This paper deals with fatigue strength of paper-based friction materials under cyclic shear-compressive loading condition which is regarded as a real loading condition in an automotive automatic transmission. The fatigue tests under various shear and compressive stress conditions are carried out for four kinds of friction materials in order to evaluate the fatigue properties and to clarify the influence of constituents on fatigue strength. The constituents of the friction materials are aramid, cellulose, carbon fiber, diatomite-filler, and phenolic resin. The S-N curves of the friction materials under shear-compressive loading are described by straight lines in a log-log diagram. The fatigue strength increases with increasing compressive stress component. The fatigue strength of the friction material composed of cellulose fiber and phenolic resin is higher than that of the friction material composed of aramid fiber and phenolic resin. The fatigue strength of the aramid-based friction material slightly improved due to addition of small amount of diatomite-filler. The compressive cyclic deformation tests are also carried out to investigate the fatigue strength under compressive-dominant stress condition. When the compressive stress increases, the friction material becomes dense and the elastic modulus becomes high. The cyclic strain range remains as low value, although the cyclic compressive stress is high. Microscopically, the net stress range carried by each fiber also seems to remain as low value. Therefore, the fatigue strength of the paper-based friction material is remarkably high under the compressive-dominant stress condition.

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To clarify the effect of graphite nodule size and ferritic gain size on fatigue strength of ferritic spheroidal graphite cast iron, tensile tests and fatigue tests were carried out. Six types of test specimens were constructed with different gain sizes from the speroidal graphite cast iron blocks. Two block sizes were considered as 32mm and 80mm in thickness. The ferritic spheroidal graphite cast iron was constructed by three types of ferritization heat treatment of the speroidal graphite cast iron. The ferrite grain refinement improved both tensile and proof strengths. The initiation-site of fatigue fracture was different based on the graphite nodule size. The fatigue cracks of large graphite nodule iron initiated from abnormal graphite, that is, closely adjoining graphite nodules or coarse graphite. On the other hand, the fatigue cracks of small graphite nodule iron initiated from small shrinkage cavity. The fatigue strength with large graphite nodules was improved, while the fatigue strength of small graphite nodule was unchanged by the ferrite gain refinement. It was also noted that the fatigue strength of spheroidal graphite cast iron with different ferritic grain size was determined by the maximum length of the non-propagating micro-crack.

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Micro-hardness distribution was measured by using an ultra-micro hardness test at a crack tip under a plane strain condition for a crack propagation test specimen made of a low-carbon austenite stainless steel JIS-SUS316L. Moreover, crystal orientations were analyzed by EBSD for individual crystal grains in the plastic strained area at the crack tip. The conclusions can be summarized as follows. (1) The mean strain in a 500-μm region around the crack tip was supposed with 3% from the hardness distribution in an ultra-micro hardness test. Therefore, the plasticity strain distribution of the crack tip under a plane strain condition can be visualized based on the ultra-micro hardness and an experience equation of the true strain by measuring the hardness distribution. (2) When the analysis by EBSD increased the step size of the KAM map, the local misorientation increased. On the other hand, the color map of some grain boundary neighborhoods reversed when the step size changed in a GROD map. Therefore, an analysis of KAM is suitable for the local transformation of the crack tip neighborhood. (3) From the results of an EBSD analysis, it became clear that a local heterogeneous transformation occurred in random grain boundaries at the crack tip, and the transformation hardly occurred at the CSL grain boundary of the crack tip.

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This study investigated the strength of piping in boiling water reactors (BWRs) subjected to detonation of flammable gas that accumulates in piping. Accumulated gases in the piping of BWRs are stoichiometric hydrogen-oxygen and steam. Stoichiometric hydrogen-oxygen gas and about 5% nitrogen gas were detonated in carbon steel pipes with an initial pressure from 2.5 to 4.0 MPa at room temperature in our experiment. Plastic strains were measured with strain gauges and the behaviours of pipe ruptures were recorded with a high speed camera. Pipe specimens were ruptured rapidly with large plastic circumferential strain of more than 8%. A dimple pattern was observed in the fracture surfaces. Therefore, the fracture mode of carbon steel pipes under detonation pressure is ductile fracture. Although the maximum pressure of detonation was about 20 times higher than the initial pressure, it did not have greatly influence the strength of piping, since the oscillation of detonation pressure was shorter than the period that plastic strain was increasing. The effect of piping elements was also investigated. The detonation experiment was conducted with an elbow specimen and the highest strain was observed in the downstream pipe from the elbow rather than in the elbow element. Strain of 0.5% was induced by a detonation wave at a matching pipe for a closed pipe specimen that simulated a closed valve. However, a reflected wave ruptured the matching pipe. Since the pressure of the reflected wave at the closed end is much higher than that of the detonation wave, the integrity of the piping system is governed by the strength of pipes attached to closed valves.

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Adhesively bonded joints are frequently used in aircraft and aerospace structures. A bonding technique called overlamination, where the parts to be joined are connected by adherends that are laminated directly upon the assembly, is more common in the marine industry, and there is a need to evaluate the stress distribution in such joints. In the present paper, the interfacial stress distribution in double-lap joints is investigated. A new analytical model of the shear and normal stresses are derived by using the beam bending theory. This method does not require an assumption of stress distribution in the lap. Both the shear stress and the normal stress along the adhesion layer can be evaluated by the present theoretical method. It is shown that both the shear stress and the normal stress depend on the thickness of adhesion layer. Its validity is verified by using numerical results of FEM. It is shown that our solutions provide a better prediction than the original theoretical solutions.

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In this paper, a parameter-free optimization method is proposed for designing the optimal free-formed shell with an arbitrary surface. The compliance minimization problem of a linear elastic shell is dealt with here as an application example of this method. The optimum design problem is formulated as a distributed-parameter shape optimization problem under the assumptions that a shell is varied in the normal direction to the surface. The shape gradient function and the optimality conditions for this problem are theoretically derived by using the material derivative method and the Lagrange multiplier method. The shape gradient function is applied to the shell surface as a pseudo distributed force under a Robin condition for varying the surface, for minimizing the objective functional and for regularizing the mesh. With this approach, an optimal global and local curvature distribution of shell surface can be determined without any shape design parameterization. The validity and practical utility of this method are verified through several design problems. It is also confirmed that a membrane stress state is obtained by this method.

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In electronic packages such as BGA and LGA packages, it is very important for the reliability of packages to reduce the residual stress on the surfaces of semiconductor chips. In recent years, product defects caused by changes in the electrical operating characteristics of the semiconductor devices in the chip produced by residual stress generated in the semiconductor chip within the semiconductor package have also become a problem. That has resulted in a need to accurately estimate residual stress and electronic characteristic changes within the package from the design stage and the widespread use of simulation by the finite element method (FEM) or other techniques for that purpose. In this research, the authors proposed the evaluation method to predict the electronic characteristic changes of stress-induced multilayer chips in resin-molded electronic packages. The developed technique considering the stress singular field and the piezoelectric effect made it possible to predict electronic characteristic changes of multilayer chips in resin-molded electronic packages accurately.

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This paper describes the homogenization of fin layers for structural analysis of heat exchanger cores composed of flat tubes and wavy fins. It is assumed that uniform deformation prevails at the bonded interfaces between fins and tubes, and also that the fins have the Y-periodicity in the fin layers. The homogenization method for 3D periodic solids is then shown to be applicable to the homogenization of fin layers, provided that the uniform deformation condition is imposed at the bonded interfaces between fins and tubes. The resulting homogenization method is applied to designed and real shapes of outer and inner fins in an intercooler. The evaluated, homogenized elastic stiffnesses of fin layers are verified by performing finite element analyses using full-scale and fin-homogenized models of tube-fin connected pieces subjected to uniaxial compression. An experiment of a tube-fin laminated block under uniaxial compression is further performed to demonstrate that the real shapes of outer and inner fins are definitely important for the homogenization of fin layers.

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The accuracy of fixed boundary condition is compared between the Multi-dimensional Moving Least Method (C-MultiMLS method) and the Element Free Galerkin Method (EFG method) with 2D dynamic problems, showing the advantage of the former over the latter. In this study, the dynamic explicit method is employed in order to solve the dynamic equation. It is also observed that the latter gives unstable solutions when a large penalty number is employed to improve the accuracy of the fixed boundary.

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In this research, interlaminar shear strength of medium-density fiberboard (MDF) as obtained by a three-point short-beam shear test was examined. The three-point short-beam shear tests were conducted on MDF, which were used in a previous research on the asymmetric four-point bending tests. Interlaminar shear strength was measured using the specimens with rectangular and I-shaped cross sections with varying the span lengths. It is less useful to obtain the interlaminar shear strength by the three-point short-beam shear test than the asymmetric four-point bending test because the effective span length for obtaining an appropriate value of interlaminar shear strength is extremely restricted.

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This study describes an investigation of the effect of peening on the fatigue limit of rolled steel containing a crack at the weld toe. 3-point bending specimens with a weld zone were prepared for fatigue test. An artificial semi-circular slit was made into the weld toe, and subsequently the weld toe was peened by needle-peening. Using those specimens, bending fatigue tests were carried out. The following results were obtained. (1) The fatigue limits of specimens containing a slit improved considerably by peening. (2) The fracture occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to that of non-slit specimens. (3) A slit of 0.4- 1.2 mm in depth was rendered harmless by the peening.

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A pressure test was carried out using a thin CFRP pressure vessel to consider artificial AE signals propagating path. In the test, artificial AE signals were emitted and were received by several AE sensors. The artificial AE signals were emitted under several pressure conditions which included the case where the vessel was empty. The test results revealed that existing water in the vessel changed AE signal propagating path against the empty condition. In the case of the empty condition, the artificial AE signals propagated on the surface of the CFRP vessel. However, in the case of water existing fully in the vessel, the artificial AE signals propagated in the water mainly. Furthermore, the results indicated that the appropriate AE sensors arrangement leads to accurate AE source locations using AE signals which propagate in water.

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