•The misfit dislocation patterns of hcp/bcc semicoherent bimetal interfaces with B and PS ORs were characterized.•The deformation mechanism of dislocation nucleation and phase transformation is ...revealed, where the former is closely related to dynamic evolution of misfit dislocation patterns and the latter is correlated to the specific loading mode and interface structure.•The phase transformation path for the required atomic rearrangements were revealed.•Competition relationship between non-basal dislocation nucleation and phase transformation were revealed via twisted interface models.
The nucleation of lattice dislocations and interface sliding at bimetal interfaces are two fundamental mechanisms of plasticity that are responsible for the mechanical responses of nanostructured materials; however, the interface-facilitated phase transformation is rarely considered owing to its relatively high energy barrier for activation. Taking the bimetal hcp/bcc interfaces with Pitch-Schrader and Burgers orientation relationships (ORs) as an illustration, we show that both non-basal dislocation nucleation and hcp-to-bcc phase transformation can be activated at the interface under external loading when the basal slip systems are effectively suppressed. The non-basal dislocation nucleation is shown to be closely related to the dynamic evolution of misfit dislocation patterns at the semicoherent interface, in which the 1/6022¯3¯ pyramidal dislocation is not strictly parallel to the (011¯1) stacking fault plane owing to the corrugated feature. In contrast to non-basal dislocation nucleation, phase transformation requires specific crystallographic ORs of the constituent metals under certain loading conditions, which corresponds to the process of alternate shuffle and shear deformation that involves atomistic migration. To further reveal the competition between non-basal dislocation nucleation and phase transformation, a series of twisted interface models were constructed to systematically investigate the optimal condition of the interface geometry for phase transformation. The phase transformation occurred only when the dislocation nucleation was further hindered at some specific twist angles, suggesting a strong dependence of phase transformation on the interface structure. These findings provide a foundation to the atomistic mechanism of various interface-mediated deformation and a solution to tune interface-facilitated plasticity via interface engineering.
The density of geometrically necessary dislocations (GND) obtained from the lattice curvature was studied in commercially pure copper up to extreme large strains (von Mises strain of 63). Its ...evolution shows an increase to a maximum at a strain of about 2, then decreases until reaching the stationary limiting stage of grain refinement at a von Mises strain of about 14. At the same time, the total dislocation density is also decreasing. It is shown that the variation in the GND density correlates with the difference between the correlated (first neighbor grains) and the non-correlated (random neighbor) misorientation angle distributions. The low quantity of GND at extreme large strains is a consequence of the near Taylor-type homogeneous behavior of the polycrystalline ultrafine-grained structure.
Display omitted
Helical dislocations are widely observed in metallic, ionic and covalent crystals and have significant impacts on the material properties. In this paper, a coupled glide-climb model is proposed based ...on three-dimensional discrete dislocation dynamics (3D-DDD) to reveal the intrinsic formation mechanism of helical dislocations. First, a dislocation climb model controlled by the diffusion of the supersaturated vacancies is developed and validated. Then, a sequentially coupled scheme is adopted to bridge the time scale separation between dislocation climb and glide. By incorporating the dislocation climb model into the 3D-DDD framework, a coupled glide-climb model is established to investigate the formation of helical dislocations. From the aspect of kinematics, dislocation climb gives rise to winding up, and the prismatic glide ensures the spaces between spirals. While from the aspect of kinetics, it is the applied stress, the osmotic force and line tension that act together to drive the dislocation line into a helix. The simulations further quantitatively reveal that: (1) It is the evolution velocity that breaks the stable equilibrium state and drives the helix into a configuration with multiple turns; (2) Both the external stress and the initial dislocation configurations influence the final helical configuration and the number of spirals increases linearly with the external stress, which are very similar to the buckling configuration of a column under axial loading which is sensitive to the critical loading and initial geometry imperfection; (3) The formation time of helical dislocation decreases exponentially with the vacancy concentration.
•A coupled glide-climb model is proposed based on three-dimensional discrete dislocation dynamics (3D-DDD).•Both multi-field and multi-time-scale issues are addressed in the coupled method.•The intrinsic formation mechanism of helical dislocations are studied by the new method.•Dislocation climb gives rise to winding up, and the prismatic glide ensures the spaces between spirals.•Vacancy concentration, external applied stress and initial configuration play important roles in final configurations.
Instability remains a devastating complication following total hip arthroplasty. Here we describe a mini-posterior approach with a monoblock dual-mobility implant without “traditional posterior hip ...precautions” yielding excellent results.
There were 580 consecutive hips in 575 patients who underwent total hip arthroplasty utilizing a monoblock dual-mobility implant and a mini-posterior approach. With this technique, the acetabular component positioning does not rely on tradition intra-operative radiographic abduction and anteversion goals but rather uses patient-specific anatomic landmarks (anterior acetabular rim and, when visible, the transverse acetabular ligament) to set cup position; stability is assessed with a significant, dynamic intra-operative test of range of motion. Patients’ mean age was 64 years (range, 21 to 94), and 53.7% were women.
Mean abduction was 48.4° (range, 29° to 68°) and mean anteversion was 24.7° (range, −1° to 51°). Patient Reported Outcomes Measurement Information System scores improved in every measured domain from preoperative to final postoperative visit. There were seven (1.2%) patients who required reoperation, with mean time to reoperation of 1.3 months (range, one to 176 days). Only one patient (0.2%) who had a preoperative history of spinal cord injury and Charcot arthropathy dislocated.
A posterior approach hip surgeon may want to consider using a monoblock dual-mobility construct and avoidance of traditional posterior hip precautions to achieve early hip stability with an extremely low dislocation rate and high patient satisfaction scores.
•Dislocation–voids interactions are simulated by the CAC method.•Epinning mechanisms as the void spacings in submicrons are discovered.•5nm voids can even act as weak barriers to dislocations under ...dynamic conditions.
Dislocation interactions with distributed condensed vacancy clusters in fcc metals were simulated via a concurrent atomistic–continuum method. Due to void strengthening, the dislocation lines are found to bow as a result of pinning on the original glide plane and undergo depinning through drawing out screw dipoles and forming prismatic loops on the secondary slip plane. We discovered an inertia-induced transition between Hirsch looping and void shearing mechanisms as the void spacing ranges from the scale of nm to hundreds of nm. Contrary to prior understanding, simulations suggest that large voids (∼5nm in diameter) can behave as weak barriers to dislocation motions under high strain-rate dynamic conditions.
Arthroscopic rotator cuff repair has been shown to have favorable outcomes following traumatic rotator cuff tear with concomitant shoulder dislocation. The aim of this study was to compare outcomes ...and tear characteristics between patients who underwent arthroscopic rotator cuff repair following traumatic tear with shoulder dislocation to those without dislocation.
A retrospective review of 226 consecutive patients with traumatic rotator cuff tears who underwent arthroscopic repair between 2013 and 2017 with a minimum of 1-year follow-up was performed. Patients with traumatic dislocations and concomitant rotator cuff tears were placed in the Dislocation & Tear cohort (DT cohort) and were matched 1:2 with a second cohort sustaining traumatic cuff tears without dislocation (T cohort). Primary outcomes were injury characteristics including tendon involvement and atrophy and tear size and thickness. Secondary outcomes were postoperative strength and range of motion (ROM) in forward flexion (FF), external rotation (ER), and internal rotation (IR); patient-reported outcomes including Subjective Shoulder Value, visual analog scale, and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form; complications including repair failure (defined as symptomatic retear confirmed on postoperative magnetic resonance imaging), infection, adhesive capsulitis, and impingement; and rates of revision surgery.
There were 18 patients in the DT Cohort and 36 patients in the T Cohort with no significant differences in time to final follow-up (50.4 ± 24.5 months vs. 49.0 ± 30.4 months, P = .73). The DT cohort displayed a larger mean tear size (34 ± 12 mm vs. 19 ± 12 mm, P = .01) and had greater infraspinatus involvement (78% vs. 36%, P = .004) and subscapularis involvement (72% vs. 39%, P = .02) than the T cohort. With regard to strength, postoperative ER strength was less likely to be 5/5 in the DT Cohort (53% vs. 94% of patients with 5/5 strength, P = .002) compared with the T cohort. With regard to ROM, the DT cohort had significantly lower preoperative FF (90° ± 55° vs. 149° ± 33°, P < .001), ER (36 ± 21° vs. 52° ± 14°, P = .02), and IR (5.4 ± 2.1 vs. 7.5 ± 1.2, P = .002) compared with the T cohort but had similar FF, ER, and IR outcomes postoperatively. There were no differences between the groups for complications and postoperative patient-reported outcomes.
Traumatic rotator cuff tears with concomitant dislocations are associated with larger tear size and greater infraspinatus and subscapularis involvement than traumatic tears without dislocation. Arthroscopic repair of this injury is associated with lower preoperative ROM in FF, ER, and IR, as well as lower postoperative ER strength compared with traumatic tears without dislocation. Nonetheless, excellent patient-reported outcomes can be achieved following arthroscopic repair similar to patients without dislocation.
Purpose
The purpose of this study is to report on the global distribution and clinical outcomes of published articles related to trochleoplasty.
Methods
The online databases OVID Medline, OVID ...EMBASE, and the Cochrane Library were searched for the literature assessing trochleoplasty performed for lateral patellofemoral instability (LPI). Study data were abstracted looking at global trends in the literature, as well as clinical and patient-reported outcomes following this technique.
Results
For the assessment of global distribution, 29 studies including 998 patients met the inclusion criteria. The majority of the studies were conducted in Europe (93%) and most used an open thin flap technique (52%). For the secondary analysis of clinical outcomes, 21 studies were included with significant heterogeneity in patient selection, reporting on the degree of trochlear dysplasia, and patient-reported outcomes. All trochleoplasty techniques showed statistically significant improvement in clinical outcomes at average 50 months (range 3–228 months) post-operative, with most patients being satisfied with their procedure. Re-dislocation and complication rates were low.
Conclusions
European centers have published majority of data on trochleoplasty surgery, which has been shown to be an acceptable procedure for patients with high-grade trochlear dysplasia and LPI. Trochleoplasty has demonstrated good clinical outcomes, a low re-dislocation rate, and an acceptable complication profile in both short and long-term follow-up. This study highlights the difficulty in reporting outcomes in this group of patients due to heterogeneity in patient selection, grading of trochlear dysplasia, and the lack of disease-specific outcome measures.
Level of evidence
IV.
Denoising of crystal orientation maps Hielscher, R.; Silbermann, C. B.; Schmidl, E. ...
Journal of applied crystallography,
October 2019, Letnik:
52, Številka:
5
Journal Article
Recenzirano
This paper compares several well known sliding‐window methods for denoising crystal orientation data with variational methods adapted from mathematical image analysis. The variational methods turn ...out to be much more powerful in terms of preserving low‐angle grain boundaries and filling holes of non‐indexed orientations. The effect of denoising on the determination of the kernel average misorientation and the geometrically necessary dislocation density is also discussed. Synthetic as well as experimental data are considered for this comparison. The examples demonstrate that variational denoising techniques are capable of significantly improving the accuracy of properties derived from electron backscatter diffraction maps.
This paper compares several well known methods for denoising orientation data with methods adapted from mathematical image analysis.
In this paper, we show a novel measurement approach for determination of the threading dislocations density in GaN/sapphire structures using X-ray diffractometry at edge scans geometry. The presented ...method is based on measurements carried out both: classically from the surface and from the edge of the sample. Edge scans allow measurements of planes parallel to the growth direction, which permit the unambiguous determination of the number of edge dislocations. This is a new measurement approach that facilitates the characterization of structures. In addition, obtained results have been confirmed by using the wet etching method. In comparation with the obtained results, it can be concluded that both methods give the same results within the experimental uncertainty.
•The edge dislocation density can be determined using measurements from the edge of the sample.•The presented method allows direct determination of the size of edge dislocations.•Wet etching of GaN layer confirms the values obtained from the XRD methods.
CHST3‐related chondrodysplasia with congenital joint dislocations (CDCJD, #MIM 143095), is a rare genetic skeletal disorder caused by biallelic loss of function variants in CHST3. CHST3 is critical ...for the sulfation of chondroitin sulfate. This study delineates the clinical presentation of nine individuals featuring the key symptoms of CDCJD; congenital joint (knee and elbow) dislocations, short trunk short stature progressive vertebral anomalies, and metacarpal shortening. Additional manifestations include irregular distal femoral epiphysis, supernumerary carpal ossification centers, bifid humerus, club foot, and cardiac abnormalities. Sanger sequencing was carried out to investigate molecular etiology in eight patients and exome sequencing in one. Genetic testing revealed five homozygous variants in CHST3 (four were novel and one was previously reported). All these variants are located on sulfotransferase domain of CHST3 protein and were classified as pathogenic/ likely pathogenic. We thus report on nine individuals with CHST3‐related chondrodysplasia with congenital joint dislocations from India and suggest monitoring the health of cardiac valves in this condition.
PDF
