Design and Evaluation of Protective Head Gear to Mitigate Head Injuries Due to Falls

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

Transparent nanocomposite coatings based on epoxy and layered double hydroxide: Nonisothermal cure kinetics and viscoelastic behavior assessments

International audienceLayered double hydroxide (LDH) has a particular place in clay family because of its flame retardant action. The nanoplatelet-like structure of LDH makes possible development of polymer composites with cationic or anionic nature structures in which macromolecules are positioned in between nanoplatelet galleries. In this work, neat epoxy and its transparent nanocomposite coatings with sodium dodecylbenzene sulfonate (SDBS)-modified LDHs; Mg-Al and Zn-Al LDHs, were prepared and their cure kinetics and viscoelastic behavior were tracked through nonisothermal calorimetric and dynamic mechanical analyses. The higher progression of crosslinking in the epoxy network was observed for epoxy/Zn-Al LDH nanocomposites, while activation energy of cure reaction took a higher value for Mg-Al LDH-incorporated systems. Moreover, epoxy/Mg-Al LDH system revealed higher value of storage modulus and glass transition temperature thanks to larger galleries of Mg-Al nanoplatelets. Network formation in the presence of SDBS-modified Zn-Al LDH nanoplatelets was facilitated due to the action of Zn metal as an adduct with a lone-pair of oxygen atom of epoxy leading to an enhanced epoxy ring-opening. Viscoelastic behavior of transparent coatings containing Zn-Al LDH and Mg-Al LDH was studied through temperature-sweep test at various frequencies to compare the results of calorimetric and thermo-mechanical analyses