Load-transfer between fibers

There are two principal theories on how load transfer between fibers is achieved in fiber RPs where they either operate alone or together... 

Studies from the composite deformation mechanism and interfacial bonding between nanofillers and the polymer matrix have been performed [46-48]. In these reports, the authors performed straining studies to determine the load transfer between carbon nanotubes and the polymer and observed the phenomena of crack propagation and polymer debonding. In some cases, the mechanical deformation processes were followed over the electrospun composite fibers. Microscopic images revealed information on the dispersion and orientation of nanotubes within the fiber and their impact in the mechanical performance regarding strain at break and stress concentration at the pores of the nanotubes. 

It is difficult to assess the oxidation resistance of all of the coatings that have been proposed in the literature. However, it is worthwhile to discuss the potential capabilities of the best oxidation-resistant coatings. In order to maintain a practical level of load transfer between the matrix and fiber, fiber coatings can be a maximum of 1 pm (0.04 mils) thick for fiber bundles and several microns for monofilaments that are more than 100 pm (4 mils) in diameter. For the present discussion it was assumed that the coating was about 1 pm (0.04 mils) thick. 

Creep resistance is of primary concern in rotating components of a turbine engine. High creep rates can lead to both excessive deformation and uncontrolled stresses. Creep resistance of fiber-reinforced ceramic matrix composites depend on relative creep rates of, stress-relaxation in, and load transfer between constituents. The tensile creep behavior of SiC/RBSN composites containing 24 vol% SiC monofilaments was studied in nitrogen at 1300 C at stress levels ranging from 90 to 150 MPa. Under the creep stress conditions the steady state creep rate ranged from 1.2 x 10 to 5.1 x 10 At stress levels below... 

Naturally, fibers and whiskers are of little use unless they are bonded together to take the form of a structural element that can carry loads. The binder material is usually called a matrix (not to be confused with the mathematical concept of a matrix). The purpose of the matrix is manifold support of the fibers or whiskers, protection of the fibers or whiskers, stress transfer between broken fibers or whiskers, etc. Typically, the matrix is of considerably lower density, stiffness, and strength than the fibers or whiskers. However, the combination of fibers or whiskers and a matrix can have very high strength and stiffness, yet still have low density. Matrix materials can be polymers, metals, ceramics, or carbon. The cost of each matrix escalates in that order as does the temperature resistance. 

Eibers find application essentially in all conventional mbber compounds. The functions of the mbber matrix are to support and protect the fibers, the principal load-carrying agent, and to provide a means of distributing the load among and transmitting it between the fibers without itself being fractured. The load transfer mechanism in short and long fibers is different. When a short fiber... 

Fig. 5.6 Relationship between the creep rate of a composite and the stress and temperature dependence of the creep parameters of the constituents.31 (a) Temperature dependence of constituent creep rate, (b) Stress dependence of constituent creep rate, (c) Intrinsic creep rate of constituents as a function of temperature and stress illustrating the temperature and stress dependence of the creep mismatch ratio. In general, load transfer occurs from the constituent with the higher creep rate to the more creep-resistant constituent, (d) Composite creep rate with reference to the intrinsic creep rate of the constituents. The planes labeled kf and em represent the intrinsic creep rates of the fibers and matrix, respectively.

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