Modelling and process optimization for functionally graded materials

Abstract

SUMMARYWe optimize continuous quench process parameters to produce functionally graded aluminium alloy extrudates. To perform this task, an optimization problem is defined and solved using a standard nonlinear programming algorithm. Ingredients of this algorithm include (1) the process parameters to be optimized, (2) a cost function: the weighted average of the precipitate number density distribution, (3) constraint functions to limit the temperature gradient (and hence distortion and residual stress) and exit temperature, and (4) their sensitivities with respect to the process parameters. The cost and constraint functions are dependent on the temperature and precipitate size which are obtained by balancing energy to determine the temperature distribution and by using a reaction-rate theory to determine the precipitate particle sizes and their distributions. Both the temperature and the precipitate models are solved via the discontinuous Galerkin finite element method. The energy balance incorporates non-linear boundary conditions and material properties. The temperature field is then used in the reaction rate model which has as many as 10 5 degrees-of-freedom per finite element node. After computing the temperature and precipitate size distributions we must compute their sensitivities. This seemingly intractable computational task is resolved thanks to the discontinuous Galerkin finite element formulation and the direct differentiation sensitivity method. A three-dimension example is provided to demonstrate the algorithm.

Computational Techniques for The Evaluation of Inhomogeneity Parameters on Transient Conduction in Functionally Graded Layers

“…Furthermore, spark plasma sintering and powder metallurgy techniques can be given for examples of solid phase methods [2]. Bellur-Ramaswamy et al [3] developed an algorithm to optimize continuous quench process parameters to produce functionally graded aluminum alloy extrudes. The gradual changes in volume fraction of the constituents and non-homogenous structure provides continuous graded macroscopic properties, such as hardness, wear resistance, corrosion resistivity, thermal conductivity, specific heat and mass density that are critical for thermal barrier coatings (TBCs) as well as thermal protection of the re-entry capsule, furnace liners, body armour, piezoelectric actuators and electromagnetic sensors [4][5][6][7].…”