ABSTRACT
In modeling structural crash dynamics, a broad-brush approach is often taken, just as we saw for rollover analysis in Chapter 16. Of course, detailed finite element models of a crashing vehicle are available, but they are not commonly used for reconstruction purposes. In a vehicle, the structural elements are known as load paths, and a stiffer load path carries more of the load than a flexible one. As forces travel through the load paths, they are distributed into the vehicle body, until they are entirely dissipated by the time they reach the opposite (unloaded) surface of the body.
Each load path has a force–deflection curve. In crash dynamics, such curves go well beyond the elastic limit, and generally reflect both loading and unloading (and possibly reloading). Energy is absorbed when the loading and unloading paths are different; restitution occurs according to the shape of the unloading portion. A single-degree-of-freedom analytical model is used to show the effects. It is also employed to illustrate the difference between large and small cars in barrier crashes, and to examine impacts with narrow fixed objects. Chapter 17 also uses a two-degree-of-freedom model to illustrate some basic truths about vehicle-to-vehicle crashes, particularly when a large car hits a small car. Other topics discussed include barrier equivalence, load–deflection curves from crash tests, and measures of crash severity.
