The rotating bending fatigue tests concerning coaxing effects were carried out on the plain specimens of pre-strained S10C, aged S10C and annealed S10C. The main results obtained are summarized as follows: 1) Fatigue limit is controlled by a critical condition for the propagation of a micro-crack. This is closely related to the coaxing effect. 2) The origin of the final fracture during the coaxing experiment is the non-propagating micro-crack formed at the first stress level. 3) In the pre-strained S10C having aging power at room temperature, the increasing rate of fatigue limit is 16%, and the coaxing effect is the most remarkable among the three materials.

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Sharply notched specimens of 3 % silicon iron were fatigued under several stress ranges, either above or below the notched fatigue limit for complete fracture. The growth behavior of short fatigue cracks near the notch root was analyzed based on the crack closure. A computer-aided high-resolution unloading elastic compliance method was employed to measure the closure of short fatigue cracks. The etching susceptibility of 3 % silicon iron was used to observe the plastic zones around notches and cracks. The growth rate of short fatigue cracks first decelerated with increasing crack length, and then accelerated or became non-propagating, depending on the applied stress range. Similar deceleration was observed when the growth rate was correlated with the stress intensity range. The effective stress intensity range was a unique parameter in correlating the growth rate of short fatigue cracks, and the relation was identical to that obtained for long cracks. Notch plasticity was not a direct cause for the deceleration. The highly strained zone size, measured by the etch pit technique, was useful for estimating the effective stress intensity range for short cracks.

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The introduction of a superposition technique makes it possible to evaluate the effects of residual stress on fatigue crack growth characteristics. Under compressive residual stress, however, the classical method sometimes yields to an overlapping of the crack surfaces, which is physically unacceptable. A more careful estimation procedure is now desired. In this study, the validity of a method incorporating the partial crack surface contact was confirmed to account for the effect of residual stresses. When the crack surfaces are fully closed at minimum stress intensity, K_min, the conventional supperposition technique gives the same results as this method. On the other hand, when partial crack surface contact occurs at K_min with the original crack tip open, the conventional technique gives an unconservative prediction of the actual crack growth rates. It is shown that the physically acceptable solution adopted here should be used in the latter cases.

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This paper presents the numerical analyses of dynamic crack propagation in visco-plastic solids. A tangent modulus formulation based on σ_yd=h(ε^^-vp, ε^^(-^^·)^vp) is used to take into account visco-plasticity. A linear relaxation technique of nodal forces is also employed for the modeling of continuous dynamic crack propagation. The fracture mechanics parameter calculated here is a path independent integral, T*, which is applicable to both quasi-static and dynamic fracture phenomena of non-linear materials. First, a parametric calculation of dynamic crack propagation at a constant velocity in a visco-plastic solid is performed to investigate the high-strain-rate effects on the T* integral and the stress-strain fields near the crack tip. Secondly, a generation phase calculation of an experiment performed by Brickstad is carried out to obtain a relationship between a fracture toughness and a crack velocity.

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The electric potential CT method proposed by the three of the present authors was applied to the quantitative measurement of three-dimensional surface cracks embedded in steel plates. The values of the electric potential on the back side surface or those on front and back side surfaces were computer-processed by an inverse analysis scheme to identify the location and shape of cracks. As an inverse analysis scheme, "the least residual method" was used, in which observed potential values were compared with those computed by the boundary element method for various assumed cracks. Cracks were determined efficiently by using a hierarchical analysis scheme which involved two-dimensional scanning inverse analyses and following three-dimensional inverse analyses. The location, shape and size of three types of cracks, i.e., a semi-circular crack, a semi-elliptical crack and an asymmetrical crack, were determined with good accuracies, demonstrating the usefulness of the electric potential CT method.

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The present paper is concerned with the transient thermal stress in a transversely isotropic infinite solid containing an annular crack with heat exchange on the crack surface. It is very difficult to obtain the analytical solution for the temperature field so that the finite difference method with respect to the time variable only is introduced. Thermal stresses are analyzed by means of the transversely isotropic potential functions method. The numerical calculations of the stress intensity factor were carried out for a graphite which belongs under transverse isotropy. The effects of the Biot number and size of the annular crack on the stress intensity factor are shown in the figures.

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In this paper, we obtain an asymptotic solution of wave propagation in an inhomogeneous elastic half-space due to a surface source. It is assumed that shear modulus varies with depth as a probability density function of normal distribution. To solve the problem, we apply double integral transforms which are the Laplace and Fourier transforms to the displacement, and the inversion is performed by Cagniard's technique. Numerical computations are carried out in detail and show the effect of the inhomogeneity to wave propagation phenomenon.

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This paper treats an optimal heating problem for transient thermal stress in a long circular cylinder so as to determine the temperature of the surrounding medium under prescribed mechanical boundary conditions. In the present investigation, the Laplace transform is used, and the exact solutions for the surrounding temperature and thermal stresses are obtained. The numerical results for the temperature and thermal stresses are shown in figures.

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The effects of stress and temperature on ultrasonic velocities are studied experimentally in order to establish the acoustoelastic law applicable to thermoelastic stress analysis. A specimen for uni-axial tensile test is prepared from a rolled plate of S45C, and the sing-around method is used to measure the round-trip time of ultrasonic waves incident normally to the specimen. Since Salama et al. proposed a non-destructive method for measuring residual stresses based on the stress-dependence of velocity change due to temperature, particular attention is paid to this effect, and two kinds of experiment are carried out to confirm it quantitatively. At first, velocities of longitudinal and transverse waves are measured by varying the temperature under several constant uni-axial stresses, and it is confirmed that the velocity change due to temperature depends linearly on stress. Then the velocities of three waves are measured by varying uni-axial stress under several constant temperatures, and the velocity change due to stress is shown to be linearly dependent on temperature. From both results, the stress-temperature coefficients of velocities are determined together with the acousto-elastic constants and temperature coefficients of velocities, and are compared with those obtained by Salama et al.

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It is important to get reasonable design indications for the joint structures of FRP with metallic materials. In this paper, a stress analysis system, which consists of FEM code, preprocessor and postprocessor, has been developed to design the joints. The stress distributions of a joint can be easily calculated by using this system. The elastic stress analyses of the metal-FRP single lap joints have been carried out to study the influences of the materials and sizes of the joints on the stress distributions. The stress concentrations at the end of the adhesive layer are much affected by the adhesive modulus and length of bond. The experimental results about the joint strength have been explained well by the calculated maximum equivalent stresses which arise at the end of the adhesive layer. The developed system is a useful tool for the design of bonded joints.

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Plane-wave propagation in a particle-reinforced composite medium with interfaces was studied for both compressional and shear incidences. The composite medium contains a random distribution of same sized spherical inclusions with elastic properties different from those of the matrix. The interface is assumed to be a thin layer of the same thickness with nonhomogeneous elastic properties which separates the inclusions from the matrix. The scattering of plane elastic waves by a spherical inclusion with an interface is analized and the results of the single scattering problem are applied to the wave propagation in the composite medium. Numerical solutions for some practical materials are carried out and the effect of interface properties on the scattering cross sections and attenuation coefficients of energy is shown graphically.

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This paper is concerned with the wave propagation in a sandwich structure bar, the free end of which is struck in the direction of the length by a rigid hammer. The bond layer in subjected to a dynamic shearing strain by the resulting elastic waves, which are generated in both the facing and the core by the longitudinal impact. In taking note of the fact that the magnitudes of the axial strains in the facing and the core as well as the shearing strain in the bond layer depend greatly on the modulus of rigidity of the bond layer, the modulus of rigidity of the bond layer was estimated by comparing the calculated values of the ratio of the axial strain in the core ot that in the facing with experimental values. As a result, the values of the modulus of rigidity estimated by this method for two different sandwith structures bars almost agreed.

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The deformation and strength of tubular shaft joints having various adhesive thicknesses were investigated analytically and experimentally. The strain distributions of the joints with two different adhesive thicknesses under the combined tensile and torsional loads were analyzed using the finite element method. The analytical strain distributions coincided approximately with the experimental results. On experimental stress-strain curves of the joints, it was observed that the initial fracture occurred at the edge of a coupling before the joint was completely broken and that the initial cracking stress of the joint with thinner adhesive was smaller than the joint with thicker adhesive. However, the effect of adhesive thickness on the final strength was little in the case of the adhesive bonded joints of tubular metal shafts. The strength of the joints was estimated by applying the strength laws of carbon steel, the adhesive layer and their interfaces to the calculated stress distributions. The predicted results were in good agreement with the experimental results.

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For polymers, in general, the effects of hydrostatic pressure on mechanical properties are considerably different from those for metals : the yield stress and elongation at fracture have been reported to change with hydrostatic pressure to various degrees, depending on temperature and strain rate. Results of tension tests on PVDF under pressures up to 392 MPa, at temperatures up to 90°C, and with strain rates up to 1 s^-1 are reported in this paper. As pressure increased, the yield stress increased and the elongation decreased ; as temperature was raised the yield stress became lower and the elongation higher. The brittle-to-ductile transition was observed near 30 MPa. Empirical formulas for the stress-strain curves were obtained in the post yield region. The glass-transition temperature Tg of PVDF was found to be -35°C. When the pressure was raised from 300 to 400 MPa, Tg shifted to 35°C.

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In this paper a fracture problem in unidirectionally fiber-reinforced composites containing a T-shaped crack at the interface is considered. The T-shaped crack consists of an interface crack and a crack perpendicular to the interface. A system of integral equations is formulated based on the two-dimensional elasticity and Fourier transforms. The integral equations are evaluated by a numerical method using only the Gauss-Chebyshev integral formula, which was developed by the present authors in the last paper. First, the numerical results are compared with the previous results for a T-shaped crack in an homogeneous material, verifying the present method to be highly satisfactory. Next, three kinds of stress intensity factors (SIF), such as Mode I SIF of a perpendicular crack and Mode I and II SIF of an interface crack, are presented for Glass/Epoxy, Carbon/ Epoxy and Tungsten/Copper composite systems with various geometrical parameters.

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The extraction of heat energy from hot dry rock masses in the earth's crust has received wide attention. In the geothermal energy extraction system of this type, heat energy is recovered by circulating water through artificial cracks created in the hot dry rock masses. The present paper is concerned with the theoretical evaluation of water loss through a prefractured plane intersecting an artificial crack. Firstly we derive the equation of continuity in terms of the water pressure in the prefractured plane and the aperture. By solving the equation by means of the difference method, the influences of the tectonic stress, water pressure in the artificial crack and topography of the fracture surfaces on the water loss from the artificial crack are evaluated for no heat extraction. Secondly we discuss the water loss during heat extraction. It is found that the influence of the heat extraction on the water loss is negligibly small.

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Recently, the authors have derived new types of path independent integrals in which the theoretical limitations of the so-called J integral are overcome. For elastodynamic crack problems, a path independent J' integral which has the physical meaning of the energy release rate was derived. Later, the J' integral was extended to a more general form of path independent integral T* which is valid for any constitutive relation under quasi-static as well as dynamic conditions. In this paper, the T^* integral in a compact tension (CT) specimen for elastoplastic dynamic fracture testing was analysed using an efficient nonlinear dynamic finite element method. The T^* integral exhibits excellent path independency despite the impact loading and large plastic deformations. This indecates the validity of the T^* integral as a fracture parameter in nonlinear dynamic fracture mechanics. This paper also shows the possibility of experimental measurement of the T^* integral.

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This paper is concerned with the dynamic fracture behavior of anisotropic plates with a mixed-mode crack by means of the dynamic photoelastic method using a high speed image converter camera. A rectangular plate is made of fiber reinforced plastic with an inclined edge crack parallel to the fiber direction. According to examinations, the static stress intensity factor and the dynamic stress intensity factor of the tensile stress was required, and was compared with the results for an isotropic plate by changing the fiber direction, and with an increasing crack length.

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In this paper, the methods using thick shell elements to compute the nonlinear fracture mechanics parameters, the J-and J^^^-integrals, are discussed for the through-wall cracked shell problems. To verify the accuracy of the methods, the fracture parameters are calculated for circumferentially through -wall cracked SS 304 piping. The results are shown to have good agreement with the referenced values. Finally, the analysis of crack propagation is performed for circumferentially through-wall cracked SS 304 piping subjected to bending load. Applicability and accuracy are demonstrated by comparing with the experimental results.

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Fatigue crack growth rates under elastic-plastic conditions have been reported to correlate well with the J-integral range, ΔJ, evaluated experimentally from load-point displacement using formulae developed for specific specimen configurations. However, the theoretical basis ofΔJ still remains unestablished. In this paper, path-integral expressions ofΔJ and their approximate path-independence in the presence of the effects of strain hardening and crack closure were discussed. Finite element simulations of elastic-plastic crack growth under cyclic loading were conducted. It was found that ΔJ-values evaluated by the path-integral were almost path-independent when the minimum-load level or the crack-opening level was selected as a reference level for the evaluation. The examination of the relationship between ΔJ and crack-tip-opening displacement or strain distribution near the crack tip led to the conclusion that ΔJ evaluated on the basis of the crack-opening level was the most appropriate parameter characterizing the near-tip stress and strain fields under fatigue conditions.

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The influence of notches on static tensile strength was studied for a composite material. Tension tests of notched plate for glass cloth/epoxy laminates have been carried out for a wide range of notch tip radii. All notched specimens failed in a brittle manner through the formation of small deformation near the notch tip. The experiment shows that the nominal stress at failure decreases with decreasing notch tip radius and it approaches a constant value when the notch tip radius is less than about 0.2mm. It has been verified that the maximum elastic stress at the notch tip when the specimen fails is governed by notch tip radius alone, and is independent of notch depth. On the basis of the concept of linear notch mechanics, the experimental results mentioned above can be clearly explained, and the limiting condition for the fracture of notched plates of composite materials is expressed. The condition is the as same as what is expressed in the case of a notched solid polymer.

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The fracture toughness test and the partially loaded and unloaded tests were conducted for Ni-Cr-Mo-V steel at the transition temperature. Stereographic observation of SEM (Scanning Electron Microscope) photographs was conducted on the fracture surface of the test specimen to measure both the amount of microscopic tearing crack extension and the distance from the originating site of brittle fracture, measured from the tip of the tearing crack. Elastic stress distribution around the crack tip was also discussed. It was concluded that the microscopic tearing crack initiates when the stress intensity exceeds the plane strain fracture toughness, and that the originating site of brittle fracture is situated slantwise and forward from the crack tip. The stress intensity of a postulated microcrack ahead of the tearing crack was found to reach the maximum value at this site. The formerly proposed procedure for the modified J_IC test to determine the initiation of the microscopic tearing crack was proven to be effective.

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This paper is concerned with singular stress distribution near a crack tip yielding by two inclined slip planes. Based on the method of eigenvalue expansions of Williams, the mode I near crack tip singular stress field is obtained in the form with an undetermined constant similar to the stress intensity factor. It is found that unbounded stresses occur near the crack tip with the strength of the singularity being somewhat weaker than for the case without slip planes. Finally, in the case of mode III crack, the results from the closed form solution are compared with the present study.

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This paper is concerned with the extension and application of a multiplication factor method to the identification of dominant failure modes in structural systems. First, the multiplication factor method proposed for a simple limit state function consisting of two basic variables, i. e., a resistance and a load, is extended to estimate the failure probabilities of the general cases where the resistance and the load effect are expressed as linear combinations of basic random variables. Second, the proposed method is compared through numerical examples with the advanced first-order second-moment method, and its effectiveness is verified. Third, the multiplication factor method is implemented to the automatic selection of dominant failure modes in structural systems by using the branch-and-bound method. Finally, the validity of the proposed procedure is demonstrated by identifying the dominant failure modes which include the non-normal basic variables.

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This paper is concerned with the dynamic fracture behavior of cracked plate which is made of epoxy resin. A tensil pulse wave, whose height σ and width T₀ are controlled, is generated by an impact apparatus and travels through a plate. The crack propagation phenomenon are analysed by the photoelastic technique using the high speed camera and the crack extension values are measured for the several cases of σ and T₀. The obtained values are compared with the theoretical values estimated by using the dynamic finite element method and applying the maximum stress intensity criterion for this experimental model.

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A formula of finite strain expressed in terms of each distance between Moire fringes is newly deduced which is useful for the analysis of in-plane large deformation. This formula allows us to draw the two-dimensional distributions of Euler-Almansi strain on the flat surface from the measurement of the distances between Moire fringes on the initial and deformed material. The strains thus measured are inevitably total ones (not incremental). A few examples of finite strain distributions measured by this method are demonstrated with respect to flat specimens deformed under uniaxial tension beyond the onset of diffuse-necking.

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The fringe order obtained by the photoplastic test gives important information on the mechanical properties of transparent polymers. However, the effect of viscosity on the fringe order has not been investigated sufficiently. In this paper, the time-dependent photomechanical properties of cellulose acetate was examined by means of the creep test under uniaxial tension. As a result, the creep behavior of cellulose acetate is considerably influenced by both stress and temperature. Moreover, the creep strain and the creep fringe order are described simply by the power-law of time, respectively, and constants of these equations are determined only by the ratio of stress to the yield stress at several temperatures. Finally, the relation between strain and fringe order during creep deformation is equivalent to that under uniaxial tensile loading, which does not depend both on stress and on creep time.

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An investigation concerning the effects of sheet thickness on the in-plane stretch forming limit in 1100 aluminum sheets with thicknesses of 0.5 to 1.0 mm prepared by electro-polishing have been carried out experimentally and analytically. Development of surface roughness is represented by linear relation between surface roughness and effective strain, and both little thickness dependence and little strain ratio dependence are observed. However, the forming limit which depends on the thickness is observed, and less thickness shows less forming limit. Good agreement between measured strains and theoretical ones from modified M-K analysis are obtained. The thickness dependence of a half angle of pointed vertex, θ₀, in Gotoh analysis, assuming that the onset of localized necking in a sheet is the result of a bifurcation from a state of uniform deformation, is introduced. Agreement between measured and theoretical ones from Gotoh analysis are also good and the θ₀-values equal to 70°∼90° and satisfy the relation θ₀=π/2-q₁ε^^-lt;q0> where q₁ and q₀ are material constants.

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Using a polycarbonate specimen, a wedge-type indentator was applied to the straight edge of a semi-infinite plate under a plane strain condition to conduct photo- plastic and Moire analyses. As a result, it was found that the strain distribution at the tip of the indented depth was largely dependent on the shape of the wedge applied.

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The effects of preheating and prestraining, which are the methods of improving the strain sensitivity of foil gauges, on grain nucleation and grain growth were inspected in detail. Based on the test results, applying stress measurement method which takes notice of grain growth threshold to such treated copper foils, the possibility of far more sensitive stress measurement was examined. Preheating completes grain nucleation and prestraining accelerates grain growth respectively. Due to such treatments to copper foil, and with the value of grain growth threshold being lowered, high precise stress measurement can be done under much lower stress amplitude compared with the conventional electroplating method based on the calibration curve.

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In this paper, the method of calculating the lateral deflection of coiled springs caused by parallel compression is reported. When coiled springs are compressed between parallel plates, they are eccentrically loaded. Lowery has given a solution of the lateral deflection of nonparallel compression. Kuhn reported the wobble behavior of the centrally loaded coiled springs. In this study, these two studies are combined by the model of the moving Tip-Contact Point accompanied with the compression. By using this model, the quantities of the lateral deflection can be calculated within not-too-large lateral deflections and compressions.

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In this paper, an automatic sensing system measuring contact pressure distributions is proposed. The sensing material is made of piezoelectric ceramics. To measure electric charge in the material produced by contact pressures, a special electric circuit is designed by using a peak hold circuit. A micro computer (NEC PC-9801) and a multiplexer controller are used to automatically measure the contact pressure distributions. By using the ceramic sensor for 5×5 measuring points, the pressure distributions for several contact problems are measured. The obtained total forces and the pressure distributions are compared with the corresponding acting forces and the theoretical values, From the results, it is recognized that the proposed sensing system is excellent in reliability and durability.

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This paper is concerned with an analytical formulation and a numerical solution of the elasto/visco-plastic problems of multi-layered shells of revolution under asymmetrical loads with application to a cylindrical shell. The analytical formulation is developed by extending the Sanders theory on elastic shells. It is assumed that the total strain rates are composed of an elastic part and a part due to visco-plasticity. The elastic strains are proportional to the stresses by Hooke's law. The visco-plastic strain rates are related to the stresses by Perzyna's equation. As a numerical example, the elasto/visco-plastic deformation of a two-layered cylindrical shell composed of a titanium and a mild steel layer subjected to locally distributed loads is analyzed. Numerical computations have been carried out for three cases of the ratio of the thickness of the titanium layer to the shell thickness. It is found from the computations that the stress distributions and the deformation are significantly varied depending on the ratio.

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