Papers by Keyword: Crack Propagation Rate

Abstract: Particulate reinforced composites show viscoelastic behavior under various loading conditions. It is important to estimate mechanical behavior when this material is used for solid fuel on rocket motor. Cracks can be generated and propagated due to high combustion pressure in the service time. These cracks expand the burning area and lead to excessive combustion. Consequently, the rocket motor can cause malfunction or the performance deteriorated. In this study, edge cracked sheet specimen was used to perform the crack propagation tests. These tests were conducted in the range of temperature from -60°C to 60°C under 2.54 and 12.7 mm/min of strain rates. Based on the results, the stress intensity factors and the crack propagation rests were calculated. The crack resistance curves show the transition that stress intensity factors increases as temperature decrease. Also, fracture surfaces were investigated by scanning electron microscope to determine the fracture behavior under various temperatures.

Abstract: Fatigue behavior of reinforced concrete (RC) beam can be improved by externally bonded fiber reinforced polymer (FRP). However, propagation behavior of a crack on the RC beam will have serious effect on the fatigue life of the beam strengthened with FRP. In this paper, a finite element (FE) procedure was developed to analysis the stress intensity factor (SIF) of the main crack and an experimental study was conducted to investigate the propagation rate of the main crack of the RC beam strengthened with carbon fiber laminate (CFL) under cyclic bending load. The FE analysis results show that the SIF near the main crack tip increases at the beginning and then decreases with the fatigue crack propagation. When relative crack length α is equal to 0.3, the SIF is maximum. When α approaches 0.75, the SIF approaches zero. A total of 3 RC beams strengthened with CFL were tested. The experimental results show that it is possible to divide the process of the crack propagation into three distinct phases, including crack initiation and then quickly propagation, stable propagation and then rest and unstable propagation. A semi-empirical equation based on the Paris Law was developed to predict the crack propagation rate.

Abstract: For most of structural failure in engineering structures , fracture often takes place due to a phenomenon called fatigue. Therefore, many studies about the effect of the various mode-mixities on fatigue characteristics have been performed. However, most of the former studies are about metal/metal interface or delamination of composite. In this study, the fatigue characteristics of a composite/metal interface are investigated. The fatigue tests were performed using single-leg bending (SLB) specimens bonded with composite and steel using co-cure bonding method. This paper focuses on the fatigue characteristics depending on different mode ratios (GⅡ/GT). The overall results obtained in this study show that the crack propagation rate increases with the mode Ⅱ loading component.

Abstract: The crack growth rate test of XCQ16 and XCQ16-1 axle steels were introduced using MTS material test machine. The test data of the crack propagation rate of axle steels has been analyzed by Paris formula. The results showed the crack propagation rate test of XCQ16 was faster than XCQ16-1, and the fatigue residual of XCQ16-1 life is longer. The correlated coefficient of the experimental data indicates that the result of this paper is comparatively ideal and has reference value to appraising the life span.

Abstract: The equation of fatigue crack propagation rate is indispensable to precisely predict the fatigue life of structure containing three-dimensional crack under constant amplitude loading. Considering the crack closure effects and thickness effects in real structures, the equation of fatigue crack propagation rate under tri-axial stress state is presented. And the fatigue propagation lives of LY12-BCZYU aluminium alloy plate specimens with central through crack are predicted by this equation and validated by experimental results. Validation against calculations by the model and experimental data shows a good agreement.

Abstract: 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.

Abstract: Environmental fatigue crack propagation of CF8M and CF8A steels used in the domestic nuclear power plants (NPPs) were investigated on the simulated pressurized water reactor (PWR) condition (temperature: 316°C, pressure: 15MPa). The test equipment for environmental fatigue (high temperature-high pressure loop, autoclave, load frame, and measurement system) was designed. As-received and 60-year aged specimens were used in the test. To compare with environmental fatigue test, another test in the air condition was performed. The fracture surfaces of specimens were difficult to verify the fracture modes such as striation, inter-granular crack and cleavage and so on. As the ferrite content of CF8M is increased, more particles on the fracture surface were peeled.