J.C. Marín

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.

Determination of G12 by means of the off-axis tension test.: Part I: review of gripping systems and correction factors

Abstract The determination of the intralaminar shear modulus G 12 in composite materials is by no means a straight forward task. Several different tests and procedures have been proposed, with the off-axis test achieving popularity as a result of its apparent simplicity. A review of the most significant studies and proposals connected with the determination of G 12 by means of the off-axis tension test is presented in this paper. The majority of the contributions can be classified in two general approaches. The first approach contains the proposals to modify the gripping system in order to allow the ideal deformation of the specimen. Particular attention is paid to the use of rotating grips and the results obtained. Reasons why other authors did not achieve satisfactory results are explored. In the second approach a coherent correction scheme, based on an iterative procedure applied to measurements obtained from the test, is presented. Finally, the dependence of the correction factor, based on the Pagano and Halpin analysis, upon the properties of the material is discussed.

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.

Determination of G12 by means of the off-axis tension test. Part II: a self-consistent approach to the application of correction factors

Abstract Several different tests and procedures have been proposed for the determination of the intralaminar shear modulus G 12 in composite materials. The off-axis tension test, the ±45° test and the Iosipescu test are the most widely used. The advantages of the off-axis test are the ease of specimen preparation and the simplicity of the test procedure. A detailed review of the most significant papers on the determination of G 12 by means of the off-axis test has been presented in Part I of the present study. In this paper, a new graphical procedure, based on the numerical results from a test with clamped end conditions, is introduced. The use of these graphs requires the use of clamping conditions in the tests. Thus, an experimental study, using Moire interferometry, has been carried out to check the satisfaction of this condition in the most commonly used methods of performing the test. It has been found that a specimen with bonded end tabs reproduces the most reliable clamped condition. Finally, the results of several 10° off-axis tests on a graphite–epoxy composite are presented as a demonstration of the applicability of the correction scheme proposed in a wide range of specimen aspect ratios.

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.

The effect of frequency on tension-tension fatigue behavior of unidirectional and woven fabric graphite-epoxy composites

ABSTRACT In this paper, the effect of different values of load frequency on the evolution of the stress versus number of cycles to failure curve for a graphite-epoxy composite is studied. Two types of materials have been considered: unidirectional tape and woven fabric laminates. Fatigue tension-tension tests at different orientation angles and several frequency values have been carried out. The results show there is almost no effect of the load frequency in the S-N curve of unidirectional laminates. For woven fabric laminates, only under off-axis tension, the effect of frequency becomes a remarkable parameter in the fatigue behavior.