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Persistent URL http://purl.org/net/epubs/work/52214
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Record Id 52214
Title Temperature dependence of low cycle fatique behaviour in extruded
Abstract In situ neutron diffraction has been used to investigate the low cycle fatigue behaviour of magnesium at room temperature, -150 °C and 150°C. In magnesium alloys, the plastic strain is typically accommodated by a mixture of dislocation slip and twinning deformation modes, giving rise to rapid texture changes at relatively small macroscopic strains. Whether slip or twinning deformation dominates depends upon the sense and direction of applied load in relation to the crystallographic texture. In extruded magnesium alloys, the texture is such that basal poles tend to lie in the transverse plane, i.e. perpendicular to the extrusion axis. In uniaxial compression parallel to the extrusion axis, strain is mainly accommodated by twinning. However, due to the inherent directionality of twinning, this mechanism cannot accommodate the deformation introduced during tensile straining along the same axis, and thus under this loading condition slip deformation dominates. Throughout low cycle fatigue cycling, reversible twinning is prevalent, the deformation twins form during compression along the extrusion axis and completely disappear when subsequent tensile loading is applied. This influences both the macroscopic response and the generation of intergranular stresses. The present study builds upon previous research on the deformation behaviour of magnesium by investigating the dependence upon temperature of the twinning/slip balance, as well as the behavior during low cycle fatigue. To our knowledge, this is the first report on neutron diffraction studies of low cycle fatigue tests at temperatures below ambient. Samples were fatigued in situ on the ENGIN-X stress-strain diffractometer at the ISIS spallation neutron source in Chilton, UK. The load was applied parallel to the extrusion axis in all tests. Diffraction spectra were acquired at a series of load levels, enabling measurement of both grain family lattice strains and twin volume fractions. The successive production and destruction of mechanical twins was observed to be a dominant deformation mode throughout the fatigue life. Significant differences in the active twinning/slip systems, attributed to the strong crystallographic texture and temperature dependence, were observed for samples tested parallel and perpendicular to the extrusion axis.
Organisation ISIS , ISIS-ENGIN-X , STFC
Keywords Engineering
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Language English (EN)
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Presentation Presented at 5th International Conference on Mechanical Stress Evaluation by Neutrons and Synchrotron Radiation, Mito, Japan, 10-12 Nov 2009. 2009