This paper is concerned with a dual reciprocity boundary element method (DRBEM) applied to the thermoelastic problem of temperature-dependent materials. The fundamental solution of homogeneous materials is used in the integral equation, and hence a domain integral arises in the resulting boundary integral equation. This domain integral is transformed into boundary integrals based on the dual reciprocity introducing a new set of radial basis functions. The details of the proposed DRBEM are presented, and a computer code is developed for two-dimensional problems. Through discussion of the results obtained by the computer code, the usefulness of the present DRBEM is demonstrated.

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Most of the structural health monitoring systems adopts parametric method based on modeling or non-parametric method such as artificial neural networks. The former method requires modeling of each structures and latter method requires a large number of data for the training. The modeling and data for the training demands high costs, and it is impossible to obtain training data of damaged state of inservice structure. By the present method, damages are detected by judging statistical difference of data of intact state and present state. The method requires data of un-damaged state and does not require the complicated modeling and large number of data for the training. As an example, the present study deals monitoring of delamination detections of a composite beam. The damages are detected from the change of strain data measured on the specimen surface by the statistical tools such as Response Surface and F-Statistics. As a result, the new method successfully diagnoses the damage without using the modeling and the data of damaged state.

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The stress state on the membrane of bellows type air springs made of woven fabric reinforced rubber is bi-axial when they are pressurized. The material properties for a numerical calculation are needed to use the value examined by bi-axial tensile test. It is very difficult to carry out the bi-axial tensile test because of the problem of making specimens or the way of restraining specimens. Therefore, we have proposed a simplified bi-axial testing method in order to obtain the mechanical properties under bi-axial stress state and presented a database of the material properties by this testing method. Moreover we have calculated the transverse spring constants of the bellows type air springs by nonlinear finite element analysis using this database. These results showed good agreements with the experimental results.

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In this study, the sensitivity analysis method for the steady-state fluid-structure interaction problem is presented. A strong coupling formulation and the Newton-Raphson method are utilized to solve the equilibrium equations for fluid and structure simultaneously. The semi-analytical differentiation method is adopted to calculate the sensitivities of the response. As the consistent tangent stiffness is already obtained in the finite element analysis, the sensitivities are efficiently calculated. One illustrated example of large deformation structure subjected to fluid force is demonstrated. The accuracy of the sensitivities by the present method is discussed. Finally, a simple optimization problem is solved by using the calculated sensitivities along with the steepest descend method. The satisfactory result is obtained.

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This paper presents the procedure of two dimensional buckling analysis considering fluid-structure interaction. In the formulation, the buckling of thin structures subjected to the pressure of viscous flow is modeled, where the geometrically nonlinear equation and the Navier-Stokes equation should be considered. These equations are solved by the strong coupling formulation and the Newton-Raphson method with the so-called arc-length technique. The buckling load and mode are determined by checking the determinant of stiffness and the scaled corrector method. In order to confirm the validity of the present formulation, the arch subjected to only the static pressure of fluid is analyzed. In the subsequent examples, the effect due to the fluid-structure interaction on the buckling of structure is investigated.

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Off-axis stress relaxation behavior of a unidirectional carbon fiber-reinforced composite (T 800 H/3631) has been examined at high temperature. Stress relaxation tests are performed at 100°C on plain coupon specimens with various off-axis angles: θ=0, 10, 30, 45, and 90°. For each of these off-axis angles, the stress relaxation tests are carried out at three different strain levels. Just after the total strain is kept constant, the stress rapidly relaxes with time in a short period. Then, the relaxation rate of the composite stress tends to vanish. The extent of the transient stress relaxation is significantly dependent on the total strain kept constant and the fiber orientation angle. Simulation of the off-axis stress relaxation behavior is performed using a macromechanical viscoplasticity model based on an overstress. It is demonstrated that the model succeeds in moderately reproducing the time-dependent behavior of this system.

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For the accurate finite element analysis of solder joints in electronic packaging, a constitutive model which can describe the large time dependent deformation has been required. The requirement is not only the proposal of such a constitutive model but also the establishment of the determination method for the material parameters used in the model. In this study, we discussed on the constitutive model for solder alloys and the determination method of the material parameters for the model. First, the constitutive model that can divide the inelastic deformation into the plastic and creep parts is proposed. Next, we show the numerical method for the determination of the material parameter used in the model. In this method, the material parameters for creep part are determined firstly by pure tensile tests under several strain rates, and the creep strain is calculated. Subtracting the calculated creep strain from the pure tensile deformation, the stress-strain relation for the time independent parts is obtained. Then, the material parameters for the time independent parts such as elastic and plastic deformation are easily determined from the obtained stress-strain relations. The simulations of the stress relaxation after several different preloading are carried out to verify the applicability of the proposed model and numerical method.

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It is widely used in the industry field, because the ceramics coating materials have many excellent features. However, that clear criterions for evaluation on the character of films have not been determined is made to lower the reliability of the materials. It is necessary to quantitatively grasp the damage conditions and growth in order to determine the criterions. In this study, the technique that quantitatively evaluates the damage conditions of the films with AE method and image processing technique, when the thermal shock was repeatedly given to the film by YAG laser, is proposed. Concretely, the detected AE signals by a laser irradiation are divided into heating and cooling process, and the features of AE signals in the individual process are extracted. And, the features of damage conditions in the irradiation area are quantitatively extracted by the image processing. The detected AE signals in heating process correspond with the image data on the damage before a laser irradiation. Therefore, the neural network for estimating the damage before an irradiation learned the relationship between the signals and the image data. On the other side, the detected AE signals in cooling process correspond with the image data on the damage growth after an irradiation. Therefore, the network for estimating the damage growth after an irradiation learned the relationship between the signals and the image data. From the output of the two networks, it was possible to evaluate the conditions and the growth of the thermal shock damage. The effectiveness of the constructed network became clear by the comparison with the experimental results.

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Fatigue tests were carried out for 1600 MPa and 2000 MPa class modified-ausformed and tempered SCM 440 steels. The materials were called AF1600 and AF2000, respectively. The 2000 MPa class quenched and tempered steel, called QT2000, was also tested. The 1600 MPa class quenched and tempered steel, called QT1600, had been tested in the previous report. In the QT1600, fish-eye fracture had occurred from TiN inclusions and the fatigue limit at 10⁸ cycles had been 840 MPa. AF1600 successfully achieved no fish-eye fracture and a higher fatigue limit of 920 MPa. Although fish-eye fracture occurred, AF2000 also achieved a higher fatigue limit of 1010 MPa than QT2000 of 840 MPa. The fatigue limit of QT2000 was equal to that of QT1600. The origins of fish-eye fracture for AF2000 and QT2000 were Al₂O₃ and TiN inclusions and matrix cracks. On the fracture surfaces of QT2000 broken at over 10⁷ cycles, large and clear ODAs were observed whatever the origins were. On the other hand, AF2000 did not break at over 10⁷ cycles. It suggests that AF2000 could not have ODAs on the fracture surface.

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In this paper, the result from rotating bending fatigue tests of notched specimens are carried out on aluminum cast alloys and high strength steels with H_B≃600 are reported. The threshold stress intensity factor range under a stress controlled condition, ΔK_w, is introduced for the purpose of predicting the fatigue limit of a metal with an arbitrary crack. The ΔK_w value of a long crack, ΔK_wUL, is obtained from the fatigue crack propagation limit σ_w2 of specimens with a sharp and deep notch: ΔK_w increases with crack length, and ΔK_wUL is an upper limit of ΔK_w. Since there are few σ_w2 data of steels with H_B≥400, the σ_w2 values are evaluated by the fatigue crack initiation limit predicted using Linear Notch Mechanics and the relation between σ_w1 and σ_w2 at the branch point. Using ΔK_wUL values of many metals with a long crack, the ΔK_wUL values are approximated with a simple formula. Moreover the lower limit value of ΔK_w versus the crack length, ΔK_wLL, is proposed. Then using the ΔK_w and ΔK_wUL formulae and the ΔK_wLL value, the smallness of a fatigue crack is clarified.

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The method of fatigue life prediction is presented for structures which suffer from flow-induced vibration. A small wind tunnel was made and used to reproduce fatigue failure by flow-induced vibration. A medium carbon steel specimen attached to a larger styrofoam cylinder was fixed to the experimental equipment. A small artificial hole was introduced onto the specimen surface. Fatigue crack initiated from the artificial hole. A small portable strain histogram recorder (Mini Rainflow Corder, MRC) developed in another project of the authors' team was used to acquire the service strain histogram at a critical point of the specimen and to measure the variation of natural frequency. Fatigue damage D defined by the Modified Miner Rule was calculated by using the strain histogram at the initial stage of the operation of the wind turbine. The values of D were all smaller than 1.0 and ranged approximately from 0.2 to 0.8. The reason for small values of D is explained from the behaviour of small crack growth.

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For studying the mechanical properties of composite material at high temperature, fatigue and creep tests were carried out for two types of ceramics matrix composites, that is, the reaction bonded and the precursor SiC/SiC composites. And then analysis of data regression was conducted for evaluating damage accumulation. As a result, following conclusions were obtained. 1) At room temperature, fatigue strength of precursor CMC is above twice higher than that of reaction bonded CMC, but at 1 300°C, fatigue strength of both composites is reversed in the range of longer life. 2) Fatigue and creep strength of reaction bonded CMC correspond each other if it is explained that fractures are caused by the crack extension process of time dependence except for flexure strength. 3) In precursor CMC, fatigue and creep strength for a short term coincide with flexure strength, which can be also explained by the crack extension process of time dependence. But high temperature strength for a long term rapidly decline because of internal oxidation.

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Mechanical properties and cyclic stress-strain behavior of thermal barrier coatings under uniaxial compressive loading were examined. Specimens of plasma-sprayed ZrO₂-8%Y₂O₃, Al₂O₃, CoNiCrAlY and NiCr were fabricated to test the coating materials independent of the substrate. Stress-strain response was measured using the laser speckle strain/displacement gauge (SSDG). The coatings showed a nonlinear stress-strain response with a considerably lower elastic modulus compared with that of the bulk material. The nonlinearity of the stress-strain response was less significant when the coating contained less microscopic defects and pores. In the case of the coating with many defects, the compliance was found to decrease after the coating underwent a compressive stress and the compliance was also found to decrease with increasing the number of compressive stress cycles.

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Residual stresses of plasma sprayed coatings, NiCr alloy, CoNiCrAlY alloy, Al₂O₃ ceramics and ZrO₂-8%Y₂O₃ ceramics, were measured in this study. SACHS method with a strain gauge was used to measure the residual stress. Type 304 stainless steel and mild steel were selected for the substrate. The results obtained were summarized as follows: 1) Tensile residual stresses were generated in plasma sprayed coatings. 2) The values of residual stress in ceramics coatings were relatively small and the values took lower than 40 MPa. 3) Tensile residual stress values of metal alloy coatings on carbon steel substrates were higher than those on type 304 stainless steel substrates. 4) Residual stresses in Low Pressure Plasma Sprayed (LPPS)-coatings were larger than those in Atmospheric Plasma Sprayed (APS)-coatings. 5) Pre-heating of a substrate will effectively reduce tensile residual stress in a coating.

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For studying sliding wear properties at high temperature, the cyclic wear tests were carried out for typical metals and coating material by use of experimentally manufactured apparatus, and then analysis of data regression was conducted for evaluating wear damage. As a result, following conclusions were obtained. 1) In the case of a little difference of strength of test materials, wear mass loss was observed in both materials. But large difference of strength caused material transference to high strength material. 2) Wear damage state in relation to time is divided into initial wear region and steady state wear region, and wear rate in each region is evaluated by static work of material of both materials. 3) Contact pressure accelerated wear damage, and is an important factor to enlarge the difference of wear properties, which reflects wear rate and wear damage behavior.

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In this study, the effect of loading rate on the strength and the absorbed energy of paper foam board was examined by a series of dynamic and quasi-static compression tests. For comparison, polystyrene foam board was also tested. In dynamic compression tests, a polyvinyl chloride (PVC) tube instead of an ordinary metal bar was used for the measurements of the load applied to the specimens, in order to relieve the impedance mismatch between stress bars and specimens. The absorbed energy up to a strain of 50% in compression tests of paper foam board is about 1.5 times greater than that of polystyrene foam board. It was also found that the absorbed energy obtained from dynamic tests for paper foam boards was about twice comparing with the results at quasi-static rates.

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This paper presents analyses of anti-plane problems for isotropic and anisotropic semi-infinite body due to single force, dipole-force and screw dislocation with two surface boundaries such as free and fixed conditions. Distributions of stresses and displacements under single force and screw dislocation for the above two boundaries are illustrated by some graphical representations as numerical examples.

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Stiffness is one of fundamental properties in structural design, such as in maximum stiffness design. The nonlinear structural property is an attractive characteristic to be designed although majority of structural design problem deals with the linear elastic property. This article discusses the concept of force-dependent variable stiffness. The mean compliance measures the structural stiffness from the viewpoint of external load and the deformation at the loading sight. A certain gap is introduced as an internal boundary in the continuum structure, and its open/close status may depend on working force condition. Such a gap is expected to work as the switching mechanism, which brings the force-dependent variable stiffness. The attention is forced on the bilinear stiffness design having only one switching point of stiffness in the context of structural topology and geometry determination. First, the topology determination problem is formulated by using SIMP method and solved by sequential linear programming supported by moving limit strategy. Second, the geometry determination problem is formulated based on the topology obtained under the constraints of bilinear stiffness with the specified external load for stiffness switching, and is solved by the traction method. A couple of numerical cases studies demonstrated the feasibility and effectiveness of the proposed design concepts.

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Machine structures assembled by adhesive bonding are expected to possess a high damping capacity because of the high damping capacity of the adhesive. In this study, the damping characteristics of an adhesively bonded beam in which two steel strips are joined by an adhesive and the effect of temperature are investigated. In the analysis, vibration modes of the bonded beam and strain energies distriburted in each strip and the adhesive in motion are analyzed by the finite element method. Then the damping capacity of the bonded beam is estimated using the strain energies and damping ratios of the two materials, namely, the steel strip and the adhesive, which were obtained beforehand independently by experiments. In the analysis, the temperature dependence of Young's modulus, Poisson's ratio and the damping ratio of the adhesive are considered. In order to confirm the estimated damping capacity, the damping ratios of the first three modes of vibration of the adhesively bonded beam were measured at several constant temperatures. The estimated values of the damping capacity are in good agreement with the experimental results. Thus, the effects of temperature, vibration modes and the thickness of the adhesive layer on the damping capacity of a bonded beam are clarified.

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In general, the structural shape optimization method based on the fully stressed design gives us a solution of too complex shape which will be difficult to be manufactured. The present paper proposes a novel approach to the determination of moderately complex shapes that satisfy the requirement for lightweight, high stiffness and enough strength. There are two original ideas in this method. One is for the clear definition of shape complexity. A new parameter CD (curvature deviation) which represents the degree of structural shape complexity is proposed. The other is a method of derivation of moderately complex shapes that satisfy the requirement for lightweight, high stiffness and strength. A smoother shape is derived by an evolutional change of CD, while a structural shape is obtained by an iterative change of an allowable stress region. The proposed method has been verified by applying it to the design of a hook.

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