TAILIEUCHUNG - Engineered Interfaces in Fiber Reinforced Composites Part 12

Tham khảo tài liệu 'engineered interfaces in fiber reinforced composites part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 314 Engineered interfaces in fiber reinforced composites 12 10 c 8 .0 0 0 6 Id Q 4 177 c 121 c o Fig. . Maximum deflections of 05 905 5 AS4 carbon fiber-3501-6 epoxy matrix composites plotted as a function of temperature. After Crasto and Kim 1993 . cure temperature. The laminate returns to a completely flat sheet at a temperature slightly above the cure temperature and produces a reverse curvature with further increase in temperature. The lamination residual stresses can be reduced to some extent within a given temperature range by selecting an optimum stacking sequence and ply orientation Ishikawa et al. 1989 . . Other sources of residual stresses In addition to those induced thermally there are other sources of residual stresses. These include mechanical residual stresses and those induced by phase transformation in composites based mainly on ceramics and crystallization in semicrystalline thermoplastic composites. Mechanical residual stresses are present mainly in ductile metal matrix composites due to the difference in flow stress between the components Metcalfe 1974 . This type of residual stress becomes important when the composite is highly loaded to plastically deform one or both components. Phase transformation in certain ceramics and ceramic composites accompany significant volume changes while the transforming component is mechanically restrained. As a result the surrounding material is locally strained by this volume change. A good example of the phase transformation is partially stabilized zirconia ZrO2 which contains small amounts of MgO CaO or Y2O3 and undergoes a volume expansion during cooling below approximately 1000 C due to transformation from the tetragonal phase to the monoclinic phase Porter and Heuer 1977 . A very high fracture toughness can be achieved if the particle size and processing conditions are carefully controlled. Chapter 7. Improvement of transverse fracture toughness with interface control 315 . Control of

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