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Simulations of impact events in the automotive industry are now common practice. Vehicle crashworthiness simulations on plastic components cover a wide range of strain rates from 0.01 to 500 s-1. Because plastics mechanical properties are very dependent on strain rate, developing experimental methods for generating stress-strain curves at this strain rate range is of great technological importance. In this paper, a modified Charpy machine capable of acquiring useful information to obtain the stress-strain curve is presented. Strain rates between 300 to 400 s-1 were achieved. Three thermoplastics were tested: high-density polyethylene, polypropylene-copolymer and polypropylene-homopolymer. Impact simulations using LS-DYNA were performed using the acquired high-strain rates stress-strain curves and compared with experimental data. Simulations using stress-strain curves from quasi-static tests were also performed for comparison. Very good agreement between the simulation and experimental results was found when the ASTM D1822 type S specimen was used for testing each material.

Bicycle helmets effectively mitigate skull fractures, but there is increasing concern on their effectiveness in mitigating traumatic brain injury (TBI) caused by rotational head acceleration. Bicycle falls typically involve oblique impacts that induce rotational head acceleration. Recently, bicycle helmet with dedicated rotation-damping systems have been introduced to mitigate rotational head acceleration. This study investigated the impact performance of four helmets with different rotation-damping systems in comparison to a standard bicycle helmet without a rotation-damping system. Impact performance was tested under oblique impact conditions by vertical drops of a helmeted headform onto an oblique anvil at 6.2 m/s impact speed. Helmet performance was quantified in terms of headform kinematics, corresponding TBI risk, and resulting brain strain. Of the four rotation-damping systems, two systems significantly reduced rotational head acceleration, TBI risk, and brain strain compared to the standard bicycle helmet. One system had no significant effect on impact performance compared to control helmets, and one system significantly increase linear and rotational head acceleration by 62 and 61%, respectively. In conclusion, results revealed significant differences in the effectiveness between rotation-damping systems, whereby some rotation-damping systems significantly reduced rotational head acceleration and associated TBI risk.

This study focuses on the behavior of hybrid polymer composites made from glass fiber and natural fiber-based flax fabric when subjected to low velocity drop-weight impacts. With the rise in the utilization of composites in structural components in various industries like the marine, aerospace and automotive industries, it is of paramount importance to study the effects of low velocity drop-weight impacts and their damage assessment on the composites. Low velocity drop-weight impacts can occur due to a tool falling on a composite part or due to an impact with a small object. The experimental tests were carried out according to ASTM standards with a drop-weight impact testing machine. Simulations were done to replicate the tests using explicit finite element software LS-DYNA. The experimental tests were carried out on samples of thickness ~2.5 mm and the energy at impact was 50 J. Upon comparing the experimental results, it was seen that an error percentage in the deformation varied between a minimum of 3.32% and a maximum of 8.93%, and the maximum force at impact varied between a minimum of 0.06% and a maximum of 17.14%. The variations between the experimental and simulated values can be attributed to the presence of voids or other defects that would have inadvertently crept in while making the composite. Additionally, composite laminates lined with a layer of EPS (expanded polystyrene) foam were tested and compared with composite laminates which were not lined with the foam. An improvement in the performance of the composite laminates lined with the EPS foam was observed.

Rotational acceleration of the head is a principal cause of concussion and traumatic brain injury. Several rotation-damping systems for helmets have been introduced to better protect the brain from rotational forces. But these systems have not been evaluated in snow sport helmets. This study investigated two snow sport helmets with different rotation-damping systems, termed MIPS and WaveCel, in comparison to a standard snow sport helmet without a rotation-damping system. Impact performance was evaluated by vertical drops of a helmeted Hybrid III head and neck onto an oblique anvil. Six impact conditions were tested, comprising two impact speeds of 4.8 and 6.2 m/s, and three impact locations. Helmet performance was quantified in terms of the linear and rotational kinematics, and the predicted probability of concussion. Both rotation-damping systems significantly reduced rotational acceleration under all six impact conditions compared to the standard helmet, but their effect on linear acceleration was less consistent. The highest probability of concussion for the standard helmet was 89%, while helmets with MIPS and WaveCel systems exhibited a maximal probability of concussion of 67 and 7%, respectively. In conclusion, rotation-damping systems of advanced snow sport helmets can significantly reduce rotational head acceleration and the associated concussion risk.

This paper presents a study on the low-velocity impact response of lightweight steel foam concrete (LSFC) composite slabs. The LSFC composite slab consisted of a W-shaped steel plate, foam concrete and oriented strand board (OSB). Low-velocity impact tests on the LSFC composite slabs were conducted by employing an ultra-high heavy-duty drop hammer testing machine. The tests revealed the failure mode, impact force and displacement response of LSFC composite slabs. The effects of density and thickness of foam concrete and drop height on the peak impact force and energy absorption ratio were investigated. A finite element (FE) model was set up to predict the impact resistance of the LSFC composite slabs, and a good agreement between simulation and test results was achieved. In addition, an equivalent-single-degree-of-freedom (ESDOF) model was set up to predict the displacement response of the LSFC composite slabs under impact loading.

The best way to prevent severe head injury when cycling is to wear a bike helmet. To reduce the rate of head injury in cycling, knowing the nature of real-world head impacts is crucial. Reverse engineering real-world bike helmet impacts in a laboratory setting is an alternative to measuring head impacts directly. This study aims to quantify bike helmet damage using computed tomography (CT) and reconstruct real-world damage with a custom, oblique test rig to recreate real-world impacts. Damaged helmets were borrowed from a helmet manufacturer who runs a helmet warranty program. Each helmet was CT-scanned and the damage metrics were quantified. Helmets of the same model and size were used for in-lab reconstructions of the damaged helmets where normal velocity, tangential velocity, peak linear acceleration (PLA) and peak rotational velocity (PRV) could be measured. The damage metrics of the in-lab dropped helmets were quantified using the same CT scanning process. For each case, a multiple linear regression (MLR) equation was created to define a relationship between the quantified damage metrics of the in-lab tested helmets and the associated measured impact velocities and kinematics. These equations were used to predict the impact kinematics and velocities from the corresponding real-world damaged helmet based on the damage metrics from the original damaged helmet. Average normal velocity (3.5 m/s), tangential velocity (2.5 m/s), PLA (108.0 g), PRV (15.7 rad/s) were calculated based on a sample of 23 helmets. Within these head impact cases, five notes reported a concussion. The difference between the average PLA and PRV for concussive cases versus other impacts were not significantly different, although the average impact kinematics for the concussive cases (PLA = 111.4 g, PRV = 18.5 rad/s) were slightly higher than the remaining cases (PLA = 107.1 g, PRV = 15.0 rad/s). The concussive cases were not indicative of high magnitude impact kinematics.

In this paper, the influence of different fiber materials on the dynamic splitting mechanical properties of concrete was investigated. Brazil disc dynamic splitting tests were conducted on plain concrete, palm fiber-reinforced concrete, and steel fiber-reinforced concrete specimens using a split Hopkinson pressure bar (SHPB) test device with a 100 mm diameter and a V2512 high-speed digital camera. The Digital Image Correlation (DIC) technique was used to analyze the fracture process and crack propagation behavior of different fiber-reinforced concrete specimens and obtain their dynamic tensile properties and energy dissipation. The experimental results indicate that the addition of fibers can enhance the impact toughness of concrete, reduce the occurrence of failure at the loading end of specimens due to stress concentration, delay the time to failure of specimens, and effectively suppress the expansion of cracks. Steel fibers exhibit a better crack-inhibiting effect on concrete compared to palm fibers. The incident energy for the three types of concrete specimens is roughly the same under the same impact pressure. Compared with plain concrete, the energy absorption rate of palm fiber concrete is decreased, while that of steel fiber concrete is increased. Palm fiber-reinforced concrete and steel fiber-reinforced concrete have lower peak strains than plain concrete under the same loading duration. The addition of steel fibers significantly impedes the internal cracking process of concrete specimens, resulting in a relatively slow growth of damage variables.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has had a global impact, underscoring the importance of personal protective equipment (PPE). Use of N95s reduces the risk of airborne infection; however, in the absence of equitable designs, health care workers (HCWs) who do not fit the average White male head and face are at an increased risk of airborne infectious diseases. Primary: Feasibility of a mixed-method study, with a sample size of 100, 50% of participants self-identifying as non-White and having at least one characteristic of interest. Secondary: (1) Generate quantitative evidence on N95 fit using a PortaCount fit test, (2) describe participant-reported feelings on fit and breathability, and (3) evaluate the impacts of the pandemic on a HCW's physical and mental well-being. This was a mixed-method prospective pilot and feasibility study. Quantitative fit was assessed using a TSI PortaCount test and measurements of bizygomatic breadth and Menton-Sellion length. A survey was administered to collect sociodemographic information, HCWs' assessment of N95 fit, comfort, and the impact of PPE-related challenges on well-being. This study was limited by a small sample size, as COVID-19 pandemic restrictions prevented adequate recruitment to detect differences between groups. We describe key findings that should inform analyses of the impact of gender and ethnicity on N95 respirator fit. Following a study amendment to increase eligible sites, 37 of the 41 (90.2%) approached HCWs consented to participate. Compared to other HCWs, non-White females had the lowest mean fit factor. Differences in Menton-Sellion length and bizygomatic breadth were observed between males, females, and White and non-White HCWs. Most HCWs reported physical discomfort and negative impacts on their psychological well-being. We identified gender and ethnicity as key factors in the fit of N95s. Differences in gender, ethnicity, and anthropometric measures must be considered in respirator designs.

Currently, the mechanical performances of polylactic acid (PLA) samples prepared using the fused filament fabrication (FFF) technique are relatively poor. Hence, the carbon fiber (CF) is used to improve the thermal stability and mechanical property of FFF-ed PLA samples in this paper. The crystalline structure, thermal stability, melt flow rate, tensile strength and fractured surface morphology of PLA and PLA/CF samples were investigated with an X-ray diffraction device, differential scanning calorimeter, thermogravimetric analyzer, melt flow rate equipment, universal tensile test machine and scanning electron microscope, respectively. Meanwhile, the reinforcement mechanism of CF on the mechanical property of PLA samples was also analyzed. XRD results revealed that the diffraction peaks intensities of PLA/CF sample were obviously lower than those of PLA sample. TGA and DSC curves illustrated that the initial thermal decomposition temperature, thermal stability and crystallinity of the PLA/CF sample improved significantly. The tensile strength of the PLA/CF sample was 91.58 MPa, which was 42.49% higher than that of the PLA sample. Moreover, SEM images showed that the fractured behavior of the PLA sample varied from brittle fracture to ductile fracture after the introduction of CF. The results concluded the CF is a feasible fiber for enhancing the performances of the PLA sample.

Polymethyl methacrylate (PMMA) is widely used for the fabrication of removable prostheses. Recently, zirconium oxide nanoparticles (nano-ZrO ) have been added to improve some properties of PMMA, but their effect on the optical properties and tensile strength are neglected. The aim of this study was to investigate the effect of nano-ZrO addition on the translucency and tensile strength of the PMMA denture base material. Eighty specimens (40 dumbbell-shaped and 40 discs) were prepared out of heat-polymerized acrylic resin and divided into four groups per test (n=10). The control group for each test included unreinforced acrylic, while the test groups were reinforced with 2.5, 5, and 7.5 wt% nano-ZrO . Acrylic resin was mixed according to manufacturer's instructions, packed, and processed by conventional method. After polymerization, all specimens were finished, polished, and stored in distilled water at 37°C for 48±2 hours. Tensile strength (MPa) was evaluated using the universal testing machine while the specimens' translucency was examined using a spectrophotometer. Statistical analysis was carried out by SPSS using the paired sample -test ( ≤0.05). A scanning electron microscope was used to analyze the morphological changes and topography of the fractured surfaces. This study showed that the mean tensile strength of the PMMA in the test groups of 2.5%NZ, 5%NZ, and 7.5%NZ was significantly higher than the control group. The tensile strength increased significantly after nano-ZrO addition, and the maximum increase seen was in the 7.5%NZ group. The translucency values of the experimental groups were significantly lower than those of the control group. Within the reinforced groups, the 2.5%NZ group had significantly higher translucency values when compared to the 5%NZ and 7.5%NZ groups. The addition of nano-ZrO increased the tensile strength of the denture base acrylic. The increase was directly proportional to the nano-ZrO concentration. The translucency of the PMMA was reduced as the nano-ZrO increased. Based on the results of the current study, the tensile strength was improved with different percentages of nano-ZrO additions. However, translucency was adversely affected. Therefore, it is important to determine the appropriate amount of reinforcing nano-ZrO that will create a balance between achieved properties - mechanical and optical.