Calibration and Modelling of Adipose Tissue Under Impact Loading

Abstract: Vehicular injury is one of the main reasons for traumatic injuries. Finite Element HumanBody Models (FEHBM) have become very popular to assess car crashes and the subsequentinjuries. It provides the possibility to predict stress and strain values in tissue level byrepresenting anatomical structures in details. An essential requirement for the FEHBMis to exhibit human-life response, i.e. being biofidelic. Obese occupants are one of thevulnerable populations at higher risk of death and severe injuries in car crashes. However,the developed FEHBMs do not, neither in body shape nor the material properties,represent obese population. In particular, there is no appropriate constitutive model foradipose tissue (fat tissue) in FEHBMs. In the interaction between obese occupants andrestraint systems both the body shape and the material property of adipose tissue playsan important role.Therefore the first goal of this research (and the main goal of this thesis) is findingand calibrating a biofidelic constitutive model for adipose tissue. To this end a nonlinearviscoelastic constitutive model was formulated. To have a reliable model calibrationat large deformation and a wide range of strain rates (similar to car crash situations),test data of two experiments were used; the frequency-sweep test and the ramp loading-unloadingshear test. Prescribing the power-law relation for shear stiffness, which issuggested in the frequency-sweep test, as a constraint in the ramp loading-unloadingshear test considerably improved the model prediction for large deformations and highstrain rates. To investigate the effect of uncertainties in model parameters and identifyimportant parameters in different experiments, commonly used mechanical testing setupswere analyzed. Global sensitivity analysis was used for this purpose. It was found thatthe amount of compressibility highly affects the behavior of adipose samples in high rates.It is important specially when studying how adipose tissue behavior affects the dynamicsof obese occupant responses during crash situations.