Fracture and Strength of Solids VI

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Authors: Seon Jin Kim, Seok Hwan Ahn, Yu Sik Kong, Sang Woo Kwon
Abstract: Constant K fatigue crack growth tests were performed by applying an intermediate multiple overloads for S45C steel. The purpose of this study is to investigate effects of specimen thickness at various baseline stress intensity factor range levels (Kb), the application position of the overload (a/W) and the application frequency of the overload (OLHz) on fatigue crack growth retardation behavior. The principal results are summarized as follows. The number of retardation cycles for the constant baseline stress intensity factor level (Kb ) decreases with increasing specimen thickness. The normalized number of retardation cycles ( Nd / Nc ) decreases with increasing specimen thickness. But, at Kb = 45 MPa(m)1/2, the cycle increases with increasing specimen thickness.
Authors: Byeong Choon Goo, Sung Yong Yang, Dong Hyung Lee
Abstract: We surveyed literature and proposed a procedure to identify the fatigue properties from the Brinell hardness and Young’s modulus. And we developed a parameter similar to the S.W.T. parameter with the Brinell hardness and Young’s modulus. Using the parameter and finite element analyses, we evaluated fatigue lives of four kinds of welded joints. The predicted results are in a good agreement with experimental results.
Authors: Do Hyun Jung, Sell Song, Pilsu Shin, Sung In Bae
Abstract: Automatic belt tensioner for stabilization of Engine accessory belt system is made increase its life, decrease noise and vibration and increase its commercial value. Therefore, it is important finding test mode to assess life of automatic belt tensioner. However, measurement and analysis test result in practical test condition on real road needs requiring much test time and finance. In this study, there is analyzed and established test mode which is loaded measured equivalent damage in real working condition, compared test condition of pre-established test mode and FTP- 75 mode of fuel efficiency test and verified advantages and disadvantages of each mode. Because FTP-75 Mode is for measuring fuel efficiency related with engine, applying FTP-75 mode is estimated suitability for test of engine accessory. Comparison and assessment of damage is investigated structure and pulley part. Equivalent damage is calculated with Palmgren-Miner Rule and representative stress method, test condition of automatic belt tensioner is investigated. This investigation is regarded as being useful to life evaluation of both automatic belt tensioner and other engine accessory component.
Authors: Hyun Woo Lee, Se-Jong Oh
Abstract: Crack growth behavior of S45C notched tubular specimen was studied to predict fatigue crack initiation and crack propagation under biaxial loading conditions. Stress-strain field near the hole was analyzed by ANSYS. The crack initiation lives and the crack initiation locations were predicted from strain based theories, and the analysis results were compared with the test results. Crack propagation behaviors were studied to understand the reason of crack branching and crack growth rates changing under biaxial loading conditions. Crack growth direction was also observed to find the governing factors of the fatigue damage under biaxial loading conditions.
Authors: Sheng Wu Wang, Ai Ling Wen, Shinichi Nishida, Nobusuke Hattori
Abstract: Nearly 90% of failures of machines and mechanical parts are caused at the area of stress concentrated in the structural components [1]. Hence, it is important to investigate the method of improving fatigue strength for notched parts, and method of evaluation the fatigue strength of notched parts for mechanical engineering. In this paper, the tests were carried out for improving the fatigue strength of specimens, with the hole notches that have been chamfered by die-pressing. The fatigue strength of notched part is enhanced to around 100% by die-pressing, comparing with notched specimen without die-pressing. Based on the above results, the new method for evaluation the fatigue strength with both the effects of work hardening and residual stress caused by the cold working. The estimated results by the method revealed good agreement with the tested results.
Authors: Priyo Tri Iswanto, Shinichi Nishida, Nobusuke Hattori, Yuji Kawakami
Abstract: In order to study the effect of plastic deformation on fatigue behaviors of plastically deformed specimen, bending fatigue tests had been performed on notched deformed stainless steel specimens. Also pulsating fatigue tests were done on notched non-deformed specimens to evaluate the influence of mean stress on fatigue behavior of notched non-deformed specimens. The result showed that according to increase of deformation value, the fatigue limits of these specimens also significantly increase. Fatigue limit of rolled specimen does not linearly increase with increase in plastic deformation value. Based on fatigue limit diagram, the effect of compressive residual stress on fatigue limit improvement of stainless steel is higher than that of work-hardening. In case of non-deformed specimen, when the compressive mean stress increases, the fatigue limit and the number of cycles to failure increase. In case of tensile mean stress, this kind of mean stress decreases the fatigue limit.
Authors: B.R. Hu, J.Z. Liu, B. Chen, L.F. Wang, Xue Ren Wu
Abstract: Experimental and analytical studies were made on the fatigue behavior and life prediction for argon-arc welded titanium alloy joints, TA15. High cycle fatigue tests at two stress ratios, R=0.5 and 0.06, were carried out on smooth specimens with the argon-arc weld joint located at the specimen center section. Through macroscopic observation and SEM fractographic analysis, it was found that most of the cracks were initiated at weld defects such as voids and inclusions at the edge of weld and in the heat affected zone (HAZ). A small crack methodology based on the plasticity-induced crack-closure concept and the effective stress intensity factor range, ΔKeff , was used to predict the total fatigue life of the weld joints. Large crack growth curve for cracks in the HAZ area was employed as the da/dN-ΔKeff base-line of the TA15 alloy. From fractographic measurements, an average defect size of 100 microns was assumed as the initial small crack size in the life predictions. Predicted total fatigue life by solely considering small crack growth stage agreed well with the experimental data.
Authors: Jae Hoon Kim, Duck Hoi Kim, Young Shin Lee, Young Jin Choi, Hyun Soo Kim, Won Shik Park
Abstract: Low cycle fatigue tests are performed on the Inconel 617 super alloy that be used for structural material of hot gas casing for gas turbine. The relations between strain energy density and number of cycles to failure are examined in order to predict the low cycle fatigue life of Inconel 617 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. And, the cyclic behavior of the Inconel 617 super alloy is characterized by cyclic hardening with increasing number of cycles.
Authors: Young Jin Choi, Young Shin Lee, Jae Hoon Kim, Won Shik Park, Hyun Soo Kim
Abstract: The hot gas casing of the gas turbine has operated in high temperatures and thermal gradients. The structure safety of hot gas casing will be highly depend on the thermal stress. In this paper, flow and thermal stress analysis of the hot gas casing is carried out using ANSYS program. The obtained temperature data by flow analysis of hot gas casing is applied to the load condition of the thermal analysis. The thermal stress analysis is carried out the elastic-plasticity analysis. The pressure, temperature and velocity of the flow and thermal stress of the hot gas casing are presented
Authors: Hui Ji Shi, Hai Feng Zhang, Yan Qing Wu
Abstract: Effect of recrystallization on DZ4 directionally-solidified nickel-base superalloy was investigated both at room temperature and high temperature of 673K. In-situ SEM surface observation were performed. Experimental results reveal that the material performance is strongly influenced by surface recrystallization layer. All specimens were prepared under conditions of shot peening and 4h 1220°C high temperature annealing. Different shot peening pressure specimens have different recrystallization states. High shot penning pressure specimens have clear and straight grain boundaries and the grain size appears to be a little bit larger. Recrystallization state seems not only affect the fatigue life, but also the crack initiation pattern and crack initiation life. Low shot peening pressure specimens have much lower fatigue life which is around 8-10% of virgin one, and SEM Real-time observation reveals that channeling cracks initiated at the early stage of fatigue life. High shot peening pressure specimens have higher fatigue life comparing to low shot peening pressure specimens, although it’s almost half lower than the virgin one, and cracks initiated not until middle or latter stage of fatigue life. Crack initiation life is also much longer than those of low shot peening pressure. Low shot peening pressure specimens seems not fully recrystallized, and its grain boundaries are much fragile which is responsible for high density microcracks initiation, and finally leads to the failure. Further nano-indention experiments on surface recrystallized layers show that higher shot peening recrystallized layers have much lower elastic module, which may explain the longer crack initiation life.

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