• Maxillofacial Plastic and Reconstructive Surgery
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• v.40
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• pp.3.1-3.8
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• 2018

Background: In this research article, we evaluate the use of sub-periosteal tunneling (tunnel technique) combined with alloplastic in situ hardening biphasic calcium phosphate (BCP, a compound of β-tricalcium phosphate and hydroxyapatite) bone graft for lateral augmentation of a deficient alveolar ridge. Methods: A total of 9 patients with deficient mandibular alveolar ridges were included in the present pilot study. Ten lateral ridge augmentation were carried out using the sub-periosteal tunneling technique, including a bilateral procedure in one patient. The increase in ridge width was assessed using CBCT evaluation of the ridge preoperatively and at 4 months postoperatively. Histological assessment of the quality of bone formation was also carried out with bone cores obtained at the implant placement re-entry in one patient. Results: The mean bucco-lingual ridge width increased in average from 4.17 ± 0.99 mm to 8.56 ± 1.93 mm after lateral bone augmentation with easy-graft CRYSTAL using the tunneling technique. The gain in ridge width was statistically highly significant (p = 0.0019). Histomorphometric assessment of two bone cores obtained at the time of implant placement from one patient revealed 27.6% new bone and an overall mineralized fraction of 72.3% in the grafted area 4 months after the bone grafting was carried out. Conclusions: Within the limits of this pilot study, it can be concluded that sub-periosteal tunneling technique using in situ hardening biphasic calcium phosphate is a valuable option for lateral ridge augmentation to allow implant placement in deficient alveolar ridges. Further prospective randomized clinical trials will be necessary to assess its performance in comparison to conventional ridge augmentation procedures.

• Applied Chemistry for Engineering
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• v.19 no.1
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• pp.105-110
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• 2008

The high-purity purification of 2,6-dimethylnaphthalene (2,6-DMN, 10.43 wt%) from the concentrate of DMN isomers recovered from light cycle oil (LCO) through distillation-extraction combination was examined by a crystallization operation. To select the most suitable crystallization solvent for purification of 2,6-DMN, several conventional solvents, which have been employed commercially as crystallization solvents for high-purity performance, were tested, through measurement of purity and yield of 2,6-DMN. The solvents used were acetone, cyclohexanone, ethanol, ethyl ether, ethyl acetate, isopropyl ether, methanol, n-hexane, n-heptane, pyridine, THF, toluene, and a mixture of methanol and acetone. The mixture of 60 vol% methanol and 40 vol% acetone (M/A = 1.5) was found to be suitable for purification of 2,6-DMN in the concentrate of DMN isomers based on purity and yield. Increasing the operation temperature and the volume ratio of solvent (M/A = 1.5) to feed (concentrate of DMN) resulted in improving the purity of 2,6-DMN, whereas the yield decreased. The crystal recovered by crystallization run using the concentrate of DMN isomers contained about 76 wt% 2,6-DMN. Furthermore, for recovery of high-purity 2,6-DMN, crystal containing 76 wt% 2,6-DMN was crystallized. As a result, crystal with 99.7 wt% 2,6-DMN was recovered with 40% yield.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.527-533
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• 1999

Hertzian indentation tests with spherical indenters in water were conducted to examine the contact fatigue in three dental ceramics, such as feldspathic porcelain, micaceous glass-ceramic (MGC) and glass-infiltrated alumina, which was used as dental restorations, and evaluated the effect of contact damage on strength. Initial damage was dependent of microstructure, showing cone cracks of brittle behavior in the feldspathic porcelain and deformation of quasi-plastic behavior in the MGC, with an intermediate case in the glass-infiltrated alumina. However, as increasing the number of cyclic loading (n=1~n =$10^6$)all materials showed an abrupt strength degradation, at which fracture was originated from damage in the contact fatigue. There were two strength degradation with increasing the number of cyclic loading in specific loads (200N, 500N, 1000N):first was from the cone cracks, and second was from the radial cracks created by cyclic loading. The radial cracks, once formed, led to rapid degradation in strength properties, Finally the material was failed at the high number of cyclic loading. Strength degradation with indentation load at fixed number of cyclic loading indicated that the feldspathic porcelain should be highly damage tolerant to the contact fatigue.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.216-225
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• 2023

This paper describes the finite element analysis and die design change of cold heading punching process to increase the cold forging tool life and reduce the tool wear and stress concentration. Through this study, the optimization of punch tool design has been studied by an analysis of tool stress and wear distribution to improve the tool life. Plastic deformation analysis was carried out in order to understand the cold heading process between tool and workpiece stress distribution. Cold heading punch die design was set up to each process with different four types analysis progressing, the cold heading punch dies shapes with combination of point angle and punch edge corner radius shapes of cold forging dies, punch die material properties and frictional coefficient. The design parameters of point angle and corner radius of punch die geometry, die material properties and frictional coefficient were selected to apply optimization with the DoE (design of experiment) and Taguchi method. DoE and Taguchi method was performed to optimize the cold heading punch die design parameters optimization for bolt head cold forging process, it was possible to expect an reduce the cold heading punch die wear to the 37 % compared with current using cold heading punch in the shop floor.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.298-301
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• 2007

Magnesium alloy sheets have unique mechanical properties such as high in-plane anisotropy/asymmetry of yield stress and hardening response. The unusual mechanical behavior of magnesium alloys has been understood by the limited symmetry crystal structure of HCP metals or by deformation twinning. In the present study, the continuum plasticity models considering the unusual plastic behavior of magnesium alloy sheet were derived for a finite element analysis. A new hardening law based on two-surface model was developed to consider the general stress-strain response of metal sheets such as Bauschinger effect, transient behavior and the unusual asymmetry. Three deformation modes observed during the continuous tension/compression tests were mathematically formulated with simplified relations between the state of deformation and their histories. In terms of the anisotropy and asymmetry of the initial yield stress, the Drucker-Prager's pressure dependent yield surface was modified to include the anisotropy of magnesium alloys.

• Journal of the Korean Society for Heat Treatment
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• v.15 no.1
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• pp.9-15
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• 2002

Deformation behavior of nickel-rich Ti-51.5at.%Ni single crystals was investigated over a wide range of temperatures(77 to 440K) and strain levels(up to 9%) in compression. These alloys combined superior strength with wide range of pseudoelasticity temperature interval(~200K). The slip deformation in [001] orientation did not occur due to the prevailing slip system, and consequently, exhibited pseudoelastic deformation at temperatures ranging from 77 to 283K and 273 to 440K for the solutionized and over-aged cases, respectively. The critical transformation stress levels were in the range of 800 to 1800MPa for the solutionized case, and 200 to 1000MPa for the over-aged case depending on the temperature and specimen orientation. These stress levels are considerably higher compared to these class of alloys having lower Ni contents. The maximum transformation strains, measured from incremental straining experiments in compression, were lower compared to the phenomenological theory with Type II twinning. A compound twinning model depending on the successive austenite(B2) to intermediate phase(R) to martensite(B19') transformation predicts lower transformation strains compared to the Type II twinning case.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.35-40
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• 2006

Ultrasonic cold forging technology (UCFT) utilizing ultrasonic vibration energy is a method to induce severe plastic deformation to a material surface, therefore the structure of the material surface becomes a nano-crystal structure from the surface to a certain depth. It improves the mechanical properties; hardness, compressive residual stress, wear and fatigue characteristics. Applying UCFT to a rolling process in the steel industry is introduced in this study. First, the UCFT specimens of a tool steel (SKD-61/equivalent H13) are prepared and tested to verify the effects of the UCFT in a variety of mechanical properties, the UCFT is applied to the trimming knives in a cold rolling process. It has been determined that UCFT improves the mechanical properties effectively and becomes a practical method to improve productivity and reliability by about two times compared with the conventionally treated tooling in the trimming process in a cold rolling line.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.381-383
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• 2005

This paper is concerned with the prediction of micro structural changes of Al alloys during cryogenic rolling using an Eulerian finite element analysis. The main objective of cryogenic rolling is to obtain ultra-fine grains by severe plastic deformation at the extremely low temperature. Thereby, this simulation focuses on micro structural developments - the texture development and the changes in the size and shape of grains. The former one may be modeled using a crystal plasticity theory while the other can be predicted by a streamline technique. Applications to three pass rolling are given.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.42-51
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• 1985

The dynamic fracture toughness, fracture characteristics, impact tension and tensile properties of Al-Mg-Si T5 alloy and Al-Zn-Mg T6 alloy respectively welded with filler metal of Alcan 4043 were investigated. The dynamic fracture toughness values were obtained rapidly and simply for the specimen of small size by using instrumented Chirpy impact testing machine. the testing temperatures of the specimen were a range of room temperature and-196.deg. C. The results obtained in this experiment are summarized as follows. With decreasing the testing temperatures, dynamic tensile stress and fracture load were increased, on the other hand the deflection and impact value showed decreasing tendency in order of base metal>HAZ>weld. Changes of total absorbed energy were more influenced by the crack propagation energy than the crack initiation energy. At the low temperatures, the unstable rapid fracture representing the crack propagation appeared for the specimens of Charpy press side notched in Al-Zn-Mg alloy, but it was difficult to obtain the unstable rapid fracture in Al-Mg-Si alloy. Because of the development of plastic zone at the notch root, it was difficult to obtain thevalid $K_{1d}$ value in Al-Mg-Si alloy. Therefore the fatigue cracked specimens were effective in both Al-Mg-Si and Al-Zn-Mg alloys. With decreasing the impact testing temperatures, specimens underwent a transition from dimple-type transgranular fracture to lamella surface-type intergranular fracture because of the precipitate at the grain boundaries, impurities and crystal structure of the precipitates.s.

• Design & Manufacturing
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• v.10 no.1
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• pp.12-18
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• 2016

Although magnesium alloy has received much attention to date for its lightweight and high specific strength, their applications are impeded by the low formability which is caused by the hexagonal crystal structure at room temperature. In general, equal-channel angular extrusion(ECAE) is recognized as one of the attractive severe plastic deformation techniques where the processed bulk metals generally achieve ultrafine-grained microstructure leading to improved physical characteristics and mechanical properties. ECAE process has several parameters such as angle of die, process temperature, process route and speed. During ECAE process of Mg alloy, these parameters has great influence on the extrudability and the mechanical properties of alloy. The aim of this study is to estimate the influences of process conditions on the formability of AZ31 and AZ31-CaO alloys. Mg alloys are processed through ECAE at elevated temperatures using three types of die with channel angle of $90^{\circ}$, $110^{\circ}$, $135^{\circ}$ using route $B_c$, respectively. This study discusses the feasibility of using ECAE to improve both formability and strength on magnesium alloys by comparative analyzing the mechanical properties and microstructural evolution in each condition.