Fracture and Damage Mechanics V

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Authors: Guang Hui Zhao, Nian Mei Zhang, Gui Tong Yang
Abstract: Drillstring in oil drilling is simplified as a half-infinite bar. Taking account of Peierls-Nabarro(P-N) force and viscous effect of solid, dynamic response is simulated under harmonic driving at the end of the bar. With the physical properties specified, periodic, quasi-periodic and chaotic motions would appear as a function of the amplitude of external driving. We find that all the particles of the bar have the same qualitative characters, while vibrating amplitude decreases along the bar. It appears that particles of the bar reach chaotic motion through quasi-periodic motion. Investigation of this half-infinite bar will provide references for design of drillstring to keep motion away from chaotic region.
Authors: Seung Bok Choi, Jung Woo Sohn, Y.S. Lee
Abstract: In the present paper, temperature effect on yield stress of electrorheological fluids is experimentally investigated. A rotational shear-mode type electroviscometer is designed and manufactured for the identification of Bingham characteristics of ER fluids. Optimization of ER fluids is undertaken with carrier liquid, particle and additive treatment and then four different ER fluids are prepared for the test. The field-dependent yield stress, current density and response time of optimized ER fluids are compared at various temperature conditions.
Authors: Seung Bok Choi, Kum Gil Sung
Abstract: In this study, the dynamic fatigue characteristics of chemical starch-based ER fluid are experimentally investigated. A flow mode type apparatus is manufactured to activate the flow motion of the ER fluid. After evaluating the field-dependent Bingham property, three important dynamic fatigue characteristics; yield stress, current density and response time of the ER fluid are investigated as a function of the operating cycle. The dynamic operation for the flow motions is undertaken up to one million cycles and electric voltage is applied to the electrodes. In addition, the change of the particles of the ER fluid is microscopically observed to advocate the variation of the yield stress.
Authors: Chang Su Woo, Wan Doo Kim, Jae Do Kwon
Abstract: The interest of the fatigue life for rubber components was increasing according to the extension of warranty period of the automotive components. In this study, the fatigue lifetime prediction methodology of the vulcanized natural rubber was proposed by incorporating the finite element analysis and fatigue damage parameter determined from fatigue tests. Finite element analysis of 3D dumbbell specimen and rubber component was performed based on a hyper-elastic material model determined from the mechanical tests. The Green-Lagrange strain at the critical location determined from the finite element analysis was used for evaluating the fatigue damage parameter of the natural rubber. Fatigue tests were performed using the 3D dumbbell specimens and rubber component with different levels of maximum strain and various load. Fatigue life curves can be effectively represented by a following single function using the maximum Green-Lagrange strain. Fatigue lives of the natural rubber are predicted by using the fatigue damage parameters at the critical location. Predicted fatigue lives of the rubber component for automobile vehicle agreed fairly with the experimental fatigue lives.
Authors: Hong Nan Li, Ying Wu Zhou, Su Yan Wang, Mei Yang
Abstract: External bonding fiber reinforced polymers (FRP) to the tension faces of reinforced concrete (RC) beam as an effective approach of rehabilitation and strengthening of reinforced structures have attracted significant interests of researchers in the past decade. Since the load-carrying capacity of RC beams strengthened with the FRP is dominated by interfacial delaminated failure, the anchorage strength in FRP to concrete bonded joints under shear and the debonding stress transferring behavior at the end parts of flexural concrete members bonded with FRP have been deeply studied. Recently, methods of fracture mechanics have been introduced into analyzing the above issues. Compared with the traditional methods, the analytical models of existing fracture mechanics are reviewed and analyzed. Based on them the debonding bearing capacity of FRP-strengthened RC beams is calculated and the corresponding finite element models are created. These models of fracture mechanics are then evaluated with the finite element results and the experimental data from author’s and the literature. Some conclusions with engineering significance are drawn.
Authors: Xiao Jie Li, Xing Hua Xie, Long Jiang Zou, Hong Hao Yan, Yan Dong Qu, Qiang Xu, Xin Ouyang
Abstract: Nanostructured spherical lithium manganese oxide (Li-Mn-O) with about 30nm in diameter was synthesized for the first time by explosive method. The water-solubility explosive was prepared using a simple facility at room temperature. The growth of lithium manganese oxides via detonation reaction was investigated with respect to the presence of an energetic precursor, such as the metallic nitrate and the degree of confinement of the explosive charge. The detonation products were characterized by scanning electron microscopy. Powder X-ray diffraction and transmission electron microscopy were used to characterize the products. Lithium manganese oxides with spherical morphology and more uniform secondary particles, with smaller primary particles of diameters from 10 to 50 nm and a variety of morphologies were found. Lithium manganese oxides with a fine spherical morphology different from that of the normal is formed after detonation wave treatment due to the very high quenching rate. It might also provide a cheap large-scale synthesis method. Explosive detonation is strongly nonequilibrium processes, generating a short duration of high pressure and high temperature. Free metal atoms are first released with the decomposition of explosives, and then theses metal and oxygen atoms are rearranged, coagulated and finally crystallized into lithium manganese oxides during the expansion of detonation process. For detonation of the water-solubility explosive, the detonation pressure, the detonation temperature and the adiabatic gamma were close to 3 GPa, 2300 K and 3. The inherent short duration, high heating rate (1010 – 1011 K/s) and high cooling rate (108 – 109 K/s) prevent the lithium manganese oxides crystallites from growing into larger sizes and induce considerable lattice distortion.
Authors: Xing Hua Xie, Xiao Jie Li, Shi Long Yan, Meng Wang, Ming Xu, Zhi Gang Ma, Hui Liu, Zi Ru Guo
Abstract: This paper describes a new method for prediction of the Chapman–Jouguet detonation parameters of CaHbNcOdLieMnf explosives for mixture of some of low temperature explosion explosives at 0 = 1000 kg/m3. Explosion temperatures of water-gel explosives and explosive formulations are predicted using thermochemistry information. The methodology assumes that the heat of detonation of an explosive compound of products composition H2O–CO2–CO–Li2O–MnO2–Mn2O3 can be approximated as the difference between the heats of formation of the detonation products and that of the explosive, divided by the formula weight of the explosive. For the calculations in which the first set of decomposition products is assumed, predicted temperatures of explosion of water-gel explosives with the product H2O in the gas phase have a deviation of 153.29 K from results with the product H2O in the liquid state. Lithium and manganese oxides have been prepared by the explosion of water-gel explosives of the metal nitrates, M (NO3) x (M = Li, Mn) as oxidizers and glycol as fuels, at relative low temperature. We have also used the Dulong-Petit’s values of the specific heat for liquid phase H2O. Lithium manganese oxide powders with chrysanthemum-like morphology secondary particles, but with smaller primary particles of diameters from 5 to 30 nm and a variety of morphologies were found. The oxides produced by this cheap method affirmed the validity of explosion synthesis of nano-size materials for lithium ion batteries.
Authors: Gong Shun Guan, Bao Jun Pang, Run Qiang Chi, Yao Zhu
Abstract: In order to simulate and study the hypervelocity impact of space debris on dual-wall structure of spacecrafts, firstly a non-powder two-stage light gas gun was used to launch AL-sphere projectiles. Damage modes in rear wall of dual-wall structure were obtained, and while the law of damage in rear wall depends on projectile diameter and impact velocity were proposed. Finally, numerical simulation method was used to study the law of damage in rear wall. By experiment and numerical simulation of hypervelocity impact on the dual-wall structure by Al-spheres, and it is found that AUTODYN-2D SPH is an effective method of predicting damage in rear wall from hypervelocity impact. By numerical simulation of projectile diameter, projectile velocity and the space between bumper and back wall effect on damage in rear wall by hypervelocity impact, and fitting curves with simulation results, the law of damage in rear wall and dominant factors effect damage in rear wall by hypervelocity impact were proposed.
Authors: Shan Yong Wang, K.C. Lam, Ivan W.H. Fung, Wan Cheng Zhu, Tao Xu, Lian Chong Li
Abstract: Many stiff clays forming part of natural slopes and earth dams exist in the fissured state. When these cracks are subjected to gravity induced normal and shear stresses they may propagate. The present discussion presents a numerical method to study the propagation direction of cracks under stress fields similar to those found in the field. Not only did the results on one crack propagation direction obtained from the numerical method and the analytical results agree well, but numerical results have been used to investigate the mechanisms of the whole process of two horizontal cracks initiation and propagation and coalescence in stiff soils.
Authors: Qing Guo Fei, Ai Qun Li, Chang Qing Miao, Zhi Jun Li
Abstract: This paper describes a study on damage identification using wavelet packet analysis and neural networks. The identification procedure could be divided into three steps. First, structure responses are decomposed into wavelet packet components. Then, the component energies are used to define damage feature and to train neural network models. Finally, in combination with the feature of the damaged structure response, the trained models are employed to determine the occurrence, the location and the qualification of the damage. The emphasis of this study is put on multi-damage case. Relevant issues are studied in detail especially the selection of training samples for multi-damage identification oriented neural network training. A frame model is utilized in the simulation cases to study the sampling techniques and the multi-damage identification. Uniform design is determined to be the most suitable sampling technique through simulation results. Identifications of multi-damage cases of the frame including different levels of damage at various locations are investigated. The results show that damages are successfully identified in all cases.

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