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Stochastic finite element simulations of real life frontal crashes: With emphasis on chest injury mechanisms in near-side oblique loading conditions
Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Surgery. ÅF Industry.ORCID iD: 0000-0001-9360-0707
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Introduction. Road traffic injuries are the eighth leading cause of death globally and the leading cause of death among young people aged 15-29. Of individuals killed or injured in road traffic injuries, a large group comprises occupants sustaining a thorax injury in frontal crashes. The elderly are particularly at risk, as they are more fragile. The evaluation of the frontal crash performance of new vehicles is normally based on barrier crash tests. Such tests are only representative of a small portion of real-life crashes, but it is not feasible to test vehicles in all real-life conditions. However, the rapid development of computers opens up possibilities for simulating whole populations of real-life crashes using so-called stochastic simulations. This opportunity leads to the aim of this thesis, which is to develop and validate a simplified, parameterized, stochastic vehicle simulation model for the evaluation of passive restraint systems in real-life frontal crashes with regard to rib fracture injuries.

Methods. The work was divided into five phases. In phase one, the geometry and properties of a finite element (FE) generic vehicle buck model were developed based on data from 14 vehicles. In the second phase, a human FE model was validated for oblique frontal crashes. This human FE model was then used to represent the vehicle occupant. In the third phase, vehicle buck boundary conditions were derived based on real-life crash data from the National Automotive Sampling System (NASS) and crash test data from the Insurance Institute for Highway Safety. In phase four, a validation reference was developed by creating risk curves for rib fracture in NASS real-life crashes. Next, these risk curves were compared to the risk of rib fractures computed using the generic vehicle buck model. In the final phase, injury mechanisms in nearside oblique frontal crashes were evaluated.

Results. In addition to an averaged geometry, parametric distributions for 27 vehicle and boundary condition parameters were developed as guiding properties for the stochastic model. Particular aspects of the boundary conditions such as pulse shape, pulse angle and pulse severity were analyzed in detail. The human FE model validation showed that the kinematics and rib fracture pattern in frontal oblique crashes were acceptable for this study. The validation of the complete FE generic vehicle buck model showed that the model overestimates the risk of rib fractures. However, if the reported under-prediction of rib fractures (50-70%) in the NASS data is accounted for using statistical simulations, the generic vehicle buck model accurately predicts injury risk for senior (70-year-old) occupants. The chest injury mechanisms in nearside oblique frontal crashes were found to be a combination of (I) belt and airbag loading and (II) the chest impacting the side structure. The debut of the second mechanism was found for pulse angles of about 30 degrees.

Conclusion. A parameterized FE generic passenger vehicle buck model has been created and validated on a population of real life crashes in terms of rib fracture risk. With the current validation status, this model provides the possibility of developing and evaluating new passive safety systems for fragile senior occupants. Further, an injury mechanism responsible for the increased number of outboard rib fractures seen in small overlap and near-side oblique frontal impacts has been proposed and analyzed.

Place, publisher, year, edition, pages
Umeå: Umeå University , 2015. , 68 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1731
Keyword [en]
EDR, Real life crashes, Oblique, Finite element, Simulation, HBM, Injury mechanism, Pulse shape, Stochastic, Rib fracture, THUMS, Generic, Statistics
National Category
Surgery
Research subject
biomechanics; injury prevention
Identifiers
URN: urn:nbn:se:umu:diva-102927ISBN: 978-91-7601-293-2 (print)OAI: oai:DiVA.org:umu-102927DiVA: diva2:811579
Public defence
2015-06-05, Sal D, Tandläkarhögskolan 9 trappor, Norrlands Universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Projects
Vinnova Project: Real Life Safety Innovations
Funder
VINNOVA, 2009-02780 ; 2011-03679
Available from: 2015-05-13 Created: 2015-05-11 Last updated: 2015-05-13Bibliographically approved
List of papers
1. Analysis of Delta Velocity and PDOF by Means of Collision Partner and Structural Involvement in Real-Life Crash Pulses With Modern Passenger Cars
Open this publication in new window or tab >>Analysis of Delta Velocity and PDOF by Means of Collision Partner and Structural Involvement in Real-Life Crash Pulses With Modern Passenger Cars
2014 (English)In: Traffic Injury Prevention, ISSN 1538-9588, E-ISSN 1538-957X, Vol. 15, no 1, 56-65 p.Article in journal (Refereed) Published
Abstract [en]

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 (V) 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 V between EDR measurements and WinSMASH calculations. Methods: NASS-CDS inclusion criteria were model-year 2000 through 2010 automobiles, frontal crashes with V higher than 16km/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 V at the time of peak longitudinal V. This angle was compared to the NASS-CDS investigator's estimated PDOF with regard to structural engagement and the collision partner or object. Multiple linear regression was used to establish adjustment factors on V 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 V 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 V 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 V 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 publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Place, publisher, year, edition, pages
Taylor & Francis, 2014
Keyword
EDR, real life, PDOF, delta velocity, small overlap, multiple linear regression
National Category
Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:umu:diva-84503 (URN)10.1080/15389588.2013.793796 (DOI)000327421900009 ()
Available from: 2014-01-15 Created: 2014-01-08 Last updated: 2017-12-06Bibliographically approved
2. Influence of Vehicle Kinematic Components on Chest Injury in Frontal-Offset Impacts
Open this publication in new window or tab >>Influence of Vehicle Kinematic Components on Chest Injury in Frontal-Offset Impacts
2014 (English)In: Traffic Injury Prevention, ISSN 1538-9588, E-ISSN 1538-957X, Vol. 15, no Supplement 1, S88-S95 p.Article in journal (Refereed) Published
Abstract [en]

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%.

Place, publisher, year, edition, pages
Taylor & Francis, 2014
Keyword
yaw rotation, intrusion, small overlap, oblique, simulation, approximation
National Category
Surgery
Research subject
biomechanics
Identifiers
urn:nbn:se:umu:diva-102938 (URN)10.1080/15389588.2014.933477 (DOI)000354471600013 ()25307403 (PubMedID)
Funder
VINNOVA, 2011-03679
Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2017-12-04Bibliographically approved
3. Pulse shape analysis and data reduction of real life crashes with modern passenger cars
Open this publication in new window or tab >>Pulse shape analysis and data reduction of real life crashes with modern passenger cars
2015 (English)In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 20, no 6, 535-546 p.Article in journal (Refereed) Published
Abstract [en]

The increased use of computer simulations such as finite element modelling for evaluating passive safety applications has made it possible to simplify and parameterize complex physical processes. Crash pulses derived from laboratory tests have been used in many studies to evaluate and optimize 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 optimize passive safety systems for the wide variety of scenarios experienced during real-life crashes, there is a need to study and characterize this variation. In this study, crash pulses from real-life crashes as recorded by event data recorders were parameterized, and the influence of vehicle and crash variables was analysed. The pulse parameterization 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 optimizing passive safety systems that are robust to the wide variation in real-life crashes.

Place, publisher, year, edition, pages
Taylor & Francis, 2015
Keyword
EDR, real-life crash, pulse shape, eigenvalue analysis, frontal crash
National Category
Surgery Mechanical Engineering
Research subject
biomechanics
Identifiers
urn:nbn:se:umu:diva-102939 (URN)10.1080/13588265.2015.1057005 (DOI)000362878500002 ()
Funder
VINNOVA, 2011-03679
Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2017-12-04Bibliographically approved
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
Open this publication in new window or tab >>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
2016 (English)In: Accident Analysis and Prevention, ISSN 0001-4575, E-ISSN 1879-2057, Vol. 95, 42-56 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2016
Keyword
Stochastic simulation, Logistic regression, Rib fracture, Generic model, THUMS, HBM
National Category
Surgery Public Health, Global Health, Social Medicine and Epidemiology
Research subject
biomechanics
Identifiers
urn:nbn:se:umu:diva-102941 (URN)10.1016/j.aap.2016.06.020 (DOI)000383527600006 ()27393912 (PubMedID)
Funder
VINNOVA, 2011-03679
Note

Originally published in theses in manuscript form.

Available from: 2015-05-11 Created: 2015-05-11 Last updated: 2017-12-04Bibliographically approved
5. Evaluation of chest injury mechanisms in nearside oblique frontal impacts
Open this publication in new window or tab >>Evaluation of chest injury mechanisms in nearside oblique frontal impacts
Show others...
2013 (English)In: Annals of advances in automotive medicine, ISSN 1943-2461, Vol. 57, 183-196 p.Article in journal (Refereed) Published
Abstract [en]

Despite the use of seat belts and modern safety systems, many automobile occupants are still seriously injured or killed in car crashes. Common configurations in these crashes are oblique and small overlap frontal impacts that often lead to chest injuries.To evaluate the injury mechanism in these oblique impacts, an investigation was carried out using mathematical human body model simulations. A model of a simplified vehicle interior was developed and validated by means of mechanical sled tests with the Hybrid III dummy. The interior model was then combined with the human body model THUMS and validated by means of mechanical PMHS sled tests. Occupant kinematics as well as rib fracture patterns were predicted with reasonable accuracy.The final model was updated to conform to modern cars and a simulation matrix was run. In this matrix the boundary conditions, ΔV and PDOF, were varied and rib fracture risk as a function of the boundary conditions was evaluated using a statistical framework.In oblique frontal impacts, two injury producing mechanisms were found; (i) diagonal belt load and (ii) side structure impact. The second injury mechanism was found for PDOFs of 25°-35°, depending on ΔV. This means that for larger PDOFs, less ΔV is needed to cause a serious chest injury.

Place, publisher, year, edition, pages
Association for the Advancement of Automotive Medicine, 2013
National Category
Surgery
Identifiers
urn:nbn:se:umu:diva-90978 (URN)24406957 (PubMedID)
Conference
57th AAAM Annual Conference, Annals of Advances in Automotive Medicine, September 22-25, 2013
Available from: 2014-07-04 Created: 2014-07-04 Last updated: 2015-08-14Bibliographically approved

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