Mats Lindquist

Car structural characteristics of fatal frontal crashes in Sweden

Abstract This paper provides results from in-depth real world crash investigations of fatal frontal crashes with belted occupants. A new method has been used regarding data collection of vehicle deformations. This method allows a detailed analysis of actual load paths acting on the vehicle during the crash event. By using this method it was identified that small overlap crashes accounted for 48% of the belted fatalities which corresponds to an overlap < 30% and not including the drive train as an active load path. Crashes that correspond to load paths usage similar to the Euro & US NCAP crash test protocols accounted for 23% of the fatalities. A comparison of the new data collection methodology to the existing SAE J224 practice indicates that the SAE J224 practise overestimates the width of front structural involvement. These results points out the necessity to identify actual load paths involved in crashes in order to evaluate current crash test standards and future vehicle compatibility issues.

Real World Car Crash Investigations - A New Approach

By actively researching real world crashes it has become apparent that existing methodologies for recording car deformation for severe injuries and fatalities are limiting our ability to effectively interpret the cause and effect relationship to the sustained injuries. This paper provides a historical view of crashworthiness development, explaining current data collection methods for analysing real world crashes before presenting a new approach in real world crash data collection. The new methodology aims to substantially improve our understanding and analysis of the cause and effect of injuries that are seen in everyday crashes. This improved understanding is achieved by examining the behaviour of the structural elements in the car body during a crash. A generic car model has been developed, consisting of beams, joints and plate areas, which is used during car inspection. The main goal is clear identification of the load path usage during the crash. It is identified that there is a need for better understanding of real world crashes so as to be able to provide the automotive industry with more accurate statistical information for different crash types. The authors note that accurate statistical information is required in order to guide future changes in the crashworthiness testing protocols to be effective in reducing the crash dynamics that are the cause of real world injuries. This paper singularly presents a new methodology, whilst referring to current ongoing work using this approach.

Pulse shape analysis and data reduction of real-life frontal crashes with modern passenger cars

The increased use of computer simulations such as finite element modelling for evaluating passive safety applications has made it possible to simplify and parameterise complex physical processes. Crash pulses derived from laboratory tests have been used in many studies to evaluate and optimise passive safety systems such as airbags and seat belts. However, a laboratory crash pulse will only be representative of the acceleration time history of a specific car crashing into a barrier at a specified velocity. To be able to optimise passive safety systems for the wide variety of scenarios experienced during real-life crashes, there is a need to study and characterise this variation. In this study, crash pulses from real-life crashes as recorded by event data recorders were parameterised, and the influence of vehicle and crash variables was analysed. The pulse parameterisation was carried out using eigenvalue analysis and the influence that vehicle and crash variables had on the pulse shape was determined with multiple linear regression. It was shown that the change in velocity, the subject vehicle mass, and the properties of the collision partner were the variables that had the greatest effect on the shape of the crash pulse. The results of this study can be used to create artificial real-life pulses with different crash parameters. This in turn can be used for stochastic computer simulation studies with the intention of optimising passive safety systems that are robust to the wide variation in real-life crashes.

Modelling and simulation of seat-integrated safety belts including studies of pelvis and torso responses in frontal crashes

Abstract The aim of the present study is to investigate how the physical properties influence the interaction of the seat back frame and the safety belt. Seat-integrated 3- and 4-point configurations with both non-rigid and rigid seat back frames were compared with common 3-point configurations with anchor points on the car body. The LS-DYNA FE-analysis software was used in order to perform frontal crash simulations with a belted 50th percentile Hybrid III FE-dummy model as occupant. The belt-webbing distribution between the lap and the torso belts via a slip-ring and in combination with a non-rigid seat back frame increases the ride-down efficiency compared to a system with no belt-webbing distribution. No tendencies of pelvis submarining were observed regardless of belt configuration. The dynamic response of the seat back frame has some influence on the ride-down efficiency.

Numerical studies concerning upper neck and head responses in frontal crashes with seat-integrated safety belts

Abstract Mitigation of neck and head injuries is critical in automotive occupant protection. The aim of the present study is to investigate how the physical properties influence the interaction of the seat back frame and the safety belt. Seat integrated 3- and 4-point configurations with both non-rigid and rigid seat back frames were compared with 3-point configurations with anchor points on the car body. The LS-DYNA FE-analysis software was used in order to perform frontal crash simulations with a belted 50th percentile Hybrid III dummy model as occupant. The belt-webbing distribution between the lap and the torso belts via a slip-ring and in combination with a non-rigid seat back frame had an advantageous influence concerning the loads of the upper neck and injury criteria compared to a system with no belt-webbing distribution.

Analysis of Delta Velocity and PDOF by Means of Collision Partner and Structural Involvement in Real-Life Crash Pulses With Modern Passenger Cars

Objective: In the widely used National Automotive Sampling System (NASS)-Crashworthiness Data System (CDS) database, summary metrics that describe crashes are available. Crash angle or principal direction of force (PDOF) is estimated by the crash examiner and velocity changes (ΔV) in the x- and y-directions are calculated by the WinSMASH computer program using PDOF and results from rigid barrier crash testing combined with deformations of the crashed car. In recent years, results from event data recorders (EDRs) have been added to the database. The aim of this study is to compare both PDOF and ΔV between EDR measurements and WinSMASH calculations. Methods: NASS-CDS inclusion criteria were model-year 2000 through 2010 automobiles, frontal crashes with ΔV higher than 16 km/h, and the pulse entirely recorded in the EDR module. This resulted in 649 cases. The subject vehicles were further examined and characterized with regard to frontal structure engagement (large or small overlap) as well as collision properties of the partner (impact location; front, side, or back) or object. The EDR crash angle was calculated as the angle between the lateral and longitudinal ΔV at the time of peak longitudinal ΔV. This angle was compared to the NASS-CDS investigators estimated PDOF with regard to structural engagement and the collision partner or object. Multiple linear regression was used to establish adjustment factors on ΔV and crash angle between the results calculated based on EDR recorded data and that estimated in NASS-CDS. Results: According to this study, simulation in the newest WinSMASH version (2008) underestimates EDR ΔV by 11 percent for large overlap crashes and 17 percent for small overlap impacts. The older WinSMASH version, used prior to 2008, underestimated each one of these two groups by an additional 7 percentage points. Another significant variable to enhance the prediction was whether the crash examiner had reported the WinSMASH estimated ΔV as low or high. In this study, none of the collision partner groups was significantly different compared to front-to-front impacts. However, with a larger data set a couple of configurations may very well be significantly different. In this study, the crash angle denoted by PDOF in the NASS database underestimates the crash angle calculated from recent EDR modules by 35 percent. Conclusion: On average the ΔV and crash angle are underestimated in NASS-CDS when analyzing the data based on collision partner/object and structural engagement. The largest difference is found in small overlap crashes and the least difference in collision scenarios similar to barrier tests. Supplemental materials are available for this article. Go to the publishers online edition of Traffic Injury Prevention to view the supplemental file.

Influence of Vehicle Kinematic Components on Chest Injury in Frontal-Offset Impacts

Objective: Frontal crashes in which the vehicle has poor structural engagement, such as small-overlap and oblique crashes, account for a large number of fatalities. These crash modes are characterized by large intrusion and vehicle yaw rotation. Results from previous studies have shown mixed results regarding the importance and effects of these parameters. The aim of this study was to evaluate how vehicle yaw rotation, instrument panel intrusion, and the time history of the pulse angle influence chest injury outcomes. Method: This study was conducted using kinematic boundary conditions derived from physical crash tests, which were applied on a finite element simulation model of a vehicle interior including a finite element human model. By performing simulations with different levels of simplified boundary conditions and comparing the results to a simulation with a full set of boundary conditions, the influence of the simplifications was evaluated. The injury outcome measure compared between the simulations was the expected number of fractured ribs. The 3 simplifications simulated were (1) removal of vehicle yaw rotation, (2) removal of vehicle yaw rotation plus an assumption of a constant pulse angle between the x- and y-acceleration, and (3) removal of instrument panel intrusion. The kinematic boundary conditions were collected from 120 physical tests performed at the Insurance Institute of Highway Safety; 77 were small-overlap tests, and 43 were moderate overlap tests. For each test, the full set of boundary conditions plus the 3 simplifications were simulated. Thus, a total of 480 simulations were performed. Results: The yaw rotation influences occupant interaction with the frontal airbag. For the approximation without this kinematic boundary component, there was an average error in injury outcome of approximately 13% for the moderate overlap cases. Large instrument panel intrusion increases the risk of rib fracture in nearside small-overlap crashes. The mechanism underlying this increased fracture risk is a combination of increased airbag load and a more severe secondary impact to the side structure. Without the intrusion component, the injury risk was underestimated by 8% for the small-overlap crashes. Conclusion: The approximation with least error was version 2; that is, a model assuming a constant pulse angle, including instrument panel intrusion but no vehicle yaw rotation. This approximation simulates a sled test with a buck mounted at an oblique angle. The average error for this approximation was as low as 2–4%.

Development and validation of a generic finite element vehicle buck model for the analysis of driver rib fractures in real life nearside oblique frontal crashes.

OBJECTIVE Frontal crashes still account for approximately half of all fatalities in passenger cars, despite several decades of crash-related research. For serious injuries in this crash mode, several authors have listed the thorax as the most important. Computer simulation provides an effective tool to study crashes and evaluate injury mechanisms, and using stochastic input data, whole populations of crashes can be studied. The aim of this study was to develop a generic buck model and to validate this model on a population of real-life frontal crashes in terms of the risk of rib fracture. METHOD The study was conducted in four phases. In the first phase, real-life validation data were derived by analyzing NASS/CDS data to find the relationship between injury risk and crash parameters. In addition, available statistical distributions for the parameters were collected. In the second phase, a generic parameterized finite element (FE) model of a vehicle interior was developed based on laser scans from the A2MAC1 database. In the third phase, model parameters that could not be found in the literature were estimated using reverse engineering based on NCAP tests. Finally, in the fourth phase, the stochastic FE model was used to simulate a population of real-life crashes, and the result was compared to the validation data from phase one. RESULTS The stochastic FE simulation model overestimates the risk of rib fracture, more for young occupants and less for senior occupants. However, if the effect of underestimation of rib fractures in the NASS/CDS material is accounted for using statistical simulations, the risk of rib fracture based on the stochastic FE model matches the risk based on the NASS/CDS data for senior occupants. CONCLUSION The current version of the stochastic model can be used to evaluate new safety measures using a population of frontal crashes for senior occupants.

Methodology for mass minimisation of a seat structure with integrated safety belts constrained by biomechanical responses on the occupant in frontal crashes

A methodology using finite element (FE) modelling and simulation with a property-based model (PBM) is presented. A generic 3-D FE model of a seat structure with a three-point seat-integrated safety belt configuration was established. A 50th percentile Hybrid III FE dummy model was used as occupant. Metamodelling techniques were used in optimisation calculations performed in two steps. Step 1: Six separate optimisations minimising biomechanical responses of the FE dummy model. Step 2: Four separate optimisations with different start values of the design variables, with the total mass of the seat structure as objective function and with the minimised biomechanical responses from Step 1 as constraint values. Six design variables were used in both Step 1 and Step 2. The four optimisations performed in Step 2 generated four different results of the total mass. Thus, different local minima were found instead of one single global minimum. The presented methodology with a PBM may be used in a concept design phase. Some issues concerning the FE model suggest further improvement.

Evaluation of finite element models of seat structures with integrated safety belts using full-scale experiments

Any numerical model needs to be evaluated in order to perform as accurately as possible. The aim of the present study is to develop an FE model of a seat structure with integrated safety belts evaluated to full-scale experiments. Simplified seat structures with 3-point integrated safety belt configurations and corresponding FE models were established. The dimension and the material states of the seat back frame were varied. A 50th percentile Hybrid III dummy was used as occupant. A number of biomechanical and mechanical responses of both experiments and simulations were compared and evaluated. The majority of the simulated responses showed good agreement with or slightly underestimated the corresponding experimental responses during belt loading but differed during belt unloading in some cases. Some inadequacies of the FE model were discovered and areas for further development are suggested. The FE model developed and evaluated in the present study may well be used in future studies.