Dislocation Displacement Research Articles

Investigation of mechanical properties and crack resistance parameters of steel reinforcements of reinforced concrete structures of long-term special term

It is known that the fatigue process begins with the plastic deformation of the surface layers of the metal fittings. Moreover, the displacement of dislocations under conditions of re-alternating loads is observed at loads below the elastic limit of the metal. The rate of local plastic deformation during cyclic deformation is several orders of magnitude higher than the rate of deformation under static loading. Dislocation slip begins in grains with a favorable orientation near stress concentrators. As the number of cycles in the surface layers increases, the density of dislocations and the number of vacancies increases. When the base number of NR cycles is reached, a surface reinforced layer of metal with a large number of germinal cracks is formed, the size of which does not reach a critical value. Increasing the number of cycles cannot cause further development of fracture in such a layer. Only when the stresses exceed the endurance limit of the crack reach a critical length, after which the process of their discharge into the main crack begins with the spread of the latter. The results of experimental studies indicate a strong effect of diffusion hydrogen on static and cyclic parameters of crack resistance. It was found that with increasing flooding, especially when the hydrogen content exceeds 5 cm3/100g, both static strength and long-term strength (fatigue) decrease sharply. Moreover, for these areas of hydrogen solution in reinforcing steel is characterized by a viscous nature of fracture, while for heavily flooded reinforcement (from 5 to 12 cm3/100g is characterized by brittle fracture by the mechanism of microfission in the hardened (martensite or troostite structure). allowed to determine the optimal hydrogen content in reinforcing steel (3…5 cm3 /100g), the excess of which will reduce the crack resistance of reinforcement during long-term operation, especially in corrosive environments. The results of the research confirm the above data. bainite structure y sharply reduces the crack resistance of reinforcing steel, which makes it impossible to use in the manufacture of reinforcement involved in reinforced concrete structures designed for long-term operation (more than 50…60 years). Thus, the obtained diagram can be recommended to designers of reinforced concrete structures for hydraulic purposes, as it greatly facilitates the reasonable choice of reinforcement in the development of reinforced concrete structures for responsible and long-term use.

Displacements and Stress Functions of Straight Dislocations and Line Forces in Anisotropic Elasticity: A New Derivation and Its Relation to the Integral Formalism

The displacement and stress function fields of straight dislocations and lines forces are derived based on three-dimensional anisotropic incompatible elasticity. Using the two-dimensional anisotropic Green tensor of generalized plane strain, a Burgers-like formula for straight dislocations and body forces is derived and its relation to the solution of the displacement and stress function fields in the integral formalism is given. Moreover, the stress functions of a point force are calculated and the relation to the potential of a Dirac string is pointed out.

Incompatible strain gradient elasticity of Mindlin type: screw and edge dislocations

The fundamental problem of dislocations in incompatible isotropic strain gradient elasticity theory of Mindlin type, unsolved for more than half a century, is solved in this work. Incompatible strain gradient elasticity of Mindlin type is the generalization of Mindlin’s compatible strain gradient elasticity including plastic fields providing in this way a proper eigenstrain framework for the study of defects like dislocations. Exact analytical solutions for the displacement fields, elastic distortions, Cauchy stresses, plastic distortions and dislocation densities of screw and edge dislocations are derived. For the numerical analysis of the dislocation fields, elastic constants and gradient elastic constants have been used taken from ab initio DFT calculations. The displacement, elastic distortion, plastic distortion and Cauchy stress fields of screw and edge dislocations are non-singular, finite, and smooth. The dislocation fields of a screw dislocation depend on one characteristic length, whereas the dislocation fields of an edge dislocation depend on up to three characteristic lengths. For a screw dislocation, the dislocation fields obtained in incompatible strain gradient elasticity of Mindlin type agree with the corresponding ones in simplified incompatible strain gradient elasticity. In the case of an edge dislocation, the dislocation fields obtained in incompatible strain gradient elasticity of Mindlin type are depicted more realistic than the corresponding ones in simplified incompatible strain gradient elasticity. Among others, the Cauchy stress of an edge dislocation obtained in incompatible isotropic strain gradient elasticity of Mindlin type looks more physical in the dislocation core region than the Cauchy stress obtained in simplified incompatible strain gradient elasticity and is in good agreement with the stress fields of an edge dislocation computed in atomistic simulations. Moreover, it is shown that the shape of the dislocation core of an edge dislocation has a more realistic asymmetric form due to its inherent asymmetry in incompatible isotropic strain gradient elasticity of Mindlin type than the dislocation core possessing a cylindrical symmetry in simplified incompatible strain gradient elasticity. It is revealed that the considered theory with the incorporation of three characteristic lengths offers a more realistic description of an edge dislocation than the simplified incompatible strain gradient elasticity with only one characteristic length.

Analysis of fracture deformation field and energy evolution of granite after high confining pressure cyclic load pre-damage.

Considering the recent developments of deep mining, investigating the rock properties under high ground stress periodic load is highly demanded. Studies show that these characteristics are important factors affecting the long-term steadiness of rock. However, the mechanical properties of rock mass without macro failure after cyclic load should be studied. In the present study, granite in a mine is considered as the research object. A rock pre-damage experiment is conducted with the same cycles under different confining pressures and constant cycle upper and lower limit loads. The pre-damaged rock sample is subjected to a uniaxial compression test, and a high-speed charge couple device camera is used to record the speckle field image of the sample surface during the whole loading process. The digital speckle techniques are used to analyse the image of the pre-damaged sample, the deformation field of the specimen surface, the displacement dislocation value of the localized deformation area and the deformation energy value of the specimen surface. The results show that for the same cycle times, the confining pressure is less than 80 MPa, which has a weakening effect on the rock's axial strength. As the confining pressure approaches 120 MPa, the pre-damaged rock uniaxial peak strength increases. The characteristics of displacement dislocation energy evolution of the localized deformation bound are divided into three stages (pre-peak stage, peak point and post-peak stage). After pre-damage under the same cycle times and different confining pressure conditions, the deformation field evolution of rock is relatively consistent.

Generalized Susceptibility of Mixed Dislocation in Ferroelastics near Structural Phase Transition

Bending vibrations of a mixed dislocation in ferroelastics near structural phase transition were considered. It was assumed that the dislocation line performs small bending vibrations near equilibrium position. Complete system of equations describing the vibrations of a mixed dislocation near the structural phase transition is written. Based on these set of equations describing the vibrations of a crystal with a dislocation near the structural phase transition, written equations for dynamics of the mixed dislocation in linear approximation of dislocation displacement. Fourier transform of these equations is satisfied. Expression for Peach-Kohler force acting on the dislocation is obtained, and linear response function (generalized susceptibility) of the mixed dislocation in ferroelastics is found.

Through the Dark Mirror: Philip Roth’s The Plot Against America as Noir Fantasia

Philip Roth’s 2004 alternative history novel, The Plot Against America, was his best-selling work in decades, firmly reestablishing his prominence among a general readership. The novel’s popularity was due at least in part to its deliberately accessible prose style and exciting, cliffhanger-rich plot. Seizing upon this accessibility, this article examines the style of The Plot Against America as a literary version of film noir, the influential cycle of downbeat American crime films spanning roughly 1941–1958. To read the novel through this cinematic lens is to highlight certain pulp and Surrealist aspects not typically associated with Roth’s fiction. Testing filmic understandings of noir themes and strategies against the novel’s genre experiment, this article ultimately demonstrates how these conventions (including the femme fatale, narrative dislocation, and racial displacement) endure as vital expressions of American Modernism.

Investigation of novel multi-layer sandwich panels under quasi-static indentation loading using experimental and numerical analyses

In this study, the effect of multi-layering in sandwich panel composite structures with different configurations of corrugated cores under the effect of quasi-static indentation loading is investigated experimentally and numerically. Composite plates and corrugated cores with equal weight fraction were manually made using ML506 epoxy resin with 15% hardener and the overall volume fraction of 45% for woven glass fibers. Experiments were performed using a cylindrical indenter with a diameter of 20 mm and a semi-spherical nose shape, and the behavior of the composite structure was evaluated in the case of energy absorption, contact force, and fracture mechanisms for different corrugated cores (rectangular, trapezoidal and triangular). Progressive damage analyses of the composite samples were investigated using well-known 3D failure criteria developed in ABAQUS software, and an acceptable agreement between the experimental and numerical results was observed. Experimental results show that multi-layering of composite sandwich panels not only increases the structural strength in quasi-static indentation process but also increases the energy absorption of specimens by increasing the peak load, instantaneous force, and dislocation displacement up to the complete penetration. By comparing different geometries of the corrugated cores in terms of maximum force, energy absorption, and specific energy, it was shown that the functionality of specimens with rectangular cores is the best. Among the most important damage mechanisms of the examined sandwich panel specimens (visual analysis) in the quasi-static indentation process, matrix cracking, fiber breakage, delamination, cell walls buckling and crushing, face sheets and core debonding, and specimens complete penetration are noticeable.

Displacement field due to glide and climb of rectilinear dislocations in gradient elasticity

ABSTRACT The aim of this article is to provide the displacement field of a straight dislocation in gradient elasticity that can be implemented in dislocation dynamics simulations. The displacement and plastic strain fields of a dislocation depend on the history of the dislocation motion. The cut surface (or the branch cut) represents this history. When an edge dislocation glides, the branch cut must be parallel to the Burgers vector, and when a dislocation moves by a combination of glide and climb, extra terms need to be added to the displacement field to capture the correct discontinuity in the displacement field. The existing formulas for the dislocation displacement in gradient elasticity lack such considerations, which make them unsuitable for simulations. In addition, the previous formulas both in classical and gradient elasticity have contained some inaccuracies and miscalculations. In this paper, the displacement field of a dislocation and the corresponding plastic strain are derived in detail and a distinction between the dislocation due to glide and that due to climb has been made. Moreover, we discuss the shortcomings of Mura's [Micromechanics of Defects in Solids, 2nd ed., Martinus Nijhoff Publishers, 1987.] and Lazar and Maugin's [Dislocations in gradient elasticity revisited, Proc. R. Soc. Math. Phys. Engin. Sci. 462(2075) (2006), pp. 3465–3480.] calculations. We illustrate that Orowan's law is a direct result of the correct displacement and plastic strain fields.

Extracapsular Condylar Fractures Treated Conservatively in Children: Mechanism of Bone Remodelling.

This study aims to reveal the reconstruction process in pediatric patients with extracapsular condylar fractures after conservative treatment. We clarify that the "upright" position (or "recontouring" or favorable prognosis) of condyles is not a result of the anatomical reduction of the deviated condylar processes but originates from the remodeling of the skeleton. We also explore the related mechanism. The sample consisted of 27 pediatric patients aged less than 12 years who presented with extracapsular condylar fractures and were treated conservatively within an 8-year period (June 2011-April 2019). Data on the age, gender, date of injury, mechanism of trauma, location and pattern of mandibular condylar fracture and associated injuries and treatment methods of the patients were obtained. The process of bone remodeling in condyles was also recorded and analyzed. The 27 children in this study sustained 33 extracapsular condylar fractures over the 8-year period of record retrieval. Amongst these fractures, 8 (24.2%) and 25 (75.8%) were condylar neck and condylar base fractures, respectively. Deviation and green-stick fractures were the predominant types and accounted for over 3 quarters of the condylar neck and base fractures (28, 84.8%), followed by dislocation fracture (3, 9.1%), displacement fracture (1, 3.0%), and non-displaced fracture (1, 3.0%). The period of follow-up ranged from 2 days to 257 days (average, 58.78 days). Only 1 patient with bilateral extracapsular condylar fractures showed vertically reconstructed condyles, which indicates an upright position of the condylar processes. One patient showed less angulation after treatment than before treatment, 1 patient revealed greater angulation after treatment than before treatment and all other patients (20 patients) showed the same angulation pre- and post-treatment. Both patients with only extracapsular condylar fractures showed no obvious deviations in dentition and facial asymmetry after their injury and treatment. The shortest and longest times observed for bone remodeling were 33 and 256 days, respectively. Children whose condylar head remained completely or at least partly inside the glenoid fossa showed satisfactory remodeling results during follow-up. Computed tomography scan during follow-up generally showed bone regeneration in the lateral condyle articular surface and the medial portion of the ascending ramus and bone resorption in the displaced direction (ie, the medial condyle head became sharp). Condylar heads displaced completely outside of the glenoid fossa showed serious shortening of the ascending ramus, and no obvious bone remodeling was observed. Only 1 patient with bilateral extracapsular condylar fractures showed a normal contour (ie, a vertically reconstructed condyle reflecting the upright position of the condylar processes) after 8 months. Stress stimulation originating from the glenoid fossa and ascending ramus of the mandible is a prerequisite for good condylar reconstruction. Conservative treatment could be carried out if the condylar head remains completely or at least partly inside the glenoid fossa. When the condylar head is dislocated completely outside the glenoid fossa, the glenoid-condylar relationship ceases to exist, joint function is lost and the height of the ascending ramus is significantly reduced. In this case, open reduction may be suitable.

Stacking fault formation created by plastic deformation at low temperature and small scales in silicon

Several studies have recently reported the formation of stacking faults in silicon compressed at low temperatures and high stresses. This observation contradicts the generally accepted framework for the plastic deformation of silicon. We propose here an original plasticity mechanism that could potentially explain stacking fault formation in these conditions: the nucleation and migration of a partial edge dislocation with Burgers vector $\frac{1}{3}\ensuremath{\langle}112\ensuremath{\rangle}$. These results are obtained thanks to a multiscale approach combining three computational methods. Dislocation nucleation is determined by molecular dynamics in both a nanowire and a 2D slab. The latter results are used as inputs for hybrid MD/DFT ``learn on the fly'' calculations, allowing for studying the dynamical propagation of the dislocation. Selected configurations at different steps are next used for initiating nudged elastic band density functional theory calculations. These calculations revealed that the dislocation displacement mechanism depends on the compression strain. For low values, a dangling bond is temporarily created in the core, resulting in high activation energies. For compression strains larger than about 8%, the reduction of the interlayer distance allows for a more complex displacement mechanism with no dangling bonds in the dislocation core and a significant decrease of the activation energy.

The Cultural Underpinnings of Subjectivity and Inter-Subjectivity: A Discussion of “Trump Cards and Klein Bottles: On the Collective of the Individual”

In “Trump Cards and Klein Bottles: On the Collective of the Individual,” Dr. González (this issue) argues for the centrality of dynamic and shifting group identifications in shaping our subjectivity and our inter-subjective linking from moment to moment. My commentary about this paper is organized around the themes of cultural dislocation and cultural displacement, experiences related to large-group identifications and identity. These constructs, cultural dislocation and displacement, can deepen our understanding of how inter/intra-group tensions (historic and current) can play a determinative role in shaping individual subjectivity and inter-subjective linking. They complement and amplify claims regarding the centrality of our group identifications on ego functions. They also point toward the determinative impact of context and clashing cultural systems on our object relations and unconscious fantasies. Studying the links between individuals, collectives, and the cultural systems that structure them will deepen our theories and extend our relevance.

Derivation of lattice resistance for a straight dislocation movement through displacement of the dislocation from its own stress field core

An analytic approach has been carried out to calculate the lattice resistance for movement of a straight dislocation in the crystal lattice at a velocity corresponding to common tensile test, which provides a different method from the classic Peierls-Nabarro (P–N) model. In the present model, movement of dislocation is supposed to consist of oscillation at equilibrium sites and instantaneous jumping from an equilibrium site to the next equilibrium site. Resistance of dislocation movement is derived from the displacement of dislocation to its own stress field core during jumping. Estimated values of the resistances in the present model are in accordance with the experimental results of Cu and Al, which are obviously lower than the results of existing models. Meanwhile, the applicative condition of the present model has been discussed.

Determining dislocation love number of vertical displacement using GPS observations: case study of 2011 Tohoku-Oki earthquake (Mw 9.0)

SUMMARYThe concept of determining the dislocation Love numbers using GNSS (Global Navigation Satellite System) data and calculating the corresponding Green's functions is presented in this paper. As a case study, we derive the dislocation Love number h of vertical displacement by combining 1232 onshore GPS data and 7 GPS-Acoustic data with the 2011 Tohoku-Oki earthquake (Mw 9.0). Three fault-slip distributions are used to compare and verify the theory and results. As the GPS stations are only located in Japan Island and along the Japan trench, we use the theoretical vertical displacements of a spherically layered Earth structure to constrain the low-order signal. The L-curve and an a priori preliminary reference skill are applied in the inversion method. Then, the GPS-observed vertical displacement changes are used to invert for the vertical displacement dislocation Love numbers h based on three different fault-slip models. Our results indicate that the estimated dislocation Love numbers $h$ fluctuate significantly from the earth model (i.e. the preliminary reference earth model), especially for the $h_{n1}^{32}$ component, and these changes in $h_{n2}^{12}$ and $h_{n0}^{33} - h_{n0}^{22}$ are relatively small. The vertical displacements derived from the inversion results agree well with the GPS vertical observations. The inverted dislocation Love numbers are considered to profile the regional structure which differs from the mean 1-D heterogeneous structure of the Earth, and the corresponding Green's functions of four independent dislocation sources describe a more reasonable seismic deformation field.

Dynamic Atomic Displacements and Athermal Dislocation Glide in Crystals

A dislocation glide mechanism at low temperatures is proposed. The mechanism is based on the inclusion of dynamic atomic displacements, i.e., those caused by nonadiabatic transitions of atoms in a crystal with a dislocation under action of an external force. The dynamic displacements initiate the instability of a rectilinear dislocation with respect to low-amplitude displacements during atomic vibrations. The instability development leads to the formation of a double kink and the dislocation displacement by one interatomic distance.

Radiographic displacement of acute acromioclavicular joint dislocations fixed with AC TightRope

BackgroundThe arthroscopic approach to acromioclavicular (AC) dislocation with methods such as AC TightRope fixation has reported radiographic failure rates between 18% and 50% with functional results graded as good or excellent. Our objective was to review the outcomes after arthroscopic fixation for acute AC joint dislocation using the TightRope device.MethodsWe reviewed the records of 52 patients, with a mean age of 31 years, who underwent arthroscopic fixation with the TightRope device for acute AC joint dislocation. Outcomes were evaluated using the Constant and University of California, Los Angeles scores. The coracoclavicular (CC) distance before and after surgery was compared by radiography.ResultsThe mean follow-up period was 36.7 months (range, 6-65 months). Postoperatively, the mean Constant score was 97.13 and the mean University of California, Los Angeles score was 33.2. The CC distance was maintained in 73% of the patients, whereas partial loss of reduction occurred in 19.2% and failure of reduction occurred in 7.7%.ConclusionArthroscopic fixation using the TightRope device for acute AC joint dislocation achieves satisfactory clinical outcomes. However, CC reconstruction appears to result in subluxation in cases with AC dislocation for a period of more than 10 days.

Factors Related to Failure of Conservative Treatment in Volar Plate Avulsion Fractures of the Proximal Interphalangeal Joint.

BackgroudVolar plate avulsion fractures of the proximal interphalangeal (PIP) joint are a common hand injury and have been treated conservatively with favorable results. We assumed that conservative treatment of volar plate avulsion fractures of the PIP joint would be unsuccessful if the fracture fragment, even if small, was much displaced or rotated and that delayed excision of the avulsion fractures would result in good outcomes. We report clinical and radiological outcomes of conservative treatment of volar plate avulsion fractures of the PIP joint and risk factors for failure of conservative treatment.MethodsWe retrospectively reviewed the clinical and radiological outcomes of 88 volar plate avulsion fractures (85 patients) treated conservatively at first. In 18 of these fractures, delayed excision of the fracture fragment was required after an average of 75 days of conservative treatment for limited motion or pain of the joint. We compared parameters between failed cases and successful cases after conservative treatment.ResultsCompared to the successful cases, the failed cases had a higher prevalence of joint dislocation at the time of injury and greater pain, larger flexion contracture, and less further flexion after conservative treatment. The shape, comminution, and size of the fracture fragments were not related with the need for operation, but the operative cases had greater displacement and rotation of the fracture fragments than the conservative cases. After fragment excision, postoperative protection of the joint was not necessary, pain was reduced, and the mean range of motion increased.ConclusionsThe presence of joint dislocation and greater displacement and rotation of the fragments may be associated with the failure of conservative treatment of volar plate avulsion fractures. Failed cases after conservative treatment could be resolved by delayed fragment excision with favorable results. Therefore, it might be appropriate to consider conservative treatment at first in almost all volar plate avulsion fractures of stable PIP joints.

A novel multiscale approach to brittle fracture of nano/micro‐sized components

AbstractPrinciples and advantages of a new concept based on the ab initio aided strain gradient elasticity theory are shown in comparison with the classical Barenblatt cohesive model. The method is applied to the theoretical prediction of the critical energy release rate and the crack tip opening displacement at the crack instability in nanopanels made of germanium and molybdenum crystals. The necessary length scale parameter l1 is determined for germanium and molybdenum by the best gradient elasticity fits of ab initio computed screw dislocation displacements and phonon dispersions. Values of ab initio computed critical energy release rates and crack opening profiles revealed that the length l1 is related to inflexion points of profiles. A novel ab initio method in combination with continuum mechanics was successfully tested to replace molecular statics dependent of availability of interatomic potentials. The asymptotic strain gradient elasticity solution for displacement components near the crack tip in materials with cubic lattice was also derived.

The linear response function of a mixed dislocation in ferroelectrics

Bending vibrations of a mixed dislocation in a uniaxial ferroelectric are considered, the dislocation line is located along the ferroelectric axis. Based on the complete system of equations describing the vibrations of a ferroelectric crystal with a dislocation, system of equations for the mixed dislocation dynamics in a linear approximation in the dislocation displacement is written. An expression for the Peach–Koehler force acting on the dislocation is obtained, and the linear response function of the mixed dislocation is found.

Generalized susceptibility of a screw dislocation in ferroelastics near structural phase transition

Small amplitude bending vibrations of a screw dislocation near structural phase transition is considered. Based on the full set of equations describing the vibrations of a crystal with a dislocation near the structural phase transition, written equations for the dynamics of screw dislocations in the linear approximation of the dislocation displacement. Fourier transform of the Peach-Koehler forces projection on the dislocation slip plane is obtained and a linear response function of a screw dislocation in ferroelastic crystal to an external force is found.

Variation Among Pediatric Orthopaedic Surgeons When Treating Medial Epicondyle Fractures.

Medial epicondyle fractures are a common pediatric and adolescent injury accounting for 11% to 20% of elbow fractures in this population. This purpose of this study was to determine the variability among pediatric orthopaedic surgeons when treating pediatric medial epicondyle fractures. A discrete choice experiment was conducted to determine which patient and injury attributes influence the management of medial epicondyle fractures by pediatric orthopaedic surgeons. A convenience sample of 13 pediatric orthopaedic surgeons reviewed 60 case vignettes of medial epicondyle fractures that included elbow radiographs and patient/injury characteristics. Displacement was incorporated into the study model as a fixed effect. Surgeons were queried if they would treat the injury with immobilization alone or open reduction and internal fixation (ORIF). Statistical analysis was performed using a mixed effect regression model. In addition, surgeons filled out a demographic questionnaire and a risk assessment to determine if these factors affected clinical decision-making. Elbow dislocation and fracture displacement were the only attributes that significantly influenced surgeons to perform surgery (P<0.05). The presence of an elbow dislocation had the largest impact on surgeons when choosing operative care (β=-0.14; P=0.02). In addition, for every 1 mm increase in displacement, surgeons tended to favor ORIF by a factor of 0.09 (P<0.01). Sex, mechanism of injury, and sport participation did not influence decision-making. In total, 54% of the surgeons demonstrated a preference for ORIF for the included scenarios. On the basis of the personality Likert scale, participants were neither high-risk takers nor extremely risk adverse with an average-risk score of 2.24. Participant demographics did not influence decision-making. There is substantial variation among pediatric orthopaedic surgeons when treating medial epicondyle fractures. The decision to operate is significantly based on the degree of fracture displacement and if there is a concomitant elbow dislocation. There is no standardization regarding how to treat medial epicondyle fractures and better treatment algorithms are needed to provide better patient outcomes. Level V.