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The effect of aging on the microstructure, precipitation response, and fatigue behavior in an Al-Li-Cu alloy

Fragomeni J. M., Wheeler M. F., Jata K. V.

Engineering Transactions

2005

Vol. 53, iss. 4

375-396

The interrelationships between precipitate characteristics and mechanical properties of an Al-Li-Cu alloy was quantified. The microstructure, precipitation response, and fatigue crack growth rates in the Al-Li-Cu alloy AF/C458 were studied following single and duplex aging treatments for varying aging times on specimens that were given a six percent stretch after solution heat treatment. Aging response was studied using hardness and compression yield strength measurements. Quantitative transmission electron microscopy methods were used to characterize average size, volume fraction, number density, and interparticle spacing of strengthening precipitates, ?' (Al3Li) and T1 (Al2CuLi). Strength and fatigue crack growth rates for select heat treatments were obtained and were related to the precipitate microstructure and yield strength data.

Preconditioning GMRES for discontinuous Galerkin approximations

Banaś K., Wheeler M. F.

Computer Assisted Mechanics and Engineering Sciences

2004

Vol. 11, No. 1

47-62

The paper presents an implementation and the performance of several preconditioners for the discontinuous Galerkin approximation of diffusion dominated and pure diffusion problems. The preconditioners are applied for the restarted GMRES method and test problems are taken mainly from subsurface flow modeling. Discontinuous Galerkin approximation is implemented within an hp-adaptive finite element code that uses hierarchical 3D meshes. The hierarchy of meshes is utilized for multi-level (multigrid) preconditioning. The results of numerical computations show the necessity of using multi-level preconditioning and insufficiency of simple stationary preconditioners, like Jacobi or Gauss-Seidel. Successful preconditioners comprise a multi-level block ILU algorithm and a special multi-level block Gauss-Seidel method.