Use this URL to cite or link to this record in EThOS:
Title: The implementation and validation of orthotropic material models for sheet metal forming
Author: Kilpatrick, William
Awarding Body: Ulster University
Current Institution: Ulster University
Date of Award: 2012
Availability of Full Text:
Access from EThOS:
Aluminium alloys have been the primary material utilised for aerospace components since the 1930s. The continued requirement for weight reduction coupled with reliable performance and formability by the aerospace and automotive industries is satisfied by advanced aluminium alloys. The mechanical performance of these alloys requires numerical analysis using advanced yield criteria, such as the Leacock 2006 phenomenological yield criterion. The enhanced accuracy of this advanced yield criterion over several yield criteria including Hill 1990 has been previously reported by Leacock (2006). Constitutive equations based on the von Mises, Hill 1948, Hill 1990 and Leacock 2006 yield criteria, in combination with two non-linear hardening laws, have been implemented as a rate independent, elastoplastic user material subroutine (UMAT) within the Finite Element software PAM-STAMP 2GTM. The UMAT architecture incorporates the Associated Flow Rule and the Cutting Plane Algorithm for the integration of the elastoplastic constitutive equations. The 2024-O and 6451-T4 (Anticorodal-600 PX) aluminium alloys were characterised using uniaxial and equibiaxial tension tests. This test data formed the basis of an initial computational verification of the UMAT. A stress path specific comparison of the Finite Element results with the theoretical prediction and the experimental values showed excellent agreement. In addition, the Leacock 2006 UMAT showed favourable comparison with the theoretical and experimental uniaxial yield strengths and r-values versus the angle from the rolling direction. The Leacock 2006 UMAT was verified using two validation studies incorporating drawing and stretching modes of deformation. The Leacock 2006 UMAT provided an accurate prediction of the thickness and the punch force versus displacement in the stretching of the AA2024-T3. In particular, the Leacock 2006 UMAT exhibited the best quality of fit to the experimental major strain in the 0°, 45° and 90° orientations from the rolling direction for three depths of stretch. The Leacock 2006 UMAT also provided an earing profile prediction with an increased statistical accuracy over the Hill 1990 yield criterion of 31%, 40% and 14% for the experimental draw profiles of AA2024-0, AA6451-T4 and AA6111-T4 (NUMISHEET 2002 Benchmark A), respectively. The Leacock 2006 yield criterion has been shown to provide the best combination of earing profile and magnitude prediction over all other criteria considered with a similar minimal calibration cost.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available