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During some deep drawing operations liquid lubricants are used under the blankholder to reduce friction coefficients. Under the clamping action of the blankholder, lubricants will be squeezed out resulting in a changing film thickness after the initial application of the blankholder load. A relationship between kinetic friction coefficient values and the loading duration of the blankholder can be observed from analysis of results recorded during simulative testing. By using a numerical model to combine empirical measurements, friction coefficients during boundary lubrication, lubricant film thickness with sheet surface topography data, it can be shown that the coefficient of friction can reliably be predicted for a given loading duration.

The test method detailed in ASTM Standard Test Method for Shear Testing of Thin Aluminum Sheet Alloy Products (B 831) approximates the conditions of pure shear. The newly proposed test regime removes the rigid body rotation associated with pure shear and hence creates a simple shear deformation. The test also makes available an additional volume of empirical data by facilitating the measurement of both shear stress and strain throughout the test. The proposed test procedure was used to analyze the directionality of simple shear deformation in an aerospace 2024-T3 aluminum alloy. The shear yield strength determined using the newly proposed method was found to be approximately half of the uniaxial yield strength. The orthotropic response in shear was seen to differ from that exhibited during uniaxial testing. The stress-strain response in simple shear also illustrated the effect of the deformation restrictions through the appearance of serrated yielding.

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Recent advances in computational technology have allowed engineers to conduct previously impractical analyses, particularly with the development of the Finite Element Method (FEM). In turn, this has led the sheet metal forming industry into an economy drive, with an increasing necessity for ‘first time’ forming operations and reduced scrap rates. The successful prediction of large-scale plastic deformation in a sheet component relies on the accuracy of the material model used, especially when anisotropic materials are considered. Some stretch formed or deep drawn forms are geometrically complex and may require several draws with inter-stage anneals and/or solution heat treatments to achieve full form, and the varying material properties create significant difficulties in the modelling of these forming processes. Current orthotropic yield criteria do not allow for any sense of time dependency and although the atomic effects of solution heat treatment and precipitation hardening are well understood, the macroscopic effects of deformation behaviour are not. A test program was developed to investigate the effects of an increasing age hardening time on an aerospace Alclad 2024-O material after a solution heat treatment. With access to industrial heat treatment equipment, extensive tensile tests were conducted at varying age hardening times and a test rig was manufactured to obtain balanced biaxial tension data. Through the subsequent analysis, a method of predicting the data needed to generate a materials model suitable for FEA was developed, based on a modified version of Hill’s 1990 non-quadratic yield criterion. This was used to generate yield loci for the various age hardening times and compared with the loci generated with the predicted loci. Evaluation of the accuracy of the new criterion, and hence the predictive method, was achieved through its implementation in a finite element code used to model a punch-stretch test. Modelled surface strains were then compared with those measured strains determined during an empirical validation test programme. With the knowledge that the analysis came from data predicted from a minimum of empirical tests, the predicted results were found to be in good agreement with the experimental values.