• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.697-700
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• 2000

Fatigue damage to reinforced concrete bridge decks have been found in many bridges. Failure mode of most reinforced concrete decks is caused by local punching shear rather than flexural moment due to cumulated damage. In this study, mechanical degradation of unstrengthened and strengthened bridge deck specimens is experimentally investigated. The unstrengthened deck specimens were damaged under the pulsating loading condition. After the test, deteriorated deck specimens were strengthened with Carbon Fiber Sheet, then loaded to observe the improvement of the fatigue behavior. It is shown that fatigue damaged specimens are similar to real bridge rather than static damaged specimens.

• The Journal of Advanced Prosthodontics
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• v.5 no.2
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• pp.133-139
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• 2013

PURPOSE. This study was to evaluate the effect of the solution temperature on the mechanical properties of dualcure resin cements. MATERIALS AND METHODS. For the study, five dual-cure resin cements were chosen and light cured. To evaluate the effect of temperature on the specimens, the light-cured specimens were immersed in deionized water at three different temperatures (4, 37 and $60^{\circ}C$) for 7 days. The control specimens were aged in a $37^{\circ}C$ dry and dark chamber for 24 hours. The mechanical properties of the light-cured specimens were evaluated using the Vickers hardness test, three-point bending test, and compression test, respectively. Both flexural and compressive properties were evaluated using a universal testing machine. The data were analyzed using a two way ANOVA with Tukey test to perform multiple comparisons (${\alpha}$=0.05). RESULTS. After immersion, the specimens showed significantly different microhardness, flexural, and compressive properties compared to the control case regardless of solution temperatures. Depending on the resin brand, the microhardness difference between the top and bottom surfaces ranged approximately 3.3-12.2%. Among the specimens, BisCem and Calibra showed the highest and lowest decrease of flexural strength, respectively. Also, Calibra and Multilink Automix showed the highest and lowest decrease of compressive strength, respectively compared to the control case. CONCLUSION. The examined dual-cure resin cements had compatible flexural and compressive properties with most methacrylate-based composite resins and the underlying dentin regardless of solution temperature. However, the effect of the solution temperature on the mechanical properties was not consistent and depended more on the resin brand.

• Structural Engineering and Mechanics
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• v.24 no.4
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• pp.429-446
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• 2006

Experimental investigation was conducted to evaluate the seismic ductility of earthquake-experienced concrete columns with an aspect ratio of 2.5. Eight circular concrete columns with a diameter of 600 mm were constructed with three test parameters: confinement ratio, lap-splice of longitudinal bars, and retrofitting with Fiber Reinforced Polymer (FRP) materials. The objective of this research is to examine the seismic performance of RC bridge piers subjected to a Quasi static test (QST), which were preliminary tested under a series of artificial earthquake motions referred to as a Pseudo dynamic test (PDT). The seismic enhancement effect of FRP wrap was also investigated on these RC bridge piers. Six specimens were loaded to induce probable damage by four series of artificial earthquakes, which were developed to be compatible with earthquakes in the Korean peninsula by the Korea Highway Corporation (KHC). Directly after the PDT, six earthquake-experienced columns were subjected to inelastic cyclic loading under a constant axial load of $0.1{f_c}^{\prime}A_g$. Two other reference specimens without the PDT were also subjected to similar quasi-static loads. Test results showed that specimens pre-damaged by moderate artificial earthquakes generally demonstrated good residual seismic performance, which was similar to the corresponding reference specimen. Moreover, RC bridge specimens retrofitted with wrapping fiber composites in the potential plastic hinge region exhibited enhanced flexural ductility.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.888-895
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• 2006

In this study, anisotropically consolidated undrained shear(CAU) test was performed to examine the variation of the shear strength according to the stress history. The specimen having 30% relative density was homogeniously prepared, and 200KPa of back pressure was applied to increase the B value more than 0.95. To make NC specimens, the vertical stress was applied on the specimen by 100KPa, 200KPa and 400KPa, and to make OC specimens, the vertical stress was applied upto 400KPa and was reduced to 200KPa and 100KPa resulting in OCR 2 and 4 respectively. The test result indicates the shear strength for the OC specimens are slightly higher then that of the NC specimens at the same confining pressure. The elastic modulus varies according to the confining stress and considerably affected by preconsolidation stress.

• Journal of Technologic Dentistry
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• v.42 no.2
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• pp.73-79
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• 2020

Purpose: The aim of this study was to investigate the influence of short and long duration sintering on microstructure and flexural strength of zirconia. Methods: To conduct three-point bending test, Zirconia specimens are milled according to ISO 6872 guidelines(N=18, n=9 per group). Two specimens group(n=8) is sintered for 10 hours(Standard schedule) and 3 hours(Speed schedule) at the peak temperature of 1550℃ with silicon carbide sintering furnace. Flexural strength of specimens are measured by instron. After coating each specimen(n=1), microstructure of specimens is observed using Scanning Electron Microscope(SEM). T-test was utilized to statistically assess the data. Results: The mean and standard deviation value of the flexural strength for standard schedule group are 578.15±57.48Mpa, that of speed schedule are 465.9±62.34Mpa. T-test showed significant differences in flexural strength between two zirconia specimen group which applied standard schedule and speed schedule respectively(p<0.05). Conclusion: The result of this study showed that the increase in sintering time led to increased grain size, and also to a positive effect on the flexural strength.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.285-289
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• 2004

Micro tensile test specimens of thin film single crystal silicon for the most useful structural materials in MEMS (Micro Electro Mechanical System) devices were fabricated using SOI (Silicon-on-Insulator) wafers and MEMS processes. Dimensions of micro tensile test specimens were thickness of $7\mu\textrm{m}$, width of 50~$350\mu\textrm{m}$, and length of 2mm. Top and bottom silicon were etched using by deep RIE (Reactive Ion Etching). Thin film aluminum markers on testing region of specimens with width of $5\mu\textrm{m}$, lengths of 30~$180\mu\textrm{m}$ and thickness of 200 nm for measuring tensile strain were fabricated by aluminum wet etching method. Fabricated side wall angles of aluminum marker were about $45^{\circ}~50^{\circ}$. He-Ne laser with wavelength of 633nm was used for checking fringed patterns.

• Computers and Concrete
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• v.31 no.3
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• pp.241-252
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• 2023

Corrosion of rebar is one of the major deteriorating mechanisms that affect the durability of reinforced concrete (RC) structures. The increase in CO₂ concentration in the atmosphere leads to early carbonation and deterioration due to corrosion in RC structures. In the present study, an attempt has been made to modify the existing carbonation depth prediction empirical model. The modified empirical model is verified from the carbonation data collected from selected RC structures of CSIR-SERC campus, Chennai and carbonation data available from the reported literature on in-situ RC structures. Attempt also made to study the carbonation depth in the laboratory specimens using oxygen permeability index (OPI) test. The carbonation depth measured from RC structures and laboratory specimens are compared with estimated carbonation depth obtained from OPI test data. The modified empirical model shows good correlation with measured carbonation depth from the identified RC structures and the reported RC structures from the literature. The carbonation depth estimated from OPI values for both in-situ and laboratory specimens show lesser percentage of error compared to measured carbonation depth. From the present investigation it can be said that the OPI test is the suitable test method for both new and existing RC structures and laboratory RC specimens.

• Steel and Composite Structures
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• v.46 no.6
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• pp.745-757
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• 2023

In order to study the fatigue performance of the flat steel plate-lightweight aggregate concrete hollow composite bridge slab subjected to fatigue load, both static test on two specimens and fatigue test on six specimens were conducted. The effects of the arrangement of the steel pipes, the amplitude of the fatigue load and the upper limit as well as lower limit of fatigue load on failure performance were investigated. Besides, for specimens in fatigue test, strains of the concrete, residual deflection, bending stiffness, residual bearing capacity and dynamic response were analyzed. Test results showed that the specimens failed in the fracture of the bottom flat steel plate regardless of the arrangement of the steel pipes. Moreover, the fatigue loading cycles of composite slab were mainly controlled by the amplitude of the fatigue load, but the influences of upper limit and lower limit of fatigue load on fatigue life was slight. The fatigue life of the composite bridge slabs can be determined by the fatigue strength of bottom flat steel plate, which can be calculated by the method of allowable stress amplitude in steel structure design code.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.4
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• pp.45-52
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• 2023

This study was conducted to examine the possibility of use as a structural material for ginseng cultivation facilities of recycled plastics. In order to determine the possibility that recycled plastic can replace timber used as a structural material for ginseng cultivation facilities, the specimens collected by elapsed time were compared with timber through bending tests. In addition, in order to analyze the effect of external environmental conditions on recycled plastic products, bending test was conducted with the specimens that had completed weathering test and accelerated heat aging test respectively. As a result, the bending strength of recycled plastic specimens with the elapsed time of 360 days was lower than that of timber. But bending strength of recycled plastic specimens exceeded the design allowable stress standard set by the Korea design standard (MOLIT, 2016). There was no degradation in quality of recycled plastic due to the external environment, and it was found that there would be no problem even if it was used as a structural material for ginseng cultivation facilities.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.2001-2005
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• 2005

The tensile test is generally used to measure mechanical properties with conventional fracture test. This test is extremely certain method to measure Young's modulus, yield strength, tensile strength and so on. ASTM, by international standard, prescribes two classes of tensile tests in tubular products. One is method that specimens aren't done by any process with Tube-shape. The other is that specimens are made on process for C-shape. In this paper, we would like to present the new-shape specimens for the tensile test. The presented specimen's shape is that put two pieces of C-shape specimens together. Besides a load point and a support point are fixed like Tube-shape specimens. This shape of specimen has a difference that existing specimen is made on one-step process out this specimen is made on two-step process. This shape is considered that stress concentration phenomenon occurs at the reduced section if a specimen is made on one step process.