

World Rugby™ allows players to wear padded clothing to reduce the risk of soft tissue injuries, such as cuts and lacerations. Such padding must meet the requirements of World Rugby™ Regulation-12, which limits its density (45 + 15 kg·m-3), thickness (10 + 2 mm) and impact attenuation performance (acceleration >150 g for a 14.7 J impact). Regulation-12 was critiqued and areas for improvement were identified. From the findings from this PhD, alternative tests to replace the material density criterion in Regulation-12 were investigated and a suitable hardness test (adapted from ISO 2439) was identified. Hertzian contact modelling was used to define a suitable hardness1 limit (750 N) recommended for future testing. To assess the efficacy of the rugby padding in reducing the risk of cuts and lacerations, a silicone based surrogate model (mimicking simplified shoulder anatomy with bone, muscle and skin layer) was developed by a PhD student at the University of Sheffield. In this study, a finite element model mimicking the shoulder surrogate was generated and compared against experimental impact testing at energies of 4.9, 9.8 and 14.7 J. Material modelling of the surrogate silicone was carried out using quasi-static compression and stress relaxation testing. Different hyperelastic models were compared against experimental impact data and a 5-parameter Mooney-Rivlin material model along with the 2-term Prony series was found to be the best predictor of performance over the three impact energies. The validated model was used to predict damage to the silicone using novel FE modelling techniques. These techniques involved defining an element deletion criterion, whereby elements on the surface of the surrogate were deleted if the principal stress of the element reached a predefined value. Stud impacts were carried out at three different energies (2, 4 and 6 J), at three angular orientations (0°, 15° and 30°) and compared to simulations to analyse the validity of the FE model (difference < 15 % for force at tear and < 30 % for time to tear). The novel FE model developed was shown to predict damage for raking simulations and for testing different padding structures. The modelling techniques developed in this research can be applied to different skin simulants to assess the extent of skin injuries and assess the efficacy of PPE used to protect against such injuries. For future work, the model can be further developed into a tool for assessing efficacy of PPE in reducing skin injuries.