Strain

This chapter concerns the subject of strain which is caused by “deformation” in a body, as a result of stresses and temperature changes. This is an important consideration in the design and usage of a structure or a machine. There are design requirements that limit the degree of deformation. Strain is an “intensity” of deformation at a location in the body. Deformations include changes in the length of a straight-line segment (normal strain) and changes in the angle between two perpendicular line segments (i.e., change in the direction of the two line segments) at a corner. It is a ratio (non-dimensional) because it is measured either per unit length or as a change in angle. The main contents of the chapter are the following: Understanding the meaning of strain: intensity of local deformation; deformation of a reference element (of unit length or 90-degree corner), Two types of strain: Normal strain and shear strain, Units of strain and sign convention, Local strain and average strain, Thermal strain, and Measurement of strain using strain gauges.