Reconstruction Of Stress Fields Research Articles

Surface and Deep Structure of the Hanshan–Wuwei Basins in the Lower Yangtze Region: Implications for Mesozoic Tectonic Evolution of the South China Block

AbstractIndicating the tectonic features of the Hanshan–Wuwei basin can reconstruct the framework of the basins formed in Mesozoic and further understand the Mesozoic tectonic evolution of the South China Block. Studies on surface structure, regional stress field and deep geophysical characteristics of the Mesozoic Hanshan–Wuwei basin in Lower Yangtze region were carried out. NE–NNE trending folds and faults developed in the northern margin of the basins. The reconstruction of tectonic stress fields indicates four stress stages dominating the basins' evolution including NW–SE compression, N–S compression, NW–SE extension and NWW–SEE compression. 2D seismic profiles reveal coexistence of thrust, strike‐slip and normal faults in the basin. Combined with regional geological studies, the geodynamic processes for the formation of the Hanshan–Wuwei basin can be divided into five stages: 1) During the Late Triassic, EW trending foreland basin was formed by N–S compression; 2) From Mid‐Jurassic to Late Jurassic, continuous compression strengthened the foreland deformation and formed thrust nappes. In this stage, the integrated foreland basin was compartmentalized or fragmented, and transferred to the broken foreland basin; 3) NE‐trending sinistral strike‐slip movement at the beginning of the Early Cretaceous; 4) Regional extension resulted in normal faults and rift basins developing in the Late Cretaceous; 5) The NWW–SEE compression at the end of the Late Cretaceous caused NW sinistral strike‐slip faults to form, which partly transformed the rift basin.

A reconstruction method of stress fields, bending moments and wave parameters for floating nuclear power plants through regular wave identification

Floating nuclear power plants (FNPPs) have the potential to supply abundant electricity, hot water, and freshwater resources for offshore islands and offshore oil and gas extraction platforms. However, the consequences of a nuclear reactor accident can be extremely serious. In addition, there may be many uncertain factors in the actual operation of FNPPs. These factors lead to higher structural safety requirements. So， developing more scientific structural monitoring methods is an effective way to enhance the structural safety of FNPP. Traditional hull monitoring schemes can only track bending and torsional forces on specific cross-sections, failing to identify the overall stress field of the entire vessel structure. The paper proposes a reconstruction method for the stress field, bending moment distribution, and wave parameters of FNPP using regular wave identification. Initially, irregular waves are decomposed into a linear combination of multiple regular waves with different amplitudes and frequencies. Subsequently, the strains induced by these regular waves on the FNPP are utilized as basic functions to establish a mathematical model for reconstructing the stress field. The stress field, bending moment distribution, and wave parameters of the FNPP can be reconstructed by identifying the combination coefficients of the regular wave loads. The ill-posedness of the mathematical model for stress field reconstruction has the potential to significantly impact the accuracy of the stress field reconstruction, which was addressed by optimizing the sensor installation position in this study. Meanwhile, the optimization of the sensor installation position greatly reduces the dimensionality of mathematical models. Finally, a numerical study, i.e. FNPP being designed by China, was used to validate the accuracy of the proposed stress field reconstruction algorithm. The reconstructed stress field of the FNPP closely matched the original stress distribution under various irregular wave conditions.

Real-time stress field reconstruction method using online monitoring parameters for thick-walled power plant components based on gappy proper orthogonal decomposition

The three-dimensional stress distribution information of in-service components is of great significance for the intelligent operation and maintenance of power plants. A real-time stress field reconstruction method based on the gappy proper orthogonal decomposition (POD) and prediction function is proposed for condition monitoring of high-temperature pressured thick-walled components. Based on the “snapshots” method, the standard POD orthogonal basis is extracted from the high-fidelity data obtained from finite element analysis under various hot start load conditions to capture the main features of the stress fields. The complete stress field is reconstructed by the linear combination of the standard POD basis, and the modal coefficients are calculated using the discrete node stresses through the gappy POD procedure. Since only the online monitoring parameters of steam are available in practical operations, the prediction function is used to establish the mapping relationship between the monitoring parameters and node stress. The discrete nodes are determined by the trial-and-error method. The small global relative errors between the reconstructed stress fields and numerical solutions indicate the high accuracy of the proposed method. The spatial error of the entire stress field and the temporal error of the maximum stress were also evaluated. The computation time of the reconstruction process is significantly shorter than the sampling time step. The performance of gappy POD on different numbers of snapshots and modes was also presented.

A physics-based machine learning technique rapidly reconstructs the wall-shear stress and pressure fields in coronary arteries.

With the global rise of cardiovascular disease including atherosclerosis, there is a high demand for accurate diagnostic tools that can be used during a short consultation. In view of pathology, abnormal blood flow patterns have been demonstrated to be strong predictors of atherosclerotic lesion incidence, location, progression, and rupture. Prediction of patient-specific blood flow patterns can hence enable fast clinical diagnosis. However, the current state of art for the technique is by employing 3D-imaging-based Computational Fluid Dynamics (CFD). The high computational cost renders these methods impractical. In this work, we present a novel method to expedite the reconstruction of 3D pressure and shear stress fields using a combination of a reduced-order CFD modelling technique together with non-linear regression tools from the Machine Learning (ML) paradigm. Specifically, we develop a proof-of-concept automated pipeline that uses randomised perturbations of an atherosclerotic pig coronary artery to produce a large dataset of unique mesh geometries with variable blood flow. A total of 1,407 geometries were generated from seven reference arteries and were used to simulate blood flow using the CFD solver Abaqus. This CFD dataset was then post-processed using the mesh-domain common-base Proper Orthogonal Decomposition (cPOD) method to obtain Eigen functions and principal coefficients, the latter of which is a product of the individual mesh flow solutions with the POD Eigenvectors. Being a data-reduction method, the POD enables the data to be represented using only the ten most significant modes, which captures cumulatively greater than 95% of variance of flow features due to mesh variations. Next, the node coordinate data of the meshes were embedded in a two-dimensional coordinate system using the t-distributed Stochastic Neighbor Embedding (-SNE) algorithm. The reduced dataset for -SNE coordinates and corresponding vector of POD coefficients were then used to train a Random Forest Regressor (RFR) model. The same methodology was applied to both the volumetric pressure solution and the wall shear stress. The predicted pattern of blood pressure, and shear stress in unseen arterial geometries were compared with the ground truth CFD solutions on "unseen" meshes. The new method was able to reliably reproduce the 3D coronary artery haemodynamics in less than 10 s.

Excitation of S1-ZGV Lamb wave with a compact wedged transducer and its application in local stress measurement

Residual stress and its distribution are the key indicators to ensure structural integrity. However, current ultrasonic methods are not appropriate for complex stress measurement. Considering the proximity of zero-group-velocity (ZGV) mode with the cut-off frequency and its sensitivity to local material property, this paper proposed a local stress measurement method based on S1-ZGV mode. The stress field reconstruction was demonstrated numerically with a nonuniform plate. Then, a FE model was built to investigate the excitation of S1-ZGV mode by oblique incidence approach, proving that S1-ZGV mode can be effectively excited and received with a small distance. Thus, a contact ultrasonic system along with a tailor-made compact wedged transducer was built for experimental validation. Parametric studies were performed to obtain the optimal excitation conditions for S1-ZGV mode. At last, experimental validation was carried out by standard tensile testing. The stress coefficient between the frequency shift and the applied stress was obtained with a uniform plate. The stresses of the nonuniform plate at three different positions were measured, proving that S1-ZGV method is effective for local stress measurement in thin plates.

Fringe pattern analysis to evaluate light sources and sensors in digital photoelasticity.

When experimental photoelasticity images are acquired, the spectral interaction between the light source and the sensor used affect the visual information of the fringe patterns in the produced images. Such interaction can lead to fringe patterns with an overall high quality, but also can lead to images with indistinguishable fringes, and bad stress field reconstruction. We introduce a strategy to evaluate such interaction that relies on measuring the value of four handcrafted descriptors: contrast, an image descriptor that accounts simultaneously for blur and noise, a Fourier-based descriptor to measure image quality, and image entropy. The utility of the proposed strategy was validated by measuring the selected descriptors on computational photoelasticity images, and the fringe orders achieved when evaluating the stress field, from 240 spectral configurations: 24 light sources and 10 sensors. We found that high values of the selected descriptors can be related to spectral configurations that lead to better stress field reconstruction. Overall, the results show that the selected descriptors can be useful to identify bad and good spectral interactions, which could help to design better protocols for acquiring photoelasticity images.

DEFORMATION REGIMES AND LOW-RANK PALEOTECTONIC STRESSES OF THE WESTERN TIAN SHAN IN THE MESOZOIC – CENOZOIC

There is a description of the results of studies of deformation regimes and reconstruction of stress fields of certain time intervals of the Mesozoic – Cenozoic history of the western part of the Tien Shan based on the geological and structural data and earthquake focal mechanisms. The relevance of research is determined by the existing difficulties in the age reference of paleostress fields, which is associated with the retrospective nature of the initial data and the features of geological evolution, as well as the existence of controversial, unresolved issues regarding the development of the western periclinal part of the Tien Shan in the Mesozoic – Cenozoic. The aim of the research is to reconstruct the rank components of paleostresses in the earth’s crust in the western part of the Tien Shan at separate stages of the Mesozoic – Cenozoic development. The time intervals for which the stress field diagrams were obtained represent cyclically manifested phases of the first-rank rhythms, which are characterized by alternation of different deformation modes. The method for reconstructing paleostresses was based on the concept of the formation of superimposed systems of cracks of various generations, which were sequentially manifested at various stages of the development of deformation processes. Analysis of the data showed that with increasing age of rocks the number of different fracture systems actually increases – the earlier systems are superimposed by the later. At the same time, the characteristic elements in Quaternary rocks manifest themselves in different ways in the older rocks. This allows them to be used for the reconstruction of the Late Cenozoic stress field based on mass measurements of fracturing in rocks of earlier Mesozoic – Cenozoic ages. Based on the step-by-step identification of the heterochronous cracks system and determination of a pair of maxima of the fracture density with asymmetric scattering, region-based diagrams of the first-rank stress fields were obtained for different stages of manifestation of Mesozoic – Cenozoic deformation regimes: 1 – from the Permian-Triassic to the Middle Jurassic; 2 – Middle-Late Jurassic; 3 – Late Jurassic – Early Cretaceous; 4 – Late Cretaceous – Paleocene – Eocene; 5 – Oligocene – Quaternary. The results obtained indicate the alternation of compression and extension phases, first-rank for the region, and give an idea of the main trends in its geodynamic evolution. They can be used in the development of a tectodynamic model of the region.

РЕКОНСТРУКЦИЯ ТЕКТОНИЧЕСКИХ НАПРЯЖЕНИЙ ЦЕНТРАЛЬНОГО САХАЛИНА

The article presents the reconstruction of the tectonic stress field of the central part Sakhalin Island, obtained as a result of field tectonophysical studies in 2020–2022. The measurements made it possible to determine the predominant orientation of the main slickensides systems with different kinematics. The territory of Central Sakhalin is characterized by mainly subvertical orientation of the axis of maximum compression, as well as the subhorizontal and predominantly submeridionally directed axis of minimum compression (extension). The main revealed feature of Central Sakhalin is the predominance of horizontal extension as a type of stress state for the entire area. In its western part, horizontal shear and horizontal compression are significant. The number of horizontal extension conditions increases in the near-axial and eastern part of Central Sakhalin, closer to the Sea of Okhotsk. We found the cardinal difference between the obtained results of the stress field reconstruction and the results of similar studies in other geodynamically active regions of the country.

Reconstruction of Tectonic Stresses by Different Methods of Jointing Analysis (as the Example of the Morskoi Fault Zone in Cisbaikalia)

Abstract —Complex analysis of jointing in the Morskoi fault zone rocks (Cisbaikalia) has been carried out to compare two principally different methods of tectonophysical reconstruction of paleostress tectonic field, by geologic-structural data. A new approach to the paragenetic analysis of statistic measurements for ‘mute’ joints has been used; this approach makes it possible to reconstruct the stress state in the local rock exposure and to understand whether it belongs to the fault zone of a certain morphogenetic type and orientation. The second approach to reconstruct the stress filed is the Angelier–Delvaux kinematic analysis, which allows us to calculate the stress tensor and determine the stress regime, based on the analysis of strike-slip vectors on joints. Using the two methods we obtained the stress state solutions of local and regional levels for the study area. The paragenetic analysis gave twice as many local solutions for the same number of observation points. This is due to different environments of the formation of jointing sets and slickenlines in time (stages of fault zone evolution) and space (closeness to the fault plane). Most of the local solutions of the kinematic analysis coincide with the identical solutions of the paragenetic method on the stress state of the first or second orders. We obtained by an order of magnitude more ‘new’ (not repeated in the other method) paragenetic solutions than kinematic ones. At the next hierarchic level, the paragenetic analysis made it possible to reconstruct the stress field and fault zones of a higher rank. The results of both methods involve several stages of tectonic evolution of the rock massif. The identical regional stress fields reconstructed by different methods seem to belong to one stage. The studied fragment of the Morskoi fault, according to both methods, was activated in the three most intensively pronounced settings: compression, left-lateral strike-slip, and extension. Strike-slip stresses are concentrated closer to the fault plane. Moreover, we also revealed submeridional extension and NW compression. The results of the stress field reconstruction using the two methods are compatible and, in general, successfully complement and justify each other; however, the paragenetic method gives more numerous and variable solutions, resulting in the transition to the regional level and construction of the map for the study area fault zones. Complex application of both methods is recommended.

Stress imaging by guided wave tomography based on analytical acoustoelastic model.

A nondestructive method ( M) for stress characterization in plate-like structures is proposed. In this method, the acoustoelastic effects (AEEs) on Lamb and shear horizontal guided waves are used to reconstruct a nonuniform multiaxial stress field. The development of M starts by deriving an analytical acoustoelastic model (An-AEM) to predict AEEs induced by a triaxial stress tensor as a function of the stress components, its orientation, the wave propagation direction, and three acoustoelastic coefficients (AECs). The AECs are independent of stress but specific to each mode. The An-AEM allows one to retrieve the three components of the stress tensor and its orientation from AEEs, assuming the stress to be uniform in the plane of the plate and through its thickness. To deal with stress that is nonuniform in the plane, the An-AEM is combined with time-of-flight straight ray tomography to enable stress field reconstruction. Numerical simulation is used to illustrate how such reconstruction can be performed. It is shown that in some cases, stress components can be reconstructed with arbitrary accuracy, and in other cases, the tensorial nature of stress renders the accuracy of its reconstruction dependent on spatial variations of the stress orientation.

Accurate internal deformation measurement of an indentation test using micro-CT and self-adaptive digital volume correlation.

Mechanical indentation testing is a widely used technique for determining local mechanical properties of materials. Accurate measurement of internal deformation in the indentation test is necessary for further study of material properties. Therefore, an in situ experimental measurement strategy combining micro-CT imaging and self-adaptive digital volume correlation (SA-DVC) is proposed. Unlike conventional DVC, SA-DVC can automatically identify the optimal subvolume size for each calculation point, which can effectively minimize measurement errors. The efficacy of the proposed method is first verified by the simulated indentation experiment. Then, it is used to analyze the deformation of epoxy resin composite in a real indentation experiment. Measurement results indicate that the proposed method can estimate three-dimensional displacement and strain fields with enhanced accuracy, and further application of the obtained measurement results on material parameter identification and stress field reconstruction is expected.

Fast Reconstruction Method of the Stress Field for the Steam Turbine Rotor Based on Deep Fully Convolutional Network

Abstract Since it is difficult to directly measure the transient stress of a steam turbine rotor in operation, a rotor stress field reconstruction model based on the deep fully convolutional network for the startup process is proposed. The stress distribution in the rotor can be directly predicted based on the temperature of a few measurement points. First, the finite element model is used to accurately simulate the temperature and stress field of the rotor startup process, generating training data for the deep learning method. Next, data of only 15 temperature measurement points are arranged to predict the stress distribution in the critical area of the rotor surface, with the accuracy (R2-score) reaching 0.997. The time cost of the trained neural network model at a single case is 1.42 s in CPUs and 0.11 s in GPUs, shortened by 97.3% and 99.8% with comparison to finite element analysis, respectively. In addition, the influence of the number of temperature measurement points and the training size is discussed, verifying the stability of the model. With the advantages of fast calculation, high accuracy, and strong stability, the fast reconstruction model can effectively realize the stress prediction during startup processes, resulting in the possibility of a real-time diagnosis of rotor strength in operation.

A novel approach to reconstruct residual stress fields induced by surface treatments in arbitrary 3D geometries using the eigenstrain method

A novel approach has been proposed to reconstruct residual stress fields after surface treatments in arbitrary 3D geometries using the eigenstrain method based on bicubic spline interpolation surface and finite element (FE) method. Firstly, the complex curved surface is represented by piecewise interpolation of the smooth surface using explicit bicubic functions, then the computation of the distance and corresponding orientation are calculated by solving a constrained nonlinear multivariable problem using MATLAB, which is insensitive to the complexity of the curved treated surface and reduces the errors induced by differentiation operations when using Wall distance module in COMSOL in previous works. Three instances of 3D geometries after surface treatment studied previously in literature and finally an instance of a real turbine blade after LSP treatment conducted by ourselves are analyzed, which validate the proposed approach and illustrate its effectiveness in the reconstruction of residual stress fields for complex 3D geometries in various cases. The proposed approach provides a general and flexible way to the implementation of eigenstrain method in arbitrary 3D geometries using data interchange between the mathematical calculation software and FE analysis software for the design in industrial applications.

Paleostress regime reconstruction based on brittle structure analysis in the Shekarab Mountain, Eastern Iran

Eastern Iran, including the Sistan suture zone, comprises the boundary between Lut block and Afghan block. This research aims to reconstruct the stress regime evolution from the upper Cretaceous to Quaternary based on the brittle tectonic analysis. In this study, three episodic changes in stress regimes were recognized in the Shekarab Mountain using data inversion. In places where conglomerate outcrops are present, the Quaternary stress state is obtained using the youngest slickensides. The Quaternary stress state indicates that the direction of σHmax is close to N026°, which is compatible with the present-day Arabia-Eurasia convergence direction. Reconstruction of stress fields using age and sense of motion of faults shows that the stress regime during the Cretaceous was compressional, which caused the uplift of peridotites and ophiolites in the eastern part of the study area. The state of stress in the upper Eocene and Oligocene was transpressional; in the eastern part of the study area, there is a change from transpression to transtension. The exhumation of igneous rocks in the eastern part of the Shekarab Mountains is due to the local change of the stress regime. According to the results of this study, the first stage of stress state in the Shekarab Mountains was compressive and the average direction of maximum stress axis (σ1) was toward N337°. In Eocene, the tectonic regime was transpressional and the average direction of maximum stress axis (σ1) was toward N003°. In Quaternary, the tectonic regime is strike-slip and the average direction of maximum stress axis (σ1) is toward N026°. This implies that at least 49° clockwise rotation of σ1 happened in the Shekarab Mountain.

Stress State of Uzbekistan’s Seismically Active Areas

The current stress state of the Earth’s crust in the territory of Uzbekistan was studied by cataclastic analysis of displacements along fault sets for the collected catalog of earthquake focal mechanisms (EFM), compiled from the data of different authors. Two stages of stress field reconstruction are implemented at different levels of area detail of averaging parameters and for different magnitude hierarchies of the analyzed earthquakes. Azimuths and dip angles of principal stresses axes, Lode–Nadai coefficient values, geodynamic type of stress state, relative (normalized to the cohesion strength of the rock massif) normalized values of the maximum shear stress and effective pressure are determined for different areas of the studied territory. As a result of natural stress reconstructions based on the focal mechanisms of earthquakes with magnitudes M ≤ 4.5 and M ≥ 5, differences in the parameters of the stressed state were revealed. It has been suggested that the hierarchy of magnitude levels of the considered earthquakes reflects the stressed state of various deep layers of the crust. It is shown that strong earthquakes gravitate to zones of reduced effective pressure. On this basis, segments of active faults have been identified in the territory of eastern Uzbekistan, which are considered zones of potentially increased seismic hazard.

Locally exact asymptotic homogenization of periodic materials under anti-plane shear loading

A new implementation of the asymptotic homogenization theory for anti-plane shear loading is constructed based on locally exact elasticity solutions of unit cell problems at different orders in the asymptotic field expansion. The approach is a generalization of the previously developed locally exact homogenization theory for the determination of homogenized elastic moduli under uniform stress fields. The new theory has been developed for periodic materials in the presence of stress gradients and non-vanishing microstructural scale relative to the structural dimensions. The local interior unit cell problems are solved exactly up to the third order using Fourier series representations of the microfluctuation functions. The exterior unit cell periodic boundary value problems at different orders are tackled by an asymptotic extension of the previously introduced balanced variational principle for periodic materials. The effectiveness of the theory is verified by solving a structural problem with varying number of inclusions directly, and comparing the local fields with those reconstructed by the locally exact asymptotic homogenization approach. The theory is also employed to assess the accuracy of an uncoupled homogenization-localization approach in the reconstruction of local stress fields in periodic materials with different levels of microstructural refinement in the presence of stress gradients. The present contribution provides the foundation for further extension of the new locally exact asymptotic homogenization theory to in-plane loading problems of unidirectionally reinforced periodic materials.

КОЛІЗІЙНІ ДЕФОРМАЦІЇ ДНІПРОВСЬКО-ДОНЕЦЬКОЇ ЗАПАДИНИ Стаття 3. Геодинамічна модель тектонічної інверсії

The article concludes the trilogy on post-strip deformations of the Dnieper-Donets Basin. The results of tectonophysical analysis of collision deformations of the platform cover of the south-eastern part of the Dnieper-Donets Basin are summarized. Using the original method of reconstruction of stress and strain fields and tectonophysical analysis of geostructures, the system organization of inversion structural deformations of the Dnieper-Donets Basin and Donbass was studied. The tectonic inversion of the Dnieper-Donets Basin began in the Late Hercynian epoch in the situation of a general-plate collision under the influence of the inversion rise of the Donbas. Structural and kinematic analysis of deformations shows that the folds in the depression and linear anti- and synforms of the Donets Foldbelt were formed by the natural mechanism of longitudinal bending as a result of collisional warping of horizons in the geodynamic mode of transformation. In the late Mesozoic–­­Cenozoic inversion continued in the field of right-hand horizontal-shear deformations with a variable compressive component. This mode caused the advancing and pushing of sedimentary geomass from the Donets Foldbelt to the Hercynian neo-autochthonous and syneclise autochthonous of the South-Eastern Dnieper-Donets Basin. Due to the influence of the tectonic stamp of the Donets Foldbelt, the West Donets wedge-shaped segment was formed – the orocline of geomass tectonic wedging. Geodynamic bands of injection and displacement of sedimentary geomass were formed in the front of the invasion and in the axial zone of the orocline, where the main folded zones were formed. In Forland, at the ends of the main thrusts – “tectonic rails” of the wedging, an advanced scaly compression fan was formed. In the hinterland of the orocline, folded suture zones are formed by the roots of the covers of thrusting. The original geodynamic model of tectonic inversion provides for the destruction of the riftogenic structure in the Southeast of the Dnieper-Donets Basin by thrusting echelons of scaly covers and coulisses-articulated upliftt-folding. They compose a segment of the insertion of the geomasses of the Paleozoic cover into the territory of the West Donets Graben from the side of the Donets Foldbelt. The intrusion of the tectonic segment led to the formation of an inversion structure of a regional scale – the West Donets Cover-Folded Region.

Tectonic inversion of the Dnieper–Donetsk Basin. Part 2. Geodynamic situations and kinematic mechanism of riftogenic structure deformations

Formulation of the problem. In the second part of the article, the geodynamic mode and the kinematic mechanism of destruction of the Dnieper–Donetsk Basin by tectonic movements of the Late Hercynian and Alpine stages of tectogenesis were studied. New results of tectonophysical studies of the structural–kinematic evolution of the Earth's crust of Dnieper–Donetsk Basin at the collision stage are presented. The subject of research is a complex of deformation structures that complicate the sedimentary cover in the transitional zone of with Donetsk Foldbelt. Review of previous publications and studies. Using instrumental definitions of tectonite vergence, data of reconstruction of stress fields and quantitative modeling of deformations, a original kinematic model of tectonic inversion of the Dnieper–Donetsk Basin was developed. Methods. Structural–kinematic analysis of the structural drawings of collisional deformation and tectonics structures was used for regional geotectonic studies. Results. Tectonic inversion of the Dnieper-Donetsk Basin and Donbass began at the Late Hercynian epoch as a result of collisional movements of the compression orogen on the outskirts of the Paleotethis. Tangential compression of the southwestern direction led to the formation of gentle tectonic faults in the sedimentary cover of the Western Donets Graben, along which a lattice of thrust faults was formed. For a set of extrusion of sedimentary rocks in the reverse–thrust mode from the axial super-compressed zone, tectonic transport of geomas took place in the direction of the zones of "geodynamic shadow" on the southern side. Collisional deformations of horizons by the mechanism of longitudinal bending of the layers caused the formation of linear uplift-folding in the northern part of the Graben, and echelons of scaly thrust covers in the southern. At the Mesozoic and Cenozoic epochs, in the mode of interference of the reverse–thrust and horizontal-strike-slip fields, the Hercynian thrust lattice and the near-fault uplift folds underwent collisional deformation with the formation of coulisse–jointed folded zones and echeloned thrust covers. Based on the kinematic model of tectonic inversion of the Western Donets Graben, the geodynamics of the formation of the transition zone between the Dnieper–Donets Basin and the Donetsk Foldbelt is reconstructed. These data are the basis for adjusting the regional schemes of tectonic and oil and gas geological zoning. Scientific novelty and practical significance. The grouping of the compression axes in the western part of the Donbass caused the formation of a gorst-like geoblock-stamp, under the pressure of which the dislocated geomasses were thrusting onto the syneclisic cover of the southeastern segment of the depression. In the Western Donetsk Graben, the allochthonous stratum formed the body of the tectonic wedging geomas segment. Along the main strike–slip faults, which form the "tectonic rails" of the invasion, geodynamic zones of displacement of geomas were formed, composed of en-echelon articulated upthrust-folds. In its foreland, at the ends of the main strike–slip faults, an advanced scaly compression fan was formed, and in the hinterland, folded sutures were formed on the roots of the thrust covers. The main result of the research is a fundamentally new kinematic model of tectonic inversion of the Dnieper-Donetsk Basin. The model provides that the deformations of the riftogenic structure within the Graben were carried out according to the kinematic mechanism of the formation of a transverse orocline protruding under the pressure of the tectonic geoblock-stamp of the Donetsk Foldbelt.

КОЛІЗІЙНІ ДЕФОРМАЦІЇ ДНІПРОВСЬКО-ДОНЕЦЬКОЇ ЗАПАДИНИ Стаття 2. Кінематичні механізми тектонічної інверсії

The second article is devoted to the investigation of the natural mechanisms of tectonic inversion of the Dnieper-Donets depression. Using the materials of geological mapping of the territory of the West-Donetsk graben, structural proofs of the destruction of the riftogenic structure by collision tectonic movements of Hercinian and Alpic tectogenesis were obtained. The consequence of the inversion deformations is the formation of the West Donets cover-folding tectonic region within the Lugansk-Komyshuvasky tectonic area of the uplift-folding and the Kalmius-Toretsky region of the scalloped thrust covers, which are divided by the Main anticline. For the diagnosis of kinematic mechanisms of tectonic inversion, the data of reconstruction of tectonic stress fields and quantitative modeling of deformations of the southern outskirts of the Eastern European Platform were used. It is assumed that the tectonic inversion of the Dnieper-Donets basin began in the Zaal and Pfalz phases of orogenesis due to the collision motions of the compression orogen at the outskirts of Paleotetis. The formation of linear folding occurred in the uplifting-thrust mode in the field of stresses of the oblique left-hand compression of the sub-meridional directions. The kinematic mechanism of the folded deformations determined the longitudinal bending of the layers due to the extrusion of sedimentary geomas from the zone of maximum compression in the axial part to the zones of “geodynamic shadow” – in the direction of the sides of the depression. In the late Mesozoic and Cenozoic, uplifting-thrust and strike-slip stresses formed echeloned cover-thrust and coulisse-jointed uplift-folded structural paragenesis. According to the results of tectonophysical diagnostics of deformation structures, it was found that under geodynamic conditions of clustering of compression axes in the central part of the West-Donets graben against the reduction of the geological space horizontally and extension of the section due to the formation of the cover-folded allochthon, there were flexural deformations of the primary linear Hercinian folded forms. Such data can be considered as a kinematic mechanism of tectonic inversion of the invasion of the “tectonic stamp” by the Donets folded structure. Under its influence, the wedge-shaped segment of the tectonic thrust, which was diagnosed by the orcline of the transverse extension of the shallow type, was formed by the repeatedly deposited folds of sedimentary geomas in the articulation zone between the depression and the folded structure. In the front of the thrusted were formed folded zones of extrusion of geomas, which consist of coulisse-jointed uplift-anticlines and folded plates-coverings of tectonic thrusted. At the apex of the orocline, at the end of the dynamically coupled main thrusts, an advanced tectonic fan of compression is formed. In the rearward of the oraclline formed sutures – the roots of folded cover.

Implementation of traction constraints in Bragg‐edge neutron transmission strain tomography

AbstractSeveral recent methods for tomographic reconstruction of stress and strain fields from Bragg‐edge neutron strain images have been proposed in the literature. This paper presents an extension of a previously demonstrated approach based on Gaussian process regression that enforces equilibrium in the method. This extension incorporates knowledge of boundary conditions, primarily boundary tractions, into the reconstruction process. This is shown to increase the rate of convergence and is more tolerant of systematic errors that may be present in experimental measurements. An exact expression for a central calculation in this method is also provided which avoids the need for the approximation scheme that was previously used. Convergence of this method for simulated data is compared to existing approaches and a reconstruction from experimental data is provided. Validation of the results to conventional constant wavelength strain measurements and comparison to prior methods show a significant improvement.