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MAJOR HYPOTHESES OF MATERIAL RESISTANCE

Lecture



The resistance of materials takes into account that the structural elements under the action of external forces change their shape and size, i.e. are deformed, while in theoretical mechanics, only absolutely rigid bodies are considered.
Durability is the ability of a structural element to resist external influence without degrading.
Stiffness is the ability of a structure to maintain its original shape within the specified (usually very small) limits.
Stability is the ability of a structure to maintain the original form of balance.

  1. In the course of resistance of materials, an idealized body is considered, which is considered solid (without voids) and homogeneous.
    This means that the material properties do not depend on the shape and size of the body and are the same in all its points.
  2. The elastic properties of the material in all directions are the same, i.e. body material has elastic isotropy.
  3. The body is considered absolutely elastic, if after the elimination of the causes of the deformation, it completely restores its original shape and size.
    This assumption is valid only at stresses that do not exceed the elastic limit.
  4. The deformation of the material of the structure at each point is directly proportional to the stresses at this point (Hooke's law).
    Hooke's law is valid only at voltages not exceeding the limit of proportionality.
  5. Deformations of structural elements in most cases are so small that it is possible to disregard their influence on the relative position of loads and on the distance from loads to any points of the structure.
  6. The result of the impact on the structure of the system loads equal to the sum of the results of the impact of each load separately (the principle of independence of the action of forces).
    The principle of independence of action of forces does not apply to the work of external and internal forces and to potential energy.
  7. The cross section, flat before deformation, remains flat after deformation (hypothesis of flat Bernoulli sections)

created: 2014-09-20
updated: 2021-03-13
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