Sadayuki Kobayashi

Temperature Fall and Rise of Plastics During Uniaxial Stretching

Dumbbell specimens of common plastics—polyethylene, polypropylene, and polyamide—were uniaxially stretched and the surface temperature was measured by thermography. The surface temperature decreased at small strain below the yield point and then increased at larger strain. The endothermic deformation in the elastic regime was unexpected. It might be a characteristic of polymer material, which is possessed of free volume. The endotherm is interpreted by the volume increment with stretching as represented by Poissons ratio. The temperature rise at larger strain is not surprising for plastic deformation over the yield point. The exotherm is interpreted in terms of the melting of crystallites and re-crystallization induced by large deformation.