Finite element simulation of the human body in vehicle side impact

Bibliography: leaves 154-166.Accident statistics have shown that automotive side impacts are a major safety problem. The side impact dynamics of an occupant are very complex and difficult to investigate. Industrial research has mainly focused on the impact dynamics of man-made side impact dummies, rather than on the dynamics of real human bodies. Therefore fundamental research of the impact dynamics of real human bodies is rare. The objective of this thesis has been to make a contribution to this research by developing a computer-simulated model of the human body using the finite element technique. Fundamental research has been conducted in the past to investigate the biomechanical impact responses of the human body subjected to lateral impact. For obvious reasons, tests exceeding injury levels are not performed with living humans and hence human cadavers were used. A pendulum mass is usually used in impactor tests to impact the cadaver at different body regions with varying initial velocities. Sled tests are another test procedure, in which cadavers are impacted against a rigid or padded wall by means of a horizontally accelerated sled

Development and Validation of a Generic Finite Element Ribcage to be used for Strain-based Fracture Prediction

Finite element human body models, comprising detailed anatomical descriptions, can complementanthropomorphic test devices (ATDs) in the development of new restraint systems. Human body models (HBMs)can evaluate injury on tissue level, i.e. rib strain can be used to evaluate the risk of rib fracture, although theHBM must accurately predict the rib strain distribution to be effective. Current HBMs are not validated for ribstrain, and it remains unknown if any represent an average-shaped ribcage. Thus, a new generic ribcage wascreated, representing an average male, based on a combination of averaged geometrical and material data fromin-vivo and in-vitro datasets. The ribcage was incorporated into the THUMS AM50 Version 3, resulting in theSAFER HBM Version 9. Validation of ribcage kinetic, kinematics and strain distribution was carried out at threelevels of complexity: anterior-posterior rib bending tests; rigid impactor table-top test; and a 40 km/h frontalsled test. The rib strains in the single rib load case were predicted within \ub1 one standard deviation for 91% of themeasuring points. The biofidelity for the rib strains in the table-top and sled test load cases was deemed ‘fair’using CORA analysis. This study is an important step in the development and validation process of strain-basedrib fracture criteria for HBMs

The Development of Population-Wide Descriptions of Human Rib and Rib Cage Geometry

Elderly individuals, obese individuals, and females all have greater risk of rib fractures and other associated thoracic injuries than younger mid-sized male adults in motor vehicle crashes. Differences in body morphology between these vulnerable populations and the subjects represented by physical or computational human body models is a potential source for this risk disparity, and efforts are required to quantify these differences in order to protect a wider population. We present a novel parametric shape model of the human rib centroidal path using logarithmic spirals. It provides a more accurate and efficient fit than previous models of overall rib geometry, and it utilizes direct geometric properties such rib size, aspect ratio, and "skewness" in its parameterization. The model was fitted to 21,124 ribs from 1000 adult CT scans, and regression analyses produced a flexible rib shape model to build ribs typical for any population of a given age, height, weight, and sex. Significant differences in rib shape were quantified across populations, and a new aging effect was uncovered whereby rib span and rib aspect ratio are seen to increase with age, producing characteristically shallower and flatter overall rib shapes in elderly populations. This effect was more strongly and directly associated with age than previously documented age-related changes in rib angulation. Simulated mechanical loading of ribs showed that the specific changes in shape found with age also had implications on their ability to resist deformation. Stiffness to body-anterior loading was seen to increase with age by up to 30% across a 70-year age difference. Finally, we place ribs into their appropriate thoracic context by building a similar parametric model of the surrounding skeleton. A modular approach is used that ensures accuracy in key geometric measures, and results show the accumulated effects on overall chest shape that come from individual variations in the ribs, spine, sternum, and their relative positions. This study can be used to help build population-specific computational models of the thoracic rib cage. Furthermore, results provide quantitative population corridors for rib shape parameters which can be used to improve the assessment and treatment of rib skeletal deformity and disease.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135879/1/svenho_1.pd

Computational modelling of the scoliotic spine: A literature review

Scoliosis is a deformity of the spine that in severe cases requires surgical treatment. There is still disagreement among clinicians as to what the aim of such treatment is as well as the optimal surgical technique. Numerical models can aid clinical decision-making by estimating the outcome of a given surgical intervention. This paper provided some background information on the modelling of the healthy spine and a review of the literature on scoliotic spine models, their validation, and their application. An overview of the methods and techniques used to construct scoliotic finite element and multibody models was given as well as the boundary conditions used in the simulations. The current limitations of the models were discussed as well as how such limitations are addressed in non-scoliotic spine models. Finally, future directions for the numerical modelling of scoliosis were addressed

Computational modelling of the scoliotic spine: A literature review

open4siScoliosis is a deformity of the spine that in severe cases requires surgical treatment. There is still disagreement among clinicians as to what the aim of such treatment is as well as the optimal surgical technique. Numerical models can aid clinical decision-making by estimating the outcome of a given surgical intervention. This paper provided some background information on the modelling of the healthy spine and a review of the literature on scoliotic spine models, their validation, and their application. An overview of the methods and techniques used to construct scoliotic finite element and multibody models was given as well as the boundary conditions used in the simulations. The current limitations of the models were discussed as well as how such limitations are addressed in non-scoliotic spine models. Finally, future directions for the numerical modelling of scoliosis were addressed.Marco Viceconti and Giorgio Davico were supported by the EU funded project Mobilise-D. The charity Reuse-WithLove is gratefully acknowledged for the financial support to this research.openGould, Samuele L; Cristofolini, Luca; Davico, Giorgio; Viceconti, MarcoGould, Samuele L; Cristofolini, Luca; Davico, Giorgio; Viceconti, Marc

Development of an Experimental Model to Quantify Lumbar Spine Kinematics during Military Seat Ejection

The initial phase of a military ejection sequence exerts substantial axial loads on the spinal column. Eccentric inertial loading on the thoracolumbar spine can lead to injury. Most serious injuries due to ejection are in the form of a vertebral fracture, most commonly occurring at the thoracolumbar junction. The objective of the current study was to understand characteristics of a military seat ejection by employing an experimental model designed to simulate the boost or in-rail phase. The model incorporates realistic boundary conditions and is capable of quantifying metrics associated with injury tolerance such as applied accelerations and resultant loads and spinal kinematics. A total of four human cadaveric spine specimens (T12-L5) were tested. The test matrix consisted of two parts. The first part subjected specimens to sub-failure loading to outline spinal kinematics during dynamic vertical acceleration. The second part of the test matrix consisted of acceleration tests designed to induce compression and/or burst fractures as sustained by military aviators during ejection. The developed experimental model is the first to simulate realistic inertial loading during ejection-type accelerations using isolated osteoligamentous spines and may provide imperative injury mechanism data for future safety design considerations

An Investigation of the Effect of Trunk Musculature on the Lumbar Spine Injury During a High-Speed Frontal Central Crash

Motor vehicle crashes have been a leading cause of fatalities and injuries worldwide. Owing to new protection systems, the occurrence of injuries has been decreasing in recent years. On the contrary, the incidence of lumbar spine injuries in frontal crashes has been increasing as a function of the vehicle model year. However, only a few studies focused on lumbar spine injuries in vehicle crashes. Therefore, the mechanism of lumbar spine injuries has not been understood thoroughly. Muscle contraction is one of the factors that influence the risk of lumbar spine injuries as occupants tend to brace their muscles during a vehicle crash. Greater muscle contraction, especially anticipatory muscle contraction, may contribute to bony injury. This study aimed to investigate the effect of lumbar muscle activation and the timing of muscle activation on the lumbar spine injury risk during a high-speed frontal central crash by utilizing a finite element human body model. The study implemented lumbar musculature on two versions of the validated models against the experimental results from a previous study. Sixteen simulations with 8 of each version were set up. These 8 simulations included: fully activated at 0ms, 40ms, and 80ms; half activated at 0ms, 40ms, and 80ms; no activation and no muscle. The model was seated in a simplified vehicle seat extracted from a common vehicle model and was in a frontal pole/tree (central) crash scenario with an initial speed of 56km/h. Each simulation ran for 150ms and forces on vertebrae L1, L3 and L5 were collected. The results showed the lumbar spine forces increased with the muscle activation level and decreased with the timing of the muscle activation. This suggested that the anticipatory powerfully braced lumbar muscles had a higher risk to induce lumbar spine injuries. Since it is impossible to train occupants to avoid bracing in anticipation of a frontal crash, this study focuses the attention on enhanced protection for the lumbar region of vehicle occupants in the future

Development of a Human Body Model for the Analysis of Side Impact Automotive Thoracic Trauma

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

The influence of impact speed on chest injury outcome in whole body frontal sled impacts

While the seatbelt restraint has significantly improved occupant safety, the protection efficiency still needs further enhance to reduce the consequence of the crash. Influence of seatbelt restraint loading on chest injury under 40 km/h has been tested and documented. However, a comprehensive profiling of the efficiency of restraint systems with various impact speeds has not yet been sufficiently reported. The purpose of this study is to analyse the effect of the seatbelt load-ings on chest injuries at different impact speeds utilizing a high bio-fidelity human body Finite Element (FE) model. Based on the whole-body frontal sled test configuration, the current simulation is setup using a substitute of Post-Mortem Human Subjects (PMHS). Chest injury outcomes from simulations are analysed in terms of design variables, such as seatbelt position parameters and collision speed in a full factorial experimental design. These outcomes are specifically referred to strain-based injury probabilities and four-point chest deflections caused by the change of the parameters. The results indicate that impact speed does influence chest injury outcome. The ribcage injury risk for more than 3 fractured ribs will increase from around 40 to nearly 100% when the impact speed change from 20 to 40 km/h if the seatbelt positioned at the middle-sternum of this study. Great injuries to the chest are mainly caused by the change of inertia, which indicates that chest injuries are greatly affected by the impact speed. Furthermore, the rib fracture risk and chest deflection are nonlin-early correlated with the change of the seatbelt position parameters. The study approach can serve as a reference for seatbelt virtual design. Meanwhile, it also provides basis for the research of chest injury mechanism