In the previous papers, at first, the relationship between the stress rate and the tangent stiffness with the special orthogonal group SO (3) for finite element formulation was shown. The stress rates used were Truesdell stress rate, Jaumann stress rate, Neo-Green stress rate and Ishihara stress rate. Next, tangent stiffnesses of beam elements using those stress rates were led. Next, 6 kinds of euler-buckling equations were led by 2 kinds of rotation and with or without shear deformation and axial stretch. And, euler-buckling equations of a beam by those 4 kinds of stress rates were led in order to get the guideline of finite element formulation. Then, in this paper, euler-buckling and torsion-buckling problems of those beam elements will be solved and the euler-buckling loads of those beam elements will be compared with the loads of theoritical solutions.

View full abstract

In the previous papers, the relationship between the stress rate and the tangent siffness with the special orthogonal group SO (3) for finite element formulation was shown. The stress rates used were Truesdell stress rate, Jaumann stress rate, Neo-Green stress rate and Ishihara stress rate. And, stiffness elements of tangent stiffnesses of beam elements with SO (3) were shown. They were material stiffness ΔδΠ_m, geometric stiffness of rigid rotation ΔδΠ_rg, geometric stiffness of stretch of stress direction ΔδΠ_{sg, stress}, geometric stiffness of stretch of perpendicular line of area ΔδΠ_{sg, area} and geometric stiffness of stretch of deformation rate ΔδΠ_{sg, deform}. In this paper, the constitutive equation of the new Ishihara stress rate will be considered. And it will be shown that although the stress rate and the strain rate are nonsymmetric, the material stiffness matrix will be symmetric. And it will be proved that geometric stiffness of rigid rotation will also be able to be symmetric with 2nd order convergent rate. And it will be shown that the formulation with SO (3) will be different from the conventional formulation with infinitesimal rotation.

View full abstract

This paper proposes a new concept for dislocation simulation using a mesoplasticity FEM. This FEM system is based on the crystalline plasticity theory that takes into account twelve slip systems of an FCC lattice. This paper relates slides on these slip systems with dislocation behavior, and proposes a new anisotropic workhardening rule based on dislocation interaction. This paper also developes a new description of lattice rotation, and introduces them into a mesoplasticity FEM. This FEM is applied to simulations of tensile and compressive processes of crystalline metals. Results show that the Bauschinger effect arises even in a single crystal, and is attributed to change of active slip systems. The simulation also reviels role of dislocation behavior in a crystalline material on the Hall-Petch relationship.

View full abstract

This paper addresses internal variables for material property simulation by the thermo-elastoplastic FEM in a metal forming process. Desipite of many flow stress equations for material property prediction systems, their internal variables are not consistent with mathematics and dynamics of the continuum theory. This results in a fatal contradiction in a FEM simulation when the FEM is applied to metal forming processes of various deformation history. To overcome this problem, four mathematical requirements on internal variables are discussed, and the generalized deformation energy is proposed as the simplest internal variable that satisfies these requirements. A new constitutive equation is developed using the flow-stress equation based on the generalized deformation energy. It is applied to a thermo-elasto-plastic FEM code, and upsetting and heat treatment processes are simulated. Results show effectiveness of the new internal variable.

View full abstract

Recently integral large composite structures have been applied to many structures of vehicles because of their low cost and high reliability. Since the structures are large and complicated, a damage estimation system is required to assess the safety of inspected damage. Among fracture mechanisms of FRP laminates, delamination is the most important one because it results in stiffness degradation of the structures. In this study, a simple estimation method of delamination growth for FEM using two-dimensional plane stress elements was proposed by using energy release rate, and inexpensive FEM simulation method for delamination growth was developed. To assess the safety of inspected damage, prediction of delamination growth and stiffness degradation are more important than that of fracture strength. Analytical results of delamination growth and stiffness degradation for a CF/epoxy laminate with an open hole were compared with experimental results. As a result, the simulation method was shown to be effective and inexpensive for predicting delamination growth and stiffness degradation.

View full abstract

The microcracking behaviors of two-phase materials containing microinclusions with the various mismatch between mechanical properties of matrix and inclusions are analyzed by using the two-dimensional mesoscopic simulation method. The first mismatch considered is the one for Poisson's ratio. Under the condition of compressive stress, inclusions with higher or lower Poisson's ratio than the matrix cause different patterns of microcracking near the inclusion. The second mismatch is concerned with the stiffness and the strength against microcracking of matrix, inclusions and their interfaces. Parametric studies have been conducted for their influences on macro, stressstrain relations.

View full abstract

A simple method for structural analysis of honeycomb sandwich construction (HSC), which is used as light weight and high stiffness material, was given. It was shown that a rigidity of honeycomb material is very influential to the stiffness of HSC when HSC is subjected to bending load, and elastic and plastic moduli of rigidity are given by honeycomb parameters such as cell size and cell wall thickness. Therefore the authors proposed the finite element model for structural analysis of HSC, which can simulate the HSC deformed behavior without detailed hexagnal mesh. The analyses results given by proposed model agreed with the results of the experiment and the detaied meshing analyses. This model doesn't reduce the precision but reduce much time for pre-post processes and analyses.

View full abstract

Using the general higher order theory expanded by Fourier series, we formulate a two-dimensional theory to analyze bending vibration of coupled thermo-elastic plates. Then the governing equations are converted to two-dimensional equations. Numerical eigen-value problems are shown in the case of coupled thermo-elastic beams with bending vibrations.

View full abstract

The element free Galerkin method (EFGM) is one of the meshless methods proposed by Belytschko, et. al. in 1994. The EFGM is a new numerical method which is expected to be utilized for many problems of the continuum mechanics and for a tool of the seamless system between the CAD and the CAE instead of the finite element method. The EFGM uses the moving least square interpolation (MLSI) for the functional approximation without elements. However the EFGM needs computational time for searching nodes of the MLSI and needs to be provided the integral domain. In this study, the method of the digraph and the Delaunay tessellation are used for the division of the integral domain and the searching nodes. These techniques are useful for the simplification of the analysis and saving the computational time. Furthermore, the EFGM has not been applied to nonlinear problems such as elastic-plastic problems or creep ones under elevated temperature. In this paper, the developed EFGM using the method of the digraph and the Delaunay tesselation is applied to creep nonlinear problems. The results obtained from the EFGM agree well with those of the finite element method.

View full abstract

Recently composite laminated plates made from the prepreg sheets of the woven fabric have been produced and used. When the materials are used, the laminated construction must be optimized to use it effectively. The purpose of this study is to propose the support system for the design of the laminated construction of the woven fabric (i.e. Carbon, Glass and Aramid). The system consists of Genetic Algorithm and Neural Network. By repeating the following two sequences, the designs that satisfied the required mechanical properties are searched. (1) The character of the laminated construction of the woven fabric that was expressed by binary number is produced according to Genetic Algorithm. (2) The fitness grade of the designs to the required properties are evaluated by Neural Network. The network has learned the pattern information which are expressed by the relationship between the codes and the mechanical properties (density and tensile strength). The several composite laminated plates which were recommended by this system were produced, and the properties of the plates were measured. As the results, it was proven that the measurements are close to the required properties, and the validity of this system was confirmed.

View full abstract

Monotonic compressive loading and relaxation tests are conducted at the strain rates of 1.1×10^-1∼1.1×10^-5S^-1 and the temperature of 10, 25 and 40°C for the column specimens of polypropylene and polycarbonate following the previous study for high-density polyethylene. The observed stress-strain responses for the three engineering plastics are simulated successfully using the constitutive model based on overstress. The examination of such stress-strain behavior reveals that the effects of the strain-rates and the temperatures on the rate-dependent deformations are expressed using a unified parameter and that the viscoplastic behavior at one temperature can be related to that at another temperature by a change in the time scale only. This results indicate that the concept of timetemperature equivalence is applicable to these solid polymers within the range of test conditions, and the reconstructed viscoplastic constitutive model with use of the equivalent time has produced the deformation behavior under time-varying temperature conditions demonstratively.

View full abstract

An ultrasonic techniques was developed to study the characteristics for contact mechanics of an artificial hip joint. Total Hip Replacement model was used to determine contact pressure distribution on an artificial aceptabular cup subjected to compressive load ranged from 196 N to 588 N in four femur positions. The contact pressure was found to be nonuniform and less than 6 MPa. It was shown that the tendency of the pressure distribution is in agreement with that obtained by the computer simulation. Some preliminary results were also presented to illustrate the effect of the direction and the magnitude of the load applied to a stem on the contact pressure distribution on the aceptabular cup and to evaluate the contact mechanism of the artificial hip joint.

View full abstract

The Finite Element Method is applied to the analysis of Brinell hardness test of porous materials. The numerical calculation is performed using four different plastic constitutive rules such as Gurson's rule, Tvergaard's modification of Gurson's rule, Goya-Nagaki-Sowerby's rule and a stereology-based rule that is a modification of Goya-Nagaki-Sowerby's rule. For the investigation of the validity of the rules, the numerical results are compared with experimental data for the porous materials produced by Spark Plasma Sintering method which can product porous materials of higher porosity. From the comparison it is concluded that the numerical results obtained using Tvergaard's modification of Gurson's rule or the stereology-based modification can well predict the experimental results. However, the numerical results deviate from the experimental data for the porous material of higher porosity such as fo=0.3. This deviation is attributed to the fact that the shape of pores in the porous material of fo=0.3 are quite different from the sphere that is a fundamental assumption in developing constitutive rules.

View full abstract

In order to study dynamic mechanical properties of the titanium alloy Ti-6Al-4V, plate impact experiments with PVDF (Poly Vinylidene DiFluoride) stress gauges and the VISAR (Velocity Interferometer System for Any Reflector) were conducted using a shock gun system. From the experiments, we obtained the Hugoniot curve, the Hugoniot elastic limit and the spalling strength of the alloy.

View full abstract

This study was conducted to clarify the effect that quenching after induction heating for a short time (60 s) has on the mechanical properties and fatigue strength of Ti-6Al-4V alloy which is one of the most typical α+β titanium alloys. When heating temperature was higher than 1 173 K, the above heat treatment induced the transformation from β-phase to α martensite possessing a high hardness. Such creation of α'-phase greatly improved both the tensile strength and fatigue strength of the alloy although it decreased the ductility. However, in case that heating temperature was higher than β-transus temperature (1 268 K), the improvement of the tensile strength and fatigue strength was limited by growth of previous β grains. The above results showed that the appropriate temperature of the induction heat treatment for strengthening of Ti-6Al 4V alloy is between 1 173 K and β-transus temperature when heating time is 60 s.

View full abstract

Orientation-controlled Cu bicrystals with disperesed SiO₂ particles were tensile tested at various temperatures in vacuum and Ar-gas atmospheres. Two kinds of bicrystals having [001] twist 12°and 30°grain boundaries were employed. 30°bicrystal specimens fractured intergranularly at around the intermediate-temperature range, although 12°ones fractured transgranularly at all the temperatures. The elongation to fracture was smaller when deformed in Ar atmosphere than in vacuum almost at all the temperatures irrespective of the bicrystal specimens. The above results could be reasonably understood by considering the difference of the mean grain-boundary strength, the inherent grain-boundary strength, and the effect of gas atmosphere which would be responsible for the acceleration of void formation and growth.

View full abstract

Low-cycle fatigue strengths of spheroidal graphite cast irons (SGI's) with high strength and high toughness have been investigated to discuss their fatigue reliability. The obtained results are compared with those of cast steels (SC's), being specially focused on austempered ductile cast iron (ADI). It was found that low-cycle fatigue life under tension compression cyclic loading, i.e., load ratio (R)=-1, could be improved by increasing tensile strength for SGI's with on exception of SGI 800, and for SC's. An ADI with tensile strength of 1 122 MPa showed the highest fatigue reliability among materials examined.

View full abstract

This study was done to clarify the influence of complex deterioration on fatigue crack propagation (FCP) mechanism. Especially, Influences of the recycling process and fatigue for carbon-fiber-reinforced PEEK were attention to. The main results were as follows : (1) It was noted that the FCP property of recycled PEEK/CF materials were as nearly equal to that of virgin material. (2) FCP curves on a da/dN-ΔK diagram for three materials were expressed as one curved line on a da/dN-ΔK/E diagram. Therefore, it could be understood that there FCP curves were influenced by the elasticity modulus on fatigue crack propagation, the crack opening displacement (COP). (3) Above da/dN=10^-7 [m/cycle] on FCP curves, the'm'values of Paris's law for virgin material was smaller than that for recycled materials. This was because the bridging effect of virgin material was superior to that of recycled materials.

View full abstract

Push-pull fatigue tests were carried out on commercially pure titanium sheet at 393 K and 573 K in order to investigate the effect of elevated temperature on fatigue crack initiation behavior. The static and fatigue strengths decrease with the increase of temperature. At elevated temperatures, the sharp knee in S-N curve observed at room temperature disappears. Successive observations on specimen surface and measurements of strain hardening exponent have shown that the mechanism of crack initiation differs profoundly due to the increase in temperature. At a room temperature, fatigue microcracks initiate at a few tenth percent of fatigue life, along slip bands within not a single but multiple neighboring grains. At elevated temperatures, however, they initiate at less than 10% of their lives, along grain boundary where crowd slip bands impinge. This is ascribed to the activation of slip deformation and enhancement of strain hardening at elevated temperatures.

View full abstract

Four point bending fatigue tests were performed on cemented carbides to investigate an effect of stress ratio on the short fatigue crack growth behavior in air. At the region of high crack growth rates, the maximum stress intensity factor, K_max, is a dominating factor for crack growth behavior, while at the region of low crack growth rates, stress intensity factor range, ΔK accelerates the crack growth rates with the aid of the maximum stress intensity factor, K_max. The enhanced crack growth rate brought by cyclic stressing at the low K_max region is expected to be concerned with cyclic fatigue damages ; i.e., loosening of a interface between WC grain and binder phase ahead of the crack tip, and also removal of bridging parts at the crack wake.

View full abstract

In a previous paper, the present authors clarified that COD is a suitable parameter to interpret the fatigue damage on the basis of the fatigue crack growth in low-cycle random fatigue. Especially the COD parameter correlated well the fatigue damage counted using the rainflow method (RFM) with the crack growth life in LCF. To extend this idea to high-cycle random fatigue the present study has been done. The result showed that although the RFM is valid to evaluate total fatigue life, it is invalid to predict the crack growth life. This is due to the fact that the crack growth life is strongly affected by the effect of crack closure, which is more amplified in high-cycle fatigue than low-cycle fatigue.

View full abstract

The fracture toughness, K_max, which dose not satisfy the requirement for the plane-strain, of aluminum alloy die castings reinforced with NiAl and Ni₃Al, intermetallic compound, and SiC particles has been studied by 3 point bending tests in the temperature range from 20°C to 300°C. The K_max's were almost comparable in the materials investigated ; the highest in unreinforced alloy, and then SiC-, Ni₃Al- and NiAl-particulate reinforced one in the order. These appear to be attributed to the microscopic characteristics observed in the fracture surfaces and longitudinal cross-sections : (1) debond at matrix/particle interface and fracture of particles, (2) size and aspect ratio of particles, and (3) precipitates in the matrix. The K_max decreased with an increase in particulate volume fraction because of decrease in the amount of plastic deformation in the matrix and damages associated with particles. The K_max's in the reinforced alloys at 20°C were comparable to those at 200°C. The temperature dependencies of K_max appeared to be associated with those of 0.2% proof stress.

View full abstract

A method to evaluate the stress intensity factor of a circumferential crack in a finite length cylinder under non-linear radial temperature distribution, considering the effects of various structural parameters such as cylinder length and edge restraint, is shown. The method was derived by combining the simplified methods to evaluate the stress intensity factor for the crack under linear temperature distribution in the radial direction and under non-linear stress distribution on the crack surface, both previously developed by the authors. By applying the solution of transient radial temperature distribution for a cylinder which is suddenly cooled from inside, the maximum transient stress intensity factor of the crack under this temperature change was discussed. The maximum transient stress intensity factor increased and showed a peak as the crack becomes longer. In addition, the stress intensity factor was strongly affected by the cylinder length, and the stress intensity factor for a long cylinder was not necessarily larger than that for a short one.

View full abstract

The mechanism of electromagnetic acoustic transducer (EMAT) for fundamental symmetrical Lamb wave using magnetostrictive effect in thin steel sheet was studied. The EMAT was constructed from the magnet for loading the parallel field to the sample surface and the meander coil for carrying the transmitting current. First the field dependence of the received signal amplitude and the phase for the transmitter and the receiver EMAT at the two different positions of the meander coil was investigated. Next the driving mechanism was discussed on the basis of the experimental results. This paper shows that this type of EMAT works using the time and spatial change of the synthesized magnetic field and has the different driving mechanism under the lead lines and between the lead lines of the meander coil.

View full abstract

The crack growth behavior on the lap joints with various adhesive thicknesses was investigated by the echo characteristics of surface wave emitted toward the adhesive layer under shearing forces. The echo height reflected from the edge of adhesive layer and the round-trip propagation time from the surface wave probe to the adhesive layer were measured for evaluating the crack growth behavior. The crack was generated along the adhesive interface when the ratio of the round-trip propagation time suddenly increased. After that, the crack rapidly grew. In the case where the distance between the surface wave probe and the adhesive layer was 10 mm, the crack of the adhesive layer was able to detect when the ratio of the round-trip propagation time became about 1% and the ratio of echo height reflected from the edge of adhesive layer became about 60%. Moreover, the shearing stress of crack generation was about 52% of the shearing strength.

View full abstract

In ferromagnetic materials, magnetic properties such as the magnetotriction and the magnetization curve depend on the applied stress as well as the relative orientation of the stress and the magnetic fields due to the magnetoelastic interactions. The authors have studied stress dependence of the magnetostriction and the magnetization curve from the constitutive equations of the stress and the magnetization process of soft ferromagnetic materials. The material is assumed to be isotropic in the natural state, i.e. in the absence of the magnetic field and the stress, and undergo a thermodynamically reversible process, so that the effects of hysteresis can be neglected. It is shown that the theoretical results calculated from an appropriate choice of the material parameters in the internal energy density are in excellent agreement with the experimental data of low carbon steel (SM490A) and pure Ni.

View full abstract

For non destructive estimation of brittle fracture strength at welded joint, fracture mechanics require to monitor fracture toughness of weld metal and two dimensional flaw sizes of length and height. Up to now, many methods have been proposed to measure both flaw length and height in laboratory. However, industrial inspection methods estimate only flaw length and other advanced methods proposed have several barriers for applying industrial problems. As the results, NDE measurement data have been used only for flaw detection, and strength has never been estimated non destructively for industral structures. In this paper, the authors applied the advanced automatic ultrasonic inspection system to measure not only flaw length but also flaw height for industrial welded structures. Using this system, 22 specimens with artificial inner and surface cracks in welded joint varying crack length and height were measured non destructively. After non destructive measurement, welded joint specimens were broken by tensile test in liquid nitrogen, and the crack size were measured by fractography. Comparing the crack size by fractography to the one by ultrasonics method, errors in non destructive sizing by the ultrasonic system were estimated accurately. Using the fracture mechanics procedures, effect of the error in non destructive flaw sizing on strength estimation was investigated.

View full abstract

The friction welding for copper and aluminum is useful to minimize the diffusion thickness at the interface between copper and aluminum. The minimization of diffusion thickness is required for maintaining the joint strength. Because brittle intermetallic compounds are formed at the friction weld interface between copper and aluminum. However, the effects of intermetallic compounds on joint strength characteristics have not fully been clarified. In this experiment, pure aluminum was used as a intermediate layer for the friction welding between copper and aluminum alloy. It is confirmed that the good tensile strength distribution could be observed in the radius direction of friction welded joint by selecting the appropriate welding conditions. However, the Charpy impact energy at friction weld interface became comparatively low values, and revealed a remarkable distribution in the radius direction. It was also confirmed that the Charpy impact energy distribution was due to the thickness of intermetallic compounds, such as CuAl₂, CuAl and Cu₉Al₄. Especially, the formation of CuAl₂ and Cu₉Al₄ reduced the Charpy impact energy at friction weld interface.

View full abstract

This paper delas with numerical solutions of singular integral equations in an interaction of elliptical holes under in-plane bending. The body force method is used to formulate the problem as a system of singular integral equations with Cauchy-type singularities, where unknowns are the densities of body forces distributed in an infinite plate. In order to satisfy the boundary conditions along elliptical boundaries, the unknown body force densities are approximated by a linear combination of fundamental densities functions and polynomials. The calculations are carried out for several arrangement of elliptical holes, and it is found that the present method yields rapidly converging numerical results. The body force densities and stress distributions along the boundaries are shown in figures to demonstrate the accuracy of present solutions.

View full abstract

Indentation problems for an elastic half-space may possess similarity solutions when the local shape of the contacting body is expressed by a homogeneous function. In this situation, the desired solution for curved punches can be obtained by the integration, namely, cumulative superposition, of the solution to a single auxiliary problem which amounts to indentation by a flat-ended punch. This procedure avoids treating the moving and unknown contact boundary explicitly, so that the contact region can be determined in an accurate manner. In this study, the advantage of this procedure is explored from analytical and numerical points of view. Although the theoretical basis is laid down for frictionless indentation of an elastic half-space by a rigid punch, the method is shown to be applicable to the contact between two elastic bodies and for more general frictional behavior. To demonstrate the use of this superposition principle, the three-dimensional indentation by a punch with elliptic cross sections, as well as the plane strain indentation by an asymmetric punch are solved by this method. Numerical accuracy of the present procedure is verified employing some examples of plane-strain problems. The use of the boundary element method for the reduced flatpunch problem is shown to be effective and promising for more complicated three-dimensional indentation problems.

View full abstract

This paper focuses on the dynamical merits and demerits of organism structure and selects ginkgo nut shell as an example to analyze. Based upon the microscopic observation and mechanical experiments on the structure, material composition and mechanical evaluation of a ginkgo nut shell, the concerned conclusions are drawn up. First, by analyzing the chemical composition of the ginkgo nut shell, the rate of lignin goes from 20 percent to 35 percent higher than any other kinds of wood. while the rate of cellulose goes a little bit lower. Based upon it, each part of the ginkgo nut shell is observed by SEM and CCD camera, and it is confirmed that cellulose exists in the way of piled up layers between which lignin distributes. The lignin connects cellulose to be an oval shell, similar to FRP structure. Next we have noticed the Flange speciality of connective formation and the tiny crack of its upper part. By observing the experiments of the inside and outside pressure damage and its germination experiment, it is confirmed that the crack and flange structure are the crucial demerit structure of the ginkgo nut shell's break when the seed germinates, which reveals that the organism has its own merit and demerit structure corresponding to its function. Its harmony and practicality provide new foundation and hint in the new structural design of recycle type.

View full abstract