Characterisation and modelling of non-proportional plastic deformation in sheet metals

• Main Author: Volk, Gregor
• Published: Ulster University 2015
• Subjects: 671.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685426

While sheet metal forming process analysis is well established, the complex material models often require experimental data that is difficult to obtain using single axis test equipment. This thesis outlines a new method in describing and determining yield and a methodology to measure multiaxial yield points. For the new yield point determination method, yielding in sheet metal aluminium alloys is critically reviewed. An intrinsic method of determining the yield point is then developed. This new method is compared with the accepted standard methods along with several alternative approaches to overcome the highlighted issues with the standard method. The new method also provides a means of determining a yield range, since all metals do not yield abruptly at a specific point. The Hill family of yield criteria are reviewed and calibration methods are compared and analysed. A new experimental method of reaching specific points on the yield surface is implemented. These different modes of deformation are achieved through the adaptation of an otherwise known test which is implemented in sheet metal aluminium alloy testing. A new test rig is developed to fit on a standard tensile test machine. The test rig controller and associated data acquisition analysis are developed with LabVIEW as a standalone system. The mathematical analysis of the data is developed and validated. A set of tests for an aluminium alloy was conducted to show the efficacy of this new form of material testing. The possibility of calibrating the Hill family of yield criteria with the new test results is investigated. Alternative data visualization methods are also implemented in order to illustrate the suitability of the new technique.