• The Journal of Advanced Prosthodontics
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• v.8 no.6
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• pp.433-438
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• 2016

PURPOSE. The aim of this in vitro study was to evaluate the mechanical properties (bending strength and hardness) of seven different fiber reinforced composite posts, in relation to their microstructural characteristics. MATERIALS AND METHODS. Two hundred eighty posts were divided into seven groups of 40, one group for each type of post analyzed. Within each group, 15 posts were subjected to three-point bending strength test, 15 to a microhardess meter for the Knoop hardness, and 10 to Scanning Electron Microscope in order to determine the diameter of the fibers and the percentage of fibers embedded in the matrix. To compare the flexural strength in relation to the type of fiber, matrix, and the hardness of the posts, a Kruskal-Wallis H test was used. The Jonckheere-Terpstra test was used to determine if the volume percent of fibers in the post influenced the bending strength. RESULTS. The flexural strength and the hardness depended on the type of fibers that formed the post. The lower flexural strength of a post could be due to deficient bonding between the fiber and the resin matrix. CONCLUSION. According to the results, other factors, besides the microstructural characteristics, may also influence the mechanical properties of the post. The feature that has more influence on the mechanical properties of the posts is the type of fiber.

• Korean Journal of Materials Research
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• v.11 no.4
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• pp.278-282
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• 2001

The recombination motion of Partial dislocations on basal slip (0001) 1/3<1120> in sapphire ($\alpha$-Al$_2$$O_3$) single crystals was investigated using the four-point bending test with the prism plane (1120) samples. These bending experiments were carried but in the temperature range from $1200^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. During these tests it was shown that an incubation time was needed for basal slip to be activated. The activation energy for the incubation time was 5.6-6.0eV in the temperature range from $1200^{\circ}C$ to $1400^{\circ}C$. The incubation time is believed to be related to recombination of climb dissociated partial dislocations via self-climb. In addition, these activation energies are nearly same as those for oxygen self-diffusion in $Al_2$$O_3$ (approximately 6.3 eV). Thus, the recombination of the two partial dislocations would be possibly controlled by oxygen diffusion on the stacking fault between the partials.

• Structural Engineering and Mechanics
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• v.56 no.3
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• pp.369-383
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• 2015

In this study, effect of various material hardening models based on Holloman's isotropic, Ziegler's linear kinematic, non-linear kinematic and mixture of the isotropic and nonlinear kinematic hardening laws on springback prediction of titanium alloy (Ti-3Al-2.5V) in a tube rotary draw bending (RDB) process was investigated with presenting the keynotes for a comprehensive step by step ABAQUS simulation. Influence of mandrel on quality of the final product including springback, wall-thinning and cross-section deformation of the tube was investigated, too. Material parameters of the hardening models were obtained based on information of a uniaxial test. In particular, in the case of combined iso-nonlinear kinematic hardening the material constants were calibrated by a simple approach based on half-cycle data instead of several stabilized cycles ones. Moreover, effect of some material and geometrical parameters on springback was carried out. The results showed that using the various hardening laws separately cannot describe the material hardening behavior correctly. Therefore, it is concluded that combining the hardening laws is a good idea to have accurate springback prediction. Totally the results are useful for predicting and controlling springback and cross-section deformation in metal forming processes.

• Journal of Mechanical Science and Technology
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• v.14 no.9
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• pp.978-984
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• 2000

The aim of this study is to investigate the ductile fracture behaviour under Mode I loading using SA533B pressure vessel steel. Experiments consist of the Round Notch Bar Test (RNB), Single Edge Crack Bending Test (SECB), and V-Notch Bar Test (VNB). Results from the RNB test were used to tune the damage modelling constant. The other tests were performed to acquire the J-resistance curves and to confirm the damage constants. Microstructural observation includes the measurement of crack profile to obtain the roughness parameter. Finally, simulation using Rousellier Ductile Damage Theory (RDDT) was carried out with 4-node quadrilateral element ($L_c=0.25\;mm$). For the crack advance, the failed element removal technique was adopted with a ${\beta}$ criterion. In conclusion, the predicted simulation using RDDT showed a good agreement with the experimental results. A trial using a roughness parameter was made for a new evaluation of J-resistance curve, which is more conservative than the conventional one.

• International Journal of Safety
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• v.1 no.1
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• pp.24-27
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• 2002

Recently the steel parts used in automobiles are required to be used under high stress more than ever before due to the need of keeping the weight down. To achieve this requirement of the high strength steel, it must be necessary to decrease inclusion contents and surface defects as like decarburization, surface roughness etc. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of two-stage shot peening and single-stage shot peening. And for this study, three kinds of spring steel (JISG408l-SUP7, SAE 9254 and DIN 50CrV4) are shaped. This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotating bending fatigue test and it results from (1) decreasing the surface roughness (2) unchanging the surface hardness (3) increasing the compressive residual stress. Moreover, results also show fatigue failures originated at the inclusion near the surface, and this inclusion type is turned out to be an alumina of high hardness.

• Journal of Welding and Joining
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• v.3 no.1
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• pp.11-21
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• 1985

The line heating is a thermoplastic working technique which is used in bending work of steel plate and in correcting the distortion of welded structure. This method is considerably effective when the water-cooling is followed. In this study, an investigation was accomplished to find the effects on the change of material properties when the line heating was applied on the high tensile steel plate of 50kg/mm^2$ grade. Some steel plates were heated to various temperatures and then cooled with water or in the air. In this study, the author measured the angular distortion continuously during line heating to find out the relation between the bending efficiency and heating or water-cooling temperature. Furthermore, its material properties were examined by the V-notch Charpy impact test, the microscope observation and the Vickers hardness test. As results, the followings were clarified. (1) The amount of angular distortion increases as the heating temperature or the water-cooling temperature rises. (2) When the steel plate is heated between 700.deg. C and 900.deg. C, and then is water-cooled over 700.deg. C, some brittle structure is observed. But if the temperature of water-cooling is below 700.deg. C, no brittle one is found. (3) When the steel plate is heated over 800.deg. C and is cooled in the air, there is no unfavrable effect.

• Korean Journal of Materials Research
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• v.11 no.3
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• pp.221-226
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• 2001

The basal slip (0001)1/3<1120 > dislocation velocity in sapphire ($\alpha$-$Al_2$$O_3$) single crystals was measured by four-point bending test. The bending experiment was carried out in the temperature range from 120$0^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. The velocity of such dislocations was estimated from the bending displacement rate of the four-point bend sample. The dependence of temperature and stress in dislocation velocity was investigated. The activation energy for dislocation velocity was determined to be about 2.2$\pm$0.4eV. In addition, the stress exponent (m) describing the stress dependence of dislocation velocities was in the range of 2.0$\pm$0.2.

• The Journal of Advanced Prosthodontics
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• v.6 no.6
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• pp.491-497
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• 2014

PURPOSE. This study evaluated the influence of abutment materials on the stability of the implant-abutment joint in internal conical connection type implant systems. MATERIALS AND METHODS. Internal conical connection type implants, cement-retained abutments, and tungsten carbide-coated abutment screws were used. The abutments were fabricated with commercially pure grade 3 titanium (group T3), commercially pure grade 4 titanium (group T4), or Ti-6Al-4V (group TA) (n=5, each). In order to assess the amount of settlement after abutment fixation, a 30-Ncm tightening torque was applied, then the change in length before and after tightening the abutment screw was measured, and the preload exerted was recorded. The compressive bending strength was measured under the ISO14801 conditions. In order to determine whether there were significant changes in settlement, preload, and compressive bending strength before and after abutment fixation depending on abutment materials, one-way ANOVA and Tukey's HSD post-hoc test was performed. RESULTS. Group TA exhibited the smallest mean change in the combined length of the implant and abutment before and after fixation, and no difference was observed between groups T3 and T4 (P>.05). Group TA exhibited the highest preload and compressive bending strength values, followed by T4, then T3 (P<.001). CONCLUSION. The abutment material can influence the stability of the interface in internal conical connection type implant systems. The strength of the abutment material was inversely correlated with settlement, and positively correlated with compressive bending strength. Preload was inversely proportional to the frictional coefficient of the abutment material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.4
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• pp.483-490
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• 2013

In aluminum sheet metal forming, the conventional forming methods of T4 or T6 heat-treated sheets result in low formability and dimensional accuracy. This study suggests a new forming method for aluminum sheets called as hot forming quenching (HFQ) that solves the problems faced in the conventional method. HFQ combines the heat treatment and forming processes through the forming die during the quenching of a solid solution. To evaluate the application of HFQ to the sheet forming of aluminum, an Erichsen and V-bending test are performed in this study to measure the dimensional accuracy and formability, which are then compared with those of the conventional forming method. Furthermore, the strength and hardness of the products formed by HFQ are measured to confirm the degradation in mechanical properties compared with the conventional forming method, which shows the validity of the application of HFQ to aluminum sheet metal forming.

• Transactions of Materials Processing
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• v.7 no.4
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• pp.400-406
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• 1998

The press formability analysis of welding parts was studied in the current work by the tailor welded blank. The press formability was tested by means of the flash weldability and the formability for two kinds of materials (SPCC & S35C). The results indicate that SPCC & S35C steel sheets showed good weldability and formability after an optimum welding conditions. The independent operation variables were characterized by strength of welding parts, deformation after the welding, press formability of welding parts and productibility of welding. The weldability and the quality of welding parts of the flashed SPCC steel sheet was superior to those of the S35C steel sheet, since a higher carbon content in steel sheet led to a higher hardness. The experimental results were discussed by the evaluation of the results obtained from tensile test, hardness test, micro-structure and V bending test.