Deformation Propagation Research Articles

Hybrid FEM and peridynamic simulation of hydraulic fracture propagation in saturated porous media

This paper presents a hybrid modeling approach for simulating hydraulic fracture propagation in saturated porous media: ordinary state-based peridynamics is used to describe the behavior of the solid phase, including the deformation and crack propagation, while FEM is used to describe the fluid flow and to evaluate the pore pressure. Classical Biot poroelasticity theory is adopted. The proposed approach is first verified by comparing its results with the exact solutions of two examples. Subsequently, a series of pressure- and fluid-driven crack propagation examples are solved and presented. The phenomenon of fluid pressure oscillation is observed in the fluid-driven crack propagation examples, which is consistent with previous experimental and numerical evidences. All the presented examples demonstrate the capability of the proposed approach in solving problems of hydraulic fracture propagation in saturated porous media.

Vulnerable window of yield strength for swelling-driven fracture of phase-transforming battery materials

Despite numerous experimental and theoretical investigations of the mechanical behavior of high-capacity Si and Ge Li-ion battery anodes, our basic understanding of swelling-driven fracture in these materials remains limited. Existing theoretical studies have provided insights into elasto-plastic deformations caused by large volume change phase transformations, but have not modeled fracture explicitly beyond Griffith’s criterion. Here, we use a multi-physics phase-field approach to model self-consistently anisotropic phase transformation, elasto-plastic deformation, and crack initiation and propagation during lithiation of Si nanopillars. Our computational results reveal that fracture occurs within a “vulnerable window” inside the two-dimensional parameter space of yield strength and fracture energy and highlight the importance of taking into account the surface localization of plastic deformation to accurately predict the magnitude of tensile stresses at the onset of fracture. They further demonstrate how the increased robustness of hollow nanopillars can be understood as a direct effect of anode geometry on the size of this vulnerable window. Those insights provide an improved theoretical basis for designing next-generation mechanically stable phase-transforming battery materials undergoing large volume changes.

Along-strike structural variation in a salt-influenced fold and thrust belt: Analysis of the Kuqa depression

The Kuqa depression is associated with complex salt structures. Variation in fold geometries and subsalt fault activities were investigated using parallel cross-sections to reveal detailed along-strike variations within the Keshen 5 segment and their controlling factors. Along-strike variations were identified in both suprasalt and subsalt units. Linkages, such as the location of a transfer zone, were apparent, while the distribution of variations above and below the salt layer were decoupled. The results indicate that the pre-existing salt wall is the key factor driving along-strike variations because it acts as a weak zone that influences deformation propagation. Suprasalt structural variation results in different sediment depths, which have a significant impact on subsalt fault activity. In the eastern segment, fault activity decreases from the hinterland to the basin. In contrast, owing to the pre-existing salt wall and deep sedimentation near the hinterland in the western segment, the fault beneath the salt wall is characterized by maximum displacement. This study reveals the connection between suprasalt and subsalt deformation and the role of that a salt diapir plays in along-strike structural evolution variations for the Keshen 5 segment of the Kuqa depression. These findings are relevant for understanding along-strike deformation propagation and structural variation in other fold and thrust systems.

Comparative study on aromatic thermosetting co-polyester (ATSP) coating and nickel-aluminum bronze on under torsional fretting wear

In current work, the wear resistance of CuNiAl was improved by the application of an aromatic thermosetting co-polyester (ATSP)-based coating on its surface. Tribological behaviors of the ATSP coating at stresses of 1.52, 3.04 and 3.75 MPa under different lubrication conditions (dry friction and oil) were studied by the fretting wear test. The morphology and chemical composition of the coating were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and three-dimensional (3D) optical microscope. Results showed that at the same conditions, the friction torque of the ATSP coating was lower than that of CuNiAl. Significantly, wear was reduced by more than 90% after the application of the ATSP coating. The wear mechanism of the ATSP coating was slight deformation with pits induced by plastic deformation and fatigue crack propagation. The ATSP coating underwent molecular chain breakage during wear and chemical reaction with the friction pair to form a transfer film which played an important role in the reduction of wear.

Deformation and Fault Propagation at the Lateral Termination of a Subduction Zone: The Alfeo Fault System in the Calabrian Arc, Southern Italy

The Calabrian Arc subduction, southern Italy, is a critical structural element in the geodynamic evolution of the central Mediterranean basin. It is a narrow, northwest-dipping slab bordered to the southwest by the Alfeo Fault System (AFS) and to the northeast by a gradual transition to a collision. We used a dense set of two-dimensional high-penetration (up to 12 s) multichannel seismic reflection profiles to build a three-dimensional model that spans the AFS for over 180 km of its length. We find that the AFS is made up of four deep-seated major blind segments that cut through the lower plate, offset the subduction interface, and only partially propagate upward across the accretionary wedge in the upper plate. These faults evolve with a scissor-like mechanism (mode III of rupture propagation). The shallow part of the accretionary wedge is affected by secondary deformation features well aligned with the AFS at depth but also mechanically decoupled from it. Despite the decoupling, the syn-tectonic Pliocene-Holocene deposits that fill in the accommodation space generated by the AFS activity at depth, constrain the age of inception of the AFS and allows us to estimate its throw and propagation rates. The maximum throw value is 6,000 m in the NW sector and decreases to the SE. Considering the age of faulting, the fault throw rate decreases accordingly from 2.31 mm/yr to 1 mm/yr. The propagation rate decreases from 62 mm/yr to 15 mm/yr during the Pliocene-Pleistocene, suggesting that also the Calabrian subduction process should have slowed down accordingly. The detailed spatial and temporal reconstruction of this type of faults can reveal necessary information about the evolution of subduction systems.

Fractal evolution mechanism of rock fracture in undersea metal mining

Through rock mechanics test, similar simulation experiment, borehole photographic observation of rock fissure, numerical simulation calculation of plastic zone distribution and deformation monitoring of rock mass during undersea mining, the fractal evolution mechanisms of rock fracture in undersea metallic deposits of Sanshandao Gold Mine were studied by fractal theory. The experimental researches on granite mechanics test in undersea deposit indicate that with the increase of load, the granite deformation energy and the fractal dimension of acoustic emission (FDAE) increase gradually. However, after reaching the peak stress of specimen, the fractal dimensions of acoustic emission (FDAEs) decrease and the granite specimen fails. Therefore, the fractal dimension evolution of rock failure can be divided into four stages, which are fissure inoculation stage, fissure growth stage, fissure expansion stage and fracture instability stage, respectively. By calculating and analyzing the damage photographs of rock specimens in Sanshandao Gold Mine, the fractal dimension of rock fissure is 1.4514, which is close to the average value of FDAE during granite destruction, i.e., 1.4693. Similar simulation experiments of undersea mining show that with the excavation proceeding, the FDAE in rock stratum increases gradually, and when the thickness of the isolation roof is less than 40 m, the FDAE begins to decrease, and meanwhile the sign of water inrush emerges. The numerical simulation researches on the plastic zone distribution of undersea mining in Sanshandao Gold Mine indicate that the fractal dimension of plastic zone (FDPZ) where the failure characteristics occur is 1.4598, close to the result of similar simulation experiment of 1.4364, which shows the sign of water inrush. Meanwhile, the thickness of the isolation roof for undersea mining should be more than 40 m, which is consistent with the results of similar simulation experiment. In Sanshandao Gold Mine, the rock fissures in undersea mining were observed by borehole photography and the rock mass deformation was monitored by multi-point displacement meters, and at the same time the fractal dimensions of strata borehole fissure distribution and energy release ratio (ERR) of rock mass were calculated by fractal principle, which are 1.2328 and 1.2685, respectively. The results demonstrate that rock deformation and fissure propagation are both in the second stage of fissure growth, and have not reached the fourth stage of fracture instability. Therefore, the conclusion can be obtained that the undersea mining in Sanshandao Gold Mine is safe at present.

Segmentation and increasing activity in the Neogene-Quaternary Teruel Basin rift (Spain) revealed by morphotectonic approach

The NNW-SSE trending Teruel Basin rift is the largest Late Miocene-Quaternary extensional intracontinental structure located within the central-eastern Iberian Chain (Spain). The structural and morphotectonic study carried out in the central-northern part of this half graben basin (north of Teruel city) has allowed us to analyse rift segmentation, deformation partitioning and rift evolution. Results are based on vertical displacement calculations (fault throw and bending) of the main border and intrabasin fault zones. We use two geomorfological-stratigraphical markers, the Intramiocene Erosion Surface (IES; 11.2 Ma) and the Fundamental Erosion Surface (FES; 3.5 Ma). While the first marker reveals rift initiation under an E-W extension, the late marker records vertical displacements associated to a second, Late Pliocene–Quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ENE-WSW trending ó3. Despite the along-axis rift segmentation into three structural domains (northern, central and southern) and the distribution of deformation among border and intrabasin faults in the central and southern domains, a consistent average slip rate (post-IES) of 0.09 mm/a has been calculated on distinct transects across the basin, suggesting a homogeneous crustal-scale extension process in the region. The results also reveal that slip rates during the Late Pliocene-Quaternary (0.12–0.16 mm/a) are higher than the Late Miocene-Early Pliocene (0.05–0.07 mm/a). Slip rate increase is caused by (i) a westward propagation of deformation from the Valencia Through, and (ii) a change in the regional stress field, both enhanced by crustal doming affecting central-eastern Iberia, as well as progressive fault linkage. Throw vs. distance graphs suggest that the main faults are in a transient stage towards coalescence, less advanced within the southern domain. Regional Late Pliocene-Quaternary uplift, concomitant with increasing slip rates in the Teruel Basin rift, has caused the basin to rise, so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present-day fluvial network.

Mesoscale fracture analysis of recycled aggregate concrete based on digital image processing technique

AbstractSince recycled aggregate concrete (RAC) is valuable for green concrete and global sustainability, it has attracted many numerical research studies as a five‐phase material in mesolevel. In this study, the digital image processing (DIP) technique is used to obtain the real aggregate and mortar distribution of recycled concrete specimens. By applying the DIP MATLAB model, the real mesoheterogeneity of RAC is well represented. Based on the base force element method (BFEM), a mesomechanical model is constructed to simulate the uniaxial tension and compression tests of recycled concrete specimens subjected to displacement loads. The damage and the cracking mechanisms of RAC are analyzed in the mesolevel. Moreover, the failure process and the failure mode are investigated. Results indicate the nonlinearity deformation, stress redistribution, and cracks propagation of RAC. The stress–strain curve, fracture energy, and fracture distribution are also figured. The comparative analysis between the simulation and the experimental results of in situ RAC samples shows the applicability of the model; therefore, the failure mechanism is revealed. It also extends the application of the BFEM in the field of failure mechanism analysis of RAC as a heterogeneous composite material.

A Combined Support System Associated with the Segmental Lining in a Jointed Rock Mass: The Case of the Inclined Shaft Tunnel at the Bulianta Coal Mine

This paper presents a case study on the impact of jointed rock mass deformation on liner stability for an inclined excavation at the Bulianta Coal Mine. The tunnel was excavated by a single shield tunnel boring machine (TBM), with part of the excavation passing through a heavily jointed rock mass at great depth. Serious local instabilities occurred at one side of the liner due to highly asymmetric loading caused by large ground stresses and joint deformation. A support system with anchored cables and compressible mortar was combined with segmental lining to overcome these instabilities. With this case as a baseline, some numerical sensitivity analyses were performed to study how the ground might have responded to different combinations of support. The results show that an appropriately anchored cable system was able to limit the propagation of the asymmetric deformation of the jointed rock mass and significantly reduce the degree of anisotropy and the magnitude of the loads on the liner. The use of compressible mortar between the liner and the jointed rock mass further lowered the anisotropy of the load on the liner. There are optimum values for the rock bolt length and the compressible mortar thickness, beyond which these parameters have limited effects on the behaviour of the system. The combined effect of compressible mortar and anchor cables in promoting ground and liner stability is greater than the sum of the two individual support effects. These results clearly demonstrate that the combination of anchored cables and compressible mortar had a significant positive effect on the overall support system stability.

Numerical simulation of level ice impact on landing craft bow considering the transverse isotropy of Baltic Sea ice based on XFEM

Ice bending is a major failure mechanism of level ice when ships and marine structures interact with level ice. This paper aims to investigate the ice bending and ice load when level ice collides on ships and marine structures using numerical simulation method, and compare the numerical results with field test. The fracture of ice is simulated with extended finite element method (XFEM), and cohesive zone concept is used to describe the crack propagation. In order to consider the characteristics of S2 columnar ice, a transversely isotropic elastic material model is used for the ice bulk elements, and a transversely isotropic Tsai-Wu failure criterion is adopted to predict the initiation of cracks. A well-controlled field test of a landing craft bow colliding with level ice in Baltic Sea is simulated to verify the numerical scheme. The ice plate's continuous deformation, crack initiation and crack propagation at different impact velocities and angles are simulated and the results are discussed. In the simulation, the bending crack emerges at the midline of the top surface of ice plate, then propagates towards free boundary, and finally a circumferential crack forms. It is found that with the impact velocity increases, the bending load increases and the fracture size (perpendicular distance from the crack to the contact edge) decreases. And as the angle between the landing craft bow and vertical direction increases, the bending load and the fracture size decrease. The simulated results corresponds well with the field test. The competition between the circumferential crack and radial crack is also found in the simulation and will be discussed in this paper. The results show that this method well simulates the bending of level ice and predict the ice load, and provides a good approach for investigating the mechanism of different forms of level ice fracture.

Movements of ground and existing structures induced by slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay

This paper presents a comprehensive study of field measurement of ground movements and displacements of adjacent existing structures induced by large diameter slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay. The evolution of displacements at six transverse monitoring sections against the distance of TBM cutterhead from corresponding instrumentations is characterized and interpreted in conjunction with recorded TBM tunnelling parameters. Measured results highlight that adjacent existing structures move almost synchronously along with ground except the magnitude, and stiffer structures can greatly resist deformation than pure soil does. The cast-in-place piles constructed between current tunnel and elevated bridge can effectively block the propagation of tunnelling-induced deformation. Results also show that the compensation effect of tail grouting on ground displacements is limited to the local areas which are close to the grouting position, and this effect attenuates as the distance from grouting position increased. The final “inwards” or “outwards” trend of surrounding soil relative to the tunnel relies on the injected grouting volume. The observation indicates that TBM tunnelling parameters at a transverse section can not only influence ground settlements there but also influence ground settlements ahead and behind this section along longitudinal direction to varying degrees. This longitudinal effect can be considered by introducing the impact coefficients of face pressure and tail grouting. The measured data of surface settlements along tunnel longitudinal axis and predicted ones using Loganathan-Poulos formula with and without considering this longitudinal effect are compared. The compared results indicate the longitudinal effect should be taken into account for the accuracy of prediction. The paper can provide valuable references for settlement prediction due to TBM tunnelling in clayey soil.

Episodic out-of-sequence deformation promoted by Cenozoic fault reactivation in NW Argentina

The Central Andes are the product of contractional deformation related to subduction of the Nazca plate beneath the South American continent. In this geodynamic setting, thrust belt propagation in the Central Andean retroarc in NW Argentina and southern Bolivia has been linked with the critical wedge model implying progressive eastward migration of the deformation front during the Cenozoic. However, Eocene unconformities and growth strata within the orogenic hinterland of the Eastern Cordillera and Puna Plateau suggest selective reactivation of pre-Andean and Andean faults revealing a pattern of diachronous and spatially disparate range uplifts. The Calchaquí Valley in NW Argentina is characterized by basin-and-range morphology, which is intimately linked with the heterogeneous Neoproterozoic basement, Cretaceous rift structures, and the Cenozoic foreland. In this study, we analyze this complex deformation by reconstructing Cenozoic fault reactivation and sedimentation patterns in the Eastern Cordillera. Detailed structural mapping along the eastern Calchaquí border (Tonco area) reveals five Cenozoic unconformities in the former foreland deposits related to multiple episodes of fault reactivation during the Eocene-to-Pleistocene. A refined chronostratigraphy (U-Pb zircon), new AHe thermochronological data (apatite U-Th-Sm/He), and existing evidence for deformation indicate episodic out-of-sequence deformation and increased Eo-Oligocene (Puna Plateau) to Miocene (Eastern Cordillera) fault displacement apparently controlled by pre-Cenozoic heterogeneities. The coeval eastward propagation of deformation and continuing deformation in the west generally challenge the applicability of the critical wedge model.

An immediate response to the Indian-Eurasian collision along the northeastern Tibetan Plateau: Evidence from apatite fission track analysis in the Kuantan Shan-Hei Shan

The Tibetan Plateau offers an ideal region for understanding the processes of continental collision and related intracontinental deformation. However, when the Cenozoic deformation was initiated in the present northeastern margin of the plateau, >2000 km north to the Indian-Eurasian collision front, remains an issue in debate. Two competing end-member models have been proposed, involving immediate deformation response and progressive deformation propagation. Solving this problem partly relies on determining whether there was contemporaneous deformation with initial Indian-Eurasian collision along the northeastern margin of the Tibetan Plateau. In this study, we employ apatite fission track (AFT) analysis to shed new light on the exhumation history of the Kuantan Shan-Hei Shan along the northeastern margin of the Tibetan Plateau, with a motivation to determine whether deformation-related exhumation during initial collision stage occurred in the region. The 22 granite samples produce AFT ages ranging from 22.3 ± 2.6 Ma to 175 ± 18 Ma and mean track lengths from 11.17 ± 2.26 μm to 13.63 ± 1.93 μm. Thermal history modeling indicates five episodes of rapid exhumation-related cooling, which took place in the early Jurassic, early Cretaceous and late Cretaceous, during/since the Eocene and since the middle Miocene. The exhumation events prior to the Cenozoic are attributed to far-field responses of successive closure of fossil oceans and assembly of blocks along the southern margin of the Eurasian continent. The Eocene exhumation along the Kuantan Shan-Hei Shan is speculated to represent an immediate response to the initial Indian-Eurasian collision. These results lend support to the immediate deformation response model along the northeastern plateau. The episodic exhumation observed in this study, combined with previous geophysical findings, implies that the Kuantan Shan-Hei Shan represents the southern margin of the Alashan Block, serving as a significant and long-lived lithospheric weak zone susceptible to intracontinental deformation during episodes of far-field tectonic event.

Sliding wear and fatigue cracking damage mechanisms in reciprocal and unidirectional sliding of high-strength steels in dry contact

Rock drill components operate under tough contact conditions during rock drilling. Reciprocal and unidirectional motion under high contact stresses are the common contact conditions between interconnected components. It will result in component damage and often the observed surface damage of rock drill tools is due to wear and fatigue cracks. Nevertheless, the effects of the properties and structure of the mating materials on tribological performance, is not fully understood. The present study is dedicated to simulation and investigation of the wear mechanisms observed in reciprocal and unidirectional sliding of high strength steels for rock drill components. A high strength martensitic steel, 22NiCrMo12–F, commonly used in rock drills was tested in self-mating contact. Wear mechanisms were investigated by means of electron microscopy and wear damage was quantified by a 3D optical interferometer. Total damage, as a result of adhesive wear, severe plastic deformation and nucleation and propagation of fatigue cracks, was discussed in relation to test conditions and material properties. It was observed that the coefficient of friction decreased with increasing normal load. Moreover, the results showed that the type of motion had a significant influence on the worn volume and crack nucleation of the specimens in sliding contact. In addition, the reciprocal motion resulted in higher wear than unidirectional motion under the same test conditions.

Hydraulic fracture propagation in a heterogeneous stress field in a crystalline rock mass

Abstract. As part of the In-situ Stimulation and Circulation (ISC) experiment, hydraulic fracturing (HF) tests were conducted in a moderately fractured crystalline rock mass at the Grimsel Test Site (GTS), Switzerland. The aim of these injection tests was to improve our understanding of processes associated with high-pressure fluid injection. A total of six HF experiments were performed in two inclined boreholes; the surrounding rock mass was accessed with 12 observation boreholes, which allows for the high-resolution monitoring of fracture fluid pressure, strain, and microseismicity in an exceptionally well-characterized rock mass. A similar injection protocol was used for all six experiments to investigate the complexity of the fracture propagation processes. At the borehole scale, these processes involved newly created tensile fractures intersecting the injection interval, while at the cross-hole scale, the natural network of fractures dominated the propagation process. The six HF experiments can be divided into two groups based on their injection location (i.e., south or north to a brittle–ductile shear zone), their similarity of injection pressures, and their response to deformation and pressure propagation. The injection tests performed in the south connect upon propagation to the brittle–ductile shear zone. Thus, the shear zone acts as a dominant drain and a constant pressure boundary. The experiments executed north of the shear zone show smaller injection pressures and larger backflow during bleed-off phases. From a seismic perspective, the injection tests show high variability in seismic response independently of the location of injection. For two injection experiments, we observe reorientation of the seismic cloud as the fracture propagated away from the wellbore. In both cases, the main propagation direction is normal to the minimum principal stress direction. The reorientation during propagation is interpreted to be related to a strong stress heterogeneity and the intersection of natural fractures striking differently than the propagating hydraulic fracture. The seismic activity was limited to about 10 m of radial distance from the injection point. In contrast, strain and pressure signals reach further into the rock mass, indicating that the process zone around the injection point is larger than the zone illuminated by seismic signals. Furthermore, strain signals indicate not just single fracture openings but also the propagation of multiple fractures. Transmissivities of injection intervals increase about 2–4 orders of magnitudes.

Compliant assembly deviation analysis of large-scale thin-walled structures in different clamping schemes via ANCF

PurposeThe structure stiffness is greatly affected by the fixture constraints during assembly due to the flexibility of large-scale thin-walled structures. The compliant deformation of structures is usually not consistent for the non-uniform stiffness in various clamping schemes. The purpose of this paper is to investigate the correlation between the assembly quality and the clamping schemes of structures with various initial deviations and geometrical parameters, which is based on the proposed irregular quadrilateral plate element via absolute nodal coordinate formulation (ANCF).Design/methodology/approachTwo typical clamping schemes are specified for the large-scale thin-walled structures. Two typical deviation modes are defined in both free and clamping states in the corresponding clamping schemes. The new irregular quadrilateral plate element via ANCF is validated to analyze the compliant deformation of assembled structures. The quasi-static force equilibrium equations are extended considering the factors of clamping constraints and geometric deviations.FindingsThe initial deviations and geometrical parameters strongly affect the assembly deviations of structures in two clamping schemes. The variation tendencies of assembly deviations are demonstrated in details with the circumferential clamping position and axial clamping position in two clamping schemes, providing guidance to optimize the fixture configuration. The assembly quality of structures with deviations can be improved by configuration synthesis of the clamping schemes.Originality/valueTypical over-constraint clamping schemes and deviation modes in clamping states are defined for large-scale thin-walled structures. The plate element via ANCF is extended to analyze the assembly deviations of thin-walled structures in various clamping schemes. Based on the proposed theoretical model, the effects of clamping schemes and initial deviations on the deformation and assembly deviation propagation of structures are investigated.

Investigation of Stress Field and Fracture Development During Shale Maturation Using Analog Rock Systems

The emergence of hydrocarbons within shale as a major recoverable resource has sparked interest in fluid transport through these tight mudstones. Recent studies suggest the importance to recovery of microfracture networks that connect localized zones with large organic content to the inorganic matrix. This paper presents a joint modeling and experimental study to examine the onset, formation, and evolution of microfracture networks as shale matures. Both the stress field and fractures are simulated and imaged. A novel laboratory-scale, phase-field fracture propagation model was developed to characterize the material failure mechanisms that play a significant role during the shale maturation process. The numerical model developed consists of coupled solid deformation, pore pressure, and fracture propagation mechanisms. Benchmark tests were conducted to validate model accuracy. Laboratory-grade gelatins with varying Young’s modulus were used as scaled-rock analogs in a two-dimensional Hele-Shaw cell apparatus. Yeast within the gelatin generates gas in a fashion analogous to hydrocarbon formation as shale matures. These setups allow study and visualization of host rock elastic-brittle fracture and fracture network propagation mechanisms. The experimental setup was fitted to utilize photoelasticity principles coupled with birefringence properties of gelatin to explore visually the stress field of the gelatin as the fracture network developed. Stress optics image analysis and linear elastic fracture mechanics (LEFM) principles for crack propagation were used to monitor fracture growth for each gelatin type. Observed and simulated responses suggest gas diffusion within and deformation of the gelatin matrix as predominant mechanisms for energy dissipation depending on gelatin strength. LEFM, an experimental estimation of principal stress development with fracture growth, at different stages was determined for each gelatin rheology. The interplay of gas diffusion and material deformation determines the resulting frequency and pattern of fractures. Results correlate with Young’s modulus. Experimental and computed stress fields reveal that fractures resulting from internal gas generation are similar to, but not identical to, type 1 opening mode.

Jurassic–Early Cenozoic Tectonic Inversion in the Qilian Shan and Qaidam Basin, North Tibet: New Insight From Seismic Reflection, Isopach Mapping, and Drill Core Data

AbstractThe pre‐Cenozoic structural pattern of Asia has had a strong impact on the localization and propagation of the Cenozoic deformation that gave birth to the Tibetan Plateau. Northern Tibet represents a key area to decipher the structural and kinematic links between the Mesozoic and Cenozoic evolution of Tibet. Nonetheless, the Mesozoic tectonic setting of the North Tibet and the role that the Paleozoic inherited Altyn Tagh Fault (ATF) shearing zone played in controlling the regional tectonic pattern during the deposition of the Mesozoic strata remain controversial. This study is based on seismic reflections, isopach maps of the Mesozoic strata in the Qaidam Basin, and provenance analysis using detrital zircon geochronological and heavy mineral contents. Seismic reflections and isopach maps demonstrate that sustained strike‐slip motion along the ATF during the Early to Late Jurassic induced transtensional basin formation. Further away from the main ATF (eastern parts of the Qilian Shan and the northern Qaidam Basin), transtension also occurred along major faults, although local transpression developed in relay zones. Rotation in the regional stress field induced compression and basin inversion during the Late Jurassic to Early Cretaceous. The Cenozoic sedimentary rocks in these regions display widespread growth strata and angular unconformities characteristic of compression. This is consistent with topographic changes marked by sediment source variation evidenced by detrital zircon geochronology and heavy mineral analysis. We propose that the mechanism driving the Jurassic extension/transtension in North Tibet could be related to far‐field effects of subduction processes along the southern margins of the continent.

A bond‐based peridynamic model considering effects of particle rotation and shear influence coefficient

SummaryThe classical bond‐based peridynamic (BPD) model is limited with a fixed Poisson's ratio. To overcome this limitation, an improved BPD model is proposed to analyze the deformation and crack propagation of microelastic brittle materials with emphasis on varying Poisson's ratios. In the proposed model, the bond is subjected to axial and transverse pairwise forces, and the particle rotation angle is added to eliminate the additional bending moment caused by transverse forces, which is a key factor to satisfy the balance of angular momentum exactly. As a result, the bond not only has axial displacement but also has transverse displacement and particle rotation. This extension in the displacement mode overcomes the limitation of the fixed Poisson's ratio in the classical BPD model. The simulation results demonstrate the precision of the improved BPD model and prove its ability to predict deformations and crack propagations.

Study of wave propagation through porous lattices with buckling instabilities in an aqueous environment

Elastic lattices with cylindrical air-filled voids may undergo significant topology changes when deformed due to the buckling instabilities of the thin elastic ligaments between voids. Such phononic crystals are of interest to, for example, achieve auxetic behavior and create tunable stop bands that vary as a function of the deformation. Most studies reported in the literature by others focus on lattices made of soft elastomers, and the resulting nonlinear deformation or elastic wave propagation due to low-frequency vibrations in air. The current research focuses on transitioning these previously studied concepts on buckling lattices to an aqueous environment. Initial investigations presented here are for 3-D printed lattices comprised of rigid plastic and deformed by leveraging shape memory effects that result in softening and hardening of materials under heating and cooling, respectively. The use of rigid plastic addresses inherent difficulties that arise with soft elastomers, including high loss, fabrication at scales of interest, and appropriate frequency range for wave propagation. The present work focuses on numerical simulations and experimental measurements of wave propagation through finite, plastic lattices with air-filled voids in water. [Work Supported by the Office of Naval Research.]