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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Acoustic Emission (AE) technique have been used to detect cracks and flaws in jet planes, bridges and other structures which consist of metals, polymers, ceramics and composite materials. The sounds from the bones are called also acoustic emissions which are characteristic noises given off by materials when they are deformed beyond their elastic limits. In this preliminary investigation, the formation of microcracks in the third metacarpal bones of horses under compressive, bending and torsional loads was studied. AE signals, characteristic for microcrack formation and/or growth in osteons and Haversian systems of bone were recorded exclusively during the non-linear deformation of bone. AE method can detect smaller bone fracture than ever before and tell more precisely when a bone injury is healed by listening to the bone rather than looking at it with X ray and other medical imaging method.

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Mechanical properties and bone density of bone from the horse were studied. Two kinds of bone samples were used : one was taken from legs of horses suffering in racing (fractured sample) and the other from legs horses which were killed for other reasons (non fractured sample). The dynamic stiffness and tan δ were measured by a viscoelastic spectrometer. A bone densitometer was used in density measurement. No substantial difference in values of dynamic stiffness and density was observed in two kinds of samples. On the other hand, the values of tan δ for the fractured sample were definitely lower than those for the non fractured one. It was inferred that the fractured sample was more brittle than the non fractured sample.

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The S-N curve in axial fatigue of pre-strained 0.45% C steel specimens with a small hole is approximately composed of two straight lines. In the present paper, the physical background of this phenomenon is explained based on the behavior of a small crack expressed by the two crack growth laws corresponding to small large scale yielding.

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In this paper unloading elastic method is investigated by the analytical results based on the D-B model and by the measured hysteresis curve of load-strain. The crack closure behavior is always accompanied with plastic deformation. When the sensitivity of the measurement is not so high as it detect plastic deformation, the hysteresis looks like to be straight in the range where the crack tip is open. In this case, it is difficult to measure the crack opening point from the hysteresis curve. The unloading curve under high accuracy is found to be a "S" shape, and the point of inflection of the unloading curve is considered to be the crack closure point. The crack closure point does not coincide with the opening point. The crack propagation rate under step loadings can be expressed unifyingly by the effective stress intensity range, ΔK^cl_eff=K_max-K_cl, independently of the loading history. Based on the "S" shaped unloading curve, it is shown that the tip of a non-propagating crack does not open even under the maximum tensile load during one loading cycle.

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In order to clarify the fatigue behavior in plan specimens of a flake grahite cast iron (FC25) and a speroidal grahite cast iron (FCD45), rotating bending fatigue tests and optical microscopic observations were made successively on the fatigue process by using the plastic replica method. The main results obtained are as follows : (1) the S-N curve does not indikate the clear knee point in FC25. (2) The knee-point in the S-N curve of FCD45 coincides nearly with the point where a micro crack stops propagating. (3) The fatigue limit, in each case, is determined by the limiting condition for propagation of the micro crack initiating from grahite.

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In this paper, the fatigue fracture process of FRP (SMC) was studied with a special attention to the variation of the stiffness ratio K which takes place during cyclic loading. Experimental results showed that the fatigue fracture process might be devided into the three characteristic stages, that is, (1) First stage (N=1∼N₁) in which K dose not vary irrespective of cyclic loading, (2) Second stage in which the decreasing rate of the stiffness ratio defined by d(K)/d(logN) is constant, and (3) Final stage where the rapid decrease of the stiffness ratio at K_III leads to the final fatigue fracture. Furthermore, examination of scatters in experimental data at each stages by aid of probability plots showed that their distributions are the logarithmic normal ones. Also, it was found that the fatigue strength of SMC might be given by three characteristic parameters of N₁, d(K)/d(logN) and K_III.

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Fatigue crack growth tests were performed on grain-oriented 3% silicon iron in a high-resolution, field emission type scanning electron microscope, using a specially designed servo-hydraulic fatigue loading system, and direct, real time observations of a growing fatigue crack were made. Both microscopic and macroscopic crack growth directions were found to change with growth rates, indicating that there exists close interrelationship between fatigue crack growth rate and growth mode. A simple fatigue crack growth mechanism was proposed to explain the interrelationship.

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The corrosion fatigue crack initiation life is not affected independently by each stress rising time t_R and stress holding time t_H, but by the sum of the t_R and t_H, that is, by stress frequency, f=1/(2t_R+t_H), On the other hand, the corrosion fatigue crack propagation life is influenced independently by t_R and t_H. The t_H characteristics shows the transition behaviour from the cyclic dependent mechanism into the time dependent mechanism. The crack propagation life occupies major part of fracture life. The fracture life law diagram plotted by the fracture time t and fracture cycles N, as normalized stress corrosion life t_scc, and corrosion fatigue life (cycles) N_CF(t_H=0), respectively, shows approximately the same curve with repect to the parameter t_R.

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The deformation and strength of single lap joints having different thickness of adherends were investigated analytically and experimentally. The strain distibutions of the joints of carbon steel bonded with epoxy resin under tensile shear loads were analyzed by the finite element method. The strength of the joints was predicted by applying the strength laws of adherend, adhesive layer and their interfaces to the calculated stress distributions. The calculated results of the strain distributions in the joints were in good agreement with experimental results. The predicted strength values of the joints coincided approximately with the measured values by experiments. On the basis of the obtaind results, the effect of the adherend thickness on the joint strength are discussed.

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This paper deals with the stress concentration analysis of 60°V-shaped or partially-circular double edge notches in an infinite strip under remote in-plane bending. The stress field induced by a point force in a semi-infinite plate is used to solve these problems. The present results for semi-circular notch are in close agreement with other reports. The results calculated on the 60°V-shaped notches show that the Neuber formula gives an underestimated stress concentration factor in about 9% for a wide range of notch depth. However, in case of blunt notches, the Neuber solution of deep hyperbolic notches still gives a sufficient accuracy in engineering use. In addition, the stress concentration factors of 60°V-shaped notches are also represented by diagrams for wide use.

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This paper is concerned with the elastic-plastic analysis of an infinite plate with an elliptic hole. The method of analysis is the body force method extended to the elastic-plastic problems. In this method the solutions are obtained by superposing the stress fields of a pair of point forces in an infinite plate with an elliptic hole so as to satisfy the constitutive equation. The main results obtained are as follows : (1) If the notch root radii ρ and the maximum elastic stresses σ^e_<max> =K_tσ_∞ (K_t : stress concentration factor, σ_∞ : stress at infinity) in several notches are equal respectively, the projected lengths of the plastic zone are nearly the same. (2) When σ^e_<max>/ σ_s =1.3-2.0 ( σ_s : yield stress), the ratio of the projected length of plastic zone under plane strain condition to that under plane stress condition is about 0.5. (3) The elastic-plastic stress and strain at the bottom of a notch are almost determined by the maximum elastic stress σ^e_<max> alone.

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An X-ray fractographic study was made on the fatigue fracture surface of the structural steels with various strength levels. An emphasis was put on examining the effect of strength level on the residual stress and half-value breadth on and under the fracture surface. It was found that the residual stress on the fracture surface was controlled by K_max in a low K_max or ΔK region (Region I), while it was controlled by ΔK rather than K_max in a high K_max or ΔK region (Region III). It was also found that another transitional region (Region II) was observed between these two regions in SNCM 815 steel. An explanation for all these behavior was discussed by a proposed model. The distribution of the residual stress and half-value breath under the fracture surface was found to be useful for estimating the value of K_max, although the distribution itself was strongly influenced by strength level, particularly the work-softening behavior, of the materials.

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We have measured the tensile fracture properties of the TiC coated SUS316L stainless steel, applying the stress perpendicular to the plane of interfaces between the coating and the substrate. The fracture of the as grown or non-annealed specimens occured within the TiC layer, and took the form of partial fracture surfaces of small circular areas below about 2mm in diameters. The tensile surfaces of the TiC coated specimens after vacuum annealing at about 1373K(1100°C) showed arciform curved fracture surfaces which are understood by a statics consideration taking into account of the maximum stress plane theory and the residual thermal stress. The strengths of non-annealed and annealed specimens are 34.4MPa {350kgf/cm²} and 30.2MPa {308kgf/cm²} respectively, expressed as Weibull's 50% fracture stress.

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The author has previously presented the design method for a toroidal shell-type shock absorber for use in radioactive material shipping casks. In this paper, the effects of the shock absorber on the slump of lead in the cask body composed of three layers of steel-lead-steel after 9 m accidental falls are described. Two small models with and without the shock absorber were tested and the difference in their respective slumps was shown. To analyze these results, the friction between the steel and lead layers, and the structural stiffness of the lead layer were investigated. Impact analyses by the use of a one-dimensional lumped-mass nonlinear spring system showed that the slump is greatly influenced both by the relative rigidity of the lead layer to the shock absorber and by the above mentioned friction. Experimental results from a 1/4 scale model of the 100 ton cask were also compared with the results of these calculations.

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The static tensile testing of notched flat bars of polycarbonate, polyvinylchloride and polymethyl methacylate has been carried out for a wide range of notch radii and notch depths. Sharply notched specimens of PC and PVC failed in brittle manner after the formation of a small crack at the tip of plastic zone. Bluntly notched specimens of PC and PVC failed in fully ductile manner with large shear bands. All specimens of PMMA failed in brittle manner. The predominant factor for determining the fracture mode of ductile to brittle transition is the notch root radius in the case of a constant thickness. Experimental results were discussed in terms of the maximum elastic stress at the notch root from the standpoint of linear notch mechanics. For specimens failed in brittle manner, it is shown that the maximum elastic stress is the one-to-one correspondence to the notch root radius, and is independent of notch depth and plate thickness. The fracture criterion of notched flat bars mentioned above holds commonly for PC, PVC and PMMA.

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The maintenance of structures has now been accepted as the problem of rapidly growing importance, because structures are being operated for a much longer period of time than ever before and their operating conditions are becoming more and more severe. Although maintenance work might be formalized in their fundamental procedures, most of the work involved are difficult to put into proper form or perspective. Therefore, to perform good maintenance, wide variety of knowledge and experience is called for and what is just as much important as deep knowledge and experience is the adequate decision making as to what kinds of knowledge or experience should be applied. As the problem of maintenance is thus too much complex, an interactive decision support system for the application to an oil storage tank has been developed. What differentiates our system from others is that our system is programmed mainly using Prolog to cope with the nondeterministic and ill-formed nature of the problem. The effectiveness of introducing logical programming technique has been verified through development of the system and TSS sessions.

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The effect of uncertain stacking sequence on static response of fiber reinforced plastic laminated plate is estimated based on the stochastic finite element method. The variation of the stiffness matrix of the laminated plate is evaluated by means of Taylor series expansion with respect to the probabilistic variables representing the fluctuation of orientation and layer thickness. The second order perturbation technique is applied to the determination of the deterministic term and rates of change of unknown displacements up to the second order. Numerical analyses are carried out in regard to rectangular Boron/Epoxy laminated plate under compression. The expectations and variances of deflection and stress are computed with the aid of the second order approximation by taking all the probabilistic variables as uncorrelated Gaussian. It is shown that the orientation is more influential on the response fluctuation than the layer thickness.

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Uncertain eigenvalue problem of vibration is analysed by means of the stochastic finite element method. The fluctuation of stiffness of composite laminated plate is formulated in the form of Taylor series expansion with respect to probabilistic stacking sequence. The uncertain eigenvalue problem is solved by use of the stochastic finite element method in the case that the entire plate thickness remains constant. The second order approximation is employed to evaluate the expectations and variances of the eigenvalue and eigenvector under the assumption that the variables standing for uncertain orientation and layer boundary coordinates are Gaussian . Numerical analyses deal with the vibration of simply-supported Graphite/Epoxy plate. The sensitivity of the input stacking sequence and the correlation coefficients are evaluated quantitatively.

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In order to solve slender surface crack problems by boundary element technique, stress-type singular element is introduced to the programme, and a new method combining displacement and stress solutions is proposed to calculate stress intensity factors. The results show that the present approach gives accurate and stable apparent stress intensity factors F(r) near crack tip.

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