• The Journal of the Korean dental association
• /
• v.53 no.11
• /
• pp.804-816
• /
• 2015

PURPOSE: The aim of this study was to evaluate the influence of the oxide layer removal process in the Co-Cr-Mo (CCM) abutment after casting procedure on the prosthesis settlement and screw stability. MATERIALS AND METHODS: CCM abutments of four different interface conditions (CCM-M; machined, CCM-O; oxide layer formed, CCM-B; blasted, CCM-P; polished after blasted) and gold abutment (Gold-C; Cast with type III Gold alloy) were used. The initial settling values of abutments were evaluated according to the difference of implant-abutment length when the tightening torques were applied at 5 Ncm and 30 Ncm, and the settling values of abutments caused by loading were evaluated according to the difference of implant-abutment length before and after loading with 250 N, 100000 cycle. The loss ratios of removal torque for abutment screws were evaluated according to the difference in value of removal torques under 30 Ncm tightening torque applied before and after cyclic loading. RESULTS: The CCM-P and CCM-B group showed a higher initial settling value compared with the Gold-C group (P<.05), while the Gold-C group showed the highest settling values caused by loading (P<.05) and no significant differences were observed for between CCM groups (P>.05). The loss ratio of removal torque values for the CCM-B, CCM-P groups did not differ significantly from that of the Gold-C group (P>.05). CONCLUSION: Even though the oxide layer was removed by different methods, CCM abutment with internal conical connection structure showed lower abutment settling and similar screw loosening after cyclic loading compared with gold abutment.

• The Journal of Korean Academy of Prosthodontics
• /
• v.42 no.4
• /
• pp.412-424
• /
• 2004

Statement of problem: Several prosthetic options are available for the restoration of multiple adjacent implants. A passively fitting prosthesis has been considered a prerequisite for the success and maintenance of osseointegration. Passivity is a particular concern with multiple implants because of documented inaccuracies in the casting and soldering process. One way to avoid this problem is to restore the implants individually, however, the restorations of individual adjacent impants requires careful adjustment of interproximal contacts. Purpose: The purpose of this study was to compare the stress distribution pattern and amount surrounding Bicon implants with individual crowns and splinted restorations. Material and method: A photoelastic model of a human partially edentulous left mandible with 3 Bicon implants($4{\times}11mm$) was fabricated. For non-splinted restorations, individual crowns were fabricated on 3 abutments ($4{\times}0.65mm,\;0^{\circ}$, 2.0 mm post, Bicon Inc., Boston, USA) After the units were cemented, 4 levels of interproximal contact tightness were evaluated: open, ideal ($8{\mu}m$ shim stock drags without tearing), medium($40{\mu}m)$), and heavy($80{\mu}m$). Splinted 3-unit fixed partial dentures were fabricated and cemented to the model. Changes in stress distribution under simulated non-loaded and loaded conditions(7.5, 15, 30 lb) were analyzed with a circular polaricope. Results: 1. Stresses were distributed around the entire body of fin in Bicon implants. 2. Splinted restorations were useful for distribution of stress around implants especially with higher loads. 3. By increasing the contact tightness between the individually restored three implants, the stress increased in the coronal portion of implants. Conclusions: Ideal adjustment of the contact tightness was important to reduce the stresses around individually restored Bicon implants.

• Journal of Korea Foundry Society
• /
• v.39 no.6
• /
• pp.103-109
• /
• 2019

Cu-added SKD11 was manufactured through the casting process and the effects of Cu addition with different contents (0, 1, 2 and 3 wt%) and aging treatment on microstructure, mechanical characteristics such as tensile strength and hardness, and thermal conductivity were investigated. The microstructure was analyzed by FE-SEM and XRD, the mechanical characteristics by Rockwell hardness tester and Tensile tester, and the thermal conductivity by Laser flash. As a result, SKD11 containing Cu had higher hardness than as-received SKD11. The hardness of as-cast SKD11 containing 1 wt% Cu was 42.4 HRC, whereas the hardness of asreceived SKD11 cast alloy was 19.5 HRC, indicating that the hardness was greatly improved when Cu was added. In the case of tensile strength, Cu-added SKD11 cast alloy had lower tensile strength than as-received SKD11, and the tensile strength tended to increase as Cu content increased. After heat treatment, however, tensile strength of as-received SKD11 was significantly increased, whereas in the case of Cu-added SKD11, as the Cu contents increased, the tensile strength increased less and even reduced at 3 wt% Cu. The thermal conductivity of Cu-added SKD11 cast alloy was about 13 W m^-1 K^-1, which was lower than that of the asreceived SKD11 cast alloy (28 W m^-1 K^-1). After the heat treatment, however, the thermal conductivity of as-received SKD11 was reduced, while the thermal conductivity of the SKD11 added with Cu was increased. Thermal conductivity was generally larger with less Cu content, and this tendency became more pronounced after heat treatment.

• Applied Microscopy
• /
• v.25 no.3
• /
• pp.99-107
• /
• 1995

The morphological changes of primary solid particles as a function of process time on hypereutectic Al-15.5wt%Si alloy during semi-solid state processing with a shear rate of $200s^{-1}$ are studied. In this alloy, it was observed that primary Si crystals are fragmented at the early stage of stirring and morphologies of primary Si crystals change from faceted to spherical during isothermal shearing for 60 minutes. To understand the role of Al dissolved in the primary Si crystal by shear stress at high temperature, lattice parameters of the primary Si crystals are determined as a variation of high order Laue zone(HOLZ) line positions measured from convergent beam electron diffraction(CBED) pattern. The lattice parameter of the primary Si crystal in the rheocast Al-15.5wt%Si alloy shows tensile strain of about 5 times greater than that of the gravity casting. Increase of the lattice parameter by rheocasting is due to the increased amount of Al dissolved in the primary Si crystal accelerated by shear stress at high temperature. The amounts of solute Al in the primary Si crystal are measured quantitatively by EPMA method to confirm the CBED analysis.

• The Journal of Advanced Prosthodontics
• /
• v.6 no.4
• /
• pp.266-271
• /
• 2014

PURPOSE. The purpose of this study was to compare the fracture strength of the metal and the bond strength in metal-ceramic restorations produced by selective laser sintering (SLS) and by conventional casting (CAST). MATERIALS AND METHODS. Non-precious alloy (StarLoy C, DeguDent, Hanau, Germany) was used in CAST group and metal powder (SP2, EOS GmbH, Munich, Germany) in SLS group. Metal specimens in the form of sheets ($25.0{\times}3.0{\times}0.5mm$) were produced in accordance with ISO 9693:1999 standards (n=30). To measure the bond strength, ceramic was fired on a metal specimen and then three-point bending test was performed. In addition, the metal fracture strength was measured by continuing the application of the load. The values were statistically analyzed by performing independent t-tests (${\alpha}=.05$). RESULTS. The mean bond strength of the SLS group (50.60 MPa) was higher than that of the CAST group (46.29 MPa), but there was no statistically significant difference. The metal fracture strength of the SLS group (1087.2 MPa) was lower than that of the CAST group (2399.1 MPa), and this difference was statistically significant. CONCLUSION. In conclusion the balling phenomenon and the gap formation of the SLS process may increase the metal-ceramic bond strength.

• Korean Journal of Materials Research
• /
• v.13 no.12
• /
• pp.812-818
• /
• 2003

The aim of this study is to investigate the fabrication processes on the microstructual changes and mechanical properties of large 7175 aluminum die forgings. The billets range from 370 to 720 mm in diameter were homogenized and hot forged after direct chill casting. The strength and elongation of the homogenized cast billets were revealed nearly same level independent of the billet diameter. However, these properties of ø370 mm cast billet were superior to those of $\Pie720$ mm billet under$ T_{6}$ / condition. The tensile strength of die forged specimens under $T_{6}$ condition increased up to 20% than that of solution treatment, however, the elongation was reduced to 50%. The fracture toughness of die forged specimens under $T_{6}$ condition was 35.6∼39.0 MPa$.$$m^{1}$2 irrespective of the billet size and free forging processes, but this property increased up to 10% by$V_{74}$ treatment. The fracture toughness of die forged specimen manufactured with ø370 mm cast billet showed nearly same level of ø720 mm billet which was processed using MF or Cog free forging followed by die forging.

• Journal of the Korea Institute of Building Construction
• /
• v.16 no.5
• /
• pp.389-395
• /
• 2016

The evolution of electro-mechanical impedance (EMI) of the piezoelectricity (PZT) sensor was investigated to determine the setting times of cementitious materials in this study. The PZT sensor coated with non-conductive acrylic resin was embedded in cement paste before casting and the EMI signatures were continuously measured. Vicat needle test and semi-adiabatic calorimetry test were also conducted to justify the validity of EMI senssing technique in setting monitoring of cementitious materials. The results show that significant changes in EMI resonant peak magnitude and frequency during setting process were observed, and that the setting times determined by EMI sensing technique were relevant to the setting times measured by Vicat needle test and semi-adiabatic calorimetry test.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.11 no.1
• /
• pp.69-73
• /
• 2015

The study investigated effects of residual stresses and Charpy impact energy on brittle fractures of the butt weld between the valve and the piping, and of the valve body in nuclear power plants via a linear elastic fracture mechanics approach in the ASME B&PV Code, Sec.XI and finite element analysis. Weld residual stress in a butt weld between close check valve and piping, and residual stress in the valve due to casting process were assumed to be proportional to yield strength of base metal. Operating stresses in the butt weld and the valve body were calculated using approximate engineering formulae and finite element analysis, respectively. Applied stress intensity factors were calculated by assuming postulated cracks with specific sizes and then by substituting the residual stresses and the operating stresses into engineering formulae presented in the ASME B&PV Code, Sec.III. Plane strain fracture toughness was derived by using a correlation between Charpy V-notch impact energy and fracture toughness. Structural integrity of the weld and the body against brittle fracture was assessed by using the applied stress intensity factors, plane strain fracture toughness and the linear elastic fracture mechanics approach. As a result, it was identified that the structural integrity was maintained with decreasing the residual stress levels and increasing the Charpy V-notch impact energy.

• Korean Journal of Veterinary Research
• /
• v.7 no.1
• /
• pp.8-18
• /
• 1967

Casting specimens of portal system and hepatic vein system in livers were made by injection of vinylite into the portal vein and postcava in 20 adult dogs. The author classificated the ramification of portal system and hepatic vein system. The results obtained were summerized as follows: 1. Portal system in livers were divided into left and right trunks. The left trunk subdivided into papillary process (caudate lobe,) left medial lobe, left lateral lobe, quadrate lobe and right medial lobe rami. The right trunk were subdivided into right lateral lobe and caudate proccss(caudate lobe.) 2. The lateral superior and medial inferior rami of portal system in left lateral lobe were subdivided 1 or 2 branches from left trunk. 3. The lateral superior ramus of portal system in left medial lobe did not appeared in 40% of the cases examined. 4. Portal system in quadrate lobe were subdivided 1-3 branches from left trunk, 5. Portol system in right medial lobe rami were relatively simple in ramification. 6. The lateral superior and medial inferior rami of portal system in right lateral lobe were subdivided 1 or 2 branches from right trunk. 7. Hepatic vein system of left lateral, left medial, quadrate and right medial lobe rami were originated from same ramus divided from the postcava in all cases. 8. Hepatic vein system of left and right rami in right medial lobe were divided from postcava.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.7
• /
• pp.653-658
• /
• 2016

High pressure components of a gas turbine engine are generally made of nickel-base superalloys, using precision casting process due to complicated geometries with intricate channels and cooling holes. Turbine components manufactured from directionally solidified and single crystal materials have columnar grains; however, it is found that the crystals do not grow in its preferred direction, although the orientation can be controlled. This anisotropy can lead to the variations of elastic and Hill's parameters in constitutive equations, and they alter stress distributions and the low cycle fatigue life. We aims to evaluate the effects of perturbed crystal orientations on the structural integrity of a directionally solidified nozzle using low cycle fatigue life. We also attempt to show the necessity for the control of allowed manufacturing errors and stochastic analysis. Our approaches included conjugate heat transfer and structural analysis, along with low cycle fatigue life assessment.