Football Helmet Energy Absorption Degradation and Impact Performance Resulting From High Humidity and Temperature

The helmet is the primary means for providing head impact protection to adult and youth football players through use of energy absorbing (EA) materials placed in a crush zone located between the head and helmet shell. Ultimate safety performance of the helmet requires uniformly consistent, repeatable and reliable attenuation of the impact energy so as to minimize head injury potential throughout the helmet. However, quasi-static materials tests and dynamic helmet testing results, reported on herein, show that EA materials of current and older helmet designs are susceptible to large levels of EA degradation, or softening, when subjected to a “hot-wet” condition caused by high temperatures and high humidity, such as that produced from the sweat of a player. Depending on the size of the crush zone, and other factors, this condition can lead to increased head impact loads. The standard football helmet certification criteria do not address the issue of “hot-wet” EA degradation. Dynamic helmet testing analyzed in this study consisted of two methods. One method used the standard helmet certification approach where a human responding head form and helmet are dropped vertically, along a twin guide wire set-up, onto a soft rubber pad. The second method employed use of a human responding Hybrid-III head and neck that was incorporated into a free pendulum impact set-up where impact took place on a non-yielding surface and both direct contact impact injury potential and rotational injury aspects of the helmet performance were measured. The dynamic tests were conducted with various size head forms, energy levels, and impact speeds that ranged from the 5.5 m/s level, used in helmet certification, on up to higher speeds of 7.0 m/s that is more consistent with a “5-second 40-yard dash” speed. Based on equal kinetic energy impact comparisons, the two dynamic approaches showed that helmets that were impacted onto the soft elastomeric pad surface produced artificially lower indications of head injury severity than did the helmets tested against the non-yielding surface. The results also showed large variations and inconsistencies of impact attenuation within a specific helmet design, depending on impact location or region being tested. Also, dynamic impact testing was applied with both ambient and 3-hour “hot-wet” soak conditions applied to the EA padding of adult and youth helmets. These results showed that the relatively newer EA pad designs and the older type elastomeric foam EA pads were sensitive to “hot-wet” degradation for soak times as low as 3-hours, which is consistent with game or practice time situations. Finally, as noted above, it was shown that, depending on the size of the crush zone, this EA degradation factor could lead to increased head loads and injury severity measures. The results suggest the need for additional research on the above to enhance helmet safety.

Determination of Selected Crash Parameters in Head-on Vehicle Collision with Rollover

The paper presents complete results of the head-on small overlap crash test of vehicle with driver moving at a speed of approximately 12 m/s against stationary vehicle with post-crash rollover. When a crash does not involve the main crush-zone structures, the occupant compartment is not well protected. The emphasis in the paper was put on determination and presentation of crash parameters for the application in traffic accident analyses and for simulation with the help of software for accident reconstruction. The experimentally measured data from the crash test were analysed and important crash parameters which are necessary for accident reconstruction were obtained. The crash test was specific because of rollover of the impacting vehicle resulting from small overlap. The results have shown that small overlap accident is extremely dangerous for the crew with the possibility of vehicle rollover and occupant head and neck injury. Also in this case, at relative low speed, the driver suffered light neck and head injury in the following days and the longitudinal damage was relatively large. The input parameters for accident reconstruction software as the result of performed crash test were gained.

Crush Zone Morphology of Epoxy-Glass Fiber-Aluminium Composite Columnar Tube due to Longitudinal Crushing Force

Epoxy–glass fiber–aluminium composite may be of interest for energy absorption application due to their improved crashworthiness. In the current study, the hybrid–composite columnar tube specimen has been fabricated by a hand lay–up method using epoxy–glass fiber with aluminium columnar tube as a core material. An experimental quasi–static crush test has been performed on the specimen under axial loading. The post–crushing of composite lay–up configuration was observed during and after interaction of the axial loading with the specimen. The result of crush morphology analysis on final mode of failure of the specimen was carried out using SEM and showed combination of several failure modes such as matrix–fiber interfacial fracture, fiber breakage and hackles. However, the main failure mode is brittle type fracture comprising transverse shearing and splaying modes.

Relative tectonic activity classification in the Kermanshah area, western Iran

Due to the closing of the subduction zone and the collision of the Arabian and Eurasian plates, the High Zagros region has always been affected by a wide range of tectonic variations. In this research, the Gharasu River basin, which is located in the Kermanshah area, was selected as the study area, six geomorphic indices were calculated, and the results of each one were divided into three classes. Then, using the indices, relative tectonic activity was calculated, and their values were classified and analysed in four groups. Regions were identified as very high, high, moderate and low. In analysing the results and combining them with field observations and regional geology, the results were often associated and justified with field evidence. The highest value is located on the Dokeral anticline in the crush zone in Zagros. Most of the areas with high and moderate values of Index of Active Tectonics (IAT) are also located in the crush zone in Zagros. Crushing in this zone is because of the main fault mechanism of the Zagros region. The result in this paper confirms previous research in this region. At the eastern end of the study area, the value of Iat is high, which could be the result of the Sarab and Koh-e Sefid fault mechanisms.

Relative tectonic activity classification in Kermanshah area, west Iran

The High Zagros region because of closing to subduction zone and the collision of the Arabian and Eurasian plates is imposed under the most tectonic variations. In this research, Gharasu river basin that it has located in Kermanshah area was selected as the study area and 6 geomorphic indices were calculated and the results of each ones were divided in 3 classes. Then, using the indices, relative tectonic activity was calculated and the values were classified and analyzed in 4 groups. Regions were identified as very high, high, moderate and low. In analyzing the results and combining them with field observation and regional geology the results are often associated and justified with field evidences. The highest value is located on Dokeral anticline in crush zone in Zagros Most of the areas with high and moderate values of lat are located on crush zone in Zagros too. Crushing of this zone is because of main faults mechanism of Zagros region. The result of this paper confirms previous researches in this region. At the end of the eastern part of the study area, the value of Iat is high that could be the result of Sarab and Koh-e Sefid faults mechanism.

Proof-of-Concept of the Shape Memory Alloy ReseTtable Dual Chamber Lift Device for Pedestrian Protection With Tailorable Performance

As automobile use expands in population-dense cities across the world, there is a growing need for new approaches to mitigate the consequences to pedestrians of pedestrian/automotive collisions. This is especially challenging for passive approaches since there is an increasing internal space demand that reduces the crush zone between the relatively compliant hood and rigid underhood components. One unique approach is an active hood lift which raises the hood upon detection of a collision with a pedestrian to increase the crush zone. This approach is technically challenging due to the fast and accurate timing which is sensitive to extrinsic factors (including pedestrian height and weight and the need for reusable/automatically resettable functionality. This paper presents a novel hood lift concept: the shape memory alloy ReseTtable (SMArt) dual chamber lift device which is reusable, automatically resettable, and has tunable performance both off-line, and on-line to adjust to extrinsic factors. This device is situated under the rear corners of the hood and stores energy in the form of compressed air in opposing sides of a dual chamber pneumatic cylinder and a high-speed shape memory alloy exhaust valve (SEV) vents the upper chamber within milliseconds to allow the lower chamber to deploy the hood. A general multistage sequential design process is outlined that enables lift timing performance to be tailored by parametric design off-line and by varying operating parameters on-line. A proof-of-concept prototype was built and experimentally characterized for a midsize sedan case study confirming the timing, load capability and stroke of the device on the benchtop and the complete operational cycle in a full-scale automobile hood bay. The impact of additional mass on the lift timing was measured and two on-line adjustable operating parameters (pressure and valve timing) were investigated for their ability to compensate for the mass and other extrinsic effects. While this was a limited study of this new active technological approach to pedestrian safety, it does indicate promise to meet the strict demands of an active lift and a tailorable, resettable/reusable device.

Ballistic Impact Characteristics of Flat-nose Projectile Penetrating Concrete and Soil Compound Target

Ballistic impact characteristics on the flat-nose projectile penetrating the concrete and soil compound target are studied. The deformation process and failure zone in the target are described by numerical simulation with finite element software. The results show that penetration depth, residual velocity and deceleration amplitude of flat-nose projectile increase with initial velocity. The features of concrete target after impact are approximately in agreement with experimental results. And the cracks and the tensile crush zone formed during penetration could characterize the damage and failure of target. Meanwhile, terminal ballistic characteristics of flat-nose projectile into single soil layer are studied to compare with that of concrete compound target. The results show that the overload of projectile penetrating hard-soil is only one-third of that of concrete compound target with low velocity. Reversely, the duration of the former is more than five times as long as the latter, and the rebound velocity of projectile penetrating soil medium is greater than the concrete compound target.