In this study, the damage process of Thermal Barrier Coatings (TBC), which were exposed at 1273K for 500hours in advance, under tensile loading was observed continuously, and the influence of exposure temperature on crack initiation strength and interface strength was clarified quantitatively based upon interfacial fracture mechanics. TBC/IN738LC specimen, which is consisted of yttria-stabilized zirconia as top coat (TC) and CoNiCrAlY as bond coat (BC) in TBC, was prepared and the high-temperature exposure treatment was then conducted before tensile test. Continuous observation of damage process was revealed that (i) interfacial crack propagated along the interface between TC and BC in exposed TBC tested at room temperature however the crack propagated along BC/substrate interface in as-sprayed TBC, and (ii) interfacial crack propagated along TC/BC interface in the exposed TBC specimen as well as as-sprayed one. It was considered that the crack propagation path was changed by strong effect of a high-temperature exposure treatment. Quantitative evaluation also revealed that critical strain up to crack initiation in TC was increased by the exposed treatment and number of cracks per length was decreased in contrast with the critical strain. The exposure treatment stiffened top coat layer, which means that cohesive strength between splats became stronger. The interfacial fracture energy of the exposed TBC specimen was lower than that of as-sprayed one. Therefore, in order to assess precisely remaining life of main hot-parts of gas turbine, data for as-sprayed TBC is needed as initial information.
Low cycle fatigue tests and finite element analysis were conducted using 100A elbow specimens made of STPT 410 steel with local wall thinning in order to investigate the influences of local wall thinning on the low cycle fatigue behavior of elbows with internal pressure. Local wall thinning was machined on the inside of the elbow and was prepared at extrados, crown and intrados. The parameters of the wall thinning were same (eroded ratio=0.5, eroded angle=180 degrees and eroded length=100mm) in the all test cases. The elbow specimens were subjected to the prescribed cyclic in-plane bending displacement with constant internal pressure of 0 to 12 MPa. Also, low cycle fatigue tests using sound elbows were carried out for comparison. Low cycle fatigue life of wall thinned elbows was not so different regardless of location of wall thinning. Low cycle fatigue strength of the elbow specimens were beneath the best fit fatigue curve and its reason can be explained by combining the equivalent strain range and cumulated damage theory, considering reduction of ductility under multi-axial stress state.
A model of overload effect for hardening elastic-plastic solids is proposed to evaluate the stress intensity factor for compressive residual stress K_ at fatigue crack-tip fields. The residual stress σ_ introduced at the tip in SUS316 by overload K_= 6, 15, 30 and 45 MPa・m^<1/2> can be estimated using Finite Element Method (FEM). The K_ values as a function of fatigue crack growth length Δ_α were calculated from the σ_ according to Dugdale model. It was found that the calculated K_ decreased significantly with increasing Δ_α and reached to maximum value of |K_|. Therefore, the maximum stress intensity factor K_ will decrease apparently because of the action of K_ As a result, effective stress intensity factor range given by ΔK_=K_+K_ decreased with increasing Δ_α. Defining the fatigue crack cannot grow when ΔK_=ΔK_, the apparent fatigue crack growth threshold Δ^NK_ can be estimated. Then, we can obtain the theoretical equation as Δ^NK_=0.30K_+4.10. The equation showed in good agreement with experimental results.
The relationship between the wrinkle formation with aging and the strains by daily motion is investigated by measuring the strains of the facial skin surface for several human subjects. A digital image correlation technique based on a stereovision is used for measuring the strains of the facial skin. Results of the strain measurement show that the strains tend to be concentrated in the common place of facial skin for all human subjects. On the other hand, the different distributions of the principal direction are observed for different aged human subjects. It is also observed that the relationship between the strain and the skin surface morphology at the corner of the eye is different from that under the eye. Results of the strain measurement for various skin conditions show that the strain occurs locally under dry skin conditions whereas strain occurs uniformly under moisture skin conditions. Therefore, it is expected that skin surface morphology can be improved by moisture retention.
When the defects are detected in the nuclear components in Japan, structural integrity assessment should be performed for the technical judgment on continuous service based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code). Fatigue crack growth analysis is required when the cyclic loading would be applied for the components. Recently, fatigue crack growth rate curve in air environment for Nickel-base alloys weld metal used in BWR was proposed by the authors and it was adopted as a code case of JSME FFS Code to evaluate the embedded flaw. In this study, fatigue crack growth behavior for heat-affected zone (HAZ) of Nickel-base alloys in air was investigated. And a unified fatigue crack growth rate curve in air for HAZ and weld metal of Nickel-base alloys used in BWR was evaluated. As a result, it was found that the curve for weld metal could be applied as a curve for both HAZ and weld metal since moderately conservative assessment of fatigue crack growth rate of HAZ is possible by the curve for weld metal in the Paris region. And the threshold value of stress intensity factor range (ΔKth) is determined to 3.0 MPa√m based on the fatigue crack growth rate of HAZ.
The roll used in a heat treating furnace is called hearth roll, which has been changed very frequently. This is because high temperate of a furnace induces wear on the roll surface in short period. This paper deals with a new roller structure consisting of ceramics sleeve connected to two steel shafts by shrink fitting because the ceramics has high temperature resistance and high corrosion resistance. However, attention should be paid for the risk of fracture due to the thermal expansion difference between ceramics and steel. In this study the finite element method is applied to calculate the stress appearing at connecting parts with varying the geometries of the shaft. To design the structure safety, it is found that tapered shaft with smaller thickness is most designable for the ceramic hearth roll.
A replica method is commonly used to detect a crack initiation and propagation for rotating bending fatigue cracks. But in this method, a length of crack on the surface can be detected at only the certain cycles, and can't detect the crack initiation accurately or observe the change of fatigue crack length continuously. In this report, small fatigue cracks are detected by measuring the displacement at a notch root of specimens during fatigue test with a laser displacement meter. As a result, we can observe the propagation of fatigue cracks by measuring the amount of displacement change in real time.
Most of polymers used as structural materials are crystalline polymers that are mixtures consisting of glassy and crystalline phases. In this paper, we propose a material model representing the deformation behaviors of both crystalline and glassy phases by use of a unified manner based on crystal plasticity theory. A homogenization method is introduced into the above model in order to carry out deformation analysis connecting macroscopic specimen and microscopic unit cell. Then a further multiscale simulation bridging three hierarchical material structures, i.e., molecular chain scale, lamellar crystal scale and practical macroscopic scale is conducted for a polypropylene plate subjected to tensile load. It is tried to reproduce formation and propagation of shear bands and to visualize directly orientation of molecular chains inside the macroscopic structure. The relationship on deformation behavior between macroscopic plate and unit cell is investigated. Moreover, an inelastic response law based on a probabilistic theory considering change of local free volume is adopted as a hardening law of glassy part so as to express characteristic mechanical properties, i.e., nonlinear viscoelastic response before initial yielding, strain softening after initial yielding and nonlinear strain recovery in unloading process in crystalline polymers.
Honeycomb sandwich panels are used as lightweight panels when a high bending stiffness is required, such as aircraft, train and architectural materials. Aluminum honeycomb cores have been used as the core materials of sandwich panels, however, there is a problem that the manufacturing cost of sandwich panels using aluminum honeycomb cores is very high. By the way, we have developed the SMART SHEET® which has a large second moment of area in arbitrary cross sectional dimensions in order to increase the bending stiffness in all directions. The SMART CORE® panel, which uses the SMART SHEET as the core material instead of the honeycomb core, can be used as an alternative sandwich panel. In this study, the bending stiffness of the SMART SHEET, the SMART CORE and the honeycomb panel have been investigated using the three point bending test. The results showed that the bending stiffness of the SMART SHEET and the SMART CORE are higher than that of the honeycomb panel.
This study was aimed that Fabrication of Al/Mg clad material using a horizontal tandem twin roll caster. Magnesium is the lightest of structural metals combining high mechanical strength and low density. However, magnesium is low corrosion resistance. Aluminum alloys and magnesium alloys were fabricated as an Al/Mg composite using aluminum alloys as protective layers, improvement of the corrosion resistance of the magnesium alloys can be expected. In this study using twin roll casting process and downward melt drag process. And also in-line rolling process was used. A horizontal tandem twin roll caster consists of three kind of twin roll. AZ121 was cast by first twin roll, this is first strip. Downward melt drag process was used for casting of A1050, this is second strip. In case of narrow roll gap, AZ121 was melted by A1050 due to increased heat transfer coefficient. In this study, bonding could be better that cladding of aluminum on third twin roll would rather than cladding of aluminum on second twin roll. Thickness of clad strip was 5.5 mm, aluminum layer was 1.1 mm, magnesium layer was 4.3 mm. cladding ratio was 1.1 : 4.3. Mixed layer was 70-90μm in bonding region. Each diffuse layer of Al layer and Mg layer was 10 μm. Primary crystal size of Mg layer was 77μm at mixed layer region, 19μm at center region, 83μm at surface region.
Welding residual stress profiles of low alloy steel JIS SQV2A could be predicted by thermal elastic plastic analysis taking account of the phase transformation strain. Residual stress relaxation during post-weld heat treatment (PWHT) could be also predicted by creep analysis. Effects of welding and PWHT conditions were examined, such as heat input efficiency, preheating temperature and PWHT holding temperature and time on residual stress profiles. The effects of heat input efficiency and preheating temperature in welding conditions were found to be remarkable on the stress distribution for the thermal elastic plastic analysis taking account of the phase transformation strain. The effect of temperature in PWHT conditions was also found to be remarkable on the stress distribution for the creep analysis. However, the effect of holding time was not found. Since the creep rate was fast for large residual stress, creep strain was suggested to saturate during rising temperature period. The accuracy of these analytical results was validated by temperature measurement during on bead welding and residual stress measurement using strain release method after welding and PWHT.
Short crack propagation behavior in poled lead zirconate titanate was examined under cyclic electric loading. A crack located at edge of a partial electrode grew along the electrode edge during the loading. The crack growth rate decreased with increasing crack length until a non-propagating crack was reached. The growth rate and crack length of the non-propagating crack were affected by the amplitude, mean voltage of the electric loading and environment. In the case of high-amplitude loading or negative-biased loading, the crack growth rate varied considerably because of domain switching. At testing temperature of 20°C, moist atmosphere had no effect on the crack propagation behavior. However the crack growth rate fluctuated and non-propagating crack length was increased with increase in temperature to 40°C. Finite element analysis of a three-dimensional permeable crack showed that the mode III stress intensity factor range is independent of crack length, but it decreases as a result of the frictional force under positive electric field. Fracture surface observations showed that intergranular cracking is dominant near the tip of the non-propagating crack.
In this study, we fabricated piezoelectric strain sensors from multi-walled carbon nanotubes (MWNTs) and PVDF nanocomposites, i.e., PVDF/MWNT for measuring dynamic strains. The influence of MWNT loading on the sensor performance was evaluated by changing the MWNT loading as 0.0wt%, 0.05wt%, 0.2wt%, and 0.3wt%. To increase MWNT dispersion in PDVF matrix, a mixing process by using a planetary stirring machine and sonication processing by using an ultrasonic mixer were firstly employed together to produce nanocomposite films. Then, these films were stretched under uniaxial loading and poled under 60MV/m to fabricate the strain sensors. Moreover, crystallinity of the PVDF/MWNT nanocomposites was analyzed by using X-ray diffraction (XRD) analysis, and the fractured surfaces of pre-stretched PVDF/MWNT nanocomposites were observed by using a polarized optical microscope (POM). The piezoelectricity and signal tracking capability of the PVDF/MWNT nanocomposites sensors in vibration were investigated. From experimental results, the piezoelectricity, i.e., the sensor output voltage of the PVDF/MWNT nanocomposites reaches to a maximum peak value at 0.05wt% MWNT loading, and then decreases with further more addition of MWNTs. The result of XRD intensity was consistent with the piezoelectric sensor output results of PVDF/MWNT nanocomposites. From POM observations, compared to that of pure PVDF, the spherulite’s size in the PVDF/MWNT nanocomposites becomes smaller and its number increases. Moreover, there should exist an optimum content of MWNTs, which can result in high piezoelectric properties of the nanocomposite strain sensors.
This paper presents a design method to visualize the loading history under non-proportional multiaxial loading with the principal direction change. Definitions of principal stress and strain ranges and mean stress and strain were firstly introduced by utilizing Itoh-Sakane criterion for general multiaxial loading including non-proportional loading. Secondly, the method of calculating the non-proportional factor which expresses the severity of non-proportional loading was discussed for the general multiaxial 3D loading. The paper proposed a method of visually presenting the principal stress and strain trajectory under non-proportional loading histories that assists designers to understand the loading mode whether proportional or non-proportional under 3D multiaxial loading. An actual method of taking account of the stress and strain multiaxiality into practical design of components and structures was described.
A new technique for the evaluation of local interface adhesion energy was applied to the interface between Cu and cap layer in a Cu damascene interconnect structure, which consists of both the interfacial fracture test and the finite-element simulation. After specimens in-plane dimensions of 1×1 μm, 5×5 μm and 10×10 μm fractured by focused ion beam (FIB), the interfacial fracture test was implemented by a novel system with nano-indenter in FIB-SEM dual-beam microscope. With the maximum load measured during the fracture test employed in an elastic-plastic simulation, interface adhesion energy was evaluated and almost equal among all types of specimens. On the other hand, the variation of the evaluated interface adhesion energy tends to be larger with the decreasing specimen size. With the result of electron backscattering diffraction analysis for Cu lines whose average grain size were 400nm diameter, it is suggested that local interface strength significantly varies depending on local grain distribution in a Cu interconnect structure.
Engineering plastics provide superior performance to ordinary plastics for a wide range of the use. For polymer materials, dynamic stress and strain rate are major factors to be considered when the strength is evaluated. Recently, high speed tensile test is recognized as a standard testing method to confirm the strength under dynamic loads, and it is analyzed by the finite element method; then, the maximum dynamic stress and strain rate are discussed with varying both the tensile speed and the maximum forced displacement. The strain rate concentration factor is found to be constant independent of the tensile speed, which is defined as the maximum strain rate appears at the notch root over the average nominal strain rate at the minimum section. The maximum strain rate is controlled by the tensile speed alone independent of the magnitude of the forced displacement. It is found that the difference between static and dynamic maximum stress concentrations (σmax -σst ) at the notch root is proportional to the tensile speed when u/t≦5000mm/s.
A circular-shell deep-drawing test and an FEM simulation utilizing LS-DYNA with Barlat-Lian anisotropic yield locus (1989) were conducted in order to investigate the occurrence of earring for low-carbon aluminum-killed steel sheet and pure titanium sheet. The simulation method was developed that can accurately estimate the earring pattern of whole 360° circular wall height, where R-value is supposed to be measured within the range of uniform elongation, in particular for the case of pure titanium. The well known opinion that the earring value is proportional to ΔR/Rave does not always hold for the whole sheet materials. Despite the fact that the value of ΔR/Rave of pure titanium is nearly zero, it exhibits large earring. This is considered to stem from the characteristic planer anisotropy of R-value of pure titanium, namely large ΔTLave ((R90 - R00))/Rave) together with very small ΔR. Furthermore, it is interesting to note that the earring in 45° direction was observed experimentally and was reproduced by simulation, despite the fact that pure titanium shows the straight planer anisotropy with the maximum in 90° direction. The optimum m-values in yield locus for pure titanium and low-carbon aluminum-killed steel, which led to the fairly good reproduction of experimental results, is 8 and 2, respectively. This difference in optimum m-value between the two metals is presumably related to the difference in the number of slip system; namely the number of active slip system is very limited for pure titanium.
We proposed an electroformed mold for thermal imprint of borosilicate glass in this paper. The mold was made of Ni-W electrodeposition film that was superior to heat-resistance and removing glass. The resist pattern for electroforming was fabricated with SU8-10. Ni-W solution for electroforming was developed by mixing nickel sulfamate, tungsten sodium and citric acid. The minimum pitch and the height of the pattern on Ni-W electroformed mold were about 40 μm and 3.8 μm, respectively. The thermal imprint for borosilicate glass carried out with Ni-W electroformed mold. The shape of the Ni-W electroformed mold was printed on the borosilicate glass by thermal imprint. The borosilicate glass was removed from the Ni-W electroformed mold easily.
In mathematical problems and mechanical engineering, there are a number of examples, in which a non-symmetric Jacobian matrix is involved in solution of simultaneous linear equations. The left and right eigenvectors of such non-symmetric matrices are in general complex and must be well discerned to each other. Their properties and practical meaning are, however, hardly discussed in engineering applications. Especially when the non-symmetric matrix is singular, the critical left eigenvector corresponding to null eigenvalues is of increased significance in the examination of the solvability of the problem. The present paper describes and interprets the substantial role of the critical left eigenvector of the non-symmetric singular matrix in mechanics. Model examples in applied mathematics, solids, structures and rigid bodies will illustrate the meaning of the critical left eigenvector, when the singularity is unavoidable in the problem to be solved. The discussion will be then extended to the critical left singular vector of a rectangular matrix.
Porous Al is superior in lightweight, high sound insulation and high energy absorption. In this study, copper powder dispersed porous Al core filled in hollow pipe composite materials was fabricated by friction welding and in-situ formation of CuAl2 was attempted for the reinforcement of porous Al. Al hollow disc filled with blowing agent, stabilization agent and Cu powder was put into hollow pipe and the rotating tool was pressed into Al hollow disc. Frictional heat softened Al hollow disc and precursor of porous Al was fabricated because the rotating tool dispersed the powder into Al by means of plastic flow of Al. It was shown that porous Al core filled in hollow pipe composite materials with porosity of approximately 60% and in-situ formation of CuAl2 was successfully fabricated at a holding temperature of 1003 K and at a holding time of 6 min 30 sec.
