Reveal Hydrogen Behavior at Grain Boundaries in Fe–22Mn–0.6C TWIP Steel via In Situ Micropillar Compression Test

In this study, the effect of hydrogen on dislocation and twinning behavior along various grain boundaries in a high-manganese twinning-induced plasticity steel was investigated using an in situ micropillar compression test. The compressive stress in both elastic and plastic regimes was increased with the presence of hydrogen. Further investigation by transmission electron backscatter diffraction and scanning transmission electron microscope demonstrated that hydrogen promoted both dislocation multiplication and twin formation, which resulted in higher stress concentration at twin–twin and twin–grain boundary intersections.

Transmission of Plasticity Through Grain Boundaries in a Metastable Austenitic Stainless Steel

Austenitic metastable stainless steels have outstanding mechanical properties. Their mechanical behavior comes from the combination of different deformation mechanisms, including phase transformation. The present work aims to investigate the main deformation mechanisms through the grain boundary under monotonic and cyclic tests at the micro- and sub-micrometric length scales by using the nanoindentation technique. Within this context, this topic is relevant as damage evolution at grain boundaries is controlled by slip transfer, and the slip band-grain boundary intersections are preferred crack nucleation sites. Furthermore, in the case of metastable stainless steels, the interaction between martensitic phase and grain boundaries may have important consequences.

Topological Similarity Measurement of Region Compositions Based on Boundary Contacts

Topological relationship, one of the most important subjects in spatial analysis, has been studied thor oughly and applied to various fields. An important application of topological relations is the similarity measurement on spatial scenes. However, when considering the common topological relations, there exists dif ficulty in distinguishing different region compositions where complicated boundary contacts occur between regions. To address this problem, a method of describing detailed topological relations in a region compo si tion has been proposed [Lewis et al. 2013], by traversing a region's boundary and recording boundary intersections one by one. To implement similarity measurement on region compositions where complex boundary contacts happen, we propose a measuring model based on the boundary contact recording method. The model is struc tured in two steps, a preliminary matching step and an exact matching step. In the preliminary matching step, we recognize and filter the very dissimilar candidates comparing to the reference region composition; meanwhile, we obtain corresponding relations of regions between the potential candidates and the reference, and represent the correspondences with an association graph composed of nodes and edges. In the exact matching step, we encode boundary contact records to binary sequence, and adopt a sequence alignment method, an approach from bioinformatics to compare the sequences of DNA, RNA, or protein, to fulfill the topological similarity measurement for two region compositions. We illustrate the complete process of our model through a case study, and show the survey result on weight setting for criteria in the exact matching step.

Topological effects on vorticity evolution in confined stratified fluids

For a stratified incompressible Euler fluid under gravity confined by rigid boundaries, sources of vorticity are classified with the aim of isolating those which are sensitive to the topological configurations of density isopycnals, for both layered and continuous density variations. The simplest case of a two-layer fluid is studied first. This shows explicitly that topological sources of vorticity are present whenever the interface intersects horizontal boundaries. Accordingly, the topological separation of the fluid domain due to the interface–boundary intersections can contribute additional terms to the vorticity balance equation. This phenomenon is reminiscent of Klein’s ‘Kaffeelöffel’ thought-experiment for a homogeneous fluid (Klein, Z. Math. Phys., vol. 59, 1910, pp. 259–262), and it is essentially independent of the vorticity generation induced by the baroclinic term in the bulk of the fluid. In fact, the two-layer case is generalized to show that for the continuously stratified case topological vorticity sources are generically present whenever density varies along horizontal boundaries. The topological sources are expressed explicitly in terms of local contour integrals of the pressure along the intersection curves of isopycnals with domain boundaries, and their effects on vorticity evolution are encoded by an appropriate vector, termed here the ‘topological vorticity’.

Microstructure and Reliability of Surface Micromachined Polysilicon Used for MEMS

Surface micromachining (SMM) techniques produce complex microscale polysilicon features on the surface of a silicon wafer using a patterned maultilayer film deposition process. Failure characteristics of SMM polysilicon obtained from testing series of 2 μm and 4 μm wide ligaments fabricated using standard SMM processing techniques, fit a Weibull distribution, suggesting a behavior governed by a distribution of flaws, similar to brittle ceramic materials. However, positive identification of critical flaws that dictate the failure distribution within the ligaments remains unclear. Likely candidates are flaws associated with surface roughness or gain boundary intersections with the polysilicon microstructure. To address the possible connection between microstructure and failure behavior of SMM polysilicon, templates, based on observed polysilicon microstructure were subjected to deformation simulations using polycrystal elasticity modeling. Series of simulations were performed to capture the statistical failure of polysilicon due to local elastically driven stress concentrations between grains with different crystallographic orientations.. Simulated results are presented and discussed in the context of experimental failure data.

Dislocation structures and twinning in tungsten single crystals

Tungsten single crystals are brittle due to predominant twinning and crack formation at twin-twin intersections. Twinning and its influence on crack nucleation have been studied in detail. Despite the twinning, significant plastic deformation takes place by the generation and glide of dislocations. Hitherto uninvestigated dislocation structures and twin boundaries in tungsten <110> single crystals deformed quasistatically in compression have been studied using transmission electron microscopy.In compressed samples, cracks nucleate at twin-boundary intersections. Such a crack is indicated by an arrowhead in Figure 1 which shows an optical image of twin boundaries. Figure 2 shows a bright field (BF) image of a twin boundary (marked by an arrowhead). The inset in Figure 2 is the microdiffraction pattern taken at the twin boundary which shows a ∑3 coincidence site lattice (CSL) symmetry.