• Proceedings of the KSME Conference
• /
• 2000.11a
• /
• pp.470-474
• /
• 2000

Cold expansion of fastener holes is a mechanical process widely used in the aerospace industry. This treatment leads to an improvement of fatigue behavior due to the developed compressive residual stresses on the hole surface. The residual stress profile depends on the parameters of cold expansion, which are, expanding rate, inserting direction of mandrel, material properties etc. and the method to confirm this profile is only measurement by X-ray diffractometer. Despite its importance to aerospace industries, little attention has been devoted to the accurate modelling of the process. In this paper, Two-dimensional axisymmetric finite element simulations have been conducted for the cold expansion in an aluminium plate in order to predict the magnitude and distribution of the residual stress and plastic deformation. Maximum compressive residual stress could be increase about 7 percent using the 2-step cold expansion method.

• The Journal of Korean Academy of Prosthodontics
• /
• v.28 no.1
• /
• pp.137-163
• /
• 1990

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the Properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of the consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfate and the magnesium sulfate promoted the hardening and the aluminium phosphate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect of the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate and cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• The Journal of Korean Academy of Prosthodontics
• /
• v.29 no.1
• /
• pp.139-165
• /
• 1991

The properties of a investment material can be described by the consistency at the slurry state, the setting time, the compressive strength and the thermal expansion during the casting. In this study the effect of the production parameters which are included the ratio of quartz and cristobalite, the content of binder, the water powder ratio and the content and concentration of additives on the properties of the gypsum-bonded investments has been investigated with help of the consistency test, the vicat needle test, the compressive strength test, the thermal expansion test, x-ray diffraction and DTA thermal differential test. The experimental results showed that the constitution of a investment with W/P ratio of 0.34, 30% of gypsum, 0.8% aluminium sulfate, 2% magnesium sulfate, 0.6% sodium phosphate was adapted for the properties of the KDA Spec. No. 13 type I investment. The important experimental results are summarized as follows. 1. The consistency of the investment decreased with increasing amount of aluminium sulfate and decreasing amount of sodium phosphate. An addition of magnesium sulfate up to 2% an increase of the consistency was shown. But 3% magnesium sulfate in investment showed a decrease of consistency. The consistency did not vary significantly with a variation of the content of gypsum and cristobalite and the W/P ratio. 2. Aluminium sulfata and the magnesium sulfate promoted the hardening and the aluminium phoshpate delayed the hardening. The setting time increased with amount of gypsum. The effect of the matrix on the setting time was insignificant. With the W/P ratio of 0.34 the setting time was 14 min. 3. The compressive strength decreased with the amount of aluminium sulfate up to 0.25% and increased with the amount of aluminium sulfate greater than 3%. The compressive strength decreased as decreasing the amount of magnesium sulfate and gypsum and as increasing the W/P ratio. The effect fo the refractory on the compressive strength was also not significant. With the W/P ratio of 0.34 the compressive strength was $34Kg/mm^2$. 4. The 1st thermal expansion was found at the temperature near $250^{\circ}C$ and the steady state or the contraction stage was found at the temperature between $250^{\circ}C$ and $500^{\circ}C$. After this stage the 2nd thermal expansion took place at the temperature near $500^{\circ}C$. The amount of thermal expansion increased with decreasing the content of magnesium sulfate, aluminium sulfate and gypsum and the W/P ratio. And the amount of thermal expansion increased as the content of sodium phosphate ad cristobalite. With the W/P ratio of 0.34 the amount of total expansion was 1.2%.

• Journal of Technologic Dentistry
• /
• v.43 no.3
• /
• pp.71-76
• /
• 2021

Purpose: In this study, thermal properties were observed by measuring the extent of thermal expansion and the amount of thermal residue that appears upon burnout on a workpiece made by using a dental digital light processing (DLP) three-dimensional (3D) printer. Methods: Thermal properties of workpieces manufactured by using two 3D printers were observed. The specimens were designed in cylindrical form with dimensions 10 mm in diameter and 10 mm in height. The control specimen was made of wax, and the experimental specimen was made of resin. The thermal expansion rate was measured by applying heat to three types of specimens, and burnout residue was measured. Results: The thermal expansion rate of the wax pattern (WP) specimen was 0.93%±0.05%, of the RP1 specimen was 1.30%±0.08%, and of the RP2 specimen was 1.20%±0.09%. Measuring the recovered residue yielded residual amounts of 0.2% for the WP specimen, 1.1% for the RP2 specimen, and 1.8% for the RP1 specimen. Conclusion: 1. From measurements of the workpieces manufactured by dental DLP 3D printing, the thermal expansion rate was found to be higher than that of wax. 2. As a result of measuring burnout residues on the workpieces manufactured by dental DLP 3D printing, the required summoning temperature to obtain suitable castings was determined to >750℃.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.670-680
• /
• 1994

The thermophysical properties of Non-Newtonian fluid as the function of the temperature and the concentration are needed in many rheological heat transfer and fluid mechanics problems. The present work investigated the effects of the concentration and the temperature on the thermophysical properties of purely-viscous Non-Newtonian fluids such as the isobaric thermal expansion coefficient, density, zero-shear-rate viscosity, and zero-shear-rate dynamic viscosity within the experimental temperature range from $25^{\circ}C$ to $55^{\circ}C$. The densities of the test fluids were determined as the function of the temperature by utilizing a reference density and the least square equation for the measured isobaric thermal expansion coefficient. As the concentration of purely-viscous Non-Newtonian fluid was increased up to 10,000 wppm, the densities were proportionally increased up to 0.4%. The zero-shear-rate viscosities of test fluids were measured before and after the measurements of the first thermal expansion coefficients and the densities of Non-Newtonian fluid. Even though they were changed up to approximately 22% due to thermal aging and cycling, they had no effects on the thermal expansion coefficients and the densities of Non-Newtonian fluid. The zero-shear-rate dynamic viscosities for purely-viscous Non-Newtonian fluids were compared with the values for distilled water. They showed the similar trend with the zero-shear-rate viscosities due to small differences in the densities for both distilled water and purely-viscous Non-Newtonian fluid.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.05a
• /
• pp.73-76
• /
• 2002

This study developed SiC/Al composites for electronic packaging to which reinforcements were added with the volume fractions of 49%, 56% and 63% by the squeeze casting method. 0.8 wt.% of the inorganic binder as well as the $Al_2O_3$ fiber and SiC particles with the volume fraction of 1:10 were added to the SiC/Al composites For the produced SiC/Al composites, the CTEs (coefficients of thermal expansion) were measured from 30 to $300^{\circ}C$ and compared with the FEM numerical simulation to analyze the temperature dependent properties. The experiment showed the CTEs of SiC/Al composites that were intermediate values of those of Rule of Mixture and Turner's Model. The CTEs were close to Turner's Model in the room temperature and approached the Rule of Mixture as the temperature increases. These properties analyzed from the difference of the average stress acting between the matrix and the reinforcements proposed in this study

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.03b
• /
• pp.42-42
• /
• 2010

We have characterized the previously undescribed parameters for engineering the electrical properties of single-walled carbon nanotube (SWCNT) films for technological applications. The surface tension of the top coating passivation material and matching coefficients of thermal expansion for the substrate and carbon nanotube network are two crucial parameters for the fabrication of reliable and highly conductive single-walled carbon nanotube network thin films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.278-278
• /
• 2010

We have characterized the previously undescribed parameters for engineering the electrical properties of single-walled carbon nanotube (SWCNT) films for technological applications. The surface tension of the top coating passivation material and matching coefficients of thermal expansion for the substrate and carbon nanotube network are two crucial parameters for the fabrication of reliable and highly conductive single-walled carbon nanotube network thin films.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.04a
• /
• pp.181-186
• /
• 1999

When the expansive additives are used in concrete to reduce the shrinkage cracking, it shows variable properties with the curing method and curing temperature. Therefore, in this study, the experiments are perfomed to present the expansion of cement mortar by varying the unit additions of expansive additives and the curing method. According to the test results, the order of expansion by curing method, which is caused by hydration heat of cement, is follows ; curing at water > curing at air after curing at water for 7 days > curing at air. Cement mortar using expansive additives shows that high expansion is place with rise of temperature.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 1999.10a
• /
• pp.185-189
• /
• 1999

There has been a considerable attention in Invar alloys because of its low thermal expansion property. A low thermal expansion property of Invar alloys, lower than 10-6 near the room temperature, is attractive for precision machine tools. However, the expansion property of Invar alloys is limited below about 520。K, and mechanical properties are relatively low to apply to machine tools. In order to improve mechanical properties in this alloy, Ti alloy element was added to an invar alloy. Microstructure changes and optimum heat-treatment conditions according to Ti addition were discussed in the Ni38-Mo2-Crl-Fe Invar alloy.