Dislocation Creep of Olivine and Amphibole in Amphibole Peridotites from Åheim, Norway

Amphibole peridotite samples from Åheim, Norway, were analyzed to understand the deformation mechanism and microstructural evolution of olivine and amphibole through the Scandian Orogeny and subsequent exhumation process. Three Åheim amphibole peridotite samples were selected for detailed microstructural analysis. The Åheim amphibole peridotites exhibit porphyroclastic texture, abundant subgrain boundaries in olivine, and the evidence of localized shear deformation in the tremolite-rich layer. Two different types of olivine lattice preferred orientations (LPOs) were observed: B- and A-type LPOs. Electron backscatter diffraction (EBSD) mapping and transmission electron microscopy (TEM) observations revealed that most subgrain boundaries in olivine consist of dislocations with a (001)[100] slip system. The subgrain boundaries in olivine may have resulted from the deformation of olivine with moderate water content. In addition, TEM observations using a thickness-fringe method showed that the free dislocations of olivine with the (010)[100] slip system were dominant in the peridotites. Our data suggest that the subgrain boundaries and free dislocations in olivine represent a product of later-stage deformation associated with the exhumation process. EBSD mapping of the tremolite-rich layer revealed intracrystalline plasticity in amphibole, which can be interpreted as the activation of the (100)[001] slip system.

Evolution of texture and internal stresses within polycrystalline rock salt using in situ 3D synchrotron computed tomography and 3D X-ray diffraction

Rock salt caverns have been extensively used as reliable repositories for hazardous waste such as nuclear waste, oil or compressed gases. Undisturbed rock salt deposits in nature are usually impermeable and have very low porosity. However, rock salt formations under excavation stresses can develop crack networks, which increase their porosities; and in the case of a connected crack network within the media, rock salt may become permeable. Although the relationship between the permeability of rock salt and the applied stresses has been reported in the literature, a microscopic study that investigates the properties influencing this relationship, such as the evolution of texture and internal stresses, has yet to be conducted. This study employs in situ 3D synchrotron micro-computed tomography and 3D X-ray diffraction (3DXRD) on two small-scale polycrystalline rock salt specimens to investigate the evolution of the texture and internal stresses within the specimens. The 3DXRD technique measures the 3D crystal structure and lattice strains within rock salt grains. The specimens were prepared under 1D compression conditions and have shown an initial {111} preferred texture, a dominant {110}〈110〉 slip system and no fully connected crack network. The {111} preferred texture under the unconfined compression experiment became stronger, while the {111}〈110〉 slip system became more prominent. The specimens did not have a fully connected crack network until applied axial stresses reached about 30 MPa, at a point where the impermeability of the material becomes compromised due to the development of multiple major cracks.

Deformation-Induced Grain-Interior α Precipitation and β Texture Evolution during the β-Processed Forging of a Near-β Titanium Alloy

The effect of grain-interior α precipitation on the β texture evolution of the near-β Ti-6246 alloy during through-transus forging was investigated in two-step sequential forgings. The microstructure and texture were analyzed using scanning electron microscopy, electron-backscatter diffraction, and X-ray diffraction. The previous β forging was performed at 1253 K at 0.01/s, while the subsequent forging in the (α + β) region was conducted at 1073 K at 0.01/s. The forging in the β region facilitated the penetration of the interior α phase into β grains and reduced the formation of grain boundary α. The {001} texture intensity increased during the forging in the single β region. By contrast, the increase in the {001} texture intensity was moderate at a lower temperature (1073 K) because the Schmid factor (SF) value of the {110}<111> slip system drastically decreased, but those of the {112}<111> and {123}<111> slip systems increased before α precipitation. During α precipitation for all β forging ratios, the {110}<111> slip system was activated, resulting in a lowering of the {001} texture intensity. The lower the forging temperature before interior α precipitation under a constant total forging ratio, the more the {001} texture intensity was suppressed in the final β texture, accompanied by interior α precipitation.

A Continuum Dislocation Dynamics Crystal Plasticity Approach to Irradiated BCC α-Iron

Radiation-induced embrittlement of reactor pressure vessel (RPV) steels can potentially limit the operating life of nuclear power plants. Over extended exposure to radiation doses, these body-centered cubic (BCC) irons demonstrate irradiation damage. Here, we present a continuum dislocation density (CDD) crystal plasticity model to capture the interaction among dislocations and self-interstitial atom (SIA) loops in α-iron. We demonstrate the importance of modeling cross slip using a combined stochastic Monte Carlo approach and the role of slip system strength anisotropy in capturing stochastic cross slip interactions. Through these captured interactions, the CDD crystal plasticity model can capture both the stress response and the physical evolution of dislocation on different slip system planes. Single-crystal verification experiments are used to calibrate the CDD crystal plasticity model, and a set of simplified polycrystalline simulations demonstrates the model's ability to capture the stress response from tensile experiments on α-iron.

Evidence for 40–41 km of dextral slip on the southern Death Valley fault: Implications for the Eastern California shear zone and extensional tectonics

Recognition of a pair of pre-Neogene markers together with analysis of published data indicate ~40 km of dextral slip across the southern Death Valley fault zone, California, USA. Stratigraphic overlaps on fault rocks indicate much of the dextral slip predates the late Miocene, placing a significant fraction of the dextral slip in the same time window as regional extension and challenging interpretations that the modern strike-slip system became active post–6–3 Ma. However, these results are consistent with regional evidence that dextral transtension began by ca. 12 Ma.

Micromechanical Analysis in Applications of Active Mono-Slip and Continuum Dislocations in the MDCM

The key purpose of this paper is to propose a mono-slip-dependent continuum dislocation method for matrix-dominated composite structure (MDCS) analysis. The methodology focuses on dissipation energy theories utilizing a continuum dislocation method (CDM) integrated with small-strain kinematics. The mathematical modeling of the CDM comprises active mono-slip system formulations, thermodynamic dislocation analysis (TDA), free energy dissipation analysis, and the progression of dislocations. Furthermore, zero and non-zero energy dissipation due to dislocation progression is formulated by using an energy minimization technique with variational calculus. The numerical analysis, performed with Wolfram Mathematica©, is presented using zero and non-zero energy dissipation energy formulations. The outcomes indicate that the formulated approach can be effective for obtaining optimal analysis results for matrix-dominated composite (MDC) materials with a mono-slip system. In sum, this study confirms the feasibility of using the proposed approach to investigate MDCS with inclusions.