Polymer composite fracture surfaces

Scanning Electron Microscopy (SEM) with magnification capability of up to 20,000X was used for the study of the polymer composite fracture surfaces. The freshly fractured surfaces were coated with a 250 thick Au-Pd conducting layer. 

A second method consists in observing the composite fracture surfaces. For example, in the case of MWNTs in a poly (hydroxy-aminoether) matrix, C. Bower et al. (70) observed a lot of pulled out nanotubes and concluded that the load transfer from polymer to nanotube was not sufficient to fracture the nanotubes. In the same time, a lot of kinked MWNTs were observed, which were believed to be plastically deformed. 

Denison P, Jones FR, Brown A, Humphrey P, Paul AJ, Scanning SIMS spectography of cfrp, Ishida H ed., Interfaces in Polymer, Geramic and Metal Matrix Gomposites, 239-248, 1988. Hearn MJ, Briggs D, ToF-SIMS studies of carbon fiber surfaces and carbon fiber composite fracture surfaces. Surface Interface Analysis, 17(7), 421 et seq, 1991. 

Fractured bulk polymers and composites require only coating with a conductive layer (Section 4.7.3) before observation in the SEM, although some composite fracture surfaces are so rough as to make deposition of a thin continuous conductive film very difficult. High resolution is rarely required in these materials so the common solution is to use a thick coating, and often carbon is evaporated followed by metal coating. Fibers, particularly textile fibers and thin films, have such a small cross sectional area that the main difficulty is in handling the broken sample. 

The type of corrosive environment responsible for brittle fracture of suspension composite insulators was established. A series of FTIR experiments was performed to identify chemical functionalities formed during the degradation process of composite insulators affected by brittle fracture. It was shown that the brittle fracture process was caused by the formation of nitric acid either outside or inside an insulator leading to stress corrosion cracking of the glass/polymer composite rod material. Nitrate was detected on the composite fracture surfaces inside a 115 kV suspension composite insulator which failed in service by brittle fracture. 17 refs. 

FIGURE 12.11 Scanning electron microscopy (SEM) photomicrographs of the tensile fracture surface of the ethylene-propylene-diene monomer (EPDM) rubber-melamine fiber composites. A, before ageing and B, after ageing at 150°C for 48 h. Test specimen is cut in tbe direction parallel to the milling direction. (From Rajeev, R.S., Bhowmick, A.K., De, S.K., Kao, G.J.P., and Bandyopadhyay, S., Polym. Compos., 23, 574, 2002. With permission.)... 

The possible fatigue failure mechanisms of SWCNT in the composite were also reported (Ren et al., 2004). Possible failure modes mainly include three stages, that is, splitting of SWCNT bundles, kink formation, and subsequent failure in SWCNTs, and the fracture of SWCNT bundles. As shown in Fig. 9.12, for zigzag SWCNT, failure of defect-free tube and tubes with Stone-Wales defect of either A or B mode all resulted in brittle-like, flat fracture surface. A kinetic model for time-dependent fracture of CNTs is also reported (Satapathy et al., 2005). These simulation results are almost consistent with the observed fracture surfaces, which can be reproduced reasonably well, suggesting the possible mechanism should exist in CNT-polymer composites. 

Kalnin, I. L., and H. Jager (1985). Carbon fiber surfaces—characterization, modification and effect on the fracture behavior of carbon fiber-polymer composites, pp. 62—77. In Fitzer E., ed. Carbon Fibers and Their Composites. Springer-Verlag, New York. 

Several studies of polymer/silane coupling agent interphases have involved the use of scanning electron microscopy (SEM) [5-7]. For example, Vaughan and Peek [6] have used SEM to examine fracture surfaces to determine the mode of failure of composite materials and to draw conclusions about interfacial interactions of various coupling agents and epoxide and polymer resin systems. 

Siebert and Riew (4) described the chemistry of the in situ particle formation. They proposed that the composition of the particle is a mixture of linear CTBN-epoxy copolymers and crosslinked epoxy resin. The polymer morphology of the CTBN toughened epoxy systems was investigated by Rowe (5) using transmission electron microscopy by carbon replication of fracture surfaces. Riew and Smith (6) supported the... 

The effect of the curing agent concentration on the morphology of the polymer-polymer composites was studied by SEM. Micrographs of the fractured surfaces of samples a-1, a-2, a-3 and a-4 are shown in Figures 3, 4, 5 and 6 respectively. The average density and diameter of the rubber particles are given in Table II. The number of particles per unit area increased with... 

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