• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.105-110
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• 2001

Autoclave curing using the vacuum bagging method is widely used for the manufacture of advanced composite prepreg airframe structures. Due to increasing use of advanced composites, specific techniques have been developed to repair damaged composite structures. In order to repair the damaged part, it is required that the damaged areas be removed, such as skin and/or honeycomb core, by utilizing the proper method and then repairing the area by laying up prepreg (and core) then curing under vacuum using the vacuum bagging materials. It shall be cured either in an oven or autoclave per the original specification requirements. Delamination can be observed in the sound areas during and/or after a couple times exposure to the elevated curing temperature due to the repeated repair condition. This study was conducted for checking the degree of degradation of properties of the cured parts and delamination between skin prepreg and honeycomb core. Specimens with glass honeycomb sandwich construction and glass/epoxy prepreg were prepared. The specimens were cured 1 to 5 times at $260^{circ}F$ in an autoclave and each additionally exposed 50, 100 and 150 hours in the $260^{circ}F$ oven. Each specimen was tested for tensile strength, compressive strength, flatwise tensile strength and interlaminar shear strength. To monitor the characteristics of the resin itself, the cured resin was tested using DMA and DSC. As a results, the decrease of Tg value were observed in the specific specimen which is exposed over 50 hrs at $260^{circ}F$. This means the change or degradative of resin properties is also related to the decrease of flatwise tensile properties. Accordingly, minimal exposure on the curing temperature is recommended for parts in order to prevent the delation and maintain the better condition.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.98-104
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• 2018

Nondestructive strength Equations are commonly used to determine the strength of concrete. However, the application of the existing equations may include many errors because this method is proposed on the basis of limited experimental parameters while actual bridges have various parameters such as conditions of concrete mixtures, properties of concrete strength, etc. Also, the error among the existing equations causes the confusion when engineers select the proper estimation equation for the concerned bridge. In this study, a series of the field inspection and the test have been performed on 297 existing bridges, in order to evaluate the bridges, based on the test results of the in-depth inspection, and the estimated strengths by means of the nondestructive strength equations are analyzed and compared with results of the core specimen strengths. According to results of analyses, the nondestructive strength equation proposed by CNDT Committee of Architectural Institute of Japan had high relationship with core strength. However, the strengths predicted by this equation, are underestimated when concrete's strengths are over 30 MPa, otherwise, they are overestimated. Also in this paper, based on the relationship between the estimated nondestructive concrete strengths and the core specimen strengths the modified strength equation through simple correlation analysis is proposed.

• Clinical Endoscopy
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• v.55 no.5
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• pp.637-644
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• 2022

Background/Aims: Endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) is integral to the diagnosis of gastrointestinal (GI) subepithelial tumors (SETs). The impact of different EUS-FNB tissue sampling techniques on specimen adequacy and diagnostic accuracy in SETs has not been fully evaluated. This study aimed to compare the diagnostic outcomes of slow-pull (SP) and standard suction (SS) in patients with GI SETs. Methods: In this retrospective comparative study, 54 patients were enrolled. Medical records were reviewed for location and size of the target lesion, FNB needle type/size, technical order, specimen adequacy, diagnostic yield, and adverse events. The acquisition rate of adequate specimens and diagnostic accuracy were compared according to EUS-FNB techniques. Results: The mean lesion size was 42.6±36.4 mm, and most patients were diagnosed with GI stromal tumor (75.9%). The overall diagnostic accuracies of the SP and SS techniques were 83.3% and 81.5%, respectively (p=0.800). The rates of obtaining adequate core tissue were 79.6% and 75.9%, respectively (p=0.799). No significant clinical factors affected the rate of obtaining adequate core tissue, including lesion location and size, FNB needle size, and final diagnosis. Conclusions: SP and SS had comparable diagnostic accuracies and adequate core tissue acquisition for GI SETs via EUS-FNB.

• Composites Research
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• v.30 no.2
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• pp.132-137
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• 2017

The purpose of this paper is to investigate failure characteristics of Carbon/BMI-Nomex honeycomb sandwich on design parameters. A total of 6 types sandwich specimens were manufactured according to core height, face thickness and density, and environmental condition were applied to evaluate temperature and humidity effects of one of these specimens. The test results show that the core shear buckling loads was commonly observed in all specimens except for the joint with density of $64kg/m^3$. After core shear buckling, however, the joint carried additional loads over the buckling loads and then finally failed in the upper face and lower face at the same time. In the case of specimen having high stiffness, the maximum failure load was low due to interfacial failure of the upper face and core without initial core shear buckling. The ETW1 and ETW2 conditions, which were carried out to evaluate the environmental condition of the sandwich specimen, show an initial failure mode which was significantly different from RTD condition. Also, the ETW2 condition with increased temperature under the same humidity shows that the core shear buckling load was 18% less than ETW1 condition.

• Journal of the Korean Society of Clothing and Textiles
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• v.13 no.3 s.31
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• pp.259-267
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• 1989

In this paper, the fabric specimen undergoes repeated laundering under given condition. After this cyclic laundering was applied, the crease recoveries of the specimen were measured using shirley crease revovery tester in order to evaluate the effect of factors at given condition during crease deformation. 5 samples of grey plain cloth were desized, alkali-scoured, bleached, whased with water, and air-dried. All tests were made on samples preconditioned to $65\%\;RH\;and\;20^{\circ}C$. The experimental results were analysed statistically to relate crease recoveries and the properties of smaples, recovery periods (time) of crease. Furthermore, the crease recoveries of core-spun yarn woven fabrics were discussed in comparison with those values for $100\%$ combed cotton yarn woven fabric and $65\%$ polyester $35\%$ carded cotton blended yarn woven fabric. The results obtained are as follows; 1. Regardless of materials, remarkable decrease are observed in crease recoveries about 1-5 cycles of the repeated laundering, but slack decrease are observed in crease recoveries after 5 cycle of the re-peated laundering. 2. Crease recoveries ($\alpha$) of core-spun yarn woven fabrics are relate to recovery periods (t) of crease as follows; log$\alpha$=0.01415 log t+2.1168 ($r^2=0.94$) 3. Core-spun yarn woven fabrics were superior to $100\%$ combed cotton yarn woven fabrics and $65\%$ polyester $35\%$ carded cotton blended yarn woven fabric in crease recoveries. 4. Crease recoveries ($\alpha$) of core-spun yarn woven fabrics are relate to cover factor (CF), thickness (T) at pressure 0.5 $gf/cm^2$, weight (W) as follows; log$\alpha$=-0.3482 log CF-0.4924 log T-0.4727 W+2.4243 ($r^2=0.88$) 5. Crease recoveries ($\alpha$) of core-spun yarn woven fabrics are relate to 2HB/B, 2HB/W, $\sqrt[3]{B/W}$, WC/T which are concerning to formation of weared clothes and bending Iran formation behavior as follows: log $\alpha$=0.0091 2HB/B+0.4667 2HB/W+0.0185 $\sqrt[3]{B/W}$+0.0114 WC/T+1.8433 ($r^2=0.86$)

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.71-77
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• 2023

This study aims to investigate the structural performance of hollow-core slab (HCS) memebers with 400 mm thickness. To this end, a total of four HCS specimens were fabricated based on the individual mold method to provide shear reinforcement, unlike the extrusion method. The key variables were chosen as the presence of topping concrete, core-filling concrete, and shear reinforcements. The crack patterns and load-displacement responses of the test specimens were analyzed in detail. Test results showed that inclined shear cracking occurred all the specimens, and that the specimen with shear reinforcement on the web of HCS unit had higher strength and ductility than the specimen without shear reinforcement. In particular, shear reinforcements placed on the web of HCS unit effectively resisted not only to vertical shear force but also to horizontal shear force between the interface of HCS unit and topping concrete. In addition, it was discovered that the method in which shear reinforcements are placed on the web of HCS unit is more effective in improving structural performance than core-filling method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.6
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• pp.3363-3369
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• 2014

Recently, considerable effort has been made to maintain a pleasant and safe indoor environment in buildings. For this, the use of a ventilation system attached to a range hood in kitchens has prevailed. Accordingly, diversiform designs for range hoods have been used. Press molding is normally used for range hood construction for several reasons. On the other hand, its economic efficiency is low in the case of a small production work. Considerable research has been carried out to solve this problem and it is believed that it is useful to use the change core method to develop molds. This study designed the core of a mold using the change core method and a total of four processes were used in its manufacture. As a result, the press molds, which are needed for shorter production runs and whose form is changeable, were developed. In addition, after the measurements in three-dimensions, the specimen passed a test within a tolerance of ${\pm}2.00mm$.

• Journal of the Society of Disaster Information
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• v.13 no.3
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• pp.366-375
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• 2017

Internal factors having effects on compressive strength test results of concrete include size, shape, height-diameter ratio(h/d), section processing method, dryness and wetness, etc. of the specimen. As it is difficult to ensure dimensions of core specimen due to rebar cutting from rebar spacing, wall thickness, effects on the structure, etc. when taking core of the concrete structure, correction of dimensions and h/d of the specimen become important for quality control of the concrete. Thus, in order to review effects of specimen size and height-diameter ratio for the concretes with compressive strength within 40~60MPa, this study has experimentally reviewed compressive strength test values by applying correction factors pursuant to KS F 2422 (Method of obtaining and testing drilled cores and sawed beams of concrete), when changing specimen diameter to ${\emptyset}5{\sim}15cm$, and h/d to 2.0~1.25.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.170-176
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• 2007

Iodine-induced stress corrosion cracking (ISCC) properties and the associated ISCC process of Zircaloy-4 and an Nb-containing advanced nuclear fuel cladding were evaluated. An internal pressurization test with a pre-cracked specimen was performed with a stress-relieved (SR) or recrystallized (RX) microstructure at $350^{\circ}C$, in an iodine environment. The results showed that the $K_{ISCC}$ of the SR and RX Zircaloy-4 claddings were 3.3 and 4.8MPa\;m^{0.5}, respectively. And the crack propagation rate of the RX Zircaloy-4 was 10 times lower than that of the SR one. The chemical effect of iodine on the crack propagation rate was very high, which was increased $10^4$ times by iodine addition. Main factor affecting on the micro-crack nucleation was a pitting formation and its agglomeration along the grain boundary. However, this pitting formation on the grain-boundary was suppressed in the case of an Nb addition, which resulted in an increase of the ISCC resistance when compared to Zircaloy-4. Crack initiation and propagation mechanisms of fuel claddings were proposed by a grain boundary pitting model and a pitting assisted slip cleavage model and they showed reasonable results.

• Journal of the Korean institute of surface engineering
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• v.49 no.6
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• pp.507-512
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• 2016

Expensive silver powder is used to form electrodes in most IT equipment, and recently, many attempts have been made to lower manufacturing costs by developing powders with Ag-Ni or Ag-Cu core-shell structures. This study examined the sintering behavior of Ag-Ni electrode powder with a core-shell structure for silicon solar cell with high energy efficiency. The electrode powder was found to have a surface similar to pure Ag powder, and cross-sectional analysis revealed that Ag was uniformly coated on Ni powder. Each electrode was formed by sintering in the range of $500^{\circ}C$ to $800^{\circ}C$, and the specimen sintered at $600^{\circ}C$ had the lowest sheet resistance of $5.5m{\Omega}/{\Box}$, which is about two times greater than that of pure Ag. The microstructures of electrodes formed at varying sintering temperatures were examined to determine why sheet resistance showed a minimum value at $600^{\circ}C$. The electrode formed at $600^{\circ}C$ had the best Ag connectivity, and thus provided a better path for the flow of electrons.