This paper deals with the standardized transformation methods of systems reliability-based design for structural reliability and safety. In the structural reliability theory, though many studies are developed on the standardized space until now, a series of the systematization of standardized transformation methods have not been performed yet. Most of that these procedures are multivariate statistical techniques by structural, material and mechanical engineers. These methods should be utilized to map out design space into evaluation space for safety assessment. It is necessary to indicate these methods are important for reliability analyses and estimations. It is able to consider that the standardized transformations are classified both non-normalization of design parameters and uncorrelation of those. This is very useful for the systematization of different transformation algorithms. Therefore, it is reviewed the transformation of design space into each standardized spaces by using each procedures. Firstly, it is reconsidered about nonlinear characteristics of non-normalization transformations by introducing among approximated joint non-normal distribution models, coefficient of correlation between design parameters and the other higher order moment statistics. Secondly, the uniqueness and identity of safety indices under each uncorrelation transformations like Cholesky decomposition, and so on are derived. Finally, it is verified that each standardized transformation procedures have exactness and validity by the evaluation of numerical analyses for some examples in the structural reliability problems.

View full abstract

Two expert systems, that diagnose the sensitivity of environmentally assisted cracking (EXENAC; EXpert system for ENvironmentally Assisted Cracking）and the causes of failure of environmentally assisted cracking (EAC), based upon fractography have been developed using the OPS83 programming language. The former system is composed of three independent subsystems, which respectively diagnose the sensitivity of ⅰ）stress corrosion cracking of austenitic stainless steels in a low- or high-concentration chloride solution and/or high-temperature water, ⅱ）hydrogen embrittlement of high-strength steels in various aqueous solutions and gaseous environments, and ⅲ）hydrogen attack of steels in high-temperature high-pressure hydrogen gases. The knowledge base covers the rules relating to environments, materials, loading conditions, heat treatments, material processing including welding and their interaction as well as fracture surface morphologies. The knowledge base consists of production rules, which have certainty factors to represent the uncertainty (contribution）of each rule to environmentally assisted cracking. The adoption of certainty factors enabled the uncertain but widely applicable knowledge to be built in a knowledge base, which in turn raised the flexibility of diagnoses made by the expert system. Applying the developed expert system to the case histories the diagnoses were accurately made. We discussed the characteristics of the individual knowledge base, related diagnosis results, and the suitable knowledge base structures for diagnoses in the area of environmentally assisted cracking. It is desirable that the inference is made through the plural affirmative and negative rules being executed. We also proposed the quantitative measure to evaluate the importance of each rule in the diagnosis. The latter is composed of three independent subsystems, which respectively deal with EACs of high-strength or high-tensile strength steel, aluminum alloy, and stainless steel in dry and humidified air, water, and aqueous solutions containing Cl, Br or I ions. The concerned EAC issues cover stress corrosion cracking (SCC), hydrogen embrittlement, cyclic SCC, dynamic SCC and corrosion fatigue as well as fatigue and overloaded fracture. The knowledge base covers the rules relating to not only environments, materials, and loading conditions, but also macroscopic and microscopic fracture surface morphology. In order to deal with vague expressions of fracture surface morphology, Fuzzy theory is used in the system, and the description of rules about vague fracture surface appearance is thereby possible. Applying the developed expert system to case histories, accurate diagnoses were made. We discussed the related diagnosis results and usefulness of the developed system.

View full abstract

Hexagonal boron nitride-copper composites were prepared by hot pressing. The boron nitride in the composites possessed well-developed crystal structure charaterized with an extremely low distance between boron nitride layers. Independently on the particle size of the starting copper powder, the grains of the metal in the composites showed a narrow distribution in their size, given by the interfacial tension between the ceramic and metal phases. By the transmission electron microscopy, joints between boron nitride grains and copper granules having the highest occurrence on the boron nitride facets, represented by its (001）crystallographic planes, were observed. This confirms the strong directionalism of the metal-boron nitride interaction, mediated by π electronic orbitals of the latter.

View full abstract

The interlaminar shear strength (ILSS）in CFRP was obtained using a double-notch shear (DNS）test to study the fiber orientation effects. The laminate configuration was 〔－α/＋α/－α/＋α〕s, where α＝0°, 15°, 30°, 45°, 60°, 75°and 90°. A shear-lag analysis was conducted to predict the ILSS as a function of fiber orientation, considering that the thickness of the interlaminar shear layer is a function of fiber orientation α. The ILSS was determined by the maximum shear stress criterion. The dependence of the ILSS on fiber orientation was qualitatively predicted by the shear-lag analysis.

View full abstract

In this study, the Arcan type test method is adopted to evaluate the fracture toughness of the unidirectional FRP(GFRP, CFRP）under mixed mode loading. The effects of the mixed mode ratios on the fracture toughness and the difference of the fracture toughness between reinforced fibers are investigated. By incorporating the effect of proceeding micro crack which is observed during the experiment, it could simulate the entire fracture process including the initial failure process, and the propagation of the damage zone was also well represented by applying the analytically obtained fracture elements. Considering an orthotropic property of the unidirectional FRP, the stress intensity factor at the starting point of crack initiation was calculated by finite element method. Consequently, in the case of GFRP, a mixed mode fracture criterion is proposed in the form of an ellipsoidal curve. On the other hand, in the case of CFRP, it is proposed in the form of an ellipsoidal curve and a line on K Ⅰ and K Ⅱ plane. The physical meaning of the fracture toughness obtained in this study was discussed. A good agreement with whole fracture process between the experimental and the analytically obtained results was observed. Finally, for the unidirectional FRP specimen subjected to mixed mode loading, the validity of the elasticplastic analysis using Hoffman's law as a condition of fracture was discussed and the validity of this modeling of the proceeding micro crack was also examined.

View full abstract

Composite materials are used widely because of it's excellent functional properties. The homogenization method has been proposed to evaluate effectively both homogenized material properties and microscopic stresses of composite materials. In this paper, the authors present a variational formulation and a finite element fromulation of the homogenization method for elasticity, heat conduction, thermoelasticity and dynamic viscoelasticity. To design composite materials, the authors develop a homogenization analysis system based on general-purpose finite element method code, ABAQUS. The results of the numerical analysis show that the proposed analysis system is useful from the point of accuracy.

View full abstract

A convenient method for quantitative evaluation of time dependent stress and strain around a contact region under moving load is discussed. In this study, a rectangular viscoelastic strip made of an epoxy resin is loaded by a cylindrical hard roller moving along the upper edge. In order to realize a typical non-proportional loading condition, the cylindrical roller is moved at a constant velocity from rest under two different temperature conditions covering remarkable viscoelastic response of the material. The well-known Diagonal Summation Theorem in photoelastic technique is extensively applied to a number of sets of plane polariscope images under viscoelastic conditions of the material. Time variation of fringe order and principal birefringence direction at two different fixed points located near contact are successfully measured and not only the time dependent principal stress and strain differences but also their principal directions evaluated.

View full abstract

The tensile static and fatigue tests for the conical shaped FRP joints using polymeric adhesives (FRP joint）were conducted at wide ranges of loading rate and temperature. The time and temperature dependencies on the static and fatigue strengths of the FRP joint were investigated from the viewpoint of the viscoelastic behavior of the matrix resin of FRP rod. The static and fatigue strengths of the FRP joint and these fracture modes are remarkably dependent on time to failure and test temperature. The time-temperature superposition principle for the viscoelastic behavior of the matrix resin of FRP rod holds for the static and fatigue strengths of the FRP joint. Therefore, the master curves of static and fatigue strengths for the FRP joint can be obtained, and this fact enables us to estimate the fatigue strength at an arbitrary loading rate, temperature and number of cycles to failure.

View full abstract

Cold drawing products obtained from preliminarily rolled sheets of HDPE, PP, POM, PC, ABS and PVC were studied on their elastic and thermal recovery, and secular change of dimension. The optimum amount of reduction in thickness in rolling, and effect of heat treatment, were made clear in order to attain the best qualities of cold drawing products. The cold drawing products obtained from preliminarily rolled sheet was found to have extremely good dimensional stability by low of reduction in thickness and cross rolling. This cold drawing process was applied to make small cups and dishes, and good results were obtained.

View full abstract

In recent years, plastic packing is causing a new social problem as a generator of plastic garbage or a new source of environmental pollution. Attracting attention in this respect is laminate packing with which plastic can be more efficiently utilized than with conventional plastic packing. Since the laminate packing uses composite material consisting of sheets of extremely thin film pasted together, easy breakage has been experienced in many cases during services. A countermeasure experimentally applied was to increase thickness of a part of sealed portion of the laminate film to improve tensile and impulsive tensile strength. Investigated in addition was the effect of seal length. As a result, it was confirmed that up to a certain thickness a proportional relationship was maintained between the thickness and tensile/impulsive tensile strength. Also found was that there was a certain seal length with which the tensile/impulsive tensile strength was effectively improved.

View full abstract

This paper describes the influence of molding conditions on residual stress in injection molds. Polypropylene (PP) resin plates are molded under various molding conditions which changed dwelling, injection speed and molding temperature. First, the fundamental equations for residual stress are derived using a thermoviscoelastic model and the generation mechanism of residual stress is explained qualitatively. Second, the thermoviscoelastic properties of PP resin plates which have a direct effect on the residual stress are carefully measured. Finally, the residual stresses in PP resin plates are measured by a layer-removal method and are calculated by using fundamental equations considering thermoviscoelastic properties. By comparing these residual stresses under various molding conditions with the thermoviscoelastic properties mentioned above, the influence of molding conditions on generation mechanism of residual stress in injection molds is discussed.

View full abstract