This paper on "FE Simulation of a Circular Keypad - Combined Use of Tests and Modelling Techniques" was presented at the NAFEMS World Congress on The Evolution of Product Simulation From Established Methods to Virtual Testing & Prototyping - 24-28 April 2001, The Grand Hotel, Lake Como, Italy.

Abstract

A rubber/elastomer product like a keypad exhibiting hyperelastic hysteretic material behaviour must sustain practically an unlimited number of perpetual loading and unloading without any damage. Besides strength, there are other imperative issues: The performance of such a product and its acceptance by the proper client depends primarily on some characteristic parameters (so called actuation force with related displacement, contact force, snap ratio, etc.) which can be derived from its specific force - displacement curve. This curve varies strongly depending on the shape i.e. geometry of the product and on the rubber properties including hardness. Due to inherent nonlinearities it is practically not straight forward to predict such a curve by means of the uniaxial test data of the material alone. Normally, its optimisation according to the product specification requires several measurements on many prototypes of the end product which can be a time consuming and expensive process. For the industry producing rubber end products it is of crucial importance to shorten the development phase by means of powerful simulation techniques based on finite element method with hyperelastic material modelling capabilities.
Within the framework of the evaluation of possible tools and procedures allowing for efficient product optimisation Sulzer performed recently a parametric study for Abatec-Maag Ltd. After adjustment of the main parameter concerning OGDEN type of material modelling by means of experimental data several simulations for the keypad have been carried out on axisymmetric ABAQUS FE models, consisting of 500 elements only. These investigations aimed firstly to quantify the repeatability of the product tests under "operational conditions" and on the other hand to find out the influence of the overall size and the contribution of small geometric modifications (i.e. fillets) on the stiffness characteristics of the product. The combined use of experimental data and simulation techniques has proved to be an efficient tool for product design and for better understanding of its mechanical behaviour. The results obtained as well as their comparison with the experimental data wherever possible are presented and interpreted in this paper. Potential causes of some shortcomings, i.e. poor agreements between test and analysis results, and possible steps for improvements are discussed also.