Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Mechanical and Materials Engineering


Mao, Haojie


Traumatic brain injury (TBI) is a severe health problem for society. Meanwhile, predicting and preventing TBI remains challenging in the field. Peak rotational velocity was demonstrated to be correlated to brain strain responses, and hence could potentially serve as a good predictor for brain injury. Brain strain was influenced by impact direction, deceleration and impact loading curve shapes. Wearing helmets is an effective way to protect the brain from TBI, but there lacks a study on evaluating helmet performance based on both energy absorption and brain strain response, which this study addressed. Interestingly, helmet shell absorbed around half of the energy, followed by interior foams close to impact locations. Facemask also affected brain strain response as it changed both the rigidity and inertia of the helmet.

Summary for Lay Audience

Traumatic brain injury (TBI) is mostly induced by head motion which is caused by external impact. When the head moves linearly, the skull tends to compress one side of the brain, which induces coup pressure, and compresses the other side of the brain, which induces contre-coup pressure. The high pressure can cause brain damage such as contusion. When the head moves in a rotational manner, the skull shears and stretches the brain tissues because the brain tends to move slower than the skull does. Hence, the neuronal cells in the stretched region will be damaged, which will induce TBI. Generally, there are two ways of biomechanical investigation in protecting the brain: predicting brain injury and preventing brain injury. Different kinds of correlations between kinematic accelerations and TBI were reported to predict TBI. However, the correlations between kinematics and injury lack a fundamental understanding of brain mechanical responses. In this study, the correlation between head rotation and brain strain response was systemically investigated. It was demonstrated that peak rational velocity correlated to brain strain response. Brain strain induced by impact was direction dependent. Axial rotation induced the highest strain, while lateral bending produced the lowest. However, for the deep brain, lateral bending produced the largest brain to the corpus callosum and thalamus. Wearing a helmet is an effective way to protect brain, largely reducing brain strain. The helmet outer shell absorbed around half of the energy, followed by foams close to impact locations. The facemask affected brain strain distribution differently as impact location changed. The helmet rigidity influenced by facemask was correlated closely to brain strain change induced by facemask.