Problems of identification of strength properties of rubber materials for purposes of numerical analysis: a review

Proper selection of elements of an industrial-grade adhesive joint consisting of various types of rubber materials, supported by a detailed analysis of the phenomena occurring within the joint, especially with respect to fatigue performance, is still a very difficult and largely unresolved issue. Only single studies using FEM numerical modelling have made attempts at assessing and analyzing the phenomena occurring within the joining area of a rubber conveyor belt. This has been caused by a number of problems that have made obtaining reliable and repeatable results impossible, including the problem of defining appropriate material models for the rubbers of the individual layers of the belt and the joint, which introduce strong non-linear effects into the calculations. Rubber as an adhesive base and a construction material is unique, and its properties can be quite diverse dependent on its composition, content of additives, etc. A vulcanized rubber composition, for instance, consists of one or more rubbers and different types of additives which shape its future properties. That is why solution of the problem of identification of the strength properties of this type of materials for developing an adequate numerical model of an adhesive joint is an important issue from the point of view of industrial application of this method of bonding rubber materials; and especially so that expertise in proper use of appropriate adhesives and appropriate joining parameters is indispensable for obtaining optimal properties and maintenance characteristics of the joint. A typical error in preparing material models of rubber is that strength tests for determining stresses and strains are conducted with reference to the initial value of a specimen's cross-section. A large, unanalyzed reduction in the area of the specimen during a strength test has a significant effect on the precision of a FEM model of the analyzed structure. This article analyzes this problem with regard to the modelling of adhesive bonding of rubber materials with a rubber adhesive by presenting a mode of action to be adopted in identifying the strength characteristics of the analyzed materials which eliminates the imprecision of the FEM model.