Abstract
Numerical simulations are used as a standard tool in automotive industry. Generally, it speeds up development, enables to test and evaluate more variants and select the best one for the final solution.
Explicit finite element solvers are used to simulate crash processes. Despite their fast evolution, their numerical and physical principles are still the same and bring specific restrictions. The need of stable time step for numerical solution (dependency of computation time on size of modelled details) is usually the most limiting issue; the other problem can be that FE solvers generally presume the mesh size uniformity over the whole model. In resume, it is uneasy and ineffective in standard FE code to run a model with regions of different level of details. Unfortunately, it is exactly what is often needed to have physically realistic model with predictive failure behaviour and acceptable computation time.
The reason is that advanced materials with failure work generally well on small elements, but are less precise with growing element size. And material failure plays often the role of bifurcation point in crash process, determining the deformation mode of all structure. Typical example is frontal impact with potential failure of frontal cross member or engine mounting components.
The Multi-Scale-Modelling brought by PAM-CRASH resolves this problem by means of the solver coupling technology. Model is split in several modules, each of them being computed separately and communicating through defined interfaces. Thus, computation runs on the basis of standard model, and at the same time it contains details of selected parts. Effects like crack propagation or brittle failure can then be studied, what is unfeasible on models used for standard crash simulations.
Methodology is demonstrated on frontal impact of Skoda Fabia basic model (courtesy of Skoda Auto). The frontal bumper reinforcement, torque brace and welded transition of tunnel to dashboard are excluded from car. These parts are remodelled by small elements and computed in separate domain with reduced (10 times) time step. Results show detail behaviour and realistic rupture of selected parts. Compared to model without the solver coupling technology, speed up factor of 2.7 (from 34 to 12.5 hours) was reached.
Keywords: numerical simulation, finite elements, PAM-CRASH, solver coupling, material failure