Ductile polymer composites

However, the toughness characterization of the more ductile polymer composites is more challenging. Traditionally, toughness of these composites has been characterized... 

The Izod and Charpy tests are the test methods usually employed for the determination of the toughness of a material and they are especially useful in comparing the toughness of a particular polymer-particle system. Fracture mechanic theories are the conunonly employed routes for the study and characterization of the toughness of, in particular, ductile polymer composites. 

Bell J.P., Chang J., Rhee H.W, and Joseph R. (1987). Application of ductile polymeric coatings onto graphite fibers. Polym. Composites 8, 46-52. 

Figure 5.90 Schematic illustration of tensile strength as a function of fiber volume fraction for a continuous, unidirectional fiber-reinforced, ductile matrix composite. Adapted from N. G. McCrum, C. P. Buckley, and C. B. Bucknall, Principles of Polymer Engineering, 2nd ed., p. 268. Copyright 1997 by Oxford University Press.

The stress-strain curves for cortical bones at various strain rates are shown in Figure 5.130. The mechanical behavior is as expected from a composite of linear elastic ceramic reinforcement (HA) and a compliant, ductile polymer matrix (collagen). In fact, the tensile modulus values for bone can be modeled to within a factor of two by a rule-of-mixtures calculation on the basis of a 0.5 volume fraction HA-reinforced... 

Unlike ductile metals, composite laminates containing fiber-reinforced thermosetting polymers do not exhibit gross ductile yielding. However, they do not behave as classic brittle materials, either. Under a static tensile load, many of these laminates show nonlinear characteristics attributed to sequential ply failures. One of the difficulties, then, in designing with laminar composites is to determine whether the failure of the first ply constitutes material failure, termed first-ply failure (FPF), or if ultimate failure of the composite constitutes failure. In many laminar composites, ultimate failure occurs soon after first ply failure, so that an FPF design approach is justified, as illustrated for two common laminar composites in Table 8.9 (see Section 5.4.3 for information on the notations used for laminar composites). In fact, the FPF approach is used for many aerospace and aircraft applications. 

In postyielding fracture mechanics, the EWF concept has been successfully employed to characterize the fracture toughness of ductile polymers and tough composites due to its simplicity over conventional 7-integral analysis (70-75). The EWF approach involves the determination of the total fracture energy (Wf) of notched specimen. It can be divided into two components ... 

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