STRAIN ANALYSIS

Chapter 4 Strain Analysis
Topics Covered Plane Strain and Principal Strains Mohr's Circle for Strain Strain Gauges and Strain Rosette		The topic menu above allows you to move directly to any of the four sections for each topic. The sections are: Case Intro: To help introduce and understand the basic principles, a case study is presented. Theory: This section will review the basic principles and equations that you should know to answer the exam questions. It does not give detailed derivations of the theory. Case Solution: The case study is solved in detail in this section. Graphics, narrations, animations, and equations are used to help you understand how the problem was solved.

DEFINITION OF STRAIN

The Cauchy strain or engineering strain is expressed as the ratio of total deformation to the initial dimension of the material body in which the forces are being applied. The engineering normal strain or engineering extensional strain or nominal strain e of a material line element or fiber axially loaded is expressed as the change in length ΔL per unit of the original length L of the line element or fibers. The normal strain is positive if the material fibers are stretched or negative if they are compressed. Thus, we have

where is the engineering normal strain, L is the original length of the fiber and is the final length of the fiber. The true shear strain is defined as the change in the angle (in radians) between two material line elements initially perpendicular to each other in the undeformed or initial configuration. The engineering shear strain is defined as the tangent of that angle, and is equal to the length of deformation at its maximum divided by the perpendicular length in the plane of force application which sometimes makes it easier to calculate.