TY - JOUR

T1 - Measuring the stress field around an evolving crack in tensile deformed Mg AZ31 using three-dimensional X-ray diffraction

A1 - Oddershede,Jette

A1 - Camin,Bettina

A1 - Schmidt,Søren

A1 - Mikkelsen,Lars Pilgaard

A1 - Sørensen,Henning Osholm

A1 - Lienert,Ulrich

A1 - Poulsen,Henning Friis

A1 - Reimers,Walter

AU - Oddershede,Jette

AU - Camin,Bettina

AU - Schmidt,Søren

AU - Mikkelsen,Lars Pilgaard

AU - Sørensen,Henning Osholm

AU - Lienert,Ulrich

AU - Poulsen,Henning Friis

AU - Reimers,Walter

PB - Pergamon

PY - 2012

Y1 - 2012

N2 - The stress field around a notch in a coarse grained Mg AZ31 sample has been measured under tensile load using the individual grains as probes in an in situ high energy synchrotron diffraction experiment. The experimental set-up, a variant of three-dimensional X-ray diffraction microscopy, allows the position, orientation and full stress tensor of each illuminated grain to be determined and, hence, enables the study of evolving stress fields in coarse grained materials with a spatial resolution equal to the grain size. Grain resolved information like this is vital for understanding what happens when the traditional continuum mechanics approach breaks down and fracture is governed by local heterogeneities (e.g. phase or stress differences) between grains. As a first approximation the results obtained were averaged through the thickness of the sample and compared with an elastic–plastic continuum finite element simulation. It was found that a full three-dimensional simulation was required to account for the measured transition from the overall plane stress case away from the notch to the essentially plane strain case observed near the notch tip. The measured and simulated stress contours were shown to be in good agreement except at the highest applied load, at which stress relaxation at the notch tip was observed in the experimental data. This stress relaxation is attributed to the initiation and propagation of a crack. Finally, it was demonstrated that the measured lattice rotations could be used as a qualitative measure of the shape and extent of the plastic deformation zone.

AB - The stress field around a notch in a coarse grained Mg AZ31 sample has been measured under tensile load using the individual grains as probes in an in situ high energy synchrotron diffraction experiment. The experimental set-up, a variant of three-dimensional X-ray diffraction microscopy, allows the position, orientation and full stress tensor of each illuminated grain to be determined and, hence, enables the study of evolving stress fields in coarse grained materials with a spatial resolution equal to the grain size. Grain resolved information like this is vital for understanding what happens when the traditional continuum mechanics approach breaks down and fracture is governed by local heterogeneities (e.g. phase or stress differences) between grains. As a first approximation the results obtained were averaged through the thickness of the sample and compared with an elastic–plastic continuum finite element simulation. It was found that a full three-dimensional simulation was required to account for the measured transition from the overall plane stress case away from the notch to the essentially plane strain case observed near the notch tip. The measured and simulated stress contours were shown to be in good agreement except at the highest applied load, at which stress relaxation at the notch tip was observed in the experimental data. This stress relaxation is attributed to the initiation and propagation of a crack. Finally, it was demonstrated that the measured lattice rotations could be used as a qualitative measure of the shape and extent of the plastic deformation zone.

KW - Crack propagation

KW - Stress and strain

KW - High energy X-ray diffraction

KW - Plastic deformation

KW - Finite element modeling

U2 - 10.1016/j.actamat.2012.02.054

DO - 10.1016/j.actamat.2012.02.054

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

VL - 60

SP - 3570

EP - 3580

ER -