40207_34 - MECHANICAL TESTS Yu.M. Tarnopolskii and V I L. K...

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MECHANICAL TESTS 34 Yu.M. Tarnopol’skii and VI L. Kulakov 34.1 STRUCTURAL HIERARCHY OF FIBROUS COMPOSITES Fibrous composites are inhomogeneous mate- rials with multiple levels of structural scale. The three levels of structural scale can be arranged in a hierarchy. The characteristic dimensions for the three levels are: fiber diam- eter, lamina thickness and plate thickness. The most appropriate test methods and structural analysis techniques are different for each level in the hierarchy. Test objectives and associated problems are also different for each level. The smallest scale is the diameter of the reinforcing fiber. The properties of the rein- forcing fiber and polymer matrix and their interaction are studied in the field of microme- chanics. The second level scale is the thickness of the unidirectional lamina. Macromechanics describes the properties of a monolayer under loading at an angle to the fiber direction. A monolayer is defined as a flat or curved ele- ment of material composed of a polymeric matrix and reinforcement of the same type and orientation throughout the layer. It is the basic structural element of laminated and fibrous composites. The characterization of monolay- ers by mechanical test methods is given particular emphasis in this chapter since test- ing of anisotropic materials is a relatively novel and seldom studied field of mechanics. Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 The test results are used to calculate the properties of materials with more complex configurations of fiber arrangement and of hybrids, i.e. materials with different reinforce- ments in the same lay-up. For multilayered composites, the largest structural scale is the thickness of the lami- nated plate that is equal to the sum of stacked laminae and interleaves. The theory of lami- nated plates allows one to determine the properties of the plate using the properties of the monolayers and their stacking sequence. If the monolayers are part of a structural ele- ment, then the highest level of scale is the characteristic size of the object. The dimen- sions of structural elements typically exceed the thickness of the plate by several times. The properties of components are measured by tra- ditional mechanical and physical test methods’. The results of the analyses or tests at the first level are used as input for the analyses at the second level. The same relationship holds for the second and third levels. Upon convert- ing each scale to a continuum at the next higher scale, it is important that for each level under consideration the number of elements be sufficient, e.g. through the width and thick- ness of the lamina or through the thickness of the plate, so the transition from a discrete medium to a continuum is performed without great error. This progression up the hierarchy eventually leads to solutions of real life prob- lems involving structural elements or prototypes.
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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40207_34 - MECHANICAL TESTS Yu.M. Tarnopolskii and V I L. K...

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