tailieunhanh - Handbook of Industrial Automation - Richard L. Shell and Ernest L. Hall Part 12

Tham khảo tài liệu 'handbook of industrial automation - richard l. shell and ernest l. hall part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Figure 23 Schematic views of microstructure partitioning strengthening a Single crystal b Polycrystalline material with grain size D. c Polycrystalline material with dislocations. d Polycrystalline material with twins or faults spaced A. e Dislocation cells of spacing d in polycrystalline material. 1 Polycrystalline material with precipitates or dispersoids with wear spacing L. This kind of relationship can also approximate the case of dispersed particles or discontinuous fibers in a matrix as shown in Fig. 18a which is clearly an isostress situation. CERAMIC AND POLYMERIC MATERIALS Up to this point we have treated industrial materials science and engineering in the context of primarily metals and metallurgy because they are somewhat historically at the heart of the industrial revolution and evolution worldwide. In addition metals continue to dominate industrial materials utilization with metal cast parts accounting for a significant fraction of all manufactured products. Ceramic materials are also a significant materials component because they include glass products which constitute very old and continuous manufacturing and artistic commodity businesses. In contrast to polymeric or plastic materials ceramics represent the extreme in brittle behavior while polymers represent the extreme in ductile or plastic behavior. Ceramics are characterized by traditional crystal unit cells while polymers are unique in their structure constituted primarily by complex and often continuous molecular chains. Ceramics are characterized by ionic and covalent bonds between their atoms while polymers are characterized by covalent bonds. Both ceramics and polymers are normally poor electrical conductors some are excellent insulators. On the other hand the so-called high-temperature superconductors such as YBa2Cu3O7 yttrium barium copper oxide which have superconducting transition temperatures above 90 K are also oxides. Some oxides are semiconductors and simple structural .