Progresses in Fracture and Strength of Materials and Structures

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Authors: Xiang Dong He, Yi Min Zhang, Yu Chun Xue, Bang Chun Wen
Abstract: Based on the reliability-based design theory and sensitivity analysis method, the reliability-based sensitivity design of beam structure with non-normal distribution parameters is extensively researched and a numerical method for reliability-based sensitivity design is presented. The variation regularities of reliability sensitivity are obtained and the effects of design parameters on reliability of beam structure are studied. The method presented in this paper provided the theoretic basis for the reliability-based design of beam structure with non-normal distribution parameters.
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Authors: Tao Yu, Ying Yang, Qing Kai Han, Hong Liang Yao, Bang Chun Wen
Abstract: Rotating machinery, such as steam turbo, compressor, and aeroengine etc., are widely used in many industrial fields. Among the important rotor faults, the fatigue crack fault, which can lead to catastrophic failure and cause injuries and severe damage to machinery if undetected in its early stages, is most difficult to detect efficiently with traditional methods. In the paper, based on the truth of the change of the mode shapes of the cracked structure, a new method by combining accurate finite element model of rotor with multi-crack in shaft and artificial neural network (ANN) is proposed to identify the location and depth of cracks in rotating machinery. First, based on fracture mechanics and the energy principle of Paris, the accurate FE model of the rotor system considering several localized on-edge non-propagating open cracks with different depth, is built to produce the specific mode shapes. Then a set of different mode shapes of a rotor system with localized cracks in several different positions and depths, which will be treated as the input of the designed ANN model, can be obtained by repeating the above step. At last, with several selected crack cases, the errors between the results obtained by using the trained ANN model and FEM ones are compared and illustrated. Meanwhile, the influences of crack in the different position on the identification success are analyzed. The method is validated on the test-rig and proved to have good effectiveness in identification process.
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Authors: Yao Feng Zhang, Bo Qin Gu
Abstract: 08Cr2AlMo steel is a type of material developed especially for heat exchanger pipe bundle used under H2S condition in the recent years. In this paper, some researches were carried out on the stress corrosion cracking (SCC) susceptivity of 08Cr2AlMo steel in H2S water solution and the inhibition of imidazoline and diethylene triamine on the SCC by means of slow strain rate tensile test, scanning electron microscopy, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results indicate that 08Cr2AlMo steel is highly susceptible to SCC in saturated H2S solution for the fracture surfaces of specimen show typical quasi-cleavage fracture. The addition of both imidazoline and diethylene triamine into saturated H2S solution is effective on inhibiting the SCC. The inhibitors can reduce the potential of the cathodic hydrogen evolution, which prevents the penetration of hydrogen into the specimen effectively. Furthermore, inhibitors accelerate the formation of the chemically bonded film on the steel surface. It is also found that when the concentration of inhibitors is below 0.2%, there is no obvious inhibition effect on SCC, and the inhibition effect of diethylene triamine is better than that of imidazoline.
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Authors: Yan Jun Lu, Yong Fang Zhang, Ying Wu Fang, Heng Liu
Abstract: In this paper, a numerical method is presented to determine the periodic response of hydrodynamic bearing-rotor system. The observed state information of the system is used to solve inversely the Jacobian matrix, and to trace the periodic response with the change of the control parameter. Jacobian matrix obtained is used to calculate the Floquet multiplier, so the stability of the periodic response can be determined by Floquet theory. The proposed method is applied to a rotor system with the elliptical bearing supports to solve the periodic response and determine its nonlinear stability. Validity of this method is illustrated by comparing numerical results with the traditional method.
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Authors: Yan Jun Lu, Zhao Hui Ren, Hong Chen, Nai Hui Song, Bang Chun Wen
Abstract: Because of wrong setting or long-term running of rotating machinery, the looseness may ouur in the bearing seats or bases. And also bring impact and rubbing of rotor-stator, That is the looseness and rub-impact coupling fault. In the paper,a mechanics model and a finite element model of a vertical dual-disk cantilever rotor- bearing system with coupling faults of looseness and rub-impact are set up. Based on the nonlinear finite element method and contact theory, the dynamical characteristices of the system under the influence of the looseness rigidity and impact-rub clearance is studied. The results show that the impact-rub of rotor-stator can reduce the low frequency vibration caused by looseness, and the impact-rub caused by looseness has obvious orientation. Also, the conclusion of diagnosing the looseness and rub-impact coupling faults is given in the end of the paper.
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Authors: Yoon Suk Chang, Dae Geun Cho, Sang Min Lee, Jae Boong Choi, Young Jin Kim, Poong Hwan Chun, Jae Youn Kong
Abstract: The purpose of this paper is to investigate principles of levitation and restitution of blowing nozzle prior to fabricating a prototype of air handling system. Since air force distributions streaming bottom surface of a flat panel display (FPD) highly dependent on operating as well as design condition and configuration of air handling system, influences of various parameters such as flow rate, supply air pressure, floating height and tilted angle are examined through a series of computational fluid dynamics (CFD) analyses. Moreover, dynamic finite element analyses of the FPD are carried out to assure that an oscillation effect caused by disturbances is not significant. Key findings from the both CFD and structural analysis results are presented and discussed, which can be utilized as technical bases for development of the practical air handling system.
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Authors: Zhong Yan Zhai, Ming Fei Feng, Yong Xiang Zhao
Abstract: Probabilistic cyclic constitutions are investigated and safety assessment on the ASME code-based design curves is given to 0Cr18Ni10Ti pipe steel. Incremental and group fatigue tests were carried out respectively to reveal the cyclic deformation and life characteristics. The results showed that the material acted as cyclic strengthening and masing behaviour. A phenomenon of random cyclic constitutions was observed. The modified Ramberg-Osgood equation combining an assumption of the cyclic stress amplitude following normal distribution is applied to describe the constitutions. Fine modeling effect is obtained on both considerations of survival probability and confidence. Probabilistic characteristics are also given to the fatigue virtual stress amplitude-life relations and then a safety assessment is carried out on the design curves. The results exhibit that the ASME curves with constant reduction factors are not matching the evolutionary scattered statistical trend of fatigue lives. The curves with 2 reduction factor on stress amplitude and 20 on fatigue life are much conservative for the present material, which is great different from the previous observation to weld metal. It indicates that the fatigue design by analysis for the piping should be based appropriately on the welded joint data.
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Authors: Yong Xiang Zhao, Bing Yang, Wei Hua Zhang
Abstract: A Monte-Carlo simulation method for the reconstruction of one-dimensional probabilistic mechanical and fatigue strengths is developed to realize reliability analysis at arbitrary probability and confidence levels. This method is valid to the cases of the probabilistic parameters given at special probabilities (Ps) or probability-confidences (P-Cs). To overcome the shortage of common simulations with numerous samples which is out of true production practice, a simulation policy is newly suggested with 7 to 20 samples for material small specimens and, at most 10 for structural specimens and 5 percentages for the error of simulated parameters fitting the original ones. Details of the method in practice are studied for the six possible statistical distributions i.e. normal, lognormal, three-parameter Weibull, two-parameter Weibull, maximum value, and minimum value ones. The reconstructions of the fatigue limits of 10 Chinese engineering materials have indicated the availability and feasibility of the present method.
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Authors: Li Yang Xie, Xue Hong He
Abstract: The present paper interpreted the traditional stress-strength interference model as an equation expressing the statistical average of the probability of strength preponderating over stress. Thus, the same equation, which was traditionally applicable only in the situation of same-measure parameters, can be applied to more general situation of different-measure parameters. In other words, the traditional model was extended to the situation of any two variables, as long as one variable can be expressed as a function of the other. With a specific load amplitude distribution, the method is to calculate the statistical average of the probability that fatigue life random variable under the individual constant amplitude cyclic load is greater than an assigned value. The extended interference analysis method can be applied directly to calculate fatigue reliability under constant amplitude cyclic load with uncertainty in the stress range.
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