Design and Simulation of Automotive Plastic Pillars for Occupant Protection

Safety is nowadays an increasingly important issue for automotive manufacturers. Plastic components, asides from its aesthetic function in the car interior, are required to act as passive safety components. In this work, the impact of an anthropomorphic mass with a given mass and velocity in a plastic pillar cover is simulated by a finite element code (ABAQUS/Explicit). The pillar is modelled as a solid discretised by 3D solid elements. The material’s properties (polypropylene) used in the pillar are obtained at high strain-rates and described by an elasto-plastic model, being adopted a maximum allowable strain failure criterion. The contact between the mass, the plastic component and the steel chassis are considered. A complete deceleration-time plot is obtained, being calculated the values of the Head Injury Criteria (HIC(d)) and maximum deceleration. The deformed geometry, resultant stress distribution and damaged zones are also predicted. The properties of the material (elastic modulus, yield stress and allowable strain level) are optimised, making extensive use of numerical simulations and a design of experiments approach, in order to meet the envisaged standards requirements and thus mitigating occupant injuries.

Influence of centroid acceleration acquisition and filtering class on head injury criterion evaluation

Proper evaluation of ski helmet designs and safety standards should rely on head impact conditions involved in skiing and snowboarding head injuries. To study these impacts, main crash scenarios involving head injuries are numerically replicated. Multibody models of skiers and snowboarders were developed to investigate five common crash scenarios involved in traumatic brain injury: forward and sideways skiing falls, snowboarding backward falls, collisions between users and collisions with obstacles. For each scenario, the influence of crash conditions on head impact (location, speed, linear and rotational accelerations) and risk of injury are evaluated. Crash conditions were initial velocity, user height, position and approach angle, slope steepness, obstacles, and snow stiffness. One thousand one hundred forty-nine crashes were simulated and three significant levels of impact conditions were discriminated over the investigated crash scenarios: 1) the smallest normal-to-slope impact velocities (6 km·h; 22 km·h) and peak linear accelerations (42g; 75g) were obtained during forward and sideways skiing falls; 2) snowboarding backward falls and collisions between users were associated with high normal-to-surface impact velocities (26 km·h; 32 km·h) and head accelerations (80g; 149g) above one published threshold for mild traumatic brain injury but below the pass/fail criteria of helmet standard tests; 3) collisions with obstacles were associated with high normal-to-surface impact velocities (19 km·h; 35 km·h) and the highest head accelerations (626g; 1885g). Current impact conditions of helmet standard evaluations consistently replicate collisions with obstacles, but need to be revised to better reflect other significant crash scenarios leading to traumatic brain injury.

Bicycle helmets are highly effective at preventing head injury during head impact: Head-form accelerations and injury criteria for helmeted and unhelmeted impacts

ABSTRACTObjective: Soldiers in military vehicles subjected to underbelly blasts can sustain traumatic head and neck injuries due to a head impact with the roof. The severity of head and neck trauma can be influenced by the amount of head clearance available to the occupant as well as factors such as wearing a military helmet or the presence of padding on the interior roof. The aim of the current study was to examine the interaction between a Hybrid III headform, the helmet system, and the interior roof of the vehicle under vertical loading.Methods: Using a head impact machine and a Hybrid III headform, tests were conducted on a rigid steel plate in a number of different configurations and velocities to assess helmet shell and padding performance, to evaluate different vehicle roof padding materials, and to determine the relative injury mitigating contributions of both the helmet and the roof padding. The resultant translational head acceleration was measured and the head injury criterion (HIC) was calculated for each impact.Results: For impacts with a helmeted headform hitting the steel plate only, which represented a common scenario in an underbelly blast event, velocities of ≤6 m/s resulted in HIC values below the FMVSS 201U threshold of 1,000, and a velocity of 7 m/s resulted in HIC values well over the threshold. Roof padding was found to reduce the peak translational head acceleration and the HIC, with rigid IMPAXX foams performing better than semirigid ethylene vinyl acetate (EVA) foam. However, the head injury potential was reduced considerably more by wearing a helmet than by the addition of roof padding.Conclusions: The results of this study provide initial quantitative findings that provide a better understanding of helmet–roof interactions in vertical impacts and the contributions of the military helmet and roof padding to mitigating head injury potential. Findings from this study will be used to inform further testing with the future aim of developing a new minimum head clearance standard for occupants of light armored vehicles.

Road restraint systems are used to protect vehicle occupants if the vehicle runs off the road and potentially collides with a dangerous obstacle. These road restraint systems must successfully pass the tests defined in EN 1317, or the Manual for Assessing Safety Hardware (MASH) before they are allowed to be installed. The safety assessment is carried out according to the criteria of ASI (Acceleration Severity Index), THIV (Theoretical Head Impact Velocity), OIV (Occupant Impact Velocity), ORA (Occupant Ridedown Acceleration), and PHD (Post-Impact Head Deceleration). Usually very old vehicles are used for these tests, and there is no assessment of occupant criteria such as HIC (Head Injury Criteria), chest deflection, etc. The objective of the study was to compare the occupant safety of vehicles that are commonly used in EN 1317 with vehicles that have improved safety equipment. Test results from two different vehicles (a commonly used vehicle in EN 1317 and a vehicle with improved safety equipment) and two different impact conditions (full overlap and an overlap of 50%) were compared. Measurement data from a Hybrid HIII 50th percentile anthropomorphic test device (ATD) (Denton ATD, INC.) was recorded during the tests to assess occupant safety. The tests have shown that vehicles with improved safety equipment perform better than vehicles that are commonly used in EN 1317-3 tests. The values for the occupant safety criteria assessed were well below the Euro NCAP (New Car Assessment Programme) or Federal Motor Vehicle Safety Standard (FMVSS) limits. However, the limits of the road safety criteria were in some cases considerably exceeded regardless of the vehicle. This has been observed in particular for the offset impact condition. THIV and OIV were supposed to be able to assess the risk of head injuries. However, these two criteria correlated negatively with the head criteria, HIC or a3ms. However, a positive correlation was found for the ASI with the HIC and the a3ms head acceleration. Even if some of the criteria for road safety correlate with the criteria for occupant safety, it is doubtful whether the criteria for road safety are suitable for assessing the risk of injury to vehicle occupants.

Objectives Elevated head injury incidence in infants compared to toddlers involved as occupants in motor vehicle crashes has been demonstrated in multiple population-representative crash databases. Further, experimental studies have revealed a potential injury mechanism via impact between a rear-facing, CRS-restrained child and the back of the vehicle seat or console on the row in front of the CRS. Subsequently, experimental studies have suggested that bracing the CRS against the seat immediately in front of the CRS could mitigate head injury, but also indicated that more research was necessary. Thus, we investigated the effect of bracing against the front seat, as well as distance from the front seat with rear-facing infant carriers and rear-facing convertibles, with a focus on changes to measured head, neck and chest injury metrics in rear facing CRSs. Further, we examined the effect of using the infant carrier with and without a base on these injury metrics. Methods 34 frontal sled tests at 30 or 35 mph were conducted using a simulated rear-row vehicle seat and structure representing the front seatback. A Q1.5 anthropomorphic test device (ATD) was placed in a single make/model LATCH-affixed rear-facing convertible or single make/model infant carrier; infant carrier without base was affixed with lap and shoulder belt. To evaluate the effect of bracing and distance, tests were conducted with a 300, 140, 70, or 15 mm gap between the CRS seatback and the front seatback, or a touching (0 mm) or braced (-20 mm) condition. Bayesian regression models quantified the effects of various predictors and model uncertainty. Results For tests with the convertible CRS, no head contact was observed between the head and the front vehicle seatback. For the infant carrier, head contact occurred at both 70 and 140 mm distances but not the other distances. On average, the −20, 0, or 15 mm distances yielded a 60% reduction in head injury criterion with 15 millisecond window (HIC15), and a 60% to 80% reduction in neck tension, compared to the 70 and 140 mm distances; chest acceleration also decreased for the convertible seat only. In the case of both carriers and convertibles, each mm of distance the CRS moves away from the front seatback up to 70 mm, adds 5.3 HIC15 points (95% Credible Interval (CrI):[4.6, 6.2]), and 3.5 Newtons (95% CrI: [2.2, 4.8]) of neck tension, on average. Conclusions Placing a rear facing CRS, both convertibles and infant carriers, against or close to the seatback of the seat immediately in front of the CRS reduces head and tensile neck injury criteria in ATDs. The amount of gap between the front seat and the rear facing CRS is strongly and positively correlated with HIC for both convertibles and infant carriers. RF infant carriers with and without a base yield comparable injury metrics and kinematics when touching or nearly touching the back of the front vehicle seatback.

Objectives The rapid increase in E-scooter usage has led to more scooter-related head and neck injuries. Yet, experimental data on head impacts and helmet effectiveness during crashes are scarce. The objectives of this study are to experimentally evaluate bicycle helmets in E-scooter falls, assessing head kinematics, impact conditions, and injury risks in two crash scenarios with and without helmets. Methods Six E-scooter forward falls, induced by a curb collision at 20 km/h, were simulated in sled tests using a Hybrid III 50th anthropomorphic test device with and without a helmet. The curb was positioned either perpendicularly or at a 55° angle to the E-scooter’s trajectory. Head velocity, head acceleration, neck load, chest acceleration, and chest deflection were measured. Results The average normal and tangential head velocities at impact were 5.9 m/s and 3.7 m/s, respectively. In configurations without helmet, both head accelerations and neck loads exceeded some injury thresholds, indicating a risk of severe injury. Using a helmet significantly reduced peak head linear (143 g vs. 571 g) and rotational (9.8 krad/s2 vs. 23.1 krad/s2) accelerations, and Head Injury Criterion (HIC) (792 vs. 5868). However, it did not significantly affect peak head rotational velocity (44.5 rad/s vs. 41.5 rad/s), neck load (in flexion-compression) nor Neck Injury Criterion (NIJ) (1.2 vs. 1.0). Conclusion The bicycle helmet significantly reduced most head injury metrics. Yet, the risk of severe head and neck injuries remains high. These results offer valuable data for evaluating head protection and developing and validating numerical crash test reconstructions for further investigations.

The National Highway Traffic Safety Administration (NHTSA) has been conducting biomechanical studies to reduce head injuries sustained during automotive collision. Furthermore, NHTSA added a new regulation to the Federal motor vehicle safety standard FMVSS201, limiting the equivalent head injury criterion (HIC) value to under 1000. In the present study, a methodology is developed for the optimum design of the A-pillar trim with rib structures, which can maximize the energy dissipation during head impact. The design variables for the rib structures are the transverse spacing, the longitudinal spacing and the thickness. The required set of design variables is decided upon on the basis of the design of experiments. A series of simulations for head impact to A-pillar trim are carried out by using the explicit finite element (FE) code LS-DYNA3D, and the HIC(d) values are computed using results from simulations utilizing design variables determined by a combination of the central composite design and the full factorial design. A proper regression function with an R 2 value above 0.9 was constructed using the response surface method, and it was used as an objective function for optimization. An HIC(d) value under 850 for 15 mile/h head-trim impact was obtained using the rib structures suggested by the present design methodology.

Objective: The aim of the current study was to study the kinematics of adult pedestrians and assess head injury risks based on real-world accidents. Methods: A total of 43 passenger car versus pedestrian accidents, in which the pedestrian's head impacted the windscreen, were selected from accident databases for simulation study. According to real-world accident investigation, accident reconstructions were conducted using multibody system (MBS) pedestrian and car models under MADYMO environment (Strasbourg University) to calculate head impact conditions in terms of head impact velocity, head position, and head orientation. Pedestrian head impact conditions from MADYMO simulation results were then used to set the initial conditions in a simulation of a head striking a windscreen using finite element (FE) approach. Results: The results showed strong correlations between vehicle impact velocity and head contact time, throw distance, and head impact velocity using a quadratic regression model. In the selected samples, the results indicated that Abbreviated Injury Scale (AIS) 2+ and AIS 3+ severe head injuries with probability of 50 percent were caused by head impact velocity at about 33 and 49 km/h, respectively. Further, the predicted head linear acceleration (head injury criterion, HIC) value, resultant angular velocity, and resultant angular acceleration for 50 percent probability of AIS 2+ and AIS 3+ head injury risk were 116 g, 825, 40 rad/s, 11,368 rad/s2 and 162 g, 1442, 55 rad/s, 18,775 rad/s2, respectively, and the predicted value of 50 percent probability of skull fracture was 135 g. Conclusions: The present study provides new insight into pedestrian head impact conditions in terms of velocity, angle, and impact location based on a number of real-world cases. Therefore, it may perform a critical analysis for current pedestrian head standard tests.

Head injury remains one of the most frequent and severe injuries sustained by vehicle occupants, motorcyclists, pedestrians and cyclists in road accidents and account for approximately 40% of road fatalities in the European Union (EU). One essential requirement for reducing the incidence of fatal and severe head injuries is to develop head injury assessment methods that can accurately and comprehensively assess the potential head injury risk under a broad range of head impact conditions. At present, the most widely accepted method of assessing head injury risk in road safety research is the Head Injury Criterion (HIC). However, HIC only considers the injury risk to the head resulting from linear head accelerations. In an attempt to develop improved head injury criteria for specific mechanisms, 68 head impact conditions that occurred in motor sport, motorcyclist, American football and pedestrian accidents were re-constructed with a state of the art finite element (FE) human head model (ULP head model). Statistical regression analysis was then carried out on the head loading parameters from the accidents, such as the peak linear and rotational acceleration of the head, and predictions from the head model, such as the Von Mises stress or strain and pressure in the brain, in order to determine which of the investigated parameters provided the most accurate metrics for the injuries sustained in the real world head trauma under consideration. The results show that Von Mises shearing strain within the brain is much better correlated with moderate Diffuse Axonal Injuries (DAI) as HIC or acceleration peaks are. For severe DAI, however, this improvement is less important. Another significant improvement of injury prediction based on FE head model is the one related to skull fracture, for which the proposed criteria present a higher correlation factor than HIC. Finally, SubDural Haematomas (SDH) are also better predicted with the FE model than HIC even if improvement is still needed for this injury mechanism.

This paper proposes a new procedure for designing helmets for head impact protection to road users such as two-wheeler riders and pedestrians. The new procedure suggests that a helmet be mounted on a featureless Hybrid III headform that is used for assessing upper interior head impact safety specified in the vehicle safety standard FMVSS 201 in the USA. To ascertain a helmet's effectiveness as a countermeasure for minimising the risk of severe head injury, an impact velocity of 6 m/s (13.5 mph) was used for the helmet-headform system striking a rigid target. The resultant head impact response is measured by Head Injury Criterion (HIC). The threshold HIC(d) limit of 1000 is applied for adjudging the efficacy of helmets. The proposed procedure is demonstrated with the help of a validated LS-DYNA model of a featureless Hybrid III headform and a helmet. The helmet model consists of an outer General Electric (GE) plastic-based shell to the inner surface of which is bonded a protective energy-absorbing foam padding of a given thickness. Based on simulation results of impact on a rigid surface, it appears that foam padding of suitable strength and a minimum thickness of 35–40 mm along with a shell thickness of 3–4 mm is necessary for obtaining an acceptable value of HIC(d), and therefore, an acceptable helmet safety design.

To determine the pedestrian's head injury criteria in a vehicle–pedestrian accident and the crack propagation and distribution laws for use in accident reconstruction, headform–polyvinyl butyral (PVB) laminated windshield upright impact tests were conducted at different impact speeds with a newly designed dropping impact hammer. A real vehicle was used considering the buffer performance of the entire vehicle. The crack propagation and distribution characteristics of the PVB laminated glass were explained by wave propagation. The resultant acceleration–time curves of headform were obtained, while a high-speed camera captured headform movement and glass crack propagation. The results showed that head injuries occur primarily in the initial collision stage. The crack propagation and distribution characteristics are related to the internal random defects of glass and the frequency, strength, and angle of impact. These results will help to better understand a pedestrian's head movement and injury criteria, and provide the foundation for simulation analysis.

The safety of civil aircraft seats is evaluated by dynamic testing using two sets of impact conditions. For transport category aircraft seats, the potential for head injury due to impact on seat backs or bulkheads must be determined. The dynamic tests are conducted with a 50th-percentile Hybrid II dummy, and pass/fail criteria include the Head Injury Criterion (HIC). Computer simulations were performed to investigate the variation of HIC and neck loads with dummy size and type and for a range of seat row pitch. Another variable was the break-over resistance of the forward seat back. As expected, predicted values of HIC were higher for larger dummies at a given seat row pitch. Potentially more significant was the result that the HIC values obtained with the 50th-percentile Hybrid III model were generally much higher than those for the Improved Hybrid II under otherwise identical conditions, indicating the need for further investigation. Finally, for many of the cases that were modelled, neck moments and or forces were predicted to exceed recommended tolerance levels, even when the HIC was significantly below 1000.

The compliance with Head Injury Criteria (HIC) specified in 14 CFR 23.562 [1] and CFR 25.562 [2] poses a significant problem for many segments of the aerospace industry. The airlines and the manufacturers of jet transports have made claims of high costs and significant schedule overruns during the development and certification of 16G seats because of the difficulties encountered in meeting this requirement. The current practice is to conduct Full Scale Sled Tests (FSST) on impact sleds. This approach can be expensive, since a new seat may be needed for each test. Moreover, some consider the HIC sensitive to changes in the test conditions, such as sled pulse, seat belt elongation, etc., resulting in HIC results from FSSTs showing poor repeatability. These difficulties make it desirable to devise a cheaper, faster, and more repeatable alternative to FSSTs. This paper describes an attempt to address these issues by designing a device, the National Institute for Aviation Research (NIAR) HIC Component Tester (NHCT) using various multibody tools. This device was then fabricated and its performance evaluated against FSSTs conducted under similar test conditions for some typical impact events that occur in an aircraft cabins e.g. impact with bulkheads. The factors compared for this evaluation are the head impact angle, head impact velocity, HIC, HIC window, peak head C.G. resultant acceleration, average head C.G. resultant acceleration, and head C.G. resultant acceleration profiles. The results of these evaluations show that the NHCT already produces test results that correlate significantly with FSST results for impact targets such as bulkheads and its target envelope is expected eventually to include objects such as seat backs.