Computational modeling of the human body is becoming an increasingly necessary and utilized tool in the field of automotive safety. Because it couples the ribs to the sternum, the structural behavior of the costal cartilage has the potential to affect the mechanical characteristics of the ribcage as a whole and should be considered in the development of computational models of the thorax. There are several factors that may result in a disconnect, however, between the material behavior of the costal cartilage and the structural behavior of whole segments of the costal cartilage. The first is the perichondrium - a fibrous, tendon-like layer of connective tissue that surrounds the costal cartilage that is not represented in current finite element (FE) models of the thorax. Second, the costal cartilage can undergo dramatic changes with age, specifically manifesting in the deposition and growth of local mineralized regions called calcifications. Third, computational models of the whole human body and the whole thorax are limited in their mesh resolution capabilities, typically representing the costal cartilages with elements ranging from 6 to 10 mm in size.

The goal of this dissertation was to investigate the roles of calcification and the perichondrium in the structural behavior of the costal cartilage, and to provide recommendations on how to model the costal cartilage in finite element models of the whole human body. The specific hypotheses of this dissertation were as follows:​

1. Calcifications change the structural force-displacement behavior of individual costal cartilage segments under fixed-fixed cantilevered loading.
2. The perichondrium contributes to the structural force-displacement behavior of the costal cartilage under fixed-fixed cantilevered loading.
3. The structural force-displacement response of the costal cartilage under fixed-fixed cantilevered loading can be reproduced in limited-mesh finite element models of cartilage segments using parameter identification techniques, resulting in an "effective modulus" representation of the cartilage segments.

To asses these hypotheses, the structural behavior (the force-displacement characteristics) of the costal cartilage was quantified experimentally, using costal cartilage segments harvested from the 3rd and 4th ribs of human cadavers. The structural contribution of the perichondrium was quantified by performing tests with the perichondrium intact and with the perichondrium removed. Data from these tests suggested that the perichondrium contributes an average of approximately 50% of the structural stiffness of the cartilage segments under the loading condition, investigated.

The effect of calcification on the structural behavior of the costal cartilage was studied with detailed FE models of selected cartilage specimens. Those simulations suggested that the structural stiffness of the costal cartilage may increase by an average of 20% with mild calcification, and may increase by as much as a factor of 3.5 when calcified regions occupy 25% of the cartilage volume.

Finally, a set of limited-mesh representations were developed for each tested and simulated cartilage segment. Parameter optimization techniques were used to determine the effective material properties' required to reproduce the structural behavior of the cartilage segments with each of their limited-mesh counterparts. Those results suggested that the average effective moduli of the costal cartilage segments (22 MPa) was significantly greater than the cartilage elastic moduli determined from material characterization testing (indentation tests), presumably due to the presence of calcification and the perichondrium. These limited mesh simulations were also used to estimate a relationship between age and effective modulus resulting from the growth of calcified regions.