Tomokazu Matake

Bio: Tomokazu Matake is an academic researcher. The author has contributed to research in topics: Stress concentration & Stress (mechanics). The author has an hindex of 3, co-authored 8 publications receiving 277 citations.

An Explanation on Fatigue Limit under Combined Stress

Abstract: Fatigue crack initiates in the slip band and exists also in it near fatigue limit; many slip bands are apt to appear in the direction of the maximum shearing stress; crack propagates by the normal tensile stress; the maximum shearing stress on a plane at fatigue limit is reduced by the effect of the normal stress on the same plane. From these results of the experiment, a new criterion is proposed, which coincides with the Gough's empirical formula for the brittle materials under combined stress. As the plane of the maximum shearing stress is varied by the various combination of torsion and bending, the isotropic material should be used in the combined stress experiment. In this paper, the results of experiments on three isotropic and one anisotropic materials are discussed and compared with the criteria proposed up to the present.

Fatigue Strength of Notched Specimen under Combined Stress

Abstract: From the fatigue test of notched specimens of isotropic 70:30- brass, under bending, torsion, and combined stress state of them, a simple criterion for the slip-band crack initiation has been obtained. In spite of the complexity of the triaxial stress state below the notch root, only two stress components, the maximum shearing stress τmax and the normal stress σn acting on a particular slip plane, are responsible for initiating slip-band cracks. Using the averaged stress values over the half-grain-size depth below the notch root, linear sum of them, τmax + a·σn, acts just as the torsional stress in unnotched specimens. At the fatigue limit, therefore, the value for any combined stress state coincides with the torsional one. This relation is more general than the one which has been obtained before for unnotched specimens because of including the case for the unnotched as an extremely shallow notch.

Effect of Side Grooves for Three-point Bending Fracture Toughness Specimens : Three-dimensional Elastic-plastic Finite Element Analysis

Abstract: Elastic-plastic stress states on three-point bending fracture toughness specimens are analyzed by the three-dimensional finite element method. Effect of side grooves on the stress state around the crack tip is discussed on specimens about 30 % side-grooved in U, V, and slit types comparing with a regular flat specimen. Side grooves restrict the plane stress type deformation, which is commonly observed near the side face of a flat specimen. Consequently, over 80-90 % of the thickness of the side-grooved specimens, practically even distributions of the stress intensity factors, plastic zone geometries, crack tip dilatant stresses, and three-dimensional J integrals are achieved.

Growth of Ring-shaped Edge Cracks under Reversed Torsional Fatigue

Abstract: Mode III fatigue crack growth was studied using cylindrical specimens with ring-shaped edge cracks under reversed torsion. Cracks grew locally in Mode I making small branches but their macroscopic growth direction was perpendicular to the specimen axis. The crack depth was successively estimated by the compliance calibration method and the growth rate of torsional cracks was related to the applied stress intensity factor range ΔKIII. In torsion, friction must be considered together with mutual sliding of pre-fatigue crack surfaces. Consequently, the applied torsional torque should be modified in evaluating the effective stress intensity factor. Effect of the surface friction on the stress state around the crack tip was examined by an elastic-plastic finite element analysis.

Temperature Variation associated with Stable Crack Growth and the Fracture Toughness Value

Abstract: The temperature of specimens during the fracture toughness testing, varies due to the heat generation associated with a plastic flow near the crack tip. The temperature has been analyzed using a simple heat balance model and the generated heat has been calculated. Heat generation rate changes in a clear slope corresponding to the stable crack initiation. Hence, this phenomenon can be used for detecting the stable crack initiation. J-integrals were estimated based on the heat variation for three kinds of steels and were found to be close to the ones evaluated by the R curve method.

A Review of Critical Plane Orientations in Multiaxial Fatigue Failure Criteria of Metallic Materials

Abstract: The paper presents a review of multiaxial fatigue failure criteria based on the critical plane concept. The criteria have been divided into three groups, according to the fatigue damage parameter used in the criterion, i.e. (i) stress, (ii) strain and (iii) strain energy density criteria. Each criterion was described mainly by the critical plane orientation. Multiaxial fatigue criteria based on the critical plane concept usually apply different loading parameters in the critical plane whose orientation is determined by (a) only shear loading parameters (crack Mode II or III), (b) only normal loading parameters (crack Mode I) or sometimes (c) mixed loading parameters (mixed crack Mode). There are also criteria based on few critical plane orientations and criteria based on critical plane orientations determined by a weighted averaging process of rotating principal stress axes.

A bi-parametric Wöhler curve for high cycle multiaxial fatigue assessment

Abstract: This paper presents a method for estimating high-cycle fatigue strength under multiaxial loading conditions. The physical interpretation of the fatigue damage is based on the theory of cyclic deformation in single crystals. Such a theory is also used to single out those stress components which can be considered significant for crack nucleation and growth in the so-called Stage I regime. Fatigue life estimates are carried out by means of a modified Wohler curve which can be applied to both smooth and blunt notched components, subjected to either in-phase or out-of-phase loads. The modified Wohler curve plots the fatigue strength in terms of the maximum macroscopic shear stress amplitudes, the reference plane - where such amplitudes have to be evaluated - being thought of as coincident with the fatigue microcrack initiation plane. The position of the fatigue strength curve also depends on the stress component normal to such a plane and the phase angle as well. About 450 experimental data taken from the literature are used to check the accuracy of the method under multiaxial fatigue conditions.