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An engineering approach was developed to extract the failure plastic strain, thinning failure strain, and major in plane failure strain for finite element simulation applications. This approach takes into account the failure strain dependency on the element size when element deletion scheme is invoked in the simulation of material fracture. Both localized necking fracture and tensile shear fracture can be predicted when appropriate elements and material models are used in LS-DYNA simulations. This leads to a more accurate prediction of fracture and tearing in the finite element simulation of vehicle structure and crash loading conditions.

Inertia force during dynamic testing exists in any testing system. A generic system is analyzed using the principle of rigid body dynamics. It is shown that the load recorded by a load cell includes both the load experienced by the test specimen and the inertia force from the mass between the specimen and the load cell, when the load cell is placed on the fixed side of the test specimen. An impact fixture designed for spot weld strength test was then studied as an example. Test data were collected and analyzed to show the effect of inertia on the impact strength of the spot weld.

A previously developed finite element human head/cervical spine model was further enhanced to include the major muscles in the neck. The head/cervical spine model consists of the skull, C1-C7, disks, facets, and all the ligaments in this region. The vertebral bodies are simulated by deformable bodies and the soft tissues in the cervical spine are modeled by nonlinear anisotropic viscoelastic material. The motion segments in the cervical spine model were validated against three-dimensional cadaver test data reported in the literature. To simulate the passive and active muscle properties, the classical Hill muscle model was implemented in the LS-DYNA code and model parameters were based on measurements of cadaver neck musculature. The head/neck model was used to simulate a human volunteer flexion whiplash test reported in the literature. Simulation results showed that the neck muscle contraction and relaxation activities had a significant effect on the head/neck motion.

The purpose of this study is to help understand the thoracic response and injury mechanisms in high-energy, limited-stroke, lateral velocity pulse impacts to the human chest wall. To impart such impacts, a linear impactor was developed which had a limited stroke and minimally decreased velocity during impact. The peak impact velocity was 5.6 ± 0.3 m/s. A series of BioSID and cadaver tests were conducted to measure biomechanical response and injury data. The conflicting effects of padding on increased deflection and decreased acceleration were demonstrated in tests with BioSID and cadavers. The results of tests conducted on six cadavers were used to test several proposed injury criteria for side impact. Linear regression was used to correlate each injury criterion to the number of rib fractures. This test methodology captured and supported a contrasting trend of increased chest deflection and decreased TTI when padding was introduced.

A finite element human thorax model was developed for predicting thoracic injury and studying the injury mechanisms under impact. Digital surface images of a human skeleton and internal organs were used to construct the three-dimensional finite element representation of the rib cage, the heart, the lungs, and the major blood vessels. The mechanical properties of the biological tissues in this model were based on test data found in the literature. The constitutive equations proposed in the literature for describing the mechanical behavior of the heart and the lungs were implemented in the code for modeling these organs. The model was validated against cadaver responses for both frontal and lateral impact. Good correlation between the model and the cadaver responses were achieved for the force and deflection time-histories.

Using finite element technique to model the human cervical spine can be found in a number of publications in the literature. These efforts have illustrated viable techniques and approaches for simulating the three-dimensional motion of the human cervical spine. However, these earlier studies also revealed difficulties due to insufficient geometric description for such a complex structure and the lack of experimental data for characterizing the mechanical behavior of the biological tissues in this anatomical region. Recent advancement of the computer technology has resulted in a large quantity of digital images of the human anatomical structure with high precision. In addition, new experimental techniques have also produced new test data on human biological tissue properties. In this study, we developed a finite element representation of the human cervical spine using detailed 3D anatomical data.

In this study the side airbag design for a large car was investigated. The assessment of the airbag efficacy was based on the TTI response of the SID. In general, large size cars have low TTI values to begin with due to their higher mass, stronger structure, and more spacing between the occupant and the door. The CALOPT optimization program was used to search the design space. We found that for this particular impact environment an airbag design with a high mass flow rate and a large vent resulted in the lowest TTI for the SID. The high mass flow rate enables the airbag to contact the dummy thorax early, which causes the dummy to begin to move away from the door before contact is established with the door. The large vent is necessary to avoid excessive force from the airbag during the dummy/airbag interaction. For the two inflators considered in this study it was found that the less aggressive inflator achieved a marginal reduction of 10% from the baseline TTI response.

In this study a mathematical model was developed for the BIOSID dummy using the CAL3D simulation program. This model was correlated to the dummy impact response using pendulum tests on various body regions, and a side sled test. Favorable comparisons were achieved between the test results and the model responses. This model was then used for identifying optimal side airbag designs for a large car.

A modeling technique was developed to simulate the door/occupant interaction in the FMVSS 214 test. The door components, including all the panels and the side airbag, were modeled by finite elements and the Side Impact Dummy was modeled by rigid segments with finite element contact surfaces. The DYNA3D finite element code and the CAL3D lumped-mass code were coupled together such that features in each program can be utilized in this modeling approach. A numerical scheme was developed to simulate the door crush due to the barrier impact to obtain the proper door interior stiffness. Material constants for the model were derived from the available test data. The model exhibited good correlation with the barrier test data for the dummy acceleration response. Using this model, potential countermeasures, including thorax padding, an armrest design, and a side airbag, were evaluated.

This study examines the combined effects of the passenger airbag and the seat belt on the occupant impact response. It was found that while an airbag is beneficial in reducing unbelted occupant injury, its restraint force is in general additive to that of the belts in a 30 MPH barrier impact and tends to increase belted occupant response numbers. A number of possible design strategies were discussed and the inherent performance trade-offs among various impact conditions were illustrated. Concepts for two types of Adaptive Restraint System (ARS) are discussed which might achieve even greater levels of occupant protection for both belted and unbelted occupants. For a belted occupant, these ARS designs have embedded logic to determine when and how to use an airbag and/or a belt under various impact conditions. These ARS designs try to utilize the combined strengths of the airbag and the seat belt systems. Possible design strategies for these systems were also discussed.

A design strategy to simultaneously address the interaction of two restraint systems (airbag and belt) and two test conditions (FMVSS 208 and NCAP) was investigated. This design strategy was implemented using a math-based methodology for a midsize car passenger side restraint system. A number of airbag and safety belt design variables were examined and optimized resulting in improved NCAP performance for the midsize car used in the simulations. The result of this study shows that this math-based methodology could be used to project the potential performance of restraint systems for future vehicle programs. As is the usual recommended procedure for math-based results of highly complex nonlinear mechanical analyses of the type under consideration herein, test validation should be carried out prior to implementation of specific results in a production program.

A procedure was developed to model the vehicle side impact response. This method uses rigid segments to represent the important structure components such as the door, the upper B-pillar and the lower B-pillar. These rigid segments were connected by joints and spring-damper elements. The moment-rotation and the force-deflection characteristics of the structure are obtained by conducting component tests. Two CAL3D models were constructed based on this approach for a two-door experimental car; one simulating the baseline design and one simulating the modified design with a modification to the R-pillar and the addition of padding. Parametric study indicated that lower TTI and pelvis acceleration found in the modified car were due to the lower B-pillar enhancement. The padding used in the modified car only has a marginal effect. Parametric study also indicated the lower A-pillar enhancement reduced TTI.

A set of algorithms was developed in the CAL3D occupant simulation program to allow belt sliding in a direction perpendicular to the beltline. Such algorithms were used to construct a belt-restrained occupant model that would predict the occurrence of submarining. The lower torso of the previously developed Hybrid III dummy model was improved for more detailed description of the geometry and assessment of abdominal compression due to submarining. The simulation results compared favorably with two sled tests having two different seat angles; one resulted in occupant submarining, one did not. The model was then used to examine a number of design parameters which may influence the occupant submarining tendency. The most dominant design parameters for the vehicle investigated in this study appear to be the the seat back angle (which determines the occupant upper torso angle), and the lap belt angle.

The ‘Harness Model’ in the CAL3D occupant simulation program is improved to incorporate a reference point generation scheme and a new belt slip algorithm. The reference point generation scheme results in more accurate belt geometry and alleviates the need to manually specify the reference points coordinates on the occupant body. The new belt slip algorithm balances the belt force and the friction force at each reference point in a successive fashion. This approach gives satisfactory results and does not have the convergence problem found in the old slip algorithm. These new enhancements were used to developed a model to simulate the Hybrid III dummy response in a barrier test. Good correlation was obtained between the model response and the test results. Parametric studies indicated that the shoulder belt stiffness has a significant effect on the head motion, the abdomen deformation, and the peak shoulder belt force.

This study examines the influence of padding in thorax side impact response under free-flight impact and velocity pulse impact. It was found that padding reduces rib and spine accelerations in both types of impact. However, in free-flight impact, padding reduces chest V and VC response without significant deformation change, while in velocity pulse impact, padding reduces chest V but substantially increases VC and deformation. It appears that free-flight impact lacks spacing effect and the correct velocity profile to simulate the door/occupant impact in car-to-car side collision. On the other hand, velocity pulse impact has the essential characteristics of the door/occupant impact in car-to-car side collision and is a more suitable method for subsystem test.

A previously developed car-to-car side impact model was further exercised in this study. This model consists of a vehicle with a deformable side structure representation, and an occupant simulating the SID dummy impact response. It has been demonstrated that the vehicle model correlates well with side impact test data. The occupant model has similar impact acceleration response as the SID dummy in the head, thorax and pelvis regions. In addition, good correlations were also found in the force-time histories of the thorax region when compared to cadaver drop tests. The model provided insights to the effects of various design parameters such as side structure stiffness and padding. Examining the side structure stiffness effect shows that there is a significant benefit for occupant protection by reducing the amount of intrusion until it is roughly equal to the initial distance between the occupant and the door inner panel.

The Cal3D simulation program was used to study the interaction between the belt restraint systems and a Hybrid III dummy in two sled tests. The elastic properties of the dummy joints and thorax were obtained from static tests. The two belt algorithms in the Cal3D program were compared and simulation results indicated that the “harness model”, which utilizes multi-segment representation for the belt is more suitable than the “simple belt model”, which has only one fixed point on the torso. Simulating a frontal impact of a lap belt restrained dummy indicated that the dummy motion consists of two distinct phases; a forward translation followed by a rotation. During forward translation the belt is primarily in contact with the abdomen while during rotation the belt is interacting with the upper legs. For a lap and shoulder belt restrained dummy, considerable head acceleration was induced by chin/chest impact.