No description available.

abstract: The football helmet is a device used to help mitigate the occurrence of impact-related traumatic (TBI) and minor traumatic brain injuries (mTBI) in the game of American football. The current design methodology of using a hard shell with an energy absorbing liner may be adequate for minimizing TBI, however it has had less effect in minimizing mTBI. The latest research in brain injury mechanisms has established that the current design methodology has produced a helmet to reduce linear acceleration of the head. However, angular accelerations also have an adverse effect on the brain response, and must be investigated as a contributor of brain injury. To help better understand how the football helmet design features effect the brain response during impact, this research develops a validated football helmet model and couples it with a full LS-DYNA human body model developed by the Global Human Body Modeling Consortium (v4.1.1). The human body model is a conglomeration of several validated models of different sections of the body. Of particular interest for this research is the Wayne State University Head Injury Model for modeling the brain. These human body models were validated using a combination of cadaveric and animal studies. In this study, the football helmet was validated by laboratory testing using drop tests on the crown of the helmet. By coupling the two models into one finite element model, the brain response to impact loads caused by helmet design features can be investigated. In the present research, LS-DYNA is used to study a helmet crown impact with a rigid steel plate so as to obtain the strain-rate, strain, and stress experienced in the corpus callosum, midbrain, and brain stem as these anatomical regions are areas of concern with respect to mTBI. / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2014

No description available.

Recent applications of medical imaging, advanced polymers, and composites have led to the development of new equipment for athletes and soldiers. A desire to understand the performance of headgear that resists impacts ongoing since the 1970’s has found more traction in recent years with the usage experimental models that have a greater degree of bio-fidelity. In order to determine which features of helmets from different sports (Soccer, Lacrosse, Football, and Hockey) were tested on a Hybrid III 50th Percentile Male headform with an accelerometer rig at the center of mass.Testing was performed by administering impacts to the headform with an impulse hammer that provides transient force data in order to quantify inputs and outputs of the system to develop a non-dimensional transfer function. Helmet performance is compared by sport worn in order to determine desirable manufacturing features and develop prototype helmets that outperforms current athletic equipment.

An increase of 153,375 to 248,418 traumatic brain injuries (TBI) due to incidents in sports and recreation activities has been reported in the past couple of years in the US alone. These are grounds for concern for athletes partaking in sports with a high incidence of TBI’s such as football and soccer. The latter, traditionally not classified as a contact-sport, has attracted research due to participants using their head as an instrument for heading. Voluntary heading, in combination with lenient laws and regulations concerning TBI expose how soccer players are easily at risk of injury. On the other hand football, an aggressive sport by nature, has brought attention to the possible neurocognitive and neurophysiological ramifications of repetitive subconcussive impacts. One of these is in the form of a progressive neurodegenerative pathology known as chronic traumatic encephalopathy (CTE). A priori reasons revealed, led to a need to characterize the most important variables involved in ball-player interactions within soccer simulated gameplay. By understanding these, it would be possible to obtain parameters to design and manufacture new composite-material based protective headgear unlike products that are commercially available nowadays. In addition, development of a testing protocol focused on frequency domain variables - transmissibility and mechanical impedance - would allow to evaluate the performance of football helmets. A focus would be set on low impacts categorized as subconcussive impacts. Incoming velocity and inflation pressure were identified as the most influential variables affecting the peak impact force of a soccer ball. An innovative 6-layer carbon fiber headband, with silicone padding, was manufactured that out-performed existing headgear at attenuating peak linear acceleration. Lastly, quantification of the transmissibility and mechanical impedance indicated poor performance of football helmets below 60 Hz.

This dissertation presents an investigation and design optimization of energy absorbent protective systems that protect the brain. Specifically, the energy absorption characteristics of the bighorn sheep skull-horn system were quantified and used to inform a topology optimization performed on a football helmet facemask leading to reduced values of brain injury indicators. The horn keratin of a bighorn sheep was experimentally characterized in different stress states, strain rates, and moisture contents. Horn keratin demonstrated a clear strain rate dependence in both tension and compression. As the strain rate increased, the flow stress increased. Also, increased moisture content decreased the strength and increased ductility. The hydrated horn keratin energy absorption increased at high strain rates when compared to quasi-static data. The keratin experimental data was then used to inform constitutive models employed in the simulation of bighorn sheep head impacts at 5.5 m/s. Accelerations values as high as 607 G’s were observed in finite element simulations for rams butting their heads, which is an order of magnitude higher than predicted brain injury threshold values. In the most extreme case, maximum tensile pressure and maximum shear strains in the ram brain were 245 kPa and 0.28, respectively. These values could serve as true injury metrics for human head impacts. Finally, a helmeted human head Finite Element (FE) model is created, validated, and used to recreate impacts from a linear impactor. The results from these simulations are used to train a surrogate model, which is in turn utilized in multi-objective design optimization. Brain injury indicators were significantly reduced by performing multi-objective design optimization on a football helmet facemask. In particular, the tensile pressure and maximum shear strain in the brain decreased 7.5 % and 39.5 %, respectively when comparing the optimal designs to the baseline design. While the maximum tensile pressure and maximum shear strain values in the brain for helmeted head impacts (30.2 kPa and 0.011) were far less than the ram impacts (245 kPa and 0.28), helmet impacts up to 12.3 m/s have been recorded, and could easily surpass these thresholds.

This dissertation focuses on the development of and applications for Nano-Composite Piezoresponsive Foam (NCPF). This self-sensing foam sensor technology was discovered through research in a sister technology, High Deflection Strain Gauges (HDSG), and was subsequently developed with some of the same base materials. Both technologies use nano and micro conductive additives to provide electrically responsive properties to materials which otherwise are insulative. NCPF sensors differ from HDSGs in that they provide a dual electrical response to dynamic and static loading, which is measured through an internally generated charge, or a change in resistance. This dissertation focuses on the development of the dynamic or piezoresponsive aspect of the NCPF sensors which tends to have more consistent electrical response over a larger number of cycles. The primary development goal was to produce a sensor that was accurate, while providing a consistent, repeatable response over multiple impacts. The hypothesized electric generation is attributed to a triboelectric interaction between the conductive additives and the polyurethane foam matrix. This hypothesis was validated by examining different conductive additives with varying loading levels and specific surface areas while accounting for other design considerations such as the electrode used to harvest the response. The results of this analysis support the triboelectric model and point to carbon or nickel-based additives for optimal performance. The NCPF response measured by digital signal acquisition devices is directly dependent upon its input impedance. Increased input capacitance has a negative effect on the signal, however, higher input resistance has a positive linear correlation to voltage. Other considerations that affect the electrical response include the temperature and humidity in which the sensor is used and result in a scaled electrical response.NCPF sensors are ideally suited for use in systems which benefit from impact energy attenuation while measuring the same. This work demonstrates how the NCPF sensors can be used to detect severity and location of impacts in systems with multiple sensors (football helmets), and those with one continuous sensor (carpets). When NCPF sensors were used in a football helmet the impact severity and location of impact was accurately identified. NCPF sensors provide the benefit of simplified design by replacing existing foam while providing a direct measure of the forces. Additional research was conducted on the changes in material properties, specifically how it affects the foam structures ability to absorb energy in quasi static loading scenarios. NCPF sensors are demonstrated as viable tool to measure many different biomechanical systems.