Publication

Human body models (HBM) are used as tools in crash simulations when investigating the interactions between the human body and the vehicle, thus gaining insight into the evolution of stresses and strains influencing the different parts of the body. In todays crash simulations two broad categories of mathematical HBM are in usage, namely multibody dynamics and finite element. Due to decreasing cost of computational resources there is a shift towards the more biofidelic finite element HBM. Recent  studies have shown correlations between increased risk of death in severe motor vehicle crashes and different categories of obesity, namely the moderately and the morbidly obese. Due to an increasing trend in the obese population there is a need for deeper knowledge and understanding of the constitutive  behaviour of the human fat tissue, more specifically the white adipose tissue. Through a literature study the current research field was explored, and a summary of mechanical properties and available experiments were compiled. It was found that the white adipose tissue behaves as an incompressible solid with nonlinear strain stiffening and nonlinear strain rate stiffening. Further the tissue was found to be isotropic. Unrecoverable deformation was also found to be present in three studies but it was explained in two different manners. One study used plastic deformation and another claimed the tissue hadn't been given enough relaxation time for it to be fully recovered. Three experiments were chosen to be modeled with the Finite Element code LS-DYNA. One experiment was chosen for material model calibration while two experiments were chosen for evaluation. Three material models were chosen for calibration, Ogden Rubber 77 with linear viscoelasticity, Soft Tissue 92 with viscoelasticity and Simplified Rubber 181 with strain rate dependency. The results of the work reveals a good fit of the Ogden Rubber material model to low and intermediate strain rates. The Soft Tissue material model is less suited to accomodate the nonlinear strain stiffening of the adipose tissue since it is only of order two. The Simplified Rubber material model accomodates the nonlinear strain stiffening as the Ogden Rubber material model but suffers from the drawback of an instant response in the stress to a change in the loading velocity. The main contribution of the work is two material models that produce a good fit to compressive tests performed at strain rates 0.2/s and 100/s, however, more simulations and tests are needed in order to properly validate the models. The work also contributes with an extensive search through the current research field indicating a paucity of experiments conducted in the high strain rate regime.