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An experimental evaluation of mixed mode fracture tests conducted on adhesively bonded wood specimens using a dual actuator load frame is presented. This unit allows the fracture mode mixity to be easily varied during testing of a given specimen, providing improved consistency, accuracy, and ease of testing over a range of loading modes. Double cantilever beam (DCB) type specimens made of southern yellow pine (Pinus spp.) wood substrates bonded with a commercially available one part polyurethane adhesive were tested over a wide range of mode mixities from pure mode I to pure mode II. The critical strain energy release rate (SERR) values were calculated from the measured load, displacement, and crack length data, in combination with material properties and specimen geometric parameters, and compared on a versus fracture envelope plot. Mean quasi-static fracture energy values were calculated to be 390 J m-2 and 420 J m-2 for mode I and mode II fracture, respectively. For various mixed mode phase angles, the critical SERR values were partitioned into mode I and mode II components. In mixed mode loading conditions the cracks were typically driven along the interface, which resulted in lower total fracture energy values when compared with those measured under pure mode I loading conditions. A drop in measured fracture energy of approximately 45% was observed with mode mixity phase angles as small as 16°, implying that engineering designs based on results from the popular mode I DCB test could be nonconservative in some situations. Fracture surfaces obtained at different mode mixities are also discussed. An improved understanding of fracture behavior of adhesively bonded wood joints under mixed mode loading through generation of fracture envelopes could lead to improved designs of bonded wood structures.

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Elastomeric gaskets are commonly used between cells within a fuel cell stack to ensure that the reactant gases are isolated. Failure of a fuel cell gasket can cause the reactant gases to mix and can lead to failure of the fuel cell. An investigation of the durability of a hydrocarbon elastomeric seal material developed for proton exchange membrane fuel cells was performed by comparing the tearing energy required for crack propagation of as‐received and environmentally aged samples. Tear force was recorded as a function of crosshead displacement rate and the critical strain energy release rate was calculated and plotted against crack growth rate. Data obtained at different temperatures were then used to generate a fracture energy master curve. Additional samples were aged in selected relevant environments and compared to the as‐received material to study the effect of environmental aging on tear energy master curves. Comparison of tearing energy master curves for different test conditions showed an increase in the tearing energy for all aging environments. The tear energy master curve for testing carried out in water suggested that the crack propagation rates as low as of 10–8 ms–1 can be seen as the fracture energy approaches 80 Jm–2.

The effects of temperature and preconditioning in deionized (DI) water and a cyan ink vehicle used in inkjet printer cartridges on the durability of glass=epoxy and silicon=epoxy systems have been investigated. A test matrix consisting of test temperatures, preconditioning temperatures, preconditioning times, and nature of adherends and adhesives was developed and a series of experiments was conducted using wedge test specimens (glass or silicon coupons bonded with epoxy) to investigate the subcritical adhesion performance of the glass=epoxy and silicon=epoxy interfaces. The glass=epoxy and silicon=epoxy interfaces were found to be relatively insensitive to temperature over a range of 22-60 , but significant temperature effects, more complex than suggested by time-temperature superposition (TTSP), were observed above 60 C, depending on the environmental chemistry and nature of the adhesive used.Specimens made of silicon coupons bonded with epoxy were subjected to preconditioning in DI water and the cyan ink vehicle prior to wedge insertion to study the effect of prior environmental exposure. The wedge test data from preconditioned specimens were compared with standard wedge test results and the Si=epoxy interface was found to be insensitive to preconditioning in DI water but was affected significantly by preconditioning in the cyan ink vehicle. Plots of crack velocity versus applied strain energy release rate for particular sets of environmental conditions are presented and a comparison is made for different environmental conditions to quantify the subcritical debonding behavior of systems studied.