Origin of the Bauschinger effect in a polycrystalline material

Abstract

There is a long and lively debate in the literature about the origin of the Bauschinger effect in polycrystalline materials, the most widely accepted explanation being the easier movement of dislocations during reverse loading causing the reduction of the yield stress. Other explanations include incompatible deformation at the grain scale and change of dislocation cell structures during forward and reverse loading, but recent publications show these phenomenological explanations of the Bauschinger effect are not holistic. In the experimental work presented here, we have investigated the role of micro residual lattice strain on the origin of the Bauschinger effect in type 316H austenitic stainless steel using in-situ neutron diffraction. Standard cylindrical specimens were tensioncompression load cycled at room temperature with the loading interrupted at incrementally larger compressive and tensile strains followed by reloading to the tensile loop peak strain. Mirror symmetric cyclic tests were also performed with tensile and compressive load interruptions followed by compressive reloading to the compressive 2 loop peak strain. A strong correlation is demonstrated between the evolution of residual lattice strain in the grain families and the change in magnitude in macroscopic yield stress, peak stress and the shape of the yielding part of the stress-strain curve for both the cyclic tension yield and compression yield tests. This implies that the residual lattice strain generated by grain scale elastic and plastic deformation anisotropy is the primary source of the Bauschinger kinematic hardening effect observed in type 316H austenitic stainless steel.

Analysis of the Bauschinger Effect in Cold Drawn Pearlitic Steels

“…The reduction of strength due to plastic pre-strain is a question of major relevance in various research and application areas. This finding furthered the advancements in the theory of the mechanical behaviour of materials in the plastic regime under cyclic loading [1,3,[8][9][10][11][12][13][14][15][16], as well as the technological innovations in cold plastic strain conforming processes [17][18][19][20]. On the one hand, deeper knowledge about the material mechanical response allows one to optimise the plastic strain conforming processes, avoiding excessive material damage in load reversals, and on the other, this facilitates more accurate predictions (e.g., from numerical simulations) of the performance of materials undergoing cyclic strain hardening.…”

Comparison of self-consistent and crystal plasticity FE approaches for modelling the high-temperature deformation of 316H austenitic stainless steel

“…The SCM models described here provide information about the grain-average behaviour. It is ideally suited to validation using the neutron diffraction (ND) technique [83], which also provides the average stress state following deformation averaged over different grain families with the same crystallographic…”

The effect of cyclic-loading generated intergranular strains on the creep deformation of a polycrystalline material

“…At a microstructural level, back-stress refers to the stress associated with local strains arising from long-range interactions of mobile dislocations whilst at a continuum mechanics level, the back-stress corresponds to the translation of the yield surface origin during kinematic hardening. The existence of back-stress is well evidenced from various deformation phenomena in metals such as the Bauschinger effect [15], anelasticity and creep rate changes during transient…”