Malcolm H Ray

Experience with Cable Median Barriers in the United States: Design Standards, Policies, and Performance

A review of the experience of 23 states on the use and effectiveness of cable median barriers is presented. As of 2007, 23 states have installed more than 4,183 km (2,600 mi) of cable median barriers. Experiences of the pioneering states, such as New York, Missouri, Washington, Oregon, North Carolina and Arizona that initiated the utilization of cable median barrier in the United States are included in this paper. Results of the review show that the use of cable median barriers in depressed medians with moderate slopes had a significant effect on the reduction of cross-median crashes in many states. While these results are encouraging, occasional fatal crossover crashes penetrating the cable barrier still demand attention and improved techniques or procedures for selecting or locating cable median barrier will continue to evolve.

Modeling Tire Blow-Out in Roadside Hardware Simulations Using LS-DYNA

Often when vehicles interact with roadside hardware like guardrails, bridge rails and curbs, the interaction between the roadside hardware and the tire causes the tire to lose its air seal and “blow-out”. Once the seal between the rim and rubber tire is lost, the tire deflates. The behavior of the deflated tire is much different than the behavior of an inflated tire such that when this behavior is observed in real world crashes or in full-scale crash tests, the vehicle kinematics are strongly coupled to the behavior of the deflated tire. Accounting for this behavior in LS-DYNA models is crucial in many types of roadside hardware simulations since the forces generated by the deflated tire often introduce instability into the vehicle that can cause rollover or spinout. This paper will present a method for accounting for tire deflation during LS-DYNA simulations and will present examples of the use of this type of improved model.Copyright

Dynamic Failure Properties of the Porcine Medial Collateral Ligament-Bone Complex for Predicting Injury in Automotive Collisions

The goal of this study was to model the dynamic failure properties of ligaments and their attachment sites to facilitate the development of more realistic dynamic finite element models of the human lower extremities for use in automotive collision simulations. Porcine medial collateral ligaments were chosen as a test model due to their similarities in size and geometry with human ligaments. Each porcine medial collateral ligament-bone complex (n = 12) was held in a custom test fixture placed in a drop tower to apply an axial impulsive impact load, applying strain rates ranging from 0.005 s-1 to 145 s-1. The data from the impact tests were analyzed using nonlinear regression to construct model equations for predicting the failure load of ligament-bone complexes subjected to specific strain rates as calculated from finite element knee, thigh, and hip impact simulations. The majority of the ligaments tested failed by tibial avulsion (75%) while the remaining ligaments failed via mid-substance tearing. The failure load ranged from 384 N to 1184 N and was found to increase with the applied strain rate and the product of ligament length and cross-sectional area. The findings of this study indicate the force required to rupture the porcine MCL increases with the applied bone-to-bone strain rate in the range expected from high speed frontal automotive collisions.

Acceptance criteria for validation metrics in roadside safety based on repeated full-scale crash tests

This paper proposes acceptance criteria for quantitative comparison metrics to be applied in the Verification and Validation (V&V) process of computational models used in roadside safety. Typically, the degree of verification or validation of a numerical model is assessed by qualitatively comparing the shapes of two curves, but qualitative comparisons are subjective and open to interpretation. Using quantitative comparison metrics in the V&V process allows for an objective measure of the reliability of a numerical model. Two comparison metrics were selected from a group of 16 metrics found in the literature. Acceptance criteria suitable to the typical scatter of full-scale crash tests were established by comparing ten essentially identical vehicle redirectional crash tests. Since the tests were as identical as can be achieved experimentally, the values of the quantitative metrics represented the reasonable range for the metric corresponding to matched experiments. Typical residual errors expected in full-scale tests are also discussed.

A Finite Element Parametric Study of Femur Fracture Force in Out-of-Position Seating Positions Fracture Femoral Forces to Abbreviated Injury Scale Level 2+ and 3+

This research aimed at investigating the relationship between the femur forces of an out-of-position vehicle occupant and the potential injury severity occurring to the lower extremities during a frontal car crash. A better understanding and prediction of injuries allows for deriving thresholds to theoretically define values at which injuries could potentially occur, with the purpose of guiding engineers in the design of safer vehicles. A validated Knee-Thigh-Hip (KTH) finite element model of a 50th percentile male was used with the code LSDYNA to explore injury mechanisms in frontal impacts. The KTH joints were positioned at different angles of thigh flexion, adduction and abduction. Values for the Abbreviated Injury Scale (AIS) level 2+ and 3+ were calculated using peak femur forces obtained with the FE simulations and regression equations for predicting KTH injuries developed by Kuppa [1]. The study shows that the probability of KTH bone fracture is higher when the thigh is initially abducted. The study also shows that the probability of KTH bone fracture is lower when the thigh is initially flexed, rather than in a neutral position. When considering combinations of adduction and flexion, results show that the probability of KTH bone fracture is not significantly affected by the angle of thigh flexion. On the other hand, results also show that the probability of KTH bone injury when the thigh is flexed and either adducted or abducted to a relative high angle is lower.Copyright

Quantitative Validation of a Finite Element Model of a Knee-Thigh-Hip Complex of a 50th Percentile Male

Traditionally the validation process of FE models is carried on by visually comparing two curves, respectively from an experimental test and the numerical simulation. A more rigorous way to quantitative compare two curves in the validation process would be provided by comparison metrics.In this work the component validation of the Finite Element model of a Knee-Thigh-Hip complex was carried on by quantitatively comparing the results from the experimental tests with the corresponding numerical curves. An LSDYNA finite element model of the lower extremities was developed and the condyle, pelvis and femur and components were carefully validated using three comparison metrics. The good match.Copyright

Finite Element Investigation of Out-of-Position Failure Modes for the Knee-Thigh-Hip of a 50th Percentile Male During a Frontal Car Crash

The introduction of air bags has reduced injuries to the upper region of the body for occupants of vehicles in frontal crashes, such as head and thorax. Airbags have not, however, improved the safety of occupants with respect to injuries to the lower extremities. Though lower extremity injuries are usually not life threatening, they can have long lasting physical and psychosocial consequences. A validated Knee-Thigh-Hip (KTH) finite element model of a 50th percentile male was used to investigate injury mechanisms during frontal car crashes with the occupant in different positions. Simulations of frontal impacts were performed with the Knee-Thigh-Hip joints at different angles of thigh flexion, adduction and abduction. Results show that the failure mechanism can significantly depend on the occupant position prior to impact. Failure mechanisms in the simulations were compared to results found in literature to ensure the model provides a useful tool for predicting fractures in the lower limb resulting from out-of-position frontal vehicle crashes.Copyright

Validation of a New Finite Element Model for Human Knee Ligaments for Use in High Speed Automotive Collisions

A finite element model of knee human ligaments was developed and validated to predict the injury potential of occupants in high speed frontal automotive collisions. Dynamic failure properties of ligaments were modeled to facilitate the development of more realistic dynamic representation of the human lower extremities when subjected to a high strain rate. Uniaxial impulsive impact loads were applied to porcine medial collateral ligament-bone complex with strain rates up to145 s−1. From test results, the failure load was found to depend on ligament geometric parameters and on the strain rate applied. The information obtained was then integrated into a finite element model of the knee ligaments with the potential to be used also for representation of ligaments in other regions of the human body. The model was then validated against knee ligament dynamic tolerance tests found in literature. Results obtained from finite element simulations during the validation process agreed with the outcomes reported by literature findings encouraging the use of this ligament model as a powerful and innovative tool to estimate ligament human response in high speed frontal automotive collisions.Copyright