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Blunt abdominaltrauma leads mainly to injuries of the kidney, the liver and the spieen, all of which may result in death or disabilityof the injured person. This dissertation describesthe developmentand Validation of realistic finite element (FE) model of the abdominalregion. Such a model is critical to understanding the mechanisms of blunt impact injury. The presentwork gains importance given the relative paucity of abdominalimpact modelling studies in the literature. In this dissertation, the main emphasis is on the kidney, for which a detailed FE model has been developed that (i) is based on realistic anatomical and mechanical properties of the involved soft tissues under dynamic loading conditions, (ii) reflects the particular location and surroundings of the kidney in the human body and (iii) is subjected to typical loading patterns derived from accidental impact situations. In addressing the issues of realistic boundary conditions and loading conditions, it was necessary to develop considerationsfor the neighboring abdominalorgans, and ultimately the entire human body. To this end, a finite element model of the entire human abdomen was developed. The abdominal model is compatible with a prototype human body FE model (THUMS) made available by Toyota Central R&DLaboratories. This abdominalmodel has been developed in stages, and these stages are described in detail in the following chapters. First, the preliminarysteps in the developmentof a high fidelityFE model of the human kidney are described. The geometry, material properties, and the use of viscoelastic/hyperelastic constitutive equations to model realistic, rate-dependentmaterialbehavior are discussed. This preliminary model consists solely of the renal parenchyma, with no consideration given to the blood vessels, renal capsule, or urine collection system. Next, in order to create a more realistic model, the strain-rate dependent mechanical properties of the renal capsule were measured and appropriaterate dependentconstitutive equations were developed. This dissertation describes the dynamic mechanical testing of the porcine renal capsule, as weh as presentsa quasi-static comparisonwith the corresponding human tissue. Many global injury criteria have been suggested for blunt abdominalimpact,including force criteria, compression criteria, and viscous criteria. The establishment of failure criteria for individual abdominalorgans is less prevalent. This dissertation also describes work performedin an attempt to quantifya failure thresholdfor the kidney in terms of strain-energy density. High-speedimpacttests were performedusing falling weights and pneumatically driven projectiles. The strain-energy failure thresholdof the kidney is identified,and a quantitative comparisonbetweenporcineand human tissues is made using quasi-static compression tests. The previously developed model of the right kidney parenchyma,with additional considerationsfor the renal capsule, calyces, veins and arteries,is usedto explore the resulting strain-energy distributions of the whole organ experiments. A relationship is established between impact tests on excised tissue samples, and impact tests on whole, perfused organs. Potential renal injury mechanisms are also identified. Next, the dissertation introduces the Toyota Total Human Model for Safety (THUMS) as it was implemented in a parallel study performedon pedestrian impact. In this chapter, the structure and materialproperties of the THUMS are described,and a typical example for which the model may be applied is illustrated. This work is particularly relevantto the dissertation since the ETH renal model is ultimately inserted into this detailed human body FE model. Such modeis permit a realistic application of traumaticloads and boundary conditionsto the kidney that would be otherwise difficult to representin an isolated finite element model oftherenal system. Finally, the dissertation presents the developmentand Validation of a model of the human abdominal region specifically suited for use in investigating renal trauma. The default THUMS abdominalmodel is replaced with a model of the abdomen that is divided into compartments which represent the anatomical segmentation of the abdominal cavity. The model is validated in lateral impact using experimental results from human cadaver impact tests. Possible renal injury mechanisms are explored and discussed.

Towards a finite elemente human body model for use in trauma research