3.2 Choice of parameters for stress and strain
Figure 3.1 shows the characteristics of material behaviour, but axes of stress and strain
are not carefully defined. The choice of axes will depend on the tests carried out to
examine the material behaviour and the parameters required. For metals that are essentially
elastic and then plastic the parameters required are Young’s modulus E, Poisson’s
ratio ν and the yield and ultimate stresses, and these can be obtained from a simple
uniaxial extension test. For concrete, the required parameters can be obtained from a uniaxial compression test. For soils, volume changes that occur during compression
and shearing are very important and to describe soil behaviour we must examine separately
shearing and volumetric strains and responses to shearing and normal loading
and unloading.