Key Engineering Materials Vols. 353-358

Abstract: This study contains several estimation methods of the static buckling load for the spacer grid of nuclear fuel assembly in pressurized water reactor. Three different estimation methods were proposed for the calculation of the static buckling loads of spacer grid. The linear and non-linear static buckling analyses were performed to estimate the static buckling load of the spacer grids using ANSYS program. The analyses results were compared with the static buckling test results. Based on the analysis and test results, the applicability of the proposed estimation method for the static buckling load of the spacer grid was investigated.

Abstract: The precision diagnosis of subway electric multiple units (EMUs) was conducted with various types of engineering analysis techniques for the current performance and wear evaluation. The evaluation was conducted on detailed parts of EMUs, such as car bodies, bogies, braking systems, and electrical systems of EMUs. Several characterization means including nondestructive evaluation techniques, corrosion testing, and three-dimensional measurements, were employed for the evaluation of car bodies and bogies. For braking system, degradation and performance tests were conducted, while the functional and degradation tests were performed on electrical system in order to identify the actual performance of the system. Moreover, stress and structural analyses using commercial finite element method (FEM) software provided important information on stress distribution and load transfer mechanisms. In this investigation, various advanced engineering analysis techniques for the safety analysis of subway EMUs have been introduced and the analysis results have been used to provide the critical information for the criteria of safety assessment.

Abstract: During fuel irradiation tests of material and fuel rods, all parts of cylindrical shells with multiple holes act as heat sources due to fission heat and γ-flux. The thermal stress is induced by a temperature difference among the heat sources. In this study, the thermal stress of the cylindrical structure is minimized by using an optimization method about the geometric variables. The circular shapes of the multi-specimens are investigated. For the thermal analysis of the structure, the finite element method code, ANSYS 8.1 is used. A sub-problem approximation method is used for the structural design optimization.

Abstract: The difference in the Coefficient of Thermal Expansion (CTE) between the chip and the substrate generate thermal displacement in the solder joint. It seems to be a main cause of failure in the solder joint when the chip and the substrate are heated repeatedly. The failure of the solder joints by thermal fatigue is known to be influenced by varying boundary conditions such as the difference in CTE, the height of solder, the Distance of the solder joint from the Neutral Point (DNP) and the temperature variation. In this paper, the effects of varying boundary conditions on the failure probability of the solder joint are studied by using the probabilistic approach methods such as the First Order Reliability Method (FORM) and the Second Order Reliability Method (SORM).

Abstract: The resonance phenomenon is suppressed by adjusting the damping of the comb accelerometer structure to widen the frequency bandwidth of the capacitive accelerometer. The capacitive accelerometer with asymmetrical combs, fabricated with DRIE and anodic bonding, is presented. The damping category of the accelerometer is introduced, in which the squeeze-film damping coefficient and the damping ratio factor are detailed. The damping ratio factor of the accelerometer, measured by a vibration method, is 0.17. The damping ratio factor of the optimized structure is calculated of 0.15 to 0.18 with the change of experiential modulus C from 25 to 30, theoretically.

Abstract: Pressure steel pipings in a water power plant have been in service for over fifty years. In order to assess the safety of the piping, whole check and tests for the piping were carried out. The material for some piping is ST3 from former USSR, the other is A3 made in China. The mechanical properties were investigated by tests and were compared with the original material properties. The result shows the yield strength and tensile strength of serviced steels are less than those of original materials. The surfaces of the piping were checked to investigate the corrosion, surface defects. The flaws in the welds and near the welds of the pipings were detected by UT and MT, and several weld flaws were found. Based on the test and NDT investigation results, the strength, fracture and fatigue life of the pipings are assessed according to Chinese standard GB/T19624-2004 and British standard BS7910-2000. The assessment results show that the strength of the piping is enough, and the pipings with these flaws does not fracture. The piping can be safe in service under the normal operating condition for 104 to 106 cycles.

Abstract: The measurement of crack propagation in solids is of vital importance for the research of the fatigue characteristic of solid materials. By analysis of the image based measurement technique, a contact-free crack measurement approach was proposed based on image cross correlation algorithm. Experiment was performed to verify the validity of this method and it was found that the method is of high precision. The approach distinguished itself from traditional methods by several characteristics: it has relatively high measuring accuracy, the crack propagation can be continuously measured with this method, the amount of information that the approach provide is much more abundant than that of other methods. The method is proved to be an efficient method for crack measurement and can be applied in fatigue induced material cracking researches.

Abstract: The corrosion behaviors of thixoformed AZ91D alloy immersed in 3.5% NaCl aqueous were studied by using the weight lose method and observed by scanning electron microscopy and analyzed by electron probe micro-analysis.The results showed that corrosion rate of thixoformed AZ91D alloy was higher in initial stages and decreased as the immersion time increased. Compared with the thixoformed alloy, the change of corrosion rate of permanent mould cast (PMC) alloy was smoothly. The observation on the corrosion surfaces showed that the primary αphase spherical particles were first suffered from corrosion during corrosion testing, and then the eutecticαgrains. the composition of primaryαphase particles in the thixoformed alloy was quite uniform, and thus the protective film of the corrosion products on the alloy surface was more intact. The amount of the eutectic β phase in the inter-particle eutectics was relatively higher and the distribution was more uniform, so the protective film consisted by eutectic β phase was also more intact. That is to say the protective role from the surface film on the thixoformed alloy was better than that on the PMC alloy which was the cause of lower corrosion rate of the thixoformed AZ91D alloy.

Abstract: The paper deals mainly with the corrosion of 16Mn steel under the condition of three different high temperatures and in NACE solution saturated with H2S at 1MPa partial pressure of CO2, by means of autoclave, SEM, XRD, weight loss method and electron-probe micro-analysis. The result showed: under the experimental conditions, the serious CO2/H2S corrosion happened to 16Mn steel ,so that the main corrosion films, ferrous sulfide, could be clearly found on both sides of the samples; at 60°C, characteristics of pitting corrosion manifested centered chiefly around CO2 corrosion ; at 90°Cand 120°C, around H2S ones . It was the cooperating effects of both the hydrogen damage and pitting corrosion caused by CO2/H2S corrosion that formed the special corrosion features on the surface of steel to a certain degree. It was indicated that the corrosion of CO2/H2S was the result of interaction of multi-factors.

Abstract: Since the construction method of tailings dams determines the uneven distribution of tailings, a reliability theory is introduced to analyze the stability of tailings dams. Based on the limit equilibrium method and reliability theory, the sensitivity and reliability of a typical tailings dam are analyzed. Reliability analyses with different types of the variable probability distribution types show that the effect of the probability distribution type on reliability analysis can almost be ignored. Besides, the sensitivity analyses of different variables show that the strength indexes and density of tailings will affect the analysis results of stability reliability. Therefore the strength indexes c, φ and density ρ must be considered as basic variables to analyze the stability reliability of tailings dams.