Modelling the superplastic process using finite element analysis can enable optimum process parameters to be determined and lead to a better understanding of the process. Constitutive equations, which accurately represent a material's behaviour, are very important in the development of representative process models. The development of a set of constitutive equations for superplastic grade Inconel 718 alloy based around a hyperbolic sine relation is described in this paper. The hyperbolic sine relation with strain dependant parameters is shown to represent the relationship between stress, strain and strain rate over a wide strain range. The valid strain range is sufficient to cover both strain hardening and flow softening behaviour.
This study is aimed at analyzing the formation and propagation of grinding induced lateral crack of nanostructured ceramic coatings using "indentation fracture mechanics" approach. It turns out that (1) Two major crack patterns are identified: median/radial cracks, lateral cracks; (2) Inelastic deformation and brittle fracture simultaneously occur in the grinding process; (3) Critical grinding condition model predicting grinding induced lateral cracks in nanostructured ceramic coatings is proposed. The critical grinding condition model is also verified by the experiments. Grinding mechanisms are discussed for nanostructured ceramic coatings. This study provides important insights into selecting appropriate grinding parameters for successful grinding of nanostructured materials.
In order to solve the presently disputed problems on local resonance of the acoustic system, research focused on the lapping plate, transformer and transducer in the ultrasonic vibration lapping system was put forward by the method of statistical energy analysis (SEA). Firstly, the mathematic model of statistical energy analysis was set up to calculate the energy and its distribution of the each subsystem of ultrasonic vibration lapping system. Then according to the calculation result of coupling factors between lapping plate and ultrasonic transformer, it is explained theoretically that it is on the condition of weakly coupling between lapping plate and transformer subsystem does the local resonance vibration occur. This conclusion discloses the principle of local resonance of power ultrasonic machining system.
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