Cementitious materials are by definition inhomogeneous containing cement paste, sand, aggregates as well as air voids. Wave propagation in such a material is characterized by scattering phenomena. Damage in the form of micro or macro cracks certainly enhances scattering influence. Its most obvious manifestation is the velocity variation with frequency and excessive attenuation. The influence becomes stronger with increased mis-match of elastic properties of constituent materials and higher crack content. Therefore, in many cases of large concrete structures, field application of stress waves is hindered since attenuation makes the acquisition of reliable signals troublesome. However, measured wave parameters, combined with investigation with scattering theory can reveal much about the internal condition and supply information that cannot be obtained in any other way. The size and properties of the scatterers leave their signature on the dispersion and attenuation curves making thus the characterization more accurate in case of damage assessment, repair evaluation as well as composition inspection. In this paper, three indicative cases of scattering influence are presented. Namely, the interaction of actual distributed damage, as well as the repair material injected in an old concrete structure with the wave parameters. Other cases are the influence of light plastic inclusions in hardened mortar and the influence of sand and water content in the examination of fresh concrete. In all the above cases, scattering seems to complicate the propagation behavior but also offers the way for a more accurate characterization of the quality of the material.

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In order to clarify the thermal and/or mechanical failure behavior of the plasma sprayed thermal barrier coating (TBC) system in connection with their coating characteristics depending on the coating process condition, two kinds of the failure analytical tests were conducted for TBC systems processed under different conditions. One was the high-temperature oxidation test, which was conducted at 1100°C under both the isothermal and thermal cycle conditions. The other was the in-situ observation of mechanical failure behavior, which was conducted under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. It was found that the thermal and mechanical failure behavior of TBC system depends strongly on the top-coat (TC)/bond-coat (BC) interfacial condition, the reheat-treatment (RHT) after spraying and so on. For the TBC system with vacuum plasma sprayed (VPS) BC as well as for that with atmospheric plasma sprayed (APS) BC, in particular, the RHT at an appropriate temperature in Ar atmosphere was found to be effective for improving the oxidation property. For the TBC system with APS-BC, however, it was impossible to prevent the crack growth into the BC interior under the tensile loading in spite of conducting the RHT, since the microdefects such as oxides within the APS-BC tend to provide an easy crack propagation path. Furthermore, it was clarified that the smoothening process on the BC surface is able to prevent perfectly the occurrence of the wart-like oxide during oxidation, but at the same time increases also the risk of the TC spalling under the mechanical loading.

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The potential of fatigue crack growth experiments to sensitively analyze the anisotropic mechanical behavior of injection-molded, multiphase polymer blends is presented. The properties of immiscible blends based on poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) is investigated, both in perpendicular and in parallel to the injection-direction. As a result of the limited interfacial adhesion and the orientation of the blend phases, the direction in parallel to flow revealed to be the weaker link. In order to enhance the toughness behavior, the PPE/SAN blends were systematically modified by the addition of different polystyrene-b-polybutadiene-b-poly(methyl methacrylate) triblock terpolymers (SBM), potentially acting as a compatibilizing and toughening agent. Such a compatibilization step of PPE/SAN blend leads to the formation of nanostructured morphologies. Depending on the composition of the triblock terpolymer, the resistance to crack growth was either further degraded or, in the case of high interfacial presence and compatibilization efficiency, significantly improved. The results were correlated to the fracture mechanisms of the blends as analyzed by scanning electron microscopy of the fracture surfaces. In contrast to poorly-compatibilized blends, a significant plastic deformation, an enhanced phase adhesion and a strongly reduced anisotropy could be detected in case of well-compatibilized blends. In summary, the presented study of the fatigue crack growth behavior revealed a detailed insight into the mechanical property profile of the selected multiphase blends and, moreover, demonstrated the potential of this method to sensitively analyze the anisotropy of such materials.

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Welding is widely used for construction of many structures. It is well known that residual stress is generated near the bead because base metal is heated near the bead. Tensile residual stress on the surface degrades fatigue strength. Some reduction methods of residual stress are practically used, for example, heat treatment and shot peening. The authors developed a new method for reduction of residual stress using vibration during welding. In this method, single vibration was used. The effectiveness of the method was demonstrated. In this paper, the effect of vibrations with different frequencies on reduction of residual stress is examined. The effect is examined experimentally by butt-welding of thin plates. First, two thin plates are butt-welded using ultrasonic vibrations with different frequencies on each plate. Some plates are welded using single ultrasonic vibration and without ultrasonic vibration for comparison. When thin plates are welded using vibrations with different frequencies, tensile residual stresses are reduced and reduction rate is largest compared with other conditions. Second, two thin plates are butt-welded using ultrasonic vibration and vibration with low frequency. Some plates are welded using single vibration and without vibration for comparison. In this case, tensile residual stresses are reduced and reduction rate is largest compared with other conditions. Obtained results are examined by analytical method.

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When an ultrasonic wave is injected into a crack, if the width of the crack opening is of almost the same order as the displacement of the ultrasonic wave, the crack may be closed or opened. As a result, the waveform of the received ultrasonic wave is different from that of the incident ultrasonic wave. Therefore, regarding the incident ultrasonic wave, its harmonic frequency components change as it penetrates the crack. However, the nonlinearity of a solid material is very low compared to that of a liquid medium, therefore, a liquid medium with a high nonlinear efficiency had to be used as a coupling medium. We then attempted to apply an electromagnetic acoustic transducer (EMAT), which does not require a coupling medium. In addition, we tried to develop an EMAT that could alternately drive a Lamb wave (S₀-mode, A₀-mode) and a Shear Horizontal (SH₀) -plate wave to detect any nonlinearity in an ultrasonic wave. We actually tested the performance using fabricated fatigue specimens. As a result, we observed that the harmonic components increased when we used the specimen with a specific loading condition and a specific ultrasonic mode. This indicated that the harmonic component detection using the trial EMAT could also provide useful information on the damage to any structures or any materials

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In this research, a microchannel type mixer composed of micropillars and micronozzles was developed for effective mixing of biochemical samples. To estimate the performance of the newly designed micromixer, flow patterns were simulated using computational fluid dynamics (CFD) software. The simulation showed that the mixing efficiency increased from 87.9% to 97.5% as the flow rate varied from 50 to 500 μl/min. When liquid was injected into the fabricated micromixer, it was difficult to prime the microchannel because of the hydrophobicity of the polydimethylsiloxane (PDMS) surface. To overcome this problem, the inside of the micromixer was coated with polyvinylpyrrolidone (PVP). It was found that 0.25 wt.% PVP concentration in the DI water solution is optimal. After appropriate PVP coating, the DI water and the mixture of blue dye and DI water were mixed in the fabricated micromixer and the mixing efficiency was measured. The mixing efficiency increased from 69.7% to 91.7% as the flow rate increased from 50 to 500 μl/min. The new micromixer showed very good mixing performance when the flow rate was over 300 μl/min. Due to the simple structure and uncomplicated fabrication process, the proposed micromixer can be easily integrated into a micro total analysis system (μ-TAS) or lab-on-a-chip (LOC).

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Lysine tri-isocyanate (LTI) was added to a biodegradable polymer blend of poly(lactic acid) (PLA) and poly (ε-caprolacton) (PCL) under melt-mixing condition in order to improve the miscibility of PLA and PCL. It was found that the mode I fracture energy of the polymer blend effectively increases with increase of LTI content. Microscopic examination also showed that the size of PCL phase decreases due to LTI addition, leading to the reduction of void formation and suppression of local stress concentration, thus the improvement of the fracture energy. The improved miscibility also contributes to the ductility enhancement, which further increases the fracture energy.

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Serious shear failures in reinforced concrete (RC) structures were reported in the Hanshin-Awaji Earthquake. In particular, it was demonstrated that a diagonal-shear failure could lead to disastrous damage. However, mechanisms of the diagonal-shear failure in RC beams have not been completely clarified yet. In this study, the diagonal-shear failure in RC beams is investigated, applying acoustic emission (AE) method. To identify source mechanisms of AE signals, SiGMA (Simplified Green's functions for Moment tensor Analysis) procedure was applied. Prior to four-point bending tests of RC beams, theoretical waveforms were calculated to determine the optimal arrangement of AE sensors. Then, cracking mechanisms in experiments were investigated by applying the SiGMA procedure to AE waveforms. From results of the SiGMA analysis, dominant motions of micro-cracks are found to be of shear crack in all the loading stages. As the load increased, the number of tensile cracks increased and eventually the diagonal-shear failure occurred in the shear span. Prior to final failure, AE cluster of micro-cracks was intensely observed in the shear span. To classify AE sources into tensile and shear cracks, AE parameter analysis was also applied. As a result, most of AE hits are classified into tensile cracks. The difference between results obtained by the AE parameter analysis and by the SiGMA analysis is investigated and discussed.

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Anisotropy of the bridge fraction of middle isoprene block chains in the directions parallel and perpendicular to the shear flow direction in sheared films of sphere-forming polystyrene-b-polyisoprene-b-polystyrene triblock copolymers are examined by breaking stress under simple elongation measurements at a fast draw rate, which reflect the bridge fraction. There was no practical difference between the data obtained in two directions at tested shear rate region (5-15 sec^-1). The absolute values are close to the values for non-sheared samples. Thus, we conclude that when flow is applied to sphere-forming triblocks, only small portion of end blocks are pulled out to flow and there is no orientation dependent anisotropy of bridge fractions.

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Unsteady thermal and mechanical loading in turbine components is caused due to the transient regimes arising during start-ups and shut-downs and due to changes in the operating regime in steam power plants; this results in nonuniform strain and stress distribution. Thus, an accurate knowledge of the stresses caused by various loading conditions is required to ensure the integrity and to ensure an accurate life assessment of the components of a turbine. Although the materials of the components of the steam turbine deform inelastically at a high temperature, currently, only elastic calculations are performed for safety and simplicity. Numerous models have been proposed to describe the viscoplastic (time-dependent) behavior; these models are rather elaborate and it is difficult to incorporate them into a finite element code in order to simulate the loading of complex structures. In this paper, the total lifetime of the components of a steam turbine was calculated by combining the viscoplastic constitutive equation with the ABAQUS finite element code. Viscoplastic analysis was conducted by focusing mainly on simplified constitutive equations with linear kinematic hardening, which is simple enough to be used effectively in computer simulation. The von Mises stress distribution of an HIP turbine rotor was calculated during the cold start-up operation of the rotor, and a reasonable number of cycles were obtained from the equation of Langer.

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The fatigue properties of extruded magnesium alloy AZ31 were evaluated using material processed under two different extrusion ratios and two different extrusion temperatures. The effect of the extrusion ratios and extrusion temperatures on the fatigue lives and crack propagation behavior is discussed. The fatigue crack initiation and propagation processes were observed by the replica method. It was found that cracks initiated early in the fatigue process, and therefore the total fatigue life can be approximated as the crack propagation life. The crack propagation behavior observed in those materials was analyzed using a modified linear elastic fracture mechanics parameter, M. The relation crack propagation rate vs. M parameter was found to be useful in predicting fatigue lives and crack propagation curves.

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Most spectacle frames are now made of titanium alloy. Recently, however, frames made of gum metal have become available. Gum metal is a new material having a low Young's modulus, high strength and high elastic deformation. The effectiveness of these spectacle frames, however, has not yet been mechanically evaluated. In this study, by using the recently proposed optical 3D shape measurement method, the deformation behavior of full-rim and rimless spectacle frames, made of gum metal and available on the market, were compared with that of conventional titanium frames. In addition, CAD models of these frames were created and their mechanical characteristics were evaluated in detail by the finite element method. Consequently, the gum metal frames were found more comfortable to wear than titanium ones. However, the rimless type of gum metal frames allowed more load to reach the front than did the titanium frames, causing lens damage due to stress concentration at the screws.

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Mechanical stress-strain hysteresis, temperature and electrical resistance measurements were performed to characterize the fatigue behavior and to calculate the lifetime of metals under constant amplitude loading and random loading. Constant amplitude sequences were periodically inserted in random load tests to measure the plastic strain amplitude as well as the deformation-induced changes in specimen temperature and electrical resistance. These data are plotted versus the number of cycles for the fatigue assessment under random loading, similar as commonly practiced under constant amplitude loading. On the basis of Morrow and Basquin equations in generalized formulations, to be applicable for mechanical, thermal and electrical measurement techniques, a physically based fatigue life calculation method “PHYBAL” was developed. This new short-time procedure requires data of only three fatigue tests for a rapid and nevertheless precise determination of Woehler curves for constant amplitude loading or fatigue life curves for random loading.

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An improvement of the already proposed phase unwrapping algorithm for directly processing the triangular-typed wrapped phase map of the isochromatic parameter, photoelastically generated by an arccosine function based on the well-known technique of phase-shifting, is presented. In phase unwrapping algorithm, at any pixel, a three-dimensional plane and its normal vector are generated using three fractional (relative) fringe order values. Its generated plane is then adjusted using the orthogonal projection associated with the reference plane. Such point is unwrapped on the basis of regularization. The quality guide map is used to guide phase unwrapping and to mask out the conflictive regions such that they are lastly processed. The circular disk under compression demonstrated the performance of the improved algorithm. Results showed the accuracy improvement in such conflictive regions with reasonable agreement to theory.

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The full-filed evaluation of the isoclinic parameter in digital photoelasticity is presented. The proposed method is based on the four-step color phase shifting technique and the phase unwrapping (PU) algorithm. It is experimentally applied to an eccentrically loaded split ring (C-shaped model). Experimental results show that the isoclinic-angle map obtained is almost free from the influence of the isochromatic parameter and the isoclinic values lie in the physical range, -π/2 to +π/2, regardless of the presence of the isotropic point or region.

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In the failure analysis of fatigue fracture, the estimation of applied stress by examining the fatigue fracture surface is important in order to investigate the cause of accident. A fractographic method using striations has been established. Striations, however, can be observed only when a crack propagated at relatively high rate. In the case of fracture accident after a long period of operation under low stress condition, striations are rarely observed on the fracture surface. The estimation of applied stress is almost impossible in such a case. Therefore, an estimation method which can be applied in the low stress intensity region without striations is desirable. In this study, the high frequency current impedance method and the hardness measurement method were investigated as candidates aiming the application to failure analysis. The former uses the electrical impedance of fatigue fracture surface. A positive relationship was found between the electrical impedance and stress intensity factor range. The latter uses micro hardness which was measured directly on the fatigue fracture surface. The hardness of fatigue fracture surface was correlated with the stress intensity factor range. These parameters might be used as parameters in the estimation of applied stress by examining the fatigue fracture surface without striations formed in low stress intensity region.

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Photoelasticity is one of the most widely used whole-field optical methods for stress analysis. The technique of birefringent coatings, also called the method of photoelastic coatings, extends the classical procedures of model photoelasticity to the measurement of surface strains in opaque models made of any structural material. Photoelastic phase-shifting method can be used for the determination of the phase values of isochromatics and isoclinics. In this paper, photoelastic phase-shifting technique and conventional Babinet-Soleil compensation method were utilized to analyze a specimen with a triangular hole and a circular hole under bending. Photoelastic phase-shifting technique is whole-field measurement. On the other hand, conventional compensation method is point measurement. Three groups of results were obtained by phase-shifting method with reflective polariscope arrangement, conventional compensation method and FEM simulation, respectively. The results from the first two methods agree with each other relatively well considering experiment error. The advantage of photoelastic phase-shifting method is that it is possible to measure the stress distribution accurately close to the edge of holes.

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The compressive stress-strain loops of several commercial polymers at strain rates of nearly 700/s are determined in the standard split Hopkinson pressure bar. Four different polymers or typical thermoplastics: ABS, PA-6, PA-66 and PC are tested at room temperature. Cylindrical specimens with a slenderness ratio (= height l /diameter d) of 0.5 are used in the Hopkinson bar tests, and those with l/d = 1.5 as specified in the ASTM Designation E9-89a are used in the static tests. The stress-strain loops in compression at low and intermediate strain rates are measured in an Instron testing machine. The influences of strain rate on the Young's modulus, 2.5% flow stress and dissipation energy are investigated. It is demonstrated that the area within the stress-strain loop (or dissipation energy) increases with increasing strain rate as well as given strain, that is, all polymers tested exhibit intrinsic dynamic viscoelasticity and a high elastic aftereffect following complete unloading.

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The fracture behavior of a brittle polymer, polymethyl methacrylate (PMMA) resin, under impact tensile loading was studied using single-edge-cracked specimens. The dynamic load and displacement were measured with a Piezo sensor and a high-speed extensometer, respectively. The load and displacement diagram, i.e., the external work U_ex applied to the specimen was used to determine the elastic energy E_e and non-elastic energy E_n due to viscoelastic and plastic deformation, and the fracture energy E_f for creating new fracture surface A_s. The energy-release rate was then estimated using G_f=E_f/A_s. The values of E_e, E_n, E_f and G_f were correlated with the fracture loads, and compared with the ones earlier determined for the static loading conditions.

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The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheet is the material fabricated by adhering two aluminum skins to one polypropylene core. When it has the same flexural rigidity as a steel sheet, it is 65% lighter than the steel sheet and 30% lighter than an aluminum alloy sheet. Therefore, it is notified exclusively as good substitutive materials for a steel body to improve the fuel efficiency. Through AA/PP/AA sandwich sheet, however, it has relatively lower formability than that of the steel sheet for automotive application. In this study, we developed formability evaluation techniques in order to apply AA/PP/AA sandwich sheet for an automotive parts. For this purpose, newly adopting formability evaluations (using limit dome height and plane strain test) were carried out in order to secure the fundamental data for the measurement of sheet metal forming and the establishment of optimum forming conditions of the sandwich sheet. The results showed that there were in good agreements between the old formability evaluation method and the new one which was more simplified than that of the old one. From the results of these formability evaluations, the formability of sandwich sheet was higher than that of aluminum alloy sheet alone which was the skin component for the sandwich sheet. In addition, it was found that sandwich sheet could reduce the weight and could have the same flexural rigidity simultaneously when it was compared to the automotive steel sheet.

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