Dislocation Model Research Articles

Crystal crack dislocation model in the hydrogen environment

A new hydrogen embrittlement fracture model is proposed based on the discrete distributed dislocation method. The effect of hydrogen atoms distribution at the crack tip on dislocation emission before micro-crack nucleation in the early stage of corrosion fracture is investigated. The results show that hydrogen can promote the emission, diffusion and movement of dislocations, increasing the plastic zone at the crack tip. In the hydrogen environment, the critical stress intensity factor of the crystalline material decreases by a maximum of about 11%. Within the theoretical framework of this model, it is believed that hydrogen atoms accumulated closest to the crack tip will promote the emission of dislocations from the crack tip, thereby suppressing passivation of the crack while promoting brittle fracture of metallic materials. These results are helpful to analyze the hydrogen embrittlement fracture behavior of the material.

Supersolid induced by dislocations with superfluid cores (Review Article)

The dislocation model of the supersolid state of 4He was proposed in 1987 by one of the authors of the review. The model obtained strong support by numerous experimental and theoretical investigations from 2007 to date. In these investigations, the validity of the idea put forward in 1987 was confirmed, and new conceptions of the superclimb of dislocations and of the giant isochoric compressibility or the syringe effect were proposed. In this paper, we review the main achievements of theoretical and experimental studies of a dislocation-induced supersolid and present current understanding of this phenomenon.

Gouge fabrics reset by thermal pressurization record stress on faults after earthquakes

Abstract Stress on seismogenic faults provides critical information about how much elastic energy is stored in the crust and released by earthquakes, which is crucial in understanding earthquake energetics and recurrence. However, determining post-earthquake stress states on faults remains challenging because current borehole methods are rarely applicable to damaged fault zone rocks. We applied neutron texture analysis to gouge samples of the 1999 Chi-Chi earthquake in Taiwan to infer the stress state after the earthquake. Results indicate that the clay fabric within the principal slip zone is orthogonal to the fault plane, whereas outside the principal slip zone the fabric is predominantly parallel to the bedding-parallel fault plane. We suggest that the clay fabric in the slip zone was first neutralized by the coseismic fluidization caused by thermal pressurization and later re-oriented to the new direction of post-earthquake principal stress. Such stress orientation is consistent with the orientations inferred from core-scale fault slip data and dislocation models constrained from global navigation satellite system displacements. If thermal pressurization is a ubiquitous process during earthquakes, gouge fabrics can be used to help probe the post-earthquake stress state of faults.

Ongoing tectonic subsidence in the Lesser Antilles subduction zone

SUMMARYGeological estimates of vertical motions in the central part of the Lesser Antilles show subsidence on timescales ranging from 125.000 to 100 yr, which has been interpreted to be caused by interseismic locking along the subduction megathrust. However, horizontal GNSS velocities show that the Lesser Antilles subduction interface is currently building up little to no elastic strain. Here, we present new present-day vertical velocities for the Lesser Antilles islands and explore the link between short- and long-term vertical motions and their underlying processes. We find a geodetic subsidence of the Lesser Antilles island arc at 1–2 mm yr−1, consistent with the ∼100-yr trend derived from coral micro-atolls. Using elastic dislocation models, we show that a locked or partially locked subduction interface would produce uplift of the island arc, opposite to the observations, hence supporting a poorly coupled subduction. We propose that this long-term, margin-wide subsidence is controlled by slab dynamic processes, such as slab rollback. Such processes could also be responsible for the aseismic character of the subduction megathrust.

Stress-strain response properties of the KhN55MVTs nickel alloy under uniaxial compression and their mathematical modeling

The rheology of the KhN55MVTs alloy has been studied at finite quasi-static strains and at operational and elevated temperatures to develop methods for calculating the emergency conditions of heat-stressed equipment. Some basic features of the stress-strain response of the alloy and the physical mechanisms responsible for them were revealed. Constitutive models are proposed to describe the most significant and crucial effects in assessing the structural integrity. The rheological properties of the alloy were studied under isothermal uniaxial compression within a temperature range of 24 – 1150°C with log-strains up to 1.0 and deformation rate of 0.001 – 0.125 sec–1. The main deformation mechanisms have been revealed via optical microscopy. A constitutive model predicting the shape of stress-strain curves (a modification of the Bergström dislocation-based model of rigid-plasticity) is proposed which make it possible to obtain the rate and temperature dependencies of the mechanical properties. The dependence of maxima (peak values) of stresses on the deformation rate and temperature exhibits a non-monotonic character, while the yield stresses are weakly rate-dependent, and the linear slope is almost rate and temperature independent. The microstructure tests revealed the absence of a correlation between the softening stage and the onset of dynamic recrystallization process. No microcracks were found. Serrated flow and acoustic emission were observed within a temperature interval of 24 – 900°C probably attributed to dynamic aging (above 500°C), deformation twinning, and autowave effects during localization of the plastic strain. The proposed models of rheological effects differ from the existing dislocation models in a wider range of application — in terms of strain rates (10–8 – 1,0 sec–1) and temperatures (0 – 80% of the melting point). The rheological effects revealed in the experiments, analysis of their physical nature and constitutive description can be used in assessing failures of heat-stressed equipment and improving the methods for calculating emergency situations.

Dislocations in a layered elastic medium with applications to fault detection

We consider a model for elastic dislocations in geophysics. We model a portion of the Earth’s crust as a bounded, inhomogeneous elastic body with a buried fault surface, along which slip occurs.We prove well-posedness of the resulting mixed-boundary-value-transmission problem, assuming only bounded elastic moduli. We establish uniqueness in the inverse problem of determining the fault surface and the slip from a unique measurement of the displacement on an open patch at the surface, assuming in addition that the Earth’s crust is an isotropic, layered medium with Lamé coefficients piecewise Lipschitz on a known partition and that the fault surface satisfies certain geometric conditions. These results substantially extend those of the authors in [Arch. Ration. Mech. Anal. 263, 71–111 (2020)].

Investigation on fatigue life prediction and reliability design of 304 stainless steel manufactured by laser metal deposition

Laser metal deposition (LMD) is an advanced technology to manufacture the specimen by layer-by-layer method. In this paper, the fatigue tests of 304 stainless steel (SS304) smooth specimens manufactured by LMD are conducted with the stress ratio of −1 and the frequency of 10 Hz. Considering that the fatigue crack is caused by the material defect on the subsurface, the fatigue life of smooth specimen under the different cyclic stress amplitudes are predicted based on the dislocation model, equivalent initial crack size and empirical formula. Lognormal, two-parameter Weibull and extreme maximum value distributions are applied to describe the fatigue life of the smooth specimens at the different cyclic stress amplitudes. The result shows that two-parameter Weibull distribution has the best ability to describe the fatigue life distribution. Based on two-parameter Weibull distribution, the probabilistic-stress-number ( P- S-N) curves at the four different reliability levels are plotted. Combined with the material strength degradation rule, the design checkpoint method is adopted to analyze the fatigue life reliability of smooth specimens under the different cyclic stress amplitudes. The reliability results are close to those of two-parameter Weibull distribution.

Time series interferometric synthetic aperture radar-based modeling and analysis of complex land subsidence caused by multi-seam coal mining on the Liaohe Plain, China

Land subsidence is generally caused by stress concentration of the overlying strata, which may reach the rock failure limit, causing surface collapse. The Liaohe Plain is an important resource producing area in China. Concentrated exploitation of underground resources leads to the generation of underground cavities, and surface subsidence gradually occurs as cavities increase. We used small baseline subsets synthetic aperture radar interferometry to monitor large-scale surface deformation on the Liaohe Plain. Field investigations found that the spatial distribution of land subsidence on the Liaohe Plain is highly correlated with coal mining areas. Taking the interferometric synthetic aperture radar deformation as the real constraint, a nonlinear Bayesian inversion algorithm was used to reconstruct underground reservoir parameters, such as the position and attitude of underground coal seams, based on a multi-source dislocation model. The R2 between observed and modeled deformation in multiple coal mining areas was above 0.9. On this basis, relying on the Coulomb failure stress (CFS) criterion, the elastic model parameters and regional geological data were used to calculate the stress field caused by underground resource exploitation on the ground surface. The results show that the CFS fields of multiple groups of coal seams at close distances have mutual influence, and it is more concentrated at the perimeters than in the central portions of the subsidence area. The proposed dislocation model of closely spaced multiple coal seams improved the inversion accuracy of complex mining conditions, and would provide important information for risk assessment and prevention from the perspective of geodesy.

Suppression of serrated flow in medium Mn steel under pulsed electric current

Based on the electroplasticity effect and dynamic strain aging interpretations, serrated flow under the influence of electroplasticity in Fe-0.23C-9.85Mn-2.15Al (wt.%) medium-Mn steel was investigated. Tensile tests under different electropulsing parameters were performed. When the pulsed current increased from 0 A to 100 A, the critical strain of serrated flows increased from 10.6% to 24.6% and the number of serrated flows was decreased from 35 to 0. The suppression effect is the best at the current parameter of 100 A-100 Hz-100 μs. With the decrease of dislocation waiting time and the increase of critical strain, the continuity of plastic deformation stage can be extended by the action of electron wind force. Meanwhile, the dislocation density that affects the plastic instability due to the interaction of mobile dislocations with obstacles is greatly reduced, which plays a dominant role in suppressing Portevin-Le Chatelier effect. Through the experimental results of pulsed current suppression of Portevin-Le Chatelier effect in medium Mn steel, the mathematical model of current density and dislocation waiting time is established. It is found that the current density is proportionate to the reduction of dislocation waiting time.

Anisotropic change in apparent resistivity before earthquakes of M S ⩾ 7.0 in China mainland

Since 1967 when DC apparent resistivity observation was carried out in China, there have been 16 times or groups of earthquake of M S ≥ 7.0 occurred within about 400 km from the monitoring stations. The apparent resistivity showed medium-short term continuous changes before 13 times or groups of these earthquakes. The medium-term changes usually lasted for several months to about two years. Apparent resistivity of monitoring arrays placed in different directions at the same station showed anisotropic change related to the maximum principal compressive stress orientation (i.e. P axis). The larger the angle between a monitoring array and the P axis is, the greater the magnitude of change in apparent resistivity is. According to the results from rock physics experiments, resistivity model of cracked rock-soil medium, and fault virtual dislocation model, the changes in apparent resistivity before earthquakes may be related to the seismogenic process through a way of resistivity change caused by medium deformation.

Present-day crustal deformation and slip rate along the southern Sagaing fault in Myanmar by GNSS observation

The Sagaing fault in Myanmar runs through the entire country and is responsible for major earthquakes, yet only its northern half has been studied geodetically to date. We analyzed Global Navigation Satellite System (GNSS) data to estimate crustal deformation along the central and southern parts of the Sagaing fault. We used a 2-dimensional dislocation model to estimate slip rate, locking depth and lateral offset between surface fault trace and downdip edge of the locked fault along the Sagaing (SGs), Meiktila (MTLs) and Bago (BGOs) segments of the fault. The estimated slip rate is 16–24 mm/yr with a locking depth of 10–16 km in our analysis for the central to southern segments, which is deeper than the locking depth of northern segment from previous studies. The slip rate is ~23–24 mm/yr in the central part of the Sagaing fault, while it is probably slower (~16 mm/yr) in the southern part of our study area. The predicted maximum shear strain from the optimal model is shifted from the surface fault trace. If the locked part of the fault connects directly from the deeper offset dislocation to the surface fault trace, it may be dipping with inferred values of 71°E for the SGs and 78°W for the MTLs, based on the distance between surface trace and the dislocation line at depth. The estimated potential magnitude of earthquakes for each segment as of 2021 are Mw ~7.3 in SGs, Mw ~7.4 in MTLs and Mw ~7.3 in BGOs, respectively.

Long head of biceps transfer to augment Bankart repair in chronic anterior shoulder instability with and without subcritical bone loss: a biomechanical study.

Treating recurrent anterior shoulder instability in participants in collision sports, patients with capsulolabral defects, and patients with bipolar bone loss remains challenging. The study purpose was to investigate the effect of long head of the biceps transfer (LHBT) on load-to-dislocation biomechanics in a repetitive serial shoulder dislocation cadaveric model comparing LHBT with the Latarjet and Bankart procedures-the first-line treatment methods for chronic traumatic anterior shoulder instability with and without anterior glenoid bone loss, respectively. In this controlled laboratory study, 8 fresh-frozen cadaveric shoulders with different conditions were dislocated in sequence using a custom test frame. The muscle loading configuration simulated the arm in the apprehension position, and biceps loads of 20 N and 40 N were used for the static glenohumeral position analysis to evaluate the sling effect. Sequential experimental conditions consisted of the intact state, second and third dislocations, chronic instability, Bankart repair, first LHBT, subcritical glenoid bone loss, second LHBT, and Latarjet procedure. The pectoralis major and joint reaction loads to dislocation sequentially decreased with serial dislocations in all specimens, with the lowest value in the subcritical glenoid bone defect condition. In the setting of chronic instability, the pectoralis load to dislocation was significantly higher with the Bankart repair (P = .031) and LHBT (P < .001), at 71% and 85% of the intact value, respectively. Direct comparison of the pectoralis load to dislocation favored LHBT over Bankart repair (P = .015). In the subcritical defect scenario, LHBT did not significantly increase the load to dislocate, and the Latarjet procedure demonstrated a higher load to dislocate than LHBT (P < .001). All 3 surgical procedures tested significantly increased the angle of horizontal abduction at the time of dislocation and restored the glenohumeral position to closer to the intact state. Doubling the biceps load leveraged the sling effect, pulling the humeral head farther posterior-superiorly, but this was not enough to overcome the effect of a 20% subcritical glenoid bone defect. In a serial dislocation model, LHBT effectively stabilized the glenohumeral joint in a simulated chronic instability scenario, increasing the pectoralis major load-to-dislocate and glenohumeral joint reaction force components at the time of dislocation and restoring relative glenohumeral positioning to close to the intact state. The Latarjet procedure outperformed LHBT in stabilizing shoulders in the 20% subcritical glenoid bone defect condition.

Neotectonics of Turkey (Türkiye) and surrounding regions: a new perspective with block modelling

This paper aims to present a new neotectonic perspective concordant with the seismic activities in Turkey and surrounding regions. The neotectonic structures have been re-evaluated mainly by using focal mechanism solutions and high-resolution satellite (Google Earth) images. The Southeast Anatolian Wedge explains thrust/blind thrust and asymmetrical folding relationship in SE Turkey, Syria, and Northern Iraq. The neotectonic structures of the Turkish-Iranian Plateau are enlightened by the rhomboidal cell model which creates a base to determine multiple intersection points between the region-wide left- and right-lateral shear zones. The releasing stepover between the North Anatolian Fault Zone and Southeast Anatolian-Zagros Fault Zone plus their connections with the Northeast Anatolian Fault Zone and the East Anatolian Fault Zone are described in a more meaningful way with the Anatolian Diagonal concept. It also clarifies the role of left-lateral shear zone in the west-southwest movement of Anatolian plate and its relationship with the Aegean and Cyprus arcs. A neotectonic region under the influence of NW-SE contraction is determined between the North Anatolian, Eskişehir, and Kırıkkale-Erbaa fault zones in which the Elmadağ-Eldivan and Abdüsselam pinched crustal wedges and the Beypazarı Blind Thrust Zone are developed. A new route for the southern branch of the North Anatolian Fault Zone is determined between Bolu and Değirmenlik (Milos) Island in the Aegean Sea via Mudurnu, Bursa, Balıkesir, and İzmir. All main neotectonic structures mentioned in this paper are evaluated by the elastic dislocation modelling and new neotectonic provinces are suggested.

Structural controls on coseismic rupture revealed by the 2020Mw 6.0 Jiashi earthquake (Kepingtag belt, SW Tian Shan, China)

SUMMARYThe Kepingtag (Kalpin) fold-and-thrust belt of the southern Chinese Tian Shan is characterized by active shortening and intense seismic activity. Geological cross-sections and seismic reflection profiles suggest thin-skinned, northward-dipping thrust sheets detached in an Upper Cambrian décollement. The 2020 January 19 Mw 6.0 Jiashi earthquake provides an opportunity to investigate how coseismic deformation is accommodated in this structural setting. Coseismic surface deformation resolved with Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) is centred on the back limb of the frontal Kepingtag anticline. Elastic dislocation modelling suggests that the causative fault is located at ∼7 km depth and dips ∼7° northward, consistent with the inferred position of the décollement. Our calibrated relocation of the main shock hypocentre is consistent with eastward, unilateral rupture of this fault. The narrow slip pattern (length ∼37 km but width only ∼9 km) implies that there is a strong structural or lithological control on the rupture extent, with updip slip propagation possibly halted by an abrupt change in dip angle where the Kepingtag thrust is inferred to branch off the décollement. A depth discrepancy between main shock slip constrained by InSAR and teleseismic waveform modelling (∼7 km) and well-relocated aftershocks (∼10–20 km) may suggest that faults within sediments above the décollement exhibit velocity-strengthening friction.

Recent progress in the phase-field dislocation dynamics method

The phase-field dislocation dynamics (PFDD) method, originated in 2002, is a continuum dislocation model that uses order parameters to describe dislocation slips in crystalline materials. In the past two decades, and especially since it was last reviewed in 2016, PFDD was advanced significantly in terms of the mathematical formulation, numerical implementation, and applicability. The main purpose of this short review is to summarize recent progress made to improve the energy functional formulation and numerical techniques of PFDD as well as its recent applications. Some recommendations for future work to further extend the PFDD method are presented.

Nonlinear thermo-elastic analysis of edge dislocations with Internal Heat Generation in Semiconductor Materials

In this work, the nonlinear thermo-elastic analysis of edge dislocations with internal heat generation is performed by the extended finite element method (XFEM) in semiconductor materials. The nonlinearity due to the temperature dependent electrical conductivity, thermal conductivity and thermal expansion coefficient is examined. The presence of an electric field in the direction of the dislocation line results in internal heat generation due to the electrical resistivity. The continuous Volterra model of dislocation is used for XFEM analysis of dislocations. The influence of Joule heat on thermal and elastic fields is observed. Different temperatures and electric field intensity values are taken for understanding the dislocation behavior. The Peach-Koehler (P–K) force for different dislocation configurations such as dislocation-dislocation interaction, dislocation-free surface interaction and dislocation-material interface interaction is evaluated. The results are found quite different with the amount of heat generation. The P–K force values are found more than that of pure elastic case. With the knowledge of the movability function, the obtained results can be used to predict the velocity of the dislocations.

Computer-aided automatic planning and biomechanical analysis of a novel arc screw for pelvic fracture internal fixation

Background and ObjectiveThe sacroiliac joint screw is a common fixation method for pelvic posterior ring fractures. The complex anatomical structure around the pelvis makes it impossible to find a suitable fixed path, which increases the difficulty of surgical operation. In this paper, we propose an automatic planning algorithm based on a computer-aided internal arc fixation channel for pelvic fractures for the first time. MethodsA channel generation algorithm based on seed derived points was designed, and the optimal channel was selected by scoring rules based on 3D erode algorithm for the generated channel. The biomechanical properties of the internal arc fixation screw and traditional internal straight fixation screw in three postures were compared using biomechanical finite element analysis. ResultsThe proposed algorithm verified the existence of a more adaptable internal arc fixation channel and can quantitatively plan a relatively optimal constant-curvature internal arc fixation channel in pelvises of ten adults. Significantly high stresses concentrated around the interaction region between the screws and bone may increase the risk of bone fractures and screw loosening in the long term. The experimental results show that the internal arc fixation screw has better strain and deformation performance than the internal straight fixation screw. ConclusionsA novel arc internal fixation method for pelvic fractures was proposed to improve the safety and stability of screw fixation of pelvic fracture. The nonparametric test proved that the sacroiliac dislocation model repaired by internal arc fixation screw was significantly different from that repaired by internal straight fixation screw. The computer-aided automatic planning algorithm provides the possibility of robot-assisted pelvic fracture fixation.

Relativity 4-ever?

This essay is about superluminal motion. It is generally believed that special relativity prohibits movements faster than the speed of light. It is explained which motion is actually forbidden by special relativity and why. Tachyons are breafly discussed and it is explained that, due to internal instability, tachyon fields cannot be used to transmit information faster than the speed of light. However, as John Stuart Bell remarked, “what is proved by the impossibility proofs is lack of imagination”. Inspired by the Frenkel–Kontorova model of crystal dislocations, we demonstrate the way to overcome the light speed barrier by introducing elvisebrions. Elvisebrions are defined as objects that can exist in the case when some hidden sectors, very weakly interacting with the visible sector, are either not Lorentz invariant, or Lorentz invariant but with different limiting velocities. In this case, elvisebrions can move in a superluminal manner without violating our existing physical models.

Inversion of dislocation densities under mixed mode fracture

Mixed-mode crack growth is here investigated through experiments and computations for 34X and P2M steels, 7050 aluminium, and Ti-6Al-4V alloys in a compact tension shear (CTS) specimen. In this study, we use the mechanism-based strain gradient (MSG) plasticity theory to evaluate both crack tip dislocation density behaviour and the coupled effect of the material plastic properties and the intrinsic material length on local stress distributions. The constitutive relations are based on Taylor’s dislocation model, which allows to gain insights into the role of the increased dislocation density associated with large gradients in plastic strain near cracks. The material model is implemented in a commercial finite element (FE) software package using a user subroutine, and the nonlinear stress intensity factors (SIFs) are evaluated as a function of the intrinsic material length. As a result of the FE calculations of dislocation density distributions, the effects of both the fracture mode and the stress–strain state are determined. Strain gradient effects associated with dislocation hardening mechanisms elevate crack tip stresses relative to conventional plasticity. Dislocation densities, stress fields and nonlinear SIF solutions are determined for experimental curvilinear crack paths by taking into account the transition from the initial Mode II crack to the mixed-mode fracture.

Coarse-grained atomistic modeling of dislocations and generalized crystal plasticity

Recent developments in generalized continuum modeling methods ranging from coarse-grained atomistics to micromorphic theory offer potential to make more intimate physical contact with dislocation field problems framed at length scales on the order of microns. We explore a range of discrete dynamical and continuum mechanics approaches to crystal plasticity that are relevant to modeling behavior of populations of dislocations. Predictive atomistic and coarse-grained atomistic models are limited in terms of length and time scales that can be accessed; examples of the latter are discussed in terms of interactions of multiple dislocations in heterogeneous systems. Generalized continuum models alleviate restrictions to a significant extent in modeling larger scales of dislocation configurations and reactions, and are useful to consider effects of dislocation configuration on strength at characteristic length scales of sub-micron and above; these models require a combination of bottomup models and top-down experimental information to inform parameters and model form. The concurrent atomistic-continuum (CAC) method is extended to model complex multicomponent alloy systems using an average atom approach. Examples of CAC are presented, along with potential to assist in informing parameters of a recently developed micropolar crystal plasticity model based on a set of sub-micron dislocation field problems. Prospects for further developments are discussed.