A probabilistic fracture mechanics analysis for cracked pipe using 3-D model

For the purpose of probabilistic fracture mechanics (PFM) estimation based on elastic-plastic fracture mechanics (EPFM) in the field of reliability analysis of pressure vessels and piping, a 3-D EPFM database of fully plastic solutions for surface cracks and a PFM code for the integrity evaluation of nuclear structural components based on the above database are given. As an example, a comparison study of the PFM analysis is then performed between the 2-D and the 3-D solutions to demonstrate the 3-D effects on the solutions.     

Simplified stable crack growth analyses of welded CT specimens—comparison study of GE/EPRI, reference stress and R6 methods

This paper describes some simplified stable crack growth analyses of two kinds of inhomogeneous CT specimens. The one is machined from a submerged are welded plate of a nuclear pressure vessel A533B Class 1 steel, while the other is machined from an electron-beam welded plate of the A533B Class 1 steel and a high strength HT80 steel. In both specimens, initial cracks are placed to be normal to the fusion line. The ratio of yield stresses of the weld metal and the base metal of the A533B Class 1 steel is about 1·15, while that of the HT80 and the A533B Class 1 steels is about 1·4.

The generation phase crack growth analyses using the GE/EPRI and the reference stress methods are performed, calculating an applied load (P) and the J-value, while the application phase analyses of analyses using the R6 method are performed to calculate the maximum value of the applied load (P_max). Finally, some modification procedures of the three simplified estimation schemes are discussed in order to apply them to inhomogeneous material regimes.     

Strain distribution around a crack tip in high temperature environment using picture processing

A new optical strain measuring method developed by the authors is described. Here, we employ a simple method which uses point recognition picture processing and the least square approximation method.The surface of the specimen for which we are going to obtain the strain distribution is marked with points using a punch or a paint marker beforehand. At each loading stage, the digital data of the black and white picture of the specimen's marked surface are taken with the television camera under the control of the computer to which the data are sent. From these data, the locations of the marked points at each loading stage are obtained by the picture processing technique. Using these locations decided, we obtain the least square approximation of the displacement distribution, and then the strain distribution.To show the effectiveness of the present technique, the method is applied to the strain measurement near the crack tip in the CT specimen of Type 304 stainless steel. Because of the high ductility of this material, the crack tip blunting is notable so that the crack tip opening displacement observed by this method is as large as 2.5 mm at the specimen surface before initiation.Next, the strain distributions of a center-notched panel made of Type 304 stainless steel under high temperature creep condition are obtained.It is found from the above two experiments that the present strain measuring technique is powerful for the measurement of high strain, say more than 1%, whereas it is unsuitable to apply to the case of small strain at the present developing stage.     

Comparative study on organic constituents in polluted and unpolluted inland aquatic environments-IV Indicators of hydrocarbon pollution for waters

The ratios between organic carbons and hydrocarbon constituents were compared for polluted river waters from the Tokyo area and unpolluted river, brook, reservoir and pond waters from the Ogasawara (Bonin) Islands to derive indicators of hydrocarbon pollution fossil fuels and their products and both combustion products, and industrial products. The hydrocarbons as carbon (HCC)/total organic carbon (TOC). HCC extractable organic carbon with ethyl acetate (EOC), squalane as carbon (SgC),TOC, SqC/EOC, and unresolved complex mixture of hydrocarbons (UCMH)n-Alkane (C₁₅-C₃₃) ratios of the waters from the Tokyo area were much higher than those of the waters from the Ogasawara Islands. The values of carbon preference index (CPI₁₁) for n-alkanes (C₁₄-C₁₄) close to unity were found in all the water samples from the Tokyo area. They are considerably lower than those of the water samples from the Ogasawara Islands. These results indicate that the HCC TOC, HCC/EOC UCMH/n-Alkane and CPI₁₁ values are the important indicators of hydrocarbon pollution. Further, it was suggested that the SqC/TOC and SqC/EOC ratios are useful indicators of urban-industrial activities on water systems.     

A finite element method for contact problems related to fracture mechanics

A finite element method for contact problems in crack mechanics is developed on the basis of the penalty function method. The method is successfully applied to three important problems in fracture mechanics: a crack propagated from a pin hole, a two-point supported specimen with an edge crack loaded by a stamp, and a thick plate with a through-wall crack under bending force.     

Evaluation and control of the adhesiveness of cohesive calcium carbonate particles at high temperatures

Understanding the adhesiveness of fine particulate materials at high temperatures is important to achieving the stable, economical operation of various industrial systems. In the present research, two types of calcium carbonate (CaCO₃) particles having different mean particle sizes (often used as heat carriers in energy systems) were evaluated. The tensile strengths of beds of these materials were determined at various temperatures by tensile strength measurement tester. The adhesiveness was found to increase greatly at 500 °C even without chemical reactions or sintering, and X-ray diffraction analyses showed thermal expansion of the CaCO₃ crystals at 500 °C. Pure alumina (Al₂O₃) and silica (SiO₂) microparticles did not exhibit the same pronounced increases in tensile strength or crystal expansion at this same temperature. Because the surface distances between these primary particles were presumably small, it is proposed that van der Waals forces between the particles greatly increased at high temperatures. The addition of Al₂O₃ nanoparticles to the CaCO₃ decreased the tensile strengths of the powder beds both at ambient temperature and at 500 °C. The experimental data confirm that the surface distances between primary particles were increased upon incorporating the nanoparticles, such that the tensile strength decreased during heat treatment.     

Experimental visualization of lithium diffusion in LixFePO4

Chemical energy storage using batteries will become increasingly important for future environmentally friendly ('green') societies. The lithium-ion battery is the most advanced energy storage system, but its application has been limited to portable electronics devices owing to cost and safety issues. State-of-the-art LiFePO4 technology as a new cathode material with surprisingly high charge-discharge rate capability has opened the door for large-scale application of lithium-ion batteries such as in plug-in hybrid vehicles. The scientific community has raised the important question of why a facile redox reaction is possible in the insulating material. Geometric information on lithium diffusion is essential to understand the facile electrode reaction of LixFePO4 (0相似文献   

Growth of Cu2ZnSnS4 thin films on Si (100) substrates by multisource evaporation

Cu₂ZnSnS₄ films were grown on Si (100) by vacuum evaporation using elemental Cu, Sn, S and binary ZnS as sources. X-ray diffraction patterns of films grown at different substrate temperatures indicated that polycrystalline growth was suppressed and the orientational growths were relatively induced in a film grown at higher temperatures. Tetragonal structure of Cu₂ZnSnS₄ films was confirmed by studying RHEED patterns. The existence of c-axis ([001] direction) growth, two kinds of a-axis (〈100〉 direction) growth and four kinds of {112} twins which can be classified as two symmetrical pairs is proposed. Broad emissions at around 1.45 eV and 1.31 eV were observed in the photoluminescence spectrum measured at 13 K.     

Nanomechanical membrane-type surface stress sensor

Nanomechanical cantilever sensors have been emerging as a key device for real-time and label-free detection of various analytes ranging from gaseous to biological molecules. The major sensing principle is based on the analyte-induced surface stress, which makes a cantilever bend. In this letter, we present a membrane-type surface stress sensor (MSS), which is based on the piezoresistive read-out integrated in the sensor chip. The MSS is not a simple "cantilever," rather it consists of an "adsorbate membrane" suspended by four piezoresistive "sensing beams," composing a full Wheatstone bridge. The whole analyte-induced isotropic surface stress on the membrane is efficiently transduced to the piezoresistive beams as an amplified uniaxial stress. Evaluation of a prototype MSS used in the present experiments demonstrates a high sensitivity which is comparable with that of optical methods and a factor of more than 20 higher than that obtained with a standard piezoresistive cantilever. The finite element analyses indicate that changing dimensions of the membrane and beams can substantially increase the sensitivity further. Given the various conveniences and advantages of the integrated piezoresistive read-out, this platform is expected to open a new era of surface stress-based sensing.     

Finite element analyses of three dimensional fully plastic solutions using quasi-nonsteady algorithm and tetrahedral elements

To estimate entire elastic-plastic behaviors of cracked bodies, fully plastic solutions are utilized with linear elastic solutions in the engineering approach. Some numerical algorithms such as the Selective Reduced Integration/Penalty Function (SRI/PF) method have been developed and utlized to calculate various two-dimensional fully plastic solutions. However, only a few three-dimensional solutions have been obtained because of their numerical instability caused by the interaction among crack-tip singularity, material nonlinearity and incompressibility. This paper describes a new finite element algorithm for three-dimensional fully plastic solutions. The algorithm is basically classified into the mixed formulations. By introducing an artificial viscosity term to the governing equations, static crack problems are converted into quasi-nonsteady ones, which are solved using the fractional step method. The conversion makes the algorithm stable even in the analyses of complex crack geometries though it would need a number of iterations. In the analyses, mixed interpolation tetrahedral elements are also employed from a viewpoint of high quality mesh generation for three-dimensional cracked geometries. Numerical accuracy of the present algorithm is clearly demonstrated through the analyses of the three-dimensional fully plastic solutions of center cracked plates.