Raman Spectroscopy Investigations of Functionally Graded Materials and Inter-Granular Mechanics

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The recent evolution of micro-Raman spectroscopy as micro-mechanical experimental technique had a profound effect on the field of solid mechanics. Micro-Raman spectroscopy (MRS) is the only technique capable of measuring local stress in a wide range of materials with a spatial resolution of 1 μm. With the current trend of near-field Raman, such spatial resolution is expected to increase down to few tens of nanometers. In addition, the technique is capable of interrogating chemical and structural changes in the materials, hence, for the first time, direct correlation can be identified in-situ by means of the same technique. Such capabilities have been previously utilized in the field of fibrous composites to provide accurate measurements of axial and interfacial stress distributions along individual fibers and at fiber/matrix interface. Such experimental measurements shed light on and strengthened our understanding of crucial events taking place during composite loading such as damage initiation, propagation, and resulted in more accurate models capable of predicting composite behavior and lifetime. In this paper we demonstrate the power of MRS in investigating functionally graded joints for carbon–carbon composites and its ability to provide the necessary data for the correlation of chemical changes with mechanics of the joint. In addition, our recent demonstration of the ability of the technique to measure inter-granular stress fields in polycrystalline materials will be reviewed.



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