Epoxy resin failure surface

A 1-ft. (30-cm)-long section of steel heat exchanger tubing containing no failure was received. The section was submitted for evaluation of the internal surface, which was lined with a phenolic epoxy resin. 

Figure 4 shows typical failure surfaces obtained from tensile tests of the co-cured single and double lap Joint specimens. In the case of the co-cured single lap Joint, as the surface preparation on the steel adherend is better, a greater amount of carbon fibers and epoxy resin is attached to the steel adherend. Failure mechanism is a partial cohesive failure mode at the C ply of the composite adherend. In contrast with the co-cured single lap joint, failure mechanism of the co-cured double lap joint is the partial cohesive failure or interlaminar delamination failure at the 1 ply of the composite adherend because interfocial out-of-plane peel stress... 

Scanning electron microscopy (SEM) involves scanning an electron beam (5-lOnm) across a surface and then detecting the scattered electrons. Literature abounds, with work focussing on the use of SEM in the fracture and failure of epoxy resins and other thermoset polymers. Also work on multiphase thermosets (thermoset-thermoplastic blends, thermoset nanocomposites, interpenetrating network (IPN) polymers) is abundant. 

FTIR spectroscopy was used for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) was used to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels. Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180 C, as evidenced by the frequency shift of the absorption band characteristic for nitrile groups. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 micrometers in diameter, indicate the presence of an ultrathin layer of modified polymer still covering the substrate. 28 refs. 

Figure 20.27 SEM micrograph of the fracture surface of a carbon fiber epoxy resin laminate after a fiber buckling mode failure due to a longitudinal compression stress viewed under high magnification showing both tension and compressive fracture in a single fiber. Source Reprinted with permission from Ewins PD, Potter RT, Phil Trans R Soc London, A294, 507-517,1980. Copyright 1980, The Royal Society of Chemistry.

Figure 2 shows fracture surfaces for bonds between zinc and rubber-toughened epoxy resin (see Toughened adhesives). In Fig. 2(a), there is a region of cohesive failure within the resin the sites of bubbles, which may have initiated the fracture, can be seen. In Fig. 2(b), a piece of resin is seen adhering to what appears to be the bare zinc substrate. 

Fig. 2. Failure surfaces of bonds between zinc and toughened epoxy resin (a) region of cohesive failure within the resin (b) region of apparently mixed failure. (Source as Fig. 1.)...

Polymer composite materials which we investigated on failure occurrence are made on the basis of natural fibres, such as linen, cotton and jute. As the matrix material used epoxy resin R70 with hardener H71 often used for laminating contact while the texture is determined in advance. Jute fabric has a surface density in level 340 g- m , linen fabric 320 g-m and cotton fabric 130 g-m . For each reinforcement three components types have been prepared. Laminates structures with two, four and six layers have been prepared. 

The use is demonstrated of microscopic analysis techniques for the investigation of adhesive failure. PVC sheet was bonded to glass using a M35R hybrid UV curable adhesive based on epoxy resin. Atomic force microscopy and X-ray induction photoelectron spectroscopy were used for the chemical characterisation of of failure surfaces. 11 refs. 

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