Use of the Thin-Walled Torsion Specimen
ARMY LAB COMMAND WATERTOWN MA MATERIAL TECHNOLOGY LAB
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The thin-walled torsion specimen has been analyzed by the finite element method to determine its usefulness in material testing. A particular geometry, having a short gauge section and thick shoulder regions, was examined using material constants for 316 stainless steel. The specimen was analyzed with an eye toward determining its usefulness in approximating simple shear deformation. Both forward and single reverse behavior were examined. Classical isotropic and Prager-Ziegler kinematic hardening using Jaumann stress rates were used in the analyses. The gauge section did not contain uniform stress components throughout, but nevertheless, the macroscopic response of the specimen compared favorably with simple shear results. Plastic deformation was not entirely constrained to the gauge section but it extended some distance into the shoulder region. Consequently, the shear strain in the gauge section must be directly measured with an extensometer or a correction factor used when converting the applied machine rotation to gauge shear strain. This correction factor was determined from the finite element calculations. In reverse twisting, the macroscopic response of the specimen again matched well with simple shear results but neither material law provided even a qualitative match with experiment. The limitations of the thin-wall specimen are described and quantified in this report.
- Metallurgy and Metallography
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