Stephen W. Rouhana

Physical and chemical characterization of airbag effluents

OBJECTIVE This paper describes a study aimed at characterizing the exposure to physical and chemical by-products from the deployment of airbag restraint systems. DESIGN, MATERIALS AND METHODS Specifically, the levels of particulates and the composition of gases and bag fabric speed were measured in the passenger compartment following deployment of either a drivers side or drivers side/passengers side airbag system. MEASUREMENTS A Fourier transform infrared analyzer (FTIR) and chemiluminescence analyzers were used for gas analysis, a cascade impactor and gravimetric filter measurements for aerosol determination and high-speed films to determine fabric speed. MAIN RESULTS AND CONCLUSIONS The measured gases were found to be within the recommended guidelines for human exposures, but no guidelines exist for particle exposures of this magnitude (150-220 mg/m3) but short duration. High-speed films were also taken of the deployments to obtain an estimate of the fabric speed as it leaves the module. The maximum average speed for both types of airbag was approximately 100 mph and in both cases average speeds ranged from lows near 50 mph to highs of over 200 mph.

THE BIOMECHANICAL ASPECTS OF PEDESTRIAN PROTECTION

In this paper, a biomechanical basis for pedestrian protection is presented based on reviews of epidemiological and biomechanical studies conducted over the last three decades. Epidemiological studies reveal the nature and cause of pedestrian crashes and injuries sustained in the field. The various factors that influence pedestrian crashes and fatalities such as pedestrian demographics, time and location of crash, type of vehicles involved and their design characteristics, impact speeds, and nature and severity of injuries sustained are covered in the epidemiology section. The biomechanical studies identify the injury mechanisms and the biomechanical tolerances. Several biomechanical studies that attempt to identify the injury mechanisms and quantify the tolerances are critically reviewed in this paper, and the existing gaps in literature are identified. Further, the three primary injury mechanisms for pedestrian lower extremity injuries are highlighted, and an injury mechanism for depressed tibial fracture is hypothesised. The effect of exterior vehicle parameters such as bumper height, bumper stiffness, hood length, hood stiffness, bumper lead angle on the nature and severity of injuries sustained are also discussed. The biomechanical injury criteria and tolerance values in a proposed draft ECE pedestrian regulation are also presented. Finally, conclusions are drawn based on the epidemiological and biomechanical studies, which lead to a proposal for future work.

Development of a Six-Year Old Digital Human Body Model for Vehicle Safety Analysis

Biomechanical differences between children and adults are anatomically obvious and physiologically evident. Nevertheless, scaling laws have been used between child and adult mechanical properties in biomechanical injury studies. These laws may or may not be valid depending on the aging properties of the tissue being studied. Detailed adult human body finite element models have been developed in recent years, but not for children. Therefore, the objective of this study is to develop an industry-first, full-body digital human finite element (FE) model of a six-year old child aimed at helping improve vehicle safety for children and also validating the scaling laws between child and adult mechanical properties.The child digital model was developed based on CT scan images from a living six-year old child++. Model geometry was extracted from the CT scans through image analysis. Finite element (FE) mesh for different parts of the body was created from the geometric data obtained in the CT scan image analysis process. While the CT scans were taken with the subject supine, the model in this study is in a standing position, representing a pedestrian posture. Biomechanical properties of each component in the model were obtained from the literature. The model includes a detailed anatomical representation of human organs for a six-year old child, from head to toe. Predicted model responses are compared with test data found in the literature. Forces, displacements for the neck, chest, and abdomen; pressures for the brain are output for injury reference analysis. The analysis of the FE model was performed by using LS-DYNA software. Although the geometric accuracy of the six-year child FE model has been ensured by extracting data from living CT scan images, the mechanical property data used in the model and the impact response used for model comparison can only be considered tentative; since these data are sparse in literature.

Impact and injury response of the abdomen

The impact and injury response of the abdomen has been studied using a variety of testing modes on a variety of scales. Much of the research has focused on the whole-body level response of the abdomen to simplified inputs simulating interaction with steering components or restraint systems. These studies generally strive to provide the load vs. penetration response of the abdomen , with some correlation of injury to potential injury metrics, and they attempt to enhance our understanding of possible injury mechanisms. On the structure scale, investigators have examined the response of organ systems (or portions thereof) to impact or quasi-static tension or compression. On the tissue scale, dog bone or plug samples of solid organs have been tested in tension or compression, and cruciate samples of hollow organs have been tested under high-rate equibiaxial stretch.

Finite-Element-Based Transfer Equations: Post-Mortem Human Subjects versus Hybrid III Test Dummy in Blunt Impact

In the present study, transfer equations relating the responses of post-mortem human subjects (PMHS) to the mid-sized male Hybrid III test dummy (HIII50) under matched, or nearly-identical, loading conditions were developed via math modeling. Specifically, validated finite element (FE) models of the Ford Human Body Model (FHBM) and the HIII50 were used to generate sets of matched cases (i.e., 256 frontal impact cases involving different impact speeds, severities, and PMHS age). Regression analyses were subsequently performed on the resulting age-dependent FHBM- and HIII50-based responses. This approach was conducted for five different body regions: head, neck, chest, femur, and tibia. All of the resulting regression equations, correlation coefficients, and response ratios (PHMS relative to HIII50) were consistent with the limited available test-based results. Language: en

Laboratory Experience with the IR-TRACC Chest Deflection Transducer

In 1998, Rouhana et al. described development of a new device, called the IR-TRACC (InfraRed - Telescoping Rod for Asessment of Chest Compression). Tests have been performed with IR-TRACC units at various labs around the world since 1998. A first-generation was retrofit into a Q3 dummy at TNO. Similarly, a mid sized male Hybrid III dummy thorax and a small female Hybrid III dummy thorax have been designed by FTSS such that each contains 4 second-generation IR-TRACC units. The second generation is the result of continued development by FTSS, especially in the areas of the analysis circuit, manufacturing and calibration methods. This paper presents the results of these efforts with the IR-TRACC and the current state of knowledge relative to its use and usefulness.

Development and Validation of a 50th Percentile Male Pedestrian FE Model

The objective of this study was to develop and validate a finite element (FE) human model that represents a 50th percentile adult pedestrian male. The geometry of the previously developed and well validated Ford Human Body (FHB) model was modified to change the posture from driving to standing. The femur, tibia, and fibula were validated against published test data of human bone specimens in different dynamic loading scenarios. The leg model was validated against dynamic, three-point bending test data of human legs from Post Mortem Human Subjects (PMHS). The kinematics and dynamics of the full pedestrian model was validated against PMHS car-pedestrian impact test data under different levels of severity. The model responses were compared with the corresponding published generalized response corridors. In all the component level and full body model simulations the responses from the model correlated well with both the generalized response corridors and the responses from the individual cadavers.© 2010 ASME

Chest Deflection vs. Chest Acceleration as Injury Indicator in Front Impact Simulations Using Full Human Body Finite Element Model

The Ford Motor Company Human Body Finite Element Model (FHBM) was validated against rib dynamic tension and 3-point bending tests. The stress-strain and moment-strain data from the tension and bending simulations respectively were compared with human rib specimen test data. The model used represented a 50th percentile adult male. It was used to compare chest deflection and chest acceleration as thoracic injury indicator in blunt impact and belted occupants in front sled impact simulations. A 150 mm diameter of 23.4 kg impactor was used in the blunt impact simulations with impact speeds of 2, 4, and 8 m/s. In the Front sled impact simulations, single-step acceleration pulses with peaks of 10, 20, and 30 g were used. The occupants were restrained by 3-point belt system, however neither pretensioner nor shoulder belt force limiter were used. The external force, head acceleration, chest deflection, chest acceleration, and the maximum values of Von Mises stress and plastic strain were the model outputs. The results showed that the external contact force, head acceleration, chest deflection, and chest acceleration in the blunt impact simulations varied between 1.5–7 kN, 5–28 g, 18–80 mm, and 8–40 g respectively. The same responses varied between 7–24 kN, 13–40 g, 15–50 mm, and 16–46 g respectively in the front sled impact simulations. The maximum Von Mises stress and plastic strain were 50–127 MPa, and 0.04–2% respectively in the blunt impact simulations and 72–134 MPa, and 0.13–3% respectively in the sled impact simulations.Copyright

Further Validation of the Ford Human Body FE Model and Use of the Model to Investigate the Effects of Shoulder Belt Force Limiting of 3-Point and 4-Point Restraints in Frontal Impact

Ford Motor Company human body FE model was validated against 3-point & 4-point belted PMHS tests in frontal impact and PMHS knee impact. The chest deflection, chest acceleration, and belt force in frontal impact simulations were compared with the PMHS test data, while the impact force, femur acceleration, pelvis acceleration, and sacrum acceleration of the knee impact simulations were compared with the respective corridors from PMHS tests. The model used represents a 50th percentile adult male. It was used to study the effects of shoulder belt force limit on 3-point and 4-point restrained occupants in frontal impacts without airbags. A 25 g pulse and a shoulder belt load limit of 1, 2, 3, 4, 6, and 8 kN were used for the 3-point and 4-point restraint systems with a rigid steering wheel, front header, and windshield of a stiffer larger vehicle structure. The results showed that the head acceleration and the chest deflection of the 4-point belt system are less than the respective cases of the 3-point system while the chest acceleration levels were about the same in 3-point and 4-point belt. The mid-shaft femur forces were always higher in the 4-point belt than those of the 3-point belt.Copyright