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Letter from the Guest Editors
Youth bicycle helmet manufacturers often add shell protrusions to make helmets more attractive or fun for children, yet the safety implications of these features are not well understood. While prior work suggests protrusions may affect head impact kinematics, no study has evaluated their effectiveness in location-matched impacts between helmets with and without protrusions. Twelve youth bicycle helmet models, with protrusions intact and removed, underwent matched oblique impacts at three locations and 4.2 m/s to capture resulting peak linear acceleration (PLA) and peak rotational acceleration (PRA). A linear mixed model was used to quantify the effect of protrusion presence on PLA, PRA, and impact duration. The youth bicycle helmet models produced a wide range of kinematics. Protrusion presence had a strong effect on PLA, PRA, and impact duration. PLA averaged 103.0 ± 22.8 g for helmets with protrusions compared to 143.9 ± 21.4 g for helmets without protrusions, while PRA averaged 4432 ± 1570 rad/s2 for helmets with protrusions and 5177 ± 2110 rad/s2 for helmets without protrusions. These findings suggest that helmet protrusions can reduce peak head accelerations in youth bicycle helmet impacts.
Modern combat helmets improve wearer survivability through preventing ballistic penetration via delamination or deformation of the shell material. However, this deformation may impinge upon the skull and present a risk of behind-helmet blunt trauma (BHBT). While legacy aramid helmets from the late 1970s–1980s inform current NIJ testing standards, the advent of lower areal density ultra-high molecular weight polyethylene (UHMWPE) and modern suspensions may incur unknown changes that present an unknown effect on BHBT risk. This study investigates whether current standards relying on a peak acceleration threshold and residual clay deformation may not reflect changes in deformation geometry seen in newer shell materials and suspension designs. Thirty-eight helmets categorized into three groups, older aramid, newer aramid (with new suspension), and prototype UHMWPE (with old suspension), were mounted on Hybrid III ATD head-necks and impacted on the temporal surface with 9 mm NATO projectiles at velocities between 388 and 482 m/s. Flash x-ray imaging captured deformation geometry. Deformations were digitized to measure maximum depth, volume, and surface area recruited. Multiple linear regression identified the influence of shell material and suspension on geometry. Results indicated that shell material significantly affected deformation volume and area (p < 0.05). Notably, UHMWPE exhibited a qualitatively more “pointed” deformation profile compared to aramid, recruiting material differently as depth increased. In contrast, suspension type and helmet design did not significantly influence deformation geometry. These findings suggest that the BHBT geometry in UHMWPE helmets differs fundamentally from aramid helmets. As UHMWPE helmets encounter higher-energy threats, current acceleration threshold or depth-based standards may not fully capture the risk of skull fracture. To future-proof helmet validation, testing standards should evolve beyond current standards to include area recruitment and other geometric measures.
This SAE Standard applies to all self-propelled machines with a gross vehicle mass greater than 5000 kg that are utilized to clean material from highways, parking lots, airfield runways, outside paved areas that are principally exposed to vehicular traffic. These machines can also be involved with road construction or repaving work. Primary methods for material removal and cleaning can be by mechanical, pneumatic, washing and flushing systems, or in a combination of any system.
This SAE Standard applies to all self-propelled machines with a gross vehicle mass up to 5000 kg that are utilized to clean material from outside paved areas, parkland, floors in non-residential buildings and areas principally exposed to pedestrian traffic. Primary methods for material removal can be by mechanical, pneumatic, washing and flushing systems, or in a combination of any system.
This SAE Recommended Practice applies to fifth wheel kingpins for heavy-duty commercial trailers and semitrailers, used for off-highway operation or in hauling heavy loads (see Figure 1).
Letter from the Guest Editors
Metastable β-titanium alloys have attracted considerable interest for structural applications, owing to their superior specific strength and the ability to obtain enhanced ductility through phase transformations induced by deformation. Nevertheless, in recently developed Ti-Zr-Al-V alloy systems, the interactions among dislocation slip, strain-induced martensitic transformation, and the consequent work-hardening response remains largely unclear. Under room-temperature uniaxial tension, this work systematically investigates how the microstructure evolves and how the alloy deforms for a metastable β-type Ti-42Zr-12Al-4V (at.%) alloy. To track the progression of strain-induced α″ martensite and dislocation activity across varying strain levels, techniques including quasi-in-situ scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and focused ion beam (FIB) were employed. Findings indicate that the dominant strengthening mechanism stems from the strain-induced α″ martensite blocking dislocation motion, alongside dislocation cross-slip. Although the martensite volume fraction rises with increasing strain, its growth rate diminishes at higher strains. The martensite and the β matrix exhibited a clear Burgers-type orientation relationship, namely [001]α″//[110]β. Moreover, the appearance of martensite inside both primary and secondary slip bands generates a dynamic Hall-Petch effect, which reduces the dislocation mean free path and thereby supports continued strain hardening. These results provide deeper insight into the transformation-induced plasticity (TRIP)-assisted deformation mechanisms active in β-type titanium alloys and could guide the development of strong yet ductile materials.
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