Balance equations for higher-order materials have been widely studied. In this paper, Gibbs equations for higher-order materials are formulated introducing a concept of the equivalence between higher-order stress powers and heat flux. Gibbs equations for higher-order materials and simple materials are expressed with microscopic quantities by use of the microscopic expressions such as stress power, higher-order stress powers and internal energy. The results obtained from the simulation of molecular dynamics can be substituted into the microscopic expressions of Gibbs equations. The values of entropies for higher-order materials and simple materials can be calculated in this procedure. It is shown that the difference in entropies between higher-order materials and simple materials becomes notable in an example of the calculation.
This paper deals with stress analysis of elliptical and ellipsoidal inclusions using singular integral equations of the body force method. The stress and displacement fields due to a point force in an infinite plate and a ring force in an infinite body are used as fundamental solutions. On the idea of the body force method, the problems are formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where unknown functions are densities of body forces distributed in the x- and y-directions of infinite plates or in the r- and z-directions of infinite bodies having the same elastic constants of the matrix and inclusions. In order to satisfy the boundary conditions along the inclusions, eight kinds of fundamental density functions proposed in our previous paper are used. Then the body force densities are approximated by a linear combination of the fundamental density functions and polynomials. The present method is found to give rapidly converging numerical results for both of the axial symmetry tension and uniaxial tension. The calculations are carried out systematically for various shape, distance and elastic constant of inclusions and the stress distributions along the boundaries are shown in figures. Then the interaction effects are discussed through the comparison between the elliptical inclusions and ellipsoidal inclusions.
The object of this paper is the establishment of the method to estimate fiber length distribution in a short fiber reinforced composite without extracting fibers. In the previous paper, the author has already led the method to estimate a relationship between fiber length in the composite and partial visible length of the fibers observed from the composite surface in assuming that the matrix is transparent. But, this method has some weak points. At the first half of this paper, the proposed method is refined, and the weak points are dissolved. At the latter half, the partial visible length is measured by using a scanning acoustic microscope from the surface of the short fiber reinforced plastics, and fiber length distribution in the composite is estimated from the obtained partial visible length distribution. Furthermore, the fibers are extracted from the composite inside, and the fiber length is measured by using an optical microscope directly. The fiber length distribution estimated from the refined method is compared with that measured directly and then the cause of the difference between two distributions is argued.
In order to formulate an inelastic constitutive equation of polymer matrix composites, back stress in the kinematic hardening creep theory of Malinin and Khadjinsky extended to anisotropic materials is evaluated experimentally under various loading conditions. After brief discussion to evaluate the back stress from experimental results, we perform several tests for tubular specimens under various loading conditions ranging from monotonic loading with step-up change in stress rate to reversal loading in axial and torsional modes. Then the evolution of back stress with respect to the change of viscous strain is calculated for these tests. The stress-strain relations together with back stress-viscous strain relations are simulated also by using Armstrong-Frederick model of kinematic hardening. By comparing the results of Armstrong-Frederick model with those of the corresponding experiments, we discuss characteristics of the evolution of back stress in polymer matrix composites and further elaboration of kinematic hardening rule for the composites.
At the heading of high-tensile bolt with work-hardend drawing wire, Bauschinger effect appears and raises the tool life. On the other hand, this effect reduces the shank strength of bolt. This paper proposes the steel which has large Bauchinger effect at the heading of drawing wire and the aging process which reduces the Bauschinger effect in the bolt shank. Mn or Si do not raise the Bauschinger effect. Carbon raises this effect and the high cooling rate after rolling of wire is useful too. Reduction of yield strength and tensile strength of bolt shank after compression are 15-17% and 6-7%, respectively. These reductions in strength are recovered by aging. It is concluded that aging at 573K recovers the reduction of yield strength and tensile strength of bolt-shank by the compression under strain no more than 0.03. During the compression of drawing wire, X-ray diffraction half value breadth which corresponds to the dislocation density indicates constant value. This fact suggests that the number of dislocations which are newly genereted under compression is nearly equal to that which distinguishes by the Bauschinger effect.
An assessment method to determine delamination strength by using a peel test is proposed for a thin film on the head in a hard disk drive. Delamination strength is assessed by comparing critical delamination energy release rate measured experimentally by a peel test with delamination energy release rate analyzed using a finite element method. Critical delamination energy release rate is a parameter corresponding to adhesive strength. Critical delamination energy release rate varies from sample to sample and depends on the peel velocity, therefor it is necessary that variation and dependence on the peel velocity of critical delamination energy release rate are considered to assess delamination strength. From this method, probability of delamination can be estimated for a thin film on the head in a hard disk drive.
One of the authors has derived K (r, θ), namely the equation of extrapolation curve in a series and proposed a new short-cut method called V-line extrapolation method. Also, it was reported there are the specific angles at which we can obtain an accurate stress intensity factor by using boundary element analysis. In this paper, an application of the V-line hybrid extrapolation method was conducted to finite element analysis by an approximate angle which is easy to use. At first, it is found that the accuracy of S.I.F is considerably improved by using the angles, i.e. σy at θ=π/2, τxy at θ=π/4 in a plate with a central slant crack under remote tension. Furthermore, the effects of element types to the accuracy were discussed. It is clarified that the accuracy for KI by the V-line hybrid extrapolation method applying to 4 nodes-element is much better than the one by the conventional method applying to 8 nodes-element.
This paper describes a method of predicting the degradation in safety and determining the optimum time and degree of strengthening for existing concrete bridges. Degradation in safety is predicted by using a degradation curve based on material tests on the target bridge and statistical data for safety evaluation. For strengthening of bridges, the external prestressing is used to improve the stiffness and load carrying capacity. For optimization of strengthening, a multi-attribute utility function is introduced to express a multiple objective function as the measure of effectiveness of design lifetime, safety and load carrying capacity. The optimization problem is one of determining the optimum time and degree of strengthening in order to maximize the utility function. A genetic algorithm is applied to the procedure of searching global extreme values of the objective function. The proposed method is applied to an actual bridge of 41 years old. Remaining life and the optimum strengthening method for extending the lifetime to the expected value are shown and suitability of the method is discussed.
The modified austempering was applied on the ductile cast iron (DCI) to enhance its mechanical properties. This treatment named ausquenching consists of short time austempering, direct water quenching and light tempering. In this combined heat treatment, the first austempering process takes much effect on the tensile property and toughness of ausquenched DCI (AQDI). AQDI shows higher 0.2% proof stress, tensile strength and fracture toughness than the austempered DCI (ADI) at the temperature range of upper bainite. AQDI has a complex structure of bainitic-ferrite, light tempered martensite and retained austenite. For the purpose of quantitative evaluation on the compound matrix of the martensite and the bainitic-ferrite, the X-ray diffraction profiles of α-Fe were analyzed by the curve fitting technique using Pseudo-Voight function. The profile was able to separate into two parts by the difference of carbon content. From these results, it was possible to estimate appropriate each phase fraction of the complex structure.
A novel technique in which pulse laser irradiation is used to improve residual stress of material surface has been developed. When a material surface is irradiated by a high-energy pulse laser, the impulsive wave, which is generated by the high-pressure plasma, propagate into the material interior, thereby inducing high compressive stress on the material surface. The stress improvement for Type 304 stainless steel was evaluated to apply it to reactor internals in light water reactors as a preventive maintenance technique. Remarkable stress improvement was obtained for Type 304 stainless steel, the thickness of a compressive stress layer was much larger than that in the case of conventional peening techniques, and the compressive stress depth profiles virtually independent of the material strength (cold working rate). The effects of processing parameters, i.e., spot diameter, pulse energy and pulse number density, on the stress improvement of Type 304 stainless steel were investigated. It was also confirmed from metallographical structure and AES analysis that there was not much thermal effects on the material due to the laser irradiation.
Alumina precursor was coated on the glass fibers by sol-gel method using aluminum alkoxide solution. The addition of silane coupling agent led to high adhesion force between glass fiber and alumina precursor films. Alumina precursor coating on glass fibers enhanced alkali-resistance and tensile strength. GRC was produced using alumina precursor coating glass fiber. Microstructure of fiber reinforced cement was observed by SEM after the cure in the water at several temperatures. Alumina coating demonstrated that mechanical property of fiber reinforced cement was superior to original GRC after curing in the water at several temperatures.
Perfluorocarbon liquid coolant Fluorinert® FC-72 for electronic devices has a high thermal stability and a low chèmical reactivity. However, FC-72 has been shown to liquate some organic materials. Polyimide has been used extensively in electronic devices as an insulator and as a protective coating. In the present study, the degradation behavior of polyimide in FC-72 was investigated by measuring chemical and mechanical properties. It was found that polyimide had no change of chemical properties, such as dissolution of the constituent and swelling degree, and mechanical properties, such as tensile strength and peel strength in dry FC-72. At temperatures below 150°C, the tensile strength of the polyimide did not degrade by thermal oxidation. The swelling ratio and peel strength degraded as the saturation ratio of dissolved water increased. At temperatures above room temperature, the saturation ratio of dissolved water in FC-72 decreased because of the increasing solubility of water. The absorbed water in polyimide decreased because of the decreasing saturation ratio of dissolved water in FC-72. In this case, the water didn't have much influence on the polyimide degradation.
The hydration of cement containing quick setting agents, where the setting agents were based on calcium aluminate, was investigated to discuss the relationship between quick setting properties and hydration characteristics of calcium aluminates. The calcium aluminate with different crystallinity and different CaO/Al2O3 molar ratio of 1.74 and 2.53 were synthesized by means of air quenching method. The following results were obtained. (1) A mixture of cement and calcium aluminate without additives did not have quick setting properties. (2) when a quick setter composed as a mixture of calcium aluminate with suitable amount of NaAlO2, Al(OH)3, CaO, Na2CO3 and CaSO4, the addition of 7% of the quick setter for cement mixture with W/C ratio of 0.6 resulted to set the paste within 30s to 2min. A mortar with W/C ratio of 0.6 and SO3/CaO ratio of 0.33 set within 10min. (3) Non-crystallinity and high CaO/Al2O3 molar ratio were very important for quick setter based on calcium aluminate. (4) A cement paste with 7% of quick setter evolved a large amount of heat of initial stage of hydration, which corresponded to the amount of ettringite formed. The larger the heat of hydration, the faster the setting time. In a paste having a good quick setting property, ettringite with 5 to 10μm in size were formed and these hydration products were well connected each other.
In this study, the application of electrodeposition method to repair reinforced concrete damaged by drying shrinkage cracks was investigated experimentally. Especially, it was clarified that electrodeposition had an effect on the reduction of water permeability and carbonation. The contents of this study were as follows; (1) the selection of external solution, (2) the influence of electrodeposition on the crack closure, and the effect of electrodeposition on the water permeability and carbonation restraints, (3) the influence of electrodeposition on the surface coating and minuteness on the non-cracked mortar, and the effect of electrodeposition on carbonation restraint, (4) the water permeability and adhesive strength after the electrodeposition. As a result, it was clarified that the electrodeposition led to improvement of mortar watertightness and carbonation restraints.
Grain boundary corrosion of SUS304 and SUS304L stainless steels sensitized for 0.1 to 24h at 675°C was studied by atomic force microscopy (AFM) and an electrochemical potentiokinetic reactivation (EPR) technique. The specimens for AFM observations were polished carefully and exposed to 10% oxalic acid. The width, depth and angle of the grain boundary grooves of variously sensitized specimens were measured from the profile of grain boundary groove observed by AFM. It is shown that both the depth and width of grain boundary grooves increase and the angles of grooves become narrower with an increase in sensitizing time. The relationship between the degree of intergranular corrosion, profiles of grain boundary groove and estimated grain boundary energy of the sensitized stainless steels was discussed. It is suggested that the grain boundary energy obtained from the grooves angle becomes large with an increase in sensitizing time. This result coincides with that obtained from EPR measurment. AFM is a powerful technique for investigating the mechanism of grain boundary corrosion.
Corrosion resistance of coated TiN film is governed by pinhole defect. Therefore, it is necessary to evaluate the existing state of defects. The Critical Passivation Current Density (CPCD) method had some problems though this method could quantitatively estimate defects as a pinhole defect ratio (%). The most important problem is the overestimation in defect ratio evaluation in the cases when large corrosion pits were generated and some parts of TiN films were exfoliated due to its low adhesion strength and high residual stress. Therefore in this study, the adhesion characteristics of TiN films which was coated by plasma CVD was investigated by the scratch test. The applicable range of the CPCD test was made clear for the defect ratio evaluation of TiN films with various film thickness and adhesion strength. And then, some improvements of CPCD test for avoiding the overestimation of defect in film are discussed.
There are weathered and erosive reddish soils called “Kunigami Maaji” in the northern part of Okinawa-jima. The distribution area of the reddish soils inclines steeply toward the seashore. The running water due to the typhoon and heavy rain erode the reddish soils. The flow out soils have made the sea water contamination, and it gives us the problem of environmental geotechnics. The non-woven sheet has been used to filter the muddy water running into the deposit pond. The purpose of this experimental study is to investigate the changes of the permeability of the filter caused by clogging of the reddish soil particles. The experiments with 3 types non-woven sheets were carried out in order to find the effect of the types of sort of sheet, for representative soils and concentration of muddy water.