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Experimental Investigations on Subsequent Yield Surface of Pure Copper by Single-Sample and Multi-Sample Methods under Various Pre-Deformation

1
Key Lab of Disaster Prevent and Structural Safety, Guangxi Key Lab Disaster Prevent and Engineering Safety, College of Civil Engineering and Architecture, Guangxi University; Nanning 530004, China
2
College of Mathematics and Information Science, Guangxi University, Nanning 530004, China
*
Author to whom correspondence should be addressed.
Materials 2018, 11(2), 277; https://doi.org/10.3390/ma11020277
Received: 7 January 2018 / Revised: 1 February 2018 / Accepted: 5 February 2018 / Published: 10 February 2018
Using copper thin-walled tubular specimens, the subsequent yield surfaces under pre-tension, pre-torsion and pre-combined tension-torsion are measured, where the single-sample and multi-sample methods are applied respectively to determine the yield stresses at specified offset strain. The rule and characteristics of the evolution of the subsequent yield surface are investigated. Under the conditions of different pre-strains, the influence of test point number, test sequence and specified offset strain on the measurement of subsequent yield surface and the concave phenomenon for measured yield surface are studied. Moreover, the feasibility and validity of the two methods are compared. The main conclusions are drawn as follows: (1) For the single or multi-sample method, the measured subsequent yield surfaces are remarkably different from cylindrical yield surfaces proposed by the classical plasticity theory; (2) there are apparent differences between the test results from the two kinds of methods: the multi-sample method is not influenced by the number of test points, test order and the cumulative effect of residual plastic strain resulting from the other test point, while those are very influential in the single-sample method; and (3) the measured subsequent yield surface may appear concave, which can be transformed to convex for single-sample method by changing the test sequence. However, for the multiple-sample method, the concave phenomenon will disappear when a larger offset strain is specified. View Full-Text
Keywords: pure copper; subsequent yield measurement; pre-strain; concave pure copper; subsequent yield measurement; pre-strain; concave
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Liu, G.-L.; Huang, S.-H.; Shi, C.-S.; Zeng, B.; Zhang, K.-S.; Zhong, X.-C. Experimental Investigations on Subsequent Yield Surface of Pure Copper by Single-Sample and Multi-Sample Methods under Various Pre-Deformation. Materials 2018, 11, 277.

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