This report deals with numerical verification of the theory, developed in the first report, on microscopic symmetric bifurcation of cellular solids subjected to macroscopically uniform compression. The theory is applied to analyzing the in-plane biaxial buckling of an elastic hexagonal honeycomb. It is shown that microscopic symmetric bifurcation takes place in the heneycomb in spite of the complex buckling behavior under in-plane biaxial compression. It is also shown that the complex buckling behavior is a consequence of the multiplicity of buckling modes ; for example, a triplet of buckling modes under equi-biaxial compression, each of which is relatively simple, are linearly combined to generate a flower-like complex mode, which was observed recently to occur in a hexagonal honeycomb with circular cells.

View full abstract

A homogenization method based on the finite element method for beam/bar structures subject to torsion, bending and axial stretch/compression, is derived. The detailed configurations of the beam/bar structures are assumed to be periodic. They are composed of repeating unit cells. The unit cell is represented by three dimensional finite element model. Displacement fields based on the three dimensional finite element model for the unit cell and those based on Euler-Bernoulli hypotheses for the bending deformation of beam and also based on the torsion of circular bar, are superposed, representing a complete deformation field within the structures. Proposed formulation is, in rigorously speaking, valid when the size of the cross section of the beam/bar structure approaches zero in limiting sense. However, as an approximation, the theory can be applied to the case that the cross section of the beam/bar structure is finite but is small compared with their length. Some numerical examples are presented to discuss the validity of the proposed method. The proposed homogenization technique can be applied to analyses for composite beam/bar and also for other types of structures having complex internal structures, such as holes of complex shape, complex cross sectional shape, etc.

View full abstract

A series of studies have been made by one of the present authors to develop a method of estimating the stress and strain at a notch root in the elastic-plastic range. In this paper, simple evaluation methods of elastic-plastic stress and strain concentration factors of pressurized cylinders were proposed on the basis of numerical analysis by a finite element method. In the case of small-scale yielding, the normarized stress concentration factor K^*_σ/K ^*_t and strain concentration factor K^*_ε/K ^*_t, of shallow and deep notched cylinders subjected to internal or external pressure were estimated with good accuracy by using the master curves as a function of a dimensionless parameter K ^*_tσ_n/σ_y. A limitation of the use of the master curves expressed in terms of the parameter K ^*_tσ_n/σ_y was also discussed.

View full abstract

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture changes due to plastic deformation, and their relationship was systematically analyzed by Sayers. According to Sayers's proposed model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be derived by using ultrasonic wave velocity changes. In the previous paper, the Sayers's model was examined by experimental work and the effect of plastic deformation on texture development of an aluminum alloy specimen was studied by using ultrasonic pole figures as one of its applications. In the present paper, the ultrasonic pole figures based upon Sayers's model are constructed under various loading conditions of uniaxial tension, pure torsion, biaxial tension-compression, biaxial compression and biaxial tension, respectively. To examine its accuracy and reliability, the ultrasonic pole figures are compared with ones analyzed by the finite element polycrystal (FEPM), which has already been considered as a well-developed technology for the analysis of microstructural behaviors due to plastic deformation. The results show a remarkable qualitative similarity among the two methods.

View full abstract

The present paper describes the adaptive Free Mesh Method (adaptive-FMM) applied to elasto-plastic large deformation analysis. The adaptive-FMM is a combined technique to incorporating adaptive remeshing technique in Free Mesh Method. The present paper shows the formulation of adaptive-FMM in elasto-plastic analysis to investigate the validity of the present method in 2-Dimensional and 3-Dimensional analysis. The adaptive remeshing technique is based on h-approach, and compared to conventional FEM and FMM numerical results for largely deformed shear problem. The present paper also describes the 3-Dimensional Delaunay method used in making local mesh geometry around the central node.

View full abstract

We consider the transient thermal singular stress problem of multiple surface cracking in glassfiber reinforced plastics due to a thermal shock at low temperature. The layered composite is made of a layer bonded between two cracked layers of different physical properties, and it is suddenly cooled on the surfaces. The surface layers contain parallel arrays of the embedded or edge cracks perpendicular to the boundaries. The thermal and elastic properties of the material are dependent on the temperature. Finite element calculations are carried out, and the transient thermal stress intensity factors are shown graphically.

View full abstract

This paper is concerned with the theoretical treatment of transient problem of piezothemoelasticity involving a cylindrical panel of crystal class mm2 due to nonuniform heat supply in the circumferential direction. We obtain the exact solutions for the two-dimensional temperature change in a transient state and the transient piezothermoelasticity of a simple supported cylindrical panel under the state of plane strain. As an example, numerical calculations are carried out for a cadmium selenide solid, and the piezoelectric effects and the effects of the electric surface charge on the thermal displacements and thermal stresses are examined precisely.

View full abstract

In this study, generalized stress intensity factors K_{I, λ1}, K_{II, λ2}, and K_{III, λ4} are calculated for a V-shaped notched round bar under bending using the singular integral equation of the body force method. The body force method is used to formulate the problem as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the unknown functions are the densities of body forces distributed in an infinite body. In order to analyze the problem accurately, the unknown functions are expressed as piecewise smooth functions using two types of fundamental densities and power series, where the fundamental densities are chosen to represent the symmetric stress singularity of 1/γ^1-λ₁ and the skew-symmetric stress singularity of 1/γ^1-λ₂, and 1/γ^1-λ₄. Then, generalized stress intensity factors at the notch tip are systematically calculated for various shapes of V-shaped notches. The accuracy of Benthem-Koiter's formula proposed for a circumferential crack is also examined through the comparison with the present analysis.

View full abstract

The Neutron diffraction technique was applied for the internal stress measurements of a composite material consisted of chromium alloy and titanium nitride manufactured by the powder metallurgy. The material has been developed for the valve seat insert of diesel engines in automobiles, because material has high wear-resistance and heat-resistance. In this study, the influence of the titanium nitride on the stresses in each phase was investigated. The Fe-Cr 200 diffraction peak occurs at 2θ=93.4 deg. and the TiN 311 diffraction peak at 2θ=109.5 deg are available. Neutron differaction data obtained from both phases were compared to the Micromechanics model based on Eshelby's approach and the Mori-Tanaka theorem. It was found that experimental phase stress agrees well with the theoretical estimation. It has been shown that neutron diffraction method is suitable to determine the residual stress of composite materials.

View full abstract

The purpose of this study is to evaluate the optimum forming condition which is related to improvement of strength reliability in recycling FRTP by the hybrid method involving experiment and simulation. The results are shown in the following. (1) In the PEEK material, by the observation results of the short shot samples (SSS), the reinforced fibers are randomly arranged by the generation of the vortex in melted resin flow, for this reason the anisotropy in the PEEK is little. On the other hand, in the MXD6 material, the tip of flow track in SSS shows the sharpened shape, and the fibers are arranged to one direction. Therefore, the strong anisotropy is found in MXD6 material. (2) X-ray reflection quantity of the PEEK material that has stable property for recycling don't change after recycling. In contrast, reflection quantity of the MXD6 material that shows the strength degradation after recyclmg, increases by conducting the recycling. (3) Since the melt viscosity of the PEEK material has been stabilized, the vortex flow occurs in metal mold, and the uniform three -layer structure is formed. In the meantime, the flow is biased to one direction in FRTP of which temperature dependence of melt viscosity is large like the MXD6 material. The stability of the melt viscosity of plastics on injection molding process is necessary in order to produce good FRTP for recycling.

View full abstract

The long fiber reinforced thermoplastic molding has better some mechanical properties than the short fiber reinforced thermoplastic molding. Recently, a new molding process has been developed to be appropriate for the long fiber reinforced thermoplastic pellets and the fiber length in the molding is longer than conventional injection molding one. But in the new process molding, the fiber dispersion, that is a filamentization, is not better than in the conventional injection molding. In this study, we noticed the fiber filamentization in the molding and investigated the relationship between the fiber filamentization and some mechanical properties. The fiber length in the molding decreases in the case of well impregnation. In the case of well impregnation, in spite of short fiber length, tensile and bending strength increased. But Izot impact value decreased. Therefore we confirmed the mechanical properties of molding are greatly influenced by the fiber filamentization.

View full abstract

The present study employs an electric voltage change method for the identifications of location and size of embedded delamination cracks of CFRP plates. Measurements of electric voltage change at multiple points are robust against electric resistance change of electrodes, and the method is usually called four-probe method for high precision measurements of electric resistance change. However, our previous analysis showed the method is less sensitive than the method that uses change of electric resistance between the electrodes. In the present study, high precise measurement system of electric voltage change is developed, and the electric voltage measurement method is adopted for identification of embedded delamination location and size. As a result, the electric voltage change method is shown to be useful for the identifications of embedded delamination cracks of CFRP plates.

View full abstract

TiN films were deposited on pure titanium specimens by reactive RF magnetron sputtering and gas nitriding methods. Pin-on-disk type wear tests were carried out to evaluate the effect of interfacial strength on the wear resistance of TiN films. The results showed that the wear property was improved remarkably by both methods, but the effect quickly disappeared after a certain number of rotation cycles. Optical observation of wear scars during wear tests showed that delamination of a small part of the film occurred and the area extended within a small increase in rotation cycles. When a coated specimen with an interfacial crack receives shear load by the friction of moving pin, the interfacial fracture toughness, G_C1/2, is calculated by the following equation : G_C1/2= (μ-μ₁₂)² P² /8 E₁(B₁- h_d){R² - (R-h_d)²} where P is the normal load of the pin at delamination, R is radius of curvature of pin, B₁ and E₁ are thickness and elastic constant of the film, μ is the friction coefficient between pin and film, μ₁₂ is that between partially delaminated film and substrate, and h is the depth of the wear scar. The G_C1/2 decreased with increase in the number of rotation cycles, which indicated the degradation of the interfacial fracture toughness caused by damage accumulation during the wear test.

View full abstract

The change of morphology and the tensile strength properties in various environment temperature (-40∼50°C) of PP by injection-modeled speed were determined. The results on the increase in the injection-modeled speed are following as (1) The decrease in the thickness of the skin and intermediate layer, however, the increase in the core layer. (2) The average hardness decreased on the speciment section, and the ductile showed a enlarge trend. It was the same as the result of dynamic Visco elasticity. (3) The change of the crystallinity was not obviously on the FT-IR, but the crystallinity increased by the density measurement. (4) The orientation of the core layer was a little change, however, it showed a lot of change on the intermediate layer. (5) The tensile strength decreased, but the ductile property showed increased at the various temperatures. Therefore, the crack origin of the various specimens on the tensile conditions occurred on the intermediate layer with high hardness and orientation. The low ductile property specimen due to a low injection-modeled speed will form the asymmetry inner multi-structure and the difference mechanical property as well as the distortion on the intermediate and core layers.

View full abstract

Fatigue tests in room air and in 3%NaCl solution have been conducted on a duplex stainless steel, SUS329J4L, in order to clarify the influence of volume fraction of ferrite and austenite phases on crack initiation and early crack growth. Three materials with different volume fractions were prepared with solution treatment at 1050°C, 1150°C and 1250°C, resulting in the volume fractions of austenite phase of 50%, 28% and 12%, respectively. The crack initiation sites in three materials were predominantly within austenite phase in both environments. The fluctuation of crack growth rates was found in the microstructurally small crack region for three materials and the crack growth rates decreased at phase boundaries. This behavior was more remarkable in the material solution treated at 1050°C, because small cracks encountered frequently with phase boundaries. Early crack growth immediately after the initiation was enhanced by 3%NaCl solution.

View full abstract

The influence of carbon content and forging ratio on fatigue strength and fatigue crack propagation properties has been studied in 0.8∼2.5 mass%C forged materials with 1.6∼6.1 forging ratio for the purpose of improving the crack and wear resistance as steel rolling mill roll. The main experimental results are shown as follows ; (1) Fatigue limit decreases as carbon content, and be affected by forging ratio. (2) Paris-Erdogan equation da/dN=C(ΔK_I)^m holds good, and there is a constant relation of C=13.2×10^-3/32.4^m. (3) Crack propagation rate depends on carbon content and forging ratio when the forging ratio is less than 3, and adequate volume and anisotropic carbide restrain crack propagation. (4) Crack propagation rate shows similar value with constant m≒4 when the forging ratio is larger than 3. (5) Fatigue fracture toughness K_Ifc Shows the highest value at 1.91%C material.

View full abstract

Fatigue tests were conducted on CFRP angle ply laminates with three-layered stacking sequence, which were damaged beforehand by means of a lateral impact using a free fall rod. Fatigue damage propagation process after the lateral impact consists of the extension of surface matrix crack inter-laminar delamination and damages at the edge of specimen. From a series of fatigue tests, it was found that there exists two extension mechanisms in surface matrix crack propagation. One is extension rates decreasing type with crack propagation, the other is almost constant rates type. In the former, it seems that the decrease in crack extension rates is due to the shielding effects, since small deflections in crack growth were observed on the specimen surface. In addition, from the SEM observation of fracture surfaces, it is shown that the out-of-order in fiber alignment and the fiber breakage were remarkable in the former, while in the latter, fibers were straightforward and few breakage was found. Based on the results, it is suggested that the shielding effects induced by the crack deflection and by the out-of-order in fiber alignment result in the decrease in extension rates of matrix crack.

View full abstract

The smooth specimen was machined from 99% purity copper and heat-treated at 940°C for 9 hours in a vacuum after straining of 3%. The resultant grain size was about 320 μm in average. The push-pull low cycle fatigue tests were performed and the height of step developed at grain boundary during cyclic loading was measured using Atomic Force Microscope (AFM) . According to the AFM observations, steps were generated at grain boundaries with the inclined angles ranged from 60° to 80° with respect to the loading axis at first tensile loading, and the step heights grew as cyclic straining process progresses. Its growth rate dH/dN reduced with increase in number of straining cycles. The variation in step height during one strain cycle increased with increase in number of loading cycles. The development of step height with progress in the cyclic loading process was plotted against cumulative effective plastic strain range ΣΔε_pe, which might dominate fatigue damage. It was found that the growth behavior of grain boundary-step was successfully assessed in terms of ΣΔε_pe. The step height at crack initiation H_c decreased with increase in stress level, showing that crack initiation seems to be caused by stress concentrated at the root of grain boundary step.

View full abstract

To examine experimentally the effect of the restraining condition on the reliability of foil, strain controlled tension compression fatigue test and microscopic observation were made using metal foil embedded in an epoxy resin. The foil was 10 μm thick, 1 mm, 2 mm, 4 mm, 8 mm, 100 mm long and silicon oil was applied on it to change the restraining condition. As a result, (1) Micro buckling occurred in a foil under repeated load and crack initiated at the area were observed. (2) When silicon oil was applied, the energy spent during foil deformation decreased, and the fatigue life fell off. (3) When a restraining condition changed the fatigue life changed 3 times to 10 times. (4) Because of the temperature dependent characteristics of a resin or an elastomer, it is conceivable that the temperature change of flexible printed circuit exerts a large influence on the fatigue life.

View full abstract

In this study, plastic-strain-controlled low cycle fatigue tests were carried out on austempered spheroidal graphite cast iron (ADI) The crack propagation behavior from the crack initiation to the fracture was investigated on the surface of specimen and their fracture section. As a result, fatigue life in ADI was shorter than that in pearlitic spheroidal graphite cast iron (PDI) which had smaller fracture ductility. This result could also be rationally explained by considering three controlling factors for low cycle fatigue life. That is, decrease of fatigue life in ADI was caused by acceleration of relative crack growth rate in ADI. It was found that the cause of acceleration was embrittlement at the crack tip accompanied with fatigue.

View full abstract

Wave motion in a layered plate, including loading regions, were fomulized using the semi-analytical finite element method (strip element method) and calculated at every frequency step, which resulted in the simulations of Lamb wave exitated by angled beam transducers in the time domain. These calculations required less computational time and memory than the conventional methods such as FEM and BEM. The numerical results were visualized and the snapshots of Lamb wave propagation revealed the some phenomena regarding S 0 mode exitation and stress distributions of S 0 and A 0 mode. The pure S 0 mode cannot be exited by angle beam transducers due to its long wavelength in a low frequency thickness range. The normal stress in the propagation direction in S 0 and A 0 mode and shear stress in S 0 mode abruptly varied with the position in the thickness direction in a crossply plate.

View full abstract

Strain component due to grain-boundary sliding was attempted to separate from creep and creep- fatigue deformation in order to evaluate creep damage as the function of the accumulation of grain-boundary sliding. It was supposed that inelastic strain is composed of 4 components i. e.ε_gb, ε_pl, ε_cr andε_dp, where ε_gb is the strain due to grain-boundary sliding, ε_pl is plastic strain, ε_cr is creep strain and ε_dp is some inelastic strain categorized between ε_pl and ε_cr. Considering the inequality of each strain component and the inner stresses due to inharmonious values of components, the equations were devised by trial and error to simulate the creep and creep-fatigue behavior. The result of simulation with the evaluation of creep damage by ε_gb shows good agreement with the result of experiment in creep deformation, creep-fatigue deformation and creep rupture behavior, but the agreement with creep-fatigue failure behavior of experiment is not enough. This may suggest that creep damage is not only the function of sliding of grain-boundary but also the function of normal stress.

View full abstract

Modern engineering has contributed greatly to the welfare of human beings and the development of society. The steam engine and electric motor released humans from severe physical labor such as work in a coal mine. Electric home appliances and utensils also released women from continuous physical labor in their homes. Now, the computer is reducing brainworks and will take the place of more sophisticated occupations such as teachers, physicians and lawyers in the near future. Although the development due to engineering appears to human beings happier lives, it can be said that it has also deprived them of the functions human beings. It was pointed out that the impact which engineers have given to human society was huge in relation between "Materials civilization" and "destruction of Mental" by engineering since industrial revolution. Ever since the Industrial Revolution, the impact which engineers have brought about to human society has been great in terms of the relationship between "material civilization" and the "loss of human function" through engineering. In other words, power became the complete alternative to the activity of muscles as a human function, as much as labor and family ties are collapsed by home electrical appliances and industrial society system, and home electrical appliances and the industrialized system of society destroyed the structure of labor and family ties. Computers and information may deprive a man of abilities such as thought, impression, and creativity. These changes may not be concluded as being contrary to engineering ethics. But if engineering is to be defined as "the application of the principles of nature to contribute to human welfare", we should advance research of the alternatives to and the losses of human functions an well as increasing the production of materials and environmental issues.

View full abstract