Learning topic
Strength, Stiffness and Stability
Three fundamental structural performance requirements: strength, stiffness, and stability, their differences and engineering meaning.
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Strength of Materials is an engineering discipline that studies deformable structural members under loads and provides methods for assessing their strength, stiffness, and stability.
- Strength is the ability of a member to resist loading without failure or unacceptable permanent deformation.
- Stiffness is the ability to limit deformations and displacements to acceptable values.
- Stability is the ability to preserve a given equilibrium configuration and avoid a sudden transition to another configuration under load.
- Deformation is a change in the shape and/or dimensions of a body caused by loading, temperature, or other effects.
- Displacement is a change in the position of a point or cross-section of a body in space.
Three different checks
Strength concerns failure or an unacceptable material state. Stiffness limits deformation and displacement even when strength is adequate. Stability concerns the ability to preserve the intended equilibrium configuration.
Why strength alone is not enough
A beam may have acceptable stresses but excessive deflection. A slender compressed member may buckle at stresses below those associated with material failure. The governing performance criterion therefore depends on the structure and loading.
Engineering approach
Real designs often require several checks simultaneously. Later topics provide the equations used for these checks.