ABSTRACT
This chapter explores ways of characterizing the stiffness and strength of materials and structures. In order to begin to design for stiffness by minimizing deflection, we must understand how to characterize the deformation a loaded body will undergo. Both tensile and compressive deformations result in normal strain, defined as the change in length of our material relative to its initial undeformed length. As for normal strain, several definitions of shear strain exist. In 1931, the first electrical strain gage demonstrated that strain could also be measured directly. Most modern strain gages are resistive electrical meters. For most engineering materials, a simple relationship exists between stress and strain. For each increment in stress, there is a proportional increase in strain, provided that a certain limit of stress is not exceeded. The stress–strain diagram is another example of a force being linearly proportional to an extension. Each material has its own characteristic stress–strain curve that illustrates its constitutive law.
