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This paper proposes a method of inelastic structural analysis for YH61 nickel base single crystal superalloy. Hill's anisotropic constitutive equation was applied to describe the elastic-plastic deformation of the superalloy. The equation well described the static tensile curves of the solid bar specimen with and axes at 1173K. The equation also well expressed the torsion curves of hollow cylinder specimens with axis at 1173K. The Hill's equation was applied to simulate the creep deformation of the superalloy. The equation gave satisfactory results for predicting the creep deformation of solid bars having and axes. The Hill's equation was used to predict the creep-fatigue deformation of a cruciform specimen in biaxial loading, resulting in a good agreement with the experimental deformation.

Cell sheet technology enables novel approaches to tissue engineering without the use of biodegradable scaffolds. Cell sheet technology consists of a temperature-responsive culture dish, which enables reversible cell adhesion to and detachment from the dish surface by controllable hydrophobicity of the surface. This allows for a non-invasive harvest of cultured cells as an intact monolayer cell sheet including deposited extra cellular matrices. The monolayer cell sheet can be transplanted to host tissues without using biodegradable scaffolds and sutures. Thick tissue constructs and patterned cell sheets using two or more kinds of cell source are also developed by means of layered cell sheets in vitro. This Progress Report summarizes temperature-controlled cell adhesion-detachment behavior and applications of the cell sheet technology to regeneration of cornea, periodontal ligament, bladder epithelia, oesophageal epithelia, myocardium, and liver.

This paper studies crack growth behaviors in thermal fatigue tests for Rene80 conventional cast and YH61 single crystal nickel base superalloys. A cylindrical specimen with 19.5mm outer diameter and 2mm thickness was used in the thermal fatigue tests. A rapid temperature gradient in cylinder thickness was realized by induction heating of the outer surface and water cooling of the inner surface. Thermal fatigue tests were conducted by changing the outer surface temperature from 303 to 1173K and temperature holdings of 10 and 60minits were inserted at 1173K. Temperature gradient in thickness was 650K. Crack growth behaviors were inspected with interrupting tests. Crack initiation sites coincided with the ‹100› direction on the outer surface whereas ‹110› direction on the inner surface. It was confirmed that crack initiation sites coincide with stress distribution obtained from a structural analysis considering the anisotropy of the single crystal. Cracks were arrested at the depth of approximately 1.0mm due to stress gradients in the specimen.

In order to develop a thermal fatigue life assessment method for high temperature components, out-of-phase thermal fatigue tests were carried out using cylindrical specimens of cobalt-based superalloy HA188 under various temperature ranges. The experiments were conducted in the temperature ranges peaking at 1000°C while starting at 350°C, 760°C and 900°C. A unique testing method was used in which thermal gradients were generated by induction heating for one edge of the specimen and water cooling for the inner and outer surfaces. The results of thermal fatigue test correspond well with the plastic strain range-life data of standard isothermal tests conducted at the peak temperature.

This paper deals with the effects of two types of corrosion resistance coatings, CoNiCrAIY and Al chemical vapour deposition (CVD) coating, on the fatigue-creep interaction life of a cast Ni base superalloy Rene80. Under a fatigue condition, CoNiCrAIY coating improved the resistance to surface crack initiation, while AICVD coatings reduced the number of cycles to surface crack initiation. However, the surface crack propagation rates of both the coated and non-coated specimens were about the same value. It was found that the fatigue life of the coated specimens was affected by the oxidation of the specimen surface and the properties of the coating material. The life under fatigue creep interaction was affected by the failure mechanism (intergranular cracking) of the base metal Rene80 rather than the oxidation and properties of the coating material.

A new life prediction method is proposed for a cast Ni base superalloy, Rene80, under fatigue -creep interaction (FCI) conditions based on its surface crack propagation behavior.In the previous paper, we proposed that the frequency modified total strain energy parameter was useful for evaluating the failure life (Nf) and crack initiation life (Nc) of a high strength superalloy under FCI conditions. The tensile strain energy parameter was obtained from the total tensile strain energy (ΔWTT) and the loading time (τTT) under tensile stress.In this paper, not only the failure and crack initiation lives but also surface crack propagation behavior are found to be evaluated by this parameter under FCI conditions. The surface crack propagation rate (da/dN) is a function of the parameter and surface crack half length (a); da/dN=B'(ΔWTTτnTT)l·awhere B', l, n are material constants.A new life prediction method taking account of surface crack propagation behavior and initiation life can be defined; N2a=A(ΔWTTτnTT)m+B(ΔWTTτnTT)-l(log(2a)-log(2a0))If the grain size (2a0) and the number of cycles [Nc2a0=A(ΔWTTτnTT)m] needed for the surface crack length to grow to 2a0 are known, the number of cycles (N2a) in a certain crack length (2a) can be determined from the above equation.

It is significant to study the difference between thermal fatigue behavior and high temperature low cycle fatigue, in order to understand the fracture mechanism of metals.In this study, thermal fatigue tests (the upper temperature 800°C, the lower temperature 400°C) and low cycle fatigue tests at 800°C were carried out for super alloy IN738LC, and the initiation of a short crack and its propagation behavior were observed.The results of these fatigue tests showed that the difference in fatigue life between them were caused by the differences in crack initiation life and crack propagation rate during the time of the short crack (2a≤2.0mm).On the other hand, it was observed that the fatigue crack propagation behavior was affected largely by the fracture resistance of grain boundary and cell boundary in crystal grains at high temperatures.

CdSb films with various composition were prepared by the two-source vacuum deposition method. Crystallization of the films was investigated for the various evaporating conditions, and electrical properties such as conductivity, Hall mobility and Seebeck coefficient were measured using as-deposited and annealed films with various Cd contents. The films with 10–25% Cd content (weight %) were amorphous of a low conductivity and large Seebeck coefficient. Crystalline state of CdSb appeared at the Cd content of above 30%. Annealing of amorphous films had a remarkable effect on those properties, while crystalline films had little effect.

The correlation between tensile strength and low cycle fatigue life at elevated temperatures was discussed on a cast Ni base supper alloy (16Cr-3Al-3Ti-9Co-Ni) and a Co base super alloy (11Ni-29Cr-7W-Co). Also, an equation for predicting low cycle fatigue life was developed.In the low cycle fatigue tests, the Co base super alloy showed similar fracture behavior in a wide range of temperature. However, the Ni base super alloy showed brittle fracture behavior at low temperatures (ex. 500°C) because of poor ductility, but showed ductile fracture behavior at high temperatures (ex. 900°C) because of high ductility. In the Ni base super alloy, the failure life was defined as the number of cycles when the nominal stress value of a specimen began to decrease from a steady state stress. Tensile and low cycle fatigue data obtained at 500-900°C for the Ni base super alloy and 600-900°C for the Co base super alloy were analyzed by the stepwise multiple regression procedure, and the effect of tensile strength characteristics on the low cycle fatigue strength was discussed. The results of this analysis showed that the relationship between the plastic strain range (Δep) and cycles to failure (Nf) was expressed by a function of ef, while the relationships between the elastic strain range (Δee) and cycles to failure was given by a function of (σ0.2/E) for both super alloys in a wide range of high temperatures, unlike the results of the Universal Slope method. The life prediction equation obtained was as follows:Δe=Δee+Δep=A(σ0.2/E)lNkf+BenfNmfwhere A, B, k, l, m and n are material constants that are independent of temperature.

A new life prediction method was proposed for high strength materials under fatigue-creep interaction (FCI) based on their tensile total strain energy behavior.The net tensile hysteresis energy is now being used to evaluate FCI life in the frequency modified damage function rule developed by W.J. Ostergren. For high strength materials, however, this damage rule seems to require some modification to give good life assesment, because the elastic strain range is much larger than the inelastic strain range in the FCI behavior of these materials.In this paper, strain controlled tensile or compressive strain hold tests with F-F, F-S and S-F wave forms were performed for Cast Rene 80. The total strain energy including a large elastic strain energy was defined, and FCI life was obtained against this strain energy. Multiple regression analysis was carried out to assess the relationship between strain energy and cycles to failure and was expressed numerically to improve life estimation accuracy.Finally, a frequency modified total strain energy parameter was defined to evaluate the failure lives (Nf) of high strength materials such as Rene 80 under the FCI condition. The total tensile strain energy (ΔWTT) and the time (τTT) under tensile stress loading were used to define this tensile strain energy parameter. Thus, ΔWTT·τnTT·Nmf=Cwhere, n, m and C are constants. A similar relation was also obtained between total strain energy (ΔWTT) and crack initiation life (Nc).