Lattice dislocation interactions with semicoherent interfaces are investigated by means of anisotropic field solutions in metallic homo- and hetero-structures. The present framework is based on the ...mathematically elegant and computationally powerful Stroh formalism, combining further with the Fourier integral and series transforms, which cover different shapes and dimensions of various extrinsic and intrinsic dislocations. Two-dimensional equi-spaced arrays of straight lattice dislocations and finite arrangements of piled-up dislocations as well as any polygonal and elliptical dislocation loops in three dimensions are considered using a superposition scheme. Self, image and Peach–Koehler forces are derived to compute the equilibrium dislocation positions in pile-ups, including the internal structures and energetics of the interfacial dislocation networks. For illustration, the effects due to the elastic and misfit mismatches are discussed in the pure misfit Au/Cu and heterophase Cu/Nb systems, while discrepancies resulting from the approximation of isotropic elasticity are clearly exhibited. These numerical examples not only feature and enhance the existing works in anisotropic bimaterials, but also promote a novel opportunity of analyzing the equilibrium shapes of planar glide dislocation loops at nanoscale.
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.
Molecular dynamics simulations were performed to investigate the nucleation and growth of helium bubble on W/Ta semi-coherent interface. It is found that misfit dislocation has a significant impact ...on the nucleation and growth of helium bubble. He bubble energetically prefers to nucleate at the intersections of the misfit dislocations or on some misfit dislocations. During the bubble growing process, metal interstitial atoms pushed out by the bubble are directly absorbed into nearby misfit dislocations, leading them to climb towards the Ta side; in turn, the climbed misfit dislocations induce He bubble moving away from the bimetal interface and into Ta side. Finally, the misfit dislocation effect on the bubble growth was further discussed in terms of wetting theory.
In this study, for the first time, the evolution of geometrically necessary dislocation (GND) and statistically stored dislocation (SSD) densities, as well as their roles in strain hardening during ...mechanical twinning, was experimentally investigated in a tensile-deformed Fe-22Mn-0.6C twinning-induced plasticity (TWIP) steel. GND and SSD densities were estimated via EBSD-acquired orientation data and a modified strain hardening model, respectively. The analysis demonstrates that the GND density increases non-linearly due to mechanical twinning. The SSD density increases much faster than the GND density, which shows that multiplication of the SSDs is heavily dependent on the imposed strain level. It is revealed that the GND density is higher at early strain stages (below 0.14 true strain), dominating dislocation hardening, but thereafter the SSD density contributes more. It is also found that the GND density is several times higher in this TWIP steel than in metals or alloys, which deform through dislocation slip only. We attribute this difference to the planar slip of dislocations and the occurrence of mechanical twinning, which leads to much more pile-ups of the GNDs at/near boundaries. Mechanical twinning directly contributes less than 100 MPa to flow stress increment in the studied true strain range of 0 to 0.34. Consequently, depending on dislocation types, dislocation multiplication governs strain hardening at all deformation ranges. The findings provide insight into the evolution behaviors of GNDs and SSDs in TWIP steels, which are particularly important for further understanding of the dynamic Hall-Petch effect and useful for TWIP alloy design efforts.
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The elbow is the joint that most usually dislocates in children. In contrast to the widely known recent increase in the incidence of upper-extremity fractures and their operative treatment in ...children, potential trends in elbow dislocation are not clear. In this study we aimed to clarify the recent epidemiology of childhood elbow dislocation, in particular the potential change in incidence and treatment.
A population-based study was performed to evaluate the annual incidence and the characteristics of injury, patients and treatment. All children < 16 years of age with an elbow dislocation in 1996-2014 in the Oulu University Hospital District, Finland, were included. Elbow dislocations with and without an associated fracture were included. The mean number of children in the population at risk was 85,600, according Statistics Finland.
There were 104 patients with a mean age of 11.3 years (SD 2.6). The annual incidence was 6.4 (mean) per 100,000 children in 1996-2014 and no changing trend in incidence during the study period was found. Trampoline jumping was the most usual reason for the dislocations (N = 15, 14.4%). The majority (N = 73/104, 70.2%) were treated non-operatively by reduction and casting. There was no change in surgical treatment during the study time.
In contrast to increasing incidence of upper-extremity fractures in children, there has not been a change in the incidence of elbow dislocation in children. There was no change in surgical treatment in 1996-2014.
Developmental dysplasia of the hip (DDH) is the most common hip abnormality in children. Closed or open reduction and cast immobilization are the most commonly used treatments for patients aged 6 to ...18 months with dislocation; they are also used in children younger than 6 months when brace treatment is not effective. During cast immobilization, surgeons need reliable and timely imaging methods to assess the status of hip reduction to ensure successful treatment and avoid complications. Several methods are used, but they have disadvantages. We developed and, in this study, evaluated a hip medial ultrasound method to evaluate the status of hip reduction in children treated with a spica cast.
Is hip medial ultrasound more accurate than radiography for determining the status of hip reduction in children treated with a spica cast?
Between November 2017 and December 2020, we treated 136 patients with closed or open reduction and spica casting for DDH in our department. These children were 3 to 18 months old at the time of surgical reduction and had a specific medical history, physical examination findings, or AP radiographic evidence of unilateral or bilateral DDH. None had a concomitant femoral/acetabular osteotomy procedure in these hips. All patients underwent hip medial ultrasound, AP radiography, and MRI under sedation within 2 to 7 days after open or closed reduction. The examination time was from the second day after reduction to enable the patient to recover from anesthesia. MRI was performed within 7 days after reduction because of a few long appointment times, and ultrasound and AP radiography were always performed 1 or 2 days before MRI. Based on that, 65% (88 of 136 88 hips) of patients were excluded due to the absence of MRI, ultrasound, or AP radiography; 3% (4 of 136 4 hips) of patients were excluded because of concurrent congenital spina bifida, Larson syndrome, or Prader-Willi syndrome; and 1% (1 of 136 1 hip) of patients were excluded because the patient underwent MRI before ultrasound. A total of 32% (43 of 136 43 hips) of patients were eligible for analysis in this cross-sectional diagnostic study, and these 43 patients underwent AP radiography, ultrasound, and MRI. In this retrospective study, the mean age at the time of surgery was 10 ± 4 months (male:female ratio 5:38; unilateral DDH: 34; bilateral DDH: 9). To ensure the independence of the results, the study was limited to one hip per patient (in patients with bilateral DDH, the right hip was evaluated). The reduction of 43 hips (left:right ratio 26:17; closed:open reduction ratio 30:13) was evaluated by MRI, hip medial ultrasound, and radiography. Children with spica casts were placed in the supine position, which is necessary to expose the perineum for ultrasound. We used a broad-spectrum, microconvex, and intracavitary probe. The acetabular medial wall was identified by the triradiate cartilage of the ischial tuberosity and the pubis superior, and the femoral head was identified by the femoral neck. Then, the acetabulum coronal midsectional plane was used to determine the positions of the femoral head and acetabulum and to measure the triradiate cartilage-femoral distance. MRI examinations were performed using a 1.5-T MRI system with an eight-channel body coil. Each reviewer evaluated each reduction independently. Additionally, to further assess the hip medial ultrasound method's reliability and reproducibility, we investigated the interobserver and intraobserver agreement in evaluating the reduction using hip medial ultrasound. Using ultrasound or radiography, the reviewers classified hips as reduced, uncertain status, or dislocated. MRI was considered the gold standard for assessing hip reduction, and the reviewers classified hips as reduced or dislocated by MRI. Patients with hips with an uncertain reduction status according to ultrasound or radiography were retained in the analysis. Thus, the test results of radiography and ultrasound were classified into three classifications (positive, negative, or uncertain) in the present study. The test was considered positive or negative when patients were assessed with dislocation or without dislocation, respectively. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of ultrasound and radiography were calculated and compared. We combined uncertain and positive into the positive classification to be conservative in the statistical choices. The specificity, sensitivity, PPV, and NPV were analyzed based on this premise. Furthermore, a subgroup analysis was conducted by sex. MRI evaluation revealed that 41 hips were reduced and two hips were dislocated.
The sensitivity, specificity, PPV, and NPV of ultrasound were 100% (95% CI 16% to 100%), 95% (95% CI 84% to 99%), 50% (95% CI 7% to 93%), and 100% (95% CI 91% to 100%), respectively. The sensitivity, specificity, PPV, and NPV of radiography were 50% (95% CI 1% to 99%), 68% (95% CI 52% to 82%), 7% (95% CI 0% to 34%), and 97% (95% CI 82% to 100%), respectively. Ultrasound showed a higher specificity (95% versus 68%; p < 0.001) and PPV (50% versus 7%; p = 0.02) than radiography. The sensitivity, specificity, PPV, and NPV of ultrasound were 100% (95% CI 16% to 100%), 94% (95% CI 81% to 99%), 50% (95% CI 7% to 93%), and 100% (95% CI 90% to 100%), respectively, for female patients (with only five male patients, we could not perform these analyses in this group). The sensitivity, specificity, PPV, and NPV of radiography were 50% (95% CI 1% to 99%), 64% (95% CI 46% to 79%), 7% (95% CI 0% to 34%), and 96% (95% CI 79% to 100%), respectively, for female patients. The κ values for intra- and interobserver reliability both were 1.0.
Hip medial ultrasound can directly visualize the femoral head and acetabulum. Hip medial ultrasound is more reliable than radiography as a preliminary evaluation method and does not involve irradiation. We recommend using hip medial ultrasound during outpatient follow-up visits for patients younger than 2 years treated with hip reduction and cast immobilization.
Level III, diagnostic study.
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