Chirag S. Shah

A Partially Validated Finite Element Whole-Body Human Model for Organ Level Injury Prediction

A finite element whole-body human model, which represents a 50th percentile male, was developed by integrating three detailed human component models previously developed at Wayne State University (WSU): a thorax model with detailed representation of the great vessels [1], an abdomen model [2], and a shoulder model [3]. This new model includes bony structures such as scapulae, clavicles, the vertebral column, rib cage, sternum, sacrum, and illium and soft tissue organs such as the heart, lungs, trachea, esophagus, diaphragm, kidneys, liver, spleen, and all major blood vessels including the aorta. In addition to model validations already reported at the component level, the new whole-body model was further validated against two sets of experimental data reported by Hardy [4]. In these experiments, human cadavers were loaded either by a seatbelt or by a surrogate airbag about the mid-abdomen, approximately at the level of umbilicus. It is believed that exercising a validated human model is an inexpensive and efficient way to examine potential injury mechanisms. In some cases, this can provide insight into the design of subsequent laboratory experiments.Copyright

High-Speed Biaxial Tissue Properties of the Human Cadaver Aorta

Traumatic rupture of the aorta (TRA) is one of the leading causes of mortality in automobile crashes. Finite element (FE) modeling, used in conjunction with laboratory experiments, has emerged as increasingly important tool to understand the mechanisms of TRA. Appropriate material modeling of the aorta is a key aspect of such efforts. The current study focuses on obtaining biaxial mechanical properties of aorta tissue at strain rates typically experienced during automotive crashes. Five descending thoracic aorta samples from human cadavers were harvested in a cruciate shape. The samples were subjected to equibiaxial stretch at a strain rate of 44 s−1 using a new biaxial tissue-testing device. Inertially compensated loads were measured. High-speed videography was used to track ink dots marked on the center of each sample to obtain strain. The aorta tissue exhibited anisotropic and nonlinear behavior. The tissue was stiffer in the circumferential direction with a modulus of 10.64 MPa compared to 7.94 MPa in longitudinal direction. The peak stresses along the circumferential and longitudinal directions were found to be 1.89 MPa and 1.76 MPa, respectively. The tissue behavior can be used to develop a better constitutive representation of the aorta, which can be incorporated into FE models of the aorta.Copyright

A new device for high-speed biaxial tissue testing : Application to traumatic rupture of the aorta

A biaxial test device was designed to obtain the material properties of aortic tissue at rates consistent with those seen in automotive impact. Fundamental to the design are four small tissue clamps used to grasp the ends of the tissue sample. The applied load at each clamp is determined using subminiature load cells in conjunction with miniature accelerometers for inertial compensation. Four lightweight carriages serve as mounting points for each clamp. The carriages ride on linear shafts, and are equipped with low-friction bearings. Each carriage is connected to the top of a central drive disk by a rigid link. A fifth carriage, also connected to the drive disk by a rigid link, is attached at the bottom. A pneumatic cylinder attached to the lower carriage initiates rotation of the disk. This produces identical motion of the upper carriages in four directions away from the disk center. Initial slack in a low-stretch, high-strength rope that connects the cylinder to the lower carriage allows the cylinder to achieve the desired test speed before initiating motion in the carriages. Two lasers, focused on the top and bottom surfaces of the tissue samples measure sample thickness throughout a given test.

Finite Element Modeling of Aortic Tissue Using High Speed Experimental Data

Traumatic rupture of the aorta (TRA) is responsible for 10% to 20% of motor vehicle fatalities [1]. Both finite element (FE) modeling and experimental investigations have enhanced our understanding of the injury mechanisms associated with TRA. Because accurate material properties are essential for the development of correct and authoritative FE model predictions, the objective of the current study was to identify a suitable material model and model parameters for aorta tissue that can be incorporated into FE aorta models for studying TRA. An Ogden rubber material (Type 77B in LS-DYNA 970) was used to simulate a series of high speed uniaxial experiments reported by Mohan [2] using a dumbbell shaped FE model representing human aortic tissue. Material constants were obtained by fitting model simulation results against experimentally obtained corridors. The sensitivity of the Ogden rubber material model was examined by altering constants G and alpha (α) and monitoring model behavior. One single set of material constants (α = 25.3, G = 0.02 GPa, and μ = 0.6000E-06 GPa) was found to fit uniaxial data at strain rates of approximately 100 s−1 for both younger and older aortic tissue specimens. Until a better material model is derived and other experimental data are obtained, it is recommended that the Ogden material model and associated constants derived from the current study be used to represent aorta tissue properties when using FE methods to investigate mechanisms of TRA.© 2005 ASME

Advanced Human Modeling for Impact Simulation

This paper summarizes component models of the human body, from head to foot, developed at WSU over the last decade. All of these models were validated against global response data obtained from relevant cadaveric tests. This report summarizes the capabilities and limitations of these models and points the direction for future developments.Copyright