THE EFFECT OF METHOD OF ANALYSIS ON THE SERVICE LIFE PREDICTION OF A NATURAL RUBBER COMPOUND

摘要

Every material has a service life after which it is considered to be unfit for purpose. Nowadays however, manufacturers and end users of elastomeric products are faced with materials increasingly failing before the end of their predicted service life. Increasing demands means that designers are forced to simulate service life of materials using models without adequately testing the material. Rubber is widely used in many dynamic and static applications in seals, hoses, reduction of shock vibrations in mounts. These materials are subjected to high temperatures and other service conditions, some of which fail before the expected service life. Methods such as thermogravimetry and accelerated ageing have been used for the prediction of service life of elastomers. In this paper we examine the effect of the use of different methods of analyses on the prediction of the service life of an engine mount rubber compound. Vulcanised rubber compound was aged at temperatures ranging from 70°C to 110°C for 0 to 900 hours. Tensile test and Thermogravimetric Analysis (TGA) were conducted on these materials. Activation energies were calculated using the rate laws, time temperature superposition, critical life approaches. The activation energies for tensile strength were found to be 110KJ/mol, 93KJ/mol and 103KJ/mol respectively. Activation energy of the rubber compound using thermogravimetric analysis was determined to be 127 KJ/mol. If these values are used to predict the service life of the material, then the values obtained will be different. For example the service life of the engine mount compound from tensile measurements was predicted to be approximately 31 years when operating at ambient temperatures.