A viscoelastic bump stop model for multi-body simulations based on impact test data

The studied bump stop is a hollow folded polyurethane cylinder mounted around the damper rod in a MacPherson front wheel suspension, restricting the upward wheel displacement. It is a critical component for durability since the force transfer through the bump stop determines the vertical peak loads to the car body. In extreme load cases as driving over a curb, the bump stop is subjected to impact loading giving a highly non-linear behavior. The nominal compressive strain can reach 80% under a load duration of milliseconds. The presented model is based on impact test data. By performing drop tests, high load levels and short contact times can be combined, giving a realistic loading in view of road load data from the test track. The main objective of the model is to predict the behavior at high strain rates and strain levels. The strongly progressive behavior, shown in a stress strain diagram, both in terms of the loading curve and the hysteresis, requires special attention. The main feature of the model is a linear viscoelastic Maxwell model combined with a function that takes care of the strongly progressive behavior. This function, obtained from a dynamic loading curve in the impact test, is multiplied with the Maxwell stress, giving the sought progressive behavior. The model is accurate, simple to obtain from the impact test, computationally efficient, and easy to implement in commercial multi-body-system codes as ADAMS and can thus successfully be used in the product development of new cars.