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**Unformatted text preview: **1 Lecture 17 Deformation of Materials Strains develop in a material when a set of stresses is imposed on it In general, any component of the strain will depend on the component of stress in the same direction AND ALSO on the other components of stress. The relationship between stresses and strains depend on the constitutive properties of the material. At room temperature, many materials behave in an elastic fashion when the stresses are low. Elastic deformation means that no energy is dissipated during deformation. (The deformation is fully reversible). Many materials are linear elastic- this means that strains are proportional to stresses (as well as being reversible). Additionally, many engineering materials are isotropi c - this means that the material properties are the same in all directions. In isotropic, linear-elastic materials, stresses and strains are related by two independent material properties (elastic constants). These two constants can be combined in different ways (with different names assigned to different combinations of them), but the two most common forms are (i) Young's modulus : E Units of Young's modulus are N/m 2 or Pascals (Pa) For many engineering materials GPa (10 9 Pa) is used (Only in the USA is ksi a unit for Young's modulus .....) (ii) Poisson's ratio : Poisson's ratio is dimensionless 2...

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