Showing papers in "Jsme International Journal Series A-solid Mechanics and Material Engineering in 2000"

Improvement in Fatigue Strength of Silicon Manganese Steel SUP7 by Using a Cavitating Jet.

Abstract: It is possible to strengthen metallic materials by using a cavitating jet to introduce compressive residual stress in the material surface, since the impact of collapsing cavitation bubbles peen the surface in the same way as shot peening. In order to demonstrate the improvement in the fatigue strength of a material by using a cavitating jet, an experimental study was carried out. Silicon manganese steel JIS SUP7 was chosen as a test material, since JIS SUP7 is used as a spring material after shot peening. The specimens were exposed to the cavitating jet with upstream pressure p1=20 MPa, downstream pressure p2=0.28 MPa, the cavitation number σ〓p2/p1=0.014, the nozzle throat diameter d=0.842 mm and the atandoff distance s=31 mm. The scanning speed v at which the compressive residual stress took the most significant value was 0.25 mm/s. The compressive residual stress was introduced in the entire surface peened by the cavitating jet under the above conditions. The fatigue strength of the specimen was investigated by a four point bending test. The minimum bending stress σm/n was fixed at 123 MPa and the amplitude of the load was varied. The fatigue strength of material peened by the cavitating jet is shown to be about 440 MPa, which is about 10% stronger than the strength without peening.

Determining High Temperature Properties of Weld Materials

Abstract: Welds form an integral part of most power and chemical plant structures. At elevated temperature, the service life of these structures are often governed by the creep behaviour of welds. Efforts have been made to understand creep stress distributions in and deformation behaviour of welds and to predict the failure life. In this context, the determination of the high temperature properties of welds is essential. However, due to the complex nature of the material inhomogeneity in the weld regions, accurate determination of material properties of welds is not a straight forward task. This paper describes some aspects related to the determination of high temperature material properties of welds. Experimental creep testing methods involved and the procedures for generating the material constants in creep and damage constitutive equations for the parent, HAZ and weld material zones of welds are introduced. Practical applications of these techniques are discussed and the results obtained from typical high temperature CrMoV welds in main steam pipe lines are presented.

Hill-type Muscle Model for Analysis of Mechanical Effect of Muscle Tension on the Human Body Response in a Car Collision Using an Explicit Finite Element Code

Abstract: A string of series-connected Hill-type bars is proposed for modeling the effect of muscle tension on human body kinematics in a car collision. The preliminary results indicated that such strings exhibit oscillations and instabilities when subjected to a large and transient stretch. A new algorithm for calculation of the force-velocity of the deformation relationship and the concept of the Hill-type multi-bar muscle element are introduced as countermeasures against these instabilities. In the Hill-type multi-bar muscle element, muscle force is computed from the sum of the deformations and the velocities of deformation of all the series-connected bars applied to model a given muscle. When the Hill-type multi-bar muscle element was applied to model experiments on fast stretching of an activated muscle, the calculated force well corresponded with the results published in the literature. Moreover, the current approach to muscle modeling yielded results consistent with the literature data on volunteers subjected to transient acceleration when it was utilized in simulations of the effect of muscle tension on the head-neck kinematics in a frontal car collision.

Real-Coded Adaptive Range Genetic Algorithm and Its Application to Aerodynamic Design

Abstract: Real-coded Adaptive Range Genetic Algorithms (ARGAs) have been developed. The real-coded ARGAs possess both advantages of the binary-coded ARGAs and the use of the floating point representation to overcome the problems of having a large search space that requires continuous sampling. First, the efficiency and the robustness of the proposed approach are demonstrated by test functions. Then the proposed approach is applied to an aerodynamic airfoil shape optimization problem. The results confirm that the real-coded ARGAs consistently find better solutions than the conventional real-coded Genetic Algorithms do. The designed airfoil shape is considered to be the global optimal and thus ensures the feasibility of the real-coded ARGAs in aerodynamic designs.

Analysis of Mechanical Behavior of a Short Fiber Composite Using Micromechanics Based Model : Effects of Fiber Clustering on Composite Stiffness and Crack Initiation

Abstract: An injection-molded short fiber composite often contains some fiber clusters due to a poor mixing. An analytical model for a composite with such clusters was developed to estimate a composite stiffness and stresses inside and just outside a fiber of the composite. In this paper, first the stiffness of the cluster is predicted by applying the Eshelby's equivalent inclusion method. Secondly the stiffness of the overall composite and the stress inside a fiber are assessed by applying the Eshelby's method to two kinds of inhomogeneities, i. e. cluster and fiber. Finally the stress just outside the fiber, namely the fiber-end stress, is evaluated using the Hill-Walpole-Mura's jump condition. It is concluded from this parametric study that the effective stiffness of a short fiber composite tends to decrease as the volume fraction of clusters increases, and cracks at fiber ends are more likely to occur at a lower applied stress level as the volume fraction of clusters increases since the magnitude of the fiber-end stress increases. It is found that a carbon fiber composite with higher stiff reinforcement is more sensitive to the negative effects of fiber clustering than a composite with less stiff reinforcement.

Accuracy of Real-Time Shape Measurement by Phase-Shifting Grid Method Using Correlation

Abstract: Real-time and non-contact methods are desired to measure the shape of human bodies or moving objects Grid projection methods are suitable for this purpose To obtain accurate results, it is necessary to analyze phases of a projected grid accurately Recently, we proposed real-time shape measurement with a phase-shifting grid method using correlation Contour lines of objects are obtained as phase values in real time with this method Phases are obtained without the influence of saturation of an image sensor by this method because a grid with rectangular brightness distribution is projected In practice, however, the brightness distribution of the grid is deformed because the grid is out of focus In this study, the accuracy of this method in measuring a moving object is examined by computer simulation The error is 3% for a phase of 2π in the case of worst focus when the object is stable The error increases linearly with the phase-shifting aberration ratio when the object is moving

Determination of Residual Stress in Z8CDWV12 Steel Using Critically Refracted Longitudinal Waves.

Abstract: Acoustoelasticity, i.e. the stress dependence of the phase velocity of ultrasonic waves in deformed elastic media, provides a method for determining the stress level. A primary motivation for using the ultrasonic technique is that it allowed to obtain information about stresses in the material. In fact, the velocity shift is proportional to the average stress in the region through which the waves are propagated. This leads to an ultrasonic technique of measure which may be used to determine residual stresses induced by welding processes. In this work, the experiment procedure for the determination of the residual stresses based on the critically refracted longitudinal (L er ) wave is developed. Different steps of the experiment are presented namely the travel time measurement, the calibration of the acoustoelastic effect and the residual stress determination. The application of this experimental methodology has been performed on the welded stainless steel plates, for which the residual stresses are determined in different zones and depths using the L er waves. The obtained results show that the ultrasonic technique is rather efficient for the evaluation of residual stresses and permit to control the state of the material after thermal and mechanical treatments.

Hybrid Stress Analysis of Perforated Tensile Plates using Multiplied and Sharpened Photoelastic Data and Complex-Variable Techniques

Abstract: An experimental study is presented on the effects of varying the number of terms in a power-series representation of the stress function relative to determining the stresses around a circular hole or an elliptical hole in a finite-width, tensile loaded plate. Photoelastic data are hybridized with complex variable/mapping techniques to calculate the tangential stress on the boundary of the cutout. Accuracy/reliability is enhanced by twice-multiplying and sharpening the measured isochromatics using digital image processing. Actual and calculated fringes are compared qualitatively. Far quantitative comparison, percentage errors and standard deviations of the percentage errors are calculated for all measured input data by varying the number of terms in the stress function. The hybrid results agree within three percent with those predicted by theory and finite-element analyses.

The Estimation of Temperature Rise in Low-Cycle Fatigue of TiNi Shape-Memory Alloy

Abstract: A difference in fatigue strength depending on the rotational speed between air and water was found for the rotating-bending fatigue characteristics of a TiNi shape-memory alloy wire in our previous work. The heat transfer characteristics around a shape-memory alloy wire were measured using Reynold's analogy. The rise in temperature of the metal during the rotating-bending cycles was calculated considering the heat transfer result. As a result, the rotating-bending fatigue characteristics of a shape-memory alloy wire were explained well from the viewpoint of the heat transfer characteristics.

A Study on Maximization of Dynamic Crushing Energy Absorption of Square Tubes with and without Stiffener

Abstract: The axial impact crushing behavior of square tubes with and without stiffeners are studied by Finite Element method, and comparisons of mean axial crushing force between numerical solutions and theoretical prediction as well as qualitative comparisons of folding patterns between numerical simulations and experimental observations are made and discussed. Based on the numerical analyses, maximization problems of dynamic crushing energy absorption of square tubes with and without stiffeners, respectively, are solved using the crashworthiness maximization technique for tubular structures which combined the techniques of design-of-experiment, response surface approximation as well as usual mathematical programming. In addition, the energy absorbing capability of cylindrical tubes and square tubes with and without stiffeners are also compared.

Experimental Techniques for Fatigue Reliability of BGA Solder Bumps in Electronic Packaging.

Abstract: Reliability of the solder bump has been studied by accelerated testing with several experimental techniques. A new thermal fatigue test apparatus using thermal conduction was constructed, which could produce temperature gradient effects without any additional design of test specimen and control the temperature of specimen easily. For the simulation of temperature change due to the heat generation of chip, a specimen (chip) was put on a heating plate through which heat flux was conducted. A small-sized electromagnetic type fatigue tester and a micro-mechanical testing machine were developed. High cycle fatigue test was performed by a small-sized electromagnetic type fatigue-tester. The time to failure was determined by measuring the changes in resistance. Using micro-mechanical tester, isothermal fatigue test was performed to investigate the optimum shape of solder bumps. The isothermal low cycle fatigue test of solder bumps was performed with four different shapes and the equivalent plastic strain distributions of four different cases were calculated using finite element method.

Analysis of Direct Current Potential Field around Multiple Spherical Defects

Abstract: A method for evaluating the distribution of electrical potential around multiple spherical defects was proposed. As the method is based on the known formulated solution for a single defect, the electric field could be analyzed efficiently in comparison with the other methods, such as finite element method. The electric field in a conductive material with multiple spherical defects at random locations was analyzed by the method. Result of the analysis showed that the increase in the potential difference normalized by the potential difference without defects, ΔV/V0, was in proportion to the product of the volumetric density of defects and the mean of cubed defect radius, nv[r3]m. This universal relationship held independently of the value of nv and the distribution of defect radius. Using the relationship, the damage due to the multiple defects can be evaluated from the increase in potential difference.

Improvement of Accuracy of Inverse Analysis for Stress Separation in Thermoelastic Stress Analysis.

Abstract: This paper considers determination of individual stress components from the sum of the principal stresses obtained experimentally by the thermoelastic stress analysis. The stress separation problem is divided into two parts : (1) an inverse problem to estimate the unknown boundary values from the knowledge of the sum of the principal atresses inside the analysis region, snd (2) a forward problem to compute the stress components inside the analysis region based on the estimated boundary values. These two problems can be formulated and solved by the BEM. As the inverse problem is often ill-posed, two techniques are adopted so as to attain an accurate result. One is pre-processing of experimental data, that is filtering based on the compatibility equation. The other is regularization of the inverse problem by Tikhonov's method with Hansen's L-curve method. The effectiveness of developed method is verified by applying it to an experimental data. The effect of configuration of the analysis region on the accuracy of stress separation is also discussed.

Fundamental Solutions for a Fluid-Saturated Poroelastic Infinite Space of Transversely Isotropic Permeability

Abstract: The fundamental solutions were obtained for a fluid-saturated, elastically isotropic, porous, infinite solid with transversely isotropic permeability under an instantaneous fluid point source and instantaneous point forces acting in mutually orthogonal directions, by superposing the dislocation line segments. These solutions include those for both porous solids of zero permeability in one direction and isotropic permeability as limiting cases. These solutions are intended to be used to derive the integral equations for a plane crack of arbitrary shape;these equations in turn will be implemented in a hydraulic fracturing simulator for the gas/oil production.

Finite Element Crash Analysis of Framed Structures by the Adaptively Shifted Integration Technique

Abstract: In the present study, each member of a framed structure is subdivided with two linear Timoshenko beam elements at both ends and a cubic beam element based on Bernoulli-Euler hypothesis at the center. The adaptively shifted integration (ASI) techinique is used only in the linear Timoshenko beam elements. The proposed model is applied to the explicit finite element analysis of the crashing behaviors of impulsively loaded framed structures considering the effect of large deformation by the updated Largrangian formulation. Several numerical studies have been carried out in order to show the validity of the proposed numerical technique.

Improvement in Static, Impact and Fatigue Properties of CFRP due to CNBR Modification of Epoxy Matrix

Abstract: An epoxy matrix of Carbon Fiber Reinforced Plastics (CFRP) was modified using sub-micron Cross-linked acrylo Nitrile Butadiene Rubber (CNBR) particles to improve the mechanical properties of CFRP. The static tensile strength increased more than 15% in comparison with the strength of unmodified CFRP when the rubber content was 10 wt%. The Young's modulus little changed due to CNBR modification of the matrix. Fracture toughness and fatigue crack propagation resistance under Mode I loading were also improved due to CNBR modification. The impact resistance in the flat-wise direction was improved as well. Fatigue lives under tension-tension loading were significantly extended by CNBR modification at all stress ranges, although the slope of the S-N line of CNBR modified CFRP was almost the same as that of unmodified CFRP. Differences in fractured surface and internal damage accumulation process between two CFRPs were found. Fatigue lives also increased for center hole-notched specimens due to CNBR modification.

Measurements of Near-Tip Displacement Fields, Separated J Integrals and Separated Energy Release Rates for Interfacial Cracks Using Phase-Shifting Moire Interferometry

Abstract: In this paper, first, the concepts of the separated J integrals and the separated energy release rates, which have the physical significance of the energy release rates from corresponding material sides of a bimaterial are briefly presented. Phase-shifting moire interferometry is used to investigate interfacial crack-tip behavior of a bimaterial specimen, which is fabricated of epoxy and aluminum. The loading angle to the interfacial crack is systematically changed. The inplane displacement fields near the interface crack are recorded by the phase-shifting moire interferometry. Using the measured displacement fields, the stress intensity factors and the separated energy release rates are evaluated. From the theoretical and experimental results, it is found that the compliant material (epoxy) side provides considerably larger fracture energy to the interfacial crack tip.

Approximate Solution of Interactions among Spatially Distributed Broken Fiber, Matrix and Interface in the Progress of Interfacial Debonding in Multifilamentary Unidirectional Composites.

Abstract: In order to describe the relationship of mesoscopic phenomena of interfacial debonding and breakage of fiber and matrix to the macroscopic stress-strain curve of unidirectional composites, an approximate nondimensional solution method was presented using a two-dimensional model. By applying this method to several examples in which the species and locations of broken components were varied, the following features were revealed: (a) fiber-breakage-induced debonding occurs at a lower strain than the matrix-breakage-induced one; (b) the overall debonding is hastened due to mechanical intractions under the existence of many broken fibers and matrices; (c) the progress of overall debonding is dependent on the species of the broken components and on the geometrical location of broken components and debonded interfaces;and (d) the stress-strain curve shows drops in stress due to the progress of debonding. As an extended application of the present method, a nondimensional Monte Carlo simulation method was presented to describe the behavior of the composite in which the number and location of broken components and debonded interface vary with increasing strain.

Creep Life Prediction of Ni-Base Superalloy Used in Advanced Gas Turbine Blades by Electrochemical Method

Abstract: In order to develop a methodology for creep life assessment of directionally solidifed Ni-base superalloy CM247LC, commonly used in advanced gas turbine blades, changes in electrochemical property of the alloy caused by creep have been investigated. Experimental results on electrochemical polarization measurements revealed that the peak current densities "Ip" and "Ipr", which appeared at a specific potential during potentiodynamic polarization reactivation measurements in a dilute glyceregia solution, increased linearly with the life fraction at an early stage of creep life and were uniquely correlated with a newly proposed Arrhenius-type parameter "(t/tr) exp (-Qc/RT)". The creep life fraction can be nondestructively evaluated by electrochemical polarization measurements and the above parameter.

Effect of Plastic Deformation by Roller-Working on Fatigue Strength of Notched Specimen

Abstract: In this study, the fatigue test is performed to investigate the effect of plastic deformation by roller-working on the fatigue limit of a notched specimen. Three types of specimens are tested, whose different deformation values are obtained by roller-working and whose final finishing shape and dimensions are the same. The reason why fatigue limit changes with a change in the plastic deformation value is examined by analyzing residual stress, micro-Vickers hardness distribution and crack-tip opening displacement. The main results are as follows : (1) The resistance against fatigue crack initiation increases with an increase in the plastic deformation value. ( 2 ) When the deformation value becomes too large by roller-working, residual stress is released by cycle stress amplitude and the critical stress amplitude of non-propagating crack tip opening decreases. (3) The fatigue limit of the roller-worked notched specimen does not necessarily increase when the plastic deformation value becomes too large. (4) The optimum deformation value exists and is about 0.5 mm, to improve the fatigue limit of the roller-worked notched specimen.

High Temperature Creep under Bend Loading in Si-Ti-C-O Ceramic Fiber Bonded Body

Abstract: The Si-Ti-C-O fiber bonded ceramic material was creep-tested under three-point bend loading at 1 673 K, where deflection was measured at the loading point by means of the laser beam type extensometer. Furthermore, creep process was analyzed by using the proposed convenient analytical method and FEM. The creep constitutive equation was successfully determined through an inverse analysis using FEM ; parameters included in the equation were settled so that the calculated deflection-test time curve might coincide with the measured one. The calculation exhibited that compressive creep hardly occurred in this material. The convenient analysis method was useful for setting the initial values of the parameters in the FEM calculation.

Lattice Strain and Domain Switching Induced in Tetragonal PZT by Poling and Mechanical Loading

Abstract: The X-ray diffraction method was applied to measure the change of the lattice strain and domain switching in tetragonal lead zirconate titanate (PZT) due to poling and external mechanical loading. The lattice strain was determined from the linear relation between the diffraction angle and sin 2 ψ (ψ is the angle between the normals of the diffraction plane and the specimen surface). The lattice strain measured by X-rays is less than 50% of the macrostrain determined from the dimensional change due to poling. The applied strain induced the increase of the lattice strain, and the amount of increase was about 50% of the applied strain. The amount of domain switching was evaluated by the change of the intensity ratio of 002 to 200 diffraction. The intensity ratio was decreased with the applied strain. The broadening of X-ray diffraction profiles obtained from the diffraction plane perpendicular to the poling direction was the maximum, indicating the largest microstrain in the poling direction.

Inelastic response and stability of titanium alloy tubes under cyclic bending

Abstract: The response and stability of titanium alloy tubes subjected to cyclic bending are presented in this paper. The curvature-ovalization measurement apparatus, designed by Pan et al., is used for conducting the present curvature-controlled experiments. It is observed from the moment-curvature curve that the titanium alloy tube is cyclically harden and becomes steady after a few cycles for symmetric curvature-controlled bending. However, from the ovalization-curvature curve, the ovalization of the tube cross-section increases in a ratchetting manner with the number of cycles. Owing to the progressive accumulation of the ovalization of the tube cross-section during the cyclic bending, the titanium alloy tubes buckle eventually. Theoretical formulation, proposed by Kyriakides and Shaw, is used for investigating the relationship between the magnitude of the controlled curvature range and the number of cycles to produce buckling. Good agreement between the experimental and theoretical results is achieved. Furthermore, experimental data of the titanium alloy tubes from present study are compared with the experimental results of 6061-T6 aluminum and 1018 steel tubes tested by Kyriakides and Shaw. It is shown that for similar outer diameter/wall thickness ratio, the stronger metal tube exhibits a shorter number of cycles to produce buckling.

Application of the Statistical Design Support System toward Optimization of Vehicle Safety Equipment.

Abstract: The "Statistical Design Support System" produces a new practical optimal design method. It can be used even on nonlinear behavior. The optimization can be done with this system using a small number of calculation results. Therefore, the effect is especially significant when applied to a problem that needs large-scale calculation. The authors applied it to the optimization of design parameters of the occupant restraint system, and have tried to reduce the injury criteria of occupants based on the crash simulation. According to the improvement of interest and technology on vehicle safety, many countries have declared new safety assessments that are more severe than used one. In order to meet them all, it will be needed to consider some different crash situations simultaneously when vehicle safety equipment is designed. The authors made optimal design with consideration of different conditions of collision. This paper draws attention to the effectivity analysis and optimization.

Thermal Deformation of a Piezothermoelastic Composite Plate. (An Antisymmetric Angle-Ply Laminate Plate).

Abstract: The response of a thin piezothermoelastic composite plate subjected to stationary thermal and electric fields is investigated. Solutions are obtained using the thin plate theory and the Rayleigh-Ritz method. As an analytical model, we consider a simply supported antisymmentric angle-ply laminate poezothermoelastic plate. The plate is exposed to an environment with a temperature rise on the upper surface only. To reduce the deflection produced by the thermal loading, electric potential is applied to the piezoelectric layer in the composite. Numerical results show the effects of the ply angle of the laminate configuration and the number of layers on the response of the thermal deflection and the applied voltage.

Problems and Progress in the Characterisation and Stress Analysis of Moulded Fibre-Reinforced Composites : A Thermoelastic Approach

Abstract: Fibre-reinforced composite components manufactured by compression moulding present special difficulties to the stress analyst because of the spatial variations in the material and mechanical properties developed as a result of the moulding operation. Two procedures have been developed, based on the thermoelastic stress analysis technique, to help in the stress analysis of such components. The first, a development of the Brazilian disc test, allows the directions of the principal material axes, the local fibre content and the principal material and mechanical properties at a point in a flat area of a moulding to be determined. In the second procedure, the results of a numerical stress analysis are iteratively modified until a satisfactory comparison with thermoelastic stress data is obtained.

Photoelastic Analysis through Jones Matrix Imaging Fourier Polarimetry.

Abstract: The paper presents further development of the authors' hybrid method for the three-dimensional nondestructive photielastic analysis. The general arrangement and measurement procedure of a Jones matrix imaging Fourier polarimeter is described with emphasis in error analysis. Errors that are due to orientational misalignment of the polarization elements are considered, an analytical treatment is given and is followed by experimental examples.

Biaxial Deformation Behaviors of C/C Composite at High Temperatures.

Abstract: Biaxial deformation behaviors of carbon fiber reinforced carbon (C/C) composite were investigated at three biaxial stress ratios T = 0, 0.5 and 1 using a cruciform-type specimen with slots at high temperatures. The biaxial displacements were measured in center area of the specimen by means of a biaxial capacity-type extensometer. Finite element method was also performed to examine the validity of the geometry of the cruciform-type specimen with slots and to assess biaxial deformation behaviors of C/C composite at high temperatures. As a result, it was found that thermal stresses were restrained from generating at high temperatures and uniform distributions of strains and stresses were realized in the center area of the specimen. The calculated biaxial strains were in quite good agreement with the measured ones by the biaxial extensometer. Accordingly, the analysis that used orthotropic theory was effective method to examine the biaxial deformation behaviors of C/C. composite at high temperatures. Furthermore, it was indicated that C/C composite exhibited linear stress-strain response at high temperatures, independent of biaxial stress ratio.