• Korean Journal of Materials Research
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• v.25 no.11
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• pp.630-635
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• 2015

The fatigue strength of a nickel-base superalloy was studied. Stress-controlled fatigue tests were carried out at $700^{\circ}C$ and 5 Hz using triangular wave forms. In this study, two kinds of testing procedures were adopted. One is the conventional tension-zero fatigue test(R = 0). The other was a procedure in which the maximum stress was held at 1000 MPa and the minimum stress was diverse from zero to 1000 MPa at 24 and $700^{\circ}C$. The results of the fatigue tests at $700^{\circ}C$ indicate that the fracture mechanism changed according to both the mean stress and the stress range. At a higher stress range, ${\gamma}^{\prime}$ precipitates are sheared by a/2<110> dislocation pairs coupled by APB. Therefore, in a large stress range, the deformation occurred by shearing of ${\gamma}^{\prime}$ by a/2<110> dislocations, which brought about crystallographic shear fracture. As the stress range was decreased, the fracture mode gradually changed from crystallographic shear fracture to gradual growth of fatigue cracks. At an intermediate stress range, as it became more difficult for a/2<110> dislocation pairs to shear ${\gamma}^{\prime}$ particles, cracks started to propagate in the matrix, avoiding the harder ${\gamma}^{\prime}$ particles. High mean stress induced creep deformation, that is, ${\gamma}^{\prime}$ particles were sheared by {111}<112> slip systems, which led to the formation of stacking faults in the precipitates. Thus, the change in fracture mechanism brought about the inversion of the S-N curves.

• Archives of Plastic Surgery
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• v.40 no.4
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• pp.397-402
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• 2013

Background Fracture-dislocation of the proximal interphalangeal (PIP) joint is a relatively common injury. Various treatments for fracture-dislocation of the PIP joint have been reported. In the present study, we performed open reduction through a midlateral incision using absorbable sutures to reduce the small bone fragments and performed volar plate repair. Methods We treated nine patients with fracture-dislocation of the PIP joint with small fractured bone fragments too small for pinning or screw fixation. Patients with volar plate injury were treated with open reduction and volar plate repair at the periosteum of the middle phalangeal bone base by the modified Kessler method using absorbable sutures. All patients were placed in a dorsal aluminum extension block splint, which maintained the PIP joint in approximately 30 degrees of flexion to avoid excessive tension on the sutured volar plate. Results At a mean final follow-up of postoperative 9 months, all patients were evaluated radiographically and had adequate alignment of the PIP joint and reduction of the displaced bone fragments. Range of motion was improved and there were no complications. Conclusions This technique is an excellent alternative to the current method of treating patients with fracture-dislocations that include small fragments that are too small for pinning or screw fixation. It is a less invasive surgical method and enables stable reduction and early exercise without noticeable complications.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• Journal of Trauma and Injury
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• v.19 no.2
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• pp.164-172
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• 2006

Background: The authors conducted a retrospective study to evaluate the mechanism of injury, the surgical techniques, the clinical features, the combined injuries, the treatment results, and the surgical complications in patients with atlantoaxial fracture/subluxations. Methods: The authors reviewed 71 cervical fracture/dislocations during a four-year period from September 2002 to August 2006. Among them, there were twenty one C1,2 fracture/subluxations. There were thirteen men (mean age : 43.5 years) and eight women (mean age : 50 years). Their follow-up period was at least 6 months, and the mean follow-up period was 9.6 months. Gardner-Wells tongs traction was used in all patients immediately on presentation. Surgical treatment was performed, depending on the pathologic conditions. Results: Of all 21 cases, 14 cases were injured in motor vehicle accidents, 5 were falls, and 2 were miscellaneous. There were four C1 fracture (5.6%), fourteen C2 fracture (66.7%), one C1 and 2 combined fracture (4.8%), and one C1-2 subluxation (4.8%). The C1 fractures in our series were classified as two Jefferson's fractures and two C1 lateral mass fracture. The C2 fractures were classified as one odontoid type I fracture, two odontoid type II fractures, five odontoid type III fractures, one hangman's fracture, and four C2 body tear-drop fractures. Atlantoaxial fractures were associated with six (28.6%) head injuries, four (19.0%) other spinal injuries, two (9.5%) chest injuries, and three (14.3%) spinal cord injuries. Surgical treatment was performed in nine cases, which included anterior odontoid screw fixation in two cases, transarticular screw fixation with iliac bone graft in one case, posterior fixation by using C2 pedicle screw and C3 lateral mass screw in three cases, lateral mass screw fixation C1-2 with iliac bone graft in one case, O(occipito)-C1-3-4 screw fixation in one case, posterior C2-3 wiring with allograft in one case, and halo vest in six cases. Conservative management was used in the rest of the patients in our trials. Bone fusion was complete in all cases. There were no operation-related complication, except one pin site infection in the case of halo vest. Conclusion: In this study, the choice of appropriate treatment according to the fracture types resulted in safe and effective management of unique atlantoaxial fracture/subluxations.

• Clinics in Shoulder and Elbow
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• v.9 no.1
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• pp.50-59
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• 2006

Purpose: The nonoperative outcome of elbow dislocations with associated radial head and coronoid fractures are often unsatisfactory because of chronic instability and stiffness from proloned immobilization, Therefore we managed these injuries with well programed surgical appproaches. Method: Ten patients with this injury were evaluated retrospectively from May 1998 to June 2004 after a minimum of 12 months. These injuries include elbow dislocation and associated fractures of both the radial head and the coronoid process. All ten patients were treated by one clinic operatively with similar scheduled surgical methods which started on the lateral side and terminated on the medial side of the elbow. Radial head and neck fractures were classified Mason types, as two and three types respectively with six and four cases and six cases were fixated. Coronoid process were fixated with screws anteroposterior directly or anchor suture in all cases, each type was classified one, two and three. where were three type one, four type two, and three type three were according to Regan and Morrey classification. Results: The outcome was three resulting in excellent, four good, two normaland and the remaining case was one poor according to the Mayo Elbow Performance score. At a terminal follow up, the range of motion of the elbow averaged flection contracture, $6^{\circ}(0{\sim}20^{\circ})$ and further flection, $129^{\circ}(115{\sim}140^{\circ})$. Two patients had complications requiring additional care. One, displaced coronoid process which was repaired with capsule and the other patient experienced, palsy of ulnar nerve and contracted elbow joint. Conclusions: Usage of early operation as the minimum injury of medial ligaments complex and the rigid fixation of fractures to prompt motion with our scheduled management for elbow dislocations with associated radial head and coracoid fractures provided excellent results.

• Journal of Korean Foot and Ankle Society
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• v.13 no.2
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• pp.156-161
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• 2009

Purpose: The fracture of talus has critical complications and results in various clinical outcomes. The purpose of this study is to evaluate clinical outcome and influence on involvement of ankle and subtalar joint. Materials and Methods: From December 1999 to December 2008, a total of 66 fractures and dislocations of talus was treated with minimal 9 months follow up period. Ankle-hindfoot scale of the American Orthopedic Foot & Ankle Society (AOFAS) was used to evaluate the clinical outcome. The complications and sequential radiologic findings were also analyzed. Results: There were 28 neck fractures, 11 lateral process fractures, 10 body fractures, 7 osteochondral fractures, 4 posteromedial tubercle fractures and 4 medial process fractures. In 38 cases, there were concomitant injuries. Ipsilateral ankle fracture, which found in 19 cases, was most common. The surgical treatment was performed in 36 cases. Mean AOFAS score was 85.5 (range, 72 to 96). In 13 of 47 cases, one or more fracture lines involving weight bearing surface were confirmed. The involvement of ankle or subtalar joint had resulted in unsatisfied outcome. Complications were developed as follows, post-traumatic arthritis in 8 cases, avascular necrosis in 3 cases, and deep infection in 2 cases. Conclusion: The involvement of ankle or subtalar joint in fractures of talus seemed to be common and to impact the clinical outcome. Meticulous consideration about that will be positively necessary.

• Journal of Trauma and Injury
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• v.21 no.2
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• pp.91-99
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• 2008

Purpose: Multiple rib fracture (MRF) and a hemopneumothorax accompany with most blunt chest traumas. We aimed to analyze the factors increasing the probability of a hemopneumothorax. In addition, other injuries accompanying MRF were analyzed. Methods: We retrospectively reviewed the medical records of 154 mutiple rib fracture patients who visited our hospital between January 2005 and December 2007. The medical records were reviewed for sex, age, mechanism of injury, location, number of fractures, distance of dislocated rib fragments, and presence of complications. We measured the distance of bony dislocations by using the PACS (Picture Archiving and Communication System). Results: The average number of rib fractures was $3.7{\pm}2.1$, and the number of rib fractures significantly influenced the incidence of a hemothorax (p<0.001). The risk of a hemothorax was increased in a bilateral MRF compared to a unilateral MRF (p=0.027). The distance of dislocated rib fragments influenced the probability of a hemothorax significantly (p=0.018), and subcutaneous emphysema and lung contusion were significantly associated with a pneumothorax (p=0.021, p=0.036). Conclusion: The number of MRFs did not influence the risk for a pneumothorax, but did influence the risk for a hemothorax. The laterality, distance of dislocation, also had an influence on the risk for a hemothorax. Also, subcutaneous emphysema and lung contusion were increased in cases with a pneumothorax. We must consider the possibility of a hemothorax even when the initial chest X-ray shows no evidence of a hemothorax. If a lung contusion is present, then an occult pneumothorax must be considered.

• Clinics in Shoulder and Elbow
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• v.1 no.2
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• pp.205-211
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• 1998

The comminuted fracture and dislocation of the proximal humerus occur more frequently in older patient group and operative treatment is difficult due to poor bone quality. Based on Neer's work, hemiarthroplasty has now become widly accepted for the management of the three-part fracture and four-part fracture-dislocation of the proximal humerus in old age group. The purpose of this study is to evaluate function, pain relief, and patient satisfaction after hemiarthroplasty for proximal humerus fractures and dislocations. Authors reviewed and analyzed 14 prosthetic replacement in comminuted proximal humeral fracture and dislocation at the Department of Orthopaedic Surgery, Yonsei University Wonju College of Medicine from March, 1988 to May, 1997. The results were as follows the average age was 58.9years and the ratio of males and females was 5:9. The most common cause of injury was traffic accident(43%). According to the classification of Neer, three part fracture were three(21%), four-part fracture and four-part fracture-dislocation were eleven(79%). The prosthetic replacement was performed within two weeks in eight patient and six were performed after two weeks. The results were analysed according to Neer's criteria and five cases showed satisfactory results. We concluded that hemiarthroplasty for fracture and dislocation of the proximal humerus facilitated the restoration of humerus length and pain relief, thereby allowing earlier motion to prevent the development of painful shoulder: stiffness.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.256-261
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• 2007

The purpose of this study is to investigate the effect of shot peening on the fatigue strength and fatigue life of two kinds of aluminum alloys. The fatigue strength behavior of aluminum alloys were estimated by the stress ratio and shot velocities. The fatigue life and strength increased with increasing the test shot velocity. However, at the shot velocity range between 50m/s and 70m/s, the compressive residual stress phenomena were observed in test conditions of different shot velocity. The optimal shot velocity is acquired by considering the peak values of the compressive residual stress, dislocations, brittle striation, slip, and fisheye on the fracture surface of test specimen. It was observed from the SEM observation on the deformed specimen that the brittle striation, fisheye were showed in the intergranular fracture structure boundaries at the this velocities. Therefore, fatigue strength and fatigue life would be considered that shot velocity has close relationship with the compressive residual stress.

• Transactions of Materials Processing
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• v.32 no.5
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• pp.287-293
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• 2023

This study aims to develop a computational framework based on the finite element method for modeling the hydrogen embrittlement in martensitic steel. The hydrogen embrittlement is a well-known phenomenon, in which the hydrogen penetrates into the surface, flows through the microstructure and finally leads to pre-mature fracture under external or internal stresses. The current numerical model takes into account the effect of hydrogen on the plasticity and failure behavior of martensitic steel under various stress states. This allows for the construction of a failure criterion that accounts for conventional stress states and hydrogen concentration. The developed model is capable of simulating hydrogen diffusion through the lattice based on the distribution of hydrostatic stress. Additionally, it can calculate the hydrogen concentration in trapped sites, such as dislocations, using a local equilibrium assumption, often referred to as Oriani's equilibrium. The developed model parameters are identified through the tensile tests with and without hydrogen environment, and the performance of model can be validated by analyzing fractured automotive part in the hydrogen environment.