Learning topic
Basic Concepts and Types of Deformation
Introduction to strength of materials: deformation, displacement, strength, stiffness, stability, elastic and plastic deformation, tension, compression, shear, torsion and bending.
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Strength of Materials studies the behavior of deformable structural members under load. Before studying tension, compression, torsion, or bending, it is useful to establish a common set of concepts: deformation, material and structural models, and the criteria used to assess structural performance.
This introductory section covers the scope of Strength of Materials; deformation and displacement; elastic and plastic behavior; basic deformation modes; strength, stiffness and stability; isotropy, anisotropy and orthotropy; composite materials; and the principal assumptions and engineering idealizations used in calculation models.
Key concepts
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.
Map of basic deformation modes
| Classification | Type | Description |
|---|---|---|
| By recovery after unloading | Elastic | Disappears after the load is removed; within the adopted model, the body recovers its original shape and dimensions. |
| Plastic | Does not disappear completely after unloading; a permanent component of deformation remains. | |
| By loading and deformation of a structural member | Tension | Axial forces elongate the member. |
| Compression | Axial forces shorten the member. | |
| Shear | Adjacent layers tend to slide relative to one another, changing the angles between material directions. | |
| Torsion | Cross-sections rotate relative to one another about the longitudinal axis. | |
| Bending | The longitudinal axis becomes curved; in a typical beam model, cross-sections rotate and deflections develop. |
In real structures, several deformation modes may occur simultaneously. Such cases are treated as combined loading.
The purpose of this section is not to introduce every specialized equation, but to establish the language and assumptions used throughout the rest of the course. Detailed equations and calculation methods are introduced in the corresponding loading and material-behavior topics.