Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Mechanical Engineering

First Advisor

King Yang

Abstract

Elderly females are found to be one of the most vulnerable segments of population during motor vehicle crashes and their population is increasing in the coming decades. Current design of restraint systems as well as other passive safety measures are designed based on anthropomorphic details of younger population. Developing another dummy representing elderly female population is a costly effort, while a finite element (FE) model of elderly female with similar anthropomorphic details and age- and gender-specific material properties can be a better alternative solution. The current research focuses on the development of a FE model of an elderly female torso, because a thorough search through literature has identified thorax as the most severely injured body part for elderly females due to rib fractures in motor vehicle induced trauma.

Therefore, data from previously conducted rib bending experiments on 278 rib specimens taken from antero-lateral portion of 82 cadavers were analyzed to see the effect of age, gender, height, and weight on the rib bio-mechanical response parameters such as the maximum bending moment (MBM), maximum bending angle (Ɵmax), slope of moment-angle curve (SMT), and on average cortical thickness value. It was found that, in comparison to males, females had significantly lower values for the MBM (p = 0.000), SMT (p = 0.000), and average cortical-bone thickness (p = 0.001). Samples of ribs taken from elderly specimens failed at lower values of MBM than those from younger specimens, and had lower SMT, both in males and females (p < 0.05). The generalized estimating equations were developed for each bio-mechanical response parameter in terms of dependent variables, namely the age, gender, height, and weight.

Further, the material model parameters for elderly female rib specimen with constant cortical bone thickness were optimized, which in turn were used in developed whole body FE model. The cortical thickness variations in different sections (anterior, antero-lateral, lateral, posteo-lateral, and posterior) of whole rib were also assigned based on those reported in the literature. The model predicted peak responses as well as the fracture locations of the ribs were analyzed against whole rib bending tests with favorable result. Once the response of single whole rib was validated, further the response of elderly female whole rib cage was validated against data reported from frontal pendulum impacts at different speeds as well as data reported for belt loading. The validations results showed that the developed FE model can represent the overall behavior of elderly female during the type of loading as experienced in motor vehicle crashes.

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