COMPOSITE_MATERIALS_module_3_MATRIX_a

COMPOSITE_MATERIALS_module_3_MATRIX_a - 1 ME 624: MECHANICS...

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Unformatted text preview: 1 ME 624: MECHANICS OF COMPOSITE MATERIALS Module 3: The Matrix (Material Based on: Composite Materials by Matthews & Rawlings and other References) 2 . Metal Matrix Materials 3 y the nature of their atomic (metallic) bonding, metals are strong/ tough CC (Face-Centered Cubic) 0.74 Packing (most dense) CC (Body-Centered Cubic) 0.68 Packing (least dense) CP (Hexagonal-Close Packed) 0.74 Packing (most dense) atrix materials : metals review crystal structure FCC BCC HCP 4 atrix materials : metals review crystal structure of some materials 5 atrix materials : metals review raditional Strengthening of Metals rystalline imperfections exist in any one or all of these forms: . Point defects (0-D) such as a vacancy, interstitial, or substitutional point defect. . Line defects (1-D) such as an edge dislocation. . Planar or interfacial defects (2-D) such as grain boundaries . Volume defects (3-D) such as voids, porosity, .. (Note that the motion of imperfections 1 under mechanical stress (0-D) is mostly responsible for plastic behavior in metals also do imperfections 2 (1- D). However, increasing edge dislocations density results in reducing the plasticity due to interference and entanglements among defects thus causing the plastic flow to decrease (and increasing yield strength). 6 atrix materials : metals review raditional Strengthening Methods of Metals Traditional metal strengthening techniques have focused on obstructing (or pinning down) the movement of these dislocations primarily the line defects. 1. Cold working : for example, there exists a linear relationship between the flow stress , τ , and (the ‘dislocation density’ in the material ρ is not the density that we know also as ρ ) where ρ is the dislocation density. Following plastic deformation, the dislocation density is greatly multiplied (thus increasing the metal’s strength and hardness) ρ ρ α τ τ GB + = 7 atrix materials : metals review raditional Strengthening Methods of Metals 2. Grain Refinement : Another relationship (Hall-Petch) describes the relation between the flow stress and mean grain size: where D is the mean grain diameter. 3. Interstitial solutions : introduce a tetragonal distortion which interacts with the edge dislocations. (Carbon in Iron for example: Body-Centered Tetragonal, BCT, is created in the case of quenching of Austenite to produce Martensite ). 4. Precipitation Hardening : decomposing a supersaturated solution to form a finely dispersed second phase. Classical examples are Al-Cu (2XXX series that results in an CuAl 2 precipitate), the Al-Zn (Duraluminum 7005-T4), and the Al-Zn-Mg alloys all popular in the aircraft industry. 5. Particle Dispersion : inert oxide powder particles (0.5% Al 2 O 3 in Al for example) show high strength performance at high temperatures....
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COMPOSITE_MATERIALS_module_3_MATRIX_a - 1 ME 624: MECHANICS...

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