TABLE OF CONTENTS Understanding the physical properties of stress and strain is a prerequisite to utilizing the many methods and results of structural analysis in design. This chapter provides the definitions and important relationships of stress and strain.
Stress is simply a distributed force on an external or internal surface of a body. To obtain a physical feeling of this idea, consider being submerged in water at a particular depth. The force of the water one feels at this depth is a pressure, which is a compressive stress, and not a finite number of concentrated forces. Other types of force distributions (stress) can occur in a liquid or solid. Tensile (pulling rather than pushing) and shear (rubbing or sliding) force distributions can also exist.
Consider a general solid body loaded as shown in Fig. 2.1(a). P i and p i are applied concentrated forces and applied surface force distributions, respectively; and R i and r i are possible support reaction force and surface force distributions, respectively. To determine the state of stress at point Q in the body, it is necessary to expose a surface containing the point Q. This is done by making a planar slice, or break, through the body intersecting the point Q. The orientation of this slice is arbitrary, but...
