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Title: Strain-energy method for determining residual stresses in anodised thin films
Authors: Cree, A. M.
Hainsworth, Sarah V.
Weidmann, G. W.
First Published: Sep-2006
Publisher: Maney Publishing on behalf of the Institute of Metal Finishing
Citation: Transactions of the Institute of Metal Finishing, 2006, 84 (5), pp. 246-251.
Abstract: Residual stresses in thin films are usually evaluated either by measurement of elastic strains in the film or from the curvature or deflection of a film-coated substrate material (the Stoney technique). Both methods are prone to serious measurement errors particularly for thinner films or smaller curvatures or deflections. The Stoney technique is popular because the analysis does not require the elastic modulus of the film. However, residual stress can be determined more accurately using the film modulus. A simple strain-energy analysis using this modulus has been developed to investigate residual stresses in boric acid-sulphuric acid (BSA) anodized films, based on bending measurements of thin coupons. The method is an improvement over Stoney’s equation because the square root of the thickness of the film, rather than the thickness itself, is involved, so reducing one of the larger sources of error. The modulus of the film was determined from nanoindentation measurements. The strain-energy method allows analysis of residual stress development in the coupons as functions of film thickness and time. The results show that the residual stress in BSA-anodized films formed on high strength Al-Cu alloy is highly tensile with stress levels up to 400 MPa. The effects of coupon geometry on stress development were also studied and were found to influence the final levels of residual stress developed. These results have implications for the measurement of residual stresses by beam deflection methods.
DOI Link: 10.1179/174591906X130310
ISSN: 0020-2967
Type: Article
Rights: This is the author's final draft of the paper published as Transactions of the Institute of Metal Finishing, 2006, 84 (5), pp. 246-251. The final version is available from Doi: 10.1179/174591906X130310
Description: Awarded the Jim Kape Memorial Medal for 'a paper of significance in the field of aluminium finishing'.
Appears in Collections:Published Articles, Dept. of Engineering

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