Materials exhibit both elastic and plastic behavior when subjected to mechanical loads. Three key factors to consider in laboratory tests are the nature of the applied load, load duration, and environmental conditions. For tensile and compressive loading, engineering stress is defined as the load divided by the original cross-sectional area, while engineering strain is the change in length divided by the original length. Most materials first undergo proportional, nonpermanent elastic deformation, as seen by the linear relationship between stress and strain on the stress-strain curve. The slope of this linear elastic region is the modulus of elasticity or Young's modulus.

1. Materials Science
Properties of
Materials

2. Elastic and plastic behaviour of
solids
1. Three factors that should be considered in
designing laboratory tests to assess the
mechanical characteristics of materials for
service use:
1. The nature of the applied load (e.g., tension,
compression, shear),
2. Load duration
3. Environmental conditions.

4. 2. For loading in tension and compression;
Engineering stress is defined as the instantaneous
load divided by the original specimen cross-
sectional area.
3. Engineering strain is expressed as the change
in length (in the direction of load application)
divided by the original length.
4. A material that is stressed first undergoes
elastic, or nonpermanent, deformation.
5. When most materials are deformed elastically,
stress and strain are proportional— that is, a plot
of stress versus strain is linear.

5. 6. For tensile and compressive loading, the slope
of the linear elastic region of the stress–strain
curve is the modulus of elasticity (E), or Young’s
modulus per Hooke’s law.
7. For a material that exhibits nonlinear elastic
behavior, tangent and secant moduli are used.
8. On an atomic level, elastic deformation of a
material corresponds to the stretching of
interatomic bonds and corresponding slight
atomic displacements.