X‐ray diffraction from dislocation half‐loops consisting of a misfit segment with two threading arms extending from it to the surface is calculated by the Monte Carlo method. The diffraction profiles ...and reciprocal space maps are controlled by the ratio of the total lengths of the misfit and the threading segments of the half‐loops. A continuous transformation from the diffraction characteristic of misfit dislocations to that of threading dislocations with increasing thickness of epitaxial film is studied. Diffraction from dislocations with edge‐ and screw‐type threading arms is considered and the contributions of the two types of dislocations are compared.
X‐ray diffraction from dislocation half‐loops consisting of a misfit segment with two threading arms extending from it to the surface is calculated by the Monte Carlo method.
Purpose
The commonly described congenital atlanto-axial dislocation and Basilar-Invagination is antero-posterior or rotational or vertical plane. However, congenital dislocation in lateral plane has ...received scant attention. The purpose of this manuscript is to describe this unusual entity and discuss its management.
Materials and methods
The clinic-radiological feature of seven patients with congenital lateral angular AAD (CLAAAD) were studied and managed. The unilateral C1 facet had subluxed lateral to C2–3 complex. The C1 and C2 facets were drilled comprehensively and repositioned with distraction, placement of metallic spacers and facet manipulation after insertion of screws. The post operative outcome was studied.
Results
The presentation is usually with neck tilt (progressive in 3) and/or progressive spastic quadriparesis. The mean C1–2 tilt was 25.2°. C1 was bifid in six patients. C1 lateral mass was assimilated with occipital condyle on dislocated side in and the other side was normal (6 patients). The dislocated C1–2 joint was abnormally oblique as compared to contralateral side. The relationship of occiput and C1 was normal. Correction of dislocation and lateral tilt was achieved in all patients with subsequent correction of neck tilt and deficits. One patient required reoperation.
Conclusions
The acute angulation of joint on one side and near normal on other side leads to differential vertical movement, further accentuated by splaying of bifid C1. The entity is seen in young patients and often present with neck tilt and spastic quadriparesis. Management requires reshaping the joints and facet manipulation. If the reshaping is inappropriate, the joint is likely to redislocate before fusion occurs.
FeCrAl ferritic alloys are excellent cladding candidates for accident tolerant fuel systems due to their high resistance to oxidation as a result of formation of a protective Al2O3 scale at high ...temperatures in steam. In this study, we report the irradiation response of the 10Cr and 13Cr FeCrAl cladding tubes under Fe2+ ion irradiation up to ∼16 dpa at 300 °C. Dislocation loop size, density and characteristics were determined using both two-beam bright field transmission electron microscopy and on-zone scanning transmission electron microscopy techniques. 10Cr (C06M2) tube has a lower dislocation density, larger grain size and a slightly weaker texture compared to the 13Cr (C36M3) tube before irradiation. After irradiation to 0.7 dpa and 16 dpa, the fraction of type sessile dislocations decreases with increasing Cr amount in the alloys. It has been found that there is neither void formation nor α′ precipitation as a result of ion irradiations in either alloy. Therefore, dislocation loops were determined to be the only irradiation induced defects contributing to the hardening. Nanoindentation testing before the irradiation revealed that the average nanohardness of the C36M3 tube is higher than that of the C06M2 tube. The average nanohardness of irradiated tube samples saturated at 1.6–2.0 GPa hardening for both tubes between ∼3.4 dpa and ∼16 dpa. The hardening calculated based on transmission electron microscopy was found to be consistent with nanohardness measurements.
Purpose
Most elbow dislocations can be treated conservatively, with surgery indicated in special circumstances. Surgical options, apart from fracture fixation, range from repair or reconstruction of ...the damaged ligaments to static external fixation, usually entailing either a long period of immobilization followed by carefully monitored initiation of movement or dynamic external fixation. In general, no consensus regarding surgical treatment has been reached. A new method of open ligament repair and augmentation of the lateral ulnar collateral ligament using a non-absorbable suture tape in cases of acute and subacute elbow instability following dislocations has been described here, which allows an early, brace-free initiation of the full range of motion. This is the first description of the technique of internal bracing of the lateral elbow with preliminary patient outcome parameters for acute treatment of posterolateral rotatory instability.
Methods
Seventeen patients (14 males and 3 females) with acute or subacute posterolateral elbow instability as a result of dislocation or fracture dislocation were treated in our centre (Sporthopaedicum, Straubing, Regensburg, Germany) from 2014 to 2015 with open LUCL re-fixation and non-absorbable suture tape augmentation. The elbows were actively mobilized immediately after the operation and a maximum bracing period of 3 days.
Results
At 10 month median follow-up, none of the patients showed clinically apparent signs of instability or suffered subluxation or re-dislocation. One patient required re-operation for heterotopic ossification. The median range of motion was from 10° (0–40) to 130° (90–50) and median Oxford, Mayo Elbow Performance score, Simple Elbow Value, and DASH Scores were 41(29–48), 100 (70–100), 83% (60–95), and 18.5 (1.6–66), respectively. All patients reported a complete return to pre-injury level of activity.
Conclusion
Augmentation with a non-absorbable suture tape acting as an ‘Internal Brace’ following an elbow dislocation is a safe adjunct to primary ligament repair and may allow the early mobilization and recovery of elbow stability and range of motion.
Level of evidence
IV.
• The new dislocation density based continuum model is dislocation evolution mechanism based. • Cross slip is taken into consideration in dislocation evolution mechanism. • The defects density is ...incorporated to consider the effect of irradiation. • This model is a breakthrough by bridging the discrete dislocation dynamics and crystal plasticity.
Continuum dislocation dynamics (CDD) with a novel constitutive law based on dislocation density evolution mechanisms was developed to investigate the deformation behaviors of single crystals. The dislocation density evolution law in this model is mechanism-based, with parameters predicted by lower-length scale models or measured from experiments, not an empirical law with parameters back-fitted from the flow curves. Applied on iron single crystal, this model was validated by experimental data and compared with traditional single crystal constitutive models using a Hutchinson-type hardening law or a dislocation-based hardening law. The CDD model demonstrated higher fidelity than other constitutive models when anisotropic single crystal deformation behaviors were investigated. The traditional Hutchinson type hardening laws and other constitutive laws based on a Kocks formulated dislocation density evolution law will only succeed in a limited number of loading directions. The main advantage of CDD is the novel physics-based dislocation density evolution laws in describing the meso-scale microstructure evolution. Another advantage of CDD is on cross-slip, which is very important when loading conditions activate only one primary slip system. In addition to the dislocation hardening, CDD also takes into consideration dislocation defect interactions. Irradiation hardening of iron single crystal was simulated with validation from experimental results.
This work presents a regularized eigenstrain formulation around the slip plane of dislocations and the resultant non-singular solutions for various dislocation configurations. Moreover, we derive the ...generalized Eshelby stress tensor of the configurational force theory in the context of the proposed dislocation model. Based on the non-singular finite element solutions and the generalized configurational force formulation, we calculate the driving force on dislocations of various configurations, including single edge/screw dislocation, dislocation loop, interaction between a vacancy dislocation loop and an edge dislocation, as well as a dislocation cluster. The non-singular solutions and the driving force results are well benchmarked for different cases. The proposed formulation and the numerical scheme can be applied to any general dislocation configuration with complex geometry and loading conditions.
Atomic-level simulations are used to investigate the interaction of an edge dislocation with 〈1
0
0〉 interstitial dislocation loops in α-iron at 300
K. Dislocation reactions are studied ...systematically for different loop positions and Burgers vector orientations, and results are compared for two different interatomic potentials. Reactions are wide-ranging and complex, but can be described in terms of conventional dislocation reactions in which Burgers vector is conserved. The fraction of interstitials left behind after dislocation breakaway varies from 25 to 100%. The nature of the reactions requiring high applied stress for breakaway is identified. The obstacle strengths of 〈1
0
0〉 loops, 1/2〈1
1
1〉 loops and voids containing the same number (169) of point defects are compared. 〈1
0
0〉 loops with Burgers vector parallel to the dislocation glide plane are slightly stronger than 〈1
0
0〉 and 1/2〈1
1
1〉 loops with inclined Burgers vector: voids are about 30% weaker than the stronger loops. However, small voids are stronger than small 1/2〈1
1
1〉 loops. The complexity of some reactions and the variety of obstacle strengths poses a challenge for the development of continuum models of dislocation behaviour in irradiated iron.
High-entropy and medium-entropy alloys are presumed to have a configurational entropy as high as that of an ideally mixed solid solution (SS) of multiple elements in near-equal proportions. However, ...enthalpic interactions inevitably render such chemically disordered SSs rare and metastable, except at very high temperatures. Here we highlight the wide variety of local chemical ordering (LCO) that sets these concentrated SSs apart from traditional solvent-solute ones. Using atomistic simulations, we reveal that the LCO of the multi-principal-element NiCoCr SS changes with alloy processing conditions, producing a wide range of generalized planar fault energies. We show that the LCO heightens the ruggedness of the energy landscape and raises activation barriers governing dislocation activities. This influences the selection of dislocation pathways in slip, faulting, and twinning, and increases the lattice friction to dislocation motion via a nanoscale segment detrapping mechanism. In contrast, severe plastic deformation reduces the LCO towards random SS.
Solutions to the differential equations of linear elasticity in the continuum limit in arbitrary crystal symmetry are known only for steady-state dislocations of arbitrary character, i.e. line ...defects moving at constant velocity. Troubled by singularities at certain ‘critical’ velocities (typically close to certain sound speeds), these dislocation fields are thought to be too idealized, and divergences are usually attributed to neglecting the finite size of the core and to the restriction to constant velocity. In the isotropic limit, accelerating pure screw and edge dislocations were studied some time ago. A generalization to anisotropic crystals has been attempted for pure screw and edge dislocations only for some special cases. This work aims to fill the gap of deriving a general anisotropic solution for pure screw dislocations applicable to slip systems featuring a reflection symmetry, a prerequisite to studying pure screw dislocations without mixing with edge dislocations. Further generalizations to arbitrary mixed dislocations as well as regularizations of the dislocation core are beyond the scope of this paper and are left for future work.
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