This study is concerned with a new adaptive boundary element method based on sample-point error analysis for thermoelasticity under steady-state heat conduction. Mathematical formulations of the adaptive boundary element method are presented in detail for two-dimensional thermoelasticity. This scheme of adaptive meshing makes use of only the residual between the interpolated and calculated solutions as an error indicator. Adaptive boundary element analysis can be performed by checking simultaneously the'displacement error indicator'and the'temperature error indicator'. The h- and p-version mesh refinements based on this scheme are applied to some typical examples, and the usefulness of the proposed adaptive BEM is demonstrated through discussion of the results obtained.

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A crack initiated from a v-notch corner in the molding resin such as a corner of die pad is one of the main causes of the failure of plastic packages. The stress intensity factors of the asymptotic soiution of a corner of jointed dissimilar materials are utilized for the evaluation of a solder reflow crack in a quad flat package (QFP). At first, we estimate the critical vapor pressure, which causes a crack from a corner in the molding resin, using the critical stress intensity factor of a v-notch corner measured by v-notched three points bending tests and the displacement extrapolation method with the three dimensional (3-D) finite element method (FEM). Moisture concentration in the QFP after absorbing moisture is analyzed, and vapor pressure caused by the solder reflow process is estimated. The critical moisture absorption time, which results in crack occurrence during the solder reflow process, can be predicted by this evaluation technique. Furthermore, we perform infrared solder reflow tests of the QFP for verifying the present failure evaluation technique.

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A flywheel is applied in the various engineering fields for the energy storage system. The flywheel rotor in this study rotates at a high rotational speed of about 30 000 rpm. In the design, it is important to consider the fatigue strength under the condition of cyclic centrifugal force due to the varlation of rotation rate and to prevent the fracture accident of a high speed flywheel from the spincrack after the rotor has cracked by any chance. This paper proposes the reliable structure of flywheel rotor based on the concepts of fracture control to prevent the dangerous crash scattering the pieces of broken rotor. The fatigue life of this rotor is estimated by the fracture mechanics considering the randomness of the crack growth rate and furthermore, the spintest is carried out in order to confirm the propriety of the structure of rotor.

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Stress intensity factors in cracked bodies have been calculated by various calculation methods which always have advantages and disadvantages. Especially, the so called conventional method ; i.e., the stress extrapolation method or the displacement extrapolation method has an important advantage of convenience. But the accuracy of stress intensity factor by the methods is not so high because of error due to high order terms. In this paper, errors of stress intensity factors by the stress extrapolation method and the displacement extrapolation were investigated on a mixture mode type crack model in an infinite plate. And an improved technique called V-line extrapolation method is proposed to decrease the curvature of calculated extrapolation data, therefore higher accuracy can be obtained

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Mixed-mode propagation behavior of interlaminar fatigue cracks was studied with unidirectional graphite/epoxy laminates. T800H/# 3631. Mixed-mode fatigue tests were conducted by the mixed-mode bending method under a stress ratio of R=0.2. The mixed-mode ratio, G_I/G_II, was 0.030, 0.19, 0.57 and 1.37. When the crack propagation rate da/dN, was correlated to the maximum value of the total energy release rate, G_max, the propagation rate increased as the G_I/G_II value increased. For each mixed-mode ratio, the crack propagation rate was given by a power function of the maximum value of the energy release rate in the region of rates above 10^-9m/cycle. The exponent of the power function decreased as the G_I/G_II value decreased. Below da/dN=10^-9m/cycle, there exists the threshold for fatigue crack propagation. At the threshold, the relation between the mode I and mode II components of the maximum energy release rate, G_Imax and G_IImaxth, is given by the following equation : G_Imax/G_Imaxth+G_IImax/G_IImaxth=1, where G_Imaxth and G_IImaxth are the threshold values of the maximum energy release rate for pure mode I and pure mode II loadings.

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High cycle fatigue properties of austenitic stainless steel SUS 304 were investigated for various conditions of cyclic stress amplitude σ_a-increasing tests under rotating bending and tension-compression loadings. Fatigue tests were also performed using specimens subjected to cyclic preloading. X-ray diffraction methods were utilized to measure the amount of martensitic transformation and residual stress. A marked effect of coaxing was observed under rotating bending tests and tension compression tests at 2 Hz. Stress-strain response revealed that the coaxing effect was caused by cyclic work hardening due to cyclic loading below the fatigue limit, but cyclic work softening due to temperature increase took place during stress cycling at the final step. Martensitic transformation was detected for some rotating bending specimens but not the tension compression specimens, which suggests that it is not the controlling behavior for the cyclic work hardening. Compressive residual stress was measured at the surface of the specimens exhibiting coaxing effect, which was considered to play an important role on the coaxing effect.

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Fatigue life estimation of solder bumps is one of the most critical technologies for the development of ball grid array packages. In this study, mechanical fatigue tests were carried out using Sn63-Pb 37 solder bump specimens. The cracks were initiated along the entire circumference in the vicinity of the interface. The observation results suggested that the fracture surfaces were of the intergranular creep type. The fatigue life estimation of the solder bumps was performed based on the elastic-creep FEM analysis. It was clear that the strain concentration region coincides with the crack initiation site in the vicinity of the interface. The estimation result for the crack initiation was in good agreement with the experimental results. The results reconfirmed that it was desirable to employ the equivalent creep strain range occurring at a distance of 0.05 mm from the singularity point. The life ratio, which provides the quantitative correlation between the crack initiation and the ultimate fracture, was determined from the experimental results. The number of cycles to the fatal failure can be roughly estimated by multiplying the analytical estimation results for the crack initiation by this life ratio. This simple estimation of fatal failure may well be of practical use in actual BGA design for thermal load conditions.

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Many of the ceramics coating materials are in use under the hard working conditions on the ground that these materials have the excellent characteristics. Therefore, it is expected for producing the superior coating materials to establish a methodology for evaluating the mechanical properties of these materials. In this report, 9 kinds of TiN film 5 μm thick that were deposited on the different parent materials under the different N₂ partial pressure were scratched and a method for evaluating the properties of the coating materials with Acoustic Emission (AE) is described. Its contents are follows : (1) The scratch testing apparatus that can detect the emitted AE signals from the TiN film during the testing was produced. (2) The relationship between the character of the detected AE signals and the fracture types of film (i.e. crack, chipping and flaking) were investigated. (3) It was became clear that the fractal dimension m led from AE amplitude distribution shows more than 3 when the fracture type is crack, the value shows between 1 and 3 when the type is chipping, the value shows less than 1 when the type is flaking. From these experimental results, it was found that the strength and the tight-adhesiveness of thin film are evaluated by observing the fractal dimensions of AE amplitude distribution during the scratch testing.

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In this study, a computer simulation taking into account the defects size distribution and the micro-crack propagation behavior was conducted by using virtual bending specimens. The defects size distribution in the virtual specimens was estimated by using a Monte-Calro technique based on a large number of defects diameter (approximately 72 000) measured on the Si₃N₄ specimen surface. For the cases of the simulation using micro-crack propagation behavior, the estimated bending strength well coincided with the factual bending strength. The scatter of the defect size and the crack propagation rate was estimated separately. Through the evaluation of the effects of scatter in a crack propagation rate, it is reconfirmed that the wide scatter in fracture strength mainly originated from the scatter of defect size.

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Stress intensity factor due to surface crack propagation was analyzed by using the Influence function method and inherent strain analysis of residual stress fields caused by welding. Initial residual stress in a plate-welded butt-joint was calculated by using inherent strain analysis, and redistributed residual stress and stress intensity factor due to crack propagation were analyzed as changes of structural shape. Stress intensity factor was also calculated by using the influence function database. The stress intensity factor in the residual stress fields due to crack propagation obtained by using inherent strain analysis completely agreed with that obtained by using the Influence function method. The results of the crack propagation analysis were compared with the experimental results of a fatigue test. And it was validated that both the inherent strain analysis and the influence function method were efficient for analyzing stress intensity factor in residual stress fields caused by welding.

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The position of sensor is required to be effective for measuring magnetic flux density near a specimen in order to determine stress based on the magnetoelastic interaction effect in ferromagnetic materlals. The purpose of the present study is to find a suitable area for the measurement. The distribution of two components of magnetic flux density in both directions of stress and thickness of the specimen is measured for various values of stress under low magnetic field. From the results, the suitable area is determined in connection with higher sensitivity to the change in stress and lower influence of error in sensor positioning.

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In this study, we investigated the propagation of ultrasonic waves in ceramic composite. Providing some samples of Al₂O₃ ceramics, ZrO₂ ceramics and Al₂O₃/ZrO₂ composite with different Al₂O₃ content, the effects of both pores and Al₂O₃ particles on the ultrasonic velocity (P wave speed) were examined. Resulting from the ultrasonic tests, the following facts were revealed : (1) In the porosity range below 20%, the ultrasonic propagation time increases in proportional to the porosity. (2) The ultrasonic propagation time decreases linearly with the increase in volume fraction of Al₂O₃ (3) The ultrasonic velocity is independent of the particle size of Al₂O₃ powder. We derived the relationship equations among ultrasonic velocity. Al₂O₃ content and porosity.

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Waveform distortion induced by velocity dispersion is simulated for longitudinal wave, which propagates along the length of a thin wire. In inspection of a thin wire throughout a long range, the longitudinal wave is useful, while the velocity shows the frequency dependence. In the conventional flaw detection by ultrasonics, short pulse is used as an excitation signal because of the high resolution of flew location. As a result of the velocity dispersion. the waveform is distorted, which causes the spread of the pulse width and the decrease in the signal amplitude. The signal to noise ratio will then be reduced. In this study, we simulate the waveform by giving the phase delay to each frequency component using the theoretically calculated dispersion curve. Comparing the simulated amplitude with the experimental results, we find that the signal amplitude is mainly decreased by the velocity dispersion and that the effect of the attenuation can be neglected even for 30 m propagation as long as pulse of low frequency range is used.

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Fundamental deformation and deformation-recovery behaviors of Ni-Ti-Nb shape memory alloy were experimentally investigated, especially their dependency on test temperature. Monotonic tension tests and deformation-recovery tests were conducted at low and high temperatures ranging from 253K to 473K. Stress-strain response above 323K is quite different from that below the temperature. The yield stress shows the positive temperature-dependency below 323K and the opposite trend is observed above this temperature. From this result, it is estimated that the dominant mechanism of inelastic deformation is the plastic deformation above 323 K and the pseudo-elastic one below it. The temperature at which strain recovery starts strongly depends on the maximum prestrain and prestraining temperature. Residual strain is always observed in the deformation recovery tests. Also it was found that the larger recovery strain can be obtained for the larger prestrain and at the lower prestraining temperature.

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A shape memory alloy (SMA) is intended to be used as structural elements at elevated temperatures. The mechanical and transformation properties of Ni Ti-Nb SMA were examined at room temperature and 561 K. The chemical composition of Ni-Ti-Nb SMA is 51 wt.% Ni, 38 w.% Ti and 11 wt.% Nb. The tensile strength, the 0.2% proof stress and the vickers hardness are increasing with increasing pre-strain below 14%, but the elongation, the reduction of area and the charpy impact absorption are decreasing with increasing pre-strain below 14%. The SMA is found to have sufficient mechanical strength for structural elements at elevated temperature. Maximum recovery strain due to the shape memory effect was about 5.5%. This value was obtained when 12% pre-strain was added. This means that a pre-strain of 12% is desirable when the Ni-Ti-Nb SMA is used for pipe coupling, etc.

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Ulrrasonic wave velocities propagating in a plastically deformed medium are known to be dependent upon its microstructural properties (e.g., crystallinestructure, distributions of micro cracks, residual stresses and texture, etc). The authors have proposed the theoretical modeling for an ultrasonic nondestructive evaluation method of the microstructural property of the materials under the plastic deformation. Generally, wave propagating characteristics are also dependent upon the propagating wave frequency. hence to accomplish a precise evaluation of material property changes it is necessary to examine an influence of frequency dependence on the propagating wave veloclties. In the present paper, frequency dependence of acoustoelastic and acoustoplastic effects, which correspond to wave velocity changes due to the stress and material property changes. respectively, are studied experimentally on the longitudinal and Rayleigh surface waves and also are simulated using our proposed theory via Granato Lucke's model for dislocation damping.

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Thermal stress ratcheting and shakedown is analyzed for a time-hardening structure : the yield stress increases as time goes on under exposure to neutron irradiation or thermal ageing. New three modes of ratcheting and shakedown are identified as transition to other deformation modes. Stress regimes and thermal ratchet strains are formulated as a function of time-increasing yield stress. Moreover, a new model of trouble occurrence frequency as a modification to a bath-tub curve is proposed for calculating a time period of a thermal cycle. Application of the proposed formulation tells us a benefit of taking into account the time hardening due to neutron irradiation.

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A design methodology of flexible structure is presented for the purpose of enrichment of the structural function by utilizing the mechanics realized by large elastic deformation of flexible members. The flexible member is modeled by straight bar segments linked by virtual coil springs. Its large deformation is analyzed by means of the Lagrange multiplier method, the functional of which is constltuted in line with the principle of stationary potential energy with constraints on geometrical boundary conditions. The sensitivity analysis is formulated especially for the solution obtained by the Lagrange multiplier method so as to approximate the change of the structural response in the first-order sense with respect to design variables. Owing to the sensitivity analysis, governing equation of the design variables to realize the prescribed response of the structure is derived as a set of linear simultaneous equations. The solution of design variables is determined by the Moore-Penrose generalized inverse since the coefficient matrix of the equation becomes rectangular in general. Adequacy of the proposed formulation is attested through the successful renewal of the flexural rigidity of members in numerical examples to realize the prescribed relationship between external forces and displacements.

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This paper describes local buckling strength of carbon steel thin-walled square pipes with a circular hole. Both ends of specimens are supported with spherical seats to aline compressive load. On the upper end eccentric load is applied, but on the lower end loading line is alined to the center of the square pipes. The length of specimens examined is a short column range. An empirical equation of the buckling stress for specimens subjected to the eccentric load is obtained using the ordinary stress, and a ratio of the eccentricity and opening ratio of the square pipes. Experimental results show a good agreement with the proposed equation.

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A design support CAE system was developed to reduce production cost, weight, and design time of box structures. This system assists users in : modeling structures for FEM analysis ; estimating structural dvnamics, production cost, weight, and weight balance of box structures; optimizing structures by using genetic algorithms. We applied this system to optimum problems of riveted joint structures and researched the convergence performance. We could reduce the number of rivets by 55.7 percent in a riveted box structure.

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Genetic algorithm (GA) is one of the most useful methods to optimize topology of structures. The performance of GA, however, deeply depends upon a rule of cording from a structure to a string (a chromosome), which must be decided before the execution of GA. An improper coding can cause a lot of unanalyzable structures to be generated in the process of optimization, which are separated into several pieces with no supporting or loading points. In this paper, a method to give such unanalyzable structures a fitness value based upon their topology using homology theory is proposed to raise the probability of obtaining the optimum structures. As numerical examples, topology of two dimensional frames and three-dimensional structures consisting of triangular elements supported on a rigid wall and loaded vertically on a point distant from the wall are optimized under a constraint of constant weight. As a result, it was found that the proposed method increased the average fitness value and the number of optimum structures obtained in 100 trials of GA in comparison with other methods that considered unanalyzable structures to be useless.

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In this work, a finite element sensitivity analysis method for thermal stress and creep problems is proposed. The method is characterized by the so-called semi-analytical direct differentiation approach, i.e., the formulation is based on the direct differentiation but the variation of internal force due to the perturbation of design parameters is evaluated numerically. Since the corresponding subroutine of an existing finite element analysis code may be used, it is unnecessary to manipulate the adopted constitutive relation at sensitivity analysis stage. Thus, the proposed method can be applied for various temperature and time dependent problems. The effectiveness of the method is examined through a couple of numerical examples.

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In this paper, we show the temperature effect on the deformation of 60 Sn-40 Pb solder alloys and its simulation using constitutive model for viscoplasticity. First, we investigate the temperature effect on the deformation of 60 Sn-40 Pb solder alloys from a series of tests, such as creep, pure tension and cyclic tension-compression loading tests. The larger temperature dependence of the solder alloys is found out. Applicability of the constitutive model that has been proposed previously to the temperature dependence of the solder alloys is verified. As a result, the parameters used in the model can be easily determined from the pure tension and the cyclic tension-compression loading test at several temperatures. It also can be found that the constitutive model can describe not only the temperature effect on the pure tension and the cyclic tension-compression loading but also the creep curves after preloading of cyclic tension-compression loading.

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This paper describes an ultrasonic technique for evaluating creep damage in 2.25 Cr-1 Mo steel exposed to the temperature of 923 K at various stresses. The technique is based on the electromagnetic resonance (EMAR), which is a combination of the resonant technique and a noncontacting electromagnetic acoustic transducer (EMAT). We obtain the ultrasonic velocity from the resonant frequency and the attenuation coefficient from the ringdown curve at a resonance. Two types of EMATs are used. One is the bulk wave EMAT for measuring the frequency dependence of shear wave attenuation in plate samples. The other is the axial-shear-wave EMAT for detecting the attenuation change of shear waves traveling in the circumferential direction of cylindrical samples. The attenuation showed much larger sensitivity to the damage accumulation than the resonant frequency. Approaching the rapture, it becomes ten time as large as the initial value. The frequency dependence of the attenuation also showed a remarkable change with the damage. The EMAR technicue has been proven to possess a large potential for the practical nondestructive/noncontact damage monitoring ; the EMAR is capable of sensing the attenuation evolution and indicating the damage advance to predict the creep life of the metals.

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In this report, first of all we correct the mistake of the basic equations in our previous paper. In the next place, by contriving how to solve the partial differential equations on the term of hydrostatic pressure derived from the incompressible condition and the equation of equilibrium, we propose a general method to determine the hydrostatic pressure. Furthermore, by considering the possibility of omission of the displacement functions, we clarify the structure of the analytical method of axisymmetrical surface force problems when torsional deformations do not exist, and formulate it. Finally, the analytical method of stresses and displacements is examined through a basic example.

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The plastic deformation of TiN thin films was considered by the hardness anisotropy of these films with the (111) and (200) preferred orientation. These hardness were measured by the nano-indentation technique as have already been reported. The plastic deformation of TiN films were caused by indentation of the trigonal diamond tip, and the evidence of this phenomenon was given by the cross-sectional SEM observation and the TED analysis. The influence of difference of residual stress and grain size on the hardness anisotropy was restrictive, and the hardness anisotropy can be explained by the anisotropy of the yield stress calculated by Schmid's law. This relationship suggests the existence of {100} <110> slip system of TiN crystal. The TEM observation of brittle cracks of TiN films also makes it clear that these cracks caused not by the cleavage fracture but by the intergranular fracture.

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The central burst defect, also called chevron crack, in axi-symmetric extrusion is analyzed. For the prediction of central bursting the criterion based on plastic instability is used. It satisfies the sufficient condition s_uε_u=0 for multiplicity of solution, which is derived from the discussion based on its necessary condition Δs_uΔε_u=0, where s_u denotes the nominal stress rate, and Δ shows the difference of any two multiple solutions. Stress and strain in the specimen are evaluated using FEM. As the parameter representing the risk for the occurrence of central bursting the measure y_M is introduced and it is calculated using the stress and strain on the central line of the product. When y_M<0, the bursting occurs. The value of y_M is shown in the range of combination between the cone angle of die and the reduction in working. From these values the working condition predicting y_M=0 is interpolated for several work hardening exponents, which shows the boundary between workings with and without cracking. The boundary curve predicted is compared with experimental values obtained by Zimerman and Avitzur. The prediction is found to be, on the whole, similar to the experimental results.

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Stuctural FEM analysis on railway car bodies made of aluminium hollow extrusions under uniformly distributed normal load was carried out. For the structural analysis on hollow extrusion structure car body, the method to substitute equivalent orthogonal anisotropic plates for hollow extrusions and the character of shell elements must be considered. The equivalent orthogonal anisotropic plate is obtained through the selection of four main rigidities which describe principal deformation of car body. For the characteristics of shell elements, element division on pier panel enough to describe its shear deformation must be considered. The FEM result which is calculated with orthogonal anisotropic plates and the characteristic of shell elements are in good agreement with the load test result.

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Structural characteristics of the tightening point between railway car body and interior equipments conposed of a tightening bolt and an attachment rail made with aluminium hollow extrusion is studied. To investigate the structural characteristics of the attachment rail and dispersion of axial force on the tightening bolt must be separately considered. Scatter of the structural characteristics of the attachment rall accompanied with load relies on constrained force of the tightening bolt is carried out. Dispersion of residual stress of the attachment rail which is caused by bolt tightening shows the same load-stress relationship in high load region an no-fixed model. The FEM calculation with fixed and free model of the tightening bolt is in good agreement with the load test result.

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Local and global mechanical properties of atherosclerotic aorta were measured in 6 Watanabe heritable hyperlipidemic (WHHL) rabbits. Descending thoracic aortas were obtained from animals aged 8 months. Local initial elastic modulus E_local and global incremental elastic modulus H_θθ were measured with pipette aspiration technique and pressure diameter tests, respectively. Opening angles were measured as an index of residual strain. E_local of atherosclerotic lesion (fatty streak) was 19.1±1.9 kPa (mean±SEM), which was significantly smaller than that of preserved area (38.9±7.5 kPa). H_θθ of the whole specimen was 1 260±140 kl'a at 100 mmHg, and was not statistically different from the value measured in age matched controls, Japanese White rabbits. Opening angle was significantly larger in WHHL rabbits than in their controls. These results suggest that, in the early stages of atherosclerosis. (1) the lesion is more compliant than normal aortic tissues ; (2) macroscopic mechanical properties are not sensitive to local mechanical change ; (3) residual strain increases with the development of the disease. It is important to assess local mechanical properties and residual strain when studying mechanical properties of atherosclerotic aortas.

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