• The Journal of Korean Academy of Prosthodontics
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• v.31 no.2
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• pp.181-190
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• 1993

The purpose of this study was to evaluate the effect of shear bond strength between various percentage of reused dental ceramic alloys and porcelain. One hundred specimens were made of one semiprecious alloy and three nonprecious alloys. Each alloy group was subdevided into five groups according to the additional precentage of new alloy. Group I specimens were made of 100% new alloy and served as the control of the investigation. Group II specimens were made of once-cast alloy with 75% new alloy. Group III specimens were made of once-cast alloy with 50% new alloy. Group IV specimens were made of once-cast alloy with 25% new alloy. Group V specimens were made of 100% recast alloy. Five specimens were made for each group of the alloy combinations. The test specimens were prepared by firing porcelain doughnuts on the alloy rod surface, and invested in dental stone. Bond strengths were measured by Instron universal testing machine at a crosshead speed of 0.5mm/min. The fractured surface of metal specimens were examined under the scanning electron microscope. The obtained results were as follows : 1. The shear bond strength of Albabond showed no significant difference between control group and reused alloy group. 2. The shear bond strength of reused alloy groups of nonprecious alloys were lower than that of control groups. 3. The shear bond strength between porcelain and metal in semiprecious alloy was higher than in nonprecious alloys 4. In nonprecious alloys. Rexillium III showed the highest bond strength value and Excelalloy showed the lowest shear bond strength value. 5. Regardless of the type of alloys and additional proportion of new alloys, scanning electron microscope photographs of the fracture surface between alloy and porcelain revealed simillar semiprecious alloy and nonprecious alloys.

• Steel and Composite Structures
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• v.19 no.1
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• pp.209-221
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• 2015

Results from an experimental study on the seismic response of six composite reinforced concrete column-to-steel beam interior joints are presented. The primary variable investigated is the details in the joint. For the basic specimen, the main subassemblies of the beam and column are both continuous, and the steel beam flanges extended to the joint are partly cut off. Transverse beam, steel band plates, cove plates, X shape reinforcement bars and end plates are used in the other five specimens, respectively. After the joint steel panel yielded, two failure modes were observed during the test: local failure in Specimens 1, 2 and 4, shear failure in Specimens 3, 5 and 6. Specimens 6, 3, 5 and 4 have a better strength and deformation capacity than the other two specimens for the effectiveness of their subassemblies. For Specimens 2 and 4, though the performance of strength degradation and stiffness degradation are not as good as the other four specimens, they all have excellent energy dissipation capacity comparing to the RC joint, or the Steel Reinforced Concrete (SRC) joint. Based on the test result, some suggestions are presented for the design of composite RCS joint.

• Journal of the Korean Ceramic Society
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• v.22 no.4
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• pp.33-39
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• 1985

A composition containing a-$Si_3N_4$ with 5w/0 $Y_2O_3$ and 4w/0 $Al_2O_3$ was hot-pressed at 1, $650^{\circ}C$ and 350kg/$cm^2$ for 1.5hrs and specimens of the same composition were pressureless-sintered at 1, 75$0^{\circ}C$ for 1.5 and 5hrs. By X-ray diffraction it was found that hot-pressed specimens were consisted of $\alpha$-and $\beta$-$Si_3N_4$ and sintered specimens were consisted of $\beta$-$Si_3N_4$ and $Si_3N-4Y_2O_3$ which was crystallized out from the grainboundary phase. The 5-hr sintered specimens had higher degree of crystallization than the 1.5 hr sintered specimens. Among these three different specimens the 5-hr sintered specimens showed the highest strength by hot MOR test at 1, 00$0^{\circ}C$. The SPT diagram for the 5-hr sintered $Si_3N_4$ was constructed by measurements of the stress rate dependence of fracture strength.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.4
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• pp.64-70
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• 2007

This paper presents a study on the effects of feedrate and shotpeening on the fatigue life of A17075-T6 specimens. For this purpose, six groups of specimens, each of which consists of eight specimens, were first machined at six different feedrates(0.05, 0.10, 0.15, 0.20, 0.25, 0.30mm/rev). Half of eight specimens in each group were then peened and the others remained un-peened. Then, the fatigue life was measured by using 4-point rotatry bending machine. One observation was that the fast the feedrate was, the large the diameter of a specimen was. To make sure that the bending stress was the same in all cases, different loading conditions were thus applied to specimens based on their diameters. Next, comparison of fatigue life among twelve sets of specimens(six groups times two sets, peened and un-peened) was performed. Finally, based on machining cost analysis, a guideline for optimal feedrate was presented.

• Advances in concrete construction
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• v.9 no.6
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• pp.597-610
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• 2020

Stress-strain models of fibre reinforced polymer (FRP) confined concrete have been widely investigated; however, the existing load which is always supported by structures during the retrofitting phase, namely 'preload', has been neglected. Thus, preload effects should be clarified, providing insightful information for FRP retrofitting of structures with preload conditions. Towards this aim, experiments were performed for 27 cylinder concrete specimens with the diameter 150 mm and the height 300 mm. Three specimens were used to test the compressive strength of concrete to compute the preloads 20%, 30% and 40% of the average strength of these specimens. Other 24 specimens were divided into 2 groups; each group included 4 subgroups. Four subgroups were subjected to the above preloads and no preload, and were then wrapped by 2 FRP layers. Similar designation is applied to group 2, but wrapped by 3 FRP layers. All specimens were tested under axial compression to failure. Explosive failure is found to be the characteristic of specimens wrapped by FRP. Experimental results indicated that the preload decreases 12-13% the elastic and second stiffness of concrete specimens wrapped by 2 FRP layers. The stiffness reduction can be mitigated by the increase of FRP layers. Preload negligibly reduces the ultimate force and unclearly affects the ultimate displacement probably due to complicated cracks developed in concrete. A mechanism of preload effects is presented in the paper. Finally, to take into account preload effects, a modification of the widely used model of un-preload FRP confined concrete is proposed and the modified model demonstrated with a reasonable accuracy.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.1
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• pp.24-30
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• 2009

The purpose of this study is to investigate the fatigue strength in accordance with back plate of butt welded specimens. Fatigue life of butt welded specimens was presented for determining the effect of back plates in terms of fatigue strength. As a results, fatigue strength of butt welded specimens with steel back plate show a decrease as compared against the butt welded specimens with ceramic back plate. Compared with the fatigue strength with respect to the existence of steel back plate, the specimens without back plate were much higher than the specimens with back plate.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.862-874
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• 1989

A phase evil method and spectrum analysis were instrument error which is originated from measurement system and the form error of standard specimens. An instrument with a rotating table supported by an air bearing is calibrated using standard specimens. The phase of standard specimens was measured 12 times on the rotating table with rotating 30 in turn and its measurement magnification was set by 100000 times. As a result of data analysis of all the observations, read out at each of 144 orientations(per 2.5) from recorded datafiles, the error of the performance of the instrument and those of the standard specimens are evaluated and a systematic deviation of the instrument is determined. In the particular instrument used in the present experiment, the deviation of the instrument is determined with the accuracy of 15nm and those of standard specimens with the accuracy of 23, 13 n, respectively. The reproducibility of the instrument is investigated, too. If the instrument is calibrated by using the above standard specimens, then the accuracy of the measurement of roundness error can be improved to about 15nm.

• Journal of Surface Science and Engineering
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• v.36 no.6
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• pp.491-499
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• 2003

Copper-based leadframe sheets were oxidized in a hot alkaline solution to form brown-oxide layer on the surface and molded with epoxy molding compound (EMC). The brown-oxide-coated leadframe/EMC joints were machined to form sandwiched double-cantilever beam (SDCB) specimens and sandwiched Brazil-nut (SBN) specimens for the purpose of measuring the fracture toughness of leadframe/EMC interfaces. The SDCB and the SBN specimens were designed to measure the fracture toughness of the leadframe/EMC interfaces under nearly mode-I loading and mixed-mode (mode I ＋ mode II) loading conditions, respectively. Fracture surfaces were analyzed by various equipment such as glancing-angle XRD, SEM, AES, EDS and AFM to elucidate failure path. Results showed that failure occurred irregularly in the SDCB specimens, and oxidation time of 2 minutes divided the types of irregular failures into two classes. The failure in the SBN specimens was quite different from that in the SDCB specimens. The failure path in the SBN specimens was not dependent on the phase angle as well as the distance from tips of pre-cracks.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.411-413
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• 2012

This study has been investigated about hygrothermal environmental effects on the pin-joined carbon/epoxy composites through acoustic emission technique. The specimens were classified as three types for pin loading test : Base (before immersion), RT (room temperature immersion), HT ($75^{\circ}C$ immersion). As a results, the bearing strength of RT specimens was weakly decreased than that of base specimens. The bearing strength of HT specimens was greatly decreased than that of Base and RT specimens due to effects of simultaneous moisture and higher temperature. Also, the results from cumulative hit of acoustic emission indicated that AE events induced by matrix cracks of HT specimens was lower than that of base specimens.

• Computers and Concrete
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• v.21 no.6
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• pp.669-679
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• 2018

In this paper the behavior of reinforced concrete (RC) beam-column connections under cyclic loading was analyzed. The specimens, manufactured in a reduced-scale were made of (a) recycled aggregate concrete (RAC) by replacing 30% of natural coarse aggregate (NCA) with recycled coarse aggregate (RCA) and (b) RAC incorporating Polyethylene terephthalate (PET) fiber i.e., PET fiber-reinforced concrete (PFRC) at the joint region. PET fiber (aspect ratio=25) of 0.5% by weight of concrete used in the PFRC mix was obtained by hand cutting of post-consumer PET bottles. A reference specimen was also prepared using 100% of NCA and subjected to similar loading sequence. Comparing the results the structural behavior under cyclic loading of RAC specimens are quite similar to the reference specimens. Damage tolerance, load resisting capacity, stiffness degradation, ductility, and energy dissipation of the RAC specimens enhanced due to addition of PET fibers at the joint region. PFRC specimens also presented a lower damage indices and higher principal tensile stresses as compared to the RAC specimens. The results obtained gave experimental evidence on the feasibility of RAC for structural use. Using PET fibers as a discrete reinforcement is recommended for improving the seismic performance of RAC specimens.