Date of Award

12-2017

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Vincent Caccese

Second Committee Member

Senthil Vel

Third Committee Member

Andrew Goupee

Abstract

Head injuries can occur due to accelerative forces due to impact or rapid movement. Some examples are when the head hits the windshield during car accident, an impact from a fall, an object hitting the head during sports or other recreational activities among others. Whatever the cause, head injuries can affect many aspects of a person’s life, including thinking, controlling his/her emotions, walking, or speaking, as well as affect their senses of sight or hearing. Accordingly, head injuries are a significant public health problem. To prevent or lessen these kind of injuries, many studies have been conducted to design a material system with an optimal energy absorbing ability to decrease the deleterious effect of an impact to the head. Foam material, because of their durability, lightweight, and low cost, have been studied by many researches for their energy absorbing ability, and performance. Finite element analysis (FEA) is a reliable method that can be used to analyze foam impact behavior. FEA can be an efficient alternative to extensive experimentation. In this work the FEA method was conducted to study the behavior of single-layer foam materials to resist impact. A parametric study of the influence of the foam material coefficients used in the FEA model is presented. A commercial, generalpurpose finite element code ABAQUS was used to implement the analytical evaluation which can effectively describes how sensitive the impact response of the foam material is to the change of each material parameter value (μ, ν, α). A Matlab code was written to using (Ogden-Storakers equation) to estimate single-layer foam material coefficients by fitting to the data from an experimental impact test. A genetic algorithm (GA) method was implemented in Matlab to minimize the error between the calculated and the experimental data and estimate the material coefficients. In the Ogden model, the number of terms has a significant effect on the results accuracy and the calculation run time and the number of terms were compared with the number of terms limited to three terms. The number of populations and generations used in GA were shown to have a significant effect on results accuracy and run time. Various combinations of population and generation numbers were explored to assess their effect. The influence of foam density and thickness was also explored by FEA using an idealized material coupon subjected to an initial velocity strike by a spherical shaped projectile. The estimated material coefficients from the one term solution are used as a baseline. Since some sports such as football, are looking to require impact resisting material systems that can operate over a wide range of input with a multi input level criteria and investigation of a layered structure was initiated. From this initial study is was demonstrated that a layered structure has potential to effectively mitigate the impact response at more than one impact energy level.

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