Deformation twinning is a subgrain mechanism that strongly influences the mechanical response and microstructural evolution of metals especially those with low symmetry crystal structure. In this ...work, we present an approach to modeling the morphological and crystallographic reorientation associated with the formation and thickening of a twin lamella within a crystal plasticity finite element (CPFE) framework. The CPFE model is modified for the first time to include the shear transformation strain associated with deformation twinning. Using this model, we study the stress–strain fields and relative activities of the active deformation modes before and after the formation of a twin and during thickening within the twin, and in the parent grain close to the twin and away from the twin boundaries. These calculations are carried out in cast uranium (U), which has an orthorhombic crystal structure and twins predominantly on the {130} <31̄0> systems under ambient conditions. The results show that the resolved shear stresses on a given twin system on the twin–parent grain interface and in the parent are highly inhomogeneous. We use the calculated mechanical fields to determine whether the twin evolution occurs via thickening of the existing twin lamella or formation of a second twin lamella. The analysis suggests that the driving force for thickening the existing twin lamella is low and that formation of multiple twin lamellae is energetically more favorable. The overall modeling framework and insight into why twins in U tend to be thin are described and discussed in this paper.
•Morphology and crystallography of deformation twinning are implemented in crystal plasticity finite element models.•Intrinsic twinning transformation shear strain is enforced to correspond to the plastic strain accommodated by the twin lamella.•Heterogeneities in spatial mechanical fields are correlated with microstructural changes during twin formation and thickening.•Multiple thin twin lamellae are predicted to be more favorable than a single thick twin lamella in uranium.
Pressure alters the physical, chemical, and electronic properties of matter. The diamond anvil cell enables tabletop experiments to investigate a diverse landscape of high-pressure phenomena. Here, ...we introduce and use a nanoscale sensing platform that integrates nitrogen-vacancy (NV) color centers directly into the culet of diamond anvils. We demonstrate the versatility of this platform by performing diffraction-limited imaging of both stress fields and magnetism as a function of pressure and temperature. We quantify all normal and shear stress components and demonstrate vector magnetic field imaging, enabling measurement of the pressure-driven Formula: see text phase transition in iron and the complex pressure-temperature phase diagram of gadolinium. A complementary NV-sensing modality using noise spectroscopy enables the characterization of phase transitions even in the absence of static magnetic signatures.
Estimating active earth pressure in cohesionless backfill behind rigid retaining walls has been significantly improved through the application of cutting-edge soft computing techniques in this paper. ...This study delves into the intricate interplay of negative wall-soil friction with load transfer mechanisms, underpinned by a comprehensive dataset obtained from a conservative solution that leverages statically admissible stress fields. Utilizing a Bayesian regularization backpropagation neural network, we construct an explicit function for active earth pressure estimation, ensuring the model's reliability through its remarkable alignment with measured values. Furthermore, feature importance analysis and advanced mathematical modeling enrich the study, providing a practical tool for retaining wall design and analysis. This tool is adept at addressing complex scenarios, including those involving negative wall-soil friction, thereby advancing the state-of-the-art in geotechnical engineering.
The aim of this paper is to explain that the ISSF evaluation method can apply when the fracture is cohesive as well as an interface fracture. The cohesive fracture usually occurs very close to the ...adhesive joint's interface controlled by the intensity of singular stress field (ISSF). This is the reason why the adhesive strength can be evaluated as a constant value of ISSF. In this study, the fracture origin is confirmed at the interface end to verify the ISSF evaluation method. Next, the cohesive fracture near the interface is confirmed since the slight amount of adhesive remains near the polished streaks of the adherend steel. Finally, it is found that the cohesive fracture very close to the interface guarantees the appropriate adhesive strength which can be expressed as a constant value of the ISSF.
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•Two-stage tectonic evolution of the faulted basins around the Ordos Block is rebuilt in the Cenozoic.•The periphery of the Ordos Block is presented by pure shear deformation at the ...early stage and simple shear deformation at the late stage.•The neotectonics of the periphery of the Ordos Block is originated from different driving.
The multiphase intensive intra-continental deformation of the Eurasian continent in the Cenozoic caused by Indo–Asian and Pacific–Asian collisions has been studied extensively. However, its Cenozoic intra-continental deformation process and dynamics remains poorly constrained. The western North China Plate of the Eurasian continent is characteristic of the Cenozoic faulted basin system around Ordos Block, and is a critical region to determine this deformation process. Here, new structural data and fault kinematic analysis, coupled with new geochronological results, delineate a two-stage Cenozoic tectonic evolution in the region, providing new structural evidence to decipher the intra-continental deformation due to Indo–Asian and Pacific–Asian collisions. The first stage is characterized by the formation of faulted basins in the northwestern and southeastern margins of the Ordos Block, dominated by a pure-shear mechanism. This stage further comprises the NW–SE extension spanning the Eocene to Late Miocene (ca. 10.5 Ma), and the subsequent basin inversion triggered by the NW–SE compression during the Late Miocene (ca. 10.5-9.5 Ma). Its tectonism is associated mainly with the far-field effect of the northwestward subduction of the Pacific Plate. The second stage is characterized by the development of the Shanxi and Hetao Basins in the eastern and northern parts of the Ordos Block, respectively, and an intensive mountain-building process in the western part since the Late Miocene (ca. 9.5 Ma), which is connected with a simple-shear mechanism. This stage is furthermore divided into three alternating episodes of shortening and extension events. These resulted predominantly from far-field responses to the northeastward growth of the Tibetan Plateau and partially from the Pacific subduction.
Previous studies show that the adhesive strength can be expressed as a constant value of the critical ISSF (Intensity of Singular Stress Field) for several butt joints and lap joints. This study ...deals with the scarf joints where two distinct singular stress fields appear at the interface end. How to evaluate the scarf joint strength is described in comparison with the lap joint where two singular stress fields appear but the second singular stress field is weak. It is found that the adhesive strength of the scraf joints can also be expressed as a constant value of one of the ISSF like other joints. When two singular stress fields are comparable, the debonding strength of the scarf joints can be expressed at a certain point of the sum of the two singular stress fields as
σ
θ
c
(
10
μ
m
)
= const.
The stability of rock engineering is generally dominated by existing seepage, particularly the seepage evolution due to the rock masses damage. However, the current research generally overlooks the ...seepage-damage coupling when studying the hydraulic-mechanical coupling effect in rock masses. This study aims to propose a dual-medium model, including equivalent continuous and discrete fracture media to study the coupled seepage-damage effect in fractured rock masses. The dual-medium seepage model considers the substantial water storage of the fracture network and the high conductivity of major large-scale fractures. Also, the seepage evolution is constructed to be a function of stress, seepage pressure and length of crack propagation in the rock mass. To illustrate the new model's application, a case of high-pressure water injection in a coal seam has been investigated to reveal the damage evolution in the coal seam. The results indicate that during the initial stage of the water injection, the seepage pressure in the discrete fracture medium increases faster than that in the equivalent continuous medium. Moreover, the seepage pressure difference between the two media gradually decreases with the increase of the seepage time, eventually forming a stable seepage field in the coal seam. Notably, the high-pressure water injection in the coal seam significantly affects the distribution of the coal seam's stress field, resulting in the effective minimum principle stress changing from compression to tension states. Also, during coal seam water injection, the damage zone and major fracture apertures in the coal seam gradually increase with increasing injection time.
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