To determine the transformation plasticity coefficient, a three-point bending system is employed and the large deflection due to transformation plasticity in bending is analyzed under the simplified assumption that transformations occur uniformly across the cross-section of a beam. It is shown that the deflection due to transformation plasticity is similar to that due to elastic deformation, and simple relationships are also derived between the ratio of the maximum deflection to the elastic deflection and material constants (transformation plasticity coefficient K and Young’s modulus E). Experiments are carried out for a slender bar specimen, which is loaded in a three-point bending system, and the austenized specimen is cooled so that martensite transformation accompanied by transformation plasticity occurs and the profile and maximum value of the deflection of the specimen are measured. The measured profiles of deflection agree very well with the theoretical results. This proves the validity of the proposed method. The transformation plasticity coefficient is also determined by the proposed method.
The magnetoelastic plane problems of an infinite soft ferromagnetic strip containing two symmetric edge cracks normal to the boundary are formulated in terms of a singular integral equation. The main purpose of the paper is to investigate the effect of magnetic fields on the stress intensity factors. The solutions of the problems are obtained for a uniform magnetic field normal to the crack surfaces and for uniaxial tension applied to the strip away from the crack region. A strain gage method is also employed in tensile tests to determine the magnetic stress intensity factors. The theoretical results for the plane stress case agree very well with the experimental values.
We developed a method for optimizing strain to reduce gate leakage current in metal-oxide-semiconductor (MOS) transistors by using first-principles calculations. This method was used to investigate the possibility of decreasing gate leakage current by controlling the strain on gate dielectric materials. We found that tensile strain increases the leakage current through both silicon oxide (SiO2) and silicon oxynitride (SiON) gate dielectrics, whereas compressive strain hardly changes the leakage current through SiO2 gate dielectrics and decreases the leakage current through SiON gate dielectrics. These changes reflect strain-induced changes in the band gaps of these materials. Using finite element analysis to estimate the strain in MOS transistors, we showed the usability of SiON in terms of gate leakage currents and the importance of controlling the strain on the gate dielectric materials.
As a background of the ultrasonic characterization of contact interfaces, ultrasonic wave propagation characteristics at contacting solid surfaces have been studied numerically and experimentally. The wave propagation along the contact interface has been simulated by the two-dimensional finite difference method, assuming a spring-type interface with normal and tangential stiffnesses. The analysis has verified that the antisymmetric-mode interface wave can be generated by the shear excitation at one end of the interface, and its phase velocity can be evaluated with good accuracy from the waveform received at the other end. Measurement of the phase velocity of the interface wave has been carried out for contacting PMMA surfaces under different contact pressures, together with the shear-wave reflection measurement to evaluate the interface tangential stiffness. The measured relation between the phase velocity and the tangential stiffness has been shown to agree well with the theoretical relation for the antisymmetric-mode interface wave.
Aluminum carbody for rolling stock is light and easily recycled, but includes severe defects which are very dangerous to fatigue strength. Strength evaluation of a carbody by static load test has been performed. However, true evaluation of fatigue strength could not be performed because fatigue failure is caused by dynamic alternating loads. In this study, to evaluate fatigue strength of the aluminum carbody of urban transit unit, a large scale testing method to simulate actual dynamic loads is proposed and the fatigue failures of the carbody are investigated. The test results are compared with the estimated results by static load test and structural analysis. Also, the differences between the results are discussed. The compared results show that flexural response of the carbody plays a significant role in occurrence of fatigue failure. The estimation of fatigue failure based on static load test or static analysis may provide misleading results. It was also verified that the fatigue life characteristics of the aluminum carbody can be estimated from the published fatigue test data for aluminum components with similar joint detail. Test and evaluation of fatigue strength based on the established static load test method needs to be modified to consider dynamic response of the carbody.
The effects of carbon and nitrogen on the creep strength and microstructure of precipitation-strengthened 15Cr ferritic steel have been investigated. The creep rupture lives of 15Cr ferritic steel with the addition of 0.07mass%N and with a combination of 0.05mass%C and 0.03mass%N were extended longer than that of the conventional ferritic creep resistant steel of ASME T92. However, excess addition of carbon and nitrogen resulted in a decrease in long-term creep strength. For the steel with 0.07mass%N addition, which showed excellent long-term creep strength, many plate-shaped fine precipitates and a few coarse block-type ones were observed. The volume fraction of precipitate free zone in this steel was smaller, and the coarsening rate of the fine precipitates identified as intermetallic compounds in this steel was lower than that of the other steels. The long-term creep strength of the present steel was improved by the addition of 0.07mass%N through the precipitation strengthening effect of many uniformly distributed stable fine particles.
The present work presents a method to estimate elastic-plastic J for circumferential through-wall cracked pipes for the Leak-Before-Break (LBB) analysis of pressurized piping. The proposed method is based on the GE/EPRI approach and the key issue is to propose a robust Ramberg-Osgood fitting procedure. Two different estimation schemes are given, one for the case when full stress-strain data are available, and the other for the case when only yield and ultimate tensile strengths are available. The proposed J estimates are compared with those from extensive elastic-plastic finite element (FE) analyses. Experimental validation is also performed by comparing maximum moments predicted by fracture mechanics analysis using the proposed J estimates with those from full-scale pipe test. Both results show sufficient confidence in the accuracy of the proposed J estimates.