Time-average electronic speckle pattern interferometry and digital holography are two representative full-field coherent optical techniques used in mechanical vibration measurement. In both techniques, the quantitative data processing is affected by several difficulties. The most important are the weak contrast of Bessel-type fringes and the speckle noise. The greatest obstacle in achieving complete amplitude field estimation comes from the orthogonal components of time-averaged digital holograms or speckle interferograms, where multiplicative, high-frequency phase noise covers the deterministic, vibration-related phase. Several researchers studied these problems in relation with the double-exposure method. In the present paper, the author presents in a single, unifying approach, these double-exposure methods, common to speckle interferometry and digital holography. An important reduction of multiplicative high-frequency phase noise allows obtaining fringe-averaged patterns whose intensity noise is much lower than in classical time-average holography. The analysis allows choosing the most appropriate method leading not only to a higher fringe pattern quality, lower noise and extended measurement range, but also to a method of vibration-related phase estimation, which may include in some stages subpixel precision. The method, based on the mathematical inversion of the Bessel function on monotonic intervals, is equivalent to phase unwrapping, but it only uses time-averaged fringe patterns.

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Dyneema composite panels, which contain high Ultra High Molecular Weight Polyethylene fibers, are used in armor applications. They give good protection against fragments, bullets or other projectiles. In order to be able to study the internal processes in such a composite panel, a new modeling approach is developed and is described in this paper. This approach uses a detailed modeling approach that discretises the fibrous phase in Dyneema composite. In the past, continuum approaches and layer discretisation have been used by other researchers to study the processes in Dyneema composite panels and to predict the ballistic strength of these panels. The aforementioned approaches were however not very successful in predicting the ballistic strength, because fiber sliding, fiber failure and delamination of layers were not taken into account and static properties of the material were used. In addition to this, these models were often too coarse to study the processes in the panel. This often resulted in a calculated ballistic strength that was often too low. In this research, fiber sliding, fiber failure and delamination of layers are taken into account in the proposed model together with dynamically determined material properties. It is expected that studying the physical processes in a Dyneema composite panel and a better ballistic strength prediction should be possible using the aforementioned fiber bundle discretisation approach. The modeling of Dyneema composite is done in ABAQUS/Standard for the quasi-static simulations and in ABAQUS/Explicit for the dynamic simulations.

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Carbon Fiber Reinforced Plastic (CFRP) laminates are adopted for fuel tank structures of next generation space rockets or automobiles. Matrix cracks may cause fuel leak or trigger fatigue damage. A monitoring system of the matrix crack density is required. The authors have developed an electrical resistance change method for the monitoring of delamination cracks in CFRP laminates. Reinforcement fibers are used as a self-sensing system. In the present study, the electric potential method is adopted for matrix crack density monitoring. Finite element analysis (FEA) was performed to investigate the possibility of monitoring matrix crack density using multiple electrodes mounted on a single surface of a specimen. The FEA reveals the matrix crack density increases electrical resistance for a target segment between electrodes. Experimental confirmation was also performed using cross-ply laminates. Eight electrodes were mounted on a single surface of a specimen using silver paste after polishing of the specimen surface with sandpaper. The two outermost electrodes applied electrical current, and the inner electrodes measured electric voltage changes. The slope of electrical resistance during reloading is revealed to be an appropriate index for the detection of matrix crack density.

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The ultrasonic test (UT) has been conventionally applied to estimate a surface-crack depth in concrete. A test method is based on the time-of-flight of a diffracted wave via a crack tip. It is reported that the depth is mistakenly estimated in the case that water is filled in the crack. In order to visualize a location of an internal defect in concrete, SIBIE procedure has been developed. In the present study, the SIBIE procedure is applied to estimate the depth of surface-cracks, which are artificially made in concrete samples. SIBIE results are compared with those of the conventional UT results. It is found that the depth estimation is marginally available in the UT measurement, while the SIBIE procedure could visually show the depths of a surface-crack, separating the effect of water surface.

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Cold spraying, which is one of the spraying systems for particle deposition, has been studied as a new system of bond coatings of Thermal Barrier Coatings (TBCs) for components used in hot section of advanced gas turbine systems. In this paper, mechanical and oxidation properties including residual stress of Atmospheric Plasma Sprayed (APS) yttria-stabilized zirconia (YSZ) top coating with two different bond coating spraying systems, Low Pressure Plasma Spraying (LPPS) and the cold spraying, were evaluated and compared in thermal cycle tests. From the results, the porosity of the cold sprayed CoNiCrAlY bond coating is less than 4.2%. The relatively less oxidation layer is observed due to its higher density and more stable oxide growth. In-situ measurement of residual stress in the vicinity of the interface between bond coating and top coating shows that variations of residual stress between the thermal and the cold sprayed coatings are different. In particular, both coatings' residual stresses after thermal cycle test were compression due to oxide formation. The thermal sprayed coating had more oxidation layer than the cold sprayed coating. Therefore, compressive residual stress of the thermal sprayed coating was 40 MPa higher than the cold sprayed coating.

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To provide a new composite material having a high degree of sensitivity regarding both electrical conduction and temperature for the field of robotics or sensing, we have developed magnetic rubber that contains a network-like magnetic cluster. We compared the temperature response of MCF rubber with others rubbers made under various experimental conditions, allowing us to find an optimum condition for making MCF rubber. The temperature response was obtained by an experimental equation. We also compared the electric conductivity of MCF rubber with that of ordinary electric conductive rubber and found that its electric sensitivity was lower at a small deformation, but increased at larger deformations. Therefore, MCF rubber has proven itself effective as a switching sensor when a small deformation is applied.

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The significant effects of stress raisers demand well-defined evaluation techniques to accurately determine the stress along the geometric boundary. A simple and accurate method for the determination of stress concentration around circular geometric discontinuity in a tensile-loaded plate is illustrated. The method is based on the least-squares technique, mapping functions, and a complex power series representation (Laurent series) of the stress functions for the calculation of tangential stress around the hole. Traction-free conditions were satisfied at the geometric discontinuity using conformal mapping and analytic continuation. In this study, we use only a relatively small amount of x-component displacement data of points away from the discontinuity of concern with their respective coordinates. Having this information we can easily obtain full-field stresses at the edge of the geometric discontinuity. Excellent results were obtained when the number of terms of the power series expansions, m=1. The maximum stress concentration calculation results using the present method and FEM using ANSYS agree well by less than one per cent difference. Experimental advantage of the method underscores the use of relatively small amount of data which are conveniently determined being away from the edge. Moreover, the small amount of measured input data needed affords the approach suitable for applications such as the multi-parameter concept used to obtain stress intensity factors from measured data. The use of laser speckle interferometry and moiré interferometry are also potential future related fields since the optical system for one-directional measurement is much simple.

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An ignition point of a non-combustible Mg alloy is about 300K higher than that of a Mg alloy currently in use. It is expected that the non-combustible Mg alloy can be used as a substitute for Al alloys as structure components. In this paper, the fundamentals, the notch effect and the long or small crack effect on fatigue strength of the non-combustible Mg alloy, are investigated. Moreover, the fatigue strength characteristics of the non-combustible Mg alloy are compared with that of an Al alloy to clarify the differences in the fatigue strength characteristics between the non-combustible Mg alloy and Al alloy.

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CoNiCrAlY protective coatings are used for insulation from corrosion and oxidation of super alloy substrates in gas turbine blades. The life of a gas turbine blade is significantly affected by the mechanical properties of the protective coating. However, the properties of the coatings themselves have not been clarified, because there are few proper measurement methods for thin coatings. In this study, uniaxial stress-strain responses of atmospheric plasma sprayed (APS) free-standing CoNiCrAlY coatings were examined. The coating specimen was tube with the thickness of 0.3 mm. Coating specimens independent of substrates were fabricated by chemically dissolving out the substrates only at the region of gauge area. The stress-strain response was measured using the laser speckle strain measurement method. The coating showed the significant nonlinear stress-strain response. The stiffness increased with an increase of applied compressive stress, and the coating left permanent strain when the compressive stress was released. The nonlinearity of stress-strain response became significant if the surface roughness increased. The nonlinearity was decided by the surface roughness which represented the amount of defects in the coating. On the contrary, the nonlinearity was not proportional to the fraction of oxidized area. As compared with low pressure plasma sprayed (LPPS) CoNiCrAlY, the Young's modulus of APS CoNiCrAlY was low.

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The bolts and nuts are widely used in various fields as important joining elements with long history. However, loosening induced by the vibration and external loads is still a big problem. For example, the loosening sometimes causes very serious accident without notice. This paper deals with a special nut named “Super Lock Nut (SLN)” which can prevent loosening effectively. There is a thin walled tube between the upper and lower threads, which can be deformed along the axial direction so that the phase difference of lower and upper threads is produced and SLN is developed. This phase difference induces the contrary forces on the surfaces of the upper and lower threads, which bring out the anti-loosening performance. In this study, the anti-loosening performance is analyzed and realized with the finite element method. Moreover, the anti-loosening performances under various phase difference of lower and upper threads are compared and finally best dimensions for SLN are examined.

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A new approach is expected for heat resisting metal joints with inorganic adhesive. In the present study, the mechanical characterization of the inorganic adhesive and the strength evaluation of metal joints are realized by an experimental procedure that includes a static test for single lap joints bonded with inorganic adhesives. The inorganic adhesive can be cured at 150°C, and the maximum temperature resistance proposed is up to 1,200°C. A tensile shear test for the joints with a nickel adherend is performed at an elevated temperature of up to 400°C. The effect of material property, overlap length, and thickness of adherend on the joint strength is discussed based on stress analysis for corresponding joint models using a Finite Element Method. It is important to confirm whether fracture occurred in the adhesive layer or at the interface between the adhesive and the adherend. Therefore, the deformation and fracture behavior of the adhesive layer is investigated microscopically by the photographs of a scanning electron microscope (SEM) for the fracture surface.

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Previously several kinds of anti-loosening bolts and nuts were invented. However, they usually need a certain amount of prevailing torque even before the nut touches a clamped member. A new outer cap nut named “Super loose proof (SPR)” has been developed to overcome such inconvenience. At first this outer cap nut can be rotated smoothly by hand until the nut touching the clamped member. After fastening the outer cap nut, anti-loosening performance can be realized by deforming the outer cap and producing thread contact force at the outer cap region. In this study, stress concentration and tightening-loosening behavior are analyzed by axi-symmetric and three-dimensional finite element methods. Under a certain bolt-axial force, the load distribution of the first thread decreases more than 12% with increasing initial clearance of outer cap nut. Stress concentration appearing at the first thread of the bolt is about 10% smaller than that of conventional nut, reflecting the increase of the thread contact force at the outer cap region. On the other hands, it is found that anti-loosening performance of SPR can be realized when the outer cap has high yield stress.

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A method for measuring the strain and stress distributions in structural materials has been introduced. Fine model grids were fabricated by electron beam lithography, and an electron beam scan by a scanning electron microscope (SEM) was used as the master grid. Exposure of the electron beam scan onto the model grid in an SEM produced the electron beam moiré fringes of bright and dark parts caused by the different amounts of the secondary electrons per a primary electron. For demonstration, the micro-creep deformation of pure copper was observed. The creep strain distribution and the grain boundary sliding were analyzed. The residual strain and stress at the interface between a fiber and a matrix of a fiber reinforced plastic (FRP) were measured using the pushing-out test and this electron moiré method. Also, a non-uniform deformation around the boundary of 3-point bended laminated steel was observed and the strain distribution analyzed.

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Like a diagnosis of human body, it is important to monitor conditions of electronic packages in use. Even if electronic packages are sound in the beginning, thermal cycles during operations can produce fatigue cracks that lead to the system failure eventually. If we know the crack length in the package in real-time, a fatal damage can be prevented before the system failure. Currently, there are no simple methods for real-time monitoring of electronic packages in use. In this research, we propose a non-destructive monitoring method that detects the crack length in electronic packages. The electronic package in use is heated continuously by itself. When the crack at a weak site of the electronic package occurs, thermal deformation on the chip side is changed. Therefore, we can measure these micro deformations by using Moiré interferometry and find out the crack length. The proposed monitoring method is applied to ACF type package specimens. Experimental results show that the crack length of the electronic package affects the thermal deformation of the chip. If we have data of thermal strain by a specific crack length, we can monitor the crack length in real-time. Since the failure of a super-computer or network-server system affect the tremendous damage, we must know the health conditions of electronic packages in real-time. This research focuses the health monitoring of the electronic package of these system.

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In this study, pressure losses associated with a core-annular flow (CAF) through three horizontal pipes of 25 mm, 52.7 mm and 80.1 mm in internal diameter are measured. The working fluids for the core-annular flow are two immiscible fluids, highly viscous oil and water. Oils with viscosities of 2.82 Pa·s at 20°C and 8.92 Pa·s at 20°C are used in the experiment. The oil-water flow rate ratios (ratio of oil flow rate to water flow rate) are set at 2.6, 3.0, 3.4, 4.0 and 4.6 for the pipe of 25 mm in diameter and at 4.0 for the pipes of 52.7 mm and 80.1 mm in diameter. Based on the results of the experiment, a simple model for the pressure loss of a core-annular flow is derived. This model is used to estimate pressure losses of core-annular flows at various flow rate ratios and pipe diameters. To validate the model, the pressure loss data from the experiment are compared with those of the model. The comparison shows that this model is useful for predicting pressure loss of a CAF when oil does not wet the pipe wall extensively. In addition, it is observed in the experiment that pressure loss of CAF with the two viscous liquids is slightly higher than that of single-phase water. This indicates that pressure loss of a CAF is largely independent of oil viscosity.

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