In the present study, the Bayesian inference is applied to the fatigue life data including the run-out data (up to the specified number of stress cycles) in order to utilize the censored data for the estimation of fatigue life distribution. Assuming the prior distributions of the needed parameters and using the sample data of fatigue life from the Society of Material Sciences, Japan, the posterior distributions of the parameters and the predictive distribution of fatigue life are obtained. The effects of the sample size and the censored number of cycles on the predictive distribution are also discussed.
The purpose of this study is to develop a practical analysis procedure for nonlinear structural mechanics of composites. Especially, to solve such a nonlinear mechanical problem arising from the microstructural nonlinear behavior, the new homogenization procedure named macro-micro uncoupled method is proposed. First, the homogenized macroscopic material properties are calculated by precise microscopic nonlinear analysis. Then, macroscopic analysis can be performed easily by only referring to the pre-calculated nonlinear material properties. In this paper, RVE approach is taken for the microscopic nonlinear analysis, and the proposed macro-micro uncoupled method is applied to a microstructural large deformation problem of porous media.
Under plane strain compression of two blocks with sawtoothed interface, the sawtooth growth occurred. In the previous paper it was presumed that such growth was caused by the shear-band formation starting from the tip of sawtooth and its degree depended on the material properties of the block. In this paper, the height and width of tested block are 1.6 times and about 2 times larger than those in the previous paper, respectively. The sawtooth pitch is 1mm and the initial sawtooth angles of the interface are 60° and 90° similar to the previous ones. Soft pure aluminum (A1050-O), soft or hard aluminum alloy (A5056-O, H) and pure copper (C1100-O, H) are used. Compression in the case where similar blocks are twinned and also compression in the case where dissimilar blocks are twinned are carried out in the condition of lubricated interface. Furthermore, in the latter, compression where the interface is degreased is also performed. The degree of growth is experimentally investigated. Moreover, numerical simulations are carried out by the elastic-plastic FEM for the case of the dissimilar blocks with the initial sawtooth angle of 60°. In the similar block experiment, the work-hardened material yields larger growth than the annealed material, and the growth in the case of initial sawtooth angle 60° is greater than that of 90°. Larger ratio of total height to sawtooth height gives larger growth. In the case where the dissimilar blocks are twinned, larger difference between material properties leads to smaller growth, and the degreased interface leads to smaller growth than that in the lubricated one. Furthermore, by the simulation of compression where dissimilar blocks are twinned, it is confirmed that the tendency of the general deformation pattern is consistent with the experiment.
An irreversible thermodynamics theory is developed for the constitutive and damage evolution equations for elastic-plastic-damaging materials with special emphasis on the anisotropic aspect of material damage. The internal state of the material is described first by an isotropic hardening variable r, a second rank symmetric damage tensor D and a scalar damage variable β related to the further development of the damage. The effect of crack closure under compression is described by introducing a modified elastic strain tensor εe.The Helmholtz free energy ψ is decomposed into the terms related to global elastic deformation of the damaged material, local elastic distortion due to plastic deformation, and the surface energy generated by material damage. A dissipation potential function F in the space of the conjugate forces of the internal state variables is expressed as the sum of the plastic and the damage parts. The constitutive and evolution equations resulting from these potentials are applied to elucidate the damage process of tubular specimens of spheroidized graphite cast iron under uniaxial tension and torsion.
Tensile tests of sintered tungsten alloys at elevated temperatures were carried out in air and vacuum atmospheres in order to study the temperature dependency of mechanical properties. Liquid-phase-sintered 93.0W-4.9Ni-2.1Fe and 97.2W-2.0Ni-0.8Fe (by wt%) alloy specimens were prepared. The 0.2% proof stress and tensile strength of the sintered tungsten alloys, which decreased with increasing temperature, were higher than those of conventional high temperature structural steels. From the fractographic observations, cleavage fracture of tungsten grains was dominant in the range from room temperature to 500°C, and the area fraction of decohesion of tungsten-tungsten boundary increased in the temperature range above 600°C. For the material with a high volume fraction of tungsten particles and with direct contact of tungsten particles, lower strength was observed at elevated temperatures in air compared with the material with low tungsten content and Ni-Fe layer around tungsten particles, which may result from oxidation through the boundary of tungsten-tungsten particles.
Temperature dependency of bending strength and fracture toughness are investigated for silicon nitride ceramic at high temperature. Furthermore, stable crack growth mechanism and crack propagation properties are studied. The bending strength is fairly constant from room temperature to 1173K. However, it decreases monotonously with further increasing temperature. Load-deflection curves show non-linear behavior in fracture toughness test at temperature above 1573K. Both fracture toughness and crack initiation toughness evaluated from R-curve are almost constant over the tested temperature range, but the crack growth resistance increases with temperature rise. This stable crack growth decreases with increasing cross head speed. Viscous flow area reflecting the process zone is revealed along the crack path at high temperature by thermal etching. The viscous flow area tends to extend with temperature rise and becomes smaller with increasing cross head speed.
The effect of Si-phase on tension-compression low cycle fatigue properties of Al-Si eutectic alloys was investigated. Fatigue test specimens were prepared from two materials produced by two processes, continuous-casting and extrusion. The results obtained are: (1) In the case of continuous-casting, all the fatigue fractures were caused by shear type crack initiation and propagation, resulting shorter fatigue life. (2) In the case of extrusion, the fatigue fracture origin was at Si-phase. (3) In both cases, continuous casting and extrusion, the crack initiation and growth mechanism were essentially identical with those of high cycle fatigue in the range Nf<107. (4) Manson's law can be applied only to the case (2) (extrusion) but not to the case (1) (continuous casting). This is because in the case (1) most of fatigue life is consumed by the growth process of small crack of mode I but in the case (2) crack grows by mode II.
The finite element method is applied to two-dimensional elastic-plastic analyses for underclad crack problems. The analyses are performed rectangular specimens with an underclad crack, which are composed of A533B class 1 steel and a clad material, to obtain the fracture mechanics parameter J-integral and the stress distribution ahead of a crack tip. The Q-factor proposed by O'Dowd and Shih is calculated from the stress distribution ahead of a crack tip, and the constraint effect of a crack tip due to a clad material or the effect of a clad material on the fracture toughness of a base material is discussed in terms of Q-factor. Clad thickness, crack length and the material property of a clad material are varied to examine their effects.
The effects of matrix microcracks on elastic moduli of fiber-reinforced plastics (FRP) laminates and their modeling by means of continuum damage mechanics are discussed. The anisotropic damage states in FRP laminates are described by a damage variable of second rank tensor. The damage models, based on the strain equivalence and strain energy equivalence principle respectively, are developed to describe the relations between the damage variable and the elastic moduli of FRP laminates. The two damage models for matrix cracks of lamina are first formulated. Then, these models are extended to the damage models for laminates by making use of classical laminate theory. Finally, the proposed models are applied to predict the change in elastic moduli induced by matrix microcracks for [±45°]s and [0, 90°]s laminates. Comparison with the experimental results available shows that both of the suggested models can reasonably describe the anisotropic effects of matrix microcracks on elastic moduli of FRP laminates. In case of GFRP laminates under uniaxial tension, the model based on strain energy equivalent principle is shown to give some better description of the damage influence than that based on strain equivalent principle.
In order to characterize the island-delamination type cracking pattern which appears in the brittle film on a ductile substrate under uniform tension, an analysis based on energy consideration was carried out to introduce the relation among the size of island-cracking, the tensile stress at the formation of island-cracking, film and substrate thickness, surface energy of film, interfacial energy between film and substrate, elastic and plastic constants, Poisson's ratio and yield strength of film and substrate. The bulge tests of ceramic and heat-resistant paint films on steel disks show that the size of island-cracking increases and the pressure at the formation of island crack decreases with an increase in film thickness. The film thickness dependency of tensile stress at the formation of island-cracking and the size of island calculated from the analysis agree relatively well with the experimental results.
A low-pressure-plasma spray (LPPS) process is used for the overlay coating of MCrAlY alloy to protect it against high temperature corrosion and oxidation. This coating process has been found to be very effective for gas turbine components. On the other hand, a diffusion coating process has been applied for many years to improve similarly the environmental resistance by enriching the surface of a substrate in Cr, Al, or Si. Recently, aluminizing on MCrAlY coating is used for improving further the high temperature oxidation resistance. However, the aluminizing properties of plasma-sprayed MCrAlY coating, which have an important effect on the coating performance, have not been clarified. In this study, five kinds of plasma-sprayed MCrAlY (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) coating were selected for the aluminizing tests. The heat treated MCrAlY specimens (1393K, 2h, Ar atmosphere) were pack-aluminized at 1173, 1223 and 1273K for 5, 10 and 20h, respectively. The experimental results showed that the aluminum rich layer of NiAl or CoAl phase was formed by aluminizing. It was also indicated that the thickness of the aluminum rich layer showed parabolic time dependence. There is a tendency that the reaction diffusion rate by aluminizing increases with increasing nickel content in the MCrAlY coating.
Recently, the aluminizing of MCrAlY coatings sprayed by a low-pressure-plasma spray (LPPS) process is used for improving the high temperature oxidation resistance. However, the aluminizing properties of plasma-sprayed MCrAlY coatings, which have an important effect on coating performance, have not alway been clarified. In this study, five kinds of as-sprayed MCrAlY (CoCrAlY, CoNiCrAlY, CoNiCrAlY+Ta, NiCrAlY, NiCoCrAlY) coatings were selected for the aluminizing test. The pack-aluminizing was conducted at 1173, 1223 and 1273K for 5, 10 and 20h, respectively. The experimental results showed that the aluminum rich layers of NiAl or CoAl phase were formed by the aluminizing process. It also indicated that the thickness of the aluminum rich layers could be determined, by the parabolic time dependence. There is a tendency that the reaction diffusion rate by the aluminizing increases with increasing nickel content in MCrAlY coatings and the reaction diffusion rate of as-sprayd MCrAlYs is faster than that of the heat treated MCrAlYs (1393K, 2h, Ar atmosphere) in all cases.
Viscosity of high flowing concrete is an important rheological property that dominates the flowabilty of concrete. Supposing that the mix proportion and slump flow of concrete are constant, the viscosity varies with the temperature of concrete and influences on the segregation or rate of placing of fresh concrete. In this study, the influence of temperature on rheological property of cement paste in high flowing concrete was investigated. It is confirmed that the interrelationship between yield value and plastic viscocity of fresh cement paste changed with temperature and that the viscosity became larger as the temperature of paste became lower. Furthermore, this mechanism could be explained by DLVO theory with due regard to the change in adsorption capacity of superplasticizer with temperature.
Intramyocardial pressure (IMP) in an isolated rabbit heart was measured by stretching either the vessel or the myocardial tissue surrounding the interstitial spaces. The vessel was stretched by changing coronary perfusion pressure, and the myocardial tissue was stretched by inflating a balloon in the left ventricle (LV) in noncontracted or contracted state. The IMP was measured with a servo-nulling pressure measurement system through a glass pipette of being less than ten microns. The result showed that IMP was directly related to perfusion pressure both in the noncontracted and contracted states. There was a small effect of LV pressure when the balloon was inflated from 0mmHg to 30mmHg of the LV pressure for the noncontracted state but not for the contracted state. The result indicates that IMP is increased either by internal stretching of the vessel or by external stretching of the myocardial tissue. The LV cavity pressure is not a major determinant of IMP.