The research purpose of this study is to overcome some technical weak points of the conventional non-destructive inspection technique based on the ultrasonic wave propagation visualization. It is well-known that, in thin-walled structures, propagating ultrasonic waves become Lamb waves. We focus on thin plates, where Lamb waves excited by a pulse laser are employed. When ultrasonic Lamb waves propagate in the thin plates, the particles along the through-thickness direction of the whole plate vibrate. The present experimentation employs a pulse laser scanning method in an inspection region. A remote non-contact scanning by the pulse laser with a fixed sensor enables us to inspect an arbitrarily shaped object, such as curved structures. In this study, we have put forward an improved method based on the conventional wave propagation visualization technique, which can not only estimate the existence and location of a damage, but also evaluate the damage area. In this method, more than three fixed sensors are employed and a new signal index with the corresponding processing technique is proposed based on the normalized strain energy distribution in the inspection region during a specified time period when Lamb waves propagate from the source point to the inspection region. The proposed method has been validated by using the results of both experiment and numerical analysis.

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In this study, the fatigue damage was assumed to be equivalent to the crack initiation and its growth, and fatigue life was assessed by predicting the crack growth. First, a low-cycle fatigue test was conducted in air at room temperature under constant cyclic strain range of 1.2%. The crack initiation and change in crack size during the test were examined by replica investigation. It was found that a crack of 41.2 μm length was initiated almost at the beginning of the test. The identified crack growth rate was shown to correlate well with the strain intensity factor, whose physical meaning was discussed in this study. The fatigue life prediction model (equation) under constant strain range was derived by integrating the crack growth equation defined using the strain intensity factor, and the predicted fatigue lives were almost identical to those obtained by low-cycle fatigue tests. The change in crack depth predicted by the equation also agreed well with the experimental results. Based on the crack growth prediction model, it was shown that the crack size would be less than 0.1 mm even when the estimated fatigue damage exceeded the critical value of the design fatigue curve, in which a twenty-fold safety margin was used for the assessment. It was revealed that the effect of component size and surface roughness, which have been investigated empirically by fatigue tests, could be reasonably explained by considering the crack initiation and growth. Furthermore, the environmental effect on the fatigue life was shown to be brought about by the acceleration of crack growth.

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In developing liquid rocket engine, life time of combustion chamber is an important design issue. However, it is very difficult to quantitatively predict the life time because complicated multi-physics phenomena occur under severe conditions in the combustion chamber. The LE-X engine is under study in JAXA as the next booster engine. In its research and development, shorter development time, lower cost and higher reliability are sought by using front-loading design approaches. Therefore, it is indispensable to evaluate the life time of the combustion chamber precisely in the early phase of development. In order to improve accuracy in the life prediction, we focus on the interaction between thermo-fluid behaviors and structural responses, and have developed a new analysis procedure, that is, high-fidelity multi-physics coupled simulation. By applying this procedure, we have investigated the mechanisms and the dominant factors of residual deformation occurred in the throat, which was experienced under development of the upper stage engine. It has been revealed that the throat's residual deformation strongly depends on cooling capability in the shutdown process, which is affected by the transient flows of both combustion gas and coolant.

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Cavitation often occurs in inducer pumps of space rockets. Silver plated coating on the inducer liner faces the damage of cavitation. In this study, the effects of temperature, pressure, and test liquid on the damage were discussed for the silver plated coating specimen. We carried out cavitation erosion tests in deionized water and ethanol at several temperatures and pressures. Thermodynamic parameter Σ proposed by Brennen was used of a temperature parameter, and suppression pressure p-p_v was used of a pressure parameter. Acoustic impedance was used of a liquid parameter. We discussed mass loss rate using functions of thermodynamic parameter, suppression pressure, and acoustic impedance.

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Dissimilar material joints are used in industrial products for improving functionality and reducing their weight. However, mechanism of delamination or crack for the dissimilar material joints is not still clarified. It is well known that singular stress occurs at the edge of the interface in the joints due to the mismatch of material properties. The stress on the singular stress field can be expressed by two parameters, i.e. the order of stress singularity and the intensity of stress singularity. In the present paper, an influence of the material properties of the adhesive in the shear lap joint on the intensity of stress singularity was investigated using a three-dimensional boundary element method analysis. Material property of adhesive in the shear lap joint is varied and that of adherend is fixed at Young's modulus 100GPa and Poisson's ratio 0.3. The intensities of stress singularity arranged by the different values of the order of stress singularity are expressed as a power function of the ratio of Young's modulus of adherend to adhesive.

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For the utilization of a superior nature of hypereutectic Al-Si alloy, Al-Si functionally graded material (FGM) of thick walled tube is manufactured by the vacuum centrifugal method using hypereutectic Al-25 mass% Si alloy. Then near-net-shape product of Al-Si FGM cup is produced from an FGM billet, which is machined from the FGM tube, by a backward extruding under semi-melt condition. FGM cups are obtained successfully at a molten metal and solid Si coexisting temperature range from 580 to 590°C through a visco-plastic deformation. The morphology and distribution of Si grains in both Al-Si FGM tube and Al-Si FGM cups are examined. The fraction of Si phase in the FGM tube is varied from over 60 mass% Si at outer surface to 15 mass% Si at inner surface, i.e., the outer region of Al-Si FGM tube is lighter than inner region owing to the increase of density of liquid Al-Si alloy with increasing Si content. On the other hand, the fraction of Si phase in the FGM cup is varied from over 70 mass% Si at the bottom region to less than 15 mass% Si at the cup wall region. The fine grain structure was formed regardless of the existence of initial elongated large bulky Si particles at some tested temperature. The optimum semi-solid forming condition produces a significant interaction with both plastic flow and viscous flow resistances and the most preferable temperature is inferred to be just over the eutectic melting point of around 580°C.

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In order to reduce the weight of automobile, aluminum materials has been gradually applied to various automobile parts. It is well known that high axial force of bolted joint induces the decrease in the tightening force due to the plastic deformation of clamped component caused by high surface pressure on the bearing surface. In order to prevent such decrease in tightening force, initial axial force should be set up in appropriate manner. The management of the initial axial force has been realized by the concept of the limit of bearing-surface pressure so far. However, the academic background has not been fully investigated especially in case of the aluminum applications. In this study, we have investigated the effect of the geometries of the hollow cylindrical aluminum clamped component on the initial surface pressure distribution. We have also investigated the amount of the plastic deformation on the bearing surface and the plastic region inside the clamped component by using both the elasto-plastic finite element analysis and tightening experiments. It was found that the plastic deformation increases even in the case of constant averaged surface stress as the outer diameter is decreased and cross-sectional area is decreased. In case of smaller axial force, each shape parameters do not affect the plastic deformation so much. However, as the axial force is increased and plastic region reaches the outer surface of the clamped component, the inflection point appears where the plastic deformation starts to rapidly increase. At the inflection point, the averaged cross-sectional stress reaches about 40 MPa, which corresponds to the stress which initiates the plastic deformation. Consideration of the stress condition inside the clamped component should be taken care as well as the bearing-surface pressure limit.

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A swing circle part of excavator involves many bolted joints subject to impact loading. Therefore, the structural integrity assessment for the loosening of the bolted joints is very important. In this paper, we have tried the loosening analysis for the bolted joints using explicit finite element method. As a check of the validity of the explicit finite element method, the loosening due to quasi-static transverse loading has been investigated by both explicit and implicit finite element methods. The result of the explicit finite element method shows good agreement with that of the implicit finite element method. The developed scheme applies to the loosening of the bolted joints in the swing circle part of the excavator subjected to impact loading. The vibration modes of the excavator model are fitted to the result of experimental modal analysis. All the bolts are modeled by rivets model and tightening force is applied. Bearing part of the swing circle is modeled by spring and dashpot elements. As a result, the acceleration of counter-weight part and the deformation shape of the bolts are successfully reproduced by our model. The stress of the bolts shows agreement within a factor of two. It is found that the safety margin for the loosening caused by bearing-surface slip is more than ten, which is sufficient in terms of engineering application.

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