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Super304H is a promising candidate for heat exchangers in boiler systems used in thermal power plants operating at ultra-supercritical conditions, and the mechanical properties of its welded joint play a decisive role in the reliability of the thermal power plant. Herein, we report the tensile and fatigue properties of Super304H welded joint at elevated temperatures up to 750 °C, focusing on the operating temperature range of 500–700 °C. Our results showed that the tensile strength of the welded joint was almost the same as that of the base metal at all test temperatures, meeting the requirement for weld integrity, but a significant reduction in the elongation was induced in the welded joint due to non-uniform deformation that promotes deformation localization, leading to an early occurrence of necking. As for fatigue resistance, both the welded joint and base metal had comparable fatigue lives at high strain amplitudes (≥~0.4%) in the temperature range of 500–700 °C, whereas a drastic reduction in the fatigue resistance was observed in the welded joint at low strain amplitudes (

The dependency of the static residual tensile strength for the Glass Fiber-Reinforced Plastic (GFRP) laminates after impact on the impact energy level and indent shape is investigated. In this study, two different laminates, unidirectional, [0&deg, 2]s) and TRI (tri-axial, (&plusmn, 45&deg, /0&deg, )2]s), were prepared using the vacuum infusion method, and an impact indent on the respective laminates was created at different energy levels with pyramidal and hemispherical impactors. Impact damage patterns, such as matrix cracking, delamination, debonding and fiber breakage, could be observed on the GFRP laminates by a scanning electron microscope (SEM), and it is found that those were dependent on the impactor head shape and laminate structure. Residual in-plane tensile strength of the impacted laminates was measured and the reduction of the strength is found to be dependent upon the impact damage patterns. Furthermore, in this study, stress concentrations in the vicinity of the indents were determined from full-field stress distribution obtained by three-dimensional Digital Image Correlation (3D DIC) measurement. It was found that the stress concentration was associated with the reduction of the residual strength for the GFRP laminates.

The texture modification, caused by {10-12}–{10-12} double twinning, in rolled Mg–3Al–1Zn alloy was investigated by carrying out consecutive in-plane compressions along two orthogonal directions in combination with an electron backscatter diffraction measurement and a Schmid factor analysis. The results revealed that the Schmid law still governs twin variant selection, thereby controlling texture evolution, however, the specific crystallographic feature of {10-12} twinned region in which the c -axis orients to the compression direction with a variation of ±30° on the rolling plane and one prismatic plane including the rotation axis of {10-12} twinning, corresponding to an a -axis, is aligned almost parallel to the rolling plane gives rise to a significantly different texture evolution of {10-12}–{10-12} double twinned region as compared to {10-12} twinned region.

Characterization of the strain behaviour around the matrix and fibre holes in unidirectional glas fibre reinforced plastic composite laminates was carried out. The longitudinal and transverse strain fields around holes machined in tensile laminate specimen were determined by measurement of full-field strain distributions during tensile loads using the digital image correlation (DIC) technique. From these measurements, the strain concentration around the holes and strain gradient along the hole section were quantitatively determined and the strain fields during the failure evolvement process could be characterized. It was revealed that the longitudinal strain concentration of the matrix hole was relatively greater than that of the fiber hole, while the compressive transverse strain near the fiber hole was slightly larger than that near the matrix hole. Furthermore, it was found that the normalized peak strains, eyy / e∞, for both matrix and fiber holes were increased with increasing applied stress and that the strain for the fiber hole was slightly lower than that for the matrix hole. The subsequent failure processes for glas fibre reinforced plastic composite (GFRP) UD (uni-directional) composite specimen with a hole could be visualized and monitored by acquiring digital image correlation images. Die Charakterisierung des Dehnungsverhaltens in der Umgebung von Lochern in unidirektionalen GFK-Verbundlaminaten wurde durchgefuhrt. Die Langs- und Querdehnungsfelder um Locher in Laminatproben fur Zugversuche wurde durch Messung der gesamten Dehnungsverteilung wahrend Zugbelastungen mittels digitaler Bildkorrelation bestimmt. Basierend auf diesen Messungen konnten sowohl die Dehnungskonzentration um die Locher und der Dehnungsgradient entlang des Lochquerschnitts, als auch die Spannungsfelder wahrend der Versagensentwicklung quantitativ bestimmt werden. Es zeigte sich, dass die Langsdehnungskonzentration um ein Matrixloch vergleichsweise groser ist als bei einem Faserloch, wahrend die Druckquerdehnung in der Nahe des Faserlochs geringfugig groser war als in der Nahe des Matrixlochs. Weiterhin wurde festgestellt, dass sich die normierte Dehnungsspitze, eyy/e∞, fur Matrix- und Faserlocher mit zunehmender Spannung erhohte und dass die Dehnung fur das Faserloch geringfugig niedriger war als fur das Matrixloch. Das Versagensverhalten der GFK (glasfaserverstarkter Kunststoff) UD (unidirektionalen) Verbundprobe mit einem Loch wurde mittels DIC Bildern visualisiert und uberwacht.

A wind turbine blade is an important component in wind-power generation, and is generally exposed toharsh environmental conditions. Ultrasonic inspection is mainly used to inspect such blades, but it has beendifficult to quantify defect sizes in complicated composite structures. Recently, active infrared thermography hasbeen widely studied for inspecting composite structures, in which thermal energy is applied to an object, and aninfrared camera detects the energy emitted from it. In this paper, a calibration method for active optical lock-inthermography is proposed to quantify the size. Inclusion, debonding and wrinkle defects, created in a wind bladefor 100 kW wind power generation, were all successfully detected using this method. In particular, a 50.0φ mmdebonding defect was sized with 98.0% accuracy. Keywords: Wind Turbine Blade, Optical Infrared Thermography, Lock-in Method, Quantitative Defects Detection[Received: December 18, 2014, Revised: February 3, 2015, Accepted: February 17, 2015] *과 학기술연합 대원교(UST) ** ,항공기시스템공학 한국표준과학연구원 안전측정센터 Corresponding Author: Safety MeasurementCenter, Korea Research Institute of Standards and Science, Daejeon 305-340, Korea (E-mail: mychoi@kriss.re.kr)

Rolling temperature was found to play a decisive role in the precipitation hardening of Ti–Mo microalloyed hot-rolled high strength steel, despite identical chemical composition and phase transformation condition. The different microstructural features of prior austenite grain structure and dislocation structures inside austenite and/or ferrite grain, and the change of austenite/ferrite phase transformation characteristic, depending on rolling temperature, significantly influenced the precipitation characteristics of interphase-precipitated nanometer-sized carbides and consequently led to a totally different precipitation hardening effect.

The effect of texture control using {1 0−1 2} twins was capable of being significantly improved by thermal annealing. The removal of the residual tensile stress that developed inside these twins along the c-axis retarded detwinning activity during early deformation by increasing the detwinning stress, and this consequently led to a prolonged and enhanced activity of basal slip in the twinned region, increasing its contribution to the deformation. On the basis of this mechanism, the yield strength and elongation were improved simultaneously.

Acoustic emission(AE) has emerged as a powerful nondestructive tool to detect any further growth or expansion of preexisting defects or to characterize failure mechanisms. Recently, this kind of technique, that is an in-situ monitoring of inside damages of materials or structures, becomes increasingly popular for monitoring the integrity of large structures like a huge wind turbine blade. In this study, the activities of AE signals generated from external artificial sources was evaluated and located by new developed signal mapping source location method and this test is conducted by 750 kW full-scale blade. And a new source location method was applied to assess the damage in the wind turbine blade during step-by-step static load test. In this static loading test, we have used a full scale blade of 100 kW in capacity. The results show that the acoustic emission activities give a good agreement with the stress distribution and damage location in the blade. Finally, the applicability of the new source location method was confirmed by comparison of the result of source location and experimental damage location.

Impedance based monitoring technique was investigated to evaluate the damage occurring in wind turbine blade. In this study, PVDF film piezo sensors were patched on the 10 kW wind turbine blade, and impedance was measured over the frequency range of 1~200 MHz under fatigue loading. With applying fatigue loads on the blade, change in maximum deflection of the blade and local strain values could be obtained from the strain gages attached on the blade, and difference of the impedance signatures was also observed. From these data, it could be found that local damage or geometrical change in the blade structure happened. To quantitatively compare the impedance signature patterns, a statistical algorithm, scalar damage metric M was used. It was calculated from the impedance signatures considering fatigue loads and location of the sensors. The metric values were compared to correlate the metrics with damage in the blade.

To establish an effective operation and maintenance system for the wind turbine system, techniques for early detecting the damage, which may occur during its operation, may be required. In this study, responses of impedance, which can be a technique to early detect the damage, to the damage extension in the wind turbine blade were investigated through the full-scale structural test of the 100 kW wind blade. The impedance was measured with polyvinylidene fluoride film sensors with dimension of 25 × 20 mm2 patched on the blade skin. The damages were initiated along the trailing and leading edges and extended with increasing static load level. Impedance signatures varied with increasing the damage size were analyzed in the frequency ranging from 1 to 300 MHz. It was found that the patterns of the impedance signatures are remarkably dependent upon the static load level and sensor location. The change in the signatures was quantitatively quantified by the damage metric. The scalar metric values were closely correlated to the damage extension size and the sensor locations to the extended damage.

Acoustic emission is known as a powerful nondestructive tool to detect any further growth of preexisting cracks or to characterize failure mechanisms. Recently, this kind of technique, which is an in situ monitoring of integrity of materials or structures, becomes increasingly popular for monitoring the conditions of large structures such as a wind turbine blade. Therefore, it is required to find a symptom of damage progress before catastrophic failure through a continuous monitoring. In this study, acoustic emission technology was applied to assess the damage in the wind turbine blade during step-by-step static load test. In this static loading test, we have used a full-scale blade of 100 kW in capacity, and an attempt was made to apply a new source location method using a new algorithm with energy contour mapping concept. We also measured the deflection of blade tip by linear variable differential transformer (LVDT) and the strain of inner shear web in order to analyze the correlation between stress condition and damage identification. The results show that the acoustic emission activities give a good agreement with the stress distribution and damage location in the blade, especially in bonding edges around 1000–1500 mm far from the root. Finally, the applicability of new source location method was confirmed by comparison of the result of source location and experimental damage location.

Defects that occur during the manufacturing process or operation of a wind turbine blade have a great influence on its life and safety. Typically, defects such as delamination, pore, wrinkle and matrix crack are found in a blade. In this study, the detectability of the pores, a type of defect that frequently occur during manufacturing, was examined from the full field strain distribution determined with the image correlation technique. Pore defects were artificially introduced in four-ply laminated GFRP composites with fiber direction. The artificial pores were introduced in consideration of their size and location. Three different-sized pores with diameter of 1, 2 and 3 mm were located on the top and bottom surface and embedded. By applying static loads of 0-200 MPa, the strain distributions over the specimen with the pore defects were determined using image correlation technique. It was found the pores with diameter exceeding 2 mm can be detected in diameter.

In this study, the temperature-dependency of the tensile properties of a glass fiber reinforced plastic (GFRP) used in wind turbine blades was examined. The tensile strength, elastic modulus, and Poisson's ratio of the tensile specimen manufactured from uniaxial () and triaxial () laminate composite plates were measured at four different testing temperatures-room temperature, , , and . It was found that the tensile strengths and elastic moduli of the uniaxial laminates were greater than those of the triaxial laminates over the testing temperature range. The tensile strength of the two laminates was significantly dependent on the testing temperature, while the dependency of the elastic modulus on the temperature was insignificant. Furthermore, it could be considered that the Poisson's ratio changed slightly with a change in the testing temperature.

Fatigue life of GFRP (glass-fiber reinforced plastic) composites used in wind turbine rotor blades has been evaluated considering the glass fiber orientations. Three different laminate composites with the respective laminating orientation of 0°, ±45°, and 0°±45° were prepared using vacuum infusion method. Tensile properties and S-N curves for these composites were experimentally determined at room temperature. From the tensile tests, it was found that tensile properties were greatly dependent upon the fiber orientation and the tensile strength of unidirectional composite was the largest and bidirectional (45°) composite was the weakest among three composites. The fatigue properties were determined under constant amplitude load control at different stress ratios, R, of 0.5, 0.1 and −0.2. The properties also show the dependency of stress ratios and fiber orientation. The fatigue life diagrams of these three composite were relatively well presented with the double logarithmic S-N curve. The linear slopes of the respective S-N curves for three composite were not greatly different. The fatigue limits for the composites were evaluated and predicted with linear Goodman and Gerber diagrams.

This study detected SCC defects of dissimilar metal welded(STS304 and SA106 Gr. b) pipes using the ultrasonic infrared thermography method and the lock-in image treatment method among infrared thermography method. The infrared excitement equipment has 250 Watt of output and 20 kHz of frequency. By using the ultrasound infrared thermography method, the internal defects of dissimilar metal weld joints of pipes used at nuclear power plants could get detected. By an actual PT test, it was observed that the cracks inside the pipe existed not as a single crack but rather as a multiple cracks within a certain area and generated a hot spot image of a broad area on the thermography image. In addition, UT technology could not easily defects detected by the width of fine hair cracks. but, ultrasound infrared thermography technique was defect detected.

Key Words: Wind Turbine Blade(풍력블레이드), Dual-Axis Loads(이축하중), Puck Failure Criterion(Puck파손지수), Composite Laminate(복합적층), Static Behaviors(정적거동), Inter-fiber FailureCriterion(모재파손지수), Fiber Failure Criterion(섬유파손지수)초록: 블레이드의성능평가를위하여실제사용환경과근접한하중모사에따른이축하중의필요성이제기되고있으며, 본본문에서는이러한이축하중에따른블레이드의거동을해석하였다. 100kW급풍력블레이드를대상으로하였으며, ANSYS를사용하여정적거동을분석하였다. 정적거동은파손해석과좌굴거동으로분석하였으며, 파손평가는Puck이제안한파손방정식을이용하여섬유파손과섬유간파손기준을검토하였다. 이축하중의하중비가증가함에따라루트부단면이변하는후연부와루트에서Z+ 3300~3600인지점에서응력이상대적으로크게나타났다. 또한이축하중비가증가함에따라블레이드좌굴지점이루트부쪽으로이동되고있음을확인하였다. 따라서블레이드의사용신뢰성을검증하기위해서는이축하중에의한시험이요구되고있음을본해석을통해서확인하였다.Abstract: For the assessment of the performance of a wind-turbine blade, a simulated loading test may be required. Inthis study, the blade behavior was investigated through numerical analysis using a dual-axis loading test, closelysimulating the real operation conditions. The blade structure for the 100-kW-class wind-turbine system was modeledusing the finite element (FE) program ANSYS. The failure criteria and buckling analysis under dual-axis loading wereexamined. The failure analysis, including fiber failure and inter-fiber failure, was performed with Puck's failure criterion.As the dual-axis load ratio increases, the relatively increased stress occurs at the trailing edge and skin surface 3300–3600 mm away from the root. Furthermore, it is revealed that increasing the dual-axis load ratio makes the locationthat is weakest against buckling move toward the root part. Thus, it is seen that the dual-axis load test may be anessential requirement for the verification of blade performance.

Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.

Using three-dimensional (3-D) FE analyses, this paper provides a method for analyzing the effects on stresses and strains produced by angular and concentric misalignment of a test specimen for a torsion test. To quantitativele compare of the FE results, the average bending strain for the angular, concentric, and combined misalignment was proposed. To verify the effects of axial misalignment of the test specimens, we used both circular and tubular specimens. From the FE results, we proposed general predictions for the effects caused by the various types of axial misalignment and its direction. In addition, we confirmed the effect of initial yielding moment based on the initial yielding condition for axial misalignment of specimens in torsion tests.

This paper presents the results of tensile tests for lead zirconate titanate (PZT)/Platinum (Pt) thin films of 2.15 μm thickness in atmospheric air at room temperature. An axial loading tester developed by the authors was used for the tests. The tester was equipped with a load cell with a maximum capacity of 0.5 N and a non-contact position measuring system based on the principle of capacitance micrometry. Furthermore, the tester was equipped with a CCD (charge-coupled device) system for measuring the displacement of the gage length. Specimens with three different widths (50, 100 and 150 μm) were fabricated to study the size (width of specimen) effects. The elastic moduli of the specimens with 50, 100 and 150 μm width were 72.8 ± 3.7, 75.0 ± 1.3, 73.3 ± 1.8 GPa, respectively. In addition, the ultimate tensile strength of the specimens with 50, 100 and 150 μm width were 263.4 ± 21.1, 238.6 ± 4.5, 221.1 ± 13.9 MPa, respectively. It was observed that the width of specimen has little effect on the elastic modulus of PZT/Pt thin films but has an effect on the ultimate tensile strength of PZT/Pt thin films and the ultimate tensile strength decreases as the width increases. It was assumed that the scatter in the ultimate tensile strength of 50 μm width was attributed to delamination of PZT/Pt layers before the fracture in the tensile test. The 0.2% offset yield strength could not be measured because the PZT/Pt thin film is very brittle.

Tensile and fatigue behaviors of the copper film coated by tin (Sn) were investigated considering S-N relationships and scanning electron microscope (SEM) observation of fracture surfaces. The fatigue behavior was investigated considering the effect of load ratio, R. The specimen of 2000 μm width, 8000 μm length and 15.26 μm thickness was fabricated by etching process. Tensile properties were measured using the micro-tensile testing system and in-plane electronic speckle pattern interferometric (ESPI) system for measuring the tensile strain during the test. The fatigue tests of the film were carried out in load-control mode with 40 Hz at three different stress ratios of 0.05, 0.3 and 0.5. The S-N curves, including the slope of the curve and fatigue limit, at the respective stress ratios were obtained. These curves were dependent on the load ratio. Empirical relationships indicating the dependency of the fatigue limit and S-N curve on the load ratio were suggested in this study. SEM observation of the tensile fracture surface showed that the cross-sectional area of the testing section was necked in the direction of the film thickness (i.e. parallel to the substrate surface normal) and some ductile dimples in the fracture surface were present. The fracture of the copper film under cyclic loading was progressed in the transgranular fracture mode.

The anisotropy in the fatigue behavior of rolled Mg–3Al–1Zn alloy between the rolling direction and normal direction to the rolling plane was investigated. The {10-12} twinning–detwinning characteristics were found to play key roles in the anisotropic fatigue deformation behavior by inducing a change in the predominant plastic deformation mechanism, which controlled the flow stress and finally influenced the fatigue resistance by generating mean stress. Energy-based approach was successfully used to describe anisotropic fatigue life behavior.

Many important mechanical properties of materials including tensile strength are procedure dependent. This means that test results are traceable to standard test procedures rather than SI base units. However, most of the test procedures described in the current international standards such as ISO and ASTM are not suitable to be adopted as a primary standard procedure since they were developed to be used at industrial sites as well as testing laboratories. The Working Group on Hardness under CCM is working to develop a primary standard procedure to establish traceability for hardness measurement through key comparison among NMIs. These kinds of activities are necessary for other properties such as tensile strength, impact strength, creep and fatigue for the establishment of a traceability system. KRISS has been trying to establish a traceability chain in the measurement of materials' mechanical properties through international round-robin tests, the development of certified reference materials and uncertainty evaluation. In this paper, the activities of KRISS for establishing traceability and those of related ISO technical committees are described.

Estimation of tensile properties measurement uncertainty of material was carried out. Sources of uncertainty affecting the measurement of tensile properties were classified and analyzed. The models for uncertainty evaluation of measurands to be determined from tensile test, such as elastic modulus, yield strength and tensile strength, were suggested and derived from the mathematical relations, corresponding to the respective measurands, and the measuring quantities by calculating each sensitivity coefficient of the quantities. Based on these models, the uncertainty of the tensile properties was evaluated from the experimental data of SUS316LN determined according to ISO 6892.

Fatigue limit of the copper film coated by Sn was estimated using Goodman diagram and Gerber diagram. To obtain the high cycle fatigue life curve, S-N curve, of the film, the high cycle fatigue test was carried out by applying the constant amplitude load to the film specimen with three different stress ratio of 0.05, 0.3 and 0.5 and the frequency of 40 Hz at room temperature in air. The free-standing film specimen 15.26 thick was fabricated by etching process. The fatigue limits and S-N curves at the respective stress ratios were determined from the experimental works. It was shown that the S-N curves were dependent on the stress ratio and the fatigue limit was increased with decreasing the stress ratio. The dependency of the fatigue behavior was presented in empirical relationship. Using these relationships, the fatigue limit was predicted.

Micro-tensile properties of Au thin films were measured using a membrane deflection testing system. During the membrane deflection test, the deflection of the film was measured by an out-of-plane electronic speckle pattern interferometric (ESPI) system. From the measurement, the tensile loads and strains exerted on the membrane film during the deflection of the film could be determined. Quantitative analysis of the phase maps of the ESPI speckle patterns corresponding to the respective different deflection levels provided the deflection distribution along the testing section of the film. Test pieces were fabricated by electromachining process using 0.5 and 1. 0 μm thick Au films which were deposited on the silicon wafer by sputtering technique. Tensile properties, including elastic modulus, yield and tensile strength, were evaluated in the tensile stress-strain curve determined from the load-deflection relation. These properties were compared to those obtained from the micro-tensile tests. It was found that the yield and tensile strengths obtained from the deflection tests were lesser than those from the micro-tensile tests. Furthermore, the thickness effect, showing the increasing tendency of yield strength with decreasing thickness, was experimentally examined.

In this study, fatigue tests were performed for NiCo alloy which is commonly used in probe tips of test machines of semiconductors. The smooth specimens were fabricated by MEMS process including electro-plating process on a single-side polished 6 inches (100) silicon wafer. The NiCo thin film consists of about 66.2 % Ni and 33.8 % Co. The specimen is 2000 μm long, 9 μm thick and 100 μm wide. The tests were performed using a novel test procedure, a structure of the specimen is easy to manipulate, align and grip a thin-film and a test machine proposed by the authors. The closed-loop feedback control of the magnetic-electric actuator allowed load-controlled and high cycle fatigue tests with 5 Hz frequency, in ambient environment and with a stress ratio of R = 0.1. The fatigue strength coefficient and exponent were 1324 MPa and -0.0558, respectively. In a fatigue test of thin film, it is difficult to perform the fatigue test at R = -1. However, the result of the fatigue test at R = -1 should be required when fatigue life prediction is performed under variable loading. Therefore, in this study, the modified Goodman method, Gerber method and Soderberg method were considered to investigate which method is most reasonable when mean stress is considered.

Cyclotron generated MeV protons were used to evaluate the mechanical behavior such as tensile strength and elongation of ITO/aluminum-coated Kapton that is known to be one of the most useful polymers for space missions. The mechanical properties (tensile strength and elongation) of specimens irradiated with high-energy protons were lower then those irradiated with low energy protons. A considerable increase in the mechanical properties was found at irradiation with lower fluencies that is explained by the unique characteristics of the molecular structure of Kapton. The ITO and aluminum coatings on Kapton, while contributing to the mechanical strength of the coated Kapton, were found to be affected by the proton irradiation.

Cyclic fatigue parameters governing fatigue crack propagation behavior under out-of-phase biaxial fatigue loading has been investigated considering the crack propagation direction and the growth rates. The fatigue crack was propagated by employing out-of-phase cyclic tensile-torsional loads with various phase differences to the thin-walled tubular specimen. Using two crack gages mounted near a notch, the crack propagation was measured and crack opening behaviors were monitored by unloading compliance method. The directions and growth rates of the fatigue crack propagated under respective biaxial loading conditions were examined using several cyclic fatigue parameters, including equivalent stress intensity factor range, ΔKeq, crack tip opening displacement range, ΔCTD, minimum strain energy density factor range, Δ S min . It is found that the parameters, ΔCTD and Δσθθ, max , might be useful for prediction of the crack directions and the fatigue crack growth rates were relatively well correlated with ΔKeq and Δ S min . On the other hand, the crack opening levels under in-phase loading could be relatively clearly determined, while it was ambiguous to define those under out-of-phase loading.

The process adaptability of Cu(0.7–1.2 at.% Mg) alloy films for microelectronics interconnects was investigated by comparing their electrical properties, interfacial adhesion strength, time dependent dielectric breakdown (TDDB) reliabilities, and interfacial microstructure with those of pure Cu. The resistivity of the Cu(Mg) films decreased to ∼ 2.0 μΩ cm after annealing them in a vacuum at 350 °C for 10 min. The interfacial debonding energy measured by the four-point bending method was approximately 20.1 J/m 2 for Cu(Mg)/SiO 2 which is a factor of 2.3 larger than that of Cu/SiO 2 interfaces. The median time to failure of Cu(Mg)/SiO 2 in the TDDB test was much larger than that of pure Cu/SiO 2 . The diffusion of Cu into the dielectric was found to be inhibited by the continuous very thin Mg–O layer formed at the Cu(Mg)/SiO 2 interface, which improves the interfacial adhesion, and ultimately leads to better electrical reliabilities.

Adhesion strength for single layer ceramic capacitor sheet, used in MLCC(Multilayer Ceramic Capacitor), was measured by peel tests. The peel strength was measured during the separation of the ceramic sheet from the PET film using the peel testing system developed in this study. The sheet specimen was adhered on the glass jig floating on the liquid media, which was designed to minimize the friction, and the specimen was pulled up by micro-actuator. In this study, the dependency of the specimen width, peel angle and testing speed on the adhesive strength was experimentally investigated. It was found that the adhesive strength for the ceramic sheet is nearly identical, irrespective of the specimen width ranged from 5 to 20 mm, and the adhesive strength was increased with increasing testing speed. Furthermore, the strength was shown to be dependent on the peel angle.

We tried to apply the nanoindentation technique to yield strength characterization by modifying a previous research. Although the yield strength determining technique developed by Kramer et al. has been successfully demonstrated for large scale indentations on bulky metals, its applicability is still doubtful to nanoscale indentations on thin films with severe roughness, anisotropy, and interfacial constraint. In order to overcome these problems, we combined the nanoindentation technique with a three-dimensional indent visualization technique in this study. Nanoindentation tests were performed for Au and TiN thin films and their corresponding indents were scanned by using an atomic force microscope. From the three-dimensional pile-up morphology, a circular pile-up boundary was measured and input into the yield strength formulation as an effective yielded zone radius. The yield strengths calculated were directly compared with those from the microtensile test.

A nondestructive rod compression has been proposed as a new strength characterizing technique for in-service components. Using electrical discharge machining, milling machining, and stamping, it was possible to machine small rods, typically about 0.5 mm in both diameter and height on the target surface. Static compressions of the rods were carried out using a flat punch and their deformation behaviors were recorded as load-displacement curves. Referring to initial dimension of the rods, engineering stress-strain curves implying the yield strengths were calculated from the deformation curves. Surface yield strengths from the rod compressions were directly compared with reference compression results and their slight discrepancies were discussed from the influences of pre-deformation and damage of the rod and additive compliance of the base.

Effects of crack on static behavior in steel box girder were investigated to identify the possibility of crack detection and location using conventionally measured static data including deflection and inclination. Finite element analysis with finely meshed 3-D models and experiments were performed for steel box girder with crack. To eliminate the variation according to load magnitude, compliance technique was applied to analysis of the result. Through this study, the quantitative relationship between crack size and structural responses of deflection and inclination were obtained as a form of relation-curve. This relation-curve can be utilized to evaluate crack size in the steel box girder bridge. The results also demonstrated that the location of crack can be estimated by static measurement.

The integrity assessment method for beam-like structures using continuous wavelet transform (CWT) is proposed. CWT is applied to the response acceleration of a structure to decompose the response acceleration correspond to each scale. The curvature difference of the normalized energy for each member caused by structural degradation clearly indicated the location of damaged members in the structure. It is shown that the proposed method can identify damaged members without performing complicated dynamic analyses which usually require significant effort and time.

Fatigue crack propagation behavior under cyclic tensile or torsional loading with biaxial static loads has been investigated. Two different biaxial loading systems, i.e. cyclic tensile loading with static torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular specimens. The crack propagation was measured by two crack gages mounted near the notch and crack opening level was measured by unloading compliance method. The directions of the fatigue crack propagated under respective biaxial loading conditions were examined and the growth rates were evaluated by using several cyclic parameters, including equivalent stress intensity factor range, Keff, crack tip opening displacement range, CTD, minimum strain energy density factor range, Smin. Furthermore, the growth rates were evaluated by effective cyclic parameters considering crack closure. It was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no influence on the propagation directions of the cracks. Furthermore, it was shown that the fatigue crack growth rates under biaixial faigue loading were well expressed by using the cyclic fatigue parameters, Keq,eff, CTDeff, Smin,eff considering crack closure effect.

To measure the micro-mechanical properties for micro/nano materials, out-of-plane ESPI system and micro-strip bend testing system were developed. For the bending system, PZT actuator was controlled with the stroke resolution of 0.6 nm and out-of-plane ESPI system was developed in compact and portable type. To quantitatively analyze the out-of-plane ESPI fringe patterns, 4-bucket technique was used and unwrapped phase map was obtained. Electrolytic copper foil with the thickness of 18 μm was used for preparation of the strip bend specimen with length of 8 mm and three different widths of 2, 3 and 5 mm. The strip bending tests showed that the out-of-plane deflection in the bend specimen was measured with a maximum of 8 % in error. Furthermore, from the experiment, the variation of the deflection along the supporting span could be determined and significant region was linear.

유기재료(organic material)는 위성이나 우주비행체의 열을 조절하고 우주환경에 직접 노출되는 것을 차단하기 위하여 가장 흔하게 사용되는 재료 중 하나이다. 본 논문에서는 지상설비를 이용하여 모사한 우주환경에서 유기재료의 물성변화를 관찰하였다. 대표적인 위성용 유기 열조절 재료 중 하나인 2mil ITO(Indium Tin Oxide) coated aluminized KAPTON을 실험 대상으로 선택하였다. 양성자에 의한 단일 우주환경효과를 실험하기 위하여, 한국 원자력의학원의 MC-50 싸이클로트론(cyclotron)을 이용하여 양성자를 조사(irradiation)하였으며, 조사조건은 지구궤도 주변 최고의 양성자 발생기록인 1972년 8월의 최고치 상황을 적용하였다. 조사에너지는 평균 관측에너지인 30MeV으로 고정하였으며, 등가 조사량은 우주노출 시간 1년, 3년, 5년 및 10년을 기준으로 설정하였다. 분석과정은 인장강도를 측정하여 정량적 물성저하를 확인하였고, 전계방출 전자주사현미경 등으로 결정성변화와 노출표면의 손상을 분석하였다. 【The organic material is one of the most popular material for the satellites and the spacecrafts in order to perform the thermal management, and to protect direct exposure from the space environment. The present paper observes material property changes of organic material under the space environment by using ground facilities. One of the representative organic thermal management material of satellites, 2 mil ITO(Indium Tin Oxide) coated aluminized KAPTON was selected for experiments. In order to investigate the single parametric effect of protons in space environment, MC-50 cyclotron system in KIRAMS(Korea Institute of Radiological and Medical Science) was utilized for the ion beam irradiation of protons and ion beam dose was set to the Very Large August 1972 EVENT model, the highest protons occurrence near the earth orbit in history. The energy of ion beam is fixed to 30MeV(mesa electron volt), observed average energy, and the equivalent irradiance time conditions were set to 1-year, 3-year, 5-year and 10-year exposure in space. The procedure of analyses includes the measurement of the ultimate tensile strength for the assessment of quantitative degradation in material properties, and the imaging analyses of crystalline transformation and damages on the exposed surface by FE-SEM(Field Emission Scanning Electron Spectroscopy) etc.】

Fatigue crack initiation and propagation behavior around a hole subjected to various biaxial fatigue loading modes has been investigated considering the effect of the biaxial static stress. Two different biaxial loading systems, i.e. cyclic tensile loading with static torsional load and cyclic torsional loading with static tensile load, were employed to thin-walled tubular specimens with a circular notch. Variation of the initiaiton and propagation directions of the crack around a hole under these loading ssytems was examined. The initiation directions were observed using replication technique and the crack propagation was measured by two crack gages mounted near the notch. It was found that the biaxial static stress superimposed on the cyclic tensile or torsional loading tests has no influence on the initiation and propagation directions of the cracks around a hole. The fatigue crack initiation and propagation direction under cyclic loading with biaxial static load can be very well explained by the maximum of tangential stress range, Dsqq,max. Furthermore, it was shown that the fatigue crack growth rates under biaixial faigue loading becomes higher with increment of biaxial static load.

To determine the micro-mechanical properties for micro/nano materials, it may be essential to measure the strain/deformation during micro-mechanical testing. Therefore, in this study, continuous measurement of in-plane tensile strain in micro-sized specimens of thin film materials was introduced using the micro-ESPI technique. TiN and Au thin films 1 and 0.47µm thick, respectively, were deposited on the silicon wafer and fabricated into the micro-sized tensile specimens by the electromachining process. The micro-tensile loading system and micro-ESPI system were developed to measure the tensile strain during micro-tensile loading. Micro-tensile stress-strain curves for these materials were determined using the algorithm for continuous strain measurement. Furthermore, the new algorithm for enhancing the sensitivity to measurement of in-plane tensile strain was suggested. Using the algorithm, micro-tensile strain data between interfringes were calculated. It is shown that the algorithm for enhancement of the sensitivity suggested in this study makes the sensitivity to the in-plane tensile strain increase.

This investigation aims at doing some durability and damage tolerant (DaDT) tests with 2124-T851 aluminum specimens having corner cracks under a random history, correlating with the simulation results from AFGROW and then drawing some conclusions from those comparisons. Two hydraulic actuators and a homemade Wood’s alloy grip are employed to do the test. The surface crack lengths are measured by a traveling microscope and used as a reference for the later fractography. The crack penetration and the total lives are about 17 and 27 blocks, respectively. The crack length and depth are evaluated by the fractography after completing each test and used to grasp the shape change. The Forman equation is used to simulate the fatigue crack growth behavior according to a bearing stress ratio extensively. The crack penetration life is decreased as the bearing stress ratio increases. The crack aspect ratio is very dependent on the bearing stress ratio. The LBH loading accelerates the fatigue crack growth in the crack depth direction but decelerates that in the length direction until crack penetration.

Fatigue crack initiation around a hole subjected to biaxial fatigue loads with a phase difference was investigated. Axial and torsional biaxial fatigue loads with different phase differences and biaxiality of 1/√3 were applied to thin-walled tubular specimens. Five phase differences of 0, 45, 90, 145 and 180 degrees were selected. Directions of the fatigue crack initiation around the hole were found to approach to the circumferential direction of the specimen with increment of the phase difference for fatigue tests with phase differences less than 90. Whereas directions for tests with phase differences greater than 90 got away from the circumferential direction and those were symmetric to the directions for tests with phase difference less than 90. . Furthermore, it was shown that the fatigue initiation life decreased with increment of phase difference for fatigue tests with phase differences less than 90, but it increased for tests with phase difference greater than 90. The crack initiation direction can be successfully explained by using the direction of the maximum tangential stress range obtained around the hole and at far-field.

Governing parameters for determination of the location of crack initiation and direction of crack initiation were investigated by performing fretting fatigue tests and analysis on Al 2024-T351. Fatigue tests were carried out using biaxial fatigue machine. It was shown that the dominant fatigue crack tended to initiate at the outer edge of one of the four bridge pads, growing at an angle beneath a pad, before turning perpendicular to the orientation of the axial load. Distribution of stresses generated during fretting fatigue loading along the interface was calculated by elastic FE simulation. It can be known that the location of crack initiation can be predicted by using the maximum tangential stress range. Futhermore, the crack initiation direction can also be predicted by a maximum tangential stress range.