The stress-strain response was analyzed in the cross section of circumferentially notched specimens of root radii of 2, 3 and 5 mm by F. E. M.. Then, the cyclic J-integral range, ΔJ and the strain intensity factor range, ΔK_ε were estimated for the surface crack, where the stress and strain gradients were taken into account in the cross sections of the notched specimens. The crack shape was estimated by assuming that the crack extends so that the values of ΔJ or ΔK_ε become the same along the crack front. The analysis was in quite good agreement with the test result. The growth rate of the surface crack was successfully plotted against the J-integral range and the strain intensity factor range estimated using the axial and the equivalent stress-strain responses around the notch root.

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The influences of crack length on stress corrosion cracking (SCC) crack growth of a 523K tempered high·strength steel, SCM435H (Δ_B=1 770 MPa) immersed in 3.5 % NaCl solution were investigated under dynamic loading conditions : static SCC under a sustained load, dynamic SCC under a sustained load with high frequency vibratory stresses superimposed, and cyclic SCC under 10w frequency variation. Threshold values of static and dynamic SCC of short crack, whose crack length from notch root, l, ranged from 1.52 mm to 2.81 mm, were smaller than those of long crack (l= 6.86-9.78 mm). Dissolution of fracture surface was more prevalent in short crack than in long crack, and a decrease in threshold values of short crack is considered to be caused by increased hydrogen uptake at the crack tip associated with accelerated dissolution of fracture surfaces compared to long crack. Crack growth rates of short crack (1≲6.5 mm) at the plateau region were also accelerated compared to those of long crack (l>6.5 mm). Static SCC crack growth rates of long crack were accelerated and the threshold value was lowered by deaeration of the solution. However, the deaeration had no influence on crack growth rates of static SCC of short crack. In the case of cyclic SCC at R=0.1, no influence of crack length (1>1.18 mm) on crack growth rates was observed. But at R =0.5, crack growth rates of short crack were accelerated compared to those of long crack.

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The effect of grain size on the fatigue crack initiation at grain-boundary triple junctions was investigated using austenitic SUS304 stainless steel at 973K in air. The amount of grain-boundary sliding was measured on specimens during fatigue. The grain-boundary sliding rate was fast in the specimens with large grain diameter (D), and the rates, 1ere increased in proportion to D, while the critical value of grain-boundary sliding for crack initiation increased in proportion to. Then, the number of cycles to crack initiation was in inverse proportion to √D. These results agreed well with the prediction of crack initiation based on the micromechanical analysis.

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Rotating bending fatigue tests were carried out on specimens with a small blind hole of three age-hardened Al alloys, i. e. 2017-T4, 7075-T6, and 6061-T6, in air and in oil. The main results obtained are as follows: (1) Fatigue strength of 6061-T6 decreases and those of 2017-T4 and 7075 -T6 increase, in oil as compared with those in air. (2) In 2017-T4 and 7075-T6, the mode of crack propagation is affected by the stress level and the environment. (3) The effect of oil on the crack growth rate depends on the mode of crack propagation. That is, the effect is strong in the tensile mode and weak in the shear mode.

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Torsional fatigue tests were carried out on plain specimens and specimens with a small hole, made of annealed carbon steels (S20C and S45C). The relations between the logarithm of the crack length and the cycle ratio (N/N_f, N : number of cycles, N_f : fatigue life) are expressed by the curve convex upward in the torsional fatigue and the curve concave upward in the rotating bending fatigue. The crack propagation in the torsional fatigue is of the Mode II-type in an initial stage and Mode I in the latter stage. The dependency of 1/N_f on stress amplitude T. in the torsional fatigue is nearly the same as the dependency of the crack growth rate on τ_a.

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Fatigue crack growth properties for stainless steels, SUS304 and SUS403, and low alloy steel, Cr-Mo-V, at temperatures between 25 and 550°C and frequencies between 0.0005 and 50Hz. Fatigue crack growth rates were accelerated with increasing the temperature and with decreasing the frequency for all three steels. SUS403 and Cr-Mo-V steels exhibited the transgranular fracture mode, while SUS304 steel exhibited both the intergranular fracture and transgranular mode at higher temperatures and lower frequencies. The effects of Young's modulus, yield strength, oxidation and creep damage on the behavior of elevated-temperature fatigue crack growth were discussed on the basis of Laird's model [12].

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Fretting fatigue tests at elevated temperatures were carried out using a 12 Cr-Mo-W-V steam turbine steel. The fretting reduced the fatgiue strengths by a factor of three at an elevated temperature (773 K) as well as at room temperature. The friction coefficients between the specimen and the contact pads increased in proportion to the appropriate stress amplitude, but attained saturation. No significant difference in this behavior of the friction coefficient was Observed between room and elevated temperatures. Predictions of fretting fatigue lives were made on the basis of the cyclic J-integral analysis proposed in the previous paper, where the frictional force between the fretting pad and the specimen was taken into consideration. The predicted lives were in good agreement with the experimental results both at room and elevated temperatures.

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The purpose of this study is to determine the distribution characteristics of the variances of fatigue lives of carbon and alloy steels, especially from the viewpoint of their dependence on applied stress levels. The database used in this analysis is the "Database on Fatigue Strength of Metallic Materials" compiled by the JSMS (The Society of Materials Science, Japan) Committees on Fatigue and Reliability Engineering. By quantitave analysis of the variances of fatigue lives of carbon steels on logarithmic normal distribution papers, simple expressions to give the median value and the value at several percentage points are formulated as functions of the applied stress. Results for alloy steels indicate that the scatter of the variance becomes notably large at the lowest stress level, presumably depending on the defect sensitivity of high strength alloy steels. Accordingly, the distribution characteristics of fatigue lives at those low stress levels should be considered carefully in engineering applications.

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For estimating the fatigue strength of members, the value of static tensile strength σ_B is widely used as a parameter. However, when the values ofσ_B in different types of steels are equalized, their fatigue strengths are different from each other in general. In this study, in order to examine the phyisical background of the difference in fatigue strengths, using the heat-treated low alloy steels SCM 435 and SCr 440 whose tensile strengths are nearly equal, the rotating bending fatigue tests were carried out. Results show that the difference in crack initiation life of both materials is hardly observed, however the crack growth rate of SCM 435 is smaller than SCr 440. This difference in crack propagation can be evaluated by the crack growth law : dl/dN=σ_B C3(σ_a/σ_B)ⁿl.

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Four-point bend tests were conducted for Si₃_4/S45C joints. Sensitivity analysis was also performed by the FEM method to clarify the influence of mechanical factors on the fracture strength. The results obtained are as follows: (1) The decrease in strength for the Si3N4/S45C joints compared with those for Si3N4/Si3N4 joints is well explained in terms of residual stresses and stress concentration near the interface in the joint. The fracture strength of the metal (S45C) used for the joint has no effect on that of the joint. (2) There is an optimum yield strength of an insert metal (Cu), although the residual stress decreases with decreasing the yield strength. (3) An alternative arrangement of the multiple joint layers is effective in reducing the residual stresses.

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The present paper is concerned with the fatigue of a short glass fiber reinforced SMC composite. The fatigue tests were carried out on single-edge notched specimens of the SMC composite under cyclic uniaxial tensile loading. First, the macroscopic feature of the damage near the notch front is discussed together with the variation of the compliance of the specimen. After that, the microscopic fracture mechanism is considered in view of the results of the spectrum analysis of the AE signals detected during the fatigue tests and the SEM observation of the fractured surfaces. On the basis of this knowledge, a reasonable explanation of the microscopic fracture of the SMC composite under fatigue loading is presented.

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Nonaxisymmetric bifurcation and post bifurcation behaviors of composite tubes with two different materials subjected to radial drawing at their outer edge have been investigated. The effect of material parameters normalized with respect to those of external tube on the bifurcation and surface type post bifurcation behaviors has been clarified, With regard to the bifurcation behavior, the yield stress and hardening exponent substantially affect the bifurcation point with long wave length bifurcation modes. Surface type bifurcation completely depends on the material characteristics of internal tube. However, bifurcation mode shapes change according to the change in hardening exponents. Surface type post bifurcation analysis clarifies that the effect of initial imperfection on the post bifurcation behavior is not remarkable, however, for the tubes with large bifurcation mode amplitude at boundary plane of the tubes, the strong strain localization starts near the boundary plane and then it extends to the in and out of the plane.

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The test system was newly developed for evaluating precisely the strength of ceramics at elevated temperatures, being equipped with the laser beam-type displacement measuring system. Four-point bending tests were performed on the silicon-nitride ceramics at elevated temperatures from 800°C to 1300°C. The linear relationship held between the load, P and the displacement, 6 at test temperatures below 1200°C. The P vs. δ plot, however, deviated from the linear relationship at temperatures above 1200°C, suggesting the occurrence of plastic deformation. The flexural strength remained unchanged in the test temperature range from room temperature to about 900°C, and then this decreased gradually with further increase in the test temperature. The fracture toughness measured by using the Chevron notch-type specimen was nearly constant in the temperature range from room temperature to about 1100°C. The fracture toughness obtained from the Knoop-indented specimen was discussed in comparison with that from the Chevron notch-type specimen.

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A computational procedure is presented for evaluating the dynamic stress intensity factors for compact tension (CT) and bend specimens under impact loading conditions. The dynamic stress intensity factors for the specimens subjected to arbitrary impact loads can be computed by super-imposing the step-impact response functions. The response functions for CT and bend specimens are obtained by the finite element method. The recent dynamic fracture tests indicate that a loss of contact between the bend specimen and the anvils occurs during the impact loading. The present procedure is effective for the determination of the dynamic stress intensity factors for the specimens, even if the loss of contact occurs.

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This paper is concerned with the dynamic fracture criterion of a double-cracked plate. The specimen is made of epoxy resin and subjected to a tensile pulse wave, whose height and width are control led. The behavior of the stress wave in the specimen and the crack propagation phenomena are analyzed by the photoelastic technique using a high-speed camera. The dynamic finite element method is also used to estimate the stress-intensity factors at the double crack tips. From these experimental and numerical results, the crack propagation criterion of the double-cracked plate is considered.

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The fracture toughness of optical glass fibers, the dimension of which is very small in diameter, has been evaluated directly. The method and results are summarized as follows. A silica glass fiber 125 μm in diameter without a silicone resin coating was indented with a Vickers diamond pyramid. A pre-crack was then introduced by pulling the indented fiber specimen in a longitudinal direction. Each pre-cracked fiber specimen was tested under constant tensile loads in atmospheric air. After the delayed fracture of the fiber specimen occurred, the fracture surface was observed in order to see the crack shape at the onset of the final unstable fracture. Next, based on the observed crack front, the stress intensity factor K_I at the onset of the final unstable fracture, i.e., fracture toughness K_IC was evaluated by the 3-D boundary element method. The fracture toughness K_IC of optical glass fibers was 0.77Mpa√m, which was slightly smaller than that obtained from the indirect evaluation using a WOL-type CT specimen.

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A large deformation finite element analysis has been performed to study the near crack tip growth of a long circular cylindrical hole aligned parallel to the crack plane under mixed mode conditions. The effect of microvoids is taken into account by employing Gurson's constitutive equation. Under the mixed mode condition, one corner of the crack tip sharpens while the other corner becomes blunt. A hole near the sharpened corner flattens without growing and hardly effects the crack tip deformation and distribution of the microvoid volume fraction. However, a hole near the blunted corner grows rapidly and changes its shape to an approximately elliptical cylinder under a strong interaction between the crack and the hole. The strain and the void volume fraction of microvoids became concentrated in the ligament between the crack tip and the hole. Unloaded regions also appear near the tip and the deformation of the near crack tip region is rather involved.

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A fracture surface mark is known to be formed by an interference between a primary crack front and a secondary crack front. We have shown so far that many such marks have been observed on a fracture surface of a brittle plastic specimen. The primary crack front passing through a before mark produces the succeeding behind mark as it propagates in the material, and the effect of the before mark often appears in the behind one. The cusp of the latter usually extends further as the two mark5 are closer together in front and in the rear on a fracture surface. For example, the experimentally measured chordal length at the nucleus of the behind mark increases as they close. Here, we define the proximity p^* to express the linear distance between the nuclei of the two marks in front and in the rear, and we modify the previously reported equation of fracture surface marks to express those changes as a function of the proximity of the two. This expression, of course, gives better parabola-like configuration of the observed behind mark than the previous one.

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The elastic-plastic fracture of carbon steel piping having various pipe diameters and crack angles was analyzed using the latest CEGB R6 approach (R6 method) and ASME Screening Criteria (SC method). Results obtained are as follows: (1) It is necessary to apply the elastic-plastic fracture criterion instead of the plastic collapse criterion by increasing the pipe diameter and the crack angle, (2) For the standard pipes (from 6B to 26B), the plastic collapse criterion can stand within the crack angle of 24°. (3) The SC method gives a more conservative estimation than the R6 method. (4) A simplified elastic-plastic fracture analysis procedure based on the R6 method is proposed, where the unstable fracture moment can be calculated on the basis of the plastic collapse moment and the tabulated reduction factor.

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Environment sensitive fracture is one of the important phenomenon in designing fractures for geothermal energy extraction. Material degradation and environment assisted cracking, stress corrosion cracking (SCC) under constant applied load and corrosion fatigue (CF) under alternating load were investigated in a pressurized high temperature water environment. The test results obtained were applied to two kinds of rock mass according to the permeability, that is, impermeable rock mass and permeable rock mass. In the case of a permeable rock mass, material degradation caused by permeation can reduce maximum pressure for hydraulic fracturing. Crack propagation due to degradation as well as due to SCC and /or CF during long-term service performance is found to be of importance for predicting the stability over the lifetime of the geothermal reservoir. In the case of an impermeable rock mass, conventional fracture mechanics can provide a safe evaluation.

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In the development of design and control methodolgy for hot, dry rock (HDR) geothermal reservoir cracks, a full understanding of the environmentally assisted cracking behaviors of rock under the reservoir conditions is a prerequisite. In this stdy, the significance of time-dependent material degradation is demonstrated, which is induced by the water-rock interactions. In a 350°C, 18 MPa water environment, pre-immersion of 2 inch CT specimens of granite is given for different periods using an autoclave, after which the ultrasonic wave velocity measurements and fracture toughness tests are performed. The results show that the hydrothermal environment causes the time-dependent material degradation throughout the specimens tested, and that the crack propagation resistance of the granite is also time-dependent and decreases with increasing immersion time. Based on the experimental results, an immersion time-dependent crack growth model is proposed and applied to simulate the stress corrosion cracking test which has been conducted in the 350°C, 18 MPa water. It is shown that the proposed model allows us to predict the stress corrosion cracking behaviors under the pressurized high-temperature water environments.

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Tensile strength of sintered YBCO superconductor at 77K was evaluated by Brazilian test and fracture toughness at 85K was measured by use of round compact tention specimen. Superconductivity of specimens during Brazilian tests were examined by the four-point terminal method. Density of a specimen was the principal factor of tensile strength and the fracture surface exhibited the cleavage-intergranular mixed pattern. No change in superconductivity of specimens was observed until mechanical fracture occurred. Namely, no stress dependence on superconductivity was observed for these material tested. Fracture toughness K_Q of sintered YBCO was also measured by use of a round compact specimen. The K_Q value of sintered YBCO with a density of 4, 84g/cm³ was 1.1Mpa·m^l/2. The obtained K_Q shows the value of one third or quarter compared with that of ordinary ceramics (ZrO₂, Al₂O₃).

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This paper treats the bending problem of an axi-symmetrically loaded circular plate with mixed boundaries. It is assumed that the plate is simply supported on two equal and diametrically opposite portions of its edge the remaining edge portions being clamped, or that the plate is supported and elastically constrained for rotation where the constraint is biaxially symmetric. The deflection and the bending moments at the center of the plate are calculated by the coefficient comparison method which is proposed in this paper. By using this method with the results obtained for the cases of uniformly distributed load, the problems of axi-symmetrically loaded circular plates with mixed boundary conditions can be easily solved The validity of the calculated results is assured by comparing with those obtained by the iterative method.

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A new method is presented for the determination of the instantaneous shut-in pressures in the hydraulic fracturing tectonic stress measurements. The method is developed by the analysis of the closure process of the crack induced by hydraulic fracturing and it utilizes the inverse of the decrease rate of the downhole water pressure after the shut-in. The plot of the inverse of the decrease rate vs the downhole pressure consists of two straight lines and the instantaneous shut-in pressure can be cleary determined as the pressure of the point of intersection of the two straight lines. The new method is applied to the pressure vs time records which were obtained in field experiments. It is revealed by the application to the field date that the new method can clearly determine the instantaneous shut-in pressures from all of the pressure vs time records applied.

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Modelling of elastic anisotropy induced by creep damage and its application to the analysis of creep crack growth in a copper plate are discussed. The elasticity theory of damaged materials developed by M. Kachanov is combined with the anisotropic creep damage theory of the present authors to formulate the anisotropic elastic-damage coupling in creep. The theory is implemented into the finite element analysis of the creep damage process in a thin plate with an internal crack subject to non-proportional loading. The material constants of elastic-damage coupling were identified by performing an experiment. The influence of the reduction in elastic modulus due to creep damage on the stress distribution at the crack tip, on the pattern of creep crack extension and on the final rupture time are discussed in detail.

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As one of analytical problems of thermal stresses with a moving boundary, we analyzed thermal deformations and thermal stresses caused by a phase transformation. We assumed that a cooled end surface of a semi-infinite solid cylinder, which is kept at a constant temperature, yields the phase transformation with respect to the axial direction; then as a result, the solid cylinder could be seprated into two dissimilar solid phases with thermally and thermoelastically different material properties by a moving interface. In the analytical developments, we adopted Neumann's solution for one-dimensional temperature distribution, and then we analyzed the axisymmetric thermoelastic field with aid of the thermoelastic displacement potential function and Love's displacement function. As an illustration, numerical calculations are carried out for Martensite Transformation, and the influence of the latent heat on the temperature and thermoelastic fields were examined precisely.

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In this paper, an inverse analytical technique to estimate the contact stress distributions is proposed. The technique uses the finite element method and the mea5urement values. The values are forces or displacements measured by experimental techniques on the surface of an elastic body distant from the contact area, and include 5everal errors. In order to decrease the effect of the errors. two inverse analysis schemes are presented . One scheme is a technique using an average value of many measurements. The other scheme is a technique applying the least square method. The validity of these schemes is evaluated by using numerical data produced by computer.

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Residual-stress redistribution caused by making a center-hole and the resulting deformation were experimentally investigated using specimens with longitudinal tensile residual stress near the center of a plate. The experimental results obtained by the electric discharge machining and the end milling with two kinds of rotative speeds were compared with three-dimensional analytical results on residual-stress redistribution and deformation due to material removal using the Finite Element Method. The analytical results were in good agreement with the experimental results obtained by the electric discharge machining. On the other hand, the end-milling method tended to decrease the tensile stress in the residual-stress redistribution and increase the deformation near the hole because of plastic-deformation induced by machining, especially at lower rotative speeds of an end mill, in comparison with the analytical results.

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The scattering of elastic longitudinal wave on reflection at a free plane boundary is studied using the analytical solution for a two-dimensional wave field generated by strip surface stresses. The variation of the scattered field is calculated with various incident angles of the narrow beams and displayed in polar diagrams, which show a wide range of scattered strength. The calculated result reduces to the specular reflection of the infinite plane wave with the increasing number of beams in the bundle. These results give the basis for estimating the experimental error due to the scattering of the first and second echoes launched by transducers of finite width. The scattering-induced error is well characterized by the ratio of the transducer width to the square root of the specimen thickness, both being normalized by the wavelength. As this ratio increases from zero, the error begins to increase, passes a peak, and then approaches a constant value. To minimize the error, the use of a tranducer is suggested, for which the near-field length is at least four times the specimen thickness.

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The tensile properties and fracture of the (a+γ) two phase stainless steel with very fine r grains were investigated. Two different microstructures with very fine r grains can be obtained by the thermomechanical treatments ; One has both very fine r and a grains, and the other has very fine r and large a grains. The specimens were prepared in quenched and aged (475° conditions. The results obtained are as follows. The 0.2% proof stress and tensile strength increase with the aging at 475°C for all specimens. The refinement of the γ grains plays an important role for the increase of strength in both quenched and aged conditions, and also for the ductility in the quenched condition. The refinement of α grains, however, contributes to the increase of the ductility in the aged condition. Accordingly, it is found that very good combinations of tensile strength and ductility can be achieved by the aging and the refinement of the γ and α grains (micro duplex structure).

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Nondestructive measurements of residual stresses were successfully attempted by the acoustoelastic technique on butt-welded joints of a piping carbon steel plate. Based on the measurements and evaluations of the residual stresses, the prediction of the fatigue crack growth was done using the superposition technique, and results 'were compared with the experiments. The measurement of the initial residual stress distribution on the specimen before the fatigue test and the application of a proposed evaluation method of the material anisotropy can give a more correct prediction, The sensitivity of possible errors in the acoustoelastie measurement was analyzed and discussed.

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Acoustoelastic birefringence is measured with a computerized cepstrum analysis. An ultrasonic transducer emits a broad-band shear wave pulse, polarized about 45° from the principal axes, into the stressed material. Due to the stress-induced anisotropy, it splits into a pair of shear waves polarized along the principal directions, which propagate with different velocities. The same transducer receives them together and sends the resultant signal to a microcomputer, where the signal is Fourier-transformed twice to reduce the power-cepstrum as a function of quefrency. The quefrency where the cepstrum takes the maximum peak gives the transit-time difference of the polarized shear waves. The experiment is done by uniaxially loading the specimens of aluminum alloy 7075-T 651 The results of the cepstrum analysis agree with the conventional sing-around measurements.

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Strain gauges made of nickel foil are devised for measuring the elastic surface stress of a specimen subjected to repeated loads. The nickel foil about 10μm thick composed of the crystal grains of 30μm in mean diameter is made by annealing the foil of nickel plating at 950°C for 60 s in a vacuum. Sticking the nickel foil on the surface of the specimen, the elastic stress is measured by observing slip-bands in the foil resulting from repeated strains. The calibration tests of the foil under rotating-bending are carried out at several test temperatures. The range of applicable temperatures of the gauge, and the relation between the appearance of slip-bands and the magnitude of cyclic stress are investigated. Using the "standard photographs" which show the relation between the density of slip-bands and the cyclic stress, the peak stresses in grooved shafts under bending are measured.

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The linear theory of viscoelasticity has been well formulated and successfully used. In comparison, however, the nonlinear viscoelastic-plastic behavior at finite strains is less understood because of several complexities peculiar to the polymer solids. In order to investigate a nonlinear constitutive law in polymers, torsion and compression tests were performed to reveal the effect of the strain rate, temperature and hydrostatic pressure on the stress-strain relations of polypropylene rods. The experimental results were compared with the numerical calculations based on an overstress theory. The overstress theory was found to be in good agreement with the experimental stress-strain behaviors, provided that the current strain is less than the previous strain.

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The time-space finite element method was used to study one-dimensional heat conduction problems. Optimum mesh length and time increment of this method were obtained by minimizing the condition number of the coefficient matrix, and were found to be two and three times greater, respectively, than those of the widely used Crank-Nicholson method. Several numerical analyses showed the time-space finite element method to be very stable and precise in comparison with the Crank-Nicholson method. As an application to engineering problems, the one-dimensional time-space finite element method was used for the simplified heat conduction analysis of a turbine blade. A transient analysis on trip condition was performed. This simplified approach was shown to be very effective.

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In the virtual crack extension method, the stress intensity factor, K, is obtained from the converged value of the energy release rate given by the differences of the finite element stiffness matrix when some crack extensions are taken. Instead of the numerical differences of the finite element stiffness matrix, a new method to use a direct derivative of the finite element stiffness matrix with respect to crack length is proposed. Results of some example problems by the present method are obtained with high accuracy and good efficiency. This shows the numerical assurance of the usefulness of the present method. A personal computer program for the analysis is developed.

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An axisymmetric contact problem is considered to be the cause of the indentation of a penny shaped crack by a thin disc-shaped rigid inclusion in an elastic layer. This three-part mixed boundary value problem is reduced to a solution of infinite systems of simultaneous equations in which the crack shape function is expressed as an appropriate series. The normal contact stress between the inclusion and the crack surface, as well as the stress intensity factor, are shown in curves calculated numerically. The effects of various values of nondimensional parameters on the stress field and the stress intensity factors are studied.

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The problems of the tension of a semi-infinite plate having a semi-elliptical notch with a crack are analyzed by the body force doublet method. Quite accurate values of the stress intensity factor for a crack of arbitary size can be obtained by using the stress field due to a pair of point forces (doublet) in an infinite plate with an elliptical hole. Furthermore, the error due to the use of equivalent crack length, which is the sum of notch depth and crack length, is discussed.

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The stress and strain distributions in the brain tissud as a solid are very important for under-standing the state or biomechanism of the hydrocephalus. But it is impossible to measure such mechanical factors directly in the human body. This paper proposes mechanical models of the brain whose property has not been clarified and discusses the adequacy of the models. Computer simulations are performed under the condition that the hydrostatic pressure of the cerebral ventricle is high. Elastic models show the principal stress distributions or distributions of other mechanical factors. Elastoplastic models taking large deformation into consideration show the deformation of the brain tissue. Moreover, simulations that include the "mechanical adaptation" of the living tissue are performed in elastoplastic models. It can be supposed from the result that a mechanical adaptation acts to make the stress distribution uniform in the brain and to promote the ventricular enlargemdnt.

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The axisymmetric dynamic response of a circumferential edge crack in a cylindrical cavity under normal impact is analyzed. Laplace and Hankel transforms are used to reduce the transient problem to a pair of dual integral equations in the Laplace transform plane. The solution is given in terms of a singular integral equation of the first kind which has a generalized Cauchy kernel as the dominant part. A numerical Laplace inversion routine is used to recover the time dependence of the solution. Numerical results on the dynamic stress intensity factor are obtained to show the influence of inertia, geometry and their interactions on the load transfer to the crack.

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Ultrasonic fractography technique was utilized to study dyamic crack response to mode II shear waves. In this study, dependence of the crack response on the dynamic stress intensity factor K_Id was studied quantitatively. Maximum modulation angle ξ' and fracture velocity V_f were evaluated. Values of K_Id were obtained from diameters of caustics which were taken by high-speed photography. The result showed that K_Id increases with increasing V_f. Values ofξ' decrease with increasing K_Id at constant ultrasonic amplitude.

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In the previous study, the authors had developed a Hopkinson bar-type highspeed impact fatigue testing machine, and carried out impact fatigue tests on two sorts of carbon steels. In this study, after some modifications and improvements of the testing machine, a new method was introduced to generate impact stress patterns with various loading times at maximum stress levels, and impact fatigue tests were carried out on SIOC(0.1%C) steel by changing the loading time from 470 to 940μs Fatigue crack growth tests were also carried out on the same material using another Hopkinson bar-type testing machine, with the loading times of 780 and 1050μs. It was confirmed that the impact S-N property in the high cycle range was dependent on the loading time and there was a relationship σ_max (N_fT)^m=D, whereσ_max is maximum stress, N_f the number of cycles to failure, T the loading time, and m and D are constants. It was also confirmed that the fatigue crack growth rate was affected by the loading time and N_fT (the product of the number of cycles and the loading time) was an important parameter governing the crack growth rate.

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Viscoplastic behavior of Type 304 stainless steel after cyclic prestraining and/or axial cyclic prestraining of various strain amplitudes, and of various numbers of cycles was experimentally investigated at room temperature. The difference between flow stress levels depending on strain rate considerably decreases after cyclic loading, which suggests that viscosity of metal is related to low cycle fatigue phenomena. On the other hand. the relaxation stress drop does not decrease. but increases with an increase in the flow stress level due to cyclic work hardening. Work hardening coefficient (plastic modulus) in reloading is strongly concerned to plastic work per cycle in preloading.

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A prediction method was proposed for plastic ratcheting of a cylinder, which was subjected to axially moving temperature distribution without primary stress. First, a mechanism of this ratcheting was proposed, which considered the movement of temperature distribution as a driving force of this phenomenon. Predictive equations of the ratcheting strain for two representative temperature distributions were proposed based on this mechanism by assuming the elastic-perfectly-plastic material behavior. Secondly, an elastic-plastic analysis was made on a cylinder subjected to the representative two temperature distributions. Analytical results coincided well with the predicted results, and the applicability of the proposed equations was confirmed.

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The forming limit diagrams of perforated sheet metals with holes have been theoretically determined by using the diffuse necking criterion and the rigid-plastic finite element method under biaxial tension. This plastic instability is decided by the condition that the external work change caused by external force change is zero. The forming limit line was presented of plates perforated with circular, elliptical and squar holes arranged in a regular penetration square pattern. It is shown that these forming limit diagrams are similar to those of Swift's diffuse necking in the case of positive strain ratio, and to those of Hill's localized necking in the case of negative strain ratio. The influence of the strain-hardening exponent, porous ratio and hole shape on these forming limit diagrams is discussed and comparison of the F. L. D. of a perforated plate with that of a nonperforated plate is made.

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The constitutive equation for analyzing the cyclic deformation was developed by introducing the concept of the internal stress and the dislocation multiplication into the Johnston-Gilman's equation modified by the authors. Then, the numerical simulation of the cyclic stress-strain hysteresis loop accompanied by the cyclic straining was done for the annealed copper. The stress and plastic strain ranges estimated were slightly different from the test results in the transition hardening stage under the total strain range-controlled condition. Meanwhile, the former was in good agreement with the latter in the saturation hardening stage, where the cyclic mechanical properties of materials were commonly represented in the practical use. The analyzed hysteresis loop tends to be fatter in shape than the experimental one at the larger strain range controlled in the test. This problem, however, is solved by adjusting one of the parameters included in the proposed constitutive equation, which are determined by the static tensile and stress-relaxation tests.

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Polyvinyl chloride which is reformed for impact resistance (Hi-PVC) and polycarbonate (PC) which has excellent impact resistance properties are tested by using an instrumented Charpy impact tester. Effects of temperature and notch root radius on the specific absorbed energy, the maximum load and the fractographs are studied. It is found that the specific absorbed energy of the Hi-PVC specimen does not relate to the notch root radius below 0°C and the value is lower, but it increases rapidly at 20°C. The Hi-PVC specimen represents the brittle fracture similar to the PVC specimen below 0°C. The PC specimen initiates many microvoids at the notch surface as the notch root radius is larger above 0°C. Similarly, the Hi-PVC specimen initiates the trend which has many microvoids due to the rubber particles at the notch tip at 20°C.

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