Inelastic material behaviour in structures

Abstract

It is important to be able to predict the initiation of the inelastic response of materials that are subjected to various stress states. The term, “inelastic” is used to define the material response in relation to the stress-strain diagram that is non-linear and that retains a permanent strain or returns to an unstrained state on complete unloading. The term, “plastic” or “plasticity” is used to describe the inelastic behavior of a material that retains a permanent set on complete unloading. This chapter discusses the condition for the initiation of yield in ductile metals, such as structural steels. The use of uniaxial stress-strain data and their limitations are discussed together with a general description of non-linear material behavior. The stress-strain relationship might be greatly affected by the rate at which a load is applied. If a normal ductile material is considered, then the stress-strain relationship has an elastic range followed by a non-linear inelastic or plastic range. If the loading rate is very high, then the magnitude of the inelastic strain that precedes fracture can be reduced compared to that from normal load rates that are experienced under test conditions. High load rates result in an apparent increase in yield stress and modulus of elasticity. The material response is also less ductile under such conditions and, in the case of extremely high load rates, the response resembles brittleness.