In this paper, a new non-contacting strain sensing method applying an iterative periodic time difference detection to eddy current sensor is proposed. The iterative periodic time difference detection means that the time difference between zero cross points of sensing coil voltage is accumulated repetitively. Proposed method is characterized as a simple sensor which consists of very small size coils, oscillator circuits, and a microprocessor. Previously, the periodic time difference caused by inductance changes has been detected by a synchronous amplifier, especially a lock-in amplifier. The new method proposed in this paper will be equivalent to the synchronous detection technique, in which the lock-in amplifier is needless. The accumulation can be held by repetitive drive of the oscillator circuit which consists of sensing coil connected to a capacitor in series or parallel. In the experiment, a torque test unit is used, and torque which causes up to 0.2% torsional strain in test pieces is applied. For test pieces, aluminum alloys and a stainless steel with a nonmagnetic characteristic are selected. From experimental results, a linear relation between sensor output and applied torque is observed. And it is shown that the proposed method is effective.

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In a bolted joint, it is known that failures usually happen at the root of the first bolt thread where the maximum stress concentration occurs. Previously several methods were proposed to reduce the stress concentration through improving bolts and nuts profile. Among those methods, tapering threads have been widely used in mechanical structures. Those types of threads are called CD bolts, which were proposed by Nishida as an effective method for stress reduction. Several experimental studies indicated that CD bolts have higher fatigue strength although little FEM analyses is available. In this study, therefore, the bolted joint with tapered threads is analyzed with the finite element method, and stress reduction effect of CD bolts is discussed with varying geometrical conditions. The reduction of the stress concentration is realized by tapering bolt thread. Then, it is found that the stress reduction is notable when the height of bolt threads is reduced significantly near the bolt heat and the nut is closer to the bolt head. According to those results, optimum conditions for stress reduction are discussed. Then, it is shown that the maximum stress can be decreased by 20% compared with the cases of standard bolts and nuts.

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An aluminum honeycomb which has etched cell wall is used as a shock absorbent material for the offset frontal collision test and the side collision test of automobile. In this study, based on the analyses of the shock absorption mechanism, a new crushing strength formula is proposed. Firstly, load-displacement curves obtained from compression tests in quasi-static condition showed almost linear relation between a thinning rate of cell walls R and a crushing strength. Secondly, based on Wierzbicki's theory, a new formula was proposed, which can estimate a crushing strength of honeycomb material with thinning wall. Thirdly, parametric analyses were carried out with FEM model which can simulate a delamination between cell walls. The results which were obtained from theory and FEM almost corresponded to each other for a wide range of core ratio. The proposed formula works well for R <70%. Impact tests were carried out, in which the weight was dropped freely at the speed used for automobile tests. Those results almost agreed well with the sum of the theoretical crush strength and the inside air pressure.

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In the heating method which can be available for nondestructive and in situ measurements of residual stresses, a new method is proposed for simultaneous estimation of the heat flux and residual stresses. The approach is formulated as an inverse problem by using the surface displacements relieved by local heating and the resulting nonlinear least square problem is solved by Levenberg-Marquardt method. In this procedure, the displacements of the direct problem are computed by FEM. The approach is applied to estimation of uniaxial and biaxial stresses in a plate. The numerical results show the effectiveness of the proposed method.

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For atomic-level investigation of plasticity in amorphous metal, instability analysis which can rigorously describe unstable deformation of atomic structures is a key technique. However, the analytical method cannot be applied to large-scale amorphous metal because of the enormously-increasing computational load with respect to the number of atoms. In this study, an efficient instability analysis method for a large-scale atomic system is proposed using linear elements, and it is applied to cracked amorphous metal under tension. The proposed method successfully evaluates the instability criterion as well as the highly-localized unstable deformation. Moreover, the computational efficiency is considerably improved from the original one, enabling us to address mechanical instability problems in amorphous metal consisting of a great number of atoms.

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The martensitic and the reverse transformation temperatures are directly related to the bending rigidity of the TiNi shape memory alloy (SMA) wire. In this paper, aiming at obtaining a functionally graded TiNi shape memory alloy wire that varies in bending rigidity from high to low along the wire axis, a new fabrication process of combined powder metallurgy and plastic working is proposed. First, a multi-layered TiNi green compact, where Ti-Ni compositions varied layer by layer, was sintered by means of pulse current pressure sintering technique, and then it was hot-extruded and cold drawn into a wire. In this paper, as a first step of fabrication of a wire, we investigated transformation properties and texture morphologies of sintered and solution treated compacts. From differential scanning calorimetry and X-ray diffraction measurements, it was found that in this process the solution treatment of the billet plays an important role to induce the transformation temperature gradient in the sintered compact, since it greatly activates the interdiffusion between Ti and Ni particles.

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Protective coating, MCrAIY, is used to isolate a super alloy substrate from oxidation and/or corrosion. The mechanical properties of the coating give the significant influence on the thermomechanical fatigue strength of the substrate. However, there are few proper and simple methods to evaluate the mechanical properties of the thin coatings used in actual systems. Authors have developed the lateral compression method of circular tube specimen and applied to evaluation of high temperature mechanical properties and fatigue strength in plasma spray coatings. The circular tube specimen has great merits, easy to make and easy to load. The specimen has further great merit that the test piece breaks 4 times in only one test piece. In this study, beam models were proposed to evaluate the strength of 4 locations. Loading with two plates was proposed because loading was easy and stable. However, in the case of loading with two plates, the beam model was apt to disagree with the actual deformation if the coating had low stiffness. It was because intensive load converted to distributed load and the loading point moved from original point. Then, the applicable range of thickness and Young's modulus was examined by FEM elastic contact analysis. It was found that the bending strength of thin coating is able to be obtained accurately-by selecting the proper radius of circular tube specimen. It was also found that the method does not depend on materials if the Young's modulus is greater than 50 GPa. These results were also confirmed experimentally using CoNiCrAlY coatings.

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In order to improve performance of anti lock brake system (ABS) and detect condition of road surface, intelligent tires that monitor strain of interior surface and rolling radius of tire are demanded. However, the high stiffness of an attached sensor like a strain gauge causes debonding of sensors from tire rubber. In the present study, noncontact concurrent monitoring method is proposed using digital image correlation method (DICM) and spotlight projection. In-plane strain and out-of-plane displacement (rolling radius) are calculated by using image processing with an image of interior surface of tire that is taken with a single CCD camera fixed on wheel rim. New monitoring system is applied to Al beam and commercially available radial tire. As a result, this monitoring system is proved to be able to measure in-plane strain and out-of-plane displacement with high accuracy, and confirmed to be effective for concurrent monitoring of tires.

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It is usually regarded as a common understanding that fatigue failure would not occur if all stresses were kept below fatigue limit diagram. However, it was shown that fatigue failure occurred in some special cases of variable amplitude loading condition even when all stresses were kept below fatigue limit diagram in the case of small-notched specimen. The cause of such a phenomenon was examined using two-step stress pattern for low alloy steel SCM440H. In the case of constant stress amplitude loading, non-propagating crack was formed only at low mean stress region and not formed at high mean stress. However, in the case of two-step stress pattern in which the first step stress was chosen as R=-1 and the second step stress was with high mean stress, a non-propagating crack was formed by the first step stress. This crack functioned as a pre-crack for the second step stress with high mean stress. In this study, the effect of notch shape was examined. The effect of absorbed hydrogen was also investigated. Absorption of 0.3 ppm hydrogen caused more reduction of fatigue limit.

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Hydrogen is considered to be a possible energy source in the coming future. However, it has been recognized that hydrogen has a detrimental effect on the fatigue strength of metal. The fatigue crack growth characteristic is an important property for the integrity assessment of hydrogen utilization machine. In this report, the effect of absorbed hydrogen on the fatigue crack propagation characteristic in the near threshold regime was studied using low alloy steel, carbon steels and heat resistant alloy A286. Especially in this study, very short pre-cracked specimen as small as 0.03 mm deep was used. As a result, materials with Vickers hardness higher than 300 were susceptible to absorbed hydrogen irrespective of alloy system. Fatigue crack propagation was accelerated and the ΔK_th was lowered about 25%. No remarkable change was observed in materials with hardness lower than 200.

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This research presents a practicable method to investigate the characteristics of the microcrack growth in brittle materials. The crack length measurement method using an ion-sputtered film was applied to measure the length of the microcrack growing in soda-lime glass and alumina ceramics in four-point bending tests. Since the measurement system can measure the crack length at a sampling frequency of 125 kHz, the crack length was measured almost continually, and the relation-ship between the crack growth rate and the stress intensity factor was obtained in the whole regions from low crack growth rate to brittle fracture. If the relationship between crack growth rate and stress intensity factor follows the Paris law, the n values of the soda-lime glass and alumina ceramics are obtained in the region I and region II that are very important to the fatigue life estimation for these materials.

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Honeycomb panel is widely used as flooring or wall material in various structure including buildings, aircraft, train and so on due to high stiffness and lightness at present. Honeycomb panel, however, has a disadvantage that adhesive used to glue honeycomb core and top plate may burn by fire. On the other hand truss core panel has equivalent stiffness as honeycomb panel and is expected to be a alternative to honeycomb panel as it is safer for fire. However, in general, difficulty exists to form truss core and forming techniques should be developed for practice use of truss core panel. In this paper, firstly theoretical forming limitation is discussed for tetrahedral truss core. Secondly single stage forming simulation of truss core panel using explicit FEM technique was performed for preliminary investigation to estimate formability and thickness distribution. Finally multi-stage forming simulation was presented and possibility to apply press forming for truss core panel production through the simulation. In addition some results of the simulation was compared with the experiment.

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