This paper presents an advanced Bayesian analysis method to determine the appropriate non-periodic inspection intervals of fatigue-sensitive structures. The calculation procedure of the posterior distribution is improved compared to the previous methods. The method is based on assumptions about the probability density functions of the time until crack initiation, a law of crack propagation, the probability of crack detection and the failure rate before and after crack initiation. A major feature of this method is that even when there are uncertain parameters in the equations, the next inspection interval can be determined. Moreover, the probability density function of the uncertain parameters is updated according to the results of each inspection. A simulation study was conducted to evaluate the proposed method. The proposed method is evaluated and it is statistically shown that this Bayesian approach allows (a) evaluation the inspection interval accurately even with incorrect prior knowledge about the parameters and, (b) estimation of the reliability of a system accurately, even when some of the parameters are uncertain.
Related to the importance of selectivity to natural fibers that can be used and qualify as one of the raw material composite engineering substitute for Fiber Reinforced Plastics (FRP) or Fiber Reinforced Metals (FRM), one plants that have the potential of fiber and volume growth is very abundant, namely abaca. This research aims to clarify scattering in tensile strength of an abaca single fiber through statistical approach and to search a way of suppression in the scatter with intention that abaca fibers can be used as a raw material for engineering structural components. Tensile test specimens were prepared from fiber samples from two different areas, East Aceh and North Aceh, Indonesia. Specimen gauge length is 25 mm, then as the holder of a fiber made of paper (20mm x 100mm), where the specimen size for fiber tensile test in accordance with JIS standard K-760. Diameter the specimen fibers obtained varied from 0.060 mm to 0.140 mm. The tensile strength of abaca fiber varies in the wide range from 100 MPa to 900 MPa. Coefficient of variation was calculated for East Aceh abaca fibre 0.32 and North Aceh abaca fibre 0.35. It was examined whether Weibull distribution or log-normal distribution could well express scatted experimental results. The results showed that both the distribution types could well express the experimental probabilty density, but log-normal distribution could be more rational for expression of biologial and chronological effects. To reduce scattering of tensile strength, pre-screening concept was proposed.
To date, oblique impact has not been studied and few experimental data on the local damage of reinforced concrete (RC) panels exist for oblique impact of deformable projectiles. The final purpose of this study is to propose a new formula for evaluating the local damage to reinforced concrete structures caused by oblique impact based on past experimental results and simulation results. As the first step of this final purpose, we validate the analytical method by comparison with the experimental results and simulate the damage caused by oblique impact using the validated method. First, we analyze and simulate the local damage of RC panel caused by a deformable projectile owing to an impact test normal to the target structure to verify the validity of the simulation analysis. Next, we perform simulation analyses for evaluating the perforation of RC panel due to oblique impact by the deformable projectile and present the results. Various response characteristics and perforation mechanisms to be the basis of examination of oblique impact evaluation were clarified in this paper.
To develop Pu-burner high temperature gas-cooled reactor (HTGR) attaining very high burn-up around 500 GWd/t, the security and safety fuel (3S-TRISO fuel) is proposed. The 3S-TRISO fuel employs the coated fuel particle with a fuel kernel made of plutonium dioxide (PuO2) and yttria stabilized zirconia (YSZ) as an inert matrix. Especially, a zirconium carbide (ZrC) coating is one of key technologies of the 3S-TRISO, which performs as an oxygen getter to reduce the fuel failure due to internal pressure during the irradiation. R&Ds on ZrC coating directly on the dummy kernel made of YSZ which surrogates PuO2-YSZ have been started in the Japanese fiscal year 2015. As results of ZrC coating tests on YSZ particle by the bromide process developed in Japan Atomic Energy Agency, stoichiometric ZrC coatings with 18 - 21 μm of thicknesses were obtained with 0.1 kg of particle loading weight. As indicated by a thermochemical analysis on the chemical stability of YSZ against the ZrC bromide process, no deterioration of YSZ exposed by source gases of ZrC bromide process was observed through the characterization by Scanning Transmission Electron Microscope (STEM) observation. Finally, reproducibility of stoichiometric ZrC coating on YSZ particle was demonstrated by the bromide chemical vapor deposition process.
Biocoke (BIC) is a solid fuel made from various types of biomass resources. BIC is expected to be a coal substitute fuel because of its high density and high hardness characteristics. In a previous study, we have indicated the effects of formation conditions on BIC properties. In this study, the main structural components of biomass: cellulose, hemicellulose, and lignin, were investigated to systematically deduce the forming properties from the biomass components. The initial moisture content is a critical parameter due to the solid surface reactions by lignin in the formation of BIC. The initial moisture content affects the thermal softening temperature of hemicellulose and lignin as an adhesive of BIC. Thus, we investigate the effects of biomass components and the initial moisture content on compressive strength of BIC. The raw materials of this study were woody biomass (trunk from conifer trees and bark from conifer trees) and herby biomass (bagasse and rice straw). The result of compressive strength shows that trunk BIC has the highest compressive strength among BIC made from those biomass materials. The maximum compressive strength has a directly proportional relation to cellulose content. Due to the increase of the initial moisture content, the maximum compressive strength decreased. The maximum strength could be approximated by a quadratic curve for hemicellulose content.
Levitation improvement of the bending levitation performance of thin steel plate was performed. First, the point of the steel plate where the vibration is predominantly generated was estimated using an ultrathin steel plate with a thickness of 0.18 mm. Furthermore, to decrease the vibration, levitation experiments by means of changing the bending shape and using permanent magnets were performed and the standard deviation of the displacement and levitation probability were evaluated. In addition, to determine the effect of the permanent magnets, the shape of the steel plate was analyzed using the finite difference method. As a result, the main vibration generating area was confirmed to be the longitudinal central edge area of the steel plate. In order to suppress the vibration in this area, the vibration of the steel plate was decreased by making an asymmetrical bending shape. Also, the vibration of the steel plate was suppressed by placing the permanent magnets in the positions that matched with the results of the analysis.
The coupling-matrix-free iterative s-version finite element method is extended to multiple local meshes in order to model multiple local features such as holes, inclusions, and cracks. The formulation with multiple local meshes is presented, along with the stress transfer method between the local meshes. The present method does not require the generation of coupling stiffness matrices with a very sophisticated numerical integration method between the global and local meshes or between the local meshes. Instead, stress transfers between pairs of overlapping meshes are performed. Several numerical examples, such as a patch test, a two-hole problem, and a structure with many holes, are presented. The examples demonstrate that the present method is capable of representing a uniform stress distribution as well as capturing the stress concentration of multiple holes that are located in the vicinity of each other. Moreover, numerical integration methods of the global mesh and local meshes are found to have significant influences on the convergence of the iteration. In these numerical examples, the straightforward Gaussian quadrature could not achieve convergence, whereas the element subdivision technique could. Thus, sufficient element subdivisions in the global mesh and the local meshes are necessary in order to produce a converged solution.