Permeability tensor is a key parameter for Resin Transfer Molding (RTM) of fiber reinforced plastics as well as for its simulation. For sheared textile composites such as woven and knitted fabric composites after preforming or draping, the permeability tensor includes non-diagonal components which can not be measured easily. This paper describes a numerical evaluation of permeability from both macro- and microscopic standspoints for sheared plain woven fabrics. The asymptotic homogenization theory for solid-fluid mixture is employed to characterize the micro-macro coupling effects. The nature of the macroscopic permeability tensor is discussed first. The microscopic flow field is next evaluated in detail by various ways. The differences of the microscopic flow field was recognized between the undeformed and sheared fabrics. The effects of the macroscopic pressure gradient is also discussed.

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This paper presents a method that generates a topological structure under an impulsive load by the extended distinct element method (EDEM). The EDEM model consists of non-linear springs, dampers and sliders between two elements in both the normal and tangential directions. According to the local rule using the calculated equivalent stress, elements are generated or eliminated. From numerical results, it demonstrates that various topological structures are generated by the initial shapes. It is also possible to obtain the design of the structure which is not limited to the design space.

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In this work, the homogenized elastic-viscoplastic behavior of long fiber-reinforced laminates under in-plane loading is predicted by taking directly into account the microscopic structure and stacking sequence of laminae. To this end, a homogenization theory of nonlinear time-dependent composites is applied to such laminates, leading to the macroscopic rate-type constitutive equation of laminates and the evolution equations of microscopic and average stresses in each lamina. The macroscopic constitutive equation has a stiffness tensor and a stress relaxation function which are evaluated explicitly in terms of the microscopic structure and stacking sequence of laminae. To verify the present theory, uniaxial tensile tests are performed on carbon fiber/epoxy laminates. It is thus shown that the present theory is successful in predicting the anisotropic viscoplasticity in inplane tension of unidirectional and cross-ply laminates and the negligible viscoplasticity exhibited by quasi-isotropic laminates.

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Achieving uniform preloads is an important and difficult issue, when bolting up a pipe flange connection with a number of bolts. Repeated bolt-up operations are, therefore, commonly conducted to get uniform preloads. In this study, an effective one-pass bolting up procedure to get uniform preloads is proposed by using finite element analysis with elastic interaction coefficient method being incorporated. Furthermore, some types of multi-pass bolting up procedures are also examined to avoid high initial bolt preloads that might be generated in the one-pass tightening. These procedures are applied to 20 in class 300 lb flanges specified in JPI with solid-metal flat gasket made of SS 400 and compressed asbestos sheet gasket. The validity of the procedures is substantiated by conducting bolt-up experiment using calculated initial bolt preloads.

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In the present paper is examined the vibration characteristics and optimization of rectangular symmetric CFRP laminates containing embedded shape memory alloy (SMA) fibers. The recovery stress due to the shape memory effect of the SMA fibers and the concurrent mechanical property change are taken into consideration in the vibration analysis of the laminates when the embedded SMA fibers are activated. With the use of two in-plane and four out-of-plane lamination parameters, the fundamental frequencies of the activated laminates are discussed for the case that the laminates are simply supported at four edges, while the fundamental frequencies of the inactivated laminates are discussed with the use of four out-of-plane lamination parameters. Finally, the vibrational optimization problems of the CFRP laminates with embedded SMA fibers are examined by using a mathematical programming method in which the lamination parameters are used as design variables. The laminate configurations to realize the determined six lamination parameters are also discussed.

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To investigate the influence of casting defect on the tensile strength of aluminum die casting materials, tensile tests were conducted on three type of aluminum die casting materials. The main results obtained are as follows: (1) The tensile strength basically depends on the casting defect (Region II) but to some degrees (Region I), the tensile strength seldom depends on the casting defect. (2) The tensile strength of Region I was estimated by Eq. (a) as same as the tensile strength of Aluminum wrought products. (3) The tensile strength of Region II was estimated by Eq. (b).σ_B= 1/3 HV (a) σ_B= K_IC/β√π√area (b) HV: Vickers Hardness, K_IC: fracture toughness, √area: the square root of the area which is occupied by casting defect onto to the plane normal to the maximum tensile stress

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The nucleation and motion of misfit dislocation at γ/γ' interface in Ni-based superalloy is studied by means of molecular dynamics simulations based on the Embedded Atom Method. In particular the dislocation nucleation at apices of cuboidal γ' precipitate surrounded by the other precipitates is discussed through the simulations of single crystalline γ/γ' microstructure in which eight cuboidal L1₂-Ni₃A1 precipitates are aligned three dimensionally. First, the stability of the coherent interfaces of the microstructure is discussed in view of the residual stress at equilibrium state. Then the microstructure is subjected to uniaxial loading in the [001] direction up to the strain larger than 0.05 where dislocation nucleation is observed in it. Detail observation of the nucleation process reveals the new mechanism of dislocation nucleation and motion near apices of precipitates: (1) a closed loop of a partial dislocation nucleates at a γ/γ' interface on an apex of γ' precipitate and propagates in γ channel toward the other interface on the adjoining γ' precipitate, (2) the loop branches two partials bridging between two adjacent γ' precipitates when it reaches the interface, (3) dislocation pinning takes place at the edge of cuboidal precipitate since the end of dislocation line cannot continue to glide on the junction line between the slip plane and γ/γ' interface.

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The purpose of this paper is to prove the importance of analysis conditions on FEA of axial buckling. Moreover, optimization design for crashworthiness members was carried out to improve the crashworthiness by considering forming history. As the results, it is important to consider the forming history in order to estimate the crush characteristics accurately on any type analyses. Furthermore, the results of optimization design showed that the optimized side member considering forming history could get better optimal solution than the optimized side member unconsidering forming history.

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A meso-scale analysis method using the natural element method, which is a kind of meshless methods, is proposed for the analysis of material damage of brittle microcracking solids such as ceramic materials, concrete and rocks. The microcracking is assumed to occur along the Voronoi edges in the Voronoi diagram generated using the nodal points as the generators. The mechanical effect of microcracks is considered by controlling the material constants in the neighborhood of the microcracks. The overall elastic moduli of anisotropic as well as isotropic solids containing a number of randomly distributed microcracks are calculated in order to demonstrate the validity of the proposed method.

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In the first report of the present study, the meso-scale analysis method using the natural element method was proposed for the analysis of material damage of brittle microcracking solids and applied to the evaluation of overall elastic moduli of solids containing microcracks. In this second report, the meso-analysis method is extended to the simulation of the microcracking behaviors of brittle solids subjected to uniaxial and biaxial macrostresses. The method is also applied to the analysis of the propagation of a macrocrack accompanied by the coalescence with microcracks formed near the macrocrack-tip.

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In this paper, the effective method for an elasto-plastic analysis is presented. In the overlaying mesh method, a local model is overlaid on a global model, the former represents high resolution of deformation and the latter represents rough deformation. However, when material-mixed model is analyzed using this method, the elastic constant must be the same at identical part between global model and local model. This makes modeling very inconvenient. In this paper, we clarify the behavior in the case of different elastic constant is used between global model and local model. In this case, the elastic constant of global model is ignored, and that of local model is adapted. By this theory, mesh of global model and that of local model can be made independently not only in geometric shape but also in material constant. And furthermore, this theory is applied to an elastoplastic analysis. In this method, global model is analyzed by liner analysis, and local model by nonliner analysis. We can reduce calculation cost by using this method.

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We have investigated the behavior of moisture absorption by a unidirectional CF/epoxy composite stored in a chamber, which can separately control temperature and humidity in air, and examined the effect of moisture on the dynamic viscoelastic behavior of CFRP. The moisture absorption behavior was confirmed to obey the Fick's law of diffusion. The dynamic viscoelasticity of specimen generally shifted to that at lower temperature, as an effect of plasticisation. The glass-transition temperature (T_g) of CFRP was lowered with increasing water content, and the reduction in T_g of moistened specimen was always greater than that of water-soaked specimen. The time-moisture superposition was confirmed to hold in air at various relative humidities at 60°C.

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In this paper, stress singularity at a space-jointed corner of several thin plates is studied. The thin plates are jointed along a commom line and a three-dimensional corner is formed at the edge point of the intersection line. The plates are so thin that the bending rigidities are taken to be zero. The stress singularity is analyzed by using the eigenfunction expansion method. Eigenequations are given in an explicit closed-form expression for some jointed corners.

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In this paper, a method of estimating the stress fields with strain gage's outputs and the body force method (BFM) is proposed. A notch of 3-dimensional structure surface is considered as an observed domain. The observed domain is treated as a pseudo-3-dimensional plate, not a part of a 3-dimensional body. In other words, body force is distributed along the observed domain to add the 3-dimensional influence to a plane stress problem. In this paper, the result due to the elastic FEM analysis is used instead of strain gage's outputs on real structures. A self-assessment criterion is proposed. In addition, it is possible to obtain the stress value at the 10% error by the self-assessment of the result due to the present method. In the second report, the present method will be applied to crack detection.

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The paper presents an axisymmetric solution for the stresses and displaements in an elastic thick plate containing an oblate spheroidal inclusion under axisymmetric bending around the z axis. The related spherical cavity and inclusion problems were solved by Tsuchida et al. in 1975. by using Papcovich-Neuber displacement potentials. We extended the method to spheroidal inclusion problem.

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We consider the electroelastic problem of a finite crack in a piezoelectric ceramic slab. The Fourier transform techniques are used to reduce the problem to that of solving a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and the main results presented are the variation of the energy density factors as functions of the geometic parameters, the piezoelectric material properties and the electric loads.

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Torsional fatigue tests under shear mean stress (τ_m) and tensile or compressive mean stress (σ_m) were carried out on the 0.47% C steel (JIS S45C) specimens containing an initial small crack. An initial small semi-elliptical crack was introduced by the preliminary tension-compression fatigue tests using specimens which contain a hole of 40 μ_m diameter. The initial branching angle of cracks that emanated from the initial crack tip was approximately ±70.5°to the initial crack plane, where the local tangential stress σ_o has the maximum value. The branched cracks eventually propagated perpendicularly to the plane where the range of normal stress has the maximum value, i.e. ±45°to the specimen axis. The torsional fatigue limit under mean stress is determined by the threshold condition for non-propagation of Mode I branched cracks emanating from the initial crack tip. The prediction method for torsional fatigue limit of specimens containing an initial small crack is proposed by the extended application of the √area parameter model with a combination of the maximum tangential stress (σ_omax) criterion.

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Some types of fatigue loading such as thermal fatigue may result in possible distribution of many cracks that are oriented in random directions. Numerical simulation of the fatigue crack propagation as well as stress analysis by conventional finite element method for such a situation requires huge amount of time and computational resources. The objective of the present study is to resolve this difficulty by employing the local approach of fracture based on continuum damage mechanics (CDM). The anisotropic damage variable developed in the authors' previous study is applied to represent a fatigue crack. Following the normal CDM approach with this damage variable and assumptions on crack opening/closing and damage evolution, numerical simulations are conducted for low cycle fatigue crack propagation behavior of a plate with single and two cracks. The results show good agreement with the experiments. Finally, propagations of multiply distributed cracks under low cycle fatigue loading are simulated to demonstrate the potential applicability of the present approach.

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Past efforts for aluminum alloys used for engines were focused on chemical compositions rather than heat treatment conditions of the aluminum alloys. Then, there are a few studies on optimizations of the heat treatment conditions. This paper treats artificial aging effects on two aluminum alloys such as AC 4 C and AC 2 B used for cylinder heads of engines. The aluminum alloys are subjected to additional heat treatments during several time periods after T 6 heat treatments. The effects of the aging time on the mechanical behaviors such as pure tension, cyclic loading, and thermo-mechanical fatigue failure are observed by a series of tests. The microstructural observation is also carried out by TEM to clarify the effects of microstructural change of the aluminum alloys on the mechanical behaviors.

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Impact and quasi-static tests for the axial compression of the strengthening automobile members with various types of hat-shaped cross-sections are carried out. Strengthening members play a role as an energy absorber in a car body at collision. A drop hammer type testing apparatus is used for the impact test, in which the impact velocity is set to be 10 in/s. The tested cross-sectional shapes are three types of rectangle whose height is 40, 30 or 20 mm with width of 40 mm, and a concave shape having many bent edge-corners. Test materials are a mild steel, SPCC, and 3 kinds of high tensile strength steel sheets, whose thickness is 1 mm. In the impact tests, progressive deformation patterns are recorded by a high-speed video camera. In both of the impact and quasi-static tests, an accordion type cyclic buckling mode is observed, in which the structure sufficiently absorbs the crush energy. Crush strength in the impact test is higher than that in the quasi-static test and it increases with decrease of the hat height. Increase of the number of bent edge-corners in the cross-section leads a higher crush strength. With respect to the rectangular cross-section, the crush strength is found to be roughly proportional to the material tensile strength (and its yield stress). The proportionality slope for the impact test is smaller than that for the quasi-static one.

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Polymeric materials have various characteristics of deformation, e.g., strain rate dependence (viscoplasticity) at room temperature, strain localization just after initial yielding and propagation of a localized region with strain hardening. Viscoplasticity has been usually represented by a constitutive equation of plasticity with a hardening law including a plastic strain rate. However, such a modeling is not thermodynamically consistent with the hardening law dependent on strain rate. In this paper, a strain rate tensor is introduced into free energy and a thermodynamic force conjugate to this rate is newly defined. On the basis of the principle of increase of entropy and one of maximal entropy production rate, a non-coaxial constitutive equation of viscoplasticity is derived as a flow rule in which a dissipation function plays the role of plastic potential. It is shown that a strain rate dependent constitutive equation must be always non-coaxial in a thermodynamically consistent theory.

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In the previous paper, a strain rate tensor is introduced into free energy and a thermodynamic force conjugate to this rate is newly defined. On the basis of the principle of increase of entropy and one of maximal entropy production rate, a non-coaxial constitutive equation associated with a plastic deformation rate is derived as a flow rule in which a dissipation function plays the role of plastic potential. Material moduli in this equation, however, are still not expressed as functions of hardening law. In this paper, the constitutive equation is newly generalized into corner theory which permits an existence of a vertex on dissipation surface. A non-coaxial angle of a plastic deformation rate is related to the non-coaxial angle of a stress rate by use of strain rate sensitivity. Furthermore, a finite element analysis is carried out for a plane strain tension of homopolymer. Some remarkable numerical results of strain localization for homopolymer are discussed in detail.

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