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Technical Paper

Improvements to the SMAC Program

1983-02-01
830610
The Simulation Model of Automobile Collisions (SMAC) computer program has seen more than a decade of use under NHTSA auspices. Although SMAC has proven itself to be a useful investigative tool, the program has several shortcomings which either have been addressed by the authors or need to be addressed by further work. This paper presents the results of our ongoing work to improve SMAC and our recommendations for further work. Those model features discussed herein which either have been or need to be revised consist of (1) the calculation of crush forces when penetration is deep (2) the representation of the vehicles' crush pressure vs deflection relationship and (3) the distribution of tire normal forces in reaction to pitch and roll. An input interfacing program called SMACED has been written and is discribed. This editing program greatly simplifies the use of SMAC and will be found particularly useful for the inexperienced or infrequent SMAC user.
Technical Paper

A Repeated-Crash Test Technique for Assessment of Structural Impact Behavior

1986-02-24
860208
An economical alternative technique is presented for obtaining vehicle frontal crush characteristics from a series of repeated low speed barrier crashes. Results were analyzed using a technique of linear correlation of residual crush depth with a defined crush energy parameter. The data compared closely with crashes reported in the literature, and suggested that the structure exhibits only a slight strain rate sensitivity. Crush energy is shown to correlate well with dynamic crush depth. Relations among dynamic and residual crush and recovery distance are reported, Velocity restitution is shown to be about constant at 15% over the impact velocity range employed. A force-deflection relation based on the offset force linear harmonic oscillator theory is suggested, shown to agree quite well with data. Repeated crash testing can be an effective method to obtain information needed for development of analytical and predictive tools useful in design and reconstruction.
Technical Paper

Inaccuracies in the CRASHS Program

1985-02-25
850255
The CRASH3 computer program, a well known and useful tool in accident reconstruction, is shown to be innaccurate by comparison with car-to-car crash test data. Claims for accuracy of about 10 percent cannot be validated. Both the impact model and the damage only model yield results which are in error. Cases involving error well in excess of 20 percent are demonstrated. These inaccuracies are due primarily to the omission of terms in the formulation of the energy equation and to the sensitivity of the solution to the input estimate of principle-direction-of-force.
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