DEFINITION OF STRESS AND STRAIN BASIC INFORMATION



The design of a component implies a design framework and a design process. A typical design framework requires consideration of the following factors: component function and performance, producibility and cost, safety, reliability, packaging, and operability and maintainability.

The designer should assess the consequences of failure and the normal and abnormal conditions, loads, and environments to which the component may be subjected during its operating life.

On the basis of the requirements specified in the design framework, a design process is established which may include the following elements: conceptual design and synthesis, analysis and gathering of relevant data, optimization, design and test of prototypes, further optimization and revision, final design, and monitoring of component performance in the field.


When loads are imposed on an engineering component, stresses and strains develop throughout. Many analytical techniques are available for estimating the state of stress and strain in a component.

A comprehensive treatment of this subject is beyond the scope of this chapter. However, the topic is overviewed for engineering design situations.


An engineering definition of “stress” is the force acting over an infinitesimal area. “Strain” refers to the localized deformation associated with stress. There are several important practical aspects of stress in an engineering component:

1. A state of stress-strain must be associated with a particular location on a component.


2. A state of stress-strain is described by stress-strain components, acting over planes.

3. A well-defined coordinate system must be established to properly analyze stressstrain.

4. Stress components are either normal (pulling planes of atoms apart) or shear (sliding planes of atoms across each other).

5. A stress state can be uniaxial, but strains are usually multiaxial (due to the effect described by Poisson’s ratio).



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