Crash simulation
Important results are the deformations (for example, steering wheel intrusions) of the occupant space (driver, passengers) and the decelerations (for example, head acceleration) felt by them, which must fall below threshold values fixed in legal car safety regulations.
In the years 1970 attempts were made to simulate car crash events with non-linear spring-mass systems after calibration, which require as input the results of physical destructive laboratory tests, needed to determine the mechanical crushing behavior of each spring component of the modeled system.
"First principle" simulations like more elaborate finite element models, however, need only the definition of the structural geometry and the basic material properties (rheology of car body steel, glass, plastic parts, etc.)
The origins of industrial first principle computerized car crash simulation lies in military defense, outer space, and civil nuclear power plant applications.
Upon presentation of a simulation of the accidental crash of a military fighter plane into a nuclear power plant on May 30, 1978, by ESI Group in a meeting organized by the Verein Deutscher Ingenieure (VDI) in Stuttgart, car makers became alerted to the possibility of using this technology for the simulation of destructive car crash tests (Haug 1981).
These experiments culminated in a joint project by the Forschungsgemeinschaft Automobil-Technik (FAT), a conglomeration of all seven German car makers (Audi, BMW, Ford, Mercedes-Benz, Opel, Porsche, and Volkswagen), which tested the applicability of two emerging commercial crash simulation codes.
These simulation codes recreated a frontal impact of a full passenger car structure (Haug 1986) and they ran to completion on a computer overnight.
Now that turn-around time between two consecutive job-submissions (computer runs) did not exceed one day, engineers were able to better understand the crash behavior and make efficient and progressive improvements to the analyzed car body structure.
The combination of Machine learning and CAE tools allowed a much better acceleration of the simulation software.
A crash simulation produces results without actual destructive testing of a new car model.
This way, tests can be performed quickly and inexpensively in a computer, which permits optimization of the design before a real prototype of the car has been manufactured.
Using a simulation, problems can be solved before spending time and money on an actual crash test.
The great flexibility of printed output and graphical display enables designers to solve some problems that would have been nearly impossible without the help of a computer.
Pam-Crash started crash simulation and together with LS-DYNA is a software package which is widely used for application of Finite Element Method.
This method allows detailed modeling of a structure, but the disadvantage lies in high processing unit requirements and calculation time.
In comparison with FEM it has some modeling and boundary condition limitations but its application does not require advanced computers and the calculation time is incomparably smaller.
In a typical crash simulation, the car body structure is analyzed using spatial discretization, that is, breaking up the continuous movement of the body in real time into smaller changes in position over small, discrete time steps.
The discretization involves subdividing the surface of the constituent, thin, sheet metal parts into a large number (approaching one million in 2006) of quadrilateral or triangular regions, each of which spans the area between "nodes" to which its corners are fixed.
According to the explicit finite difference time integration method used by most crash codes, the accelerations, velocities, and displacements of the body are related by the following equations.
In a crash simulation, the fastest significant actions are the acoustic signals that travel inside the structural material.
When using steel, the typical value of the stable time step is about one microsecond when the smallest discrete node distance in the mesh of the finite element model is about 5 millimeters.
