Creep relaxation

The response of this model to creep, relaxation and recovery situations is the sum of the effects described for the previous two models and is illustrated in Fig. 2.39. It can be seen that although the exponential responses predicted in these models are not a true representation of the complex viscoelastic response of polymeric materials, the overall picture is, for many purposes, an acceptable approximation to the actual behaviour. As more and more elements are added to the model then the simulation becomes better but the mathematics become complex. 

Service temperatures are lower under loading because of modulus decay, strain, creep, relaxation. .. They can be of the order of ... 

TPS are handicapped by risks of creep, relaxation and permanent set, the more so as the temperature rises (high compression set at 70°C for certain grades) swelling in mineral oils and oily products limited ageing resistance for SBS limited thermal behaviour (50°C maximum for certain SBS). 

TPUs are handicapped by a lower elasticity than conventional rubbers, the more so the higher the hardness certain risks of creep, relaxation and permanent set, the more so the higher the temperature higher cost than TPOs risks of hydrolysis especially for the polyester types UV exposure yellowing incompatibility between certain polyester and polyether grades aromatic and chlorinated hydrocarbon behaviour limited thermal behaviour density inherent flammability, but FR grades are marketed risks of fume toxicity in the event of fire. 

---