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A key challenge in engineering design with elastomers for automotive applications, such as chassis suspension mounts and engine mounts, is to integrate fatigue life calculations into the design process. This will be required for life cycle engineering but is a difficult and complex task and this paper will outline some recent progress that has been made using a fracture mechanics approach together with a new finite element code, FLEXPAC, developed especially for this purpose. Finite element analysis enables the fracture mechanics approach to be generalised in principle to any geometry. In practice, however there have been serious difficulties in obtaining numerical solutions when rubber components containing internal cracks, whose surfaces are in contact, are modelled with large deformations and non linear elasticity properties. The overall problem has been approached in three parts. First, materials models are input for elasticity, stress softening and fatigue crack growth behaviour.

Push fit couplings are becoming increasingly popular for vehicle climate control systems due to the simplicity of assembly operations that they allow. An accelerated ageing test has been developed which includes the effect of vehicle vibration and thermal cycles. The couplings include elastomeric seals which after time may age, harden and lose sealing force contact. There can also be some permeation of gas through the seal material although this is usually at a low level which can be calculated provided that the permeation constants for the elastomeric materials have been measured. A novel test rig has been developed which allows 12 couplings to be tested simultaneously. There is continuous monitoring of the amount of gas that leaks past the coupling seals using sensitive transducers on the gas collection cells. A test sequence has been developed which includes a primary period of several days at 120°C followed by a secondary period of a few hours cooling to between -20 or -40°C.