It is well known that plasma spray condition affects the mechanical properties such as elastic modulus, coefficient of thermal expansion (CTE) and coating fracture strength. Therefore, residual stress formed in the sprayed coating and coating stress generated during in-service are dramatically changed with the plasma spray condition. In this study, effect of several kinds of plasma spray conditions on the mechanical property of ceramic coating in thermal barrier coating system was examined experimentally. Typical thermal barrier coating system composed of a partially stabilized zirconia (its chemical composition is 8wt% Y_2O_3-ZrO_2) and CoNiCrAlY bond coating was selected herein. In-flight particle velocity and temperature, and the substrate temperature were changed as the plasma spraying process parameter. For the ceramic coating, the microstructural parameter such as porosity and Vickers hardness, and the mechanical property such as CTE, elastic modulus and bending fracture strength were measured systematically. As the results obtained by this study, it was found that elastic modulus and bending strength of the ceramic coating were proportionally increased with Vickers hardness, which can characterize mechanical properties of the plasma-sprayed coating.

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A body force distribution method is presented for the dynamic elasticity problems of an infinite plate subjected to harmonically vibrating forces, under the plane strain condition. Recently methods of solution by using fundamental solutions are actively considered and called MFS. The method of solution shown in this paper is one of MFS. The fundamental solution used here is a steady-state solution for an infinite elastic plate subjected to a harmonically vibrating body force acting at a point in an infinite elastic plate. The principle of the method of solution is to distribute body forces so as to satisfy boundary conditions for problems to be solved. The results obtained from the present method to an infinite plate with a circular hole subjected to a harmonically vibrating pressure are in good agreement with the exact solution. The stress concentration problem of an infinite plate containing a square hole with rounded corners subjected to a harmonically vibrating pressure is considered by the present method.

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The effects of notch size and fiber orientation on the off-axis notched strength of the fiber metal laminate GLARE-3 are examined. Static tension tests are performed on unnotched and notched (center open hole) specimens with different fiber orientations for these ends. It is clearly observed that the notched strength of GLARE-3 exhibits not only notch size dependence but also fiber orientation dependence. A new and efficient failure criterion for the tensile failure of notched orthotropic materials for any notch size and for any multiaxial state of stress is developed. It is formulated by combining a net section stress criterion with a fracture mechanics based criterion for a Griffith crack so that prediction of any notch sensitivity bounded by the notch sensitive and insensitive limits is allowed. From the proposed multiaxial failure criterion for notched orthotropic materials, an analytical formula for predicting the off-axis notched strength of orthotropic laminates is also derived. This formula reveals that the proposed failure criterion is characterized by a new concept of the principal normalized fracture toughness (or the concept of the principal stress brittleness numbers) of a given orthotropic material. It is demonstrated that the off-axis notched strength of GLARE-3 can accurately be predicted by the proposed failure criterion, regardless of the notch size and fiber orientation.

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In this paper, the mixed-mode fracture problem of two penny-shaped or annular cracks in a functionally graded piezoelectric material (FGPM) strip is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under electric loading. The crack faces are supposed to be insulated electrically. The problem is formulated in terms of a system of singular integral equations, which are solved numerically. Numerical calculations are carried out, and the stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crak size, the crack location, and the material nonhomogeneity. It can be found that the normalized intensity factors are under the great influence of the geometric parameters and the effect of the material nonhomogeneity on the intensity factors depends on the geometric parameters.

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In this paper, the problem of an infinite row of parallel cracks in a functionally graded piezoelectric material strip (FGPM strip) is analyzed under transient thermal loading condition. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the bottom surface. The superposition technique is used to solve the governing equations. The transient temperature and thermal stress in an uncracked strip are the same as the previous results. This thermal stress is used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. By using the Fourier transform, the thermoelectromechanical problem is reduced to a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. The stress intensity factors for both the embedded and edge cracks are computed. The results for the crack contact problem are also included.

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In order to investigate the fatigue properties of extruded magnesium alloy in very high-cycle regime, rotary bending fatigue test was performed in ambient atmosphere at room temperature using the hourglass shaped specimens of AZ80 alloys extruded (F-specimen) and treated by an artificial aging after extrusion (T5-specimen). From the experimental results, there is no difference in fatigue lifetime between both specimens in the high stress amplitude level, but the T5-specimen had shorter lifetime compared with the F-spesimen in low stress amplitude and high number of cycles, even though higher static mechanical properties with the aging. Both specimens show a clear step-wise S-N curve on which two knees exist. Specific stress amplitude formed the knee corresponded to the yield stress of 160MPa in compression. It was concluded from the detailed observation of fracture surface that the step-wise S-N curve was induced by the crack initiation mechanism changing from the twin deformation in high stress amplitudes to slip deformation in low stress amplitudes, because of a mechanical anisotropy caused by the extrusion and the particular deformation characteristics of the hexagonal crystal structure in a magnesium alloy.

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Fatigue crack propagation behavior of ultrafine-grained copper precessed by equal channel angular pressing, ECAP, was investigated by electron backscatter diffraction, EBSD, technique as well as atomic force microscopy, AFM. The results show that the crack propagation rate, da/dN, was smaller in ECAP-processed specimen than the coarse-grained counterpart at higher stress intensity factor range, ΔK. The decrease in the da/dN in spite of the small grain size is attributed to the grain coarsening at the crack tip during fatigue which results in the increase in the roughness induced crack closure. In the range below ΔK<5MPa√<m>, Region I, large-scale grain coarsening in the limited number of grains is dominant due to the small ΔK and the large number of fatigue cycles to cross the plastic zone, N_p. In the range above ΔK>5MPa√<m>, Region II, small-scale grain coarsening in many grains is dominant due to large ΔK and small N_p. The grain coarsening was introduced as a result of the migration of high angle grain boundary. The large initial transgranular strain and unstable grain boundaries are considered to be the causes of the strain-induced grain boundary migration. The X-ray stress at the crack tip was found to be smaller than δ_<0.2> due to the strain relaxation and grain coarsening.

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Crack growth behavior of SCM440H low alloy steel enhanced by absorbed hydrogen was investigated. A continuous hydrogen charging method was designed, in which the crack tip was isolated from the solution environment and kept dry. Six materials which were tempered at different temperature were used. Effects of stress ratio, loading frequency, hold time and material hardness on the crack growth rate were examined under long term varying load and static load. An acceleration of crack growth rate about ten times compared to the uncharged material was commonly found in all materials. In addition to this, however, unexpected acceleration of crack growth up to 1000 times was experienced in certain condition. In materials with Vickers hardness higher than 280 tested at low frequency, this marked acceleration was experienced. The crack surface morphology was quasi cleavage. This critical hardness (HV=280) is a little lower than the usually accepted critical hardness for delayed failure (HV=350). In material with Vickers hardness lower than 268, however, such a marked acceleration was not experienced. The use of low strength material is desirable to prevent the cracking enhanced by hydrogen.

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Effect of microstructural control on tensile behavior for a 17Ni-0.2C steel was studied. Ultrafine microstructures with less than 1μm grain size were prepared by cold rolling of martensite structure followed by appropriate tempering. A drawback of little uniform elongation in ultrafine grained alloys has been overcome by introducing austenite grains in the ultrafine grained ferrite matrix. In this ferrite-austenite steel, work hardening after Luders deformation increased due to stress-induced martensitic transformation, so that the onset of necking was delayed resulting in large uniform elongation. The Luders deformation was suppressed by skin-pass rolling for the ferrite-austenite steel. Another method to avoid the appearance of Luders deformation was realized by changing the tempering condition, i.e., by introducing fresh martensite upon cooling after tempering. In this case, microstructure was composed of ferrite, austenite and martensite and an excellent combination of tensile strength and elongation was obtained.

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In the previous paper, it has been clarified that the worn volume of fretting wear under magnetic field increases in lower frequency. This paper deals with the effects of fretting slip amplitude that is one of the most important factors in fretting wear. The fretting wear tests were carried out in slip amplitudes ranging between D=6 and 32μm and under the Hertzian contact of steel ball and plate. The effects of slip amplitude, D, and magnetic fields on the stick-slip behavior of wear surface were evaluated with and without magnetic field. The experimental results indicated that when slip amplitude is large, stick region decreases remarkably in a magnetic field. The oxidation progressed at magnetic field was confirmed by an EPMA, and it resulted in the increased worn volumes by oxide particles trapping.

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The ultrasonic welding is a technique that makes welding easier and quicker than other techniques. It can also weld directly without insert material. In this paper, ultrasonic welding of two copper sheets at room temperature was carried out. Mechanism of welding was discussed with the results of vibration analysis. In ultrasonic welding, weldability depended on not only shape but also thickness of welding material. For example, in case that welding area is the same, welding time for square area was slightly shorter than circular area. Thickness of the material did not influence so much.

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