Advances in Fracture and Failure Prevention

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Authors: Yasuo Ochi, Kiyotaka Masaki, Takashi Matsumura, M. Wadasako
Abstract: The rotating bending fatigue tests in high cycle region were carried out on alumina short fiber reinforced aluminum alloy composites (MMCs) at room and elevated temperatures of 200, 350, 400 and 450°C. The four kind of MMCs with 0%, 10%, 18% and 25% volume fraction were prepared in order to investigate the effects of alumina short fiber volume fraction on the fatigue property such as the fatigue strength, the crack initiation and propagation behaviors. As results, it was found that the fatigue strength at 107 cycles decreased with increase in the test temperature, but increased with an increase in alumina short fiber volume fraction at room and elevated temperatures. The crack initiation sites were large size alumina short fibers; some kind of cluster of short fibers and large size alumina particles (i.e. shots). And the crack growth paths were related to the distribution of the short fibers.
1073
Authors: Ki Weon Kang, Jong Kweon Kim
Abstract: This paper presents the fatigue behavior of plain-weave E-glass/epoxy composites with impact-induced damage under constant and variable amplitude loading. The constant amplitude fatigue life of the impacted composites can be identified through the prediction model, which was proposed on the carbon/epoxy laminates by authors. Also, the models are derived to calculate the equivalent stress of the composites under variable amplitude loading, considering the impact damage. These models allow fatigue data of the unimpacted and impacted composites under variable amplitude loading to be correlated with constant amplitude data of the unimpacted composites.
1079
Authors: Cheong Cheon Lee, Akira Shimamoto
Abstract: In this paper, the TiNi fiber reinforced / PC composite material was developed, and then control of the fatigue crack growth due to the shape memory effect was studied. Enhancement of mechanical properties and resistance of deformation of the TiNi fiber reinforced / PC composite were investigated by fatigue experiments. The fatigue behavior and crack propagation were in-situ observed with a SEM servo-pulser (fatigue testing instrument with scanning electron microscope) while increasing temperature. As the results, the fatigue life was improved, and the effectiveness of fatigue resistance was confirmed. The shape memory effect and expansion behavior of the matrix caused by temperature increasing examined the effect of the fatigue crack propagation control. It was verified that the control of fatigue crack growth is attributed to the compressive stress field in the matrix due to shrinkage of the TiNi fibers above austenitic finishing temperature (Af).
1085
Authors: Yasuhiro Yamazaki, A. Ikada, M. Okazaki
Abstract: Titanium alloy matrix composites (TMCs) have received considerable interest as structural materials for aeronautical applications, because of their higher specific strength and stiffness. When applying TMCs at elevated temperatures, high temperature isothermal low-cycle fatigue (LCF)failure is one of critical issues to be concerned. A unidirectionally reinforced SCS-6/ SP-700 composite is a tentative target in this work, where the matrix alloy, SP-700 is a new generation high strength Titanium alloy developed by NKK Inc., and the SCS-6 is a beta-SiC fiber developed by Textron Specially Materials, respectively. A merit to employ the SP-700 is that this alloy enables to reduce a fabrication temperature, because of its capability for superplasticity at relatively lower temperatures. The 7-plies composite specimen was produced by hot isostatic pressing (HIP) at 800°C for 0.5 hrs. in vacuum, alternating layers of thin-foils of the SP-700 and the green tapes of the SCS-6 fibers, so that the fibers were uniformly distributed as a hexagonal array in the matrix. The volume fraction of the fibers in the composite is about 28 %. In this work, the following articles in a unidirectionally reinforced SCS-6/SP-700 composite have been studied and evaluated: (i)mechanical properties of the SCS-6/SP-700 composite and the matrix alloy at temperatures ranged between room temperature and 450°C; (ii) LCF lives and the failure modes of the composite and the matrix alloy at room temperature and 450°C; (iii) fiber push-out tests at elevated temperatures ranged between room temperature and 600°C, to represent the fiber/matrix interfacial strength; and (iv) observation and the characterization of the interfacial reaction zone by means of a transmission electron microscope (TEM) and an energy dispersive X-ray spectrometer (EDS). Based on these experimental results, the effects of temperature and the loading frequency on LCF failure of the SCS-6/SP-700 composite were discussed.
1091
Authors: Jian Liu, Xia Ting Feng, Xiu Li Ding, Huo Ming Zhou
Abstract: The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.
1097
Authors: Dong Hal Kim, W. Hwang, Hyun Chul Park, W.S. Park
Abstract: The objective of this work was to design Surface Antenna Structure (SAS) and investigate fatigue behavior of SAS that was asymmetric sandwich structure. This term, SAS, indicates that structural surface becomes antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, SSFIP elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.5 GHz and final demonstration article was 16 x 8 array antenna. In cyclic loading, flexure behavior was investigated by 4-point bending and 4-point bending fatigue test. Fatigue life curve of SAS was obtained. Experimental results were compared with single load level fatigue life prediction equations (SFLPEs) and in good agreement with SFLPEs. SAS concept is the first serious attempt at integration for both antenna and composite engineers.
1109
Authors: Yu Sik Kong, Han Ki Yoon, Yi Hyun Park, Seon Jin Kim
Abstract: The high temperature creep behaviors of heat machine systems such as aircraft engines, boilers and turbines in power plants and nuclear reactor components have been considered as an important and needful fact. There are considerable research results available for the design of high temperature tube materials in power plants, based on uni-axial tension creep tests. However, few studies on the Initial Strain Method (ISM) capable of securing repair, maintenance, cost loss and life loss have been made. In this method, a long time prediction of high temperature creep characteristics can be dramatically reduced through a short time experiment. The purpose of present study is to investigate the high temperature creep life of 1Cr-0.5Mo steel using the Initial Strain Method. The creep test was performed at 500°C, 550°C and 600°C under a pure loading. In the prediction of creep life for 1Cr-0.5Mo steel, the equation of ISM was superior to those of LMP. Especially, the long time prediction of creep life was identified to improve the reliability.
1115
Authors: T. Li, Zhu Feng Yue
Abstract: The possibility of the life prediction model for nickel-base single crystal blades has been studied. The fatigue-creep (FC) and thermal fatigue-creep (TMFC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing on the life. An emphasis has been put on the micro mechanism of the rupture of creep, FC and TMFC. Two main factors are the voiding and degeneration of the material for the creep, FC and TMFC experiments. There are voids in the fracture surfaces, and size of the voids is dependent on the loading condition. Generally, the rupture mechanism is the same for creep, FC and TMFC. If the loading can be simplified to the working conditions of the turbine blades, i.e. the hold time is at the top temperature and maximum stress, a linear life model is satisfactory to the life prediction of nickel-base single crystal superalloy from the experimental study in this paper. The temperature and the stress level of the nickel-base single crystal (SC)blades are not uniform. To predict the life of SC blades, one should consider the cycles of the temperature and stress as well as the oxidation simultaneously. In the past 30 years, there are many works on the mechanical behavior and description, such as the inelastic constitutive relationships, plastic, fracture, isothermal creep and fatigue and thermal fatigue as well as oxidation [1-3]. There are also special software (program) to analyze the deformation and life of nickel-base single crystal structures, such as blades. In order to apply to the engineering more conveniently, there should be a life prediction model for the blades. The model should not be too complex, but take more influential factors as possible into consideration.
1123
Authors: Seong Gu Hong, Soon Bok Lee
Abstract: Low cycle fatigue (LCF) tests were carried out in a wide temperature range (20°C-650°C)at strain rates of 1×10-4/s-1×10-2/s for 17% cold worked (CW) 316L stainless steel to investigate the conditions for the occurrence of dynamic strain aging (DSA) and its effects on material properties during LCF deformation. DSA introduced anomalous changes of LCF properties, and the DSA regime under LCF loading condition coincided with that in tensile loading condition. During LCF deformation, dynamic stain aging can be manifested in the forms of the occurrence of the plateau or the peak in the variation of cyclic peak stress with temperature, the negative temperature dependence of plastic strain amplitude or softening ratio, the negative strain rate sensitivity, and the negative strain rate dependence of plastic strain amplitude or softening ratio.
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