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Mitigating injury in side impact has been an important topic of research for decades. In the mid 1980's the American government began a program intended to improve the crashworthiness of vehicles in side impact. This program ultimately led to the introduction of a dynamic side impact test (Federal Motor Vehicle Safety Standard (FMVSS) 214), which new vehicles must pass, along with a very similar test aimed at consumer awareness (New Car Assessment Program (NCAP) side impact test). The work presented in this thesis involved the study and simulation of these tests to evaluate occupant response in side impact, with a focus on the thoracic response.
Car accidents are amongst the most common causes of fatalities for a younger population in developed countries and world-wide. While research using Anthropometric Test Devices (ATDs) has led to improvements in frontal impact occupant protection, epidemiological data on the effectiveness of devices for side impact protection remains inconclusive. Current regulatory physical side impact tests are limited to standardized full-vehicle Moving Deformable Barrier and rigid pole impacts, only one seating position of the occupant, and a unidirectional occupant surrogate (side impact ATD). To address some limitations of the existing research methods, and expand the understanding of the occupant response and potential for injury, numerical Human Body Models (HBMs) have been developed as repeatable, biofidelic, omni-directional, and frangible occupant surrogates. The overall goal of this study was to improve the understanding of the underlying sources of conflicting epidemiological and physical test data on thoracic response in side impacts. This study applied two highly detailed HBMs in parametric investigations with simple to complex impact scenarios ranging from a pendulum, rigid-wall side sled, to a full-vehicle lateral impact and an accident reconstruction. Subsequently, a thoracic side airbag and three-point seatbelt models were developed and integrated with the vehicle model to study the effect of occupant pre-crash position on the potential for injury. Occupant response assessment included global criteria (chest deflection and viscous criterion), local measurements at different thorax levels, spine kinematics, and prediction of rib fracture locations and lung response. This research identified limitations in current analysis methods, demonstrating effects on occupant response of pre-crash arm position, which is known to vary widely among occupants. The magnitude of the arm effect was dependent on the lateral impact scenario, where the occupant response demonstrated the highest sensitivity to arm orientation in the full vehicle impact. The arm position effect was more significant than changes in response to four restraint combinations, where the assessment of the restraint performance was also dependent on the thoracic response measurement locations and method. A parametric study using detailed HBM, vehicle and restraint models provided new understanding of occupant response in side impact crash scenarios.
Although there have been tremendous improvements in crash safety there has been an increasing trend in side impact fatalities, rising from 30% to 37% of total fatalities from 1975 to 2004 (NHTSA, 2004). Between 1979 and 2004, 63% of AIS[greq]4 injuries in side impact resulted from thoracic trauma (NHTSA, 2004). Lateral impact fatalities, although decreasing in absolute numbers, now comprise a larger percentage of total fatalities. Safety features are typically more effective in frontal collisions compared to side impact due to the reduced distance between the occupant and intruding vehicle in side impact collisions. Therefore, an increased understanding of the mechanisms governing side impact injury is necessary in order to improve occupant safety in side impact auto crash. This study builds on an advanced numerical human body model with focus on a detailed thoracic model, which has been validated using available post mortem human subject (PMHS) test data for pendulum and side sled impact tests (Forbes, 2005).
Occupant thoracic injury incurred during side impact automotive crashes constitutes a significant portion of all fatal and non-fatal automotive injuries. The limited space between the impacting vehicle and occupant can result in significant loads and corresponding injury prior to deceleration of the impacting vehicle. Within the struck vehicle, impact occurs between the occupant and various interior components. Injury is sustained to human structural components such as the thoracic cage or shoulder, and to the internal visceral components such as the heart, lungs, or aorta. Understanding the mechanism behind these injuries is an important step in improving the side impact crash safety of vehicles. This study is focused on the development of a human body numerical model for the purpose of predicting thoracic response and trauma in side impact automotive crash. The human body model has been created using a previously developed thoracic numerical model, originally used for predicting thoracic trauma under simple impact conditions. The original version of the thorax model incorporated three-dimensional finite element representations of the spine, ribs, heart, lungs, major blood vessels, rib cage surface muscles and upper limbs. The present study began with improvements to the original thorax model and furthered with the development of remaining body components such that the model could be assessed in side impact conditions. The improvements to the thoracic model included improved geometry and constitutive response of the surface muscles, shoulder and costal cartilage. This detailed thoracic model was complimented with a pelvis, lower limbs, an abdomen and a head to produce the full body model. These components were implemented in a simplified fashion to provide representative response without significant computational costs. The model was developed and evaluated in a stepwise fashion using experimental data from the literature including side abdominal and pelvic pendulum impact tests. The accuracy of the model response was investigated using experimental testing performed on post mortem human subjects (PMHS) during side and front thoracic pendulum impacts. The model produced good agreement for the side thoracic and side shoulder pendulum impact tests and reasonable correlation during the frontal thoracic pendulum impact test. Complex loading via side sled impact tests was then investigated where the body was loaded unbelted in a NHTSA-type and WSU-type side sled test system. The thorax response was excellent when considering force, compression and injury (viscous criterion) versus time. Compression in the thorax was influenced by the arm position, which when aligned with the coronal plane produced the most aggressive form of compressive loading possible. The simplified components provided good response, falling slightly outside experimental response corridors defined as one standard deviation from the average of the experimental PMHS data. Overall, the predicted model response showed reasonable agreement with the experimental data, while at the same time highlighting areas for future developments. The results from this study suggested that the numerical finite element model developed herein could be used as a powerful tool for improving side impact automotive safety.
Motor vehicle crashes claim thousands of lives each year in the US, and injure millions more. The thorax is the region of the body at greatest risk for serious injury, and thus is of interest for increased protection. In order to improve systems providing occupant protection, a better understanding of the thorax is required, particularly for vulnerable occupants. The work of this dissertation is focused on increasing understanding of the thorax, and does so by examining instrumentation commonly used on the thorax, by introducing a novel analysis technique for understanding thoracic characteristics, and finally by presenting response and injury data for side impact loading. The first study presented here provides an answer to the question, “Do chestbands alter thoracic response to impact?” This was accomplished by conducting a series of repeated impacts on two post-mortem human surrogates (PMHS), at the same impact velocity with 0, 1, and 2 chestbands. This was done for various impact speeds for a total of 22 impacts on the two subjects. `Response’ was divided into global response, defined as chest deflection and thoracic stiffness, and local response, defined as the individual rib strain. Results showed no significant difference in global or local response, thus providing support for the commonly held assumption that chestbands do not alter thoracic response to impact.
Thoracic injury is the most dominant segment of automotive side impact traumas. A numerical model that can predict such injuries in crash simulation is essential to the process of designing a safer motor vehicle. The focus of this study was to develop a numerical model to predict lung response and injury in side impact car crash scenarios. A biofidelic human body model was further developed. The geometry, material properties and boundary condition of the organs and soft tissues within the thorax were improved with the intent to ensure stress transmission continuity and model accuracy. The thoracic region of the human body model was revalidated against three pendulum and two sled impact scenarios at different velocities. Other body regions such as the shoulder, abdomen, and pelvis were revalidated. The latest model demonstrated improvements in every response category relative to the previous version of the human body model. The development of the lung model involved advancements in the material properties, and boundary conditions. An analytical approach was presented to correct the lung properties to the in-situ condition. Several injury metric predictor candidates of pulmonary contusion were investigated and compared based on the validated pendulum and sled impact scenarios. The results of this study confirmed the importance of stress wave focusing, reflection, and concentration within the lungs. The bulk modulus of the lung had considerable influence on injury metric outcomes. Despite the viscous criterion yielded similar response for different loading conditions, this study demonstrated that the level of contusion volume varied with the size of the impact surface area. In conclusion, the human body model could be used for the analysis of thoracic response in automotive impact scenarios. The overall model is capable of predicting thoracic response and lung contusion. Future development on the heart and aorta can expand the model capacity to investigate all vital organ injury mechanisms.
Abstract: Thoracic trauma is directly responsible for 25% of all trauma related fatalities and indirectly contributes to another 25%. Since most thoracic trauma is caused by automobile crashes, the need for accurate data regarding thoracic impact grows continuously as more and more cars are on the road. Many of these automobile crashes are side impacts, which lead to a primary direction of force on the person inside to be oblique and anterior to lateral. The purpose of this project is to determine the response of a denuded human thorax to oblique and lateral blunt force impacts. Specifically the project will focus on the linear and rotational stiffness characteristics of a denuded post-mortem human subject (PMHS) thorax. There is a lack of data regarding anterior oblique and posterior oblique thoracic impact response characteristics and this project will focus on obtaining the response of the PMHS thorax to these types of impacts. The current impact tests and anthropomorphic test devices (ATDs) account for frontal and lateral direction crashes only. Response in the oblique direction was previously assumed to be similar to lateral responses, but new research has shown that this may not be the case. This project consisted of both designing the fixture to be used to support the thorax during testing as well as the experimentation and analysis of the results. The thoraces were obtained from fresh post-mortem human subjects and all research was done at the Injury Biomechanics Research Laboratory (IBRL). The data from this project will be used in conjunction with results from other projects at the IBRL in order to determine a more accurate definition of the biomechanical response of the human thorax during a vehicle crash. This data can then ultimately be used to create a new anthropomorphic test dummy thorax for use in crash testing.
[Author abstract] Every year around the world various types of automobile accidents occur, out of which side impact vehicular collisions are the most severe. Of these, side crashes into fixed narrow objects like trees, poles account for quarter percent of total deaths and serious injuries. Moreover these side impacts present a difficult problem for improving automotive crashworthiness because of the limited crushable zone between the vehicle occupant and the intruding door structure. To improve the automotive safety in side impacts a new pole test has been proposed under Federal Motor Vehicle Safety Standard (FMVSS) 214 to make the existing regulation more comprehensive in addressing the critical head and neck injuries in addition to thoracic and pelvis injuries. In this thesis, a finite element model of the Ford Taurus and Moving Deformable Barrier (MDB) as developed by National Crash Analysis Center (NCAC) has been used for the impact analysis. The US DOT-SID side impact dummy taken from MADYMO dummy database has been used as the vehicle occupant and the rigid pole modeled in MSC. Patran software as the narrow object. Computer Simulations have been analyzed according to the new proposed pole test and (FMVSS) 214 regulation. The critical injury values, the occupant kinematics and the structural damage have been compared justifying the need for the new pole test for improving the occupant safety.