Effects of temperature on the material characteristics of midsole and insole footwear foams subject to quasi-static compressive and shear force loading

The use of appropriate leisure, sports and orthotic footwear can help reduce the occurrence of foot problems, maintain correct gait and provide stability for the individual. The temperature of footwear components could play a key role in the development of foot problems in certain circumstances and can also affect gait and stability too. For orthotic and sports applications, footwear should be designed to accommodate the effects of temperature to maximise their cushioning and stabilizing effect. Materials test data is therefore required for footwear foams at various temperatures to predict their performance in service and to aid materials development and product design. The mechanical properties of eight commonly used elastomeric foams (midsole and insole) have been obtained from the current study and the effect of temperature quantified under displacement control test conditions. The foams were subject separately to quasi-static compression and shear force loading under varying temperature conditions (−10 °C to 40 °C) using a new testing protocol. All material test data were subject to a least squares fit procedure within the FEA software ABAQUS to determine the coefficients of the hyperfoam model used to describe the foams behaviour at different temperature, a validation exercise for these coefficients has been performed. Further numerical methods were employed to determine the foams energy absorption characteristics. The present study indicated that all foams tested exhibit typical elastomer mechanical and energy absorption characteristics and that these characteristics are affected significantly as a function of temperature. All foams demonstrated some degree of softening with elevated temperature whereas lower temperatures resulted in a greater amount of energy absorption capability for a specific value of strain (as a result of increasing stiffness).