Introduction to Stress-Strain Relationship and Its Measurement Techniques

Introduction

The components that researchers employ in various engineering applications are exposed to numerous loading conditions, which induces stress and component failures. In the same way, the structural components placed in the flow path of fluids with high currents leads to distortion because of the high stress and strain concentration on the material surfaces, which further leads to the catastrophe of the engineering components (Karthik & Dhas, 2015, 2016, 2018). The failures from stress can be caused by excessive vibrations (Balaji et al., 2015; Leblouba et al., 2015; Balaji et al., 2016a; 2016b). Moreover, thermal stresses can be caused from the temperature distribution on the structural component (Balaji & Yadava, 2013). In the previous chapter, the authors discussed that the states of stress developed at a particular point or location in a body due to the force or load acting on the surface of the structure. To estimate the nature of stress-strain on the materials, it is important to know the graphical measure of mechanical properties of various materials. All the design engineers, university students, and academicians, who are all study or analyze the mechanics of materials, have to understand the relationship between stress and strain. This chapter mostly discusses stress and strain and their relationship. The movement of the arbitrary point due to the applied forces is a vector quantity known as displacement. In addition, every single point in a structure undergoes displacement due to applied forces that have a unique signature on displacement vectors. Each displacement component is matched with respect to the Cartesian coordinates in x, y, and z directions. Researchers can represent the motions of the structure by considering the rotational movement and translational movements as a single component. Subsequently, the authors considered the movement of the points in the structures to be relative to one another. In this chapter, the authors present a detailed overview of the numerous experimental techniques employed to measure the stress and strain.

Two Dimensional Aspects Of Strain

The two-dimensional aspects of the strain are more or less identical to the understanding of strain in the one-dimensional aspects, in which the authors defined the deformation of material by visualizing the material considered to be the group of line elements in lesser amount (Boresi & Chong, 2000). When a test specimen starts to deform, resulting in the development of stretching on the line elements, alternatively, it starts to diminish to revolve around in the space relative to one another. Thus, researchers comprehend the displacement of the line elements with respect to the indication of strain. The strain at a particular point is simply the outcome of the stretching of the line element, due to the contraction and the rotation of the whole elements originating from that particular position. Figure 1 illustrates the occurrence of strain in the z- and y-axis, respectively.