A fatigue crack propagation test has been made on HT 80 and mild steel. Fatigue life and crack through thickness behavior have been studied in detail both experimentally and analytically. The main results obtained are as follows : 1) The fatigue crack shape before through thickness is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using the K value proposed by Newman-Raju. 2) It is found that the crack growth behavior of a back surface after through thickness is unique, and it is divided into three stages, a, b and c. 3) Fatigue crack growth rate at stage b is constant for a wide range, and it is in direct proportion to the nth power of Δσ, where Δσ is the range of stress. 4) The new model is proposed to evaluate the K value after cracking through the plate thickness. 5) By using the K value proposed in this paper, particular crack growth behavior after through thickness can be explained quantatively.

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The crack propagation behavior in fretting fatigue is divided into two stages, namely : the S_I - and S_II - stages. In the S_I - stage, the crack propagation rate da/dN is very high, and decreases to a minimum with crack growth. In the S_II - stage, the da/dN increases monotonicly with crack growth. The interpretation of this kind of crack propagation behavior has been rather difficult with a conventional stress intensity factor. In this paper the stress intensity factors under fretting fatigue stress conditions were calculated by BEM. Then the crack proagation behavior was analyzed by these stress intensity factors. The equivalent stress intensity factor for fretting fatigue K_elf = √(K_If²+K_IIf²), where K_If is the stress intensity factor for mode I and K_IIf is for mode II, was used to represent the da/dN in the S_II - stage. The results agreed well with ordinany, or unfretting fatigue results. The revised equivalent stress intensity factor K_elf*=K_elf·√((a+a*)/a), where a is crack length and a* is the crack length at the end of the S_I - stage, was available to represent the da/dN from the S_I - to the S_II - stage. These results could be widely applied to data for carbon steel and aluminum alloy.

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The ultrasonic isoscan technique using shear waves is employed to monitor the surface fatigue crack growth under a constant stress istensity range. It is shown that this technique has the potential to become an effective tool for quantitative surface fatigue crack growth characteristics. Not only can the three dimensional crack profile be continuously measured with fairly high accuracy during fatigue testing, but this study indicates that the crack tip closure can be detected at the maximum depth point and near the surface. The surface regions under plane-stress conditions are closed for a greater portion of the fatigue load cycle than the maximum depth point under a predominantly plane-strain condition. The plane strain crack tip opening load is smaller than the plane stress crack tip opening load.

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Thermal fatigue tests were performed using straight pipe specimens subjected to cyclic thermal shocks of liquid sodium, and crack growth behaviors were estimated using striation patterns observed clearly on any crack surface. Crack growth rate under cyclic thermal strain reaches the maximum at one depth, and after that it decreases gradually with crack depth. The peak location of crack growth rate becomes deeper by superposition of constant primary stress. Parallel cracks co-existing in the neighborhood move the peak to shallower location and decrease the maximum crack growth rate. The equivalent stress intensity factor range calculated by Walker's formula is successfully applied to the case of negative stress ratio. Fatigue crack growth rate under cyclic thermal strain agreed well with that under the constant temperature equal to the maximum value in the thermal cycle. Simplifed methods for calculating the stress intensity factor and the crack interference factor have been developed. Crack growth behavior under thermal fatigue could be well predicted using numerical analysis results.

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In the previous reports, an experimental method to evaluate the fracture resistance of a stably growing crack by crack energy density was proposed, and its applicability and superiority were shown through the applications of the method to the stable crack growth problems of thin plates and the comparison with the fracture resistances evaluated by the J-integral. In this report, experiments on the stable growth fractures of thin plates are carried out, the fracture resistances evaluated by CTOD and CTOA are obtained, and they are compared with prior fracture resistances evaluated by crack energy density. The results are as follows : (1) Both show a similar tendency in their variations with crack extensions as was expected theoretically. (2) In comparison with the latter, the former are scattered because of the difficulty of the measurement of local deformation around a crack tip. Therefore, the proposed method is superior to the method based on CTOD and CTOA in the ease of the measurement of these quantities necessary for evaluation. The validity of the instability criterion on crack extension proposed before is also shown ion the Appendix.

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A center crack specimen is assumed under plane strain condition to calculate the stress intensity factor. For the viscous lubricant filling in a crack, it is assumed that the pressure rise from the squeeze effect follows the Reynolds equation. In the same way as the infinitely long bearing and infinitely short bearing in the case of sliding bearings, the full Reynolds equation is approximated with a one-dimensional equation. As a result of the squeeze effect of the lubricant, the effective stress intensity factor is lower than the nominal one. In the case of the ratio of the specimen thickness and the crack length filled with lubricant where B/c is smaller than 1/2, the effective stress intensity factor K_γ can be calculated by using the infinitely short approximation. And, where B/c is greater than 2, the infinitely long approximation can be applied. In the region 1/2<B/c<2, the mean value of K_γ along the crack front may be estimated by the infinitely short approximation.

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This paper deals with a two-dimensional stress analysis of adhesive butt joints subjected to external bending moments in order to contribute to an establishment of the fracture criteria of joints. Similar adherends and an adhesive bond are replaced with finite strips in the analysis. Stress distributions in adhesive joints are analyzed strictly by using the two-dimensional theory of elasticity. The effects of stiffness and thickness of adhesive bonds on the stress distributions are shown by numerical computations. For verification, an experiment is performed. The analytical result is in a fairly good agreement with the experimental one. In addition, the analytical result is also compared with the result obtained by F. E. M. in order to verify the stress distributions at the interface. It is shown that they are in a fairly good agreement.

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A numerical method of calculation by the finite difference method to obtain the stress intensity factor at the end of a crack in a rectangular plate was proposed in the previous paper, where only a rectangular domain was treated. In this paper, the above method is extended to solve the problem of arbitrarily shaped domain with curved boundaries, and by this method, the tension problem of a strip plate with an extended circular hole is treated to obtain the values of the stress concentration factor for the case when there is no crack, and those of the stress intensity factor for the case when there are two equal cracks at the ends of an extended circular hole.

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The problems expressed in the title are discussed to validate the constitutive model of cyclic plasticity formulated in the first report. Analytical expressions are first derived for the stress versus plastic strain relation in monotonic simple loading as well as for the saturated stress amplitude versus plastic strain amplitude relations in simple and circular cyclic loadings with constant amplitudes. By use of these results and the corresponding experimental results, a systematic and simple method is developed to identify eight material constants and one material function involved in the proposed model. Then, the method is applied to the type 316 stainless steel used in our previous experiments, and computer simulation is performed. Comparison of the predicted results with the corresponding experiments shows that the proposed model can describe the cyclic-hardening behavior in various proportional and non-proportional loading conditions with constant or variable amplitude with a relatively high accuracy.

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To find some features of the development of cyclic hardening in structural components with areas of strain concentration, detailed and simplified elastic-plastic analyses are performed on an axisymmetric notched bar subjected to axial cyclic loading at the ends. For the detailed analysis, the constitutive model based on the concept of the cyclic nonhardening region is implemented in an incremental finite element method. The model can describe the dependence of cyclic plastic behaviour on the cyclic stress or strain range. The simplified method using the cyclic stress-strain curve as the constitutive relation is applied to the case where the mean value of the cyclic load is nonzero, and its validity is discussed on the basis on the results of the detailed analysis. Moreover, a detailed analysis with accelerated cyclic hardening is performed.

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For the use of a Tip Ball type indenter in the various Rebound Hardness Machines or Methods, it is necessary to investigate the influence of the holding shaft of an indenting sphere on the relative equations of Rebound Hardness. For this purpose, firstly the Tip Ball type indenter's vibratory system is considered and concluded with the vibratory model of one degree of freedom by the theory of vibration, and shown that in this model, if the ratio of natural period of an indenter to the duration time of impact is very small, the movement of a holding shaft is preportional to the impact force. Therefore the energy stored in a holding shaft during impact can be calculated easily, being equal to the total of this energy and the energy of the contact areas of an indenting sphere and a material using Hertz's Contact Law to the rebound energy of an indenter. The equation of the rebound energy of a Tip Ball type indenter is shown. Next, the results of experiments with several Tip Ball type indenters are given and clarify quantitatively that measured values are consistent with the analyzed values within an accuracy of about ±5% and the influences of a holding shaft are larger as the falling height becomes higher, and the material becomes softer. Finally, the above mentioned points of that influence are confirmed for the Hardness Number by the experiment using the indenter of the D type Shore Hardness Testing Machine.

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Volume fractions of α' and ε' martensite phases induced in tensile deformation in SUS 304 steel at temperature ranges from 20°C to -196°C are investigated by X-ray using the multi-diffraction peak method with an Mo-target. The former is presented well with the relation by the shear-band intersection mechanism and the latter with an exponential function of total plastic strain. The experimental plastic strain and flow stress of a dual phase steel at those temperatures are expressed by the variable volume model equations proposed here. The equation of total plastic strain comprises both components of the austenite and martensite phases and the transformation strain which is larger the larger the total plastic strain and the volume fraction of transformation. The equation of total plastic stress comprises both components of the austenite and martensite phases and a small additive component of the ε' martensite rate and a small stress relaxation due to transformation strain in the austenite phase. Experimental data of these strains obtained from the X-ray residual stress measurement at 20°C have shown that the predicted relations agree excellently with the data.

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The yielding of polymers is highly dependent on the hydrostatic component of stress. Polymers can be considered to be isotropic when they have not been cold worked, but to become highly anisotropic when plastically deformed. The work hardening of polymers at room temperature is more extensive than that of metals. These characteristics being taken into consideration on the result of a tension test of a biaxially tensioned high density polyethylen (HDPE) sheet by forging between opposing punches, the slab method is applied to the backward extrusion of HDPE with various extrusion ratios at room temperature. A good agreement is obtained between the theory and the experiments. A consideration of anisotropy is concluded to be important in applying the slab method to polymer forming.

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