• Journal of the Korean Ceramic Society
• /
• v.35 no.8
• /
• pp.850-856
• /
• 1998

The dynaamic fatigue behavior of alumina ceramics was observed at room temperature using four-point bending method. Dynamic fatigue fracture strength was observed as function of down speed and notch length. The crack growth exponent of the specimens was calculated from the fracture strength and lifetime in dynamic fatigue test. After loading the stresses in the range of 0% to 105% compared with the average in-ert strength the value of residual fracture strength was measured for unnotched and 0.5mm notched speci-mens at the 0.001 and 0.0005 mm/min down speed respectively. After the 95% stress of the average inert strength was applied repeatedly the value of rsidual fracture strength was measured for 0.5mm notched specimens at the 0.001 and 0.0005 mm/min down speed respectively. The material constant A was found to be almost the same and not to depend on the loading mode or the down speed for unnotched and notched specimen. The value of fracture strength with time calculated from the constants n and A was in good agreement with the measured value.

• Steel and Composite Structures
• /
• v.14 no.5
• /
• pp.493-509
• /
• 2013

Bending behavior of reinforced concrete slabs encased over shallow I-sections at different levels of compression heads were investigated in present study. 1500 mm long I-sections were used to create composite slabs. Compression heads of monolithic experimental members were encased at different levels into the concrete slabs. Shear connections were welded over some of the I-sections. The testing was carried out in accordance with the principles of four-point loading. Results revealed decreasing load bearing and deflection capacities of composite beams with increasing encasement depths into concrete. Mechanical properties of concrete and reinforcing steel were also examined. Resultant stresses calculated for composite beams at failure were found to be less than the yield strength of steel beams. Test results were discussed with regard to shear and slip effect.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2000.11a
• /
• pp.44-49
• /
• 2000

Recently, PM-high speed steel(PM-HSS) has reportedly been a good alternative material for rolling mill because of its superior peformance to conventional HSS. This paper has been aimed to investigate the possibility for application to rolling contact element for PM-HSS by X-ray diffraction technique. The X-ray elastic constant for PM-HSS has been found by X-ray diffraction during the four-point bending test. Residual stress and half-value breadth on the contact surface during rolling contact fatigue process by X-ray diffraction have also been measured. The result of this study shows that the application of X-ray diffraction technique to PM-HSS could be as possible alternative material as conventional HSS. Half-value breadth on rolling contact surface by X-ray diffraction is not changed during rolling contact fatigue process. On the other hand, the residual stress is changed. This suggests that dislocation reaction has been hardly occurred in rolling contact, depending on supersaturated carbon in PM-HSS.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.223-223
• /
• 2010

본 연구에서는 Al-doped ZnO (AZO) 박막을 linear facing target sputter (LFTS) 시스템을 이용하여 성막 하였고 박막의 특성을 분석하였다. LFTS 시스템은 마주보는 두 AZO 타겟 사이에 고밀도의 플라즈마를 구속시켜 플라즈마 데미지 없이 산화물 박막을 성막 시킬 수 있는 장치이다. LFTS로 성막된 AZO 박막의 인가된 DC 파워에 따른 전기적 특성을 분석하기 위해 four-point probe와 Hall measurement 장비를 이용하여 분석을 진행 하였으며, 광학적 특성 분석을 위해 UV/Vis spectrometer 장비를 이용하여 분석하였다. AZO 박막의 구조적, 표면적 특성을 분석하기 위해 X-ray diffraction(XRD) 및 scanning electron microscope(SEM)을 사용하여 상온에서 성막된 AZO 박막의 특성을 관찰 하였다. 또한 AZO 박막의 PET 기판과의 접합성 및 구부림 시의 안정성을 평가하기 위해 bending test를 진행 하였다. 최적화된 AZO 박막으로부터 기판에 성막 중 열처리공정이나 후 열처리 공정의 진행 없이 35 ohm/square의 낮은 면저항과 약 80 % 이상의 투과율을 얻을 수 있었다. LFTS 시스템을 이용하여 낮은 공정온도에서 AZO 박막을 성막 하였음에도 불구하고 낮은 저항과 높은 투과도 특성을 나타내고 있어 기존의 투명 박막을 대체 할 수 있는 가능성을 제시하였다

• Smart Structures and Systems
• /
• v.23 no.2
• /
• pp.173-184
• /
• 2019

The main objective of this study is to evaluate the true fracture energy and monitor the damage progression in steel fibre reinforced concrete (SFRC) specimens using acoustic emission (AE) features. Four point bending test is carried out using pre-notched plain and fibre reinforced (0.5% and 1% volume fraction) - concrete under monotonic loading. AE sensors are affixed at different locations of the specimens and AE parameters such as rise time, AE energy, hits, counts, amplitude and duration etc. are obtained. Using the captured and processed AE event data, fracture process zone is identified and the true fracture energy is evaluated. The AE data is also employed for tracing the damage progression in plain and fibre reinforced concrete, using both parametric- and signal- based techniques. Hilbert - Huang transform (HHT) is used in signal based processing for evaluating instantaneous frequency of the acoustic events. It is found that the appropriately processed and carefully analyzed acoustic data is capable of providing vital information on progression of damage on different types of concrete.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.10 s.181
• /
• pp.2520-2528
• /
• 2000

Mechanical and physical properties of composite materials make a great difference due to their cure process condition. In order to clarify the effect of cure process condition on the microscopic damage behavior and failure mechanism of Carbon/Epoxy composites, three point bend test has been performed. For this purpose, two kinds of specimens with single adhesive and multiple adhesive layers were prepared. For single adhesive layer, four different types of specimen were used, that is, non-sanding, sanding, cocured, laminated specimens. Three different types of specimen were also used for the multiple adhesive layer, non-sanding, sanding, cocured specimens. Acoustic emission technique has also been employed to monitor the damage progresses associated with each micro-failure mechanism. The characteristics of AE parameters associated with micro-failure mechanism of each specimen were discussed.

• Journal of Technologic Dentistry
• /
• v.19 no.1
• /
• pp.37-42
• /
• 1997

The interfacial bond strengh and microstructural analysis of pre-heat treated porcelain-fusedmetal(PFM) were investigated using a mechanical three-point bending tester and scanning electron microscope(SEM). Four kinds of heat treated samples were prepared as follows ; A: Heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating ${\to}1850^{\circ}F$, hold 3min under vacuum, B: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$ under vacuum conditon, C: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 3min in the air, repeat same heat treatment process under vacuum condition, D: heating $1200^{\circ}F{\to}1600^{\circ}F$, holding 1min, reheating${\to}1850^{\circ}F$, holding 1min in the air. The three-point bening test result shows that the interfacial bond strength of specimen B and C were higher than that of A and D. The SEM study indicate that Specimen C shows the highest surface density.

• Structural Monitoring and Maintenance
• /
• v.10 no.4
• /
• pp.299-314
• /
• 2023

Long-gauge carbon fiber line (CFL) sensors have received considerable attention in the past decade. However, there is still a need for an in-depth investigation of their measuring accuracy. This study investigates the accuracy of carbon fiber line sensors to monitor and differentiate the flexural behavior of two beams, one reinforced with steel bars alone and the other reinforced with steel and basalt fiber-reinforced polymer bars. A distributed set of long-gauge carbon fiber line, Fiber Bragg Grating (FBG), and traditional strain gauge sensors was mounted on the tensile concrete surface of the studied beams to compare the results and assess the accuracies of the proposed sensors. The test beams were loaded monotonically under four-point bending loading until failure. Results indicated the importance of using long-gauge sensors in providing useful, accurate, and reliable information regarding global structural behavior, while point sensors are affected by local damage and strain concentrations. Furthermore, long-gauge carbon fiber line sensors demonstrated good agreement with the corresponding Fiber Bragg Grating sensors with acceptable accuracy, thereby exhibiting potential for application in monitoring the health of large-scale structures.

• Structural Engineering and Mechanics
• /
• v.75 no.5
• /
• pp.595-605
• /
• 2020

In this study, the flexural behaviors of full-scale prestressed concrete box girders are experimentally investigated. Four girders were fabricated using two types of concrete (compressive strengths: 50 MPa and 70 MPa) and tested under four-point bending until failure. The measured parameters included the deflection, the stress and strain in concrete and steel bars, and cracks in concrete. The measurement results were used to analyze the failure mode, load-bearing capacity, and deformability of each girder. A finite element model is established to simulate the flexural behaviors of the girders. The results show that the use of high-performance concrete and reasonable combination of prestressed tendons could improve the mechanical performance of the box girders, in terms of the crack resistance, load-carrying capacity, stress distribution, and ductility.

• Steel and Composite Structures
• /
• v.13 no.2
• /
• pp.123-137
• /
• 2012

Steel plate-masonry composite structure is a newly-developed type of structural technique applicable to existing masonry buildings by which the load-bearing walls can be removed for large spaces. This kind of structure has been used in practice for its several advantages, but experimental investigation on its elements is nearly unavailable in existing literature. This paper presents an experimental study on the flexural behaviour of four steel plate-masonry composite beams loaded by four-point bending. Test results indicate that failure of the tested beams always starts from the local buckling of steel plate, and that the tested beams can satisfy the requirement of service limit state. In addition, the assumption of plane section is still remained for steel plate prior to local buckling or steel yielding. By comparative analyses, it was also verified that the working performance of the beam is influenced by the cross-section of steel plate, which can be efficiently enhanced by epoxy adhesive rather than cement mortar or nothing at all. Besides, it was also found that the contribution of the encased masonry to the flexural capacity of the composite beam cannot be ignored when the beam is injected with epoxy adhesive.