High density dislocations enhance creep ageing response and mechanical properties in 2195 alloy sheet

The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.

Moiré superlattices arising from growth induced by screw dislocations in layered materials

Moiré superlattices(MSLs) are modulated structures produced from homogeneous or heterogeneous two-dimensional layers stacked with a twist angle and/or lattice mismatch. Enriching the methods for fabricating MSL and realizing the unique emergent properties are key challenges in its investigation. Here we recommend that the spiral dislocation driven growth is another optional method for the preparation of high quality MSL samples. The spiral structure stabilizes the constant out-of-plane lattice distance, causing the variations in electronic and optical properties. Taking SnS_(2) MSL as an example, we find prominent properties including large band gap reduction(~ 0.4 e V) and enhanced optical activity. Firstprinciples calculations reveal that these unusual properties can be ascribed to the locally enhanced interlayer interaction associated with the Moiré potential modulation. We believe that the spiral dislocation driven growth would be a powerful method to expand the MSL family and broaden their scope of application.

Dissociation of edge and screw pyramidal Ⅰ and Ⅱ dislocations in magnesium

Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis.Bulk single crystal Mg only presents very limited plasticity in c-axis compression,and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration.In contrast,other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes.Thus,the core structure and mode of dissociation of pyramidal dislocations are still not well understood.To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature,in this work,atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K:edge and screw Py-Ⅰ on{1011},edge and screw Py-Ⅱ on{1122}by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model.The results show that when energy minimization was performed before relaxation,in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation.Without energy minimization,the edge dislocations dissociated out-of-plane onto the basal plane.Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane.The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.

Subtalar dislocations:Mechanisms,clinical presentation and methods of reduction

Subtalar joint is a complex joint in hindfoot formed by the talus superiorly and the calcaneus and navicular inferiorly.Subtalar dislocations are high-mechanism injuries,which are caused by simultaneous dislocation of both talonavicular and talocalcaneal joints,without major fracture of the talus.They are usually classified as medial(most common),lateral,anterior and posterior dislocations,based on the position of foot in relation to talus and the indirect forces that have been applied to cause this significant injury.They are usually diagnosed by X rays,but computed tomography and magnetic resonance imaging can be used to identify associated intra-articular fractures and peri-talar soft tissue injuries respectively.Majority being closed injuries,can be managed in ED by closed reduction and cast immobilisation,but if they are open,have poor outcomes.Complications that ensue open dislocations are post-traumatic arthritis,instability and avascular necrosis.

Epidemiology of shoulder dislocations presenting to United States emergency departments:An updated ten-year study

BACKGROUND Glenohumeral dislocation is a common injury that may predispose patients to chronic pain and instability.However,there is a paucity of current data available regarding the epidemiological trends of this injury.AIM To provide an updated,comparative assessment of the epidemiology of shoulder dislocations presenting to emergency departments in the United States.We also sought to analyze patient demographic risk factors and consumer products associated with dislocation events.METHODS Data were obtained from the national electronic injury surveillance system database for glenohumeral dislocations between 2012 and 2021.Incidence,age,sex,and injury characteristics were analyzed using weighted population statistics as well as incidence rates and 95%confidence intervals(CI).RESULTS In total,an estimated 773039 shoulder dislocations(CI:640598-905481)presented to emergency rooms across the United States during the study period.The annual incidence rate was 23.96 per 100000 persons and the average patient age at the time of injury was 37.1 years.Significantly more male patients sustained dislocations than female patients(537189,69.5%,vs 235834,30.5%,P<0.001).With regard to associated consumer products,sports and recreation equipment were involved in the highest proportion of incidents(44.31%),followed by home structures and construction materials(21.22%),and home furnishings,fixtures,and accessories(21.21%).Regarding product sub-groups,stairs,ramps,landings,floors was cited in the greatest number of cases(131745).CONCLUSION The national annual incidence rate of glenohumeral dislocations throughout the study period was approximately 23.92 per 100000 persons.Male adolescents sustained the highest proportion of dislocations,with a peak incidence in age group 15-20 years,predominantly secondary to participation in sporting and recreational activities.Conversely,women experienced a relatively consistent incidence of dislocation throughout their lifespan.After age 63,the incidence rate of dislocations in females was found to surpass that observed in males.

Incidence of sports-related sternoclavicular joint dislocations in the United States over the last two decades

BACKGROUND Epidemiological understanding of acute sternoclavicular(SC)dislocations secondary to sports across the United States is poorly defined.AIM To identify and assess epidemiological trends of SC dislocations occurring secondary to sports-related mechanisms across United States over the past two decades.METHODS This cross-sectional,descriptive epidemiological study evaluates epidemiological trends of SC dislocations from sports that present to emergency departments(EDs)across the United States.Data were obtained from the National Electronic Injury Surveillance System database spanning two decades.Data on incidence,patient demographics,mechanisms of injury,dislocation types,incident locales,and patient dispositions were collected.RESULTS 1622 SC dislocations occurred nationwide from 2001 to 2020[incidence=0.262/1000000 people,confidence interval(CI)=0.250-0.275],comprising 0.1%of shoulder/upper trunk dislocations.Most patients were male(91%,n=1480)and aged 5-17(61%,n=982).Football,wrestling,and biking were the most frequently implicated sports,with contact sports responsible for 59%of athletic injuries(n=961).Recreational vehicle-related sports injuries,such as all-terrain vehicles,dirt bikes,and mopeds accounted for 7.8%of all injuries(n=126),with dirt bikes specifically comprising 3.7%(n=61).Ultimately,82%were discharged from the ED(n=1337),12%were admitted(n=194),and 6%were transferred(n=90).All recorded posterior dislocations were admitted or transferred from the ED.Patients sustaining SC dislocations from contact sports had a significantly increased risk of hospital admission or transfer rather than discharge from the ED as compared to patients whose injuries were from non-contact sports(incidence rate ratio=1.46,CI:=1.32-1.61,P<0.001).CONCLUSION SC dislocations from sports continue to be rare with a stably low incidence over the past two decades,likely comprising a smaller proportion of shoulder dislocations than previously thought.Contact sports are a frequent source of injury,especially among school-aged and teenage males.Most patients are discharged directly from the ED;however,a substantial number are hospitalized,many of which had documented posterior dislocations.Ultimately,understanding the epidemiology and mechanism-related trends of acute SC dislocations is important given the potential severity of these injuries,concentration in a specific population,and uncertainty linked to rare presentation.

Recent Traumatic Dislocations of the Shoulder in Adults: Epidemiological, Therapeutic and Evolutionary Aspects

Introduction: Shoulder dislocations represent about 50% of all joint dislocations. The objective was to describe the epidemiological, therapeutic and evolutionary aspects of traumatic shoulder dislocations in Bouaké. Methods: This retrospective and descriptive study was conducted between January 2017 and December 2019. It concerned patients over 15 years of age with a recent traumatic shoulder dislocation treated and followed in the department. The variables studied were epidemiological, therapeutic and evolutionary. The severity of the trauma was assessed according to the Injury Severity Score (ISS). Functional outcome was assessed according to the Constant score. Results: There were 49 patients (49 dislocations) out of 22,569 patients. The prevalence was 0.2%. The mean age was 32 years (17 - 62). There were 38 men (77.5%). The sex ratio was 3.4. Students predominated (n = 10;20.4%). The etiology was dominated by road traffic accidents (n = 19;38.8%). Anterior dislocation was the most common (n = 45;92%). The ISS score was minor (n = 46;93.8%). The mean time to reduction was 7 hours (4 - 16). Orthopaedic reduction using the Kocher technique predominated (n = 44;89.8%). The mean duration of external rotation immobilisation of the shoulder was 23 days (16 - 45). Recurrence occurred in 8 patients (21.6%). The functional outcome at a mean Constant follow-up of 15 months (8 - 20) was satisfactory (n = 44;89.8%). Conclusion: Traumatic dislocation of the shoulder represented 0.2%. Treatment was mainly orthopaedic. Recurrence was rare.

Quantum Mechanical Tunneling of Dislocations: Quantization and Depinning from Peierls Barrier

Theories of Mott and Weertmann pertaining to quantum mechanical tunneling of dislocations from Peierls barrier in cubic crystals are revisited. Their mathematical calculations about logarithmic creep rate and lattice vibrations as a manifestation of Debye temperature for quantized thermal energy are found correct but they can not ascertain to choose the mass of phonon or “quanta” of lattice vibrations. The quantum mechanical yielding in metals at relatively low temperatures, where Debye temperatures operate, is resolved and the mathematical formulas are presented. The crystal plasticity is studied with stress relaxation curves instead of logarithmic creep rate. With creep rate formulas of Mott and Weertmann, a new formula based on logarithmic profile of stress relaxation curves is proposed which suggests simultaneous quantization of dislocations with their stress, i.e., and depinning of dislocations, i.e., , where is quantum action, σ is the stress, N is the number of dislocations, A is the area and t is the time. The two different interpretations of “quantum length of Peierls barrier”, one based on curvature of space, i.e., yields quantization of Burgers vector and the other based on the curvature of time, i.e., yields depinning of dislocations from Peierls barrier in cubic crystals, are presented. , i.e., the unitary operator on shear modulus yields the variations in the curvature of time due to which simultaneous quantization, and depinning of dislocations occur from Peierls barrier in cubic crystals.

Investigation of dislocations in 8° off-axis 4H-SiC epilayer

This paper reports that the etching morphology of dislocations in 8° off-axis 4H-SiC epilayer is observed by using a scanning electronic microscope. It is found that different types of dislocations correspond with different densities and basal plane dislcation （BPD） array and threading edge dislocation （TED） pileup group lie along some certain crystal directions in the epilayer. It is concluded that the elastic energy of threading screw dislocations （TSDs） is highest and TEDs is lowest among these dislocations, so the density of TSDs is lower than TEDs. The BPDs can convert to TEDs but TSDs can only propagate into the epilyer in spite of the higher elastic energy than TEDs. The reason of the form of BPDs array in epilayer is that the big step along the basal plane caused by face defects blocked the upstream atoms, and TEDs pileup group is that the dislocations slide is blocked by dislocation groups in epilayer.

Dislocations-induced precipitates and their effect on mechanical properties of Mg-Gd-Y-Zr alloy

Optical microscope(OM),scanning electron microscope(SEM),transmission electron microscope(TEM)and tensile machine were used to characterize the microstructures and mechanical properties of as-forged and aged Mg-9.5Gd-3.8Y-0.6Zr alloys.The results show that a novel kind of dislocation arrays,comprising parallel arranged dislocations,were obtained in the forged alloy.The arrays tend to extend parallel and are heterogeneously distributed with adjacent distances varying from 0.3μm to 1.4μm.After aging the alloy at 265°C,a large number of preferential-oriented phases were precipitated on the dislocation arrays,forming a structure of"precipitation chains"(PCs),which results in simultaneous increments of strength and ductility.

Interaction between many parallel screw dislocations and a semi-infinite crack in a magnetoelectroelastic solid

Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach-Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state.

Asymmetrical traumatic bilateral hip dislocations with hemodynamic instability and an unstable pelvic ring: Case report and review of literature

Simultaneous anterior and posterior traumatic dislocations of both hips are very rare. Only 33 cases have been previously reported in the English language literature. Although they were all due to high-energy injuries, they were hemodynamically stable and had a stable pelvic ring. We report a unique case of asymmetrical hip dislocations with an unstable pelvic ring and hemodynamic instability. A 40-year-old man was injured in a high-energy motor vehicle accident. He was hemodynamically unstable when he presented in the emergency department. Radiolographs showed asymmetrical dislocations of both hips with an unstable pelvic ring. Under general anesthesia, he had closed reduction of the dislocations of both hips, followed by temporary stabilization with an external fixator. Transcatheter arterial embolization was performed to stop active pelvic bleeding. Delayed open reduction and internal fixation was performed 12 d later with anterior and posterior plates. The patient recovered well with an uneventful post-operative course. Asymmetrical bilateral hip dislocations with pelvic ring instability caused by trauma, as presented in this case, is very rare and potentially life threatening. Prompt treatment can give a good outcome.

Effect of interaction of dislocations with core-shell nanowires on critical shear stress of nanocomposites

The contribution to the critical shear stress of nanocomposites caused by the interaction between screw dislocations and core-shell nanowires (coated nanowires) with interface stresses was derived by means of the MOTT and NABARRO's model. The influence of interface stresses on the critical shear stress was examined. The result indicates that, if the volume fraction of the core-shell nanowires keeps a constant, an optimal critical shear stress may be obtained when the radius of the nanowire with interface stresses reaches a critical value, which differs from the classical solution without considering the interface stresses under the same external conditions. In addition, the material may be strengthened by the soft nanowires when the interface stresses are considered. There also exist critical values of the elastic modulus and the thickness of surface coating to alter the strengthening effect produced by it.

Discrimination of dislocations in 4H-SiC by inclination angles of molten-alkali etched pits

Discrimination of dislocations is critical to the statistics of dislocation densities in 4H silicon carbide(4H-SiC),which are routinely used to evaluate the quality of 4H-SiC single crystals and homoepitaxial layers.In this work,we show that the inclination angles of the etch pits of molten-alkali etched 4H-SiC can be adopted to discriminate threading screw dislocations(TSDs),threading edge dislocations(TEDs)and basal plane dislocations(BPDs)in 4H-SiC.In n-type 4H-SiC,the inclination angles of the etch pits of TSDs,TEDs and BPDs in molten-alkali etched 4H-SiC are in the ranges of 27°−35°,8°−15°and 2°−4°,respectively.In semi-insulating 4H-SiC,the inclination angles of the etch pits of TSDs and TEDs are in the ranges of 31°−34°and 21°−24°,respectively.The inclination angles of dislocation-related etch pits are independent of the etching duration,which facilitates the discrimination and statistic of dislocations in 4H-SiC.More significantly,the inclination angle of a threading mixed dislocations(TMDs)is found to consist of characteristic angles of both TEDs and TSDs.This enables to distinguish TMDs from TSDs in 4H-SiC.

Interaction between infinitely many dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal

By means of analytic function theory, the problems of interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are studied. The analytic solutions of stress fields of the interaction between infinitely many parallel dislocations and a semi-infinite crack in one-dimensional hexagonal quasicrystal are obtained. They indicate that the stress concentration occurs at the dislocation source and the tip of the crack, and the value of the stress increases with the number of the dislocations increasing. These results are the development of interaction among the finitely many defects of quasicrystals, which possesses an important reference value for studying the interaction problems of infinitely many defects in fracture mechanics of quasicrystal.

Cost analysis and outcomes of simple elbow dislocations

AIM: To evaluate the management, clinical outcome and cost implications of three different treatment regimes for simple elbow dislocations.METHODS: Following institutional board approval, we performed a retrospective review of all consecutive patients treated for simple elbow dislocations in a Level Ⅰ trauma centre between January 2008 and December 2010. Based on the length of elbow immobilisation(LOI), patients were divided in three groups(Group I, < 2 wk; Group Ⅱ, 2-3 wk; and Group Ⅲ, > 3 wk). Outcome was considered satisfactory when a patient could achieve a pain-free range of motion ≥ 100°(from 30° to 130°). The associated direct medical costs for the treatment of each patient were then calculated and analysed.RESULTS: We identified 80 patients who met the inclusion criteria. Due to loss to follow up, 13 patients were excluded from further analysis, leaving 67 patients for the final analysis. The mean LOI was 14 d(median 15 d; range 3-43 d) with a mean duration of hospital engagement of 67 d(median 57 d; range 10-351 d). Group Ⅲ(prolonged immobilisation) had a statistically significant worse outcome in comparison to Group Ⅰ?and Ⅱ(P = 0.04 and P = 0.01 respectively); however, there was no significant difference in the outcome between groups Ⅰ?and Ⅱ(P = 0.30). No statistically significantdifference in the direct medical costs between the groups was identified.CONCLUSION: The length of elbow immobilization doesn't influence the medical cost; however immobilisation longer than three weeks is associated with persistent stiffness and a less satisfactory clinical outcome.

Atomistic Simulations of the Effect of Helium on the Dissociation of Screw Dislocations in Nickel

The interactions of He with dissociated screw dislocations in face-centered-cubic （fcc） Ni are investigated by using molecular dynamics simulations based on an embedded-atom method model. The binding and formation energies of interstitial He in and near Shockley partial cores are calculated. The results show that interstitial He atoms at tetrahedral sites in the perfect fee lattice and atoms occupying sites one plane above or below one of the two Shockley partial cores exhibit the strongest binding energy. The attractive or repulsive nature of the interaction between interstitial He and the screw dislocation depends on the relative position of He to these strong binding sites. In addition, the effect of He on the dissociation of screw dislocations are investigated. It is found that Fie atoms homogeneously distributed in the glide plane can reduce the stacking fault width.

Analytical solutions of uniform extended dislocations and tractions over a circular area in anisotropic magnetoelectroelastic bimaterials

In this paper, we derive the analytical solutions in a three-dimensional anisotropic magnetoelectroelastic bimaterial space subject to uniform extended dislocations and tractions within a horizontal circular area. By virtue of the Stroh formalism and Fourier transformation, the final expression of solutions in the physical domain contains only line integrals over [0, 2π] rather than infinite integrals. As the reduced cases, the half-space and homogeneous full-space solutions can be directly derived from the present solutions. Also, in terms of material domains, the present solutions can be reduced to the piezoelectric, piezomagnetic, purely elastic materials with different symmetries of material prop- erty. To carry out numerical calculations, Gauss quadrature is adopted. In the numerical examples, the effect of different loading locations on the response at the interface is analyzed. It is shown that, when the magnetic traction or electric dislocation is applied, the physical quantities on the interface may not decrease monotonically as the loading area moves away from the interface. The distributions of different in-plane physical quantities on the upper and lower interfaces under various extended horizontal loadings are compared and the differences are discussed. The work presented in this paper can serve as benchmarks for future numerical studies in related research fields.

THE BEHAVIOUR OF1/2[112] SUPERLATTICE DISLOCATIONSIN POLYSY NTHETICALLY TWINNED CRYSTALS OF TiAl

The behaviour of 1/2〈112] superlattice dislocations in polysynthetically twinned (PST) crystals of TiAl at elevated temperatures have been investigated by transmission electron microscopy (TEM). The results showed that 1/2〈112] superlattice dislocations play an important part in the deformation. At room temperature, 1/2〈112] superlattice dislocations can be activated easily but are often dissociated into partials trailed by faulted dipoles with super extrinsic stacking faults (SESFs) and difficult to move. In situ heating observations on the faulted dipoles showed that annihilation of the partials bounding the SESFs of the faulted dipoles occurred and resulted in discontinuous stacking faults along the direction of the partials at about 500 ℃. The faulted dipoles disappeared completely at about 600 ℃. The temperature range of annihilation coincided with that of brittle to ductile transition of TiAl PST crystals reported by Inui et al (1995). At 850 ℃, they are often dissociated into partials including super intrinsic stacking faults (SISFs) and can move easily. The experimental observations suggest that the behaviors of 1/2〈112] superlattice dislocations control the phenomenon of brittle to ductile transition of PST crystals of TiAl alloy.

Dislocations in the Crystallites of Nanocrystalline α-Fe—A Molecular Dynamics Study

Molecular dynamics simulations are carried out in order to Study the atomic structure of crystalline component of nanocrystalline α-Fe when it is consolidated from small grains. A two-dimensional computational block is used to simulate the consolidation process. All the preset dislocations in the original grains glide out of them in the consolidation process, but new dislocations can generate when the grain size is large enough. It shows that dislocations exist in the consolidated material rather than in the original grains. Whether dislocations exist in the crystalline component of the resultant model nano-material depends upon grain size. The critical value of grain size for dislocation generation appears to be about 9 nm. This result agrees with experiments qualitatively.