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mudzm17

# mudzm17 - Muddy Card Responses Lecture M17*Are all of the...

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Muddy Card Responses Lecture M1 7 *Are all of the moduli valid for 3 dimensions, i.e. Young's modulus E= s/e I mean, do we find E for each direction?. How then does a material have just one E? This is an important question, and I hope by the end of term you will have a complete idea of the answer. There are a couple of points that are worth making now. First, the Young's modulus is defined as the constant of proportionality between a uniaxial applied stress and the resulting axial strain when a material is loaded in uniaxial loading. Second, for materials which have the same structure and bonding in all directions, there is just a single value of the Young's modulus. We will see that if we have a microstructure with some orientation (e.g. aligned fibers reinforcing a matrix material) the Young's modulus may be different depending on the direction that we load the material in. This is another example of why it is important to know something about the underlying structure of a material before one embarks on a process of structural design with it. *What does n stand for?. This is the Greek letter, "nu". It is used to denote the Poisson's ratio, i.e. the ratio between the transverse strain and the longitudinal strain in a specimen that is loaded in the longitudinal direction. It is defined as being the negative of this ratio, since an axial tensile loading usually results in a transverse contraction (negative strain) for most materials.

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