Abstract
An intelligent universal test machine that enables the measurement of the relationships of stress σ with time t and strain ε was developed. The accurate measurement of material mechanical characteristics was possible by selecting optimum test condition. Elastic and plastic behavior clearly became analyzable in terms of the relationship between stress σ and strain ε. In this paper, we describe the theory that can explain the relationship between stress σ and strain ε from the elastic region to the plastic region during tension, bending and torsion. First, the relationship between stress σ and strain ε was expressed by an inverse function. Next, by refening to the new theory, the ratio of stress σ to strain ε was calculated from the elastic region to the plastic region. This ratio, E_*, is called the elasticity-plasticity variable. The technique of changing variables in order to obtain the relationship between stress σ and the elasticity-plasticity variable E_* was introduced in the evaluation of the strength of materials.
