Study on the Three-dimensional Stress-relaxation Diagram of Cattlehide Shoe Upper Leathers

摘要

Leather consists of a network of interwoven fiber boundless from collagen fibrils. The fibers are separated from one another because of internal twisting. Due to the structural hierarchy of collagen and the fiber weave pattern within a hide, the leather exhibits complicated viscoelastic behaviors. In this study, the stress-relaxation behaviors of some chrome-tanned cattlehide shoe upper leathers were investigated. A generalized Maxwell model with four units is successfully used to describe the stress-relaxation behavior of leather held at the strains of 23.0%, 23.0%, 30.9%, 37.2%, 42.6% and 51.9%, respectively. Since the stress of leathers depends on strain as well as relaxation time, a three-dimensional stress-relaxation diagram with stress-strain-time coordinate can be used to predict the stress of leathers in different strain and relaxation time. A method to get such a three-dimensional stress-relaxation diagram is introduced in this paper. With stress-relaxation measurement of cattlehide shoe upper leathers and a suitable curve fitting, the three-dimensional stress-relaxation diagram of cattlehide shoe upper leathers is built up. This method can also be used to other solid viscoelastic materials if a suitable curve fitting equation can be found.