Tham khảo tài liệu 'engineered interfaces in fiber reinforced composites part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 254 Engineered interfaces in fiber reinforced composites a b Fig. . Schematics of the dependence of total fracture toughness Ạ on fiber volume fraction of short fiber reinforced thermoplastic composites at different loading rates a static loading b dynamic loading. After Lauke et al. 1985 . should be multiplied with the fiber pull-out term. This reduces effectively the fiber pull-out toughness and hence Rt. However random orientation of ductile fibers such as steel and nickel wires in a brittle matrix Helfet and Harris 1972 Harris et al. 1972 may increase Ri due to the additional plastic shear work of fibers as discussed in Section . . Fracture toughness maps Wells and Beaumont 1982 1985 have related the composite fracture toughness to the properties of the composite constituents using a toughness map based on the study of the energy absorption processes that operate at the crack tip in unidirectional fiber composites. The microfailure mechanisms dominating the whole composite fracture processes would determine which of the parameters are to be used as variables. Having predicted the maximum energy dissipated for each failure mechanism a map is then constructed based on the available material data including fiber strength modulus fiber diameter matrix modulus and toughness and interface bond strength as well as the predicted values of the debond length and the average fiber length. By varying the two material properties while the remaining parameters are being held constant the contours of constant total fracture toughness are superimposed on the map. These toughness maps can be used to characterize the roles of the constituent material properties in controlling fracture toughness but they also describe the effects of testing conditions such as loading rate fatigue and adverse environment on mechanical performance of a given combination of composite constituents. Chapter 6. interface mechanics and fracture toughness theories 255 . Continuous fiber
