[in Japanese]

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[in Japanese]

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[in Japanese]

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Fracture surface marks of the both-end-closed ones of small circles, various ellipses and the one-end-opened ones of parabolas and hyperbolas are investigated by both analytical and experimental methods especially in single edge notched plastic sheet specimens of DCB (Double Cantilever Beam), GDCB (Grooved Double Cantilever Beam) and SEM (single Edge Notched) in tension. The velocity of a main crack presumably increases rapidly to its maximum value and then decreases gradually with some oscillation as it propagates. The dynamic stress-intensity factor and the dynamic strain-energy release rate are calculated and both of them change with oscillation as the main crack proceeds. These values seem to affect the appearances of fracture surface marks in their shapes and sizes, and an e/C₀₂ value (a relative interference appearing distance) and a d/C₀₂ value (a relative critical distance) of the marks. Experimental observations give good agreement with the analytical relations. Both normal and abnormal fracture surface marks are well expressed by the two dimensional equation of marks.

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The fracture strength was varied by changing an inter-grip distance (which we call a gage length here) of a sharply notched tensile sheet specimen of unsaturated polyester resin, where the specimen width, thickness, rack length and loading method wee kept constant. the loading method is such that the main load works on a line parallel to the axis of loading and does not cross the crack length. We call this an outside loading. The number, density, area ratio of fracture surface markings vary with the fracture strength of the material. The total number of markings increases with the fracture strength. The density and area ratio of markings increase at each different rate with respect to fracture strength, and incipient bifurcation such as hangnails, appears at a certain value of the density or area ratio. These results are discussed with the analytical relations of the fracture strength, the dynamic stress-intensity factor and the dynamic strain-energy-release rate by employing the reported relations. The fracture surface markings are examined by the two-dimensional equation of fracture surface markings, and the analytical area ratio of the markings is also calculated.

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The equation of surface markings approximated in two dimensions in the previous report is discussed on its variation of the ratio of the limiting velocity of a secondary crack to the velocity of a primary crack, β', to extend the applicability of the equation over the general cases. The β' value is assumed to change along with the primary crack propagation as well as in a small interference distance of a marking. The latter is the special case for producing the abnormal fracture surface markings having their especially larger or smaller cusps. we have obtained the variations of the dynamic stress-intensity factor and the dynamic strain-energy release rate with respect to the primary crack propagation distance. These variations most likely control the e/C₀₂ and d/C₀₂ values and their fluctuations of the observed surface markings.

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The author reported the effect of laser hardening on the prevention of the fatigue fracture of cracked shafts of low carbon steel, in a previous paper. This treatment was found to be effective for comparatively small cracks. However, cracks remain open after laser hardening. In this investigation, the specimens were welded at the cracked portion using a CO₂ laser. The welding depth was 2.3mm, so small cracks were erased completely, but the deeper parts of large cracks were not welded. Rotary bending fatigue and tensile strengths of specimens with fairly large cracks (up to l=13 mm for rotary bending and 14 mm for tension) were found to be raised to those of virgin specimens by laser welding. And it was shown that laser welding is much more effective than laser hardening to prevent fracture.

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Experimental results are presented for the forming limit of in-plane stretching of brass, copper, and aluminum sheet alloys. Theoretical curves for limit strains based on the modified M-K (Marciniak and Kuczynski) analysis, where M-K analysis is applied to the post-instability (i.e., post-diffuse necking condition) straining, are used. The apparent inhomogeneity factor, estimated from the ratio of the minimum to maximum thickness of the sheet at the instability condition, is proposed to interpret the existence of an inhomogeneity factor at the instability condition. The use of best fit hardening laws for these materials, which are Voce-, Swift-, and Hollomon-law equations for brass, copper, and aluminum, respectively, shows a remarkable effect on calculating the instability strain. Good agreement between the calculated and measured limit strains suggests the importance of using the best fit hardening laws.

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To make a quantitative analysis of the effect of stress ratio on the fatigue properties for carburized steel, the fatigue properties and fatigue fracture mechanism were examined for 2 carburized steels. Carburizing, quenching and tempering were performed at one condition, and the fatigue strength was evaluated up to 10⁸ cycles under uniaxial loading of two stress ratios, R=-1 and 0, at room temperature in laboratory air. The threshold stress intensity factor when a mode I crack begins to grow was linearly related to (1-R)^γ for the two carburized steels, and by a similar relation, the fatigue life can be predicted in the long life region over about 10⁶. The lope on the Haigh diagram was discussed by fracture mechanics.

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To make a quantitative analysis of the defect size for high strength steels, fatigue properties and fatigue fracture mechanism were examined for 3 different low alloy steels tempered at several temperatures. Fatigue strength was evaluated up to about 10⁸ cycles under rotating bending at room temperature in dry air. Two types of S-N curves were found, the one has fatigue limit for medium strength steels fractured from the specimen surface, the other for higher strength steels has temporal fatigue limit because of the interior fracture in the long life region over about N_f=10⁷. Fatigue strength would be predicted by the liner relation between the threshold stress intensity factor and the hardness of the materials. It is suggested that the defect size to originate the fatigue crack would have important role for high strength steels up to about HV600.

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As a basic study for the establishment of an accuracy estimation method in the finite element method, this report deals with the problems of transverse bending of thin, flat plates. From numerical experiments for uniform mesh divisions, the following relation was deduced, ε∝(h/a)^k, k≥1, where ε is the error of the value by the finite element method relative to the exact value and h/a is the dimensionless mesh diameter. combining this relation with the results of the error analyses for local mesh refinement, an accuracy estimation method, which was based on the recursive simulation method, was presented. A computer program using this accuracy estimation method was developed and applied to nineteen problems of various shapes. The usefulness of this accuracy estimation method was illustrated by these application results.

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The influence of vacuum environments on near-threshold crack growth behavior in an annealed 60-40 brass have been studied by means of fracture mechanics and fractography. In vacuum, the crack growth rate was smaller than that in air and decreased with decreasing vacuum pressure. When the R ratio and ΔK level increased, the crack growth rate in vacuum approached that in air. The near-threshold crack growth behavior in vacuum was markedly influenced by a fracture roughness, which resulted from a crystalline fracture mode, in addition to a plastic induced crack closure.

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The corrosion fatigue crack growth rate of a high tensile strength steel HT55 has been measured in 1% NaCl solution at various stress cycle frequencies and stress ratios to elucidate the corrosion product-induced wedge effect and dominating mechanical parameters for crack growth. The wedge effect is most effective at R=0.1, whereas it is less effective in the order of R=-1 and R=0.5. At R=-3, however, the wedge effect disappears, and the growth rate in 1% NaCl solution is higher than that in air. At f=50Hz and R=0.1 and 0.5 in 1% NaCl solution, the load strain hysteresis loop traces different paths during loading and unloading periods, resulting from viscosity of the corrosive solution remaining within cracks, but the load sharing capacity of the viscosity is negligibly small. Regions I and II in the hysteresis loop must be taken into consideration to explain uniquely the corrosion fatigue crack growth characteristics under various conditions, and a contributory stress intensity factor range ΔK_cont is proposed as a difference between ΔK and ΔK_ret, deduced from the load range shared by regions I and II.

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Pulsating tensile fatigue tests were carried out, using the CT specimens cut out from a high tensile rolled steel in three different directions. The crack length in each directional specimen was measured by an optical microscope and N-l curves were approximated by quadric curves, and then the effects of stress ratio and plate thickness on anisotropy of fatigue crack propagation were examined. The fracture surface was observed by a scanning electron microscope. The main results obtained are as follow: (1) ΔK-dl/dN relations obtained from N-l curves approximatd by the quadric curves determined from each five points of data are comparatively reasonable. (2) Anisotropy of crack propagation slightly exists in this material and the resistance for fatigue crack propagation in the smallest in the specimen whose cracks propagate along the laminated structure. (3) The effects of stress ratio and plate thickness on the anisotropy are small.

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The effect of size on the growth rate of a surface crack has been investigated through rotating bending fatigue tests of 5 kinds of metals. In general, the relation dl/dN∝ΔK^m (ΔK: stress intensity factor range, l: crack length, m: constant) holds under the condition of small-scale yielding, and the relation dl/dN∝σⁿ_al(σ_a: stress amplitude, n: constant) holds under a high stress level. The effect of size on the crack growth rate is discussed based on these two relations.

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The present paper is concerned with a more elaborate modelling of creep and creep damage in polycrystalline metals and the experimental evaluation of the proposed model. By ascribing the reduction of creep rates caused by the principal stress rotation (i.e., cross hardening) to the intersection mechanism of dislocation on active slip planes in crystal grains, a constitutive equation of creep is first formulated. Then, in view of the metallurgical observations on the nucleation and the growth of grain boundary cavities in creep damage process, an evolution equation of anisotropic creep damage is expressed as a function of the stress, the damage tensor and the creep rates of the material. Finally, the validity of the proposed theory is discussed by performing systematic creep damage tests of thin-walled copper tubes under non-steady multiaxial states of stress at 250°C.

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The effect of specimen geometry, specimen thickness, stress ratio and frequency on the fatigue crack growth rate of structural steels was examined at 123K to clarify the formation mechanism of cleavage during fatigue crack growth, and the condition of the final fracture. Fatigue crack growth rate at 123 K was found to be sensitive to the stress ratio, and was considerably increased by the occurrence of cleavage during striation formation. The value of K_ci at which the first cleavage appears was about 20 MPa√(m) regardless of specimen configuration, stress ratio or frequency, except for the specimen which was 4 mm thick. The presence of cleavage during crack growth may be related to local deterioration of the material caused by cyclic straining ahead of the crack tip. The value of K_fc at which final fracture occurs was found to increase as the specimen thickness did not satisfy the size requirement for small scale yielding.

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Fatigue tests of 0.08% C Steel were made on in-plane bending at elevated temperatures up to 450°C (Room temperature, 200°C, 375°C and 450°C). the threshold stress intensity factor ΔK_th was determined by the critical condition of whether specimens broke or not at 10⁷ cycles. The threshold stress intensity factor reached a maximum at 375°C. The value of K_op/K_max increased with increasing temperature up to 450°C. Both ΔK_{eff th} and ΔK_{eff th}/E showed the same temperature dependence as described above. The oxide at 375°C was thinner than that at 450°C. The value of ΔK_th at 375°C, however, was larger than that at 450°C. It is concluded that the maximum ΔK_th is caused by strain aging rather than thick oxide induced closure.

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A method for the determination of stress intensity factors for an arbitrarily mixed mode three-dimensional crack has been developed based on the J-integral concept. J-integral for a mixed mode three-dimensional crack is expressed in the form of J=J_I(Γ)+J_II(Γ)+J_III(Γ)+J₀(Γ), where J_I(Γ), J_II(Γ), J_III(Γ) are the path-dependent line integrals equivalent to the components of mode I, mode II and mode III deformation, respectively, and J₀(Γ) is the surface integral due to the three-dimensional effect. In linear elastic material, the stress intensity factors, K_I, K_II and K_III are determined by J_I, J_II(Γ), and J_III(Γ), which are obtained by extrapolating J_I(Γ), J_II(Γ), J_III(Γ) to the crack front. This method has been applied to obtain the stress intensity factors of mode I and mixed mode three-dimensional cracks in several cases. The numerical calculation was made using the finite element method.

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In the present paper, replacing similar adherends and an adhesive bond by finite strips, stress distributions in adhesive joints are analyzed strictly using the two-dimensional theory of elasticity in the case where adhesive butt joints are subjected to tensile loads. The effects of stiffness and thickness of adhesive bonds on the stress distributions are shown by numerical computations. For verification, an experiment is performed, and the analytical result is in a fairly good agreement with the experimental one. Furthermore, comparing the analytical result with the result obtained by F. E. M., they are in a fairly good agreement.

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The finite three-point bending of a fiber-reinforced straight beam with an edge crack is analysed in the framework of the ideal theory of fiber-reinforced composite materials. The beam is reinforced in its axial direction and simply supported at its ends. An assumed deformation state is proved to be statically admissible only for a linear elastic shear response. The results of the analysis are shown in figures with a major emphasis on the crack tip opening angle and the singular fiber stress at the crack tip.

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The plane elastostatic problem for two bonded elastic half planes consisting isotropic and anisotropic materials is considered. It is assumed that the isotropic half plane contains a straight crack normal to the bimaterial interface, and the bonded plane is subjected to a constant strain away from, and perpendicular to, the crack. Two cases of the crack fully imbedded into the isotropic half plane and terminating at the interface are investigated. The problem is formulated as singular integral equations with Cauchy and generalized Cauchy kernels, using the method of continuous distribution of dislocations. Numerical results are given for the order of stress singularities and stress intensity factors, and for typical material combinations.

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The effects of interaction between crack-like defects in fiber reinforced composite materials on the local stress concentrations in their neighbourhoods are theoretically investigated from the macro and micromechanical points of view. The most simple models consisting of homogeneous and heterogeneous anisotropic elastic plates with two colinear or parallel cracks are used. Plane stress and plane strain conditions are assumed, and the mathematical formulations are made in terms of the Cauchy-type singular integral equations of the first kind through the methods of harmonic-type stress functions and Fourier transforms. Numerical calculations are carried out for the stress intensity factors, and the results thus obtained from these models are campared to each other.

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The contact problem of two-dimensional elasticity, i.e., contact between an elastic foundation and an infinite beam with a concentrated load applied at one point of the opposing edge of the infinite beam is investigated analytically. The ratio between the height of the infinite beam and the thickness of the foundation is changed from 1 to 10. Further, the ratio (E₂/E₁) between the Young's modulus of the infinite beam and that of the foundation is changed from 0.02 to 10. The "foundation modulus" is obtained analytically from the result of the investigation.

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This paper describes a new approach to treat bending problems of circular plates with uniform or a concentrated load under mixed conditions; i.e. cases when the circular plate has two portions of its boundary clamped and the remainder simply supported. The present results are compared with results obtained by other investigators.

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Strength of the bonded interface is generally low under the loading perpendicular to it. Therefore the investigation on the fatigue strength of the interfase or the fatigue crack growth along the interface seems to be important to use composite materials. In this paper, the fatigue crack growth phenomenon along the interface and the fatigue strength are investigated in detail using epoxy dissimilar plate specimens with various Young's modulus ratios and different bonding strengths. It is found that the fatigue crack growth rate (da/dN) along the interface can be characterized by the apparent stress intensity facter range ΔK_Iapp caluculated as the stress intensity factor for a crack in a homogeneous material. The da/dN-ΔK_Iapp relations for various composite specimens are independent on Young's modulus ratio and specimen type. Therefore these relations seem to be a measure usefull for the quantitative evaluation of bonding strength of the interfase. Moreover the particular behavior of fatigue strengths of smooth composite specimens can be explained by the da/dN-ΔK_Iapp relations along the interface.

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In response to a demand for light weight structures, FRP has been widely used as an advanced industrial material. However, its surface is easily damaged by harder foreign materials, nevertheless, the effect of that damage on the fatigue strength of FRP laminates has not been well investigated. Most of the investigations have been treated on artificial surface notch so far. In this study, therefore, the influence of the fatigue strength of FRP laminates with surface indentation damage was studied. Tow kinds of FRP laminates were tested under bending fatigue. Moreover, discussion of the experimental results has taken into account some stress fracture criteria, using the results of 3-D FEM stress analysis. As a result, the point stress criterion was best fitted to the present experimental results.

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In order to establish a numerical procedure for predicting the bifurcation behaviour of a non-uniformly stressed body, the generalized version of Hill's theory of uniqueness and bifurcation to materials obeying the non-associated flow rule, proposed recently by Raniecki et al., is employed. To obtain an improved lower bound to the bifurcation point, the steepest descent method is introduced to optimize a parameter r^^-, which is introduced into the constitutive equation to establish a variational principle governing the bifurcation behaviour. The obtained results for pressure-sensitive and dilatant annular plates, subjected to uniform tension at the outer edge, show that the bifurcation is notably accelerated compared with that for plates obeying the associated flow rule. The effect of the pressure-sensititve yielding on the bifurcation behaviour is more remarkable than that of the dilatant plasticity. It is clarified that optimization of the parameter r^^- is quite important in achieving considerable improvement of the lower bound of the bifurcation point.

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A constitutive equation taking into account the corner formation on the yield surface and the Bauschinger effect is developed. Long tubes subjected to external pressure and axial load under plane strain and generalized plane strain conditions are analyzed in conjunction with the proposed constitutive equation. The influence of axial load, the Bauschinger effect and corner formation, including the corner angle, and the mobility of the corner axis to the direction of stress history upon such global deformation behaviour as maximum pressure, pressure versus displacement relation, and axial strain, are clarified. With regard to local deformation, these effect on the strain rate and strain localization, surface unevenness and shear band formation are investigated.

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An analytical method for the elasto/visco-plastic dynamic problems of general, moderately thick shells of revolutions subjected to asymmetrical loads is developed in consideration of the effect of shear deformation. The equations of motion and the relations between the strains and displacements are derived by extending the Reissner-Naghdi theory in elastic shells with given consideration to the effect of shear deformation. For the constitutive relations, the elasto/visco-plastic equations by Fyfe based on the model developed by Perzyna are employed. The numerical method selected for this problem is a method using finite difference in both space and time. As a numerical example a cylindrical shell under a seimisinusoidal external load with respect to time is analyzed, and the results are compared with those from the classical theory which neglect the effect of shear deformation.

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An Updated Lagrange type finite element procedure is developed for modeling the punch stretching of peripherally clamped square plates over arbitrary shaped punches. The analysis is based on the elastic-plastic membrane theory, it accounts for finite strain and displacement and embodies the classical J2 flow law. The SQUARE BOX-SHAPE and CROSS-SHAPE are employed for the geometry of the flat-bottomed punch face. The Coulomb friction condition is introduced to account for the friction at the interface of the punch and the square blank. It is demonstrated that the region of strain (stretch) localization and the rate at which the local neck grows are strongly influenced by the friction condition and the punch geometry.

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This paper describes the creep behaviour of a plasticized PVC sheet under biaxial stress. The problem involves large deformation and material non-linearities. In addition, the specimen is the orthotropic solid although it is made by carender method. In this study, on the assumption that the creep potential exists, the creep constitutive equation for anisotropic materials was formulated, the creep potential function is similar to Hill's theory, and the time hardening theory was employed. Subsequently, this constitutive equation was adapted to the finite element method based on an incremental total Lagrangian formulation. As a result, it was found that the computed results were in good agreement with the experimental ones within the range in which the creep constitutive equation is in effect.

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In this paper, fundamental experiments are carried out to examine the occurrence of slip-bands (flecks) in copper electroplating foil under variable stresses. The following conclusions are drawn: (1) Miner's rule holds for the occurrence of slip-bands under two-level single block stressing; (2) The appearance of slip-bands is dominated by the amplitude of the primary stressing; (3) When different kinds of stresses act continuously on the plating foil, cumulative fatigue damage that causes the slip-initiation and the grain growth in the foil is not dominated by Miner's rule; (4) Both overstressing and understressing reduce the heating duration for the recrystallization of the copper plating foil and then promote the occurrence of slip-bands.

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Fracture toughness tests were carried out on compact tension specimens to obtain the fracture toughness for transverse loading of unidirectional glass fiber reinforced plastics. The fracture toughness decreases as the radius of the notch tip and the volume fraction of glass fibers decrease. During the fracture toughness tests, acoustic emission signals corresponding to the microfracture of the fiber reinforced composite were detected. By use of a crack initiation model based on the microfracture, the influence of the radius of the notch tip and the volume fraction of glass fibers on the fracture toughness was explained.

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The local J-vector, J_local, can be defined for three-dimensional cracks at any point on a crack front. The numerical determination of the J-value along the crack front is usually based this expression of J_local. The authors have previously proposed an alternative method, i.e. the global J-scalar method, for determining the J-distribution along the crack front. In this paper, elastic and elastic-plastic stress-strain and J-integral analyses were performed for center-cracked panels and plates with semi-circular surface cracks, by combining three-dimensional FEM techniques with the global J-scalar method. The J-distribution was expressed by a series of functions. It was found that good accuracies can be obtained if suitable functions are selected for the description of the J-distribution. The global J-scalar method was rather insensitive to intrinsic numerical errors involved in the FEM calculations, as compared with the usually employed local J-vector method, and is thought to be a promising J-evaluation method.

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The effects of the mechanical properties of adherend materials on the strength of adhesive joints were studied by applying a tensile and torsional load to the tubular butt joints of dissimilar adherends. The specimen materials used in the experiment were carbon steel, copper, brass, aluminium alloy for adherends and epoxy resin for adhesive. The strength of the cured adhesive joint under the tensile load was compared with that without curing to investigate the effect of the difference in the coefficient of thermal linear expansion on the strength of the adhesive joints. The strength of the cured joints was higher than that of the non-cured joints. This showed that there was no remarkable influence of the coefficient of thermal linear expansion on the joint strength. The effects of ratio of Young's modulus on the joint's strength under tensile load decreased when the difference in Young's modulus of adherends was larger. This decrease of the joint strength was discussed on the basis of the analytical stress distribution in the inter face between adhesive layer and the adherend.

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The deformation and strength of single lap joints having adherends of dissimilar materials were investigated analytically and experimentally. The strain distributions of the joints of carbon steel and aluminum alloy boded with epoxy resin under tensile shear loads were analyzed by the finite element method. The analytical strain distributions coincided approximately with the experimental results. The analytical results of the strength were less than the experimental strength, because the analytical results predicted the initial cracking loads which were different from the final fracture loads. The Young's modulus of adherends and the adhesive lap length had much effect on the joint strength. The strength of joints of carbon steel and aluminum alloy had intermediate values between the strength of joints having carbon steel adherends and aluminum alloy adherends. The curing process of the adhesive resin improved the joint strength overcoming the difference of thermal properties in the adherends.

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A theoretical analysis and quantitative experiments are performed to examine the effect of damping on the stability of a Reut-type nonconservative model. The model consists of two similar rigid rods, and is subjected to a nonconservative force produced by an impinging air jet. Damping due to an attached dash-pot is taken into account, as well as internal and external damping. The effect of damping configuration on stability is demonstrated in detail. The change in flutter force is discussed when the location of a dash-pot shifts along the rods. There exists an optical location for a dash-pot in stabilizing the model. Experimental results are compared with a theoretical prediction obtained by taking measured damping coefficients into account.

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This paper deals with the stress concentration analysis of a semi-circular or a 60° V-shaped single edge notch in an infinite strip under remote tension and in-plane bending. The stress field induced by a point force in a semi-infinite plate is used to solve these problems. The results show that the Neuber formula gives an underestimated stress concentration factor when the notch is sharp and shallow. In addition, the stress concentration factors of 60° V-shaped notches are also represented by diagrams.

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Errors included in solutions obtained by the boundary element method analysis are generally larger than those by the finite element method analysis in the case that the number of discreted elements is small. One of the reasons is supposed to be attributed to the error which will be produced in the numerical integration of the r, ^l_xr, ^m_y/rⁿ type of singular functions in two dimensional elastic problem. In this report the distance r between an observed point and a boundary element was represented graphically by two parameters. Then many functions composing the fundamental solutions could be classified into seven groups and their tendencies along an element were characterized. The following results were obtained: (1) Errors of the numerical integration of the functions are small in the region r_d/L>0.5 even if four points are chosen in gaussian quadrature formulas. (2) The larger the exponent values i, j, k, l, the more increase the errors in the integration of the functions r, ^l_xr, ^m_y/rⁿ. Then, the methods to reduce computing time and to decrease errors of the numerical integrations are proposed.

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Fracture toughness tests based on the R-curve method using the unloading compliance calibration technique were conducted under the condition of a simulated crustal environment of a geothermal reservoir (confining pressure 18 MPa, maximum temperature350°C). The results obtained indicate that a significant reduction of both the elastic modulus and fracture toughness was observed with increasing temperature, and a single linear relationship was obtained between the fracture toughness K_IC(J) and the elastic modulus E. In order to interpret the K_IC(J)-E relationship, a model was proposed using stress-strain-opening displacement at a crack tip based on the fracture process zone.

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Using the Acoustic Emission (AE) technique, the relationship among the AE spectrum, the change of the fracture toughness and micro-fracture mechanism due to the ageing effect have been investigated for commercial Cu-Be-Co alloy. The AE signals could be classified into 6 groups by spectrum analysis through all materials aged at 300°C and 420°C for given times. The classified AE signals were plotted along with the load-displacement diagram following the order of emitted time and energy. By AE signal analysis, the fracture toughness and micro-fracture mechanism and its change at the crack tip due to the ageing effect are discussed. At the early stage of deformation, the facet created by the decohesion of the intermetallic inclusion and the precipitations emitted AE, which had a certain frequency component of 200-600 kHz, where the dominent frequency components depend on the ageing process. Increasing the deformation, facet was connected suddenly by the dimple fracture which led to the pop-in crack propagation. In this step, the AE had an audible frequency and the highest energy level was emitted. A model of the micro-fracture process and AE source is proposed, paying particular attention to void nucleation and its coalescence at the crack tip.

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This paper describes the procedure for determining surface crack shape using the Line Spring Analysis in the electric potential method. Line Spring Analysis can be used to solve three-dimensional electric potential problems by use of personal computers, over a short computational time. The hardware and software systems for the determination of surface crack shape are developed using a personal computer, based on Line Spring Analysis. A demonstration was made for a semi-elliptical surface crack in a rectangular A 533 B steel plate, and the determined crack shape coincided with the real one.

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This paper presents a strain distribution measurement near the crack tip of a dynamically fracture specimen using the Point Recognition Picture Processing System. In this system, the displacement of the points marked near the crack tip is determined by the picture processing technique. The least squure approximation of the two-dimensional distribution of displacement is obtained by using the interpolation of a finite element subdivision. From the differentiation of the displacement field, the Green's strain distribution is calculated. To fracture the specimen dynamically, an electromagnetic force is employed. As the fracture event takes only few milliseconds, pictures of the marks are taken with a high-speed camera. The results are compared with those from the static three point bending test and the dynamic loading effects on strain distribution near the crack tip are discussed.

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A descriptive model for rate- or time-dependent behavior in cyclic plasticity, based on the random barriers theory, was presented by considering the velocity of a moving dislocation which was a member of movable dislocations and named as a "free dislocation" in this paper. Each of the stress- and strain-rate sensitivities on the stress-strain relation in each half cycle could be fairly estimated on the basis of an equilibrium equation derived in this study as a function of the stress-rate and the strain-rate at any stress level. Moreover, several types of transient behavior caused by a sudden change in the stress- or strain-rate might be uniformly expressed by each analysis of the processes in which a deficient or excess quantity of the free dislocations in this period came near to the moderate quantity decided by the stress and stress-rate.

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The method to obtain thee new sensitivities of shape optimization of mechanical structures are proposed to make possible to transform the structures precisely based on transposition of discreted elements using finite element method corresponding to the addition and removal of the elements. The new sensitivities are acquired by considering the changes of the nodal displacements after addition or removal of the elements in finite difference form which are far more suitable than the current one. The minimum weight problems are treated on cylindrical structures and two dimensional plate structures under constraints of equivalent stress. The obtained optimum structures are retransformed by smoothing procession using polynomials keeping the constraints and the minimalities of the weights.

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A unified inelastic constitutive relation relevant to the plasticity-creep interaction is proposed in the framework of excess stress theory in the first part of the paper. Here, two kinds of isotropic internal variables are introduced: one corresponds to the time-independent static yield stress; and the other is the time-dependent back stress. The kinematic hardening behavior of the material is expressed by the time-dependent back stress. In the second part, simulated results of five kinds of constitutive models, including the present one, are compared with the experiments of 2 1/4 Cr-1 Mo steel at 600°C to examine the validity and the applicability of the complex loading history of the plasticity-creep interaction condition. some remarks on the inelastic behavior are also stated to interpret the rate-dependence of the material under a high temperature regime and the accumulation of ratcheting strain.

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The conventional form of constitutive equations of solids is substantially and critically studied with the motivation that the τ-γ relation of a kinematically hardening plastic body subjected to simple shearing was found recently to be in the shape of a sine-curve in the range of large strain. It is concluded that the rate-type constitutive equation should take the form Σ^^(▽)=D^^:Γ^^(▽), and not the conventional form Σ^^(◯)=D^^:Γ^, where Σ=stress, Γ=strain, super-▽ denotes the objective rate and super-◯ denotes the Jaumann-rate. The objective rates should be those with the spins of the principal axes of the corresponding physical quantities, not with the continuum spin ω_c=(1/2)(L-L^T), as in the Jaumann rate. Several other fundamental and important propositions are presented.

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A theoretical relation is formulated by which the impulsive force generated at a contact part can be calculated, when an aluminium bar whose end is a circular truncated cone collides axially, perpendicularly against a plane wall at a comparatively low speed. In the formulation, the effect of the local behavior in the aluminium bar caused by stress wave propagation is neglected. By carrying out an experiment in which aluminium bars whose ends were of a variety of shapes of truncated cones, collided against a devised sensing plate, the effectiveness of the theoretical relation for calculating the impulsive force which varies complexly with the shape of the contact end and with the impact velocity is confirmed.

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This paper describes an analytical formulation and a numerical analysis of the elasto/visco-plastic problems of orthotropic moderately thick shells of revolution under axisymmetrical loads with application to a cylindrical shell, and with comparison to experimental results. The analytical formulation is developed by extending the Reissner-Naghdi theory in elastic shells with a given consideration to the effect of shear deformation. As the constitutive relation, Hooke's law for orthotropic materials is used in the elastic range, and equations based on the orthotropic visco-plastic theory derived from the orthotropic plastic theory by Hill are employed in the plastic range. The visco-plastic strain rates are related to the stresses by Perzyna's equation. In order to check the adequacy of the numerical analysis, experiments are performed on elasto/visco-plastic deformation of a titanium cylindrical shell subjected to internal axisymmetrical loads. Good agreement is obtained between the experimental results and analytical solutions.

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