Clifford C. Chou

MATHEMATICAL MODELLING, SIMULATION AND EXPERIMENTAL TESTING OF BIOMECHANICAL SYSTEM CRASH RESPONSE

A review of mathematical models simulating biodynamic response to impact acceleration is given along with the associated experimental validation studies that have been performed. The types of models surveyed include gross motion simulators, head injury models, and spinal and thoracic models. Sufficient details are provided to indicate to potential users their applicability and relative cost.

A literature review of rollover test methodologies

This paper presents a literature review of test methods that have been used to provide data for development of rollover occupant protection systems, including rollover sensor algorithms, test methodologies, and restraint-system performance. Test methods reviewed in this paper include SAE J2114, side curb trip, corkscrew ramp, critical sliding velocity, deceleration rollover sled, ditch/embankment, soil trip and various misuse tests. Historical development, procedure, application and the experience with these methods are discussed. Pros and cons of these test methodologies are summarised in relation to the rollover sensing algorithm and rollover occupant protection system development. Remarks related to test methodologies are made and issues pertaining to repeatability and dummy performance are discussed. Various component test methodologies are also reviewed and a newly developed component test device is presented. A brief review of CAE methodology and trends in test methods are also given.

A numerical investigation of factors affecting cervical spine injuries during rollover crashes.

Study Design. Factors affecting the risk of cervical spine injury in rollover crashes were investigated using a detailed finite element human head-neck model. Objective. Analyze systematically neck responses and associated injury predictors under complex loading conditions similar to real-world rollover scenarios and use the findings to identify potential design improvements. Summary of Background Data. Although many previous experimental and numerical studies have focused on cervical spine injury mechanisms and tolerance, none of them have investigated the risk of cervical spine injuries under loading condition similar to that in rollovers. Methods. The effects of changing the coefficient of friction (COF), impact velocity, padding material thickness and stiffness, and muscle force on the risk of neck injuries were analyzed in 16 different impact orientations based on a Taguchi array of design of experiments. Results. Impact velocity is the most important factor in determining the risk of cervical spine fracture (P = 0.000). Decreases in the COF between the head and impact surface can effectively reduce the risk of cervical spine fracture (P = 0.038). If the COF is not 0, an impact with lateral force component could sometimes increase the risk of cervical spine fracture; and the larger the oriented angle of the impact surface, the more important it becomes to reduce the COF to protect the neck. Soft (P = 0.033) and thick (P = 0.137) padding can actually decrease the neck fracture risk, which is in contrast to previous experimental data. Conclusion. A careful selection of proper padding stiffness and thickness, along with a minimized COF between the head and impact surface or between the padding and its supporting structure, may simultaneously decrease the risk of head and neck injuries during rollover crashes. A seatbelt design to effectively reduce/eliminate the head-to-roof impact velocity is also very crucial to enhance the neck protection in rollovers.

A REVIEW OF MATHEMATICAL OCCUPANT SIMULATION MODELS

This chapter reviews the basic features of some mathematical occupant simulation models. Models reviewed include 2D/3D complicated gross-motion simulators, such as MADYMO 2D/3D and CAL3D, an integrated crash victim simulator (CVS) model with various finite element analysis (FEA) airbag models and their couplings with CVS programs for automotive safety applications. Historical development, analytic formulation/solution, experimental validation, application, and the experience with these models is discussed. Development trends in FEA approaches by integrating structure/occupant simulation models for safety/crashworthiness analysis are also discussed, and state-of-the-art simulation models for predicting injuries of human brain, neck, and lower extremities are presented.

ON THE KINEMATICS OF THE HEAD USING LINEAR ACCELERATION MEASUREMENTS

Abstract The paper deals with an application of the nine accelerometer scheme proposed by Padgaonkar et al. (1975) to the analysis of the head kinematics including the head angular acceleration and velocity using linear acceleration measurements. The computed results have been compared with the film analysis and with the actual measured quantities in the case of the dummy experiments. The study reveals an excellent agreement among these results and indicates the feasibility of the application of the method to biomechanical studies.

Using a gel/plastic surrogate to study the biomechanical response of the head under air shock loading: a combined experimental and numerical investigation

A combined experimental and numerical study was conducted to determine a method to elucidate the biomechanical response of a head surrogate physical model under air shock loading. In the physical experiments, a gel-filled egg-shaped skull/brain surrogate was exposed to blast overpressure in a shock tube environment, and static pressures within the shock tube and the surrogate were recorded throughout the event. A numerical model of the shock tube was developed using the Eulerian approach and validated against experimental data. An arbitrary Lagrangian-Eulerian (ALE) fluid–structure coupling algorithm was then utilized to simulate the interaction of the shock wave and the head surrogate. After model validation, a comprehensive series of parametric studies was carried out on the egg-shaped surrogate FE model to assess the effect of several key factors, such as the elastic modulus of the shell, bulk modulus of the core, head orientation, and internal sensor location, on pressure and strain responses. Results indicate that increasing the elastic modulus of the shell within the range simulated in this study led to considerable rise of the overpressures. Varying the bulk modulus of the core from 0.5 to 2.0 GPa, the overpressure had an increase of 7.2%. The curvature of the surface facing the shock wave significantly affected both the peak positive and negative pressures. Simulations of the head surrogate with the blunt end facing the advancing shock front had a higher pressure compared to the simulations with the pointed end facing the shock front. The influence of an opening (possibly mimicking anatomical apertures) on the peak pressures was evaluated using a surrogate head with a hole on the shell of the blunt end. It was revealed that the presence of the opening had little influence on the positive pressures but could affect the negative pressure evidently.

Modeling of the Brain for Injury Prevention

From an ethical point of view, it is extremely difficult to propose a well-controlled human subject study aimed at understanding brain injury mechanisms and establishing the associated tolerance values. For this reason, many numerical models of the human and animal head or brain have been developed over the past several decades in an attempt to obtain in-depth insights into brain injury biomechanics, minimizing the need for human subject research. This chapter highlights and contrasts the essence of human and animal head numerical models developed for studying blunt impact and blast-induced brain injuries. Even with the vast amount of literature produced by these investigations and studies, the precise mechanisms of brain injury have not yet been fully established to date. Through this review, it is clear that a lot of information can be garnered by numerical brain modeling but few efforts have been devoted so far in using these numerical models to provide guidelines in the discovery of brain injury mechanisms. Based on the brain models reported in the current literature, there are some inherent deficiencies. However, with further revisions and improvements to the currently available models, as opposed to developing new models from scratch, these issues can be overcome, and the state of the art can be advanced. More research effort into brain injury mechanisms, especially under in vivo conditions, is needed for computational model improvements so that the injury mechanisms can be thoroughly understood and effective countermeasures for protecting human from traumatic brain injury can be developed.

Development of foam models as applications to vehicle interior

In this study, experimental studies were conducted to obtain the properties of various foam materials. Finite element foam models were developed using LS-DYNA3D and the model predictions were validated against the experimental results. Numerous simulations were carried out for foams subjected to different loading conditions including the static compression, indentation, and tensile tests, and dynamic impacts with a featureless and a spherical headform. Comparisons of predicted and experimental results such as the headform response, which were predicted prior to an experimental verification, showed excellent correlations for all the cases. Language: en

A review of side impact component test methodologies

Development of a vehicle in meeting various side impact performance requirements entails countermeasures (Side Airbags (SAB), door trims, EA foams, etc.) development and assessment using component and subsystem testing and analytical methods. Final occupant performance is verified using prototype testing at full vehicle level that are extensive and time-consuming. To expedite the timely development and assessment of countermeasures, component test methodologies were developed. This paper presents a literature review of side impact component test methodologies that have been used to aid in countermeasures development for occupant protection in various side impact test modes. Test methods reviewed in this paper were not exhaustive, but included a majority of developments beginning from the late 1980s to date. Component/subsystem methodologies presented in this paper are simplified tools for countermeasures development to meet FMVSS 214, Lateral Impact New Car Assessment Programme (LINCAP), Insurance Institute for Highway Safety (IIHS) or European side impact tests. Descriptions and remarks on each methodology are discussed. The state-of-the-art side impact component test methodology is summarised in relation to their test procedure, test mode, body component involved, key parameters, side structure used, sensor signals considered and CAE and test facility used. In addition, some basics of side impact testing are reviewed with analysis of velocity profiles. Recent developments in component/subsystem test methodologies are also presented, including a CAE-driven test method.

Image Analysis of Rollover Crash Tests Using Photogrammetry

This paper presents an image analysis of a laboratory-based rollover crash test using camera-matching photogrammetry. The procedures pertaining to setup, analysis and data process used in this method are outlined. Vehicle roll angle and rate calculated using the method are presented and compared to the measured values obtained using a vehicle mounted angular rate sensor. Areas for improvement, accuracy determination, and vehicle kinematics analysis are discussed. This paper concludes that the photogrammetric method presented is a useful tool to extract vehicle roll angle data from test video. However, development of a robust post-processing tool for general application to crash safety analysis requires further exploration.