This paper improves tetrahedral linear finite element with nodal integration points for transient dynamics analysis. Although tetrahedral finite element is effective for practical auto mesh generation, the simplest tetrahedral linear finite element brings numerical locking. In addition to this, tetrahedral high order finite elements are unsuitable for transient dynamics analysis because of inconsistent high-frequency vibrations in finite elements. To avoid numerical locking of tetrahedron linear finite element, the present study approximates constitutive variables on nodes instead of general integration points and extends to conventional explicit dynamic method for transient dynamics analysis. We test the present approach in representative computational examples comparing to results by standard tetrahedron linear finite element and reasonable hexahedron linear finite element with numerical selective reduced integration.

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Formation of fatigue dislocation structure in copper thin films under cyclic loading was studied by the discrete dislocation dynamics (DDD) simulations, in which the motion of dislocation was restricted by the interfaces. The present DDD simulations successfully reproduced planar-arrayed dislocation walls in a persistent slip band (PSB) experimentally observed in copper bulk. In copper thin films with a several-micrometer thickness, the dislocation walls were stably formed by the cyclic loading, whereas they were unstable and could not be formed in the films thinner than 1 μm. This result indicates that there exists the critical thickness in the formation of fatigue dislocation structure.

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In order to improve the reliability of rolling bearings, it is necessary to clarify effects of hydrogen on rolling contact fatigue properties of bearing steels. This study shows a new method for the rolling contact fatigue crack growth testing. A small artificial hole makes quantitative evaluation of crack growth possible under rolling contact fatigue, although the rolling contact fatigue generally induces invisible inner crack initiation and growth from defects such as nonmetallic inclusions in the bearing steels. Firstly, shape of a small hole for rolling contact fatigue crack growth test was optimized on the basis of shear stress distribution around a small hole analyzed by FEM. New rolling contact fatigue tests were performed using uncharged specimens (hydrogen content C_H = 0.4 mass ppm) and hydrogen-charged specimens (C_H = 0.8 ~ 1.2 mass ppm) with a small artificial hole (diameter d = 50 or 100 μm, depth h = 100 μm) for bearing steel SUJ2. The Mode II fatigue growth rate of the hydrogen-charged specimens was about twice higher than that of the uncharged specimens. These results demonstrated that the new rolling contact fatigue testing was useful to investigate Mode II fatigue crack growth.

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This study describes an investigation of the effect of over bending moment (Mp) on the fatigue limit of spring steel containing a crack in the stress concentration zone. 3-point bending specimens with a notch were prepared for fatigue test. An artificial semi-circular slit was made into the bottom of the notch, and subsequently Mp was loaded. Next, bending fatigue tests were carried out. The following results were obtained. (1) The fatigue limits of specimens increased with increasing value of Mp. (2) In case of specimens containing a slit of 0.2 and 0.3mm in depth, the fatigue limits of the Mp-loaded specimens were improved up to around twice those of the specimens without Mp loading. (3) A slit of 0.05mm in depth was rendered harmless by the loading of Mp, because the Mp-loaded specimens with a slit of 0.05 mm in depth showed the fatigue limits about the same as that of specimens without slit. (4) Results of calculation by FEM showed that the loaded Mp induces a large compressive residual stress in the stress concentration zone.

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In electronic packages such as BGA and LGA packages, it is very important for the reliability of packages to decrease their warpage during the manufacturing process and reduce the residual stress on the surface of the semiconductor chip at the service temperature. In this research, the authors proposed a simulation method to predict both the warpage of packages and the residual stress simultaneously. The developed technique considering initial warpage of components and the viscoelastic material properties of the die bonding adhesive and substrate made it possible to predict warpage and the stress after the die bonding process accurately.

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This study presents an analytical model to predict compressive strength of unidirectional FRP. Proposed model considers the effect of strain-rate dependency on mechanical properties of constituent materials. The model is based on the elastic foundation model and the microbuckling model of fiber which has initial misalignment in matrix. Compressive deformation of unidirectional FRP is considered by dividing into fiber microbuckling region and plastic kinking region. Additionally, to take into consideration the change in compressive deformation mode accompanying fiber volume fraction or fiber microbuckling, A mode function is introduced. The predictions from the proposed model are compared with experimental results of unidirectional E-glass/Epoxy and T700SC/Epoxy evaluated by using the conventional split Hopkinson pressure bar method. Incorporating strain-rate dependency on compressive modulus of reinforcement calculated from composite mixture law, the predictions are found to be in good agreement with experimental results of strain-rate dependency on compressive strength. Accuracy of the prediction is improved by changing the mode function.

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Three kinds of fatigue failure mode are appeared in a S-N curve of high strength steel depending on applied stress amplitude level, such as surface inclusion induced failure mode in high stress amplitude level and short fatigue lifetime, subsurface inclusion induced failure mode without GBF area and that with GBF area in low stress amplitude level and high and/or very high cycle fatigue (VHCF) regime. Fatigue life in the VHCF regime is controlled by formation of the GBF area. Method to predict the fatigue lifetime and/or S-N curve of high-strength steels in the VHCF regime was discussed. It was assumed in this study that small fatigue crack growth in the GBF area was followed by Paris power law. It was shown that there was a linear relationship in the double logarithmic diagram between value of exponent, m, and constant, C, in the power law obtained from the S-N data of some high-strength steels tested under rotating bending and axial loading condition. Also, the exponent, m, showed the linear relationship with the Vickers hardness of the materials in double logarithmic diagram. Based on these experimental facts, new prediction of fatigue lifetime in the VHCF regime was proposed in form of Basquin's equation. Predicted fatigue lifetime and experimental result accorded well together, as compared to the prior proposed predictions.

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The decrease in fatigue life of solder joints under the high temperature environment is a major problem in semiconductor packages for automotive applications. To clarify the mechanism of the fatigue-life decrease, we carried out the mechanical cyclic fatigue test of the Sn-3mass%Ag-0.5mass%Cu solder joint after high-temperature heat treatment. We studied a correlation between the heat treatment condition and the fatigue-life decrease. The method for estimating the fatigue life decrease from the heating history of heat cycle tests was also studied. The fatigue-life decrease of the solder joints after heat treatment was explained as the temporal change in the fatigue ductility coefficient of the Coffin-Manson's low, and the decreasing rate of fatigue life was converged within the range from 60 to 70%. We found that the fatigue-life decrease can be quantitatively estimated by using Arrhenius's low with the consideration of the heating temperature, hold time and the number of reliability target cycle of the heat cycle test.

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The energy absorbing ability of a crashworthy structure for a railway's rolling stock composed of welded aluminum alloys was evaluated numerically using finite element analysis (FEA). In the numerical simulation, two different material models were employed to characterize the base aluminum alloys and welding materials: one was a damage-mechanics model and the other a conventional plastic-mechanics model. The energy absorbing abilities of two different types of crashworthy structures were predicted using the FE simulations, and the numerical predictions were compared with experimental results obtained from quasi-static compression tests using mockups of these two crashworthy structures. The local phenomena, buckling and fractures, observed in the mockup tests, were also predicted numerically. The local fractures were found to be accurately reproduced in the FE simulation employing the damage-mechanics model, while the buckling behaviors were predicted with substantial accuracies in both of the two simulations. Comparison of the experimental results and the numerical predictions also showed that the FE simulation applying the damage-mechanics model had an advantage on accurately predicting the energy absorption. The relationship between the local phenomena and the structural energy absorption is discussed.

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In the present paper, the collapse behaviors of rectangular tubes subjected to pure bending are investigated using the finite element method. Such bending collapse has been investigated extensively. These studies have revealed the existence of two types of collapse. The first type is a collapse due to buckling at the compression flange, and the second type is a collapse due to plastic yielding at the flanges. Moreover, another type of collapse exists. For a rectangular tube in which the web is wider than the flange, collapse due to buckling occurs at the compression web. In the present paper, previous evaluation method of the maximum moment is refined, and systemized evaluation method is proposed. The validity of this method is verified through comparison with the numerical results obtained by FEM under various conditions.

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In this paper, the equivalent torsion rigidity for honeycomb canape is analyzed theoretically. Honeycomb canape is a honeycomb to which a face sheet is attached to the one side. We applied the rule of mixture to honeycomb canape which is composed by triangle, rectangle and hexagon cells. The theoretical analysis for triangle and rectangle honeycomb canape based on the rule of mixture is in good agreement with the results of FEM. However, there is an error factor to apply the rule of mixture to hexagon honeycomb canape. The error factor is that the rotational deformation of hexagon honeycomb core does not coincide with the face sheet. Therefore, it is necessary that the strain energy caused by the difference of the rotational deformation to calculate equivalent torsion rigidity of hexagon honeycomb canape. Then, a method to calculate equivalent torsion rigidity based on the compatibility condition of core and face sheet is proposed, and its validity is verified by using numerical results of FEM.

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In this paper, a newly developed process to fabricate micro-sized specimen for axial compressive strength evaluation of single fiber using ultraviolet (UV) lithography was proposed. Technique of UV lithography, which was used in semiconductor production, was adopted to fabricate a test specimen that fiber was partially embedded in a photo-polymer. The photo-polymer SU-8 was used as a resist for high aspect ratio test specimen. A PBO fiber, which has excellent characteristics in tensile strength, tensile modulus and chemical resistance, was used as a test fiber material. Direct axial compression test was performed using the micro-compression testing machine with a flat indenter of 50 μm in diameter and two camera units. Finite element analysis was carried out to compute the internal stress distribution in the fiber under compression and to determine the optimum fiber length. The results showed that the proposed specimen fabrication method using UV lithography was demonstrated to be effective for direct measurement of the compressive strengths of PBO fibers. Finite element analysis revealed that the PBO fiber length in the compression test should be at least 20 μm to avoid the influence of fiber rooting in the resin. The experimental values obtained for the compressive strengths of PBO fibers exhibited Weibull distribution with a mean of 217 MPa, which is lower than the values generally obtained by other test methods such as the loop test or resin embedment test.

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The authors proposed novel thin film formation method, Flashing spray CVD by using mixed solution to improve several kind of disadvantages such as decomposition and adhesion of the precursor at evaporator and supply line. In this method, the solution is injected through the injector which is installed above the cvd chamber. When the solution pressure reaches saturated pressure, flash boiling should be occurred. The flash boiling spray is leading to the homogeneous vapor without evaporator. Further, the precursor and low boiling point organic solvent mixed solution is used as the solution to improve the precursor vaporization characteristics. In the previous study, the homogeneous SiO₂ film was succeeded to form by flashing spray cvd. The film thickness distribution of SiO₂ film on 100mm diameter Si wafer was realized to be less than 4%. Furthermore, this method enables us to control the film with various thicknesses by optimizing the injection duration, cycle and frequency. In this paper, TEOS was used as the precursor and n-pentane was used as the low boiling point organic solvent. As the result, the film thickness distribution of SiO₂ film on 200mm diameter wafer is less than 7 % at ambient pressure equal to 26 Pa because flash boiling is promoted by decreasing the ambient pressure. The film thickness has the maximum at injection quantity of TEOS equal to about 6mg.

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Polymerization shrinkage of a light-cured composite resin was studied using artificial cylindrical cavities. To examine the property change as functions of cavity depth and irradiation time, we performed two experiments; micro-Vickers hardness and tensile tests. Then we determined the hardness H_v and modulus E of the resin specimens, and the following results were obtained. The values of H_v and E exhibited the maximum near the irradiation surface and then decreased gradually with the depth, and the maximum values increased as the irradiation time increased. To study the property change, we introduced an analytical model and suggested that it can predict all the important features of the property change as functions of the depth and irradiation time.

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