Aluminum (Al) based composites containing vapor-growth carbon fibers (VGCF) and carbon nanotubes (CNT) has been developed by authors for a decade using spark plasma sintering (SPS). It has been clarified that the thermal conductivity of the composite is three times higher than that of a normal Al matrix. The maximum volume fraction of VGCF within the composites to obtain high thermal conductivity was 60%. However, this high volume fraction of VGCF may have a negative effect on the strength of the composite. These composites are intended for use in controlling heat in radiation fins of a heat exchanger or a heat sink. Thus, strength properties and thermal conductivities of the composite at high temperatures should be precisely clarified. In this paper, temperature dependencies of both thermal conductivities and strength properties of the composite are investigated. Pure tensile tests and measurements of thermal conductivity by laser flash methods are conducted at high temperatures. Both the strength properties and the thermal conductivities of the composite decrease with increase in temperature. However, the decreasing behaviors of these properties were different in the Al matrix. The change in the strength of the composite due to temperature is smaller than that of the Al matrix and also smaller than the thermal conductivity of the composites.
Considering the efficient productivity and maintainability, most of machine and products has many joints (e.g., fastening, welding and adhesive joints). Especially, the bolted joints have been frequently used for these purposes as machine elements. However, many troubles such as loosening or fatigue failure of bolted joints were often experienced. More attentions must be paid on the improvement of the strength and the reliability of these bolted joints. It is generally said that the relative slippage between nuts and fastened body under the transverse loading will generate the rotation of nuts and cause the loosening of bolted joints. [1, 2]. For example, the thermal expansion due to temperature change between jointed members may cause these slippage and loosening problems. The aim of this present research is to clarify the mechanical behavior of bolted joints under transverse loadings, and present the critical relative slippage (Scr), more than this slippage the loosening will occur. To derive this critical relative slippage (Scr), at first the resistant bending moment between bolt/nut contact interface (Mn),and equivalent stiffness on bolt head/fastened body contact interface(kw) were derived.. Then the validity of resistant bending moment between bolt/nut contact interface (Mn),and equivalent stiffness on bolt head/fastened body contact interface(kw) were confirmed by the quasi-static loading test. Finally, the validity of critical relative slippage (Scr) was confirmed by the repeated cyclic loading test.
Herein, we consider the axisymmetric problem of a penny-shaped crack in an elastic material sandwiched between other materials. It is assumed that the central substance is composed of an elastic layer held between two semi-infinite bodies with different elastic constants, and that the crack is situated in the central plane of the elastic layer and subjected to uniform pressures on its internal surfaces. We consider two contact conditions; perfectly bonded and frictionless contact at the interfaces with the dissimilar materials. Dual integral equations are reduced to an infinite system of simultaneous equations by expressing normal displacements on the crack surfaces as an appropriate series function. Numerical results were obtained to examine the effects of the elastic constants of the layer and semi-infinite bodies and contact conditions on the stress intensity factor at the tip of the penny-shaped crack, the distribution of normal displacement, and stress on the crack plane. Based on the results of these numerical calculations, several conclusions can be made, as follows. 1) The distributions of normal displacement and stress at the crack plane and the stress intensity factor at the tip of the crack become larger than the results for an infinite solid when the ratio of the shear modulus of the layer to that of the semi-infinite bodies is larger than 1. 2) The numerical results for normal displacement and stress, and for stress intensity factors, in the frictionless case are higher than for the perfectly bonded case regardless of the shear modulus ratio and layer thickness ratio. The difference between the perfectly bonded and frictionless cases becomes greater as the layer thickness ratio becomes smaller. 3) There is a slight difference in the stress intensity factor values obtained from the present work and the corresponding results previously reported in the literature.
Thermal fatigue cracks may occur in a T-junction pipe due to the mixing of hot and cold fluids. To develop an evaluation method for thermal fatigue, the authors previously performed a mixing tee experiment called the T-Cubic experiment. In this study, a fluid-structure coupled simulation for conjugate heat transfer was carried out to investigate the predictive performance of the flow and temperature fields and temperature fluctuation on the pipe inner surface at a mixing tee of the T-Cubic experiment. The computational domain included 304 type stainless steel pipe as well as the working fluid of water. Time-averaged velocity and temperature were reproduced well over the entire computational domain. Although velocity fluctuation intensity at a distance from the wall was relatively smaller than experimental data, the simulation could reproduce the trend of the experimental data, especially the velocity fluctuation intensity peak near the wall. The temperature fluctuation intensity was also larger than the experimental data, though the tendency could be reproduced by the simulation. The temperature fluctuation intensity on the pipe inner surface is the most important parameter for thermal fatigue and though it was 20% to 36% larger than the experimental data at its peak, the tendency was reproduced to a certain extent. The fluid temperature in the numerical simulation fluctuated at almost the same level from 0.1 Hz to 10 Hz, but high frequency components attenuated and low frequency components around 0.1 Hz remained on the pipe inner surface.
This paper describes the J-integral evaluation methods for the case of multiple circumferential cracks in a cylinder subjected to bending moments. J-integral is one of the parameters of fracture mechanics used in the fracture assessment of materials that show ductile fracture behavior. So far, there have been various J-integral evaluation methods proposed for a single crack in a cylinder, such as fully plastic solutions and a reference stress method, but none for multiple circumferential cracks. Therefore, this study examines the stress intensity factor evaluation method for cylinders with multiple circumferential cracks. This method estimates the stress intensity factor of multiple circumferential cracks in a cylinder based on a solution for single cracks. Next, a J-integral evaluation method based on the reference stress method is proposed. With this method, the reference stress is calculated from the plastic collapse strength of a cylinder with multiple cracks. The proposed methods have generality to the crack dimensions (sizes and positions) and the material characteristics of the cylinder, and were effective in predicting the J-integral simply and with high accuracy.
Conventionally, designers of electronic equipment structures visually inspect the insulation distance or check it by using CAD software functions. However, unintentionally failed detection and overdetection of objects being inspected can cause problems. Therefore, we are developing a technique for checking the insulation distance. The technique calculates the insulation distance by using voxels, which are in orthogonal meshes. The inputs of this technique involve checking conditions such as the clearance distance threshold and creepage distance threshold, setting part attributes such as of insulation and conduction, and calculating parameters such as voxel sizes. The output of this technique is the visualization of violating parts and paths detected by calculating the insulation distance and generating a distance map. We confirmed that our technique can measure the clearance and creepage distances, detect violation parts, and reduce overdetection of a model for inspection.
For the crawl stroke in swimming, it is important that the stroke made by the upper limbs and the flutter kick made by the lower limbs are well coordinated in order to enhance swimming performance. However, the training method to acquire the appropriate flutter kick timing has not been sufficiently established. In the present study, a biofeedback training system for swimmers to acquire appropriate kick timing was proposed. In this system, the most difficult and important part is the estimation of the appropriate kick timing. Therefore, the objective of this study was to develop a kick timing estimation algorithm in the crawl stroke for biofeedback training system using neural oscillators. First, a CPG network which outputs the kick estimation timing according to the input was constructed. In order to synchronize the roll angle in the CPG network with the actual one measured by a sensor, a special algorithm to change the cycle of the oscillation for the CPG network was introduced. Validation for the output of sinusoidal input accompanying sudden change in cycle was examined. It was found that the output signal for the roll tracked the input signal well, despite the sudden change in cycle. Validation for the actual input obtained in the experiment was next examined. It was found that the output from the CPG network was sufficiently consistent with the experimental values, suggesting sufficient performance of the proposed estimation algorithm.
Several previous studies investigated comfort while soaking in hot bathwater from the perspective of thermal effects or physiology. However, few studies investigated bathing comfort from the perspective of biomechanics, although the biomechanical state in bathing, such as buoyancy on a human and the degree of muscle contraction is expected to be changed according to soaking postures. Indeed, only a few studies from the biomechanical viewpoint provided biomechanical models. In addition, the provide models were insufficient to discuss biomechanical loads in detail. The objective of this study was to evaluate soaking postures considering the effects of buoyancy, muscle contraction and passive elastic joint moment from the perspective of biomechanics and to evaluate biomechanical loads in detail. Soaking postures and reaction forces from the bathtub to a human were measured for ten healthy male participants and under two bathtub conditions (recent bathtub and conventional one). A three-dimensional motion analysis system and waterproofed three-dimensional force plates were used to measure the experimental data. A biomechanical model in which a human body was represented as a link of body segments was constructed. The torque due to buoyancy and passive elastic joint moment were considered in the model. The result showed that all the torque components due to buoyancy, gravity, reaction forces, and passive elastic joint moment contributed to the joint torques and each torque component was changed between bathtub conditions. In addition, joint torques on the ankle and knee joints in the recent bathtub were significantly smaller than those in the conventional bathtub. These results suggested that the bathing posture in the recent bathtub was more comfortable than that in the conventional one. Furthermore, the difference in joint torques between bathtub conditions suggested a potential benefit for designing bathtub shape, in which know-how of developers or subjective assessment is relied previously, with quantifying from biomechanical viewpoint.
A pantograph mounted on a high-speed train roof is exposed to high-speed air flow while traveling, and lift force is generated in the pantograph. To ensure high current collecting performance of the pantograph, it is important to appropriately adjust the lift force generated in the pantograph. The flow velocity along the roof of a train has a significant influence on the lift force. In this study, we proposed a simple calculation method that enabled us to easily calculate the flow on the train roof in a tunnel using a personal computer. To validate the effectiveness of the proposed method, model experiments were carried out and calculation and experimental results were compared. Furthermore, the influence of hydraulic friction coefficients on train roof flow velocity was examined using the proposed method, which was not time consuming.