Showing papers in "Transactions of the Japan Society of Mechanical Engineers. A in 1995"
TL;DR: In this article, a two-dimensional X-ray detector was used to measure residual stresses, introduced by grinding, as well as applied ones on a steel, and it was found that the use of IP effectively shortened the measurement time in case of triaxial stress analysis, compared with the case of plane stress analysis.
Abstract: This paper describes a study on X-ray stress analysis using a two-dimensional X-ray detector. An imaging plate (IP) was adopted in this study as one of the two-dimensional detectors, which enabled us to obtain whole diffraction patterns rapidly and accurately and also to analyze their digital data in a computer. A new X-ray triaxial stress analysis, which is fitted to use the two-dimensional detector, was presented. This method was applied to measure residual stresses, introduced by grinding, as well as applied ones on a steel. The stresses measured by the present method agreed well with those measured by the conventional Dolle-Hauk method. The scattering of stresses obtained by the present method was almost the same as that obtained by the conventional method. The time of measurement for full triaxial stress analysis by the present method was almost one-thirtieth that of the conventional one. It was found that the use of IP effectively shortened the measurement time in case of triaxial stress analysis, compared with the case of plane stress analysis.
29 citations
TL;DR: In this article, a method for prediction of fatigue strength in terms of S-N diagrams is shown, and the experimental results showed extreme delay of the crack propagation in the residual stress field, and also showed several possibilities for improving the fatigue strength by controlling residual stress distributions.
Abstract: Shot peening is one of the most effective treatments for improving the fatigue strength of transmission gears. As is well known, the improvement of fatigue strength is caused by the compressive residual stress. Fatigue crack propagation in the residual stress field was analyzed by the fracture mechanics approach, and the method for prediction of fatigue strength in terms of S-N diagrams is shown. Analytical prediction in accordance with the experimental results showed extreme delay of the crack propagation in the residual stress field, and also showed several possibilities for improving the fatigue strength by controlling the residual stress distributions.
21 citations
TL;DR: In this paper, the compression strength and the shear elastic modulus of an aramid honeycomb core have been studied theoretically and experimentally, and the results showed that the predicted mechanical properties showed good agreement with the test results although a difficulty was found in the determination of the paper material.
Abstract: The compression strength and the shear elastic modulus of an aramid honeycomb core have been studied theoretically and experimentally. Equations have been proposed for calculation of these characteristics based on the longitudinal and shear elastic moduli of the paper material composing the core and the detailed geometry of the honeycomb shape. The effects of single and double wall thickness of the materials are taken into account in the equation. The predicted mechanical properties showed good agreement with the test results although a difficulty was found in the determination of the shear elastic modulus of the paper material. It also became clear that the aramid papers used showed considerable anisotropy which seemed to strongly influence the shear property of the core.
18 citations
TL;DR: In this article, the authors apply the homogenization method to the analysis of a composite material whose constituents reveal elastoplastic character as well as finite deformation, and use the microscopic stress field, which is obtained in a localization process, in the judgement of plastic failure.
Abstract: The homogenization method is applied to the analysis of a composite material whose constituents reveal elastoplastic character as well as finite deformation. Since the updating Lagrangian scheme with rate forms guarantees the instantaneous linearity of the governing equations, it is possible to use the separation of variables in the two-scale asymptotic expansion of the solution. Furthermore, the updating scheme also enables us to utilize the microscopic stress field, which is obtained in a localization process, in the judgement of plastic failure. A review of the general procedure for the asymptotic homogenization method supports our present discussion. Although the large deformation and small strain are assumed as the mechanical responses of both macro and microscopic structures of a composite, the periodicity assumption is not violated in a local region. Thus the total deformation of the composite can be obtained as accumulation of a series of "instantaneous" solutions.
17 citations
TL;DR: In this article, the effect of packaging stress on device characteristics was determined experimentally by applying uni axial stress to the transistor and measuring the residual stress distribution using stress sensing gauges embedded in LSI chips.
Abstract: The effect of packaging stress on device characteristics was determined experimentally. The sensitivity to stress of the electronic characteristics of MOSFETs was measured by applying uni axial stress to the transistor. The sensitivity to stress was shown to depend on the transistor conduction type and the current flow direction. The packaging stress effect on a simple inverter amplifier using MOSFETs was measured by changing the packaging materials. The residual stress distribution was also measured using stress sensing gauges embedded in LSI chips. The distribution of the amplifier gain change rate agreed well with the residual stress distribution in the LSI chip. The amplifier gain change rate was calculated based on the experimental results of the sensitivity to stress of the electronic characteristics of MOSFETs and the residual stress distribution. This predicted amplifier gain change rate agreed well with the measured data.
15 citations
TL;DR: A procedure for estimation of the mechanical properties of the cranium by assuming a proportional relation between the bone mineral density and Young's modulus is developed and shows that fresh cranial fractures start at the inner table and the diploe and then propagate to the outer table.
Abstract: The purpose of this study is to understand the mechanical properties of the human cranium in order to develop a FEM simulation model of the head. Craniectomy samples, autoclave bone flaps and dry cadaver skulls were tested using values of radial bending moment considered typical in the case of head injury. In this study, we developed a procedure for estimation of the mechanical properties of the cranium by assuming a proportional relation between the bone mineral density and Young's modulus. The mechanical properties of the human cranium have been determined from the three-point bending test and the bone mineral density measured by the dual energy X-ray absorptiometry. The human cranium consisted of inner and outer tables (cortical bones) and a diploe (a cancellous bone). The stress on the cortical and the cancellous bones in the field of bending stress was assumed that the cranium was a beam in which two different materials were combined. The experiment showed that fresh cranial fractures start at the inner table and the diploe and then propagate to the outer table. The fracture of a cranium taken out of a human being will exhibit elastic-plastic fractures. This fact implies that the inner table and the diploe fractures can occur even if no fracture is detected using plain X-rays in cases of acute extradural hematomas (EDH).
14 citations
14 citations
TL;DR: In this article, the HIP treatment was carried out on three kinds of cast aluminum alloys after hot isostatic pressing (HIP) treatment, and the fatigue crack initiation site was not a cast defect but a part of the specimen surface with a high density of eutectic silicon particles.
Abstract: Rotating bending fatigue tests were carried out on three kinds of cast aluminum alloys after hot isostatic pressing (HIP) treatment. The HIP treatment was carried out to reduce cast defects and porosity of cast aluminum alloys. Efficacy of HIP treatment varied from material to material, but in the material which treatment was most effective, namely AC4CH, the fatigue strength was markedly improved. In the HIP-treated AC4CH, the fatigue crack initiation site was not a cast defect but a part of the specimen surface with a high density of eutectic silicon particles. Comparing the HIP-treated AC4CH with conventional AC4CH, crack propagation behavior was the same for both, but crack initiation life was longer for the former than the latter. Fatigue life was successfully evaluated considering lives of both crack initiation and crack propagation. Here, the crack initiation life was defined as involving scatter immediately after crack initiation, and the crack propagation life was expressed in one relation for the HIP-treated materials and the conventional material.
12 citations
TL;DR: In this paper, the transverse stress in the lamination direction plays an important role in the fracture of both the fiber bundle and the resin, and the effect of mismatched lay-up on the strength has been investigated.
Abstract: The strength of woven fabric composite materials depends on their microstructural geometry. However, the conventional methods for mechanical analysis, which have been widely used to date, are insufficient because they cannot take into account the three-dimensional microstructure. In this study, the three-dimensional homogenization method is shown to be effective for determination of the material constants, microscopic stresses and strength. It has been found that the transverse stress in the lamination direction plays an important role in the fracture of both the fiber bundle and the resin. Also, the effect of the mismatched lay-up on the strength has been investigated. It was predicted that the mismatched lay-up causes a reduction in strength and a difference of crack initiation in the resin. These simulations provide a new concept for the microstructural design of composite materials.
12 citations
TL;DR: In this article, the effect of dispersed particle size on mechanical properties was investigated, and it was concluded that the strengthening by thermal treatment in air was caused by healing of surface flaws in the specimen.
Abstract: Mullite composite ceramics contaning 20vol. % dispersed SiC particles (0. 12-1. 71μm) were prepared by hot-pressing at 1650°C under 35MPa for 4h. The effect of dispersed particle size on mechanical properties was investigated. Grain growth of mullite was prevented by the existence of dispersed SiC particles in the matrix, and the matrix grain size of mullite/SiC composites decreased with decreasing dispersed SiC particle size. As a result, bending strength for most mullite/SiC composites increased with decreasing dispersed particle size. In the case of mullite/SiC (0. 56μm), bending stregth showed a maximum value of 626MPa, which was about 60% higher than that of monolithic mullite. The influence of atmosphere of thermal treatment on bending strength of mullite/SiC composites was also investigated. It is concluded that the strengthening by thermal treatment in air was caused by healing of surface flaws in the specimen.
11 citations
TL;DR: In this paper, the one-dimensional transient heat conduction problem of a nonhomogeneous plate with arbitrarily distributed and continuously varied material properties, such as FGM (functionally gradient materials), is treated theoretically.
Abstract: The one-dimensional transient heat conduction problem of a nonhomogeneous plate with arbitrarily distributed and continuously varied material properties, such as FGM (functionally gradient materials), is treated theoretically in this paper. For such a nonhomogeneous plate, the heat conduction equation becomes nonlinear, therefore the theoretical treatment is very difficult and the exact solution is almost impossible to obtain. Introducing the analytical procedure of the laminated plate model, and thereafter, taking into account the constraint that the number of lamine becomes sufficiently large, the analytical temperature solution for such a completely nonhomogeneous plate is derived. Furthermore, the associated thermal stress components for an infinitely long non-homogeneous plate are formulated under the mechanical condition of being traction free. As a numerical example, the plate composed of alumina and aluminum alloy is considered. The numerical results for temperature change and the associated thermal stress distributions are shown in the figures, and the effects of nonhomogeneity (change of the volume fraction of two different materials)on thermoelastic behaviors are briefly examined.
TL;DR: In this article, the effects of strain-induced transformation (SIT) on X-ray residual stress of retained austenite islands in TRIP-aided dual-phase steels were examined under uniaxial tension, and were discussed using a micromechanics theory.
Abstract: The effects of strain-induced transformation (SIT) on X-ray residual stress of retained austenite islands in TRIP-aided dual-phase steels were examined under uniaxial tension, and were discussed using a micromechanics theory. If the retained austenite particles are stable against the SIT and strain hardening, high tensile residual stress of 100 to 200 MPa occurs in the particles. The stress corresponds to that estimated from the micromechanics theory. In such a case, the retained austenite particles effectively increase the internal stress of the ferrite matrix similar to bainite and martensite particles. When the retained austenite particles easily transform to martensite during straining, the residual stress is decreased by plastic relaxation resulting from expansion and shear strains on transformation, although the strain-induced martensite increases the flow stress of the steels.
TL;DR: In this paper, an incremental theory is developed to describe the elastic-plastic behavior and damage behavior of particulate-reinforced composites, based on Eshelby's (1957) solution of an ellipsoidal inclusion and Mori and Tanaka's (1973) concept of average stress/strain for a finite concentration of particles.
Abstract: An incremental theory is developed to describe the elastic-plastic behavior and damage behavior of particulate-reinforced composites, based on Eshelby's (1957) solution of an ellipsoidal inclusion and Mori and Tanaka's (1973) concept of average stress/strain for a finite concentration of particles. In the composites containing hard spherical particles in a ductile matrix, debonding of the particle-matrix interface is a significant damage process, as the accumulation of the debonding damage affects the deformation and strength of the composites. The debonding damage is assumed to be controlled by the stress of the particle and the statistical behavior of the particle-matrix interfacial strength. During debonding, the stress of the particle is released and the site of the particle is regarded as a void, resulting in a void concentration increasing with deformation. The theory describes not only the reinforcing effect due to the intact particles but also the weakening effect due to the damaged particles. Analysis of the stress-strain response under uniaxial tension has been carried out on the particulate-reinforced composite based on the present theory. The influence of the damage on the stress-strain relation of the composite is very drastic and depends on the statistical properties of the particle-matrix interfacial strength.
TL;DR: In this paper, a method of resolution of all stress components from the first invariant of stress J1 measured using a thermoelastic stress analyzer is shown, where both surface stress and internal stress can be determined by this method which is based on the following procedures.
Abstract: A method of resolution of all stress components from the first invariant of stress J1 measured using a thermoelastic stress analyzer is shown. Not only surface stress but also internal stress can be determined by this method which is based on the following procedures. ( 1 ) Select an arbitrary domain Γ where the stresses must be determined from the structure. ( 2 ) Measure J1 inside Γ. ( 3 ) Determine the optimum boundary traction along Γ by the least squares method so that the difference between the measured J1 and calculated J1 is minimum. Either FEM or BEM may be used for calculation. Examples of stress resolution for a two-dimensional stress concentration problem and a three -dimensional stress concentration problem are shown and the accuracy of stress resolution is discussed.
TL;DR: In this paper, an application limit of linear notch mechanics in elastic-plastic solids is proposed, based on theoretical and FEM elasticplastic analyses ; this limit corresponds to the condition of small-scale yielding in linear fracture mechanics.
Abstract: An application limit of linear notch mechanics in elastic-plastic solids is proposed, based on theoretical and FEM elastic-plastic analyses ; this limit corresponds to the condition of small-scale yielding in linear fracture mechanics. Moreover, tensile tests of notched plates in practical materials, which are advanced thermoplastics and their reinforced materials by means of short carbon fibers, are carried out. Then, the proposed equation for the application limit of LNM in real materials is examined from the experimental fracture data.
TL;DR: In this paper, the authors presented a numerical analysis technique for shape optimization of linear elastic structures subject to multiple loading conditions based on the traction method for determining the domain variation that reduces the objective functional.
Abstract: This paper presents a numerical analysis technique for shape optimization of linear elastic structures subject to multiple loading conditions. The technique presented here is based on the traction method for determining the domain variation that reduces the objective functional. Using the speed method, a volume minimization problem is formulated in which the mean compliances associated with individual load cases act as constraints. The shape gradient function, which is equivalent to the shape sensitivity, for this problem is obtained using the Lagrange multiplier method. With the traction method, the domain variation is numerically analyzed using a commercial FEM code. A method is also proposed for finding the domain variation so as to satisfy equality and inequality constraints. The analytical results show the effectiveness and practical utility of the proposed method in solving shape optimization problems involving multiple loading conditions.
TL;DR: In this paper, the wavelet transform is applied to time-frequency analysis of dispersive stress wave data, where the Gabor function is adopted as the analyzing wavelet and the magnitude of wavelet transforms of wave data takes its maximum value at the time when the stress wave reaches the observation point with its group velocity at each frequency.
Abstract: The wavelet transform is applied to time-frequency analysis of dispersive stress waves. The Gabor function is adopted as the analyzing wavelet. The magnitude of the wavelet transform of wave data takes its maximum value at the time when the stress wave reaches the observation point with its group velocity at each frequency. An experiment on the flexural wave in a beam shows that the dispersion relation for the group velocity can be accurately identified by the wavelet transform of measured data. In addition, the application of the wavelet transform to ultrasonic testing of a polymer alloy shows that changes in velocity and attenuation coefficient due to mechanical damaging can be evaluated at each frequency. These results suggests that the wavelet transform has potential ability to present more detailed evaluation of material damages.
TL;DR: In this paper, a genetic algorithm for continuous search space is proposed and its use for nonlinear inverse problems is further described, which uses a population of individuals each represented by a real vector.
Abstract: In this paper, a genetic algorithm for continuous search space is proposed and its use for nonlinear inverse problems is further described. The algorithm uses a population of individuals each represented by a real vector. The performance tests of the algorithm were conducted for the optimisation of some different functions with continuous variables, and the results of the tests were compared to the performance of the canonical GAs. The results show that the algorithms optimise the functions more efficiently than the canonical GAs in terms of the time and memory required for computation and the convergence rate. The algorithm was then applied to the parameter identification of a thermal conductivity problem. As a result, the algorithm was able to find a parameter set close to the exact solution even when the measured data were subject to noise.
TL;DR: In this paper, a model for the initiation of a ring crack emanating from a surface microcrack was introduced, and the dependence of the ring crack initiation load on the indenter radius was also examined.
Abstract: In our previous papers, we showed that the ring crack initiation strength (microfracture strength) of gas-pressure-sintered silicon nitride, evaluated by the sphere indentation method, is not related to the conventional flexural strength of the same material, using the concept of effective area based on the Weibull distribution function. In the present study, to clarify the reason for this, a model for initiation of a ring crack emanating from a surface microcrack was introduced. Using this model, the microfracture strength was discussed from the viewpoint of fracture mechanics. The dependence of the ring crack initiation load on the indenter radius was also examined. As a result, the essential difference between the microfracture and flexural strengths was well interpreted using this model.
TL;DR: Three new approaches were proposed and examined in detail in this study for bending stiffness optimization problem, and both the 'mixed two species model' and the 'mutant model' are applicable in the special case that there is little difference between local minimum points.
Abstract: Composite laminated plates have been widely applied to aircraft primary structures. However, composites have remarkable mechanical anisotropy, and material design on stacking sequences is needed. In recent years genetic algorithms have been worthy of notice as solutions for combinatorial optimum problems. Some reserachers have applied the genetic algorithm for optimization of stacking sequence, but not for stacking number. Therefore, three new approaches were proposed and examined in detail in this study. A 'two species GA model' uses two species which differ in their stacking numbers. The choromosomes of meta populations have one less genes by one than the chromosomes of actual populations in this model. However, these populations are independent of each other. A 'mixed two species model' is similar to the two species GA except for crossover, and the two species exchange their genes with each other. A 'mutant model' uses only mutation. Using these three models, a bending stiffness optimization problem was examined. As a result, both the 'mixed two species model' and the 'mutant model' are applicable in the special case that there is little difference between local minimum points, such as in this problem.
TL;DR: In this article, a simple equation for estimating plastic deflection of steel panels subjected to impulsive loading is presented, which describes the relation between the plastic deformation and the impulsive load through a linear approximation based on the least squares method.
Abstract: In this paper we present a simple equation for estimating plastic deflection of steel panels subjected to impulsive loading. This equation describes the relation between the plastic deflection and the impulsive load through a linear approximation based on the least squares method. In order to prove the equation's validity, the authors conducted an experiment on a panel subjected to impulsive loading caused by an underwater explosion. The resulting plastic deflection in this experiment and that determined from the estimation equation were compared, and the validity of the equation for estimating plastic deflection with sufficient accuracy was confirmed.
TL;DR: In this article, a transition of environmental fatigue strength was found with increasing humidity for ordinary structural steels such as SS400 and HT800, and the transition moves to a lower relative humidity, because corrosion and cracks initiate more easily.
Abstract: Fatigue strength in high humidity environment has been studied for ordinary structural steels such as SS400 and HT800. Cracks are easily initiated in the early stage beyond the critical humidity (between 70 pct RH and 80 pct RH), because steels are subject to localized corrosion. Fatigue strength is reduced markedly and is almost the same as that in ion-exchanged water. Thus, a transition of environmental fatigue strength was found with increasing humidity for ordinary structural steels. At high room temperature (40°C), the transition moves to a lower relative humidity, because corrosion and cracks initiate more easily.
TL;DR: In this paper, the authors used a modified compliance method to obtain the continuous GI-R curve describing the stick-slip behavior of carbon fiber reinforced Nylon laminates and found that the stable delamination is characterized by a flat region of GIstable a 1200 J/m2 for all lay-ups except for a 60°-60°specimen which shows the rising GI-r curve to final failure.
Abstract: Delamination fracture toughness and fracture mechanism in carbon fiber reinforced Nylon laminates have been investigated. The mode I interlaminar fracture toughness tests are carried out on double cantilever beam (DCB) specimens made from four kinds of angle-ply laminates. These laminates exhibit the unstable "stick-slip" behavior on the crack propagation. In order to obtain the continuous GI-R curve describing the stick-slip behavior, one modification is made to Kageyama's modified compliance method. From the continuous GI-R curves, it is found that the stable delamination is characterized by a flat region of GIstable a 1200 J/m2 for all lay-ups except for a 60°//-60°specimen which shows the rising GI-R curve to final failure. The interlaminar fracture toughness of these composite laminates is considerably higher than that of carbon/epoxy laminates. Based on the continuous GI-R curves and the observation of the fracture surfaces, a mechanism is proposed in which the unstable stick-slip behavior is explained by the development of the large-scale bridging of the fiber bundle or layer and its breakage.
TL;DR: In this article, the thermal shock resistance of three kinds of titanium boride ceramics with 3, 8, and 15% porosity was evaluated using a C02 laser.
Abstract: Nuclear power plants have the greatest potential for use in space ships, underwater vehicles, and so on. It is very important to develop new radiation shielding materials which have excellent mechanical strength and heat-resistant characteristics. Titanium boride ceramic (TiB2) is an excellent neutron absorber and has been investigated as a radiation shielding material. This report presents an evaluation of thermal shock resistance by the laser irradiation technique for three kinds of titanium boride ceramics with 3, 8, and 15% porosity. Their temperature and thermal stress distributions are analyzed by the finite-element method, and the relationship between the spot diameter of the laser beam and the maximum tensile thermal stress is derived for various power densities of the laser beams. Critical fracture curves are obtained from these relationships, which can specify a critical power density for a given laser beam spot diameter. The irradiation experiments are performed on titanium boride ceramics using a C02 laser. Finally, theoretical results are compared with experimental ones.
TL;DR: In this paper, a singular value decomposition was applied to evaluate the magnification amplitude called the condition number, which was given as the ratio of the maximum singular value to the nonzero minimum singular value of the coefficient matrix.
Abstract: Inverse boundary value problems deal with the estimation of boundary values on incompletely prescribed boundaries. Numerical analysis of inverse boundary value problems using discretization methods can be reduced to solving simultaneous equations, which are ill-conditioned due to the ill-posedness of the problems. Errors included in prescribed boundary values are therefore magnified remarkably by inverse calculation without regularization. In this study, the mathematical structure of this error magnification behavior was studied theoretically for inverse boundary value problems of the Laplace field. Singular value decomposition was applied to evaluate the magnification amplitude called the condition number, which was given as the ratio of the maximum singular value to the nonzero minimum singular value of the coefficient matrix. The condition number was found to represent the magnification amplitude of the highest frequency fluctuation mode of variables. A regularization method using effective pseudoinverse was introduced, in which the rank of the coefficient matrix was reduced to effective rank and therefore small singular values were ignored. The effectiveness of the use of the effective pseudoinverse was explained using the singular values and the right singular vectors. An equation was proposed for evaluating the condition number. The admissible condition number method was proposed for determining the effective rank. Numerical simulations showed that the proposed equation and method were useful for estimating the condition number and the effective rank, and obtaining good estimates of boundary values.
TL;DR: In this article, a simplified identification method by the boundary element method is proposed to estimate the residual stress distribution due to butt-welds of thin plates, and the validity of the proposed method is demonstrated by numerical simulation.
Abstract: A simplified identification method by the boundary element method is proposed to estimate the residual stress distribution due to butt-welds of thin plates. In general, the residual stress distribution is produced by the shrinkage source in the plate after welding. Therefore, if the value of the shrinkage source is known, the residual stress distribution can be obtained from the shrinkage source by using a numerical analysis method. In this paper, the shrinkage source is replaced by the body forces of the boundary element method, and the body forces are identified by a few measured stress that can be obtained by, for example, X-ray method. The validity of the proposed method is demonstrated by numerical simulation. By this simulation, the applicability and effectiveness of the proposed method is confirmed from examples without error. Also, the same numerical simulation with error is conducted. From the result, if the number of measured points was more than ten, a better agreement between the assumed and the identified values could be obtained.