Retarded crack propagation

In essence, this improvement in the fracture properties results from interactions between advancing cracks and dispersed phase particles. Crack initiation normally occurs with the matrix phase, whereas crack propagation is impeded or hindered by the particles, fibers, or whiskers. Several techniques are used to retard crack propagation, which are discussed as follows. 

In fiber-reinforced composites the deformation of the matrix is then used to transfer stresses by means of shear tractions at the fiber-matrix interface, to the embedded high-strength fibers. On the other hand, fibers retard the propagation of cracks and thus produce a material of high strength. 

Basically both types of fatigue crack propagation are discontinuous hence the so-called discontinuous type would be better characterized as retarded crack growth >. 

Retarded fatigue crack growth (RCG) was first observed by Elinck et al. in PVC, and was called discontinuous initially. They noted that the crack propagated step-wise and that a great number of fatigue cycles was needed for the formation of successive markings on the fracture surface. 

Fig. 4.14. Transition from retarded to normal fatigue crack growth in PMMA of LMW (Crack propagation direction is indicated by an arrow)...

Fatigue crack propagation in polymers are known to be retarded by large overloads under certain circumstances This has been attributed to crack tip... 

Interfiber distance Decrease =t> Increase reinforcement, and toughness Because of the confinement of crack propagation from fiber retardation... 

Bernard, P.J., Lindley, T.C., Richard, C.E. Mechanisms of overload retardation during fatigue crack propagation. ASTM STP 595, 78-97 (1976)... 

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