Progresses in Fracture and Strength of Materials and Structures

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Authors: Chun Liang Zhang, Li Ping Chen, Bin He
Abstract: Laser cladding of Co-base alloy on the sealing surfaces of nuclear valve clacks has been performed with a 5KW CO2 transverse flowing laser. The laser cladding was compared with plasma spraying. Both laser cladded and plasma sprayed zones were characterized by optical and scanning electron microscopes. The high temperature impact-slide wear resistance of laser cladded and plasma sprayed coatings were studied. The experimental results showed that compared with that of plasma sprayed coating, the laser cladded coating has higher microhardness, more uniform microstructure, smaller grain size, lower dilution rate, and fewer pores and impurities. The experimental results also showed that the weight loss of plasma sprayed coating during the high temperature impact-slide wear is two times larger than that of laser cladded coating.
Authors: Naoya Nishimura, Toshio Hattori, Minoru Yamashita, Naoyuki Hayakawa
Abstract: In this paper, we have evaluated the sliding and the loosening behavior of thread joints under transverse loading. Firstly, the critical relative slippage (Scr), less than which the thread joints can keep the fastening, is obtained by the cyclic loading tests. Then, this critical relative slippage is estimated according to the theoretically obtained equation considering the bending deformation of bolt and the geometrical constraint condition. The inclination compliance (kw) of the bolt head used in this equation is evaluated by comparing the experimental result with the corresponding analytical one. In consideration of the nonlinearity of kw with respect to the bolt axial tension, the Scr is well estimated by this equation.
Authors: Xue Tong Sun, Cheng Xin Lin
Abstract: In the present work, the wear behaviour of coatings produced on Ti-6Al-4V alloy by micro-arc oxidation method was studied. The wear tests were performed using a pin-on-disc wear machine under dry sliding conditions. It is found that the MAO coating can efficiently improve the wear-resistant performance of Ti alloy in the test range of this paper. The coated samples demonstrated wear rates up to 5-12 times lower than that of the uncoated substrates tested. The wear behaviours are deeply characterized by the variations of coating structure and composition.
Authors: Shu Hong Wang, Heek Wang Lee, Xing Dong Zhao, Ahmad Bashir
Abstract: When a tunnel or an underground structure is excavated in rock mass, rock disturbed or damaged zone (EDZ) is formed around the excavation due to the stress concentration resulting from stress redistribution. Recent studies on the rock EDZ revealed it’s important to structural stability around underground opening. In this study, the fracture and damage mechanisms of rock induced by the accumulation of microcracks were investigated by AE tests. The results of the experiments showed that tensile failure was the major microscopic failure mechanism of rock in excavation damaged and disturbed zone. The expression of the damage magnitudes in each AE source leads to accurate prediction of macroscopic failure mechanisms. In addition, the orientation of the macroscopic failure plane could be estimated by the orientational distribution of microcracks.
Authors: Shou Ju Li, Ying Xi Liu
Abstract: A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element model is meshed for assessing and calculating stress distribution and strength characteristics of dumpers. The stress distribution and stress concentration factors of main components of dumper at different loading cases are numerically simulated. A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule. The investigation shows that fatigue notch factor has a significant influence on the calculation of fatigue damage of dumpers.
Authors: Lian Chong Li, Chun An Tang, Jun Xing, Zheng Zhao Liang, Wei Jiang, Tian Hong Yang, Xing Dong Zhao
Abstract: With the knowledge of heterogeneous characteristics of thermal barrier coating materials at mesoscopic level, a coupled thermo-mechanical-damage (TMD Model) model was introduced and used to numerically quantify the thermal stresses and crack development of in thermal barrier coatings (TBCs) composite subjected to decreased temperatures. The effect of different surface precrack morphologies, such as precrack length and precrack density, on an interface crack subjected to thermal loading caused by a temperature change is presented. It provides us with a more sensible physical intuition and a more accurate mathematical for optimizing the design and the processing of ceramic coatings subjected to the coupled thermal-mechanical loading.
Authors: Yu Jun Zuo, Chun An Tang, Wan Cheng Zhu, Lian Chong Li
Abstract: Based on mesoscopic damage mechanics, a numerical code RFPA2D (dynamic version) is developed to simulate the spallation process of inhomogeneous medium induced by reflection of stress wave, and the influence of duration of stress wave on spallation is discussed. For convenience of description and discussion, the failure area in the immediate vicinity of loading position of model is divided into two zones, i.e. comminution zone and fracture zone; and the failure area caused by spalling in model is defined as spalling zone. The comminution zone is affected little by the duration of stress wave, but the fracture zone and the spalling zone are affected to a greater extent by duration, also, the stability of specimen is affected by the duration of stress wave. Furthermore, if the duration becomes significantly long, the fracture zone corresponding to the maximum extension of the radial tensile cracks will be dominant in specimen. If the duration of stress wave becomes short to some extent, the spalling zone corresponding to the maximum extension of the tangential tensile cracks will be dominant in specimen. In addition, if the duration of stress wave is long enough, the specimen may lose stability.
Authors: Tao Xu, Tian Hui Ma, Chun An Tang, Zheng Zhao Liang
Abstract: The Brazilian splitting tests have been commonly and widely used as a standardized test method on disc or cylinder specimens to measure the indirect tensile strength of rocks in mining engineering and other rock engineering. In this paper, a novel numerical code, 3D Rock Failure Process Analysis code, was applied to implement the splitting tensile failure tests on rock discs. The influences of the heterogeneity on stress distribution in rock are also discussed and the splitting failure patterns of specimens subjected to Brazilian tests are simulated. The simulated splitting results of rock discs were found quite realistic, which indicate that the rock failure analysis method is applicable and practical for the study of rock disc splitting failure.
Authors: Tai Quan Zhou, Tommy Hung Tin Chan
Abstract: The suspension bridge has more flexibility and repetitive vehicles produce stress cycles in members. Then fatigue of the member is accumulated with the daily traffic loadings. In order to evaluate the working condition of the Tsing Ma Bridge, the online monitoring health system has been installed in long suspension bridge. The location of the strain sensor is not exactly at the critical member locations. The hot spot stress analysis for critical members is necessary for accurate fatigue evaluation of the bridge. The global finite element analysis of the Tsing Ma Bridge under traffic loading is performed to determine the critical fatigue member locations. A detailed local finite element analysis for the welded connections is performed to determine the hot spot stress of critical fatigue location. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.
Authors: Ying Wu Fang, De Wei Wu, Yan Jun Lu, Zhi Xiong Lei, Yi Wang
Abstract: An analytical method of single field reducing-coupling on dynamic modeling is presented to analyze dynamic behaviors of thin plate structure based on dynamic fundamental solutions. In order to improve systematic modeling precision and efficiency, the method of single field reducing-coupling is introduced to deduce governing equations of thin plate structure dynamics by dynamic boundary element method (DBEM). The scale of matrix and generated time of coefficient matrixes are shortened greatly and dynamic behaviors of thin plate structure is obtained rapidly and accurately. The numerical examples and experiments show that the theory, established method and calculating program are feasible, and it has good precision and high efficiency.

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