This article focuses on the behaviour of structures which are subjected to dynamic loads (impact, blast, pulse) which produce large inelastic strains and material failure. Particular attention is given to the elementary and strain energy density failure criteria and some recent experimental results on the dynamic inelastic failure of structural members.

抄録全体を表示

An uni-axial shear elastic-plastic-viscoplastic constitutive equation has been derived from the generalized constitutive equation. The constitutive equation is in which the understress in introduced to the shear strain and the overstress is employed in the shear viscoplastic strain rate. Using the constitutive equation, an analysis is done on the one-dimensional uni-axial shear elastic-plastic-viscoplastic stress wave propagation. And the equations describing the wave propagation speed and the relation of any physical quantities are derived. The derived equation for describing the shear wave propagation speed expresses the experimental results qualitatively. Also, from the developped theory of the shear elastic-plastic-viscoplastic wave propagation, the theories of a shear elastic-plastic, elastic-viscoplastic and elastic wave propagation are derived. The wave propagation speed of the elastic-viscoplastic theory can't express that of the experimental results at all except the precursor.

抄録全体を表示

This paper is concerned with the inverse problem of impact force, which is to estimate impact force acting on bodies from measurement of their impact responses. As the authors have shown previously, both numerical Laplace transformation and its inversion are required to solve the inverse problem. Since the inverse analysis is based on experimental data and, in addition, the Laplace inversion is typical of ill-posed problems, straightforward computation tends to provide unacceptable estimate of impact force. Therefore, regularization of the Laplace inversion is necessary to obtain a good estimate of the impact force. In this paper, Tikhonov regularization in applied to the numerical Laplace inversion by using FFT. Both numerical simulation and experimental verification show that the Tikhonov regularization is effective for improving estimation accuracy of the impact force. In addition, to appropriately determine the regularization parameter, Hansen's L-curve method is found to be effective.

抄録全体を表示

In the process of optimization, expensive finite-element method (FEM) software in often applied to solve engineering design problems. To obtain the optimal solution requires an extreme numbers of iterations between the analysis software and optimization program. The work is time-consuming due to the amount of computer time required. Therefore, instead of using the FEM analysis, an approximate method using sensitivity analysis has been proposed to solve this problem. However, it is difficult to obtain an explicit form of sensitivity for the nonlinear dynamic system. While the difference method is usually used for the sensitivity analysis, it is not the most efficient method to greatly reduce the calculation. In this paper, the authors propose an efficient approximation method to simulate the objective function using the holographic neural network (HNN). This neural network exhibits a large learning capability and dynamic features of memory, of a two-degree-of-freedom nonlinear dynamic system. The optimization approach is simplified and the tremendous calculation expense is decreased, because the objective function in design areas can be approximately calculated using the trained neural network.

抄録全体を表示

Conical roof shells which have a joint between a conical roof and an attached cylinder are utilized as oil storage tanks and some containment vessels. It is known that conical roof shells and torispherical shells subjected to static internal pressure buckle with circumferential waves caused by bifurcation buckling. We reported the dynamic analysis for bifurcation bucking of a torispherical shell under dynamic internal pressure under accident conditions. For torispherical shells, the dynamic pressure of bifurcation buckling was lower than the static pressure. It seems that conical roof shells buckle more easily at the joint than torispherical shells. A short time but overpressure loading due to, for example an explosion, may cause bifurcation buckling of the shell. For disign oil storage tanks, the ability of the tank to withstand high bifurcation pressure is not necessarily safe for explosion accident. Therefore, it is important to obtain the bifurcation buckling load from the dynamic analysis in the design of conical roof shells. In this paper, we calculate the bifurcation buckling pressure for dynamic pressure under accident conditions, that is, step pressure loading, ramp pressure loadings and pulse pressure loadings.

抄録全体を表示

In this paper, Laplace transformed expressions for the torque and the bending moment in a curved beam under impact out-of-plane load were shown. Applying them to a closely coiled helical spring and using the numerical inverse transformation with FFT. the torque and the bending moment in the spring were examined for two types of boundary condition ; the first case was that impact force was applied to the end of the spring wire, and the second case was that impact force was applied on the center axis of the spring. As a result, the followings were found. The Torque induced in the spring wire propagates along its axis macroscopically with the velocity of surge wave, although it is preceded by very small one propagating with the velocity of shear wave. And large bending moment comparable with torque occurs near the end of spring just after the impact in the case of center impact, while bending moment can not occur statically.

抄録全体を表示

A method of measuring the dynamic stress concentration factor α_Dmax in a fillet has not yet established. The reflection and transmission of stress wave during the propagation through a fillet result in complex stress states. We propose a new method for analyzing the dynamic stress concentration factor α_Dmax in a fillet utilizing the stress concentration factor α_s and the reflection coefficient A obtained by a strain gauge on the incident strip plate. In this experiment, a square wave (a stress wave with a plateau of constant stress for long duration) is used. A strain gauge measures the reflection coefficient A. The factor α_Dmax in the fillet is analyzed using a dynamic photoelastic method. It is confirmed that α_Dmax is approximated by the following equation : α_exDmax=(1+A)α_s As a result, the dynamic stress concentration factor is obtained experimentally using the static stress concentration factor and the reflection coefficient.

抄録全体を表示

A numerical method to analyze three-dimensional stress waves in a laminated plate is presented, when an impulsive load is applied to the plate. The finite difference method based on integration along the bicharacteristics is used for numerical analysis of three-dimensional stress waves in the plate. Numerical results show the effects of material properties of laminated plates and the impulsive loading condition on propagation of the stress waves. Stress distributions at the interfaces are affected by reflected and transmitted waves significantly. This method has a wide application to the dynamic problems of laminated media.

抄録全体を表示

Longitudinal impact tests on a rectangular diallyl phthalate (DAP) polymer strip were performed to make clear the attenuation properties of compressive strain waves. The attenuation of the peak value of the strain pulse with travelling distance was investigated in conjunction with the duration of the pulse. Material properties, or constitutive equation necessary for the analysis of the impact response were determined by the complex compliances obtained from the Fourier components of strain waves. A method, or the offset method for correcting strain pulse profiles was newly developed. This method eliminates the influence of noise in strain signals on the amplitude spectra, and contributes to the improvement of the accuracy of determining the complex compliances. The attenuation of the peak value of the strain pulse with travelling distance was theoretically predicted. The discrepancy between the theoretical predictions and the experimental values was within 6%.

抄録全体を表示

This paper describes the analyses of impact fractures of laminated glass with interlayered polyvinyl butyral (PVB) and bilayer laminated glass with PVB on one side by using the discrete element method (DEM). A laminated and a bilayer laminated glass beams with both ends fixed are analyzed when a cylindrical rigid body impacts to the center of beams with a certain initial velocity. For the bilayer laminated glass beams, two analytical models such as bilayer type that impact surface is glass side and reverse bilayer type impact surface is PVB side are selected. The DEM is applied to simulate the impact fracture behaviors until penetration of three beams. From the numerical analyses it is obvious that the order of the maximal impact forces is bilayer type, laminated type and reverse bilayer type, and penetration energies of laminated type and bilayer type are almost equal. From above reasons, bilayer laminated glass is in safety than laminated glass as front glass of automobile.

抄録全体を表示

This paper describes alternative measuring and estimating methods for the current drop weight impact test used to determine the impact strength of fibre reinforced plastics. The measuring method is characterized by measurement of the real load responses at impact applied points and the displacement responses by the camera without contact. The estimating methods proposed here are the determination by the dynamic load and displacement relationship based on the dynamic load and displacement relationship based on the precise measurement and the estimating by the frequency response function converted from the applied load variations and the strain responses in the specimens. As a result. strength of FRP against impulsive loading and the existence of some damage can be determined with better accuracy by utilizing the proposed measuring and estimating methods.

抄録全体を表示

In the present paper, dynamic inter-laminar fracture toughness are estimated for carbon fiber reinforced plastics (CFRP). In the experiments, split Hopkinson's bar test was applied to dynamic end notched flexure (ENF) test. The dynamic deformation of the specimen is approximated by beam theory with Laplace transform. The mode II fracture toughness of unidirectional CFRP was estimated by the analyzed deflection of the specimen employing the scheme of J-integral with the measured impulsive load and reactions at the supported points. Through some numerical calculations, validity of the J-integral for the dynamic ENF test is confirmed. In addition, as a experimental result, dynamic inter-laminar fracture toughness of CF/EPOXY unidirectional specimens are estimated and it indicates dependency on deflection rate.

抄録全体を表示

Honeycomb structure is used as the shock absorbent to protect precision machines during transport. The purpose of this study is to establish the relation between the energy absorption ability and the honeycomb parameters such as cell size, cell wall thickness and material properties. The authors carried out an series of FEM analyses to establish the above relation under quasi-static condition, and further, they carried out a series of experiments about impact test to clarify the dynamic effect. As the results of the experiments, it was shown that the collapsing stress under dynamic condition is increased due to the pressure of the air inside the compressed honeycomb core. The proposed expression, which was gained by combining the results of the FEM analyses and the experiments, agreed well with experimental results under dynamic condition.

抄録全体を表示

In order to investigate the effect of loading rate on the strength and the absorbed energy of paper honeycomb cores, a series of compression tests were carried out at quasi-static and dynamic rates. The specimens used are polypropylene (PP) and polyester (PET) thermoplastic honeycomb cores, usually called paper honey comb cores. It was found that the peak stress and average crush stress increased with the increase of loading rate, especially, it was remarkable in the results of PP-core. The absorbed energy obtained from dynamic tests was also greater than that obtained at quasi-static rates. The polyvinyl chloride (PVC) long tube was ascertained to be quite useful for a device measuring stress waves in dynamic compression tests, if the manner of the wave propagation in the PVC tube such as the decreasing rate of the wave amplitude and the propagation velocity are obtained by wave propagation experiments beforehand.

抄録全体を表示

A new test method using diametral impacts of center-notched disk specimens is investigated numerically for measuring the dynamic fracture toughness under pure mode I, pure mode II and mixed-mode loadings. Changing the inclination angle θ of the center-notch relative to the line of loading, the impact fracture tests can be performed under the conditions in the arbitrary ratios of mode I to mode II loadings. Especially, pure mode I and pure mode II tests are achieved for (θ=0°) and θ≈23°(α/R=0.5) respectively, where 2α is the center notch length and R radius of the disk specimen. The dynamic energy release rates under the mdxed-mode impacts are easily evaluated from the mode I and II components of stress intensity factors, which are computed from the convolution integrals of the step-response functions. The step-response functions have been obtained by the finite element analyses for the specimen. Using this method. we can evaluate the dynamic energy release rates under the mixed-mode loading precisely.

抄録全体を表示

This paper is concerned with a new measuring method for the impact tensile strength of concretes. The method of impact tensile testing is based on the propagation and concentration of both tensile stress waves reflected from the ends of a specimen and a striking bar. The impact tensile tests of concrete are performed by making use of the Hopkinson-bar technique. The impact tensile strength and fracture behavior of concretes are discussed by the simple theory of stress wave propagation in a bar. The statistical analysis of the experimental data obtained in a series of the impact tensile strength test is presented and compared with that of the static tensile and bending tests of concretes. The impact tensile strength of the concrete is significantly influenced by loading rate, and it is found to be approximately twice the static value.

抄録全体を表示

Impact compression damage evolution in unidirectional glass fiber reinforced polymer (GFRP) composites is investigated by using the improved SHPB apparatus, where the impact loading can be stopped at any moment in the impact process so that the specimen can be recovered at various levels of loading. The effects of test temperatures and strain rates are studied experimentally. The scanning electron micrographs of the recovered specimens have revealed that the compressive failure of unidirectional GFRP composites is caused by the microbuckling of the fibers in both impact and static loadings. The compressive strength is related to the nonlinear in-plane shear property of unidirectional composites, and the theoretical prediction shows good agreement with the experimental result.

抄録全体を表示

The impact shear tests on a cyanoacrylate based adhesive (hereafter referred to as the CA adhesive) are conducted by means of a modified split Hopkinson bar using a pin-and-collar specimen. Two adherend materials (or bearing steel and 7075-T 6 Al alloy) are used in the tests. The impact shear strength of the CA adhesive bonds at loading rates of the order of 10⁶ MPa/s is determined from the peak value of the applied shear stress history in the bond-line. Comparative shear tests at low loading rates are carried out on the same design of specimen in an Instron testing machine. The effects of loading rate, thickness of adhesive layer and adherend materials on the shear strength of the CA adhesive bonds are examined. The test results indicate that the shear strength of the CA adhesive bonds increases significantly with increasing loading rate, and is much affected by both the thickness of adhesive layer and the adherend materials.

抄録全体を表示

Impact behavior of axisymmetric plastic buckling of circular tube is investigated numerically and experimentally. In order estimate performance for impact energy absorber, numerical parametric studies by FEM analyses are carried out. Tube impact experiments using aluminum circular tube have been performed for impact velocity range of 30∼70 m/s and are compared with numerical results. Good agreements are exhibited between numerical and experimental results. During the formation of one buckle, the axial load-time history shows two load peaks ; each of them corresponds to collision of outer surfaces and collision of inner sarfaces. The first peak load increases with impact velocity and presents very high value for high impact velocity, however it decays with wave propagation and after some distance propagation, it exhibits no more remarkable high amplitude and tends to approach to constant value. The mean axial crumpling load during collapsing process after the second peak load is approximately 10% higher than the static one. The axial length of one buckle shows a tendency to increase linearly with the ratio of thickness to radius of the tube. It is also showed that the crumpling mode transition from progressive buckling mode to dynamic plastic buckling mode is affected by stress-strain curve. The higher the work hardening modulus of the tube material, the more probably the tube is wrinkled over the entire length.

抄録全体を表示

An unsteady-wave-sensing-system (UWSS) is developed for evaluating the wave propagation characteristics of polymethyl methacrylate (PMMA) for loading-reloading-unloading waves using plate-impact experiments and three PVDF gauges. By applying the UWSS, stress, particle-velocity, strain and two kinds of phase velocities at one location in the PMMA are determined as functions of time. The phase velocities U^σ associated with the stress profiles are generally different from the other phase velocities U^υ associated with the particle-velocity profiles. From loading to reloading are transitions very near from the Hugoniot in the stress-strain plane, but from reloading to unloading are transitions upward off the Hugoniot. In the region of our experimental stress, PMMA does not behave as liquid and the Hugoniot of PMMA is not effective for the loading-history-characteristics.

抄録全体を表示

Dynamic compressive behaviour of bovine trabecular bone was investigated. Compression tests on cylindrical specimens of bovine distal femurs were carried out using the split-Hopkinson pressurebar (SHPB) technique at strain rates ranging from 100 to 700 s^-1. Quasi-static compression tests were also performed using an Instron-type materials testing machine at strain rates of 2×10^-4 and 2×10^-3 s^-1. Stiffness and ultimate strength were greater at greater apparent density and at higher strain rate. Both stress relaxation and creep functions were determined based on stress-time and strain-time relations obtained by the SHPB tests. Relaxation time and retardation time had no correlation with apparent density. The three-element standard linear solid model was then validated by these functions. The elastic spring stiffness of the model, E₁, had a strong positive correlation with apparent density, while the elastic spring stiffness, E₂, and the viscosity coefficient, η, showed less correlation with apparent density. No significant differences in the relaxation and retardation times, the elastic spring stiffnesses, E₁, E₂, and the viscosity coefficient, η, were observed between the specimens with and without marrow.

抄録全体を表示

In recent years, interlaminar-toughened laminates are developed in which resin rich layers are placed in interlaminar regions in order to enhance the interlaminar fracture toughness of CFRP laminates. In this paper, Young's modulus reduction due to transverse cracking in interlaminar-toughened CFRP cross-ply laminates are measured as a function of transverse crack density. Loading unloading tests are conducted at room temperature and 80°C to investigate temperature effect. Laminate configurations are cross-ply (0/A/90_m/A/0) where A denotes interlaminar resin layer and m=4.8 and 12. The experimental results are compared with the theoretical prediction based on the two-dimensional analysis considering the interlaminar resin layers and thermal residual stresses.

抄録全体を表示

It is well known that Aramid Fiber Reinforced Plastic (AFRP) is degraded by hot and wet environment. Environmental influence on tensile fracture mechanisms of [0/+45/-45/90°]_s AFRP was investigated using microscope and acoustic emission method. Specimens were immersed in pure water at 80 degrees centigrade for 320 days. Water absorption, accelerated by high temperature, reduced interfacial strength, degradation of resin and fiber, also causing occurrence of the edge delamination. Relation between fracture phenomena and the frequency distribution was investigated. On unidirectional reinforced material, fiber debonding around fibers was found, and occurred a peak at 150 kHz, from initial fracture to final fracture. But for the used material, peak effect of edge delamination at 90°/90°interlaminar of [0/+45/-45/90°]_s was observed at 60 kHz. It was possible to conclude that the variations of fracture mechanisms caused by water absorption were direct relation with the variation of fracture sound frequency distribution between virgin and immersed material.

抄録全体を表示

With the aim of studing the effect of glass fiber/matrix interface quality on the dynamics of microfractures in GFRP, we propose a new source characterization of dissipative elastic waves. We measured the out-of-plane displacement by the longitudinal wave (P-wave) by using a developed AE monitoring system, and computed it by the convolution integral of assumed fracture dynamics with the analytical transfer function of the medium (Green's function of the second kind), taking into account both the orientation dependence of velocity and attenuation of the P-wave. We also propose a new computer algorithm for estimatig the source location and fracture mode by using the arrival time and radiation pattern of the P-wave, respectively. The first report introduces the proposed AE source characterization algorithm and acoustic properties of a unidirectional GFRP. Macroscopic elastic properties of UD-GFRPs prepared by adding paraffin wax to the matrix are also reported.

抄録全体を表示

Based on the AE source characterization method proposed in the first report, we examined the dynamics of microfractures in unidireational GFRPs with different interfacial qualities. Three types of microfractures were revealed to occur by AE source characterization. AE event counts due to the Mode-I fiber breakage, Mode-I and-II interfacial fractures were observed at higher stresses in GFRP with poor interfacial quality (with wax in matrix) than in GFRP with good interface quality, but increased rapidly with an increase of stress. Dynamics of microfractures were found to change depending on the interface quality.

抄録全体を表示

A simplified method to approximately evaluate the stress intensity factor of an arbitrarily located circumferential crack in a cylinder subjected to axisymmetric loads was theoretically derived, based on the theory of cylindrical shell and compliance. Axisymmetric radial and bending loads on the edge of the cylinder are considered as axisymmetric loads, and the effects of the cylinder length and the crack position on the stress intensity factor can be evaluated by applying the method. The validity of the method was confirmed by comparing the stress intensity factor by the method with those derived by FEM, for the case where the bending loads of the same value are applied on both ends. From the results, it was shown that the stress intensity factor increases as the cylinder length decreases, and as the crack gets near the cylinder edge. These results warn us to pay attention on the effects of cylinder length and crack location, when we evaluate the stress intensity factor of cylinders with circumferential crack, under axisymmetric bending.

抄録全体を表示

The residual stresses in the subsurface layer of two contact rotating cylinders were numerically analyzed by using the elastic-plastic constitutive equation which consists of the mixture of Ziegler's Kinematic hardening theory and Prandl-Reuss elastic-plastic constitutive equation. Then, the experiment of contact rotating of two cylinders was made under the same conditions as the calculation. As a result, the residual stress (σ_xx)_r in the subsurface layer obtained by the rotating experiment and the X-ray analysis of residual stress was found to be close to the value calculated with the ratio of kinematic hardening λ=0.68, which was obtained in the uniaxial tension and compression test.

抄録全体を表示

In the ball bonding process in LSI packaging, complex non steady-state metal flow occurs in the wire ball during the process, and solid-phase bonding occurs between the wire ball and terminal pad. Optimum process design of ball bonding requires detailed analyses of the metal flow characteristics of the wire ball used in the process. The authors proposed the physical simulation method to analyze the ball bonding process. The physical ball bonding simulation and quantitative analyses, using the enlarged plane-strain models of the capillary tool made of SKD-61 steel and the wire ball and terminal pad of 1050 aluminum, were carried out successfully. Then, sequential variation of the outer profile of a wire ball and of the flow velocities, strain rates and strain in a wire ball during the process could be obtained. The simulation method is available to aid the optimum design of the process conditions of ball bonding, such as capillary tool configuration, punch speed, process temperature and terminal pad thickness, to achieve ball bonding with sufficient bonding strength, high reliability and narrow terminal pad pitch spacing.

抄録全体を表示

The fatigue properties of magnesium alloy casting, AZ91D, and the same material with HAE anodized, were investigated with a special view of mesoscopic fracture analysis. The main results obtained are as follows : (1) The fatigue strength of magnesium alloy casting was improved by HAE anodizing. Futhermore, the fatigue strength ratio, that is strength/density, of magnesium alloy casting was higher than that of aluminum alloy casting. (2) Through fractography using SEM, it was found that the crack initiated at casting defect under the film in anodized material. (3) The mesoscopic factors of fracture origin, consisted of defects and matrix microstructure, could be quantitatively related to the fracture mechanism. It could be concluded that the improvement in the fatigue strength of anodized material would be caused by the retardation of growth of "meso-crack"due to which had been formed from a casting defect under film.

抄録全体を表示

The influence of meso-factor on fracture mechanism of intermetallic compound Ti34wt. %Al was examined with the in-situ observation of fatigue mechanism by scanning electron microscope (SEM) -servo testing. Especially, the concept of High Performance Design System applying advanced structure material (TiAl alloy) was discussed by the mesoscopic fracture analysis. The main results obtain were as follows : (1) Ti34wt. %Al exhitbits a superior fatigue property to Ti36wt. %Al, Hastelloy-X and a close fatigue propagating charactaristic to CMSX-4, IN783LC. (2) Lamellar structure influence on the fatigue prorety of Ti34wt. %Al. That is, after crack initiating at the casting defect and γ phase, lamellar structure arrest mesocrack growth. In fatigue crack growth process, fatigue crack growth zigzags and deviates, deponding on lamellar structure. And lamellar structure arrest fatigue crack growth. (3) High Performance Design System applying intermetallic compound TiAl alloy is realized by understanding the effect of lamellar structure on crack inisiation and propagation, and constructing fracture controlled method constituted material design, structure design and preventive maintenance from a whole.

抄録全体を表示

The stress corrosion cracking, SCC, resistance of recrystallized Al-Zn-Mg-Cu system alloys having various grain size was discussed on the basis of SCC tests of the relationship between SCC failure time and average grain size, d_s, in 3.5% NaCl solution, fractography, then microscopic- and X-ray observations of the recrystallized structure formation. The main results obtained in this work are as follows : (1) SCC resistance in the present 7475 aluminum alloy depended on the behavior of the grain growth. Time to SCC failure reached a peak at d_s=24.1 μm, when d_s> or d_s<24.1 μm ; these times were shorter than that of d_s=24.1 μm. (2) SCC fracture pattern in this alloy was intergranular fracture by hydrogen embrittlement. (3) The behavior of recrystallization and grain growth in this alloy became clear from observations of the texture structure formation by X-ray, and the secondary recrystallized texture structure formation of the <112> direction was peculiar to an aluminum alloy start at d_s=24.1 μm. Therefore, SCC resistance in this alloy has been found to be related to the secondary recrystallization behavior.

抄録全体を表示

An impregnated metal-bonded diamond-tool was investigated to measure the retention strength of tungsten-coated grains and metal binder matrix by means of the grain scratched method. The shape and fracture model of diamond were observed using SEM. The results were as follows, : Tungsten-coated diamond improved was dislodged in wettability and retention strength of the metal binder matrix interface. Non-coated diamond was dislodged from the matrix after being scratched by the shear force, but tungsten-coated diamond remained adhered to the matrix while cleavage fracture occurred in the diamond garin. The interface of diamond- and tungsten-coated film was constructed from a non-stoichiometric compound and tungsten carbide which caused the strong chemical bonding. In particular, tungsten-coated diamond showed superior grinding ability of steel rebar in reinforced concrete.

抄録全体を表示