Prediction of Stress Relaxation in Laminated Leather Layers
Keywords:laminated leather, mechanical properties, stress relaxation behaviour, generalized Maxwell model, discrete spectrum of relaxation times.
Laminated leather, obtained by the bonding of the microporous polyurethane film to split leather surface, was used for investigation. Such hybrid leather is resistant to water penetration, but shows high breathable properties. The effect of different nature layers on mechanical properties and viscoelastic behaviour of laminated leather was examined. It was shown that leather backing mainly determines the strength of laminated leather, while polyurethane film – deformability. The combinative strengthening is characteristic for hybrid system due to the repairing of leather surface defects by adhesive layers and dissipation of kinetic energy, which releases during the elementary act of the failure. Generalized Maxwell model, possessing a regular spectrum of relaxation times, successfully describes stress relaxation behaviour of the leather in non-linear regions. The polyurethane film increases the stress relaxation rate in the laminated leather, because rearrangement at the interface of two layers arises. It was obtained that the viscoelastic nature of polyurethane film dominates on the long-term properties of laminated leather.
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