Morteza Seidi

Date of Award


Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering


Vincent Caccese

Second Committee Member

Mohsen Shahinpoor

Third Committee Member

Zhihe Jin


This dissertation describes methods to mitigate injury due to a fall-related head impact which is a growing problem among the elderly population. One of the outcomes of this dissertation is an improved the design of a protective head gear made from a combination of a dilatant material and cast urethane honeycomb. The other outcome of this work include the development of a reliable, repeatable testing method to simulate fall-related head impact that can be used to evaluate the performance different headgear.

First, a twin wire impact tower was introduced and its response compared to other head impact data from the literature. The design is based upon an ASTM drop tower typically used in testing of motorcycle and sports helmets. It was retrofitted with a Hybrid III head and neck assembly. The HIII head of the test apparatus was instrumented with an accelerometer array and angular rate sensors to measure both linear and angular motion. This test apparatus was designed to produce a reliable and repeatable test to evaluate protective headgear for people who are at risk of falling.

Second, a comprehensive experimental study was conducted to investigate the material behavior of the shock absorbing layers used in a new headgear design. The effect of material stiffness and geometry on impact properties was quantified. Strain- stress behavior of the materials was captured at both low and high strain rates. A strong strain-rate dependency was observed from the results.

Third, the results of different testing methods including the twin wire drop tower, linear impactor, ASTM F429/F1446 and dropping the whole body of Anthropomorphic Test Dummy (ATD) were compared in order to recommend a reliable and repeatable testing method to evaluate protective headgear as well as provide recommendations to improve the twin wire drop tower methodology.

Fourth, the dilatant-polyurethane honeycomb head impact protection system was evaluated using the modified twin wire drop tower. The injury mitigation of the protective headgear in reduction of head injury criterion, linear and angular motion was reported.

Lastly, recommendations for improving testing method to improve simulation of fall-related head impact were made. Also, possible improvements to the design of the protective headgear as well as future research on the subject were suggested.