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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 : ν Poisson's ratio is dimensionless 2...

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