In this report, we derived a new theory by combining the previously obtained statistical theory fracture location with the multiaxial distribution function. Using this theory, we analysed not only 3 crack-size ditribution function but also the crack-orientation distribution. Both distribution function are considerably affected by the fracture criteria. Based on the above results, we suggested new proposition to non-destructive inspection of brittle materials like engineering ceramics.

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Recently, fiber-reinforced polymer composites have been used in many fields, and in the bending mode in practical cases. However, few studies for plain-woven fabric composites under bending load have been reported. In this study, the relations between the macromechanical flexural regidity and the volume fraction of fiber, and the type of fiber in the plain-woven fabric reinforced plastic composites under bending load were analysed by 3-D F.E.M. using the smallest unit model of the particular boundary condition. As a result, the following conclusions were obtained: (1) Both flexural rigidity and Young's modulus increase with the increase of volume fraction. (2) Though flexural rigidity is increased with an increase of the distance between the longitudinal and the transverse fiber strand, Young's modulus is decreased. (3) Even if carbon fibers are used as reinforcing materials, the high young's modulus has little effect on the flexural rigidity. (4) The bending moment to the PCM plate is mainly supported by the reinforced longitudinal fiber rovings.

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In composite or concrete structures, to analyze the stress their concentration factor, stress distributions and fracture mechanics under forces by photoelastic experiment, it is necessary to develop photoelastic model materials. Thus the orthotropic photoelastic model material for the transparant-type photoelastic device was developed in this paper it is called Copper Fiber Epoxy Composite and abbreviated as C. F. E. C. It was found that C. F. E. C. as developed in this paper satisfied the properties which photoelastic model material should have. C. F. E. C. has the complete properties of a composite material. It is thought that C. F. E. C. can be applied to both medical engineering for modeling biological tissue and to the aerospace industry as orthotropic photoelastic material.

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Fatigue tests were conducted on injection-molded short glass and carbon fiber reinforced thermo-plastic composites under alternating plane bending stresses. The effects of the matrix, fiber-matrix adhesion and fiber orientation on fatigue strength characteristics were investigated in comparisons with nylon 6 (N 6), polyethersulfone (PES) and polyetheretherketone (PEEK) composites on the basis of the fractographic examinations. The short fiber reinforcement is found to be anisotropic in fatigue strength characteristics. It is indicated that in general, short fiber reinforcements seem to be more effective in improving the fatigue strength for the lower strength matrices, N 6 and PES, but not always for the higher strength matrix, PEEK.

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Rotating bending fatigue tests were carried out for smooth and small notched specimens of NiCrMoV steel, using the large-size turbine rotor shaft of the nuclear generator, in order to statistically investigate distributions of surface crack initiation and growth lives. Most of surface cracks of the smooth specimens initiated at inclusions on the surface. The distributions of the initiation life N_i, the growth life N_p and the failure life N_f determined in this study were expressed as a two-or three-parameter Weibull distributions for the smooth and the small notched specimens. The statistical scatter of the N_i, N_p and N_f distributions increased with decreases in stress amplitude σ_a for the smooth specimens, and the scatter of each life of the notched specimens was smaller than that of the smooth ones. The correlation coefficient of order between N_i, N_p and N_f increased with increases in cycles, but decreased with increases in σ_a for the smooth specimens, and that of the notched specimens was smaller than that of the smooth ones during the early stage of crack growth to less than 1 mm in length.

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Load-controlled fatigue crack growth tests were carried out on two kinds of steels, S35C and SM50A, under repeated two-and three-step loadings in the post-yield region. Crack closure was investigated using the minicomputer-aided unloading elastic compliance method. Crack closure and plastic deformation under varying loadings were found to be affected by load variation and load sequences. However, fatigue crack growth rate under varying loadings where both one-directional and cyclic plastic deformation were observed remarkably, could be well predicted by the linear summation rule of crack growth by using ΔJ* is the J-integral range-pair taking into account one-directional deformation under low-level loadings.

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Smooth specimens and two types of notched specimens were made of high tensile strength steel (HT 60) and were low-cycle fatigued. In the tests, the growth of small surface cracks was monitored by means of replicas. The crack growth rate dl/dN was examined by the strain intensity factor range ΔK_ε. Firstly, the ΔK_ε of notched specimens was calculated from the nominal strain amplitude at notch roots. The dl/dN-ΔK_ε= relation in each type of specimen was approximately expressed by a linear line on a log-log diagram. However, the lines were different from that of smooth specimens, and depended upon the shapes of notches. Secondarily, the maximum strain amplitude at notch roots was obtained by the simple method. The ΔK_ε of notched specimens was calculated from it. The dl/ dN-ΔK_ε relation of notched specimens agreed with that of smooth specimens.

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The interaction of crack propagation on multiple ended fatigue cracks in hybrid structures is examined with the coupled compact tension specimens of 0.45%C carbon steel and A2017-T4 aluminum alloy under high cyclic stresses. The crack propagation behavior of coupled specimens fatigued under the stress ratio of 0.05 and 0.7 is compared with that of single cracked specimen. The deviation of crack propagation rate from the stable relation between the rate and ΔK of a single specimen is found to take place with the difference of crack closure and the onset of the ratcheting extension of specimens. The crack growth acceleration is affected by another specimen coupled because of the incomplete reversal of plastic deformation in ratcheting deformation. Based on the theoretical prediction of an interaction curve for crack growth of a coupled specimen, it is concluded that multiple ended fatigue cracks under high cyclic stresses propagate with a mechanism such that the increment of total strain energy release per cycle in a hybrid body including some cracks is distributed to each crack with the ratio of strain constraint factor.

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In order to clarify the fatigue strength charactaristics of low alloy steels which were strengthed by tempering at low temperature (150∼200°C) after conventional quenching treatment and/or carburizing in generated gas, rotating bending fatigue tests were conducted in laboratory air and dry air using smoothened specimens with 8 mm diameter. The influence of moisture in air was only recognized for the carburized steel. The S-N diagrams of both steels revealed two knees on those curves regardless of the test enviroments and no fatigue limits were observed in the long life range up to 10⁹ cycles (10 months). The reasons were discovered from the results of fractography and the equation proposed by Murakami et al. for the prediction of fatigue limit of steel with micro defects.

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Strength of the stepped-lap bonded joint under tensile shear loading is investigated both analytically and experimentally. The joint used in this study consists of adherends of carbon steel and adhesive of epoxy resin. The strain and stress distribusions are analyzed by applying finite element method on the assumption of elastic deformation. The stress distributions is butt and lap sections are varied remarkably on both edges of steps. The joint strength is calculated by applying strength laws of three kinds of equation to the stress distributions of corresponding parts in the joint. It was predicted that the strength was smaller at the edge of butt section than at lap section in every step corners. The calculated strain distribution and strength of stepped-lap joint coincided approximately with the experimental ones. On experimental stress-strain curves of joint, however, it was observed that the joint was completely broken with the increase of load after the initial fracuture occerred at the edges of butt section.

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The fatigue strength of hard steels is frequently influenced by the existence of nonmetallic inclusions. The statistics of extreme values is useful for the estimation of the maximum or the minimum value in a statistical lot. This method can be also used to estimate the maximum size of nonmetallic inclusions in metals or to estimate the maximum size of grain size in a microstructure. However, since the observation plane does not necessarily coincide with the one which cuts the section of the maximum diameter of the maximum inclusion or grain, the estimation of the maximum values by the statistics of extreme values includes some error. In this study, this error was investigated by measuring the distribution of the size of graphites in a nodular cast iron and also measuring the grain size of a few kinds of steels. Based on the estimated errors, the applicability of the statistics of extreme values is discussed.

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This paper considers the steady-state response of the interfacial contact stress in a bonded two-dissimilar elastic half-spaces to a moving edge dislocation. Two contact conditions, "welded" and "lubricated", are treated and the contact stresses are obtained in a simple closed form. Numerical computations show the effect of the Stonely wave on the contact stress.

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This paper deals with the stress concentration analyses for fillets in a semi-infinite plate, in a stepped flat bar and in a flat test specimen under tension. The stress field induced by a point force in a semi-infinite plate is used as a fundamental solution to solve those problems. The stress concentration factors are systematically calculated under various geometrical conditions. Through the comparison of the present results with the previous research works, it is found that the Peterson's stress concentration chart based on photoelastic tests gives underestimated stress concentration factors by about 10 %. The stress concentration factors of a stepped fiat bar with fillets are found to be almost determined by the results of shoulder fillets in a semi-infinite plate.

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This paper deals with a three-dimensional stress analysis of adhesive butt joints subjected to tensile loads in order to contribute to the establishment of the fracture criteria of joints. Dissimilar adherents and an adhesive bond are replaced with finite solid cylinders in the analysis. Stress distributions in adhesive joints are analyzed strictly by the three-dimensional theory of elasticity. The effects of the stiffness of the adherents and the thickness of the adhesive bonds on the normal and shear stress distributions are shown by numerical computations. The stress singularity becomes large at the corners of the interface of which the stiffness of the adherent is large. It is shown that the fracture begins at this interface. The analytical result is also compared with the result obtained by an experiment concerning strain of the adherents. Both results are in fairly good agreement.

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Small-sized boilers are usually designed based on construction codes for Small-Sized Boilers in Japan. However, on a header consisting of two concentric circular shells and cover plates, which most of the small-sized boilers have, theoretical stress analysis has been hardly investigated. Therefore, there is no formula applicable to the similar type of header in construction codes for Boilers in Japan and ASME Boiler and Pressure Vessel Code. In this paper the analytical method and its usefulness to the similar type of pressure vessel will be shown.

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The elastic effect of graphite on elastic moduli of spheroidal graphite cast iron, that is related to fatigue strength, was studied by theoretical and experimental procedures. The equations for elastic moduli of spheroidal graphite cast iron were obtained theoretically and the elastic moduli and fatigue limits of spheroidal graphite cast iron were measured. The following results were obtained. (1) By the elastic effect of graphite, in the case of spheroidal graphite cast iron, the reduction ratio of the maximum stress of graphite boundary ranged from 1.0 to 1.2. (2) The elastic effects of graphite on the elastic moduli and the fatigue limit are approximately equal. Therefore, the elastic effect of graphite on the fatigue limit can be predicted nondestructively by measurement of the elastic modulus.

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This paper is concerned with a transient plane thermal stress problem in a nonhomogeneous hollow circular plate subjected to unaxisymmetric heating on the inner boundary surface. The nonhomogeneous plate has Young's modulus and thermal conductivity expressed in form of the different power laws of radial coordinate, the coefficient of linear thermal expansion given as an arbitrary function of radial coordinate and the constant Poisson's ratio. The transient nonhomogeneous heat conduction problem is solved by applying the Laplace transform. The associated plane thermal stress problem is formulated in terms of stress function, and the governing equation becomes Euler's differential equation. In the formulation, the single-valuedness of rotation is taken into account by the use of the Michell's conditions, which were derived for arbitrary nonhomogeneous properties by the present authors. Numerical calculations are carried out over the wide range of the nonhomogeneous thermal conductivity, Young's modulus and coefficient of linear thermal expansion.

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This study is concerned with an application of the boundary element method (BEM) to a 3-dimensional thermal elastic plastic creep analysis. The BEM has been applied to 2-dimensional or axisymmetric inelastic problems. Results of these analyses showed an applicability of BEM to inelastic problems, but did not provide a numerical example of 3-dimensional thermal elastic plastic creep analysis. We have already developed a 3-dimensional thermal elastic plastic analysis computer program using BEM, and also some numerical techniques which are valid for an accurate and efficient analysis. In this study, the function of our computer program was expanded to be applicable to 3-dimensional thermal elastic plastic creep analysis. The thermal elastic plastic creep analysis of a thick-walled cylinder was performed to confirm the applicability of BEM.

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A combination of the boundary element method and the finite element method is proposed for calculating the stress intensity factors of two-dimensional crack problems. In this method, finite elements are only allocated near a crack tip and boundary elements are used to discretize the rest of the structure. The virtual crack extension method is applied to the finite elements to obtain the stress intensity factor. The analyses are performed to examine the factors affecting the accuracy of the solution. It is shown from the analyses that we can use large-sized finite elements near the crack tip, and select the crack extension value from the wide range of values.

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A method of the structural synthesis in terms of the boundary element method is presented. The synthesis aims at the shape modification required to decrease the stress concentration in the elastic plane stress state. The method is based on the sensitivities of the boundary element solution and the notion that the objective design is searched as near the baseline design as possible. The effect of indeterminate loading and objective stress is taken into account so that the objective design is obtained with the latitude of shapes. The indeterminacy of the resultant shapes is evaluated in the form of the nodal coordinates taken as the design variables. The numerical examples concerning the flat plates with opening under tensile loading verify the validity of the formulation presented in order to decrease the surface stress near the fillet corner.

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A fracture criterion developed previously for predicting the uniaxial tensile strength of composite laminates containing notches is subjected to further experimental scrutinization. An experimental program is presented which examines the hole size effect in fractures of FRP plates. This is accomplished by obtaining experimental data on glass cloth-epoxy laminates containing through-the-thickness circular holes for a wide range of hole and specimen sizes. In the case that the ratio of hole size to the specimen width is less than 0.25, the maximum elastic stress at the edge of a hole when a specimen fails is governed by the hole size alone, and is independent of specimen width. 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 FRP plates containing a circular hole is expressed. The condition is the same as what is exprssed in the case of FRP plates containing notches.

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In order to examine the applicability of an acoustic emission source wave analysis to the detection and the evaluation of material degradtion, the acoustic emission genarated during fracture toughness test of a hydrogen attacked steel was investigated. AE signals were classified into two types according to their source wave characteristics. One was a signal due to microcracking at the non-metallic inclusions, and the other was a signal due to coalescence of the voids. AE activity of the hydrogen attacked specimen was lowered compared with that of the non-degraded specimen because the fracture of the hydrogen attacked steel was a intergranular fracture caused by coalescence of the micro bubbles on the grain surface and some inclusion had already debonded in the process of hydrogen attack. The formation of the micro bubbles caused the increase of the damping ratio of the AE signals in the higher frequency range and the reduction of the sound velocity.

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This paper describes the experimental results and the theoretical analysis concerning the size effects on fractures of plaster thin-walled and solid cylinders with a transverse hole under compression. The distribution of stresses around the hole is analyzed by the effect of the surface layer. The analytical results coincide well with the experimental data and are concluded as follows. (1) There are two types of fractures, depending on the diameter of the hole, one is the fracture occurring due to the compressive stress and the other is that caused by the tensile stress. (2) The fracture stress of the thin-walled cylinder depends on only the diameter of the hole. (3) The fracture stress of the solid cylinder is influenced not only by the diameter ratio of the hole to the test cylinder, but also by the diameter of the cylinder.

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The constant stressing rate tests of Soda-Lime glass specimens having a controlled surface flaw introduced by Vickers microhardness indentation were conducted by four-point bending of plates (uniaxial stressing) and by concentric ring loading of disks (equibiaxial stressing) under different environments of vacuum, air, and ion exchanged water. The fracture strength at a certain stressing rate became almost greater in the order of water<air <vacuum, and vacuum showed little stressing rate dependence. In both air and water environments, the parameters n for subcritical crack growth were obtained from the stressing rate dependence of the fracture strength. The biaxial stress effects were exhibited only in water, with a slightly lower n value and apparently higher strength observed. Furthermore, the n value in water was higher than that in air, and this behavior was explained by taking the change by stressing rate in the radius of the crack tip blunted in water into consideration.

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In a previous paper, the present authors discussed the path-integral expressions of the J-integral range, ΔJ, and showed that ΔJ-values evaluated based on the crack-opening level was the most appropriate parameter for characterizing the near-tip stress and strain fields under elastic-plastic fatigue conditions. In this paper, finite element simulations of fatigue crack growth in a plate subjected to tension are conducted, to compare the ΔJ-values evaluated by the path-integral with those estimated from load-point displacement by the Dowling's formula, which is commonly used for the laboratory ΔJ-determination. When the crack-opening level is selected as a reference level, ΔJ-values evaluated by using the load-point displacement are found to agree well with those evaluated by the path-integral, and to correlate well with crack-tip opening displacement, for deep cracks but not for shallow cracks. When crack-center opening displacement is used in place of the load-point displacement, a reasonable estimation of ΔJ can be made even for shallow cracks.

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Rice has shown a simplified method for estimating the J-integral for several specimens. Rice formulas have been derived based on the assumption of a deep crack. Ohji has also shown a simplified method for estimating the J-integral from the same assumption. For a CCT specimen, the J-value of the Ohji formula is equal to zero for a linear elastic material. In this study, the necessity of a deep crack for these J estimation formulas and the cause of the above-mentioned irrationality of the Ohji formula for a CCT specimen are analytically studied for two materials; rigid perfectly-plastic and strain hardening plastic. Results show that the assumption of a deep crack is not required necessarily for a rigid perfectly-plastic material and for a strain hardening plastic material when L/W=3 in case of using a load-point displacement and is required for n<3 when a mouth opening displacement is used. Results also show that the Ohji formula is equal to the plastic part of the Rice formula. Based on the results, the Ohji formula for a CCT specimen should be used when the strain hardening exponent is known.

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Time-dependent thermal stress singularities at a semi-infinite crack tip associated with a transient temperature field have been analyzed on an infinite plate with a point heat source near the crack tip. As the heating begins, a mode I singularity increases gradually with time, but, after showing its maximum, decreases to be negative. This singularity variation causes a crack to start growing at some instance, but soon after to stop. That is, crack growth may be controlled, which is desirable for a cutting device for brittle materials. Deflection of a heating point from a crack line results in a mode II stress singularity, which also leads a crack to swerve from the original crack line. In an experiment using glass plates, a crack was successfully controlled to grow and also to branch in any angle toward the heat source as long as the heating location was kept appropriately apart from the crack tip.

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Residual stress induced by sintering or machining has a large effect on the strength of ceramics. The X-ray technique can measure residual stress nondestructively. To determine accurately the stress by X-ray method, it is necessary to obtain experimentally the X-ray stress constant. By using the Gaussian curve methodν, the X-ray elastic constants E and ν, and stress constant K of a silicon nitride were determined together with their standard deviations representing the size of the variability caused by counting statistics. The planes of (323) and (212) were measured with CuKα and CrK α radiations, respectively. The 95% confidence limits of the stress constant were -779 ± 21 and -1027 ± 83 (MPa/deg) for (323) and (212) planes, respectively. The relative errors (standard deviation /measured value) of the X-ray elastic constants and stress constant for the (323) plane having a sharp and symmetrical Kα₁ single diffraction profile were 1.4 %, whereas they were 3.4 to 4.3 % for the (212) plane having a Kα doublet.

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The authors have shown that the stress intensity factor, K, can be analyzed by measuring the distribution of the sum of the principal stresses around the crack tip by an infrared stress measuring device, SPATE-8000. The errors of the measured K-values for CT-specimens are at most 10∼20%, and they decrease with the decreasing amplitude of the applied cyclic stresses. The method has been applied to the measurement of K for a surface crak. Finally, the method for analyzing K₁ and K₁₁ for mixed mode cracks has been proposed.

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In order to develop the shape memory alloy heat engine, basic output power characteristics of three types of heat engines are investigated. As a shape memory alloy, the TiNi alloy wire with an outer diameter 0.75 mm is used. The heat engines employed were the twin crank engine, offset crank engine and simple pulley engine. The results are summarized as follows. (1) The output power of engines increases with the hot water temperature. (2) The range of rotational speed where the output power is maximized is wide. (3) Specific output power is 1∼3 W/g. (4) The maximum output power increases with the number of wire loops of shape memory alloy.

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