Date of Award

Fall 12-15-2017

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

Advisor

Vincent Caccese

Second Committee Member

Senthil Vel

Third Committee Member

Zhihe Jin

Abstract

There are numerous potential causes of traumatic brain injury (TBI) and concussions, including traffic accidents, contact during sports and falls. Protection from these injuries is paramount because of the problems that result from TBI, such as loss of thinking and memory capability. Head impact from falls, especially in elderly, can also result in severe to fatal injury and some effects of brain injury are often not visible. For these reasons and more a need exists for protective head gear that can keep persons safe during at risk physical activity and that can protect fall prone persons from accidental injuries. Part of the development of protective head gear includes standard methods to quantify the effectiveness of the protective device. Many studies have been conducted to design apparatus that can be used to quantify the response including twin wire or monorail drop test apparatus and linear impactors. A combination of experimental and computational approaches can be used to develop new designs in an efficient manner. Experimental validation of head protection is typically done by using a standard apparatus. Accordingly, a validated Finite Element Analysis (FEA) model of the drop test system can be invaluable to new development efforts where FEA computer programs like ABAQUS can be used to save time and cost. The impact resisting material design can be evaluated by FEA prior to fabrication and experimental testing and adjustments made without the expense of a prototype. The goal of this thesis work is to develop a validated FEA model of the head-neck assembly quantifying both the translational and angular accelerations based upon experimental testing of the apparatus under standard conditions. The translational and angular accelerations can be used to estimate and or mitigate the risk of the head injuries based on several head injury assessment criteria. Most apparatus calibration procedures use a rubber pad as an anvil during the testing. Accordingly, a rubber pad (MEP) was studied using experimental and FEA modeling approaches. The FEA model of a head-neck assembly test apparatus is intended to be used to study headgear response. It was developed to simulate a Hybrid III head/neck assembly drop test apparatus at the University of Maine that is currently being used to quantify the response of soft headgear. Soft headgear is the type that currently is used for soccer and in the design of headgear for elderly. Through this thesis, a finite element model of the head-neck assembly was created and the geometric and material parameters were studied. The first study presented was of the MEP rubber pad material response, and it material coefficients values were determined based on the experimental and the FEA results. An FEA model was created of the MEP rubber pad and impact testing apparatus including the projectile. The MEP rubber material is modeled as hyperelastic and its coefficients were estimated according to the Mooney- Rivlin theorem. The FEA model was run at different drop heights while incrementally changing the coefficients of the MEP rubber material. From this, a best fit curve was determined based upon experiment results to estimate the coefficients of the MEP rubber material. A description of the finite element FEA model of a head-neck assembly test apparatus which is intended to be used to study headgear response is also presented. The FEA model was created using the computer program Abaqus. The material parameters of main parts of the model were studied. Some of them are assumed to be a hyperelastic material including the neck rubber, skin, rubber pads, etc. Others are liner isotropic elastic materials such as the beam and the drop arm component. The boundary conditions and the coefficient of friction COF between the head (front surface) and the impacted surface (MEP rubber pad) were studied. The peak translational and angular accelerations versus the drop heights were determined for several sets of parameters and compared them to the experimental data. A comparison between the FEA results and the experimental data for the head-neck assembly was performed. The study assessed the effect of a set of assumed parameters on the impact acceleration. The peak magnitudes of the translational and angular accelerations were compared at different drop height to the experimental response. The results of the experimental work were taken in the center of gravity CG of the head, particularly the CG accelerometer location which is in the head. Whereas, the FE model results were in an MPU location which was assumed the head center of gravity for the head-neck assembly. The comparison shows that the translational accelerations can be determined from the current FEA model with high confidence. A significant discrepancy exists with the current model in the assessment of peak angular acceleration.

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