The fatigue crack behavior of a silicon carbide was tested at an elevated temperature. The fatigue phenomenon is observed in air, but not in a vacuum. The crack growth process consists of three stages. In the first stage the crack shows a rapid growth rate, but decreases in the second stage. In the third stage, the growth rate continues to decrease under low stresses, but increases again, and the material begins to fracture under high stresses. The fatigue lifetime is subjected to the time of the second stage, in which the well-known power-law relationship between the crack growth rate and the stress intensity factor dc/dt=AKⁿ does not hold. Furthermore, the cyclic fatigue lifetime does not depend on the number of cycles but does depend on the loading time.

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The drilling pipe suffers from rotating bending stress, accompanied by axial stresss and torsional stress, It has been reported that the initiation of a crack is sulphide nonmetallic inclusions which also have a relation to the crack propagation rate. Fatigue tests have been performed in air, dripping corrosive liquids with pH 7 and pH 13 under a rotating bending load at the cyclic frequency of 300 rpm. The materials used in these tests were four kinds of normalized and tempered (NT) steels and four kinds of quenched and tempered (QT) ones whose sulphur content changed from 0.001 to 0.050 %. Corrosion fatigue strength was evaluated on corrosive liquids and sulphur content and fractographic observation has been also discussed. It was confirmed that the fatigue strength at pH 7 is not dependent on sulphur content, though the number of pits and cracks increase according to the sulphur content. In addition, the number of pits would be dependent not only on the amount of MnS

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A local strain approach has been studied to predict the fatigue strength of spot welds on thin steel structural members under bending. The strains on the inner and outer surfaces of the sheet near a nugget, where a fatigue crack would appear, were measured. The results showed that the strain on the inner surface is greater than that on the outer surface, and that the position of the sheet is under the combined load of an axial force and a bending moment. The fatigue tests of smooth specimens were performed under the same load condition as the position of sheet on the member using a developed combined loading system. It was confirmed by comparison of Δε-N_f diagrams that the strength of smooth specimens under the combined load makes an accurate prediction of the strength of spot-welded members in terms of the local strain.

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The growth of short surface cracks in a high-strength low-alloy steel, JIS SNCM439, was examined under cyclic loading in deaerated aqueous 3.5 % NaCl. Under cyclic loading, the crack 'growth rates were controlled by the stress intensity factor independent of crack size, when the value maximum stress intensity factor, K_max, was larger than the stress corrosion cracking threshold, K_ISCC. In this region of stress intensity factor, both short and long cracks grew along prior austenite 'grain boundaries. For K_max<K_ISCC>, short surface cracks grew up to 10 times faster than long cracks the same stress intensity factor. The size effect was attributed to the difference in the crack growth ode, i. e., short surface cracks grew in an intergranular mode along prior austenite grain boundaries, while long cracks propagated by a transgranular mode. The short crack size, therefore, accelerated crack growth when K_max<K_ISCC>.

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The effect of heat treatments (as cast, T4, and T6) on the fatigue crack growth resistance of a squeeze-cast Al alloy, AC 4 CH, is investigated using plain specimens subjected to rotating bending. The principal results obtained are summarized as follows : (1) The fatigue strength of the squeeze-cast Al alloy is nearly equal to that of the wrought Al alloy. (2) The effect of heat treatment on the fatigue strength is smaller than that on the tensile strength. (3) An increase in tensile strength resulting from heat treatment brings an increase in resistance against both initiation and propagation of fatigue cracks.

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The LBB (leak-before-break) design is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, LNG carriers and various other ;structures. In the LBB design, it is necessary to evaluate precisely the lifetime of steel plate. 'Furthermore, the change in crack shape that occurs during the propagation after through thickness s of paramount importance. For this reason, in a previous report, the authors proposed a simplified evaluation model for the stress intensity factor after cracking through thickness. Using this model, he crack propagation behavior, crack-opening displacement and crack shape change of surface-cracked smooth specimens and surface-cracked specimens with a stress concentration were evaluated quantitatively. The present study was also done to investigate the fatigue crack propagation behavior of surface cracks subjected to combined tensile and bending stress. Estimation of fatigue :rack growth was done using the Newman-Raju formula before through thickness, and using formula (7) and (8) after through thickness. Crack length a_T at just through thickness increases with increasing a bending stress. Calculated fatigue crack shape showed very good agreement with )experimental one. It was also found that particular crack growth behavior and change in crack shape after cracking through thickness can be explained quantitatively using the K value based on Eqs. (7) and (8).

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The approach of microcrack growth law-aided low-cycle fatigue life evaluation, derived on a cyclically stable material in a previous paper, was applied to cyclic hardening and softening types of materials. Cyclic strain controlled low-cycle fatigue tests were conducted on WT 80 and SCM 435 H steels (cyclic softening type) and SUS 304 steel (cyclic hardening type). Either constant or two-step train amplitude was selected in experiments. To simulate microcrack growth, notched specimens with a small drilled hole of 40 μm in diameter were used as well as unnotched specimens. It was found rat the previous method is essentially applicable for all materials tested. That is, the microcrack growth rate is proportional to crack length and fatigue life predicted on the basis of the microcrack growth law agrees fairly well with the measured value. Cyclic softening and hardening behaviours which afftect the cyclic stress-strain relationships, as well as cyclic strain-induced martensitic transformation observed on SUS 304 steel, hardly influence the microcrack growth.

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The problem of interface cracks along the interface of an elliptical rigid inclusion is considered. 'he inclusion is assumed to be bonded to the interior of an elastic infinite medium, except for some portions which are regarded as interface cracks. The stress intensity factors are presented in the closed forms with integral terms which cannot be evaluated analytically in the problems with two or lore cracks. Evaluating the terms numerically for the cases with two interface cracks, the effects of the length and location of the cracks and the geometry of the inclusion on the stress intensity factors are presented.

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Residual stress in IC silicon chips molded using epoxy resin is discussed. Stress-sensing chips were used for the measurement of residual stress which developed during assembly processes for IC plastic packages. It was found that the stress field in a silicon chip was almost equal to the plane stress field. The thermal expansion coefficient of molded resin had a strong effect on the chip stress. Thermal stress fields in the IC plastic packages were analyzed by the finite element analysis method. It was found that the FEM analysis could predict the stress fields in packages with about 10% error. The stress change in IC chips was measured under the reliability test condition for IC packages. It was found that both temperature cycles and moisture in the package had an effect on the stress change of IC chips. But the stress did not change in a room temperature environment.

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A stress analysis of a transversely isotropic short rectangular prism subjected to partially distributed loads on two end surfaces is presented in series form. The generalized Elliott's solution previously proposed by the authors is used for the analysis. Boundary conditions for shearing stress on the six surfaces are exactly satisfied. Numerical results for stresses in magnesium and cadmium crystals, as examples of transversely isotropic materials, as well as in an isotropic material are presented. The effect of anisotropy on the stresses is investigated through a comparison with the stresses in the isotropic material.

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In this paper, stress and strain distributions in the internal part of a winding paper roll are derived theoretically. In this theory, it is assumed that the winding roll paper is cylindrically anisotropic continuum elastic body. For the cases with various anisotropic parameters and various winding ratios, stress and strain distributions are calculated and buckling :conditions are considered. In the experimental model, the strains in the internal part of the winding paper roll are measured during winding. The results are in good agreement with the theoretical results.

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The present paper is concerned with a one dimensional generalized thermoelastic problem based on Lord and Shulman's theory. This theory is for dynamic coupled thermoelasticity which includes the time needed for acceleration of a thermal wave, and is based on the modified Fourier's law of heat conduction and the Duhamel-Neumann relation. A generalized thermoelastic problem in an infinite body with a spherical hole is analyzed by means of the Laplace transform technique. The boundary condition is that a constant heat flux is flowing into the infinite body and the displacement at a spherical hole is constrained. Because the effects of thermal and stress waves may well be short-lived, the inverse Laplace transforms are obtained in an approximate method which is valid for small time values.

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Green's functions in a closed form are shown for axisymmetric torsional body force problems of m elastic layer on an elastic half space. A Green's function is defined as a solution to the problem of an elastic layer on an elastic half space subjected to a torsional body force acting on a circle in he interior of the layer. As a special case for Green's functions, we can obtain Green's functions for torsional body force problems of (i) an elastic half space, (ii) an elastic thick plate, and (iii) an elastic layer on a rigid foundation. A general method of solution is presented for torsional body force problems of an elastic layer on an elastic foundation. Green's functions, mentioned above, are obtained by applying the general method of solution. As an example of the application of Green's functions we consider torsion of a hemispherical rigid body embedded in an elastic layer on an elastic foundation. Numerical results for the problem are shown.

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A solution is presented to a doubly mixed boundary-value problem of an elastic layer indented y a circular rigid punch, which rests on a rigid base weakened by a cylindrical hole coaxial with the punch. The problem is reduced to the infinite system of simultaneous equations in which both the normal displacement on the lower face of the layer and the contact pressure under the punch are expressed as appropriate series. Numerical results are obtained for the distribution of contact pressure under the punch, the surface deformation outside the punch, the normal displacement in the hole and the total load on the punch. The effect of the presence of the hole on the stress field is discussed.

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This paper describes a finite element which has a curved and twisted centroid in space. The element is of an isoparametric type, thus it has variable curvature and torsion in one element. Examples show the application to problems on circular cross sections, however, it is possible to expand these sections into beams with arbitrary sections.

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A dynamic line-spring model is proposed for the simplified analysis of impact response o a part-through surface crack in an elastic plate. Bending of the plate is considered based on Mindlin's theory. Stiffness of the dynamic line-spring is simply evaluated following the static model of Rice and Levy. The procedure for evaluating the dynamic stress-intensity factor K_Id is developed. The response of a semielliptical surface crack in a plate subjected to impact loading at its ends is analysed by using the present model. It is found that K_Id takes its maximum value at the deepest penetration point of the surface crack and the maximum value is much larger than that in the static case.

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CT specimens with different thickness and a CCT specimen are analyzed precisely using the three-dimensional finite element method in the elastic-plastic stress states. The stress and displacement fields at the crack tip are compared with the HRR singular stress field and discussed. It is found that in the CT specimens, the thicknesses are larger than those recommended by the standard of fracture toughness testing ; the stress and displacement fields agree very well with those of HRR fields. For the CT specimen, the thickness of which is a little smaller than the mecommednded value, the HRR field exists only on the inside of the specimen. It is shown that there are no HRR fields in the CCT specimen although its thickness is not small.

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It has previously been shown that crack energy density can be defined in any direction at a crack tip without any restrictions on constitutive equations. The crack energy density, ε_φ, in an arbitrary direction can be divided into the contributions of each mode (ε_φ=ε^I_φ+ε^II_φ+ε^III _φ;ε^I_φ, ε^II _φandε^III _φare the contributions of modes I, II and III, respectively), which can be evaluated by path-independent integrals corresponding to each. These are defined for a completely sharp crack as the limits where the notch root radius ρ approaches zero in a notch model. Therefore, it is necessary to use a notch model with a sufficiently small value of ρ in evaluations of the quantities through FEM. In this paper, ε_φandε^I_φ are evaluated by path-independent integrals through elastic-plastic finite element analyses varying the value of ρ, and we discuss which of ρ should be adopted in evaluations of them. Moreover, by applying these results to an experimental result of ductile fracture under a mixed mode, we show that^I is a potential parameter for expressing elastic-plastic fracture criterion under a mixed mode.

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The load-displacement curve of a set of disc springs shows a hysteresis due to structural damping. A method has been proposed to retard tearing instability of structures such as piping systems, by using the disc spring as a supporting member for the structures. The condition has been described theoretically for tearing instability under structural damping. The slope of the curve in unloading has been shown to be a key parameter for the tearing instability. Tensile testings of racked specimens loaded in series with the spring have shown a tearing instability depending on the structural damping and have verified the condition. It has been proved that the retardation of tearing instability is possible with the use of the disc spring with structural damping.

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In order to investigate the mechanism governing elastodynamic crack curving, a series of fast curving fracture tests were carried out. In the present experiments, high-speed photographs of the caustic patterns for dynamically curving cracks were taken by a laser caustic method which can be quickly synchronized to the initiation of brittle fracture event. The mixed-mode dynamic stress intensity factors were evaluated on the basis of a theory of tics for mixed-mode fast running cracks, which was developed by some of the authors. It found that the magnitude of the mode II stress. intensity factor is closely related to the dynamic crack curving.

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To formulate the constitutive equations for nonproportional cyclic loading, the influence of the preloading on the subsequent loading should be investigated experimentally. In this paper, the stress-strain relations and the equiplastic strain surfaces of the subsequent loading after the cyclic preloading were examined carefully from a combined tension-compression and torsion test with SUS304 stainless steel. Considering the movement of the center of the yield surface after the cyclic preloading, the equiplastic strain surfaces, which have been utilized for the determination of the material constant in the constitutive equations proposed previously, could be represented by the quadratic form of stress. As a result, the computer simulation based on this constitutive equation could accurately describe not only the stress-strain relations, but also the strain paths.

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The main objective of the present research is to investigate the surface-type flow localization in strain rate- and temperature-sensitive materials. A full thermomechanically coupled large deformation simulation of a plane strain compression test of strain rate- and temperature-sensitive blocks has been performed by the finite element method. The effect of the material strain rate and temperature sensitivities, the deformation speed, material characteristics and thermal conductivity on the initiation of surface instability and features of flow localization has been clarified under relatively slow deformation ranging 2×10^-3/s-0.2/s in nominal strain rate.

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A rigid-plastic finite element method which employ stabilization matrices and enables effective and accurate computation was applied to investigation of the effects of strain rate and temperature sensitivities, deformation rate, thermal conductivity, and size on three-dimensional deformation behaviors in blocks subjected to tension. The results clarified that the increase of the deformation rate caused thermal softening and that the displacement at the maximum load point decreased. Futhermore, the load decreased significantly. The size effect should always be taken into account for accurate prediction of the problem, including the heat generation and transfer. Under a relatively low deformation rate, the adiabatic assumption may not provide suitable information on the thermovisco-plastic deformation behaviors. It is also shown that the present results indicate more relaxed deformation than that due to the plane strain approximation.

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A fracture mechanics-based study is presented on delamination of notched laminated beams by a three-point bend test. The model crack is T-shaped ; namely it consists of an interface crack and a notch normal to the beam surface, and the delamination is identified with the extension of the interface crack. Based on the assumption that the specimen behaves like a beam with a reduced section of length of interface crack, the compliance of the specimen is derived by using theory of large deflection of beams, i.e., the problem is treated as that of elastica. The energy release rate and the condition for delamination are then obtained based on the Griffith's energy balance concept. It is found that the form of the delamination condition expressed in terms of the length of the interface crack and the deflection at the point of loading is equal to that derived from simple beam theory.

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A minimum compliance design problem of stiffener shape and layout for the stiffened thin plate structures is treated. The stiffened plate structures are discretized into the isoparametric finite shell elements, and an optimum design technique for the stiffener heights and positions subjected to the total volume is formulated by introducing the design sensitivity analysis. By applying this technique. The optimum distributions of stiffener heights for the square plates loaded uniformly under rigid support of central circular region and fixed supports of four corner points are decided numerically. The optimum stiffener layout and heights of square plate under concentric and eccentric concentrated load are also discussed for simple supports of four corner points.

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This paper deals with the study of strength characteristics and the ply-thickness optimization of multidirectional fiber-reinforced composite plates. Laminates are assumed to be symmetric about the midplane surface and to consist of plies with 0, 90, 45 and -45 degree fiber orientations. A simple transformation was introduced to normalize the loading date and express all of them in the closed tress region. Personal computer programs were prepared to find the optimal combination of a maximum of four ply groups to obtain the maximum strength for a given set of in-plane stresses. Strength discontinuities of multidirectional laminate were considered in the process of optimization. The numerical results obtained using T300/5208 graphite/epoxy comosites showed the highest point, the strength of optimized laminate, to be about six times as high as that of the quasi-isotropic one. Ply thickness ratios of optimized laminate were also found to have many transition points in the tension-dominated region.

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The nondestructive detection of cavities by ultrasonic technique was studied for the assessment of long-term degradation damage of high-temperature components. Focussing on the change of the frequency spectrum of the ultrasonic reflection echo due to cavity nucleation, two physical parameters were proposed to detect the cavity: one was the energy attenuation coefficient, a*, and other was the shift of the gravity center in the frequency spectrum of the ultrasonic reflection echo, Δf^^-*. The experimental result by means of the sintered material involving the internal pore of various volume fractions, which was prepared for simulation of cavity nucleation, showed that a* and Δf^^-* were hopeful parameters for the nondestructive detection of cavites. The theoretical equations for a* and Δf^^-* were also derived by applying the Williams theory for the scattering of ultrasonic wave. It was shown that the theoretical values of a* and Δf^^-* comparatively agreed with the experimental results by means of the above sintered material. Based on the results thus obtained, a discussion was made on both the detection limitation of cavities and the preferable method to improve the detection limitation.

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We previously reported on the flow curve of a SUS 304 stainless steel at different, temperatures, the contributions of two phases varied with strain and temperature. Here, we measure the X-ray residual stresses of two phases. The tensile X-ray residual stress of the stronger phase increases a and then decreases with an increment of strain at 20°C, 0°C and -50°C, and the compressive X-ray residual stress of the weaker phase increases with strain and temperature. Phase stresses are calculated from residual stresses and the volume fractions of two phases using an equation derived The tensile phase stress of the stronger phase increases to a maximum value and then decreases strain increment at those temperatures. On the other hand, the compressive phase stress of the weaker phase increases with an increment of strain. Using these phase stresses and volume fractions of the two phases, the contribution of each phase to the experimental flow curve of this steel is analysed at each temperature. The theoretical results of the above relations are derived using an on for a variable volume model of the dual phase, and experimental results are shown to be, consistent with the theoretical relations.

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An equation for calculating the standard deviation (s. d.) σ_IB of the integral breadth I_B of an X-ray diffraction line is derived analytically. The s. d. (σ_IB represents the size of the variation in I_B which ; attributable to counting statistics. The trapezoidal and Simpson's rules give the same results for both I_B andσ_IB the trapezoidal rule is recommended because it makes for easier calculation. The s. d. σ_IB is given by σ_IB=R/((R-1)√(y_p))√(1/(2R)(nc-I_B)²+I_B²) (1) where R is the ratio of peak to background of the diffraction line, y_p is the maximum count, n is the number of data points minus 1, and c is a step width. The s. d. σ_IB agreed closely with the sample standard deviation obtained in 70 repetitive measurements of I_B. This shows that the s. d. of I_B can e obtained from a single measurement by using Eq. (1).

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The use of pipe flange connections is standardised in the codes of JIS, ASME, DIN and so on. However, these codes are almost entirely dependant on experience, and subsequently some problems concerning pipe flange connections have been encountered. In the Present paper, the distribution of contact stresses which governs the sealing performance is analyzed as a three-body contact problem, using an axisymmetrical three-dimensional theory of elasticity. The effects of the stiffness and the thickness of raised face metallic gaskets on the contact stresses and the effective gasket seating width are shown by numerical calculations. Moreover, stresses produced on the hub, the force ratio (the relationship between an increment of bolt axial force and an internal pressure) and the maximum stress caused in bolts are analyzed. For verification, experiments are carried out. The analytical results are satisfactorily consistent with the experimental results.

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Various kinds of evaluation functions are added to the reliability evaluation system for the ceramic gas turbine 'G-FICES'. Using this new system, fast fracture of multiaxially stressed ceramic structures can be evaluated, considering the aging degradation of the components. Further, fatigue Strength and the effects of proof testing on fatigue strength can be evaluated by bimodal Weibull distribution.

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We propose an analytical model for estimating the elastic modulus of a composite flat bar with a flat braiding structure. This analytical procedure includes two. steps : three-and two-dimensional stress analysis. In the first step, the composite fiat bar is assumed to combine with several local parts which have different fiber weave geometries. The elastic moduli of each local part are calculated by three-dimensional analysis. In the three-dimensional analysis, the fibers in the composite fiat bar are expressed by a network of beam elements. Therefore, it is easy to consider the weave geometries and he dimensions of fibers. In the second step, the elastic modulus of the flat bar is calculated from the elastic moduli of local parts using two-dimensional analysis. The numerical results are compared with experimental data. An excellent agreement is found between the analytical predictions and the experimental data. Moreover, it is clear that this analytical model can estimate elastic modul for different weare geometries, such as those including the middle-end-fibers, if the network and the dimension of beam elements in the first step are changed.

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