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Grain boundary and triple junction constraints during martensitic transformation in shape memory alloys
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10.1063/1.4817170
/content/aip/journal/jap/114/5/10.1063/1.4817170
http://aip.metastore.ingenta.com/content/aip/journal/jap/114/5/10.1063/1.4817170
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

(a) Scanning electron micrograph of wire with bamboo grain structure showing characteristic lengths, d and D. (b) Inverse pole figures of two wires where each pole represents crystal orientation along the wire axis for a particular grain (the left and right IPFs are from wires with diameters of 48 and 70 m, respectively). (c) Cumulative distributions of grain aspect ratios for three wires.

Image of FIG. 2.
FIG. 2.

Stress-induced martensite morphology during the first loading cycle of a wire with diameter 32 m. The strain is measured between the grain boundaries of the grain undergoing transformation (the grain to the right of the grain boundary marked by a red arrow). The contrast of the martensite phase has been enhanced for visual clarity.

Image of FIG. 3.
FIG. 3.

Stress-induced martensite morphology near a grain boundary in a wire with a diameter of 32 m. The local strain is measured between the points indicated by red circles in panel (a). M1 and M2 in panel (e) denote two different martensite variants in the right grain. The angles in panels ((e)–(f)) are a = 60, b = 45, and c = 45° ± 5°. The angles are local angles measured at the bottom of the wires; they do not correct for wire curvature. The contrast of the martensite phase has been enhanced for visual clarity.

Image of FIG. 4.
FIG. 4.

Three versions of the same scanning electron micrograph. In (a), the raw image without contrast enhancement is shown. In (b), we have enhanced the contrast of the martensite plates that are clearly distinguishable, tracking them from earlier images at less strain. In (c), we have enhanced the contrast of all martensite plates, even those that are not clearly distinguishable in the lower center part of the wire.

Image of FIG. 5.
FIG. 5.

Stress-induced martensite morphology near a grain boundary in a wire with a diameter of 116 m. Panels ((a)–(f)) are from the loading whereas panels ((g)–(j)) are from unloading. The local strain is measured between the points indicated by red circles in panel (a). The numbers 1–4 in panel (f) denote particular martensite plates discussed in the text. The contrast of the martensite phase has been enhanced for visual clarity.

Image of FIG. 6.
FIG. 6.

Stress-induced martensite morphology near a triple junction in a wire with a diameter of 150 m. The tensile stress is in the horizontal direction and the wire is already under stress in the first panel. The local strains indicated in the upper right corner of each panel are measured through the triple point in the tensile direction. The contrast of the martensite phase has been enhanced for visual clarity.

Image of FIG. 7.
FIG. 7.

Stress-induced martensite morphology in the same wire as in Fig. 2 but for the fifth superelastic cycle. The local strain is measured between the two grain boundaries. The contrast of the martensite phase has been enhanced for visual clarity.

Image of FIG. 8.
FIG. 8.

Schematics showing the geometry and boundary conditions of (a) the grain boundary and (b) the triple junction. Mesh around the (c) grain boundary and (d) triple junction.

Image of FIG. 9.
FIG. 9.

Stresses near grain boundary after the upper grain has transformed to martensite. The contours show stresses at the wire surface ((a) and (b)), interior ((c) and (d)), and sample midplane ((e) and (f)). The images on the left ((a), (c), and (e)) show tensile stresses and the images on the right ((b), (d), and (f)) show the von Mises stresses. The scale bar on the left corresponds to the tensile stresses ((a), (c), and (e)) and the scale bar on the right corresponds to the von Mises stresses ((b), (d), and (f)).

Image of FIG. 10.
FIG. 10.

Stresses near triple junction after the upper grain has transformed to martensite. The contours show stresses at the wire surface ((a) and (b)), interior ((c) and (d)), and sample midplane ((e) and (f)). The images on the left ((a), (c), and (e)) show tensile stresses and the images on the right ((b), (d), and (f)) show the von Mises stresses. The scale bar on the left corresponds to the tensile stresses ((a), (c), and (e)) and the scale bar on the right corresponds to the von Mises stresses ((b), (d), and (f)).

Image of FIG. 11.
FIG. 11.

Maximum (a) von Mises and (b) rupture stresses at grain boundary (blue circles) and triple junction (red diamonds) from 40 simulations with different random grain orientations.

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/content/aip/journal/jap/114/5/10.1063/1.4817170
2013-08-01
2014-04-24
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Grain boundary and triple junction constraints during martensitic transformation in shape memory alloys
http://aip.metastore.ingenta.com/content/aip/journal/jap/114/5/10.1063/1.4817170
10.1063/1.4817170
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