Fractographic Analysis of Polymer Composites

Abstract This chapter deals with fractographic studies carried out with: (a) short-fiber reinforced, injection molded thermoplastics; (b) unidirectional, continuous carbon-fiber (CF) reinforced epoxy (EP) and polyetheretherketone (PEEK) laminates; and (c) unidirectional and cross-ply laminates of discontinuous CF-EP, PI and PES composites, woven fabric reinforced systems with different types of polymer matrix and fiber reinforcement, and SMCs. With the first group of materials (SFRTP) it is mainly outlined what kind of failure mechanisms dominate the fracture in these systems, and how fracture toughness and fracture energy can be understood on the basis of microfailure mechanisms. The second group of materials, the UD-CF-EP and UD-CF-PEEK laminates are studied with respect to their interlaminar fracture behavior as a function of crack-opening mode (I and II) and crack-tip displacement rate. The reasons for the higher fracture energy values of the PEEK system — compared to the EP system — and their velocity dependence are discussed in quite a detail, supported by extensive fractographic evidence. Finally, fracture studies on a wide variety of different composite systems (group c) should complete this endeavor by giving several examples that illustrate the variety of different fracture surface appearances as a function of microstructural composition of the composites. In general, this chapter should be considered as a guideline for future fractographic studies of polymer composite systems, and with respect to the numerous fracture surface photographs it can act as some kind of a small fractographic atlas for people who want to identify different fracture surface features on broken composite samples.