Simulation of reiterated mechanical load of silicone rubber

A Peristaltically Actuated Device for Minimally Invasive Surgery (PADeMIS) is being developed at Technical University of Ilmenau. The device consists of compliant segments with cushions. Periodical filling of the cushions leads to a worm-like locomotion. To prevent injuries of the patient PADeMIS has to be compliant and silicone rubber is chosen as the material. During locomotion, some parts of the device will be subject to some thousand load cycles. Optimizing the design with FEA needs a constitutive law of the silicone rubber used. But the mechanical behaviour of this elastomer changes from loading to loading up to some thousand cycles. Hence, simulating the deformation of silicone rubber structures is problematic—because the stress–strain relation is furthermore not only dependent on the present strain. This work shows a possibility to describe the complex mechanical behaviour of the used silicone rubber with modelling the Mullins effect and the decreasing of the maximum stress, reached at same stretch with increasing number of load cycles, called stress softening. The resulting equations were implemented in the FEA program MSC.Marc2005r2 and the results are shown.