A new method for high resolution curvature measurement applied to stress monitoring in thin films

By combining the well-known grid reflection method with a digital image correlation algorithm and a geometrical optics model, a new method is proposed for measuring the change of curvature of a smooth reflecting substrate, a common reporter of stress state of deposited layers. This tool, called Pattern Reflection for Mapping of Curvature (PReMC), can be easily implemented for the analysis of the residual stress during deposition processes and is sufficiently accurate to follow the compressivetensile-compressive stress transition during the sputtering growth of a Ag film on a Si substrate. Unprecedented resolution below 10-5m-1can be reached when measuring a homogeneous curvature. A comparison with the conventional laser-based tool is also provided in terms of dynamical range and resolution. In addition, the method is capable of mapping local variations in the case of a non-uniform curvature as illustrated by the case of a non-homogeneous Mo film under high compressive stress. PReMC offers interesting perspectives for in situ accurate stress monitoring in the field of thin film growth.

Multi-sensor optimal deployment based efficient and synchronous data acquisition in large three-dimensional physical similarity simulation

Purpose This paper aims to propose a deployment optimization and efficient synchronous acquisition method for compressive stress sensors used by stress distribution law research based on the genetic algorithm and numerical simulations. The authors established a new method of collecting the mining compressive stress-strain distribution data to address the problem of the number of sensors and to optimize the sensor locations in physical similarity simulations to improve the efficiency and accuracy of data collection. Design/methodology/approach First, numerical simulations were used to obtain the compressive stress distribution curve under specific mining conditions. Second, by comparing the mean square error between a fitted curve and simulation data for different numbers of sensors, a genetic algorithm was used to optimize the three-dimensional (3D) spatial deployment of sensors. Third, the authors designed an efficient synchronous acquisition module to allow distributed sensors to achieve synchronous and efficient acquisition of hundreds of data points through a built-in on-board database and a synchronous sampling communication structure. Findings The sensor deployment scheme was established through the genetic algorithm, A synchronous and selective data acquisition method was established for reduced the amount of sensor data required under synchronous acquisition and improved the system acquisition efficiency. The authors obtained a 3D compressive stress distribution when the advancement was 200 m on a large-scale 3D physical similarity simulation platform. Originality/value The proposed method provides a new optimization method for sensor deployment in physical similarity simulations, which improves the efficiency and accuracy of system data acquisition, providing accurate acquisition data for experimental data analysis.

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: insights from numerical simulations

We propose a conceptual geological model for the collision of multiple basement topographic highs (BTHs; e.g., seamounts, ridges, and horsts) with a forearc accretionary wedge. Even though there are many BTHs on an oceanic plate, there are few examples of modeling the collision of multiple BTHs. We conducted numerical simulations using the discrete element method to examine the effects of three BTH collisions with forearcs. The typical geological structure associated with a BTH collision was reproduced during the collision of the first BTH, and multiple BTH collisions create a cycle of formation of BTH collisional structures. Each BTH forces the basal décollement to move up to the roof décollement, and the roof décollement becomes inactive after the passage of the BTH, and then the décollement moves down to the base. As the active décollement position changes, the sequences of underthrust sediments and uplifted imbricate thrusts are sandwiched between the décollements and incorporated into the wedge. At a low horizontal compressive stress, a “shadow zone” is formed behind (i.e., seaward of) the BTH. When the next BTH collides, the horizontal compressive stress increases and tectonic compaction progresses, which reduce the porosity in the underthrust sediments. Heterogeneous evolution of the geological and porosity structure can generate a distinctive pore pressure pattern. The underthrust sediments retain fluid in the “shadow” of the BTH. Under the strong horizontal compressive stresses associated with the next BTH collision, pore pressure increases along with a rapid reduction of porosity in the underthrust sediments. The distinctive structural features observed in our model are comparable to the large faults in the Kumano transect of the Nankai Trough, Japan, where a splay fault branches from the plate boundary and there are old and active décollements. A low-velocity and high-pore-pressure zone is located at the bottom of the accretionary wedge and in front (i.e., landward) of the subducting ridge in the Kumano transect. This suggests that strong horizontal compressive stresses associated with the current BTH collision has increased the pore pressure within the underthrust sediments associated with previous BTHs.

Mechanical properties and constitutive model of Sn-58Bi alloy

Sn-58Bi alloy is a strain-rate-sensitive material. To study the mechanical properties of Sn-58Bi alloy, an MTS universal testing machine and split-Hopkinson pressure bar were used to conduct quasi-static and dynamic testing on Sn-58Bi alloy, obtaining the stress-strain curve of Sn-58Bi alloy at the strain rate of 0.001–6316 s−1. By comparing the tensile and compressive stress–strain curves of Sn-58Bi alloy under quasi-static conditions, it is found that Sn-58Bi alloy is brittle, with its tensile yield strength lower than its compressive yield strength. By comparing the compressive stress–strain curves of Sn-58Bi alloy at different strain rates, it is found that the yield strength of Sn-58Bi alloy increases with increasing strain rate, and a strain-hardening phenomenon is manifested at high strain rate. By revising the Johnson–Cook constitutive model, the constitutive model of Sn-58Bi alloy at different strain rates was established, with the calculated results of the model in good agreement with the experimental results.

Dike Propagation During Global Contraction: Making Sense of Conflicting Stress Histories on Mercury

Thrust fault-related landforms, smooth plains units, and impact craters and basins have all been observed on the surface of Mercury. While tectonic landforms point to a long-lived history of global cooling and contraction, smooth plains units have been inferred to represent more punctuated periods of effusive volcanism. The timings of these processes are inferred through impact cratering records to have overlapped, yet the stress regimes implied by the processes are contradictory. Effusive volcanism on Mercury is believed to have produced flood basalts through dikes, the propagation of which is dependent on being able to open and fill vertical tensile cracks when horizontal stresses are small. On the contrary, thrust faults propagate when at least one horizontal stress is very large relative to the vertical compressive stress. We made sense of conflicting stress regimes through modeling with frictional faulting theory and Earth analogue work. Frictional faulting theory equations predict that the minimum and maximum principal stresses have a predictable relationship when thrust faulting is observed. The Griffith Criterion and Kirsch equations similarly predict a relationship between these stresses when tensile fractures are observed. Together, both sets of equations limit the range of stresses possible when dikes and thrusts are observed and permitted us to calculate deviatoric stresses for regions of Earth and Mercury. Deviatoric stress was applied to test a physical model for dike propagation distance in the horizontally compressive stress regime of the Columbia River Flood Basalt Province, an Earth analogue for Borealis Planitia, the northern smooth plains, of Mercury. By confirming that dike propagation distances from sources observed in the province can be generated with the physical model, we confidently apply the model to confirm that dikes on Mercury can propagate in a horizontally compressive stress regime and calculate the depth to the source for the plains materials. Results imply that dikes could travel from ∼89 km depth to bring material from deep within the lithosphere to the surface, and that Mercury’s lithosphere is mechanically layered, with only the uppermost layer being weak.