Fatigue crack growth behaviors in weld components under compressive cyclic loading were studied. The crack growth rate not only under tensile cyclic loading but also under compressive one can be described quantitatively by the reverse plastic zone size at the crack tip. The reverse plastic zone size was calculated by finite element method taking initial weld residual stress and crack closure into account. Crack growth rate was reduced with its length in a logarithm function because of crack closure. However, the crack tip location finally progressed near the boundary position of monotonic plastic zone.

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The present study investigates plasticity-induced martensitic transformation around a part-through crack in an austenitic stainless steel SUS304 fatigued at room temperature in air. Distributions of α' phase volume fraction ξ_<α'> around a semi-elliptical fatigue crack were measured with ferrite scope. The results were compared with the distributions of vertical magnetic flux density B_z above the crack in the specimen magnetized by a strong electromagnet. It was revealed that the B_z distributions reflected the α' phase distributions around the crack : i.e., the distance between the points where B_z reached the maximum and the minimum values B_<zmax> and B_<zmin> had linear correlations with surface crack length 2α. The B_<zmax> and the B_<zmin> values also showed linear relations with maximum stress intensity factors at the surface tip K_<amax> and at the depth position K_<bmax>. Each relation, i.e., 2α vs. 2l, B_<zmax> vs. K_<amax>, etc. can be represented by a single straight line regardless of R-ratio.

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Concept of "Fractal" can be usefully applied to evaluate the irregularity of geometrical shape, profile of time-dependent phenomena and so on. Three dimensional geometry of fracture surface for any metallic material has such an irregularity which is governed by the fracture mechanisms. Geometrical irregularity of the fracture surface of SUS304 steel failed in the rotating bending was evaluated by means of the fractal analysis. Since the striation on the fracture surface has a significant orientation, anisotropy should be introduce to the analysis. It was found that this kind of anisotropy can be well evaluated by the fractal analysis proposed here.

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In order to deal with many aspects of fatigue crack growth such as constant amplitude fatigue crack growth, small fatigue crack growth, two-step and multiple two-step loadings, the effects of tensile overloads and compressive underloads, and the effect of mean stress on the fatigue limit, there is a need for a general approach which includes treatment of elastic-plastic behavior, the endurance limit, and the development of crack closure. For this purpose the following constitutive relation has been proposed : [numerical formula] where α is the crack length, N is the number of cycles, A is a material constant of dimensions (MPa)^<1/2>, ΔK_<eff> is the effective range of the stress intensity factor, K, ΔK_<effth> is the effective range of the stress intensity factor at the threshold level, K_c is the cyclic fracture toughness, and K_<max> is the maximum stress intensity factor in a loading cycle. An important feature of the relation is that it is dimensionally correct, a requirement long foreseen by such researchers as Frost and Liu. The expression within the second parentheses is included to deal with the contribution of so-called static modes of separation to the overall fatigue crack growth process, i.e., those modes of separation which are not cyclic in nature but are associated with tensile fracture processes such as cleavage and ductile rupture. These modes of separation become more important as K_<max> approaches K_c. Since K_<max>=ΔK/(1-R), where R is the ratio of the minimum to maximum stress in a loading cycle, the effects of R on the extent of static modes of fracture are included in Eq. 1. The expression within the first parentheses deals with purely cyclic fatigue crack growth, and as such deals with fatigue crack growth in the near-threshold range as a well as in the Paris range when the expression within the second parentheses can be neglected. In such a case Eq.1 becomes [numerical formula] Eq. 2 is deceptively simple. In order to make use of it information is needed about the crack closure level, since ΔK_<eff>=K_<max>-K_<op>, where K_<op> is the crack opening level, which under constant amplitude loading conditions is a function of the crack length and R. In order to deal with the important topic of short fatigue crack growth Eq. 2 must be modified to include consideration of (1) elastic-plastic behavior, since the maximum stress in a loading cycle may be a significant fraction of the yield stress, (2) the development of crack closure in the wake of a newly-formed crack, and (3) the role of the endurance limit (Kitagawa effect) in short fatigue crack growth. Ishihara has shown that even in the high-cycle fatigue range over 90% of the fatigue lifetime is spent in the process of growing fatigue cracks. Therefore the integration of Eq. 2 between the limits of the initial flaw size and the crack length at final fracture can lead to a reasonable estimate of the fatigue lifetime. In this presentation a review of the processes leading to the development of Eq. 1 which have taken place over the last fifty years, and illustrations of its use in dealing with fatigue crack growth, will be given.

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Many kinds of high strength steels have been developed and applied to mechanical structures in the variety of industries. If the static strength level is increased, fatigue strength of the material tends to increase. But, the extent of the increase of the fatigue strength depends on the static strength level and the kind of the material. It is usually expected that the notch effect of the fatigue strength becomes sensitive with increase of the static strength. In this study, such a notch effect of high carbon chromium bearing steel was experimentally examined by performing fatigue tests for notched specimens having different stress concentration factors. Thus it was found that the notch effect of this steel is not so sensitive comparing with the usual steels such as carbon steels.

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The paper shows results of fatigue properties and fracture mechanism of a modified 2.25Cr-1Mo steel. In refinery or chemical plants, Cr-Mo steels are used under hot and high-pressure environments. Recently, a new fatigue problem about these facilities becomes important, because number of cycles to failure that should be taken into consideration for maintenance increases over (10)^7. For the ultra-high-cycle fatigue, interior inclusions in materials are dominant factor in fatigue life, but the fracture mechanism is not make clear completely. Results of the elevated temperature ultra-high-cycle fatigue properties are shown. The interior fracture takes place at ultra-high-cycle region, although many cases show no inclusion in origins of the interior fracture. The crack growth life is predicted by using fracture mechanics.

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This report shows results of fatigue properties and fracture mechanism of dual phase stainless steels. The dual plase stainless steels are often used because of advantageous properties of corrosion resistance for seawater, weldability and workability. Recently, a new fatigue problem becomes important, because number of cycles to failure that should be taken into consideration for a maintenance increases over (10)^7. For the ultra-high-cycle fatigue, interior inclusions in materials are dominant factor in fatigue life, but the fracture mechanism is not make clear completely. Results of the ultra-high-cycle fatigue properties are shown. The interior fracture takes place at ultra-high-cycle region. The crack growth life is predicted by using fracture mechanics.

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In order to investigate the influence of loading frequency on the fatigue properties of Al alloy, ultrasonic fatigue tests were carried out for an age-hardened Al alloy, 6061-T6. The results were compared with those of rotating bending fatigue in view points of initiation and propagation behavior of a crack and fracture mechanism. Fatigue life was longer in ultrasonic fatigue than in rotating bending fatigue, which was mainly caused by the suppression of crack initiation. In ultrasonic fatigue, many fatigue voids and cleavage cracks were observed on the fracture surface in addition to the shear mode cracks, striations and dimples, which were typical fracture modes in rotating bending.

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In order to clarify the fatigue behavior in a wide life region, fatigue tests in the life region of N=(10)^3&acd;(10)^9 were performed for high strength steel of SCM435 by means of a multi-type testing machine. Moreover, the statistical fatigue tests were carried out at several stress levels, and the statistical characteristics of the fatigue life distribution were investigated. The origin of fracture was observed using a microscope and the fatigue process was discussed.

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A pulse laser has been used to generate ultrasonic transients in samples of the laser ultrasonic nondestructive inspection. However, it is impossible to excite ultrasonic wave in transparent materials by a pulse laser. In this study, the surface of a transparent ceramic specimen is painted black in order to absorb the laser energy. As a result, heating by pulse laser, the specimen with a black surface band makes the pulse wave. By using the pulse wave, the sound speeds in a transparent ceramic specimen are measured. The experimental results were identical with the results by the ultrasonic pulse method.

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In the present study, a new method of tensile test for small and/or thin specimens was proposed where tensile force was generated in the specimen by the thermal stress between the specimen and the loading plate. The basic mechanism of the method is as follows. Thin notched plate specimen was set on the loading plate and both ends of the specimen were adhered to the loading plate with quick-drying glue. As the loading plate has much higher linear expansion coefficient than the specimen, tensile stress was generated in the specimen with simultaneous heating of the specimen and the loading plate. A strain gauge was also glued on the loading plate in order to evaluate the load acting on the specimen. As all devices can be set on the stage of a microscope, in-situ observation of the plate specimen during tension was realized.

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A new method to evaluate welding residual stresses nondestructivly is proposed. The method is applied to estimate residual stresses in the butt welded two plates. The results show the effectiveness of the method.

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The boundary integral representation for thermoelastic problems involves a domain integral term originated from the thermal strain. Although for two-dimensional problem, this domain integral can be converted into boundary integrals by using an elastic potential, for three-dimension problem, it has not been possible but for isotrpic solids. In this paper, we start from the set of equilibrium equation for thermoelasticity and energy balance equation for steady-state heat conduction to derive the integral formulation. The fundamental solution of the set of adjoint differential equation can be obtained by applying the Radon transform. The final integral representations has no domain integral and can be splitted into one for heat conduction problem and the other for thermoelasticity for general isotropic solids.

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