Advances in Fracture and Failure Prevention

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Authors: Kwang Hwan Oh, C.K. Jung, Y.C. Yang, Kyung Seop Han
Abstract: This study investigated acoustic emission behavior during fatigue crack growth test under constant and variable amplitude loading in 304 stainless steel. To describe the acoustic emission behavior, counts rate(dη/dn) was related with stress intensity factor range (SIFR, ΔK) in log-log plot. As a result of test, the relationship was represented a curve, which forms rise and fall behavior in counts rate as the SIFR increases. AE response to a single overload was sudden drop and slow recovery in counts rate, which was similar to crack growth retardation behavior. Under block loading, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental results indicated that stress intensity factor controls the counts rate (dη/dn) as well as crack growth rate (da/dn) regardless of load range or crack length.
Authors: Kwang Joon Yoon, Kyu Young Kim, Nam Seo Goo, Hyun Chul Park, J.R. Haw
Abstract: This paper is concerned with the fatigue characteristics of LIPCA (LIghtweight Piezo-Composite Actuator) device system. LIPCA device system is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (coefficient of thermal expansion) and base layers with high CTE. The advantages of the LIPCA design are using the lightweight fiber reinforced plastic layers without compromising the generation of high force and large displacement and to have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use resin prepreg system. To investigate the degradation of actuation performance of LIPCA due to the repeated fatigue loading, the repeated loading tests up to several million cycle were performed and the actuation displacement for a given excitation voltage was measured during the test. The fatigue characteristics was measured using an actuator test system consisted of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system and evaluated.
Authors: Chun Yi Ruan, Hui Ji Shi
Abstract: This paper applies subjective speckle method to investigate the effects of temperature and stress on the initial process of stress corrosion of an aluminum alloy 2024-T3. Considering the sensitivity of this observational method, the roughness of surface is used to represent the degree of corrosion. Stress corrosion experiments are carried out by displacement-controlled loading on specimens of Al2024-T3 in the thickness of 2 mm board in 3.5% sodium chloride solution. The solution is controlled at several temperature levels from 22°C to 80°C. The results of experiments show that: the rate of corrosion increases fast concomitance the increase of temperature when stress is constant; at the same temperature and the load range used, the effect of stress is not very evident on the rate of corrosion; the effect of temperature is higher on the rate of corrosion in the stress corrosion than that in general corrosion without stress.
Authors: Rui Chun Duan, Hui Ji Shi
Abstract: In order to investigate how the corrosion dramatically reduces fatigue resistance of a 2024-T3 aluminium alloy, a series of corrosion experiments in a 3.5 wt% NaCl solution with different steeping time, and subsequent fatigue experiments under uniaxial cyclic load have been performed with the laminate specimens. The nucleation and growth of corrosion pits are found to occur mainly at the grain boundary. The optical micrographs of the experiments show that the fatigue micro-crack initiates on the bottom of the pit, expands its way through the neighbouring pits that located at the slip direction and then forms a main fatigue crack that leads to fracture. The similar corrosion experiments are also performed at different solution temperatures: 22 °C, 40°C, 60°C, and 80°C respectively. The effects of the steeping time and solution temperature on the fatigue life are investigated.
Authors: Jeong Pyo Kim, Bong Kook Bae, Chang Sung Seok
Abstract: It's required that mechanical properties of in-service facilities maintain the safety of operation in power plants as well as chemical plants. In this study the four classes of thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method at 630°C. Ultrasonic tests, tensile tests, KIC tests and hardness tests were performed in order to evaluate the degree of the material degradation. The mechanical properties deteriorated as the specimen degraded, but the attenuation coefficient and the harmonic generation level of the ultrasonic signal increased. The non-linear parameter derived from the harmonic generation level is especially sensitive and will be a good parameter to evaluate the material degradation.
Authors: Xia Ting Feng, Shao Jun Li, Sih Li Chen
Abstract: Study of effect of water chemistry corrosion on strength and cracking characters of rocks is an important aspect to improve long-term stability of rock engineering and increase efficiency of geothermal and petroleum developing. This paper reviews new progress of study on this topic. It includes effect of water chemical corrosion on triaxial compressive strength, uniaxial compressive strength, shear strength, tensile strength, and cracking characteristics of rocks. The mechanism of water chemical corrosion is analyzed. The further study on this topic is also discussed.
Authors: Dong Ho Bae, J.H. Park
Abstract: In order to develop a corrosion fatigue design method and estimate reliability of TMCP steel using as the material of heavy industries and plants, its electrochemical corrosion characteristics and determination of corrosion fatigue design criterion were investigated. And, a corrosion fatigue design method of TMCP steel was also investigated. From the results, the corrosion characteristic of TMCP steel is very susceptible in 3.5wt.% NaCl solution. Its susceptibility was linearly increased with the solution temperature increase. Corrosion fatigue strength in 25°C, 3.5wt.% NaCl solution is very lower than that of in air. And also, it was decreased with loading frequency decrease in the same environment. It was found that corrosion fatigue strength and life of TMCP steel is predictable by using the S-N curve of fatigue strength in air. Therefore, it is expected that the developed corrosion fatigue design method for TMCP steel will be useful for safe design and reliability assessment of the industrial facilities and structures.
Authors: Jae Yeol Kim, S.U. Yoon, Kyeung Cheun Jang, Myung Soo Ko, Jae Sin An
Abstract: In the present study, a Nd;YAG Laser (pulse type) was used to emit ultrasonic signals to a test material. In addition, a total ultrasonic investigation system was designed by adopting a Fabry-Perot interferometer, which receives ultrasonic signals without any contact. For non-destructive test SM45C, which contains some flaws was used as a test material. Because it is easy to align light beam in receiver, and the length of the light beam does not change much even if convex mirror leans towards one side, confocal Fabry-Perot interferometer, which has stable frequency, and PI control are used to correct interfered and unstable signals from temperature, fluctuation and time shift of laser frequency. Stable signals are always obtained by the feedback of PI circuit signals in the confocal Fabry-Perot interferometer. The type, size and position of flaws inside the test material were examined by achieving the stabilization of an interferometer. This study presented a useful method, which could quantitatively investigate the fault of objects by using a Fabry-Perot interferometer.
Authors: Zheng Li, Shuman Xia, J.W. Fan, Xian Yue Su
Abstract: In this paper, the continuous wavelet transform by the Gabor wavelet is applied to analyzing flexural waves in a cantilever beam with an edge crack. The amplitudes and arrival times of the incident, reflected and transmitted waves at a certain frequency are extracted from the wave signals to identify the damage location exactly and estimate the damage extent qualitatively. The results show that this is an effective damage detection method and can be extended to the damage detection of complicated structures.
Authors: Jin Kyung Lee, Young Chul Park, Joon Hyun Lee, Sang Ll Lee, Kwan Do Hur
Abstract: Tensile residual stress occurring due to the difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composites (MMC). In this study, TiNi alloy fiber was used to solve the problem of the tensile residual stress of TiNi/Al6061 shape memory alloy(SMA) composite as the reinforced material. TiNi alloy fiber improves the tensile strength of a composite by inducing compressive residual stress in the matrix using its shape memory effect. The fixture was made to hold TiNi shape memory fiber uniformly. Some tensile test specimens with several volume fractions are made by the hot pressing method under the optimum processing condition. In order to generate the compressive residual stress in TiNi/Al6061 SMA composite, 1%, 3% and 5% pre-strain was added in advance. It was evaluated the effect of compressive residual stress corresponding to pre-strains variation using the acoustic emission(AE) technique. AE technique was also used to clarify the damage behavior and the microscopic failure mechanism of TiNi/Al6061 SMA composite. In addition, a two-dimensional AE source location technique was applied to measure the position of the crack initiation and propagation in composites.

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