A fatigue notch factor, β, is usually greater than 1. However, it has been reported that β is smaller than 1 in the specimen with a blunt notch. For this problem, rotating bending fatigue tests of S 20 C specimens with a blunt notch were carried out. From the observations of the slip-bands and the micro-cracks on fatigued specimens, it can be concluded that the statistical factor is the cause of β<1, although Cazaud et al pointed out that the phenomenon (β<1) is caused by the stress relief due to plastic deformation near the notch root.

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A failure assessment diagram to assess fatigue fracture was developed. The basic approach was similar to the two criteria (brittle fracture and plastic collapse) method known as the CEGB R-6 failure assessment diagram for ductile fracture. Here, the method was modified by incorporating the concept of effective crack length proposed by Haddad instead of using the Dugdale model. The relation between the fatigue limit and the threshold stress intensity factor for the short-cracked specimen can be rationally predicted by the proposed method. It is shown that the coupled failure assessment diagram for fatigue and ductile fracture is especially useful for assessment of the flaw tolerance as well as the margin of the safety of the structure. Further fatigue data accumulation will be needed to construct an accurate fatigue failure assessment diagram.

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The characteristics of fatigue limit and non-propagating cracks for smooth and pre-cracked specimens were examined by varying the stress ratio (R=-1, R=0) and the pre-crack length in a carbon steel, STS 42. The maximum stress at fatigue limit for the specimen with no cracks or with a short pre-crack is lower at R=-1 than that at R=0. As the pre-crack length of the specimen becomes longer, the difference between these two decreases. Judging from the dependence of R and the pre-crack length on the length of the non-propagating crack and from the observation of the crack closure behavior of the non-propagating crack, fretting oxide induced crack closure triggered by the roughness induced crack closure has an important role in determing the length. The fatigue limit estimated from the threshold stress intensity for a long crack is considerably higher compared with those for a smooth specimen and a specimen with a short pre-crack. The growth characteristics for a non-propagating crack are quite different between points near the specimen's surface and those of deepest penetration.

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Characterization has been made of crack initiation life, propagation life and total life, respectively, under high temperature creep, fatigue and creep-fatigue interaction conditions for notched specimens of SUS 304 stainless steel. The main results are : (1) The equation for crack propagation life are derived. (2) Crack propagation life is well in accord with the thermal activation equation. (3) Crack propagation life and total life of the notched specimen are well characterized by the temperature-time equivalent parameter T(ln t+C) which looks like the Larson-Miller parameter in the case of the rupture life of the smooth specimen. (4) For prediction of the remaining life in the crack initiation stage, a new method is proposed by using relative notch opening displacement (RNOD).

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In this paper, we snow that creep crack propagation life is controlled by the size of the micro cracking region formed before crack initiation. Since, for a circular notch, the stress concentration factor is small compared with that for a V type sharp notch, the size of the micro cracking region is much larger than that for a V type sharp notch. So the creep crack propagation life becomes very short. These micro cracking regions are formed due to concentrated plastic deformation. But the relative notch opening displacement RNOD_c=Δφ_i/φ_o(Δφ_i=φ_i-φ_o, φ_i is the notch opening displacement at the crack initiation, φ_o : Initial notch opening displacement) is the accurate parameter of crack initiation, independent of such different creep crack propagation characteristics.

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The crack initiation and growth behavior of Ni-based heat-resisting alloy was investigated in a vacuum environment at 1073 K using double edge notch test specimens, with varying holding times T_h at maximum stress during the cycle. The results showed that the crack growth rate could be evaluated by the C^*-integral because of the good correspondence of the crack growth rate and the notch opening displacement rate in the case of T_h≥50 s ; however, the crack growth rate did not correspond to the deformation of the test specimen in the other range of T_h. Relative notch opening displacement at the crack initiation, RNOD_c, indicated almost constant value and agreed with the results of SUS 304 stainless steel, except for the fatigue region.

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The effect of stress hold time t_H and stress rise time t_R on corrosion fatigue crack growth rate is studied in the range from f=6.1×10^-1 Hz to 4.63×10^-3 Hz. In high frequency region, crack growth rate is almost cycle dependent against frequency as affected by t_H. As t_H increases, time effect becomes more and more remarkable. On the other hand, under corrosion fatigue for t_H=0, crack growth rate is both time and cycle dependent in wider range of frequency, da/dN is formulated as a function of t_R and t_H.

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A program of creep-fatigue interaction tests was conducted in order to evaluate a criterion for failure taking into account the detrimental effect causing by the time dependent process. From the test data on commonly used high temperature materials for gas turbine and diesel engine in air, hydrogen gas and corrosive ash, we proposed the life estimation method under the combined creep-fatigue loadings. This method based on liner cummulative creep damage expressed by the equivalent hold time is stress dependent having nothing to do with loading patterns. We confirm from this method the correlation between experimental data or available data in literatures and estimation is quite good for a several type of loadings. Our experiments are unnecessary the complicate testing for obtaining the material constants but only require the conventional simple low cycle fatigue tests with the effects of hold time inserted at peak strain or stress and creep rupture tests.

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In the primary piping systems of nuclear power plants, many valves with bellows in their seal systems are used in order to prevent the leakage of high-pressurized and high-radioactive coolant. The Ω-bellows for high-pressure valves hold rings in them in order to heighten their compressive stiffness and reduce stresses. The contact and frictional effects between the bellows and the rings prevent their stress analyses. In this paper, we analysed stresses in Ω-bellows using the finite element program applicable to contact problems, and then estimated fatigue strength for 2 types of load histories. The comparison with the results of fatigue tests shows that the locations of fatigue cracks can be predicted by the analysis.

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A analytical and experimental study of the deformation and strength of tubular shaft joints of carbon steel bonded with epoxy resin was conducted. The joints of two different types were studied changing the coupling shape ; one with a tapered coupling and the other with the straight coupling having a identical outer diameter with the shafts. The strain distribution calculated using the finite element method was in close agreement with experimental results. It was observed by the experimental stress-strain curve of the joint that the initial fracture occurred at the edge of a coupling before the joint was completely broken and that the initial cracking stress was much smaller than the final fracture stress. It was found that the effect of the dimension of internal diameter on the shaft strength was remarkable in the shaft with a tapered coupling but the effect was little in the shaft with a straight coupling, and the effect was more noticeable under the tensile load than the torsional load.

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Load-controlled fatigue crack growth tests were carried out on two kinds of steel, SM 50 A and S 35 C, under constant amplitude loading and repeated two-step loading over a wide range from the linear elastic region to the post-yield one; and crack closure was investigated by using the mini computer-aided unloading elastic compliance method. In the case of SM 50 A at the stress ratio R=0, ratcheting deformation took place remarkably under the post-yield region and affected crack growth behavior. However, it was found that this effect could be explained by considering the maximum J integral, J_max, and further, that the crack growth rate under variable amplitude loading could be well predicted by the linear summation rule of crack growth by using √(EΔJ/(1-J_max/C)) instead of ΔK_eff as the fracture mechanics parameter. In the case of S 35 C at R=-1 where only cyclic plastic deformation was observed, the J integral range, ΔJ, was found to be a good parameter in expressing the fatigue crack growth rate under constant amplitude loading. However, under repeated two-step loadings retardation of crack growth at a high load level was observed, even concerning the ΔJ.

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Rotating bending fatigue tests were carried out on plain specimens and specimens with a small blind hole of an annealed 0.42% C steel in air and in oil, and the small fatigue crack initiation and growth behavior in both test environments were examined based on successive surface observations using the plastic replica method. Fatigue strength in oil is higher than that in air. The main reason is that the earlier fatigue crack growth is suppressed by the isolation of the atmosphere due to the existence of oil.

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Fatigue crack growth threshold and closure behavior of a low carbon steel with two different grain sizes were investigated both at room temperature and 300°C. Emphasis was placed on examining the effect of fracture surface roughness and oxide products on crack closure. Crack closure was strongly affected near the threshold by the amount of oxide products on the fracture surface. The fracture surface roughness, however, had little effect on the crack closure, even when many oxide products formed on the fracture surface at 300°C. The value of the effective stress intensity factor range at threshold, ΔK_{eff, th}, was found to increase with increasing material structural size and also with test temperature.

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The rain flow method for counting fatigue damage was applied to predict microcrack propagation life under varying strain amplitudes. Low-cycle fatigue tests were conducted on a medium carbon steel under block-random and pseudo-random strain cycling as well as constant strain cycling. Through continual observation of the microcrack initiation and propagation behaviours of plain specimens and holed specimens with a small drilled hole, the results obtained are summarized as follows : (1) For a microcrack propagating under varying strain amplitudes, a fatigue damage calculated by means of the rain flow method can be fairly well correlated with a cycle ratio under constant strain amplitude. (2) The rain flow method is shown to be suitable in predicting microcrack propagation life as well as in evaluating fatigue failure life. (3) The essential conditions for Miner's rule to hold under variable strain cycling conditions are that the microcrack propagation law shows a relation of the linear type, dl/dN=Cl, and that prior fatigue damage hardly influences the subsequent microcrack growth rate.

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Ceramics are typical brittle materials and generally have a wide spectrum of strength. Therefore, we tested almina ceramics with comparatively narrow spectrum in three degrees of purity. The results show that purity influences the strength characteristics and crack behaviors of almina ceramics in bending tests at elevated temperatures, in rotary bending fatigue tests, in alternating tangential force tests and in fracture toughness tests.

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Tensile tests of a high strength steel were made on specimens having a circumferential notch. The values of the notch root radius and notch depth were varied over a side range. All the data were examined based on the concept of linear notch mechanics. For the present material, it is considered that the load for the static tensile fracture of structures can be estimated approximately by linear notch mechanics.

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A cylinder loaded with equal internal and external pressure bears without failure. While unloading only the external pressure rapidly, the cylinder fractures dynamically under the internal pressure which is greater than that of the atmosphere. In our experiment, the mediums giving rise to internal and external pressure were nitrogen gas and turbine oil respectively. A hollow cylinder of graphite was used as the specimen, and the relation between internal gas pressure at the fracture of the cylinder and the number of fragments fractured at the longitudinal section were obtained. It was shown that the analytical explanation coincides with the experiment.

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The behaviour of surface residual stress relief and lattice defect density with mechanical vibration in FC25 Cast Iron has been experimentally measured by means of X-Ray diffraction. When the vibratory stress amplitude added to the residual stress is more than 0.025% offset stress in the specimens, more residual stress and lattice defect density is relieved simultaneously. When the value is smaller than the added value, residual stress and lattice defect density are not relieved simultaneously.

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A J-estimation formula in the fully plastic regime was developed for mode III cracks emanating from notches. Power-law stress-strain relations were assumed. From examination of analytical stress and strain solutions of notches under longitudinal shear, it was found that the stress and strain distributions in the neighborhood of the notch root are approximately expressed as a function of the maximum shear stress τ_max (or the maximum shear strain γ_max) at the notch root and the notch root radius ρ, for nonlinear-hardening materials as well as for linear elastic materials. Based on this fact, the following J-estimation formula was proposed, which predicted the J-value of short cracks at notches : J=(π/2)(πn/2)^(n-1)(2n-1)τ_maxγ_maxc/(1+kc/ρ) where n is the strain-hardening exponent, c is the crack length, and k is a coefficient expressed as an increasing function of n. The accuracy of this formula was demonstrated by finite element J-integral analyses for elliptical notches with mode III cracks.

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Crack growth behavior of hydrogenated type 301 austenitic stainless steel was investigated. Hydrogen was cathodically charged at elevated temperatures in molten salt. Crack growth tests were made under cyclic loading at various temperatures between -10°C and 100°C. Accelerated crack growth rates were observed under all the temperatures tested, but the growth rates themselves were influenced by test temperature. The most accelerated crack growth rate was observed at an intermediate temperature of around 60°C. This result indicated that a threshold amount of hydrogen must be necessary at a propagating crack tip in addition to the formation of a certain amount of α' martensite to cause hydrogen embrittled accelerated crack growth. Fractographic study revealed that a transgranular quasi-cleavage pattern was dominant on the fracture surfaces of hydrogenated specimens tested at 60°C.

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The purpose of this paper is to ascertain the mechanical condition and the microstructural aspect of a crack growth in structural steel when an impact load is imposed on it. Impact tensile experiments were carried out using precracked specimens at 77 K. And the effect of superposition static pretension was also examined at room temperature and 77 K. The effect of static and impact stresses on crack growth is discussed, based on the stress intensity factor (K_I)_pre and the dynamic stress σ_cd at the moment of precrack growth. The summation of both effects is expressed by D_f, and it increased with the increase of (K_I)_pre when static prestress was applied at room temperature. On the other hand, D_f decreased with the increase of (K_I)_pre when static prestress was applied at 77 K. In addition, when only an impact load was applied to a specimen, D_f was smaller for shorter length specimens and for larger values of a/W, where a and W are the precrack length and the half width of a specimen, respectively. The size of the plastic region near the prearack tip was measured after fracture, and was independent of the loading type and about three times the grain diameter. The distribution of dislocations near the precrack tip by TEM was observed after fracture. This results showed the different aspects for impact fracture and impact fracture under static pretension.

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The line-spring model of Rice and Levy is incorporated into a boundary element program for 2-dimensional elastic stress analysis to analyze the stress intensity factor of cracks in 3-dimensional structures. The line-spring boundary element method is very economical, since it enables 1-dimensional analysis of cracks in 3-dimensional structures. The stress intensity factors are obtained for several numerical examples using the line-spring boundary element method, and comparisons are made with the available literature solutions to check the accuracy of the results.

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We analysed stress intensity factors for chevron notched bend specimens using the three dimensional boundary element method and compared this results with another ones analysed using Bluhm's slice model. Stress intensity factors were evaluated in two ways as the functions of crack length ; one is maximum values at the crack end and the other is average values by the energy method. Both average stress intensity factors evaluated by BEM and the slice model show good agreements. On the other hand, the maximum stress intensity factor is about 9 % higher than the average stress intensity factor at each minimum value. The distributions of stress intensity factors along the crack front were also evaluated for several crack lengths.

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A theoretical basis is investigated for the extrapolation techniques of determining crack tip stress intensity factors. The extrapolation technique proposed by Chan et al. is based on the first three terms of the asymptotic expansion of crack tip stress or displacement (i.e., containing γ^-1/2, γ⁰ and γ^1/2 for stress, containing γ^1/2, γ and γ^3/2 for displacement), and the second term equalling zero is the absolute requirement of straight line extrapolation. From this viewpoint, the conditions for which the extrapolation technique can be available are presented for the problems of Mode I only, Mode II only and the mixed Mode condition. Improved extrapolation procedures are presented in the case when the crack face is subjected to arbitrary tractions. These theoretical results are confirmed by use of the boundary element method (BEM) analysis for center cracked plate problems of Mode I only and mixed Mode conditions.

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In a spline shaft or a screw which is acted upon by the torsion mement, excess shearing stresses are induced by the stress concentration at the bottom of the groove or the root of a thread. Concerning not only the boundary but any point on the cross section of the curvilinear polygon, the general formulae for torsional shearing stress are theoretically deduced. Consequently, the formulae are applied to the cross section of the spline shaft and, as a special case, they are applied to the cross section of a screw thready by regarding the screw section approximately as a limacon curve.

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Analyzing the stress distribution of an elastic body to which an impact force is applied on its boundary is one of the most interesting problems in the engineering field of machine elements strength. But owing to the absence of a useful and easy method to analyse the stress distribution of arbitrary shaped elastic body, it is hard to analyze the strength of machine elements to which an impact force is applied. So firstly we should derive an easy and useful method and then analyse the stress distribution of some machine elements. This report derives an easy method which uses the complex stress function. Using this method, it well be easier to assess the strength of machine elements.

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This paper describes a three dimensional finite element analysis by the supercomputer and its application to surface crack problems. For surface cracks, calculations take a lot of time for the elastic-plastic, dynamic or crack extension problems, and sometimes they are beyond the abilities of the current main frames. So, the authors have developed a three dimensional finite element code FEM 3 D to analyze such complicated and time consuming problems. FEM 3 D uses 20 and 15 node isoparametric solid elements and the skyline method as the solver. For the elastic analysis of a surface cracked plate, FEM 3 D showed sufficiently high computing speed.

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The feasibility of the proposed Electric-Potential CT Method for detecting three-dimensional cracks was studied. This method uses techniques of inverse analysis, by which observed values of electric potential distribution on the surfaces of a cracked body are computer-processed to detect cracks. Two schemes were examined. In one scheme called the Inverse Boundary-Integral-Equation Method, boundary element equations were solved for values of the electric potential and flux on the unprescribed boundaries. Cracks were identified as flux-free boundaries. In the other scheme called the Least Residual Method, boundary element analyses of the electric potential were made for various assumed crack shapes, and the results were compared with the observed values. the least residual criterion was introduced to find the most probable crack shape. Numerical simulations of crack shape identification were made for a rectangular surface crack, a rectangular internal crack and an L-shaped surface crack. The results demonstrated the versatility of the Electric-Potential CT Method.

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To investigate the effect of hydrostatic pressure on the fracture toughness of boron steel and aluminum alloy, the compact tension test based on ASTM standard is carried out under pressure up to 400 MPa. The displacement at the crack initiation is detected by an electric potential difference method under pressure. The elastic-plastic fracture toughness J_IC increases with increasing pressure. The phenomenon of the increase of fracture toughness due to pressure is confirmed by measuring a critical stretch zone width of boron steel. The experimental J_IC values are compared with the J integral values analyzed by FEM.

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The growth of a circular hole in thin sheet material and its fracture mechanism were investigated with respect to its strain hardening exponent under a tensile test to obtain basic knowledge about a void growth and its fracture process in ductile material. The growth shape of the hole was measured exactly, and its deviation from an ellipse was found to be less than several percent. Their axial ratio and areal ratio increase almost linearly with the plastic strain before a crack is formed. The growth rate of d(a/b)/dε(a, b ; major and minor semi-axes of the ellipse, ε; strain) is shown to increase with a decrease in the strain hardening exponent. The growth rate is larger the bigger the pre-strain and, accordingly, the fracture strain is smaller the larger the latter. The results of the finite element method in a plane stress condition give good agreement with the experimental results. The theoretical relations for a plastic material by McClintock are also fairly consistent with the above results.

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The reflection and interference of stress-waves play important roles in dynamic cases. It is very desirable to study the time variation of the stress distribution, and especially the value of dynamic stress concentration factors, in three-dimensional solid bodies. Hence, we have analyzed the stress propagation and the dynamic stress concentration phenomena around a spherical cavity in a cylindrical bar by utilizing the strain gage method, the dynamic photoelastic method and also the finite element method. Emphasis was laid on the dynamic stress concentration analysis of bodies with inner cavities such as those often found in welded parts or castings. The simulation was achieved by using test models of composite specimen geometry in which a spherical cavity was introduced by a variation of the sandwich method. We found that the three-dimensional dynamic stress concentration factors obtained by the present three methods are all near the static stress concentration factors already reported for similar specimen geometries.

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This research treats two problems related to the bending of an annular plate. The first problem is that of an annular plate subjected to an eccentrically concentrated load. This problem is solved by our method, proposed formerly, for the bending problem of a circular plate with one or two eccentrically situated circular holes with free edges. The calculated results for eight cases of boundary conditions are indicated is diagrams. The second problem is that of an annular plate subjected to an asymmetrical-linearly distributed load. This problem is solved by the method of superposition, and correct solutions of closed forms are obtained for eight cases of boundary conditions.

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In this paper, we consider the problem of thermal stresses in an infinite plate with two circular inclusions. The steady state of temperature is induced by a pair of heat sources (positive and negative sources) placed on the x-axis. The analysis is developed by Airy's stress function in the case of generalized plane stress and by applying the bipolar coordinates. The method of perturbation is adopted for the determination of the unknown coefficients involved in the solution. Numerical calculations of the stress distributions along the main parts of the infinite plate and the inclusions are worked out in some detail. The maximum stresses on the common boundaries are also calculated and compared with the available results.

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This paker deals with the transient thermal stresses in a finite circular cylinder constrained at both end surfaces and subjected to axisymmetric temperature distribution on the lateral surface. The thermoelastic problem is formulated in terms of a thermoelastic displacement potential and three harmonic stress functions. Numerical calculations are carried out for the case of the uniform temperature distribution on the lateral surface. The stress distributions on the constrained end and the free suface are shown graphically, and the singularity in stresses appearing at the circumferencial edge is considered. Moreover, the approximated solution based upon the plane strain theory is introduced in order to compare the rigorous one, and it is considered how the length of the cylinder and the time proceeds affect on the accuracy of the approximation.

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Fatigue strength design techniques for spot-welded car body structures are studied. The load carrying property per spot in a spot-welded structure is estimated by the finite element method. The validity of this method is confirmed by fatigue tests of single spot-welded lap specimens and component w\models. Finally, a fatigue strength design procedure for spot-welded car body structures is shown.

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An attempt is made to develop a model of uneven road surface on the basis of two-dimensional filtered Poisson process in order to obtain the power spectra to be employed as the input to structural analysis of automobiles. Double sinusoidal waves are used as the shape function, whose number of the occurrence, amplitude and half wave length are random variables of the Poisson process. The power spectra and coherence function are obtained analytically by use of the said shape function. Numerical examples show that the Poisson process can simulate the road surfaces referred to in the ISO DP 8608 by means of proper choice of the process parameters and that the coherence function regarding the right and left wheels is small in the case of the isotropic and homogeneous process.

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In this paper, dynamic interaction phenomena on solid and liquid interfaces are discussed. Axisymmetrical responses of an infinite circular cylindrical shell perfectly filled with liquid are analyzed, based on Flugge's theory for a circular cylindrical shell and the potential theory for the ideal fluid under conditions of the impulsive external band pressure given on the outer surface of the shell. The deflection and the moment of the shell and the pressure in the fluid are evaluated by using the numerical inversion of the Laplace transformation method. The approximated solution for the shell with an equivalent mass on it is analyzed and is evaluated, abased on the solution for the solid and liquid interaction.

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In this paper, the relation between the impact load history and the impacted point on a cantilever beam is theoretically investigated and the results are verified by the experiments. In the theoretical analysis the impact load history is obtained by the use of the classical beam theory and Hertz's law of contact under the condition that steel bars or balls strike a semi-infinite beam in the vicinity of the free end. In the experiment the impact load history is measured by the use of a piezoelectric trans-ducer mounted on the cantilever beam, or by a strain gauge cemented on the bar. As a result, it is shown that the impact load history is much affected by the distance from the free end to the impacted point, and the theoretical results are in good agreement with the experimental results.

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A circular hydraulic bulge test of Zn-Al eutectoid-base alloys having various initial grain-sizes has been carried out at different temperatures. The experiment has been performed to find out the region of a combination of temperature, stress and grain-size, which is closely related to superplasticity, where a large deformation arises under an equi-biaxial tensile stress condition. Then the superplasticity-related region obtained has been compared with that obtained by a uniaxial tension test. It appears that the extent of grain-size where superplasticity arises under the biaxial stress is wider than that observed under the uniaxial stress .The values of the bulge factor are always larger than 1.0 within the superplasticity-related region. The microstructure near a polar region of the bulge after deformation is very similar to that observed in the tension test.

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Usual grid method has such serious defect that the stress solution depends on the path for numerical integration of stress derivatives. In this study, a new method which derives stress distributions independently of their numerical integrations is devised for steady state axisymmetric extrusion ; that is, on every small plastic region the mean stress distribution is assumed with second order equation with respect to γ and z, and considering the continuity of the mean stress, the unknown coefficients of all of those assumed equations are evaluated with the least squares method of mean stress derivatives. The above Lagrange's method is applied to this procedure, together with the unit division method, for shortening the calculation time, in a way which is similar to that used in the finite element method. As a result, the stress solutions can be uniquely determined in a short calculation time.

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This paper describes the experimental results and the theoretical analysis concerning the size effect on yielding in a perforated mild steel strip under tension. The main conclusions obtained are as follows : (1) There are two modes in yielding ; one is the whole section yielding and the other is the local yielding. (2) The yield point of the strip is influenced not only by the ratio of the diameter of the hole to the width of the strip, but also by the width itself. We made the theoretical analysis by taking the effect of the surface layer into account and it was shown that the analytical results coincide well with the experimental data. Moreover, we pointed out that the thickness of the surface layer is 0.08 mm which corresponds to about 6 times the grain size of the material.

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The whitening phenomena of injection molded polyoxymethylene was studied, and the influence of molecular weight on the whitening and the fracture were investigated. A high molecular weight material showed whitening at rather low stress, and its fracture toughness was fairly high, compared with low molecular weight materials. With the aid of an image processing technique, the length of the cracktip whitening area was measured clearly and continuously with the increase of the tensile load, and the cracktip area of both high and low weight materials were approximated with the Dugdale model. The experiments and theory showed good agreement and the measurement of the cracktip opening displacement (COD) was also found to be in agreement with the calculation from the Dugdale model.

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The whitening behavior of injection-molded POM of two kind of molecular weight was investigated by the measurement of trasmitted light intensity variations under constant crosshead speed condition, constant load condition, and cyclic strain condition. Under constant crosshead speed condition, despite the dependence of stress-strain relation on the crosshead speed and molecular weight, whitening-strain relation showed little diference. Under constant load condition, although whitening-time relation and strain-time relation were dependent on molecular weight, the whitening-strain relation showed little diference. Above results indicate that strain would be the main factor of whitening. Under cyclic strain conditions, the degree of whitening decreased with the reduction of the strain. Higher molecular weight specimens had a higher recovery ratio of whitening, but they showed the reduction of elongation capacity by the cyclic strain, compared with lower molecular weight specimens, which had higher crystallinity.

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For presenting technical data, Saint-Venant torsion problems of I-beams, channels and T-beams (referring to JIS G 3192) are treated by the indirect fictitious-boundary integral method.

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In this paper, Saint-Venant torsion problem of square tubes in consideration of the length of the side and the curvature of the fillet is treated. For this analysis, the indirect fictitious-boundary integral method is used.

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