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41.
A rate-dependent cohesive model for simulating dynamic crack propagation in brittle materials 总被引:5,自引:0,他引:5
Numerical investigations are conducted to simulate high-speed crack propagation in pre-strained PMMA plates. In the simulations, the dynamic material separation is explicitly modeled by cohesive elements incorporating an initially rigid, linear-decaying cohesive law. Initial attempts using a rate-independent cohesive law failed to reproduce available experimental results as numerical crack velocities consistently overestimate experimental observations. As proof of concept, a phenomenological rate-dependent cohesive law, which bases itself on the physics of microcracking, is introduced to modulate the cohesive law with the macroscopic crack velocity. We then generalize this phenomenological approach by establishing a rate-dependent cohesive law, which relates the traction to the effective displacement and rate of change of effective displacement. It is shown that this new model produces numerical results in good agreement with experimental data. The analysis demonstrates that the simulation of high-speed crack propagation in brittle structures necessitates the use of rate-dependent cohesive models, which account for the complicated rate-process of dynamic fracture at the propagating crack tip. 相似文献
42.
Yasuhide Shinohara Tadashi Dohi Shunji Osaki 《Computers & Industrial Engineering》1997,33(3-4):813-816
In a software product management, it is an important problem to determine the optimal release timing which minimizes the total expected cost incurred in both testing and operation phases. In this paper, we compare the performance between two kinds of software release methods, which are referred to as the T-policy and the N-policy. Based on the existing software reliability growth models, we formulate the expected cost functions and derive analytically the optimal policies under these control methods. Also, we derive a criterion for which control methods should be adopted. Finally, in numerical examples, we calculate the optimal release policies for several cost parameters. 相似文献
43.
A simultaneous detecting circuit system of centers and lengths of some lines in one dimension is presented applying an electronic circuit model of the nervous axon with respect to signal transmission. This model consists of series of one basic section, and has functions of Neuristor. The circuit system has a paralell processing function. It is constructed by three layers. In the first layer each visual signal of lines is changed to electric pulse signal. In the second layer edges of each line are detected, and in the third layer these detected signals are converted into voltages which correspond to lengths of the lines. These functions were confirmed experimentally using its hardware. 相似文献
44.
Yu Hua Wang Tadashi Endo Xuan Guo Yukio Murakami Mizumoto Ushirozawa 《Journal of the Society for Information Display》2004,12(4):495-499
Abstract— The broad bands at around 155 nm for GdAl3(BO3)4:Eu, at 184 nm for Ca4GdO(BO3)3:Eu, at 183 nm for Gd2SiO5:Eu, and at 170 nm for GdAlO3:Eu were observed. These bands were assigned to the charge‐transfer (CT) transition of Gd3+‐O2?. In the excitation spectrum of (Gd,Y)BO3:Eu, a broadened excitation band was observed in VUV region. It could be considered that this band was composed of two bands at about 160 and 166 nm. The preceding band was assigned to the BO3 group absorption. The later one at about 166 nm could be assigned to the CT transition of Gd3+‐O2?, according to the result of GdAl3(BO3)4:Eu, Ca4GdO(BO3)3:Eu, Gd2SiO5:Eu, and GdAlO3:Eu. The excitation spectra overlapped between the CT transition of Gd3+‐O2? and BO3 groups absorption. It caused the emission of Eu3+ to take place effectively in the trivalent europium‐doped (Gd,Y)BO3 host lattice under 147‐nm excitation. 相似文献
45.
46.
E.-A. Reinecke K. Takenaka H. Ono T. Kita M. Taniguchi Y. Nishihata R. Hino H. Tanaka 《International Journal of Hydrogen Energy》2021,46(23):12511-12521
The safe decommissioning as well as decontamination of the radioactive waste resulting from the nuclear accident in Fukushima Daiichi represents a huge task for the next decade. At present, research and development on long-term safe storage containers has become an urgent task with international cooperation in Japan. One challenge is the generation of hydrogen and oxygen in significant amounts by means of radiolysis inside the containers, as the nuclear waste contains a large portion of sea water. The generation of radiolysis gases may lead to a significant pressure build-up inside the containers and to the formation of flammable gases with the risk of ignition and the loss of integrity.In the framework of the project “R&D on technology for reducing concentration of flammable gases generated in long-term waste storage containers” funded by the Japanese Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), the potential application of catalytic recombiner devices inside the storage containers is investigated. In this context, a suitable catalyst based on the so-called intelligent automotive catalyst for use in a recombiner is under consideration. The catalyst is originally developed and mass-produced for automotive exhaust gas purification, and is characterized by having a self-healing function of precious metals (Pd, Pt and Rh) dissolved as a solid solution in the perovskite type oxides. The basic features of this catalyst have been tested in an experimental program. The test series in the REKO-4 facility has revealed the basic characteristics of the catalyst required for designing the recombiner system. 相似文献
47.
Chiba Tadachika Shirazi Hassan Miyamoto Goro Furuhara Tadashi 《Metallurgical and Materials Transactions A》2017,48(9):4204-4210
A novel method for grain refinement of martensite structures was proposed, in which transformation strain is accumulated by cyclic displacive forward and reverse transformations. This method can refine martensite structures in an Fe-18Ni alloy because a high density of austenite dislocations is introduced by a displacive reverse transformation in addition to an inheritance of dislocations in body-centered cubic martensite into austenite during cyclic transformation. The addition of a small amount of carbon accelerates structure refinement significantly, which results in the formation of ultra-fine-grained structures after ten cycles.
相似文献48.
S. Sugai Y. Mizuno R. Watanabe T. Kawaguchi K. Takenaka H. Ikuta K. Kiho M. Nakajima C. H. Lee A. Iyo H. Eisaki S. Uchida 《Journal of Superconductivity and Novel Magnetism》2013,26(4):1179-1183
The electronic and magnetic excitations at the spin density wave (SDW) transition are investigated by Raman scattering. The multi-orbital electronic states induce the Dirac nodes in the SDW gap. The excitations near the nodes and anti-nodes are separately detected in accordance with the two-orbital tight-binding model. The exchange interactions are found to be given by the second derivative of the total energy with respect to the angle of the moment from two-magnon scattering. The two-magnon peak has the large spectral weight above twice the maximum energy of magnon. It is interpreted by the magnetic self-energy of the electron spectral function in the localized spin model or particle-hole excitations in the itinerant spin model. 相似文献
49.
Koshi Takenaka Masayoshi Ichigo Taisuke Hamada Atsushi Ozawa Takashi Shibayama Tetsuya Inagaki 《Science and Technology of Advanced Materials》2014,15(1)
Magnetostructural correlations in antiperovskite manganese nitrides were investigated systematically for stoichiometric and solid solution Mn3Cu1?xAxN (A = Co, Ni, Zn, Ga, Ge, Rh, Pd, Ag, In, Sn or Sb). This class of nitrides is attracting great attention because of their giant negative thermal expansion, which is achieved by doping Ge or Sn into the A site as a relaxant of the sharp volume contraction on heating (spontaneous volume magnetostriction ωs) because of the magnetovolume effects. The physical background of large ωs and mechanism of how the volume contraction becomes gradual with temperature are central concerns for the physics and applications of these nitrides. An entire dataset of thermal expansion, crystal structure and magnetization demonstrates that the cubic triangular antiferromagnetic state is crucial for large ωs. The intimate relationship between ωs and the magnetic structure is discussed in terms of geometrical frustration related to the Mn6N octahedron and magnetic stress concept. The results presented herein also show that ωs depends on the number of d electrons in the A atom, suggesting the important role of the d orbitals of the A atom. Not all the dopants in the A site, but the elements that disturb the cubic triangular antiferromagnetic state, are effective in broadening the volume change. This fact suggests that instability neighboring the phase boundary is related to the broadening. The relation between the gradual volume change and the local structure anomaly is suggested by recent microprobe studies. 相似文献
50.
Yusuke Kitamura Yoshiaki Morisada Hidetoshi Fujii Tadashi Mizuno Genryuu Abe 《Welding International》2017,31(4):278-283
(The microstructural refinement of cobalt-based alloy (Stellite No. 6) by laser cladding and friction stir processing (FSP) was studied. A nanometer-sized microstructure consisting of fine carbide (particle size: 100–200 nm) and a grain (grain size: 150–250 nm) was successfully fabricated by the FSP on the laser clad cobalt-based alloy. The nanostructured cobalt-based alloy (Stellite No. 6) had an extremely high hardness of about 750 HV. 相似文献