Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558787
Title: Modelling the effects of residual stress and material removal in sheet metal forming
Author: Carlisle, Owen James
Awarding Body: University of Ulster
Current Institution: Ulster University
Date of Award: 2012
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Abstract:
The dimensional instability of metallic materials, following machining (or any method of material removal), is a common problem in the aerospace industry. This is because large parts have to be manufactured to very close tolerances and as much as 95% of the initial material may need to be removed. For machined, relatively complex, aerospace parts it would not be uncommon to see around 50% difference in the simulated results from the actual results, with even simple geometries showing around 19%-40% error. It is believed that a significant portion of these errors are due to a lack of: understanding of how the residual stresses redistribute following material removal; residual stress measuring capabilities; finite element (FE) modelling capabilities; knowledge of the additional residual stresses induced from the machining process (from varying cutting speeds, feed rates, tools, temperatures etc) and finally how the multiaxial residual stresses alter the shape of the part. This project improves the knowledge base of many of these topics. This work involved the development of an automated layer removal method for residual stress measurements in cold rolled sheet metal. This was needed due to the number of residual stress measurements that were required for modelling purposes. The method can determine the residual stresses in the rolling direction for cold rolled sheet material using a single strain gauge. Moreover, it is simple to set up and the total cost of the test rig and subsequent measurements is relatively low. Furthermore, in this project, a number of sheet metal aluminium parts were formed to different radii. The parts were then subsequently chemically milled in stages; the dimensional changes following each material removal being measured. This process was simulated using a commercially available FE package called PAM-STAMP. The FE results for distortion did not show good agreement when compared to the measured results; however, the residual stress measurements provided an unexpected understanding into the cause of the error. The results of the project improve the understanding of how residual stress change the shape of components and give an insight into the modelling parameters needed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.558787  DOI: Not available
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