• Korean Journal of Materials Research
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• v.22 no.1
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• pp.42-45
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• 2012

The mechanical behavior and microstructural evolution during high temperature tensile deformation of recrystallized Ni3Al polycrystals doped with boron were investigated as functions of initial grain size, tensile strain rate and temperature. In order to obtain more precise information on the deformation mechanism, tensile specimens were rapidly quenched immediately after deformation at a cooling rate of more than $2000Ks^{-1}$, and were then observed by transmission electron microscopy (TEM). Mechanical tests in the range of 923 K to 1012 K were carried out in a vacuum of less than $3{\times}10^{-4}$ Pa using an Instron-type machine with various but constant cross head speeds corresponding to the initial strain rates from $1.0{\times}10^{-4}$ to $3.1{\times}10^{-5}s^{-1}$. After heating to deformation temperature, the specimen was kept for more than 1.8 ks before testing. The following results were obtained: (1) Flow behavior was affected by initial strain size; with decreasing initial grain size, the level of a stress peak in the true stress-true strain curve decreased, the steady state region was enlarged and elongation increased. (2) On the basis of TEM observation of rapidly quenched specimens, it was confirmed that dynamic recrystallization certainly occurred on deformation of fine-grained ($3.3{\mu}m$) and intermediate-grained ($5.0{\mu}m$) specimens at an initial strain rate of $3.1{\times}10^{-5}s^{-1}$ and at 973 K. (3) There were some dislocation-free grains among the new recrystallized grains. The obtained results suggest that both dynamic recrystallization and grain boundary sliding are operative during high temperature deformation.

• Clinics in Shoulder and Elbow
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• v.19 no.2
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• pp.78-83
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• 2016

Background: We investigated the risk factors for the recurrence of anterior shoulder instability after arthroscopic surgery with suture anchors and the clinical outcomes after reoperation. Methods: A total of 281 patients (February 2001 to December 2012) were enrolled into our study, and postoperative subluxation and dislocation were considered as recurrence of the condition. We analyzed radiologic results and functional outcome including the American Shoulder and Elbow Surgeons Evaluation Form, the Korean Shoulder Society Score, and the Rowe scores. Results: Of the 281 patients, instability recurred in 51 patients (18.1%). Sixteen out of 51 patients (31.4%) received a reoperation. In terms of the functional outcome, we found that the intact group, comprising patients without recurrence, had a significantly better functional outcome than those in the recurrent group. The size of glenoid defect at the time of initial surgery significantly differed between intact and recurrent group (p<0.05). We found that the number of dislocations, the time from the initial presentation of symptoms to surgery, and the number of anchor points significantly differed between initial operation and revision group (p<0.05). The functional outcome after revision surgery was comparable to intact group after initial operation. Conclusions: Eighteen percent of recurrence occurred after arthroscopic instability surgery, and 5.6% received reoperation surgery. Risk factors for recurrence was the initial size of glenoid defect. In cases of revision surgery, good clinical outcomes could be achieved using additional suture anchor.

• Journal of Korean Foot and Ankle Society
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• v.11 no.1
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• pp.72-78
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• 2007

Purpose: This study is to analysis the outcome of patient with surgically treated Maisonneuve fracture and find out the factors that might influence the outcome. Material and methods: 20 patients who had surgical treatment due to Maisonneuve fracture between February, 2001 to March, 2005 were studied. The patients were followed for at least 1 year and average follow up period was 25 months. The average age was 41 years, 16 were male and 4 were female. Mechanism of injury according to Rouge-Hansen classification was supination-external rotation. In all cases, percutaneous screw fixation was applied proximal to tibiofibular syndesmosis. The screws were removed after 8 weeks under local anesthesis. Clinical, functional and radiographic results were evaluated. Results: 17 cases (85%) showed satisfying clinical and radiographic results. The mean functional score according to Ankle Scoring System was 91 (83 to 95). Complication occurred in 1 case with underlying systemic disease and 2 cases with initial ankle joint dislocation. Conclusion: Surgical treatment of Maisonneuve fracture showed relatively satisfying result. However, initial injury state and accompanying disease seem to have great effect on the result.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.64-71
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• 2011

In this paper, crack propagation analyses in the inner diameter (ID) repair weld of the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). To calculate the theoretical solution for the crack tip stress intensity factor, a weak type singular integral equation consisted of crack surface traction and dislocation density function was constructed and solved in conjunction with the FEAM. A two-dimensional axisymmetric finite element nozzle model was prepared and ID repair welding was simulated. An initial crack, 10% depth of weld thickness, was assumed and crack propagation trajectory from the initial crack to the 75% depth of thickness was calculated using the FEAM. Crack growth versus time curve was also calculated and compared with the curves obtained from ASME code method. With the method constructed in this paper, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.2
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• pp.40-47
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• 1993

Composites composed of a precipitation harden 2124 alloy matrix reinforced by SiC whiskers, which are fabricated by powder metallugy, are suscepttible to fatigue damage due to the pile-up of moving dislocation and the microcrack initiation along SiC-Al interfaces, especially at the external surfaces of a body. The initial process, such as pile-up of dislocation or microcrack, that corresponds to the stage I during fatigue failure process are too small to be detected and characterized by conventional ultrasonic technique. This paper describes the applicability of an acoustic microscope with Line-Focus-Beam(LFB) lens of 225MHz to evaluate fatigue damage of SiC whiskers reinforced Al alloy. The specimens which were 6.6mm thick, 13mm wide, and 105mm long in the gage section were fatigued in tension-tension under load control. The velocity of leaky surface and leaky pseudosurface acoustic waves are obtained by FFT analysis technique from V(z) curve which is a record of output of piezoelectric transducer. These results are discussed with the change of number of fatigue cycles. The result obtained by acoustic microscope is compared with that by ultrasonic technique generated at 5MHz with conventional surface wave transducers.

• Clinics in Shoulder and Elbow
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• v.20 no.2
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• pp.59-67
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• 2017

Background: The purpose of this study was to examine the clinical and radiological results of the all-arthroscopic, suture-button fixation technique to treat acute acromioclavicular (AC) joint separations. Methods: All patients with acute AC joint separations received all-arthroscopic, single suture-button (TightRope) procedure without a special guide. Postoperative Constant score (CS), pain level according to visual analogue scale, and range of motion (ROM) were evaluated. For radiological evaluation, coracoclavicular distances were measured bilaterally. Results: Between December 2010 and June 2012, 18 consecutive patients (4 women and 14 men; mean age, 29.3 years) with acute AC joint separations underwent surgical treatment after 6.4 days (range, 2-20 days) following the initial trauma. The average postoperative follow-up was 16.9 months. The mean CS was 92.4 (range, 84-96). The mean external rotation, forward flexion, and abduction were $75.8^{\circ}$ (range, $50^{\circ}-90^{\circ}$), $170^{\circ}$ (range, $150^{\circ}-180^{\circ}$), and $163.8^{\circ}$ (range, $140^{\circ}-180^{\circ}$), respectively. Five patients exhibited coracoclavicular ossifications. In two patients, superficial wound infections were successfully treated with antibiotic therapy. In one patient, a coracoid fracture was observed. No significant differences were found regarding pain, ROM, or strength parameters between both sides. The coracoclavicular distance was discovered to be approximately 2.8 mm greater on the affected side; however, this minimal reduction loss did not affect the functional results. Conclusions: The findings of this study suggests that all-arthroscopic treatment of AC joint separations using the single suture-button technique without a drill guide is safe, yielding good to excellent clinical results.

• Journal of the Korean Magnetics Society
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• v.15 no.1
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• pp.25-29
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• 2005

Magnetic properties of YIG films grown by solid phase epitaxy (SPE) was measured as a function of temperature with focus on magneto-crystalline and perpendicular magnetic anisotropy. Perpendicular magnetic anisotropy was not induced in the SPE YIG films annealed at low temperature by relaxing residual stress through formation of dislocation. On the contrary the films annealed at high temperature showed perpendicular magnetic anisotropy which shows very low density of dislocation. Perpendicular magnetic anisotropy field decreased linearly up to a high temperature of $230^{\circ}C$ above which magneto-crystalline anisotropy disappeared. Coercivity also decreased linearly with temperature up 세 $230^{\circ}C$. Magneto-crystalline anisotropy of perpendicular anisotropy induced epitaxial (111) YIG films can be measured using $H_k=4K_1/3M_s$. Temperature behavior of initial susceptibility can be successfully explained by Hopkinson effects. Curie temperature of YIG films grown on GGG substrate with high paramagnetic susceptibility can be easily measured using the results.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.326-331
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• 2007

Large-scale molecular dynamics simulations are performed to verify the deformation characteristics of grain boundaries in nanolithography process. The copper substrate made of 200,000 atoms is constructed by two grains in different crystal orientations using dynamic relaxation method. The grain boundary is located in the middle of the substrate with $45\sim135$ degree angles. The plowing tip is made of diamond-like-carbon atoms in a variety of shapes. In the simulations, the generation, propagation, and accumulation of dislocations are observed inside the substrate. From the numerical results, we address the dynamic behavior of the grain boundaries as well as the frictional characteristics in terms of the morphology of initial grain boundaries.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.215-218
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• 2006

A study was made to investigate microstructural evolution and mechanical properties of ultra-fine grained (UFG) pure-Ti produced by equal channel angular (ECA) pressings. The deformed structures were analyzed by finite element method and transmission electron microscopy with the increment of straining. After 4 isothermal ECA pressings, initial coarse grains ($30{\mu}m$) were significantly refined to ${\sim}0.3{\mu}m$ with homogeneous distribution of microstructure which was resulted from $180^{\circ}$ rotation of the sample between pressings. UFG pure-Ti exhibited the considerable improvement in yield strength while losing strain hardening capacity as compared to coarse grained microstructure at ambient temperature, which was mainly attributed to ultra-fine grain microstructure with non-equilibrium grain boundaries.

• Journal of The Korean Society of Inherited Metabolic disease
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• v.22 no.2
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• pp.37-45
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• 2022

Inherited metabolic disorders (IMD) are a large group of rare disorders affecting normal biochemical pathways. The ophthalmic involvement can be very varied affecting any part of the eye, including abnormalities of cornea, lens dislocation and cataracts, retina and the optic nerve, and extraocular muscles. Eye disorders can be initial symptoms of some IMD and can be clue for diagnosis of IMD. However, eye disorders can evolve later in the natural history of an already diagnosed metabolic disorder. Awareness of IMDs is important to facilitate early diagnosis and in some cases instigate early treatment if a patient presents with eye involvement suggestive of a metabolic disorder. Ophthalmological interventions are also an important component of the multisystem holistic approach to treating patients with metabolic disorders.