Rafael Picón

A simplified numerical analysis of residual stresses in aluminum welded plates

The residual stresses originated in a welded Al-5083-O aluminum alloy plate are numerically studied. The thermal field is simulated by means of one analytical solution of the infinite plate, after which two thermal approaches are introduced, the temperature not changing along the welding direction in either case. The thermomechanical problem is solved by using a code based on the finite element technique (ABAQUS). The influence on the residual stresses of the strain hardening and the temperature material properties dependency has been considered. A plane stress model is used, the concordance of the numerical results thus obtained with the experimental measurements obtained using the blind hole technique being excellent. A discussion of the inability of a plain strain model to reproduce the experimental results is finally presented. The general conclusions of this study can be extended to annealed aluminum alloys (type O), whose elastic properties are not susceptible to change under heat treatment.

A complete field method for the photoelastic determination of KI and KII in general mixed-mode fracture

A general approach based on photoelasticity to calculate the stress intensity factors KI and KII in any combination of geometry and load is developed. The procedure takes the information from both the near and the far field, using four complex functions which are developed in series expansions. The coefficients, two of them related to the stress intensity factors, are determined by a Newton-Raphson scheme coupled with a least squares procedure. Several modifications of the numerical procedure are introduced in order to reach convergence in an efficient and reliable manner. The necessity of using a total of four complex functions as well as the advisability of taking information from the whole field are emphasized by means of the study of two representative examples: a slant crack in a plate in traction and a simple supported beam with a crack along the neutral line.

A one-dimensional model for the prediction of residual stress and its relief in welded plates

The simulation of the welding process by means of continuum mechanics models has a very high cost both in input data preparation time and in computing time required for the integration of the complex thermoelastoplastic equations involved in solids with temperature dependent properties. For this reason, the plates in this study will be visualized as formed by a certain number of bars that can carry out elastoplastic behaviour and having temperature dependent properties. The thermal loads are simulated by analytical singular solutions, the thermomechanical problem being solved by means of an incremental algorithm of high efficiency. An excellent agreement has been found between the results numerically predicted and those previously obtained with an experimental technique and the Finite Element Method. Finally, the one-dimensional model developed here is used to predict the effects of a local heat treatment on the residual stresses originated by the welding. The versatility and rapidity of the use of this model makes it specially suitable to be used as a tool to select among different stress relieving procedures.

Analytical and Numerical Models of Postbuckling of Orthotropic Symmetric Plates

Two analytical perturbation methods which give approximate solutions of postbuckling behavior of orthotropic simply supported plates are considered in this work: the method of Chandra and Raju and the method of Shen and Zhang. The reproduction of the algebraic developments of these methods by the Mathematica symbolic manipulator program has revealed that there are errors in the formulas included in the original paper by Chandra and Raju. After a revision and correction of these errors, the analytical results of both methods for a set of 23 orthotropic plates are compared, an excellent agreement being found for a wide range of values of geometrical and mechanical parameters in which many actual plates lie. A numerical simulation performed on a reduced sample of six plates using finite-element code ABAQUS has validated analytical results. The present work is intended as a first step in the investigation of the possibility of using reliable analytical formulas in the design of composite plates.

Photoelastic determination ofK I andK II : A numerical study on experimental data

The most efficient photoelastic methods to obtain stress intensity factors are those based on stress functions series expansions. The coefficients of these expansions are fitted to the experimental isochromatic pattern using an overdeterministic Newton-Raphson least squares method. In this paper, a study has been carried out to analyze the influence on the results of several numerical and experimental factors. It is shown that accurate values of the stress intensity factorsKIandKIIcan be obtained by following some recommendations given in the text and summarized in the conclusions at the end of the paper.