The Bauschinger Effect In High Strength Steels

Brown, Peter (1995). The Bauschinger Effect In High Strength Steels. MPhil thesis The Open University.



The aim of this investigation was to characterise the Bauschinger effect (BE) exhibited by Q2N, a high strength, martensitic steel. It is defined here as "the phenomenon by which the flow stress of a metal in one direction, is reduced by plastic flow in another" and the uniaxial tension/compression test is adopted as the most appropriate mechanical test for studying the BE in Q2N. The BE is assessed by a series of primary parameters which characterise it in terms of a specific quantity, and by a range of secondary parameters which express the BE as a fraction of its theoretical maximum. The effects of tensile prestrain and heat treatment on both groups of stress, strain and energy related BE parameters is addressed and a theoretical analysis based on the Parallel Elements Model (PEM) and the Atkinson, Brown, Stobbs (ABS) model of the BE is also considered.

The results show that all of the primary BE parameters, and the stress related secondary BE parameter increased linearly with prestrain, indicating that the BE in Q2N also increased with prestrain. However, the strain and energy related secondary BE parameters decreased exponentially with prestrain, demonstrating a decrease in the BE exhibited by Q2N with prestrain. Whilst no attempt is made to resolve this dichotomy it is emphasised that the BE in Q2N can only be fully characterised, if it is quantified using all of the stress, strain and energy related BE parameters, both primary and secondary.

It is also demonstrated that a low temperature, short duration heat treatment can reduce the BE in Q2N by 25%, and that for prestrains below 1% agreement between experimental data and the predictions of the PEM/ABS model of the BE is good.

It is concluded that Q2N exhibits a substantial BE which may adversely affect the performance of any structure fabricated from it.

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