In many cathodic protection systems, the electrodes must be located directly on the wall of a structure for various reasons. An effective boundary element method for determining the optimum impressed current and optimum location of the electrode in such a cathodic protection system is proposed in this paper. This problem is reduced to minimize the power supply under the protecting condition that the electric potential of every part of a structure to be protected should be less than some critical value. In order to avoid the remeshing which is necessary in each iteration in the usual optimization procedures, the boundary integral equation is modified in such a way that the design variables become independent of the boundary element mesh. The solution is obtained by using the conjugate gradient method in which the protecting conditions are taken into account by the penalty function method. A few numerical examples are presented to demonstrate the practical applicability of the proposed method.

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Structural evaluation of local wall thinning caused by erosion is important for integrity of a high energy piping system. Acceptance criteria are required if pipe wall thinning is found or suspected. The purpose of this paper is to provide acceptance criteria for local erosion thinning in pipes. The pipe of interest is a STS 42 carbon steel pipe loaded with an internal pressure together with an axial force. The thinned region is characterized by the length, width and depth of wall loss. The length and width correspond to axial and circumferential crack lengths. Allowable combinations of length and width of wall thinning are determined from leak and break behavior of crack growth in pipes. The allowable depth of wall thinning is determined from the local membrane stress rule. Based on the crack growth behavior and the stress rule, the allowable extent and depth of local wall thinning are proposed for carbon steel pipes. Consequently, double-ended fracture and split fracture of the pipe are prevented when the local wall thinning is limited to within the allowable sizes.

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Many studies concerning the effect of prestrain have been performed using mainly annealed steels. However, such studies involving heat-treated steels are very few. In this paper, the effect of prestrain on the fatigue strength of heat-treated 0.45% carbon steel is investigated. Results show that the fatigue limit of smooth specimens decreases (about 5%), although the slight increase in yield stress and tensile strength after prestrain is recognized. Prestrain makes the crack initiation life decrease, but its decrease is not so remarkable. On the other hand, the growth rate of a small crack is fairly accelerated and it is determined uniquely by the term σⁿ_al.

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The fatigue gauge is studied as a sensor for determining the magnitude of the stress or the number of the stress cycles of the machine parts subjected to service loading. This gauge utilizes the surface roughness change of the metallic foil, caused by the slip deformathion during cyclic loading. The purpose of this paper is to clear the effect of temperature and cyclic frequency on the surface roughness of the aluminum foil gauge. It is found that the temperature dependence of the stress required to evolve a certain amount of roughness is the same as that of the critical resolved shear stress of the aluminum. Effects of temperature fluctuation and cyclic frequency are not observed. Based on these findings, a method evaluating the applied stress under fluctuating temperature can be Proposed.

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Rotating bending fatigue tests were carried out on smooth specimens of ferrite-base spheroidal cast iron at room temperature. Initiation and growth behaviors of surface cracks as well as the statistical properties of lives of initiation and propagation were discussed by detailed observation of the specimen surface and fracture surface. Surface fatigue crack initiation was mainly governed by microshrinkage existing just under the surface. A negative correlation between the crack initiation life N_i and the square root of the projected area (√(area)) of the microshrinkage as the initiation sites was found, but the correlation factor between them was very low. Surface cracks propagated with a great deal of branching and coalescence during the fatigue process, and it was found to exhibit the remarkable repetition of increase and decrease in the crack prppagation rate da/dN during the range of small cracks. The distributions of the initiation life N_i, the propagation life N_p and the fatigue life N_f in the main cracks which propagated to 2a=3000μm were well represented by a three-parameter Weibull distribution, and the dependence of the three parameters on the stress amplitude were discussed and compared with the results of other researchers and other findings of the authors.

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Quasi-static and dynamic penetration tests were conducted using thin metal sheets of extra-super duralumin, corrosion-resistant aluminum alloy and cold-rolled carbon steel. The phenomenon before crack initiation differed from that after the initiation. Therefore, formulae for estimating the energy-absorbing capacity were proposed for before and after crack initiation. By comparing the estimated values with the experimental ones, it was clarified that the proposed formulae were valid for the assessment of the energy-absorbing capacity of a thin metal sheet under penetration.

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Automatic crack length measuring equipment was developed using the crack tip singularity. The crack tip location was determined by comparing the measured strain distribution using multiple foil strain gauges and the theoretical strain distribution around the crack tip. The accuracy of crack length measurement was 0.09mm (standard deviation). This equipment can be used to automatically monitor the fatigue crack propagation in the structure under service condition.

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A large deformation finite element analysis has been performed to study the stress and strain fields near the crack-tip under mixed mode conditions. The effects of microvoids on plastic flow are taken into account by using the continuum constitutive model introduced by Gurson. The displacements characterized by the stress intensity factors are imposed at the nodes on a peripheral circle far from a crack tip. Computations are carried out for the case of K_II/K_I=0 and 1.732 with the plane strain or plane stress condition. In the mixed mode loading, contrastive deformations appear at the upper and lower regions of the crack-tip, i.e., sharpening and blunting. The deformed shape of the crack-tip is influenced by strain hardening exponent. The distributions of the equivalent plastic strain and the void volume fraction near the crack-tip are also influenced by the stress state (plane strain or plane stress) as well as the strain hardening exponent. Based on these numerical results, discussions are made on the experimental observations that under mixed mode loading conditions cracks due to shear fracture initiated at the sharpened corner of the clack tip near the surfaces of the specimen while another crack due to dimple fracture occurred at the blunted corner of the crack tip near the midthickness of the specimen.

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A statistical variation is usually observed on the crack growth behavior of metallic materials under cyclic loading. Depending on the microstructure of the material, this variation is distinctive when the crack size is less than the critical length. The authors have been investigating the statistical aspect on the crack growth behavior of such small cracks for various kinds of metals. In this study, a probabilistic model was proposed for the crack growth behavior of small fatigue cracks by combining distribution characteristics of the grain size, the crystalline orientation of the grain and the misorientation of the grain boundary. Based on this model, computer simulations were repeatedly carried out on the crack growth behavior of small fatigue cracks on the specimen surface. It was finally shown that the analytical results obtained were in good agreement with the experimental aspect on the statistical variation.

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In this paper the substantial meaning of C parameter was clarified. And it was found that C parameter does not relate to the local stress field but creep elongation rate. Also creep damage was found to be a concentrated region of micro cracking along the grain boundary and to be represented by one characteristic curve independent on gross stress, temperature, shapes of notch against the nondimensional time controlled by creep rupture life. Creep crack growth rate was influenced by creep damage and it was due to the accumulated creep damage before creep crack initiation, which was mainly influenced by the effect of notch shape.

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The fatigue crack propagation path of an aluminum alloy specimen possessing slight anisotropic mechanical properties was investigated. The crack path was also estimated using the finite-element method based on the maximum energy release rate. The results are as follows : (1) It is possible to estimate the crack path based on the maximum energy release rate ; (2) As the constraint condition sensitively affects the crack path, an accurate setup is necessary for the correct estimation : (3) As the elastic modulus of the specimen used in this experiment does not change greatly, no effect of anisotropy appears in the crack propagation rate. The slight difference of the modulus of elasticity, however, sensitively affects the crack path, and it is necessary to measure the accurate value of an elastic modulus for the estimation of the crack propagation path : (4) The effect of the anisotropy more sensitively appears in the case a complex mode condition than in that of a simple model condition.

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In this paper, a simple procedure based on the matrix method of structural analysis is proposed to estimate the stress intensity factors for various configurations of axially cracked cylinders. General formulation using matrix expression is presented at first. Then, this formulation is reformed by using the hoop stress in the uncracked configuration for the convenience of numerical ca1culations and analytical considerations. Proposed method enables us to estimate not only the mixed-mode stress intensity factors but also the J-integral for quite various configurations of axially cracked cylinders, and obtained results show good agreement with numerical data in the literature for a number of cracked configurations. In addition, explicit formulation in this study enables us to easily know the characteristic features of axially cracked cylinders ; the dependence of internal forces and K-values on mean radius, wall thickness, crack length, and the number of cracks.

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A correct form of the definition of the stress intensity factors is presented for an interface crack between dissimilar orthotropic materials, and the extrapolation methods to determine the stress intensity factors by numerical results are proposed. From some numerical results, it is confirmed that the definition is vallid and the extrapolation methods are very efficient. This study also investigates the stress distribution on the interface between dissimilar orthotropic materials. It is found that there exists a good pair for dissimilar orthotropic materials, in which the stress singularity disappears at the edge of the interface.

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The relation between the strain sensitivity and the grain size of grown grain copper foil gauge which has preferred orientation to slip is examined. We Adopted this gauge to evaluate the mode II stress intensity factor K_II of the through thickness crack in a plate subjected to cyclic torsion. The K_II values obtained are lowered compared to the calculated value by the action of frictional force on crack surfaces. Using the K_II obtained and K_I for plane bending, it becomes clear that the threshold condition of crack propagation under the mixed mode of the combination of bending and torsion is governed by the strain energy density criterion.

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When a striker of finite mass impinges on the end of bar which is imperfectly fixed at its distal end, the impact stress of striker and bar is analysed by accounting for reflection coefficient of stress wave at the striker-bar interface and terminal end of bar. The reflection coefficients of stress wave in this case are determined in the same way with the evaluation of reflection and transmission of wave passing through shafts having discontinuous cross-sectional area or interface of dissimilar materials. The results of analysis are compared with impact stress of bar perfectly fixed and experiment. The impact stress of bar imperfectly fixed is about 60%-80% of perfectly. The period of impact stress acting in imperfect fixing bar is shorter than in perfect fixing bar. Although the magnitude of impact stress predicted by the analysis is in agreement with the experiment, the shape of wave is a little difference. It is shown that the impact stress of striker-bar interface can be indirectly determined by evaluating the stress caused in striker.

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Ultrasonic waves provide efficient means for the non-destructive characterization of composite materials. In the present paper, we study phase velocity and attenuation in a metal matrix composite reinforced by particles with interfacial layers. We assume same-size spherical inclusions and same-thickness interface layers with nonhomogeneous elastic properties. The effective complex wave numbers follow from the coherent wave equations which depend only upon the scattering amplitude of the single scattering problem. Numerical results are obtained for a moderately wide range of frequencies, and the effect of interface properties on phase velocities and attenuations of coherent plane waves is discussed in detail.

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The thermoelastic problem is analyzed for an infinite plate with a crack originating from a corner of a rhombic hole. The plate is subjected to a uniform heat flux in an arbitrary direction. Muskhelishvilli's method, the rational mapping function of a sum of fractional expressions and thermal dislocation are used in the analysis. A closed solution is obtained for the temperature and thermal stresses. The distributions of thermal stresses, temperature and heat flux are calculated on the boundary of the hole, on the crack surface and on the symmetric axis. The stress intensity factor and the singularity of the heat flux at the crack tip are also investigated.

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Thermal stress in silicon chips encapsulated in IC plastic packages was discussed using stress-sensing chips which the authors developed utilizing the piezoresistive effect of silicon. Sensor chips were encapsulated in dual-in-line-type packages using various combinations of packaging materials : metallic leadframe, die-bonding paste, and resin. Thermal stress in the silicon chip was measured with changing oven temperature between 20°C and 100°C. It was found that thermal stress in silicon chips changes almost linearly with temperature. The stress varied with the material combination of the package from 75 MPa to 110 MPa when the temperature decreased from 100°C to 20°C. However, the thermal stress varied irreversibly with temperature when epoxy paste was used as the die-bonding paste. This unstable stress change with temperature was due to propagation of the delamination between a silicon chip and metallic leadframe.

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In this paper, theoretical analysis of an axisymmetric transient thermal stress problem is developed for a nonhomogeneous hollow sphere. Assuming that the hollow sphere has non-homogeneous thermal and mechanical material properties in radial direction, heat conduction problem and the associated thermoelastic behaviors for such nonhomogeneous medium are developed by introducing the theory of laminated composite as one of the theoretical approximation. The transient heat conduction problem under the condition of axisymmetric heat supply due to the inner or outer surrounding medium is evaluated with aid of the method of Laplace transform, and the associated thermoelastic field is analyzed making use of the thermoelastic displacement potential and the complementary harmonic function. Thereafter, the numerical results for the temperature change and the stress distributions are shown in figures, and the influences of the nonhomogeneous material properties are discussed briefly.

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The purpose of this paper is to evaluate creep damage along creep curves quantitatively. The present design code for the structures in high-temperature service strictly prohibits use of materials in tertiary creep. However, the creep properties of newly developed heat-resistant materials are characterized by the larger proportion of tertiary creep to creep curves. Using commercially pure alminium, creep damage was measured as a function of change in density (-ΔD/D), and as that of the ratio of creep void area to total area (A_void/A). Each value is expressed as a power law of creep strain ε_c in the range of the latter secondary creep section to tertiary creep. Although they were dependent on the magnitude of initial stresses, the relationship between dimensionless values of change in density and creep strain against their values at rupture can be reduced to a curve despite change in stress.

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The authors have developed a hybrid measurement system of three-dimensional temperature distribution. The system consists of infrared thermography by which the real time temperature distribution of a body surface can be measured, and an engineering work station (EWS) by which heat conduction finite-element analysis can be carried out. The system has been applied to (1) the analysis of temperature distribution in the body and (2) the measurement of the heat transfer coefficient of a bonded joint. It has been shown that these problems can be analyzed efficiently through the developed system.

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The deformation behaviors of thermo elasto-viscoplastic blocks with relatively sharp U-type notch, slit, and U-type notch with void, subjected to plane strain tension under mode-I loading have been investigated. These blocks have a relatively low strain rate sensitivity and comply with an elasto-viscoplastic constitutive equation which has a viscoplastic strain rate noncoaxial with the stress tensor. Attention has been paid to deformation with a strain rate in the range of 0.02-2/s. A full plane strain finite element analysis of the velocity and temperature fields has clarified the effect of deformation rate, material strain rate sensitivity and thermal conductivity on flow localization, including sharpening the notch tip and coalescence of the notch and void.

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In the present investigation, the material strain rate and temperature sensitivities are incorporated into a numerical simulation of cylindrical bars subjected to uniaxial tension. The analysis is based on a thermo-elasto-viscoplastic version of the rate-dependent constitutive equation where the viscoplastic strain rate has a component noncoaxial with the stress tensor. The effects of the deformation rate, heat conduction, and size of the block on flow localization, including the shear band-type flow localization, are clarified in a full axisymmetric finite-element analysis of velocity and temperature fields. The comparison between the present results and those for the plane strain condition will clarify the influence of the stress system applied on the flow localization.

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This paper proposes a new anisotropic yield function for void-containing materials. The plastic deformation of the material model, which has a three-dimensional regular array of ellipsoidal voids, is discussed, and using the notion of the damage tensor, the anisotropy due to variations in void spacing is taken into account. Yield loci are calculated for two specific types of loading and it is shown that void distribution can exert a very strong influence on the anisotropy of the aggregate.

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In this paper, an exact theory for determining the complex shear modulus of damping materials is presentd, by employing a torsional vibration test of an elastic rectangular rod with damping layered materials bonded on both sides. In the previous studies, the value determined by means of such a method, the so-called Composite Beam Test Method, has not taken into consideration for the effect of thin adhesive layer deformation. The difficult task of evaluating such an effect is carried out herein based on the five-layer theory presented. Theoretical and experimental results indicate some characteristics such as the adhesive layer thickness and its mechanical properties to be applied in this method, in conjunction with the damping material constants. Furthermore, an error estimation of the value determined in the high-temperature range is discussed.

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This report describes the dynamic behavior of partially liquid-filled thin cylindrical shells which are subjected to vertical excitation. In case too much liquid is contained, the structure is often damaged. The exciting acceleration, the surface deformation and the generated sound, as dynamic behavior of the shell made of a Lummiror polyester sheet, are treated experimentally. The acceleration and the deformation vary with discontinuity as if the transition phenomena occurred. The transition is caused in the lower frequency region at the longer cylinder effective length, that is, with the increased liquid potential head. The frequency response of the shell wall is observed as several spectra which change due to transition. The acoustic spectra of sound generated from the shell depend on the wall response. There are correlations between both characteristics. Therefore, the response condition of the shell wall can be predicted by the acoustic spectrum.

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An analysis for bending of a transversely isotropic, rectangular thick plate with free edges, subjected to a partially distributed uniform load is presented. A tenth-order theory of moderately thick plates is used for the analysis. A particular solution obtained from the generalized Elliott solution and a homogeneous solution composed of a plane and generalized plane stress solution and an anti-symmetric stress solution are used. Numerical results for displacements and stresses in graphite-epoxy and E glass-epoxy as well as in an isotropic material are presented. The effect of anisotropy on the displacements and stresses is examined.

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Tensile and three-point bending tests were conducted on a hot isostatic pressed silicon nitride. To examine the size effect on the tensile strength, two kinds of different-sized round test specimens were prepared. A special chucking device utilizing a powder cushion between the specimen and the grip surface was used to promote good alignment with increasing load. The percentage of bending stress at the fracture was less than 5%. The mean tensile strengths of large and small specimens were 63% and 74% of the mean value obtained by the three-point bending test on the same material, respectively. The Weibull moduil determined by the large and small tensile specimens were smaller than that in the case of the three-point bending test. These results indicate that care should be taken in Weibull-statistics-based strength comparison for different-sized specimens and different loading conditions.

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In this study, the static tensile tests of Polyethernitrile (ID 300) and CFRP in which the carbon fiber was combined in an ID 300 resin matrix with a fiber content of 30%, by weight, were done by using smooth and notched specimens at room temperature. The results were discussed based on linear notch mechanics. The relation σ_∞-1/ρ is to be classified into two parts, namely, a part where σ_∞ decreases with decreasing ρ and a part where σ_∞ is nearly constant regardless of ρ (σ_∞ : nominal stress at infinity, ρ : notch tip radius). The similar phenomenon can be seen in the fatigue tests of notched specimens under rotating bending or push-pull. The fracture of ID 300 and CFRP specimens is controlled by the elastic maximum stress, σ_maxc, and the notch tip radius, ρ, alone, independently of the other geometrical conditions. Linear notch mechanics is very useful for analyzing the static tensile fracture behavior of the notched ID 300 and CFRP specimens.

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High-strength CFRP has been applied to aircraft and spacecraft structures because of its high strength/weight and modulus/weight ratios. These have, however, laminated structures and show low resistance to delamination fracture caused by impact or fatigue loading. It is required, therefore, to evaluate and to improve delamination fracture toughness. In this study, mode I and II delamination fracture toughnesses were evaluated by using simple test methods and delamination micromechanisms were discussed based on results obtained by SEM and scanning acoustic micrography. Results obtained are as follows; (1) Mode I delamination fracture toughness shows a constant value during delamination crack growth. (2) Mode II delamination fracture toughness is three times as large as that of mode I . (3) A simple method is proposed to measure mode II delamination fracture resistance curve.

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A photoelastic image processing method which analyzes simultaneously the isochromatics and the isoclinics is presented. The photoelastic images are obtained by an infrared vidicon tube having unstable sensitivity. The values of the isochromatics and the isoclinics in the whole region are determined by means of a least-squares method from some photoelastic image data obtained under the plane polarized light. For this determination, it is required that the values of the isochromatics and the isoclinics at two reference points be known. As an example, the stress distribution in a silicon beam subjected to three-point bending is analyzed and compared with the theoretical result.

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An automatic determination method of fringe order over the whole area of a photoelastic image has not been developed because of the lack of suitable theories and algorithms for processing digitized image data corrupted by noise. In a series of authors' studies on the development of a computer-aided photoelastic system utilizing structure-driven-type image processing, a single-valued function of brightness intensity was constructed on the basis of the concepts of foliation in topology and of transversality in catastrophe theory in order to overcome the difficulty mentioned above. As a result, the reversal of increase/decrease of fringe order along an arbitrarily designated path was discriminated, and a procedure for automatic assignment of fringe order over the whole area of a photoelastic image was successfully established using a tool for monitoring analyzed results in order to facilitate judgment of the reversal of increase/decrease of fringe-order variation.

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A particular formulation of the three-dimensional finite-element method relevant to the analysis of the Vickers hardness is established. The Vickers hardness of 0.46% carbon steel and 70/30 brass is analyzed by the proposed method using the stress-strain curve of the tensile test. The calculated results are in good agreement with the experimental results on 0.46% steel and 70/30 brass. The extension of the plastic zone induced by the indentation of an indenter is investigated by the analysis. The stresses at the maximum load are investigated and are compared with the residual stresses after complete removal of the load. At the maximum load, there is no tensile stress in the vicinity of the indenter. On the contrary, after removal of the load, there is large tensile residual stress at the diagonal edge beneath the indentation in the direction perpendicular to the diagonal edge. These results imply that it is necessary to reconsider the validity and accuracy of the conventional indentation method used for the determination of K_1c of brittle materials such as ceramics.

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Two topics relating to the ΔK_th test are reported. The first is a low-cost motor-driven fatigue testing machine equipped with completely automated crack measurement and K control facilities. The second is a rapid ΔK_th test method. In this method, a small amount of crack increment is measured by fractography on a crack surface created in a short-term program loading fatigue crack propagation test. Using either technique, a low-cost and rapid ΔK_th test can be achieved.

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An experimental equipment for a torsional test of polymers under high pressure has been developed. Axial free coupling has been devised so that the specimen may be free from any axial stress due to torsion. A torque sensor set in a pressure vessel has been developed. Using the equipment, cyclic tests for crystalline polymers of PE and POM have been conducted in the pressure rage of 98 k Pa to 98 MPa. Shear stresses and initial elastic modulus increase with the hydrostatic pressure increasing for both materials. The stress-strain hysteresis in PE is not affected by the previous strain history, but stress softening occurs in POM and the hysteresis curve is strongly affected by the past strain histories.

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