Restructuring of emergent grain boundaries at free surfaces – an interplay between core stabilization and elastic stress generation

Scanning tunneling microscopy and numerical calculations are used to study the structure and relaxation of grain boundaries at the surface of planar nanocrystalline copper (111) films and bicrystals. We show that the strong energetic preference for boundary cores to lie along close-packed planes introduces a restructuring that rotates adjoining grains and generates elastic stresses in the triple junction region. The interplay of this stress field and the core stabilization determines the length scale of the restructuring and controls the shape and magnitude of the displacement field around the triple junction. Depending on the in-plane angle, restructured boundaries can extend to depths of ~ 15 nm with the associated elastic stress fields extending to even greater depths. These results point to a new mechanism of boundary relaxation at surfaces that is expected to play an important role in grain coalescence and stress evolution in growing films.

Stress generation, relaxation and size control in confined tumor growth

Experiments on tumor spheroids have shown that compressive stress from their environment can reversibly decrease tumor expansion rates and final sizes. Stress release experiments show that nonuniform anisotropic elastic stresses can be distributed throughout. The elastic stresses are maintained by structural proteins and adhesive molecules, and can be actively relaxed by a variety of biophysical processes. In this paper, we present a new continuum model to investigate how the growth-induced elastic stresses and active stress relaxation, in conjunction with cell size control feedback machinery, regulate the cell density and stress distributions within growing tumors as well as the tumor sizes in the presence of external physical confinement and gradients of growth-promoting chemical fields. We introduce an adaptive reference map that relates the current position with the reference position but adapts to the current position in the Eulerian frame (lab coordinates) via relaxation. This type of stress relaxation is similar to but simpler than the classical Maxwell model of viscoelasticity in its formulation. By fitting the model to experimental data from two independent studies of tumor spheroid growth and their cell density distributions, treating the tumors as incompressible, neo-Hookean elastic materials, we find that the rates of stress relaxation of tumor tissues can be comparable to volumetric growth rates. Our study provides insight on how the biophysical properties of the tumor and host microenvironment, mechanical feedback control and diffusion-limited differential growth act in concert to regulate spatial patterns of stress and growth. When the tumor is stiffer than the host, our model predicts tumors are more able to change their size and mechanical state autonomously, which may help to explain why increased tumor stiffness is an established hallmark of malignant tumors.

Determination of Local Stresses and Strains within the Notch Strain Approach: The Efficient and Accurate Calculation of Notch Root Strains Using Finite Element Analysis

For the service life estimation of metallic components under cyclic loading according to strain-based approaches, a simulation of the elastic-plastic stress–strain path at the point of interest is necessary. An efficient method for determining this stress–strain path is the use of the load–notch-strain curve, as this is also implemented within the FKM guideline nonlinear. The load–notch-strain curve describes the relationship between the load on the component and the local elastic-plastic strain. On the one hand, this can be estimated from loads or theoretical elastic stresses by using notch root approximations. On the other hand, this can be determined in a finite element analysis based on the elastic-plastic material behaviour. This contribution describes how this latter option is carried out in general and how it can be optimised in such a way that the FEA requires significantly less calculation time. To show the benefit of this optimisation, a comparative calculation on an exemplary geometry is carried out.

Estimation of thermodynamic stability of isoperiodic epitaxial structures whith GaInSbAs and GaInAsP solid solutions

The work studied the thermodynamic stability of GaInSbAs, GaInAsP heterosystems on different substrates. The isotherms of spinodal decomposition caused by chemical changes in the internal energy of the alloy and by elastic stresses at the layer-substrate interface are obtained with the model of quasiregular solutions. It has been found that elastic stresses lead to an expansion of the region of thermodynamic stability of isoperiodic solid solutions for GaSb substrates and a decrease in the critical temperature. The developed model can be using to selection of the technological modes and parameters of epitaxial growth.

Erratum to “Analytical Solution for the Lifetime of a Spherical Shell of Arbitrary Thickness Under the Pressure of Corrosive Environments: The Effect of Thermal and Elastic Stresses”

This note is to correct errata in the paper “quot;Analytical Solution for the Lifetime of a Spherical Shell of Arbitrary Thickness Under the Pressure of Corrosive Environments: The Effect of Thermal and Elastic Stresses”quot; published in Journal of Applied Mechanics, Vol.~88, P.~061004 (2021), doi: 10.1115/1.4050280.

Fracture Mechanics Assessment of Cracks in Areas of Large Scale Plasticity in Subsea HPHT Equipment

Subsea HPHT components may be evaluated utilizing a fracture mechanics-based approach as per guidelines in API RP 17TR8 and ASME Section VIII Division 3. Typically, the assessment is performed based on methods described in API 579-1/ASME FFS-1 and BS7910. The analysis is performed to determine critical flaw sizes and estimate the fatigue life of a growing crack as a means of establishing inspection intervals for the equipment. In most cases, the assessment is based on a linear elastic fracture mechanics approach. The effect of plasticity is generally included via the use of a failure assessment diagram (FAD); however, even with this approach the effect of plastic strain around the crack is not explicitly considered. The assessment standards do not provide clear guidance for cases involving a crack which is located within a region of large-scale plastic strain. For these cases, API 579, Annex 9G.5 recommends utilizing a driving force method whereby the J-integral is directly evaluated from an elastic-plastic finite element model. This paper presents such an approach. A simplified representative geometry is considered for this study. A region of a stress concentration, such as is typically encountered near an internal radius is considered. Such a region can potentially show localized plasticity. J-integral is calculated by explicitly modeling a series of cracks of increasing depth through this zone of plasticity and the results are compared to the different methodologies described in API 579-1/ASME FFS-1 and BS7910. Cracks are modeled both completely and partially enveloped within the plastic zone. Results are summarized and compared, highlighting the key differences between different analysis approaches with the aim of identifying the most conservative assessment method for different crack sizes. Additionally, the effect of large-scale plasticity on the crack driving force is determined relative to similar conditions without plasticity. The results indicate that for cracks lying within the regions of localized plasticity, using an API579 Level 2 approach coupled with extracting elastic-plastic through wall stresses from an uncracked geometry may result in significant under prediction of the driving force. Conversely, extracting linear elastic stresses from an uncracked geometry may significantly over predict the driving force and may prove too conservative for determining acceptable crack sizes. This paper presents a comprehensive comparison of different analysis approaches used for evaluating cracks in subsea equipment. The results indicate that, for HPHT equipment with increased safety implications, a detailed elastic plastic fracture mechanics evaluation of the cracked geometry should be performed for cases in which localized plasticity is expected to occur.

Formation of complex radiation defects in irradiated materials

The principles of formation of the complex vacancy defects (V-clusters), their ensembles and patterns of formation of superlattices of the V-clusters are determined. The inclusion of the drift component of the elementary defects into the field of elastic stresses of the V-cluster in the analysis allowed describing its genesis and development adequately. The mechanisms of motion of the V-clusters in the material are described in detail, considering their interaction with each other. The authors have developed the original physical and mathematical formalism within which it has become possible to describe the order-disorder phase transition when an ensemble of clusters chaotically distributed in the irradiated solid transforms into an ordered coherent superlattice. The critical point of the phase transition and the parameters of the defect lattice itself are determined. They are confirmed by the experimental results. The ordering process in this system is understood as the motion of the undamped wave of order parameter through the material, while other configuration states of the V-cluster ensemble constitute rapidly damping fluctuations. The article also shows the mechanism of linking the symmetry of the V-cluster superlattice to the symmetry of the initial crystal.

Seismometric monitoring of unstable rock mass in the Gunib district of Dagestan (North Caucasus)

Предгорная и горная часть территории Дагестана подвержена опасным геологическим процессам, в том числе и обвалам, что представляет определенную угрозу в местах проживания населения и соответствующей инфраструктуре (дороги, линии электропередач, газопроводы и д.р.). Вопрос контроля за опасными участками является очень важным и необходимым, поскольку управлять обвалами больших размеров человек не может, а вмешательство в естественный ход его развития представляется весьма проблематичным. Для минимизации ущерба необходим прогноз, с максимально допустимой точностью определяющий состояние предполагаемого обвала и зоной возможного поражения. Цель работы заключается в разработке новых подходов, используя геофизические наблюдения, направленные на познание исходной генетической сущности обвальных массивов, и на основе изучения полученных результатов выработать надёжные способы прогнозирования катастрофических событий. Метод исследований. Сейсмические датчики могут регистрировать колебания не только земной поверхности, но и отслеживать характерные особенности, связанные с состоянием отдельных массивов. На скорость распространения сейсмических волн влияет ряд факторов, таких как температура породы, влажность, механические напряжения и многие другие параметры. По изменениям сейсмических параметров горной породы можно отслеживать неустойчивое состояние скального массива, определить признаки, характерные для ускорения обвального процесса, накопления и снятия упругих напряжений в массиве, указывающих на растрескивание горных пород. Эти данные предоставляют важную информацию о развитии нестабильности крутых склонов в сторону катастрофического разрушения. Результаты работы. Впервые на Кавказе исследованы кинематические параметры потенциально обвального скального массива, находящегося в условиях неустойчивого равновесия на крутом склоне, представляющего опасность обрушения на районный центр Гуниб в Дагестане. Определены количественные и качественные характеристики от различных внешних динамических воздействий, микросейсмов, вызванных штормовыми циклонами в океане, землетрясениями. В рамках поставленной задачи были определены собственные частоты и амплитуды колебаний скального массива, а также его реакция на колебания удаленного сейсмического события. The foothill and mountainous part of the territory of Dagestan is subject to dangerous geological processes, including collapses, which poses a certain threat in the places of residence of the population and the corresponding infrastructure (roads, power lines, gas pipelines, etc.). The issue of control over hazardous areas is very important and necessary, since a person cannot manage large landslides, and interference in the natural course of its development seems to be very problematic. To minimize damage, a forecast is required that determines, with maximum permissible accuracy, the state of the expected collapse and the zone of possible damage. The aim of the work is to develop new approaches, using geophysical observations aimed at understanding the initial genetic essence of landslides, and, based on the results obtained, to develop reliable methods for predicting catastrophic events. Methods.Seismic sensors can register vibrations not only of the earth's surface, but also track the characteristic features associated with the state of individual massifs. The speed of propagation of seismic waves is influenced by a number of factors, such as rock temperature, moisture, mechanical stress and many other parameters. By changes in the seismic parameters of the rock, it is possible to track the unstable state of the rock mass, to determine the signs characteristic of the acceleration of the landslide process, the accumulation and removal of elastic stresses in the mass, indicating rock cracking. These data provide important information about the evolution of steep slope instability towards catastrophic failure. Results.For the first time in the Caucasus, the kinematic parameters of a landslide rock mass, which is in unstable equilibrium on a steep slope, posing a danger of collapse on the regional center Gunib in Dagestan, have been investigated. The quantitative and qualitative characteristics of various external dynamic influences, microseisms caused by storm cyclones in the ocean, earthquakes have been determined. Within the framework of the task, the natural frequencies and amplitudes of the rock mass vibration were determined, as well as its response to the fluctuations of a distant seismic event