Problem Of Dislocation Research Articles

Anti-plane stress analysis of dissimilar sectors with multiple defects

In this article, the anti-plane deformation of a typical dissimilar sector consists of two sub-sectors attached to each other on one circular edge is studied. The solution of a Volterra type screw dislocation problem in the sector is obtained through finite Fourier cosine transform. Exact closed-form solutions for the displacement and stress fields are also presented. Next, using a distributed dislocation method, integral equations of the sectors weakened by cracks and cavities under an anti-plane traction are obtained. The defects are assumed to be located only in one of the sub-sector regions. The obtained equations for the latter problem are of the Cauchy singular type and have been solved numerically. Several examples are presented to demonstrate the efficiency and applicability of the proposed solution procedure. The geometric and force singularities of the stress field are studied and compared to those reported in the literature.

A Point Dislocation Interacting with an Elliptical Hole Located at a Bi-Material Interface

The problem of a point dislocation interacting with an elliptical hole at the interface of two bonded half-planes is studied. Complex stress potentials are obtained by applying the methods of complex variables and conformal mapping. A rational mapping function that maps a half plane with a semi-elliptical notch onto a unit circle is used for mapping the bonded half-planes. The solution derived can serve as Green’s function to study internal cracks interacting with an elliptical interfacial cavity.

Elastic fields of dislocation loops in three-dimensional anisotropic bimaterials

By applying semi-analytical point-force Green's functions obtained via the Stroh formulism, we derive simple line integrals to calculate the elastic displacement and stress fields for a three-dimensional dislocation loop in an anisotropic bimaterial system. The solutions for the case of anisotropy are more convenient for treating an arbitrary dislocation loop compared with traditional area integration. With this new formulation, we numerically examine the displacement, stress, and energy due to the interaction between a dislocation loop and the bimaterial interface in an Al–Cu system. The interactive image energy due to the elastic moduli mismatch across the interface is then numerically evaluated. The result shows that a dislocation loop is subjected to an attractive force by the interface when it lies in the stiff material, and a repulsive force when it lies in the soft material. Moreover, the dependence of the interactive image energy of a dislocation loop on the position and size of the dislocation loop are also demonstrated and discussed. Significantly, it is found that the interactive image energy for a dislocation loop depends only on the ratio d/ a, where a is the loop diameter and d is its distance to the interface. The examples studied provide benchmark solutions for anisotropic bimaterial dislocation problems.

Hüftarthroskopische Therapie bei veralteten extrakapsulären traumatischen Hüftluxationen bei Kindern

We report about the first hip arthroscopies of extracapsular neglected hip dislocations with concomitant injuries in two children (2 and 4 years old). The major problem of traumatic hip dislocation is avascular necrosis. Further problems are possible concomitant injuries. It is important not to cause further damage by therapeutic procedures. In a 4-year-old child the hip could be reduced under visualization and in a 2-year-old child with epiphyseal fracture the extent of the operation could be reduced. In both children large avulsion injuries of the ligamentum capitis femoris could be resected via hip arthroscopy. Hip arthroscopy can reduce surgical morbidity considerably and can possibly contribute to prevention of the feared avascular necrosis of the femoral head.

Diffusionally modified elastic interaction of edge dislocations with circular inclusions

This research contains two relevant parts. In the first part, we investigate the problem of an edge dislocation interacting with a thickly coated circular inclusion. Both interface slip and diffusion occur on the inclusion/coating and coating/matrix interfaces. We further assume that all these stress relaxation processes on the two interfaces have come to an end. A closed-form solution to the problem is derived. It is observed that: (i) the dislocation will induce an internal uniform hydrostatic stress field within the three-phase circular inclusion; (ii) the dislocation will induce the same uniform rigid body rotation within the inclusion and within the coating layer; and (iii) when a compliant coating layer is thick enough, there exists no climb repulsion region. In the second part, an exact solution to the problem of an edge dislocation inside a circular inclusion with a fully relaxed interface is obtained. We observe that the climb force on the dislocation tends to keep it at the center of the inclusion.

A probabilistic boundary element method applied to the pile dislocation problem

In this paper a probabilistic approach is presented where the boundary element method is efficiently used to study the effect of a random shift of a given pile within a particular pile cap from its original position–the so-called pile dislocation problem–on selected output design parameters such as pile loads and bending moments in the pile cap. A new circular internal element is developed to simulate the true geometric modeling of piles. The boundary element method for the shear-deformable (thick) plate theory is employed to analyze the pile cap. The plate–pile interaction forces are considered to have constant variation over the circular pile domain. The probabilistic approach presented herein incorporates a Monte Carlo simulation technique for generating random shifts in the original position of a given pre-selected pile. The procedure has been applied to some exemplar pile caps with given pile layouts typically adopted in bridge construction. The results demonstrate that the random dislocation of piles within practical ranges/values as customarily encountered for example in pile caps pertinent to bridge applications will cause limited variations in the output design parameters investigated herein and mentioned above. In other words, it has been illustrated that the resulting dispersion in the output values due to random dislocation of piles is less than the possible intrinsic dispersion that may be practically triggered in the pile locations due to common construction inaccuracies and/or unanticipated problems during pile driving process. The study further emphasizes the efficiency and reliability of the Boundary Elements Method adopted herein for such application.

Congenital Vertical Talus in Multiple Pterygium Syndrome

Congenital vertical talus (CVT) is a rare foot deformity, but it is a commonly associated anomaly in patients with multiple pterygium syndrome (MPS). If left untreated, it can cause pain and morbidity, which will affect the patient's ambulation and quality of life. The aim of this study was to assess the prevalence of CVT among patients with MPS, to characterize the clinical and radiological features and examine the outcome of treatment. We reviewed the medical records from 1969 to 2009, and detected 14 patients with a diagnosis of MPS. Data regarding clinical findings, radiographs, associated anomalies, and treatment were collected and analyzed. CVT was seen in 10 of 14 patients (71%). All of them had bilateral involvement. Eight of the 10 (80%) were girls, and 3 of these 10 (30%) were nonambulatory patients. All 7 ambulatory patients had manipulation and casting, followed by a single-stage surgical release. The mean age at surgery was 3.0 ± 3.7 years (range, 3 mo-9 y 2 mo). At the last follow-up, all of the 7 patients (100%) had painless plantigrade feet and a reduced talonavicular joint, and none had recurrence of the deformity. The overall mean follow-up was 6 years (range, 2-19 y) and the mean age at the last follow-up was 9 years (range, 2-23 y). The commonly associated anomalies were scoliosis (93%), tethered cord (14%), hip dislocation (43%), cardiac (29%), respiratory (43%), and gastrointestinal anomalies (29%). CVT is common in MPS. The other common anomalies included scoliosis, hip dislocation, and respiratory problems. Treatment with manipulation and casting followed by, a single-stage surgical release resulted in a good outcome.

A variational approach to dislocation problems for periodic Schrödinger operators

As a simple model for lattice defects like grain boundaries in solid state physics we consider potentials which are obtained from a periodic potential V = V ( x , y ) on R 2 with period lattice Z 2 by setting W t ( x , y ) = V ( x + t , y ) for x < 0 and W t ( x , y ) = V ( x , y ) for x ⩾ 0 , for t ∈ [ 0 , 1 ] . For Lipschitz-continuous V it is shown that the Schrödinger operators H t = − Δ + W t have spectrum (surface states) in the spectral gaps of H 0 , for suitable t ∈ ( 0 , 1 ) . We also discuss the density of these surface states as compared to the density of the bulk. Our approach is variational and it is first applied to the well-known dislocation problem (Korotyaev (2000, 2005) [15,16]) on the real line. We then proceed to the dislocation problem for an infinite strip and for the plane. In Appendix A, we discuss regularity properties of the eigenvalue branches in the one-dimensional dislocation problem for suitable classes of potentials.

A screw dislocation in a functionally graded material using the translation gauge theory of dislocations

The aim of this paper is to provide new results and insights for a screw dislocation in functionally graded media within the gauge theory of dislocations. We present the equations of motion for dislocations in inhomogeneous media. We specify the equations of motion for a screw dislocation in a functionally graded material. The material properties are assumed to vary exponentially along the x and y-directions. In the present work we give the analytical gauge field theoretic solution to the problem of a screw dislocation in inhomogeneous media. Using the dislocation gauge approach, rigorous analytical expressions for the elastic distortions, the force stresses, the dislocation density and the pseudomoment stresses are obtained depending on the moduli of gradation and an effective intrinsic length scale characteristic for the functionally graded material under consideration.

The problem of a moving subsonic edge dislocation near an interface solved with only discrete image dislocations

The use of only discrete edge image dislocations to solve the problem of an edge dislocation, moving or stationary, near a welded interface separating material of different elastic constants (or a free surface) is thwarted, as is well known, because an image edge dislocation cannot deal simultaneously with the continuity at the interface of both the shear traction stress and the normal traction stress. In this paper, it is shown that the problem can be solved with only discrete edge image dislocation components if an edge dislocation is first separated into an edge dislocation component whose stress–displacement fields depend only on the shear wave velocity and an edge dislocation component whose stress–displacement fields depend only on the longitudinal wave velocity.

Analysis of Interaction between Dislocation and Grain Boundary by using a Lattice Defect Model

For understanding the macroscopic mechanical property of polycrystalline metal from a microscopic point of view, analysis of interaction between grain boundary (GB) and dislocations are very important. Especially, the driving force of each dislocation must be evaluated precisely, to apply the dislocation dynamics method to the plastic deformation analysis. While the driving force for the grain rotation is estimated as the gradient of the function of grain boundary (GB) energy with respect to the misorientation angle, GB-dislocation interactions are very important to understand grain rotation mechanism from a microscopic viewpoint. In this paper, generalized GB energy of GB-dislocation system is evaluated by using the extended finite element method with solving the problem of dislocation - disclination system. First, the comparison between the results of disclination model and atomistic model is discussed. Then, the strain energy of the GB-dislocation system is studied to evaluate the driving force of the dislocation motion

Elastic behavior of an edge dislocation inside the wall of a nanotube

The problem of edge dislocation inside the wall of a multi-walled nanotube accounting for the surface effects is addressed. Within the framework of surface elasticity the stress field is obtained, using complex potentials. Furthermore, the stress field and image forces acting on the dislocation, with and without an account of the surface stress, are compared together and discussed.

A novel method for solving the displacement and stress fields of an infinite domain with circular holes and/or inclusions subject to a screw dislocation

In this paper, the degenerate kernel and superposition technique are employed to solve the screw dislocation problems with circular holes or inclusions. The problem is decomposed into the screw dislocation problem with several holes and the interior Laplace problems for several circular inclusions. Following the success of the null-field integral equation approach, the typical boundary value problems can be solved easily. The kernel functions and unknown boundary densities are expanded by using the degenerate kernel and Fourier series, respectively. To the authors’ best knowledge, the angle-type fundamental solution is first derived in terms of degenerate kernel in this paper. Finally, four examples are demonstrated to verify the validity of the present approach.

Anti-Plane stress analysis of orthotropic rectangular planes weakened by multiple defects

The solution of a Volterra type screw dislocation problem in an orthotropic rectangular plane with finite length and width and various boundary conditions is obtained by means of a separation of variables technique. A distributed dislocation method is employed to obtain integral equations of the plane with cracks and cavities under an anti-plane traction. The ensuing equations are of the Cauchy singular type and have been solved numerically. Several examples are presented to demonstrate the applicability of the proposed solution.

TheFlâneurin Exile

In this essay, I argue that the flâneur in exile addresses and offers an alternative to the endless oscillation between sameness and difference that bedevils contemporary approaches to comparative literature. I use the phrase flâneur in exile to refer to the encounter between a paradigmatic figure of European modernity, the flâneur, and contemporary Chinese poetry, in particular the poetic prose cycle “Guihua” (“Ghost Speech/Lies”) written by Chinese poet Yang Lian during his exile in Auckland, New Zealand, after June Fourth 1989.Emerging out of the relationship between Europe and non-Europe and associated with Walter Benjamin's dialectical image, the figure of the flâneur furnishes a comparative approach based on collision, encounter, and touch, rather than the mimetic, vision-based models of comparison that claim equivalence or commensurability. I detect a similar comparative poetics in the mythologized encounter between Chinese poet Duoduo and Charles Baudelaire's “Le soleil” in the early 1970s. This encounter underscores the double movement of a text towards and beyond its engagement with the particularities of its own space and time and suggests the flâneur as a figure for this movement. I extend this implicit comparative poetics by superimposing Baudelaire and Benjamin onto contemporary Chinese poetry to explore the subsequent elaboration and negation of the figure in 1980s xungen, or “root seeking,” writing and especially in Yang's work in exile. Reading Yang's walker in the city in relation to the figure of the flâneur, I show how his exilic writing dramatizes the problem of spatial, temporal, and linguistic dislocation in exile, modernity, and comparison. Whether in Benjamin's reading of Baudelaire, Duoduo's encounter with Baudelaire, Yang's exilic writing, or my reading of each through the flâneur, touch stands as a figure for, and embodiment of, a comparative poetics that deploys a flâneur-like hypersensitivity to the duality of language to bring places and times into encounter, acknowledging their mutually constituting and irreconcilable, mutually eclipsing otherness. The flâneur in exile thus embodies a comparative poetics resistant to generalizing thinking but insistent on bringing places and times into contact and acknowledging the constitutive role that such moments of encounter play in modern and contemporary literature and in modernity at large.

What have we learned from LCS mobile-bearing knee system?

Three hundred and sixty-four low contact stress (LCS) total knee arthroplasties that could be followed up for more than 5years were clinically and radiographically analyzed. The median postoperative Hospital for Special Surgery score improved from 56 (range 32-77) to 91 (range 64-100) points, but median range of motion did not change from 120° (range 50°-135°) to 120° (range 85°-135°). Complications occurred in 16 cases (4%), and included postoperative polyethylene dislocation and intraoperative tibial condylar fracture, while five knees (1%) required revision surgery due to mechanical reasons. The overall prosthesis survival rate was 91% at 12years. Although the LCS mobile-bearing knee system has theoretical advantages in terms of wear and loosening, the problem of polyethylene dislocation, intraoperative tibial fracture, and radiolucent lines should be solved for long survival. The clinical relevance of this study is that the LCS system provided good clinical and survival results.

Structure of acicular ferrite. Part 1

Topics of classification, initiation, and morphology of intermediate structures in low-carbon steels are discussed. The morphological parameters of such structures are studied in detail. Aspects of the attainment of high strength and viscoplastic characteristics in steel upon formation of a structure of acicular ferrite are analyzed. The second part of the work will be devoted to crystallographic aspects of acicular ferrite. Problems of dislocation and carbide strengthening in this structure will be considered.

Proximal femoral resection arthroplasty for patients with cerebral palsy and dislocated hips

Background and purpose Chronic hip dislocation in non-ambulatory individuals with cerebral palsy (CP) can lead to severe problems, of which pain is often the most severe. We studied the outcome of proximal femoral resection, especially regarding pain, sitting balance, perineal care, and patient satisfaction.Patients and methods During the period 1998–2005, we operated 20 non-ambulatory patients with spastic quadriplegic CP (8 females and 12 males). 13 patients had unilateral dislocation and 7 had bilateral. The mean age at operation was 15 (3–27) years. The indications for operation were chronic hip dislocation plus severe problems with pain (17 patients), perineal care (16), and sitting (10). Patients were followed from 1 to 6 years.Results 14 patients were satisfied with the surgery, 3 were dissatisfied, 2 were uncertain, and 1 patient had died 5 days postoperatively. Of the 15 patients who had suffered from considerable pain before surgery, 8 had complete relief from pain and 7 patients experienced improvement. Of the 2 patients who had had mild pain, 1 was unchanged and 1 patient deteriorated. All patients who had not been able to sit were able to sit after the surgery. Only 1 patient had difficulties with perineal hygiene at follow-up. Postoperative complications included deep vein thrombosis (1 patient) and edema, loss of appetite, and the need for gastrostomy (1 patient). 7 patients had prolonged pain for up to 6 months after surgery. 1 of these was reoperated because of persistent pain due to a bony-spike heterotopic ossification.Interpretation Most patients with chronic hip dislocation and severe pain or other major problems appear to benefit from proximal femoral resection. Pain, sitting ability, and perineal care improved and most patients and caregivers were satisfied.

A Study on Control Structure for Slide Screw Stages

A slide screw drive is a kind of old technology. However it is usable and important technology even in high-tech fields such as semiconductor manufacturing. This paper intends to improve the slide screw controllability which has strong non-linearity due to grease characteristics. We measured the grease non-linear viscosity using a special tool. This grease property explains the shot dislocation phenomenon which occurs in slide screw stages particularly. Since we understood the phenomenon, we found one non-linear gain control method which embedded the grease property reversely. It not only fixed the dislocation problem but also enhanced the slid screw stage performance and maintainability.

Interaction between a dislocation and a core–shell nanowire with interface effects

The problem of a screw dislocation interacting with a core–shell nanowire (coated nanowire) containing interface effects (interface stresses) is first investigated. The interaction energy and the interaction force are calculated. The interaction force and the equilibrium position of the dislocation are examined for variable parameters (interface stress and material mismatch). The influence of the core–shell nanowire and the interface stresses on the interaction between two screw dislocations is also considered. The results show that the impact of the interface stresses on the motion and the equilibrium position of the dislocation near the core–shell nanowire is very significant when the radius of the nanowire is reduced to nanometer scale.