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A flexural test for the in situ measurement of the delamination toughness of the interface between a thermally grown oxide and a bond coat in the presence of a thermal barrier coating (TBC) has been implemented. To accomplish the testing, a section of the substrate was removed by microelectro-discharge machining and a precrack introduced through the TBC by center point loading. This was followed by application of an asymmetric single-point load to extend a delamination along the interface. A displacement and strain mapping method was used to locate the delamination and to ascertain its extension. To relate the energy release rate and mode mixity to the crack extension and the loads, a finite-element method was implemented. The ensuing fracture resistance was found to vary along the interface with values in the range of 25-95 J/m(2).

The role of oxidation-induced layers in the failure process of aluminide-coated nickel base single crystals subject to high-temperature fatigue cycling has been investigated experimentally and via finite element analysis. Isothermal strain-controlled compressive fatigue experiments (R=−∞) with 120 s holds in compression were conducted at 982° and 1093°C. Surface-initiated cracks containing a layer of alumina progressively grew through the coating layers into the superalloy substrate, ultimately causing failure. Growth stresses in the oxide provided a driving force for extension of the oxide into the softer coating and substrate layers. Finite element modeling shows the rate of growth of the oxide-filled cracks is sensitive to the strength of the constituent layers and the magnitude of the oxide growth strains. Implications for design of failure-resistant coating–substrate systems are discussed.

Composite bimaterial lattice structures which possess both low, tailorable thermal expansion and nearly optimal stiffness have been proposed for applications which require high structural stiffness in environments which include large temperature fluctuations, such as the surfaces of high-speed aerospace vehicles. An experimental validation of the thermal properties of these lattices when they are constructed of practical materials with easily manufactured bonded joints is contained herein. Bonded lattices, comprising aluminum and titanium alloys, have been manufactured with press-fit dovetail joints and tested in a variety of thermal environments. Results for equilibrium heating, rapid transient heating and thermal cycling leading to shakedown are presented and shown to be consistent with theoretically and numerically attained results.

Finite element modeling and linear elastic fracture mechanics are used to model the residual stresses and failure stress of ceramic composites consisting of polyhedral alumina cores surrounded by thin alumina/mullite layers in residual compression. This type of composite architecture is expected to exhibit isotropic threshold strength behavior, in which the strength of the composite for a particular assumed flaw will be constant and independent of the orientation of tensile loading. The results of the modeling indicate that the strengths of such architectures will be higher than those of laminates of similar architectural dimensions that were previously found to exhibit threshold strength behavior for a particular flaw type. Flexural testing of the polyhedral architectures reveals that failure is dominated by processing defects found at junctions between the polyhedra. Fractography revealed the interaction of these defects with the residual stresses in the compressive layers that separate the polyhedra.

High-melting-point alkylammonium tetrafluoroborates melt with water or toluene to form biphasic mixtures at much lower temperatures than their normal melting points, thus could serve as green reaction media for Suzuki and Heck couplings. Advantages of using the aqueous-ammonium biphasic catalytic system include: (1) working well with a ligandless palladium catalyst, (2) solving the solubility problem of organic substrates and (3) simplifying work-up procedures for both separation of products and recycling of reaction media.

Previous analyses have shown that refractory metallic leading edges are feasible for Mach 6–8 airbreathing hypersonic vehicles when integrated with a structural heat pipe. This article investigates the effects of a coating on the exterior surface for potential thermal and environmental protection. Two conclusions are found: (i) Adding a thermal barrier coating does not allow operation at higher Mach number because the characteristic temperature of the system is unaffected by its presence. Instead, large (adverse) temperature gradients are induced through the coating. (ii) Coatings required to protect against oxidation can be safely applied provided that they are thin (≤0.1 mm) and have sufficiently high thermal conductivity (≥5 W/mK).

Fiber-reinforced ceramic-matrix composites (CMCs) depend upon inelastic mechanisms to diffuse stress concentrations associated with holes, notches, and cracks. These mechanisms consist of fiber debonding and pullout, multiple matrix cracking, and shear band formation. In order to understand these effects, experiments have been conducted on several double-edge-notched CMCs that exhibit different stress redistribution mechanisms. Stresses have been measured and mechanisms identified by using a combination of methods including X-ray imaging, edge replication, and thermoelastic analysis. Multiple matrix cracking was found to be the most effective stress redistribution mechanism.

Analyses of debonding along interfaces and of the kinking of interface cracks into a fiber have been used to define the role of debonding in fiber-reinforced, brittle matrix composites. The results reveal that, for fibers aligned with the tensile stress axis, debonding requires an interface fracture energy, Γi, less than about one-fourth that for the fiber, Γf. Further-more, once this condition is satisfied, it is shown that fiber failure does not normally occur by deflection of the debond through the fiber. Instead, fiber failure is governed by weakest-link statistics. The debonding of fibers inclined to the stress axis occurs more readily, such that debonds at acutely inclined fibers can deflect into the fiber, whereupon the failure of fibers is dominated by their toughness.