isotropic material是什么意思

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英语翻译
For isotropic materials,application of normal stress causes extension in the direction of the stress and contraction in the perpendicular directions,but no shearing deformation.Also,application of shear stress causes only shearing deformation,but no extension or contraction in any direction.Only two material properties,Young's modulus (the extensional modulus or slope of the material's stress-strain curve) and Poisson's ratio (the negative ratio of lateral contraction strain to axial extensional strain caused by axial extensional stress),are needed to quantify the deformations.The shear modulus (ratio of shear stress to shear strain at a point) could be used as an alternative to either Young's modulus or Poisson's ratio.
For orthotropic materials,like Isotropic materials,application of normal stress in a principal material direction (along one of the Intersections of three orthogonal planes of material symmetry) results in extension in the direction of the stress and contraction perpendicular to the stress.The magnitude of the extension In one principal material direction under normal stress In that direction is different from the extension In another principal material direction under the same normal stress in that other direction.Thus,different Young's moduli exist In the various principal material directions.In addition,because of different properties In the two principal material directions,the contraction can be either more or less than the contraction of a similarly loaded isotropic material with the same elastic modulus in the direction of the load.Thus,different Poisson's ratios are associated with different pairs of principal material directions (and with the order of the coordinate direction numbers designating the pairs).Application of shear stress causes shearing deformation,but the magnitude of the shearing deformation Is totally Independent of the various Young's moduli and Poisson's ratios.That is,the shear modulus of an orthotropic material Is,unlike Isotropic materials,not dependent on other material properties.,Thus; at least five material properties are necessary to describe the mechanical behavior of orthotropic materials (we will find the correct number of properties in Chapter 2).
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