In this paper, the tensile properties and fracture behaviors of biaxial and triaxial woven fabric composites, which are one of the textile composites, were predicted using the numerical analytical method proposed in the previous paper. Both biaxial and triaxial woven fabric composites consist of carbon fiber and epoxy resin. The analytical model takes into consideration the continuity and crimp of fibers in the woven fabric composites. The validity of this analytical method is examined by comparing predicted results with experimental data. It is found that the results agree well in both woven fabric composites. Local stress states of the woven fabric composites could be confirmed from numerical results. Accordingly, it was clarified that the mechanical behavior of the textile composites could be predicted by this analytical method.

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Plasma facing components are one of the important structures in the research and development of fusion devices, such as the International Thermonuclear Experimental Reactor (ITER). In most cases divertor modules must consist of carbon fiber reinforced carbon materials (C/C) brazed on a Cu heat sink so that the armor tiles damaged during plasma disruption may be replaced or repaired. It is very important to inspect the brazed region of the divertor nondestructively after it is repaired. Infrared radiometry is believed to be very effective for this purpose, because recently the infrared radiometer has been used to defect the separation of tiles and some internal flaws in the construction structure. In this study, infrared radiometry was applied to detect the separation of the Cu/Carbon-carbon composite joint of the armor tile. Moreover, the characteristics of radiation temperature were measured for the surface of an armor tile material.

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Recently integral large composite structures have been applied to many structures of vehicles because of low cost and high reliability. However, as the structures are large and complicated, a fracture simulation system is required to assess the safety of inspected damages. The objective of this study is to investigate effectiveness of the 2-dimensional FEM damage simulation for FRP laminates using various FEM mesh divisions, fracture criteria and damage estimation methods compared with the expermental results. As a result, the equally divided mesh and the Tsai-Hill criterion were found to be most reliable, and a damage estimation method based on a fracture mechanism is needed to improve the results

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This paper analyzes the effects of acoustoelasticity and damages on propagation of ultrasonic waves in fiber-reinforced plastics. Acoustoelasticity is used for nondestructive evaluation of the internal stress of materials. The technique utilizes the speed shift of ultrasonic waves due to nonlinearity of the elastic characteristics. When a fiber-reinforced plastic is subjected to a strong load, microdamage may be caused, for example, fiber failure, matrix cracking, and matrix yielding. Thus, propagation of ultrasonic waves in such composite materials depends not only on the stress but also on the microdamage in the materials. This paper presents the constitutive equation of fiber-reinforced viscoelastic materials with damage based on damage mechanics. The effects of microdamage and stress on the speeds of ultrasonic longitudinal waves are examined in the acoustoelastic test for high-polymer composite material, PBT, reinforced with glass fiber

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An investigation of water absorption on delamination by low-velocity impact loading, and compression strength and delamination growth behavior after impact by fatigue loading was carried out on quasi-isotropic laminated ([0°/±45°/90°]_2s) carbon fiber reinforced epoxy matrix composite. Ply-to-ply delamination was evaluated by using a scanning acoustic microscope. Interlaminar strength was lowered by water absorption, and the impact-load-induced delamination area was increased by water absorption. Compressive strength after impact was evaluated as the sum of delaminated areas of respective ply-to-ply delamination ; when the delaminated area was large, compressive strength after impact was solely determined by the delaminated area, and no influence of water absorption was observed ; however, when the delaminated area was small, compressive strength after impact of the water absorbed specimen decreased. The fracture surface, in particular, topographic features of hackle patterns, was closely examined by a scanning electron microscope, and the fracture mechanism of compressive and fatigue failure mechanism were discussed

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An expert system, which diagnoses the causes of failure of environmentally assisted cracking (EAC), based upon fractography has been developed. The system uses the OPS83 programming language expressing rules in a manner of production rules and is composed of three independent subsystems, which respectively deal with EACs of high-strength or high-tensile strength steel, aluminum alloy, and stainless steel in dry and humidified air, water, and aqueous solutions containing Cl, Br or I ions. The concerned EAC issues cover stress corrosion cracking (SCC), hydrogen embrittlement, cyclic SCC, dynamic SCC and corrosion fatigue as well as fatigue and overloaded fracture. The knowledge base covers the rules relating to not only environments, materials, and loading conditions, but also macroscopic and microscopic fracture surface morphology. In order to deal with vague expressions of fracture surface morphology, Fuzzy theory is used in the system, and the description of rules about vague fracture surface appearance is thereby possible. Applying the developed expert system to case histories, accurate diagnoses were made. We discussed the related diagnosis results and usefulness of the developed system

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The maximum elastic stress in a cracked or notched body is not a unique parameter that controls the failure or fracture of the body. Therefore, we must determine the measure of severity in a cracked or notched body in order to predict the strength of real objects from the strength of specimens. Under the condition of small-scale yielding, it has been shown that linear crack mechanics (linear fracture mechanics) and linear notch mechanics are effective in the process of such a prediction. Under the condition of large-scale yielding, we must use nonlinear crack mechanics and nonlinear notch mechanics. The measures of severity are the maximum plastic strain at a crack tip in the former and the maximum plastic strain at a notch root plus the notch root radius in the latter. When the measures of se verity are the same in a specimen and a real object, the same elastic-plastic fields are assured and the same phenomena occur in both.

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The acceleration and deceleration behaviors of a semi-infinite crack in an elastic plate with a finite width, which is subjected to time-dependent loading, are analyzed and the caustic method for measuring the fast crack propagation toughness K_ID is simulated by using the boundary element method. It is shown that the "measured" K_ID depends on the shape of the specimen when the dynamic stress intensity factor K_I ( t, v) and/or the crack speed v changes rapidly. The dependence is explained by the numerical results that the K_I(t, v) -controlled field does not develop enough to cover the location of the initial curve of caustics, i. e., the displacement field near the initial curve is influenced not only by K_I (t, v) but also by (1) the superposition of stress wave reflected at the boundary and (2) the change of the crack acceleration due to the reflected stress wave

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The low-pressure plasma spray coating process has been established in the field of gas turbines and is used for parts (turbine blades, duct segments, etc. ) which are exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrAlY alloy system (M is Ni, Co or Fe) are commonly employed as oxidation-and corrosion-resistant coatings. Crack growth behaviors of coatings from coated surface to substrate were analyzed in terms of the stress intensity factors using the finite-element method. Prevention of crack growth from the coated surface to the substrate was also investigated by measuring Young's modulus and thermal expansion coefficient for eleven kinds of MCrAlY alloy coatings, which were sprayed by the low-pressure plasma spray and heat-treated at 1393 K for 2 h in Ar atmosphere. Results showed that the MCrAlY coatings with low Young's modulus and low thermal expansion coefficient were useful for preventing crack growth from the coated surface to the substrate

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Fracture of metal/ceramic bonded joints usually occurs at the edge of an interface. If the residual stress is small, a crack propagates along the interface to a critical length and then kinks into ceramics. If the residual stress is large, a crack directly kinks into ceramics. It is known that the strength and the fracture path are strongly dependent on the residual stress and the strength of the bonded interface. In this study, a method to simulate the fracture and strength of the metal/ceramic bonded joint is proposed based on the interfacial fracture mechanics, and some simulation results on 4-point bending specimens of ceramic (Si₃N₄)/metal (S45C) bonded joint are presented. It is found that the fracture path and fracture load can be well simulated by this method

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The temperature dependence of fracture mechanisms on two typical structures, a short-fiber-reinforced material and a chopped-strand material with a thermoplastic matrix, were examined by AE monitoring and SEM. It was found that the matrix became brittle as the testing temperature decreased from 60°C to -20°C, and this gave rise to different fracture behaviors of the materials used. In a short-carbon-fiber-reinforced material, matrix cracking and fiber breakage were the main fracture forms at -20°C and 0°C, whereas pull-out became the main form at 20°C and 60°C. In a chopped-strand-reinforced material, cracking between chopped tapes and debonding of fiber/matrix in a chopped tape became marked with increasing testing temperature. In particular, at 60°C, the matrix became more ductile and this resulted in decreased interfacial strength, then pull-out of fiber strands and chopped tapes occurred

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In order to evaluate the effects of the instantaneous strain rate and strain rate history on the dynamic flow stress in BCC metals at very high strain rates, strain rate change tests are performed for low carbon iron and niobium in a strain rate range from about l0000 to 20000/s. The results indicate that the instantaneous strain rate plays a dominant role. Furthermore, the σ-log ε curve calculated using activation energy E(γ) for deformation of pure iron obtained by Aono et al. shows good agreement with experimental data. It can be concluded that the deformation in the BCC metals at high strain rates is controlled by dislocation motion which surmounts the Peierls potential barriers with the aid of the thermally activated formation of kink pairs

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Electronic speckle pattern interferometry (ESPI) is a very useful method for measuring in-plane surface displacement. Using the cw-laser and image-processing system, it is possible to measure displacement and strain. Unlike traditional strain gauges or the moire method, the ESPI method requires no special surface preparation or attachments and can measure in-plane displacement with no contact and in real time. In this experiment, a specimen was loaded in parallel with a load cell, which provided loading step. The specimen was a flat plate or a plate with a 12 mm-diameter hole in its center. Strain gauges were attached to the specimen in x and y directions. This study provides an example of how ESPI has been used to measure two-dimensional displacement and strain distribution in this specimen. The results measured by ESPI are comparable with the data which were obtained by the strain-gauge method in tensile testing in the 1-ton range

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It is an important issue to predict Stress corrosion crack growth behavior in the pressure boundary components of nuclear power plants during operation. The establishment of a prediction method of SCC crack initiation and growth in LWR environment is one of the essential steps for structural integrity assessment. In this paper, growth behavior of stress corrosion cracking in a reactor pressure vessel made of SA 533 B steel in a simulated LWR environment under monotonic rising load (of slow strain rate test) and constant loading was simulated by the combination of FEM stress-strain analysis on a growing crack and dissolution model. From the simulation results, the quantitative relationship between crack tip strain rate and crack propagation rate was discussed. Crack growth rate can be evaluated in terms both of crack tip strain rate and of crack tip solution chemistry such as sulfur concentration and I_ss

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Fundamental solutions are derived for the two-dimensional elastic field in a plane of two joined semi-infinite plates, one of which is isotropic and the other anisotropic. A concentrated force or dislocation is applied at a point in the anisotropic semi-infinite plate. A closed-form solution is obtained using the complex variable method. A special case of the isotropic-orthotropic two-phase medium is derived from the general solution, including the case where the principal direction of elasticity of the orthotropic medium is not parallel to the interface of plates

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Internal stresses of constant-temperature cured adhesives (CTCA) decrease the reliability of the bonded structures. Since the internal stresses of CTCA have been neglected by researchers, a numerical analysis method has not been established to date. In this paper, a numerical analysis method for the internal stresses of CTCA was examined. Internal stresses were measured by the bimetal method and the deformation of the bimetal-curing time curve was the object of the numerical analysis. In this paper, the error was to be cleared in case the mechanical properties of solid, i. e., elastic modulus of bulk and total linear shrinkage ratio of adhesives, were used. Furthermore, the numerical analysis method was examined taking into consideration the exchange of mechanical properties of adhesives during the curing process. Exchange of volume shrinkage ratio and shear modulus were measured by a dilatometer and a rheometer, respectively. The piecewise linear analysis method was applied to the beam theory to take into consideration the exchange of mechanical properties. Good agreement was found between the calculated and experimental results

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The elastic stress field and small-scale yielding behavior of a bimaterial plate are studied for the case when surface traction is free in the vicinity of the bonding edge. It is shown that the elastic singular fields at the bonding edge can be classified into three types depending on the combination of elastic properties and bonding angles, i. e. the characteristic equation determining the strength of the singularity has (1) one real value, (2) two real values and (3) complex value. Suitable expressions of the singular stress field which are consistent with those of crack problems are presented. Finite-element analyses have been performed and features of the stress distribution and shape of plastic zone are discussed for each of the three cases

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In the present study, with respect to TIG welding of a TiNi shape memory alloy wire and sheet, the optimum welding condition was decided based on the breakig load of the weld and its standard deviation. By performing the cyclic loading-unloading and heating-cooling tests in the neighborhood of the weld, the shape memory effect was investigated. In order to investigate the shape memory effect in detail, the tensile properties of the weld metal and heat-affected zone were discussed. Based on the results, the deformation behavior of the neighborhood of the weld and the shape memory effect under cyclic deformation were clarified. Moreover, wires of different transformation temperature were welded, and the shape memory properties were investigated

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A trunnion suspension system is usually adopted for a heavy-duty truck of the 6×2 or 6×4 drive system. A rear axle fixed to this suspension system takes vertical load and axial load of very complicated stress. Stress is created on the rear cover fixed area, resulting in fatigue. This paper deals with the optimum design of the rear axle case (rear cover fixed area) using the 3-factor & 3-level structure analysis of the finite-element method based on the comparison of experimental results with stress values obtained by the finite-element method

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An exact and direct sensitivity analysis technique of large deformation and buckling load for elastoplastic material governed by a bilinear constitutive law has been developed based on the implicit differentiation method. The sensitivity equation of the displacement increments has been derived from the Newton-Raphson iteration scheme, and a practical pseudo loading terms due to the sensitivities of the stiffness matrices and the internal load vector have been formulated by considering discontinuity of the displacement sensitivity at the yielding point. The validity of the formulation suggested here was confirmed by comparing the calculated results of several examples with those of the theory and the finite difference method. The sensitivity analysis technique suggested here was also applied to determine optimum shapes of minimum weight under the buckling load constraints

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Buckling tests for nearly perfect cylinders and cylinders with intentional imperfection made by press-working technique were carried out under transverse shearing loads. The radius-to-thickness ratios were 50-200 and bending-to-shear stress ratios were 1.2-5.0, where both types of elastic-plastic buckling in shear and in bending occurred. The purpose of these tests was to clarify the effects of imperfection on these two types of buckling. From test results and numerical analyses, some margin was recognized in the design formulae even for imperfect cylinders whose imperfection amplitudes were within the wall thickness (in shear) and one-half the value of the wall thickness (in bending). We proposed the correction factors of buckling load for larger imperfections in the seismic buckling design guideline of FBR

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In this paper, a quadrilateral plate bending element based on the Mindlin plate theory is proposed. The element is a four-node quadrilateral with the three degrees of freedom per node. We suggest a method to obtain an element stiffness matrix under the condition where the transverse shear deformation is constant within an element. The deflections of thin and thick plates are calculated in order to examine the convergence and accuracy of the present element. Also, free vibration of thin and thick plates is investigated as an example of a dynamic probrems. As a result of the analyses, it may be concluded that the proposed element is very accurate for thin and thick Plates

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Using Biot's variational principle, two governing equations of general higher-order theory are formulated for the coupled thermoelasto-dynamic plates. The derived governing equations are two equations for coupled thermoelastic vibration and for the law of heat conduction. As for the law of heat conduction, a classical and a modified Fourier's law are adopted in Biot's variational principle. The two governing equations for coupled thermoelastic vibrations and the two boundary conditions are the same equations, respectively. However, the two governing equations obtained for the law of heat conduction are different from each other. Lastly, relations between the governing equations of general higher-order theory derived from Biot's variational principle and those derived from Hamilton's variational principle are considered

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In order to study the effect of the inelastic constitutive relation on Rockwell hardness, elastic-plastic FEM analyses were carried out for B-scale Rockwell hardness using a rigid and elastic indenters. Rockwell hardness tests also were carried out using SUS 304 austenitic stainless steel, T 6061 aluminum alloy, and pure copper. FEM results agree with the experimental results within 10% error. Yield stress and work hardening coefficient and exponent have a significant influence on the hardness. Friction and Young's modulus, however, have almost no effect on the hardness. A quantitative equation between Rockwell hardness and the constitutive relation is proposed

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Finite-element method codes for 2-dimensional and 3-dimensional structural analyses are reprogrammed using FEM code class libraries in an object-oriented language, C++. The readability and modifiability are improved by using C++ instead of FORTRAN. In this paper, two concepts are introduced in the construction of the class library for further improvement of modifiability. One is the application framework, which simplifies the process for FEM programming. Another is the action queue, which is an assembly of pointers of functions. It is shown that the database for action queue and functions is important for the further development of FEM class libraries

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Much attention has been focused on the problem of mesh generation because of its role as a bottleneck in the finite element analysis. One solution is to develop an efficient adaptive scheme. In adaptive mesh generation, accurate error estmation is indispensable, but it is also important to reflect the calculated result of the estimation exactly in the next step of refinement. In this paper, a new automatic adaptive mesh generation scheme based upon the technique of arbitrarily distributed random numbers is proposed. The steps outlining this scheme are as follows : (1) calculate the distribution of the desired node density from error estimation for a previous finite element solution (2) generate nodes according to the calculated node density distribution (3) construct elements by connecting the nodes. The generation of random numbers according to a given distribution is widely used in Monte Carlo simulation and this technique is applied to generate nodes of the desired density. The applicability of this scheme is examined in some examples. The decrease of the relative error obtained by iterative adaptive remeshing shows the superiority of the proposed method

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The characterization of thin film on a substrate is very important for basic research and development of thin-film-coated materials. In this study, an inverse analysis with an ultrasonic spectroscopic technique is presented for quantitatively estimating elastic properties and density of the thin film on a substrate. The inverse problem is reduced to the optimum problem of minimizing the differences between dispersion curves obtained experimentally and numerically, where the dispersion curve is determined by analyzing the ultrasonic reflectivity measured or calculated from the elastic properties and density of the thin film. First, the stability and accuracy of the solution in the inverse problem are discussed. Secondly, numerical simulation using the optimization procedure with the complex method is carried out for a few sample problems, and the validity of the present procedure is examined. Furthermore, the experiment was demonstrated for TiN-coated tool steel

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The present paper describes a new encoding method of the subchromosome and its effect on the constructive algorithms (CAs) proposed in the previous paper. In the present subchromosome, two loci in the main chromosome and the direction of transformation are encoded, while in the previous paper only two loci were encoded in the subchromosome. After the present encoding method, one transportation pattern has two different representations. Therefore, randomness of the subchromosome is maintained in the application of the genetic algorithms. To demonstrate the effectiveness of the constructive algorithm combined with the new encoding method, the algorithm is applied to the optimal design problem of the strongest column having clamped-free (C/F) and clamped-simply supported (C/S) ends. It is shown that the optimal design for the C/S condition and the quasi-optimal design, which is almost optimal, for the C/F condition are obtained

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Tomograms of a temporomandibular joint (TMJ) were analyzed by image processing. The TMJ shape was evaluated from the TMJ space, the space area and the distance between the reference points of the condyle and the glenoid fossa. The shape factors of the condyle and the glenoid fossa were also measured to examine the deformation of the bone. The borderline values were determined from the results obtained by the image analysis and they were used to select an abnormal sample from among many samples. The deformation of the condyle can be detected simply by the shape factor. The error of diagnosis is more than 10% according to the borderline values of the TMJ space and the space area. On the other hand, the error is 2. 4% when the horizontal distance between the reference points is employed. The present system will contribute to the image diagnosis of the TMJ syndrome and evaluate the TMJ shape objectively

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