ABSTRACT
Polymers are widely used because of their low moduli, which normally lie in the range 1 MN/m2 to a few giganewtons per square metre. This chapter discusses the stiffness of nominally uniform and isotropic polymers and ways of predicting the stiffness of products made from them. It discusses the behaviour of plastics where loads are applied over times ranging from a few seconds to a few years, and introduces the idea of creep under constant load, and how to allow for this in design. The chapter discusses creep under non-constant loads, and discusses the more generalized relationships between stress and strain for different models of material behaviour, including stress relaxation and the deformation response to cyclic loading. It examines the properties of rubber polymers and discusses aspects of the analysis of rubber spring units under common types of loading.
