In shape memory polymers, large strain can be fixed at low temperature and thereafter can be recovered at high temperature. If the shape memory polymer is held at high temperature for a long time, the secondary-shape forming with irrecoverable strain appears. The secondary-shape forming can be applied to fabricate shape-memory polymer elements in a simple method. In the present paper, the influence of the strain-holding conditions on shape recovery and the secondary-shape forming in polyurethane-shape memory polymer is investigated by the tension test of film and the three-point bending test of sheet. The higher the shape-holding temperature and the longer the shape-holding time, the higher the rate of secondary-shape forming is. The equation to express the characteristics of secondary-shape forming is formulated.

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The main characteristics which appear in shape memory alloys (SMAs) are the shape memory effect and superelasticity. In applications of SMAs, the thermomechanical properties of SMAs are most important. Creep and stress relaxation are induced due to the phase transformation in the subloop loading under the stress-controlled conditions. In order to design the SMA elements properly, it is important to understand the thermomechanical properties. In the present paper, the conditions for the nucleation and progress of the phase transformation in SMAs subjected to the subloop loadings are investigated under the stress-controlled conditions. The transformation-induced creep and stress relaxation and the thermomechanical neutral loading condition are discussed based on the transformation kinetics of the material.

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Efficient Joule heating and cooling are necessary for the repetition use of the shape recovery force of shape-memory alloy (SMA) fiber reinforced smart composite materials. Then, the main factor on Joule heating and the cooling speed in the SMA single fiber and the SMA fiber reinforced smart composite materials was experimentally evaluated in this research. The effect of an environmental temperature, the forced convection, and the free convection was evaluated as the main factor in the SMA single fiber, and the structural condition of the matrix was evaluated in the composite material. The significant point in the temperature characteristic of the SMA electrical resistance was used as a marker of heating and the cooling progress. As a result, the cooling speed confirmed the decrease though joule heating speed rose by the rise of the operation environment temperature. Moreover, Joule heating and the cooling characteristic change greatly in the SMA single fiber depending on the air cooling condition. In the composite material, the result of the large change depending on the heat transmission characteristic and the structural condition of the matrix material was obtained.

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It is very important to get to know the mechanical behavior of structure because of the health monitoring of structure. Industrially, a strain gage is used for a stress analysis on the surface of an object. In order to carry out full field measurement in a certain region, many gages and supporting equipment are required, as well as time. Hence, there is the strong need for the development of a stress analysis system by an optical, real time and non-contact measurement method. Digital image correlation (DIC) is suitable to this aim and has been adopted to analyze the displacement on the surface of the specimen. DIC has been successfully applied mainly to metallic materials which are homogeneous and isotropic. On the other hand, recently fiber reinforced composites are developed and are used as structural materials, especially in various fields including an aerospace field. Fiber reinforced composites are heterogeneous and anisotropic. The applicability of the stress analysis methods on such heterogeneous and anisotropic materials is not well known. In this study, the displacement, stress and strain analysis of carbon fiber reinforced plastic (CFRP) laminate that was an anisotropic material were carried out by combining digital image correlation with two-dimensional linear/nonlinear intelligent hybrid method. A material used was carbon/epoxy system. Laminate configuration was unidirectional. Tensile load was applied in off-axis (45 degrees) direction as well as longitudinal (0 degree) and transverse (90 degrees) directions on a CFRP laminate. The constitutive equation considering material anisotropy was built into the intelligent hybrid method used at the time of analyses. The validity of algorithm was verified by the comparison between the results of the present method, experimental results from the strain gage method, and the analytical results from finite element method (FEM).

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This paper presents an experimental investigation of the stress field near a crack tip of rotating disk by a hybrid method of photoelasticity and caustics. The disk is made of polycarbonate plate and its axis has been artificially decentered. A rotating force is applied to the disk externally with a constant angular velocity. During the rotation, the disk experienced stress freezing temperature cycle and so the observation of stress field caused by the centrifugal force was enabled at static state. Stress intensity factors were extracted from pictures of photoelastic isochromatics and caustic images, and evaluated in terms of the diameter fluctuation and eccentric distances. Experimental results from both methods showed a good agreement, and a significant influence of diameter fluctuation was observed whereas eccentric displacement was absorbed by the diameter fluctuation.

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In this paper, photoelastic experimental hybrid method using external traction free boundary condition and using the relative equation of two stress functions in contact problems are developed. Their validities are confirmed through experiments and discussions Hertz's contact theory and two photoelastic experimental hybrid methods explained above are applied to the stress analysis of O-ring under 10% or 20% squeeze rate. Among them, the photoelastic experimental hybrid method using the relative equation of two stress functions in contact problems is most effective. When squeeze rates of O-ring are 20%, Maximum of absolute σ_x is greater than maximum of absolute σ_y by little. But they are almost equal to each other. Maximums of absolute τ_<xy> are 1/5 of absolute σ_x when squeeze rate of O-ring is 20%.

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The resolution of three-dimensional (3-D) imaging using the synchrotron radiation has been dramatically improved, enabling the high resolution observations of microstructure and damage inside bulk materials in 3-D. In the present study, high resolution phase contrast microtomography (μ-CT) technique has been applied to obtain clear crack images together with the details of microstructural features in a cast aluminum alloy. Crack opening/closure, crack extension and damage evolution in the vicinity of a crack-tip is observed. 3-D image analysis is performed to evaluate void initiation and growth near the crack-tip. The information on physical displacement of each microstructural feature is provided for analyzing local crack driving forces at crack front. A 3-D measurement procedure for local crack-tip opening displacement is proposed using a set of 3-D tomographic volume. Inhomogeneous 3-D crack propagation behaviors are analyzed using the data obtained by means of the techniques. For example, local fracture toughness values in both ductile α-aluminium and less ductile Al-Si eutectic phases are evaluated using the techniques. It has been clarified that the local fracture toughness is several times higher in the α phase than that in the eutectic phase. The crack-tip driving force reaches the maximum just before the onset of crack propagation and decreases during the propagation. Overall, these techniques have been identified to provide a unique possibility to quantitatively interpret the 3-D cracking behavior in bulk materials.

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The present study investigates plasticity-induced martensitic phase transformation around through-thickness fatigue cracks in single V-groove butt welded SUS304 plates at room temperature in air. Fatigue crack propagation tests were made for stress ratios of R=σ_<max>/σ_<min>=0.1-0.4. The fatigue crack propagation tests were interrupted in order to measure spatial distributions of the volume fraction V_<α'> of α' martensitic phase around fatigue cracks with ferrite scope. The vertical magnetic flux density B_z induced by the α' martensitic phase transformed around fatigue cracks was also measured by flux gate sensor. The V_<α'> distributions were compared with the B_z distributions above fatigue cracks in welded specimens magnetized by a strong electromagnet. It was revealed that the B_z distributions reflected the spatial distribution of pre-existing α ferritic phase and that of plasticity-induced α' martensitic phase around weldment and fatigue cracks. The distance between the points where B_z reached the maximum and the minimum values, B_<zmax> and B_<zmin>, had linear correlations with real crack length 2a irrespective of the stress ratio R. The B_<zmax> and the B_<zmin> values also showed linear relations with applied maximum stress intensity factor value K_<max>. These results reveal that not only crack length 2a but maximum stress intensity factor K_<max> can be estimated by measuring the vertical magnetic flux density B_z in welded SUS 304 plates as reported previously for fatigue cracks in SUS 304 base material.

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Previous NDE techniques, which utilize materials' magnetic characteristics, depend on magnetization and demagnetization of materials. The process of magnetization and demagnetization costs much and takes time. The evaluation system we propose focuses on the material inherent magnetic characteristics. The system can evaluate the damage of materials by detecting the changes in the inherent magnetic characteristics of materials with the ultra sensitive magnetic flux density meter. Therefore, it requires neither magnetization nor demagnetization of materials. To confirm the effectiveness of the method, we conduct tensile and biaxial fatigue tests on various stainless steels. Measured magnetic flux curves indicate that magnetic flux at the stress concentration part increases before crack propagation. Then, it decreases due to stress release by crack propagation. We confirm that the measured magnetic flux curve depicts local periodical cycles with global increasing tendency.

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Mechanical properties of resinless bamboo fiber green composites were experimentally investigated by changing molding temperature and pressure. The composites made of bamboo fibers obtained from the steam explosion were made by hot-press method, their fiber orientation was unidirectional. This composite material has advantages, that is, it is composed of sustainable natural resources, to use bamboo is prevention of progressing devastated bamboo grove and it has biodegradability. The influence of molding conditions on their mechanical behavior was examined by tensile and bending tests. The molding temperature was from room temperature to 200℃. The molding pressure was 10 MPa, 50 MPa and 100 MPa. The molding temperature has a much greater effect on the mechanical properties such as tensile property and bending property. The optimum molding temperature was 130℃. The tensile strength and Young's modulus of the composites molded at 120℃ and 50 MPa were 636 MPa and 48 GPa, respectively. Bending strength and bending modulus of the composites molded at 140℃ and 50 MPa were 483 MPa and 50 GPa, respectively. Molding pressure has an insignificant effect on tensile and bending strength of green composites. Fracture elongation of the composites tends to decrease with rise of temperature above 140℃ due to the decreasing of the strength of single fiber bundle during hot-pressing.

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A mullite/SiC whisker/SiC particle multi-composite, having excellent crack-healing ability and mechanical properties, was hot-pressed in order to investigate the crack-healing behavior under stress and the resultant fatigue strength at the temperature of healing. A semi-elliptical surface crack of 100 μm in surface length was introduced on each specimen. The pre-cracked specimens were crack-healed under cyclic or constant stress by using a three-point bending stress at 1473 K, and the resultant bending strength and fatigue strengths were measured at 1473 K. The pre-crack on the surface of the specimens could be healed even under stress. The threshold stresses for crack-healing, as determined by evaluating the strengths of crack-healed specimens at a healing temperature of 1473 K, were 170 MPa for both constant and cyclic stresses, corresponding to 77% of the bending strength of the pre-cracked specimens. The static and cyclic fatigue strengths of crack-healed specimens were also investigated at a healing temperature of 1473 K.

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In order to drive the micro robot which we developing using IPMC as a propellant actuator effectively, it is necessary to clarify abilities of IPMC such as displacement and generation force. Since ability of IPMC is greatly influenced by species of counter ion (movable ion that is responsible for bending of IPMC). Then, in this research, we evaluated displacement characteristics and generation force of IPMC when the counter ion was changed. As a result, displacement of IPMC including Ca^<2+> or K^+ as counter ion, was larger by 1.7 times compared with that including Na^+. Moreover, the generation force was larger by 2.3 times in the case of Ca^<2+> and by 1.8 times in the case of K^+, compared with the case of Na^+. As a result, it was confirmed that the performance of IPMC changed greatly with the counter ion.

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The majority of fly ash pipes in thermal power stations use steel pipes. This makes frequent replacement inevitable due to severe abrasion near the hot and curved section of pipes. Recently, there have been efforts to prevent this abrasion with lining techniques using ceramic or basalt on the inner wall of the pipe. This study uses composite and anti-wear material to maximize the anti-abrasion effects on the hot section of the pipe. The thickness of the abrasion layer was determined by the abrasion ratio of material found through the experiment; the thickness of the reinforcement layer was determined by micromechanics. Experiments were conducted on epoxy resins to test for heat and abrasion. Anti-abrasion test using particle impingement was intended to recreate realistic conditions when abrasion occurs within the hot section of an actual pipe. This study analyzes the abrasion ratio obtained from both the specimen experiment and from on-site measurement and provides evidence that a combination of composites and anti-wear agent can be used to create a fly ash pipe that is lower in costs and higher in quality than what is used currently.

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We are developing novel variable-focal length lenses using IPMC. In this paper, we propose the structure of the novel variable-focal length lens using IPMC and describe the results of the experiment for the principle verification of the lens. The relation between generated force of IPMC and focal length of the proposed lens was modeled. Moreover, the possibility of the proposed variable-focal length lens was confirmed, since the basic operation is verified by using liquid as a lens material.

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An acoustic resonant spectroscopy technique for measuring the acoustic properties of micron-scale polymer films, i.e., the acoustic impedance, ultrasonic velocity and density of the film, has been developed. The method, which is based on spectral analysis and observes the acoustic resonance between water, the film and a tungsten plate with high acoustic impedance, is introduced, and the technique is demonstrated for characterizing the low-density polyethylene, poly(vinyl chloride), poly(vinyl alcohol) and nylon films. The values of acoustic impedance, ultrasonic velocity and density of the films are successfully determined by the spectroscopy technique.

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For laminate films used for packaging bags, we developed a new method of joining films that does not require the use of conventional adhesive tape. A tensile test of the joining area was carried out at various ambient temperatures to examine the joining strength and to compare the fabrication loss with that of the conventional method using adhesive tapes.

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Recently, machine structure is operated under the severe conditions. Moreover, the use of the compound material has been chiefly used for the part with few loads so far. Compound material has more performance and economy than single material. It is important to evaluate the stress state when the crack exists in such a heterogeneous phase shaft obviously on the safety design of the machine structure. Then, we used epoxy resin for the sample material in this research. Double cylinders that inserted a surface crack axially is produced. And, we experimented putting the static loading on the cylinder. We used using of the photoelasticity method and the method of caustics together for the analysis, and calculated the stress intensity factor. The results from these experiments will be presented at the conference.

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The effect of tool geometry on microstructure and static strength in friction stir spot welds of 6061 aluminium alloy sheets was studied. Tools with three different probe pin lengths were used to join the aluminium sheet with different tool rotational speeds and tool holding times. The weld microstructures varied significantly depending on probe pin length, tool rotational speed and tool holding time. Two particular aspects were identified: the thickness of the upper sheet under the shoulder indentation and the nugget size. The former decreased with increasing probe pin length at the shortest tool holding time and the slowest tool rotational speed, but there were no discernible differences in other welding conditions, while the latter increased with increasing probe pin length, tool rotational speed and tool holding time. The tensile shear strength increased with increasing probe pin length, while the cross tension strength was not affected significantly by probe pin length. Two fracture modes were observed: shear fracture of the nugget and mixed mode fracture under tensile shear loading, and nugget debonding and pull-out under cross tension loading. Based on experimental observation of the microstructures, the effect of probe pin length on static strength and the fracture mechanisms were discussed.

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Under the multi-axial stress field, creep crack growth is considered to occur in brittle manner. From the point of practical use, it is important to conduct the characterizations of the creep crack growth rate and its life under the multi-axial stress field to predict the life of creep crack growth. In the present paper, using the W added 9Cr ferritic heat resistant steel, ASME grade P92, developed as a boiler tube material, the effect of multi-axial stress caused by weld joint with HAZ region on the creep crack growth rate and its life were investigated under the high temperature creep condition. Furthermore, the 3-dimensional elastic-plastic creep finite element analyses (FEA) were conducted to clarify the effect of stress multi-axiality of welded joint on creep crack growth rate.

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The time and temperature dependent tensile behavior of glass bead and talc-filled polypropylene was investigated. It could be observed that the addition of rigid particles result in an increase in stiffness below and above the glass transition temperature (T_g). The yield stress of the compound was increased above T_g and reduced below T_g. This was related to the deformation behavior that is, the ductile to brittle transition of the matrix. Furthermore the effect of particle size and aspect ratio on the mechanical behavior of the compound is discussed.

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This paper presents results from analyzing the formation of a damage band comprising a number of minute cracks, which align almost in parallel to one another, under far-field compression. Under favorable mechanical conditions, an excessive compression often causes a shear faulting in brittle solids, in which the macroscopic failure plane is inclined from the axis of principal compression. In the case of compressing an intact rock such as granite, the flaw induced by severe compression is often preceded by the formation of an array of sub-parallel cracks that align into a band inclined about 30° from the axis of principal compression. One of the prominent mechanisms that explain why micro-cracks form a damage band is considered to be an interaction among cracks. In the present study, using a crack analysis code based on the Body Force Method and the Finite Element Method, the mechanical background as to why tensile cracks may align into a band to form the damage zone was investigated computationally. Numerical results suggest that most of line cracks in the array may open even under far-field compression, if some geometrical requirements are satisfied. That is, there exits a favorable configuration, under which the majority of cracks composing the damage band open even under far-field compression. Furthermore, the favorable configuration of the array of cracks correlates well with an inclination, where the shear faulting takes place in brittle solids under severe compression.

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The fracture control and specific strength in the material have improved by the development of the bonding technique. And, a further lightening and high stiffness become possible as for the material. However, when the material became complex, the analysis of the fracture behavior became difficult. A lot of analyses of a static fracture in the adhesive line are reported in recent years. However, the paper concerning the impact fracture behavior of the interfacial crack is few. Therefore, clarifying the impact fracture behavior of the interfacial crack becomes extremely important in the contribution and the strength evaluation to the design of the bonded material. In this study, the impact shearing fracture behavior of the interfacial crack in the bonded material was analyzed. The deformation and the strain near the interfacial crack tip were examined by using the digital image correlation method for the analysis. The shape of the specimen adopted the ENF specimen. The experimental setup is composed of a high-speed video camera, the YAG laser, the Metalharaid lighting system, the personal computer, and the falling weight type impact-loading device. As a result, when the upper layer material of the specimen is brittleness, the crack propagates to an upper material. When the fracture toughness value of the upper layer material of the specimen is higher than the fracture toughness value of the adhesive line, the crack propagates to the interface. As for the fracture of the bonded material, it has been understood that evaluating the fracture toughness value of the adhesive line is necessary.

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Due to its filterability and thermostability, porous ceramics have a large attention as a suitable material for filters such as a diesel particulate filter. Since damages induced by contact stress on filters cause serious degradation of their strength and life span, the standardization of sphere indentation test is necessity to evaluate the indentation strength of porous ceramics quantitatively. The sphere indentation examination was carried out to investigate the effects of pore diameter on indentation strength under different conditions of indentation sphere sizes and indentation speed. Three porous ceramics were tested; each porous ceramic contains different pore diameter. The result shows that indentation load increased monotonically along with an increase in indentation depth when the porous ceramics has small pore diameter. However, with large pore diameter, the graph of load-displacement displays load increases with vertical fluctuation along with increasing indentation depth. The strength of specimen with large pore diameter relies on indentation sphere size not depending on indentation sphere material. While the fracture strength of specimen with small pore stays constant, the strength of specimen with large pores rises with increasing sphere diameter. The strength of specimen with large pore is also dependent on indentation speed. The strength of specimen with large pore rises in the company of increasing indentation speed, although the strength of specimen with small pore is relatively constant.

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Directionally solidified single crystal eutectic ceramics have many advantages as high temperature structural materials because of strength temperature dependence, high creep resistance, and good oxidation resistance. However, it is difficult to perform very high temperature fatigue tests in air. For that reason, little information of long-term durability and very high temperature fatigue reliability is available. This study newly developed a very high temperature tensile fatigue testing methodology using a locally heated, cold-gripped, round-bar type specimen and determined high cycle fatigue strength characteristics for Al_2O_3/YAG and Al_2O_3/GAP eutectic ceramics at temperatures greater than 1500°C in air. Temperature dependence and materials comparison show that single crystal eutectic ceramics also have good very high temperature fatigue durability compared to representative high temperature structural ceramics and ceramic matrix composites.

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A new approach is expected for heat resisting metal joints with inorganic adhesive. In this study, the mechanical characterization of the inorganic adhesive and the strength evaluation of metal joints are composed of an experimental procedure including static test for single lap joints bonded with inorganic adhesives. The inorganic adhesive can be cured at 150℃ and the maximum temperature resistance proposed is up to 1200℃. Tensile shear test for the joints with nickel adherend are performed at elevated temperature up to 400℃. Effect of material property, overlap length and thickness of adherend on the joint strength is discussed with stress analysis for corresponding joint models by a Finite Element Method. It is important to make sure which the fracture is occurred, in adhesive layer or at interface between adhesive and adherend. Therefore, deformation and fracture behavior of the adhesive layer is investigated microscopically with SEM photographs of the fracture surface.

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The technology of smart structures is evolving to actively control vibration, noise, damping, shape, and stress distribution, and now wider applications are envisaged for aerospace and other systems. Embedded or surface-bonded smart materials on an airplane wing or large flexible space structures should help to control static and dynamic problems for the enhancement of structural performances. This article introduces several analytical and experimental researches on the application of smart materials to control shape and vibration of the composite and aerospace structures.

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This study deals with the deformation and mechanical response of a shape-control plate which consists of an aluminum alloy plate and a pre-strained NiTi shape memory alloy (SMA) wire. The shape-control plate exhibits reciprocating bending deformation by heating and cooling. Bending deformation tests of the plate are carried out by electric heating and natural cooling of the SMA wire, and then mechanical response of the bent plate under electric heating is examined by three-point-bending. The experimental results exhibit that the bending deformation of the plate is considerably stable over more than two thousand heating-cooling cycles, and that the load-deflection relation of the bent plate is almost linear. Furthermore, the bending deformation and mechanical response of the plate are analyzed by a simple beam theory for the aluminum alloy plate and Brinson's one-dimensional constitutive model for the SMA wire. The numerical results describe well the deformation behavior and mechanical response of the shape-control plate observed in the experiments. The proposed numerical model can be useful in the design and estimation of the shape-control plate.

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Carbon-nanofillers have good mechanical, thermal and electrical properties and enhance the functional properties of polymers. Elastomers filled with a small percentage of carbon nanofillers have electrical conductivity and large deformation capability. These conductive elastomers may be useful for sensing large strain based on the electrical resistance change. In this study, conductive elastomer composites were produced by adding VGCF, which is a kind of multi-walled carbon nanofiller, to flexible-epoxy resin. The electrical resistance change under strain of VGCF/flexible-epoxy composites was investigated experimentally and the mechanism of the electrical resistance change was discussed analytically.

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Active Fiber Composites (AFC) consist of one layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes. They show orthotropic mechanical properties due to their design and manufacturing. The small thickness and the conformability to curved surfaces make them suitable for applications in structural health monitoring (SHM) with acoustic nondestructive testing methods. The piezoelectric properties of the AFC allow for both actuation and sensing capabilities with the same element which enables emitting and receiving of structural waves (e.g., Lamb waves) for monitoring of critical structural elements. Before realizing specific applications for AFC in SHM systems, it is necessary to characterize the transfer behavior of AFC bonded on a structure for excitation and sensing of transient waves which propagate in the structure. To characterize this behavior experimentally, the acoustic wave field in a thin, planar structure excited from surface bonded AFC is explored with a laser interferometer. Surface velocities at different positions around an AFC bonded on an aluminum plate during transient excitation are recorded. The transfer function is calculated for different angles from the fiber direction of the AFC for both the first symmetric and the first antisymmetric Lamb wave mode. The sensing process is also investigated: structural waves generated by surface bonded piezoelectric ceramic discs are measured likewise with laser interferometry in the vicinity of the AFC and with the AFC itself. Results show, that the emitting and receiving capabilities of the AFC decrease with increasing angle from the fiber direction of the AFC. Typical maxima and minima in the transfer function depend on the length of the AFC.

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For Unmanned Aerial Vehicles (UAV), "Morphing wing" is desired to improve the maneuverability and reduce the total weight of structures. Morphing wing is defined as an aircraft wing or structure that can change shape during flight. It enables the aircraft to change its standard performance. In this paper, a new Partially-flexible Composite is proposed for the material of morphing wing. The Partially-flexible Composite consists of two kinds of matrices: high-stiffness matrix and low-stiffness matrix in a structure. Sealant is adapted to the low-stiffness matrices, and epoxy resin is used for the high-stiffness matrix. These matrices have good adhesive properties with each other. Reinforced fiber continues in the whole structure. To investigate the performance of the Partially-flexible Composite, tensile tests, cyclic bending tests, and flight test are performed. In the tensile tests, the results show that there is no strength reduction due to the flexible part comparing usual CFRP. In the cyclic bending tests, two kinds of specimens are used whose widths of flexible part are 2mm and 10mm. It is proved that the Partially-flexible composite with more than 10mm-long flexible part can maintain its stiffness and has the strength to apply actual structures. In the flight test, tail assemblies of the model plane are made of Partially-flexible Composite. The model plane can be controlled and it is found that Partially-flexible composite has applicability to the material of morphing wing.

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The measurement of strain of tires in-service is effective in improving the reliability of tires and ABS systems. Since conventional strain gages have high stiffness and require lead wires, conventional strain gages are cumbersome for the strain measurement of tires. The present study proposes a novel flexible patch-type strain sensor utilizing electric capacitance change. The sensor is made from flexible polyimide substrates and ultra-flexible epoxy resin, which makes the sensor low in stiffness and high in elongation as a whole structure. The sensor utilizes capacitance changes due to the applied strain, and wireless measurements are conducted using amplitude modulation. The sensor is applied to an automobile tire, and compression tests are performed. The effects of the temperature changes are also measured. The proposed sensor is found to successfully measure the applied strain of the tire wirelessly.

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This paper presents an application for wireless structural health monitoring (SHM) in composite structures with piezoelectric Active Fibre Composite (AFC) elements. Previous studies have shown the potential of piezoelectric AFC elements used as sensor or emitter for structural waves in SHM applications. The objective of the present study was to demonstrate the functionality of a piezoelectric AFC element used as wireless sensor. The wireless sensor consists mainly of two parts. For measuring changes in the impedance of the composite structure, a piezoelectric AFC element is used. A simple electric circuit transmitted the measured signals wirelessly to a receiver outside the structure thus eliminating the need for wire connections and the related decrease in mechanical integrity. Also, a wireless connection to a sensor network is feasible. For the experiments, the piezoelectric AFC element is surface bonded on a composite plate, a laboratory scale model system, and connected to a wireless transmitter. The AFC on the composite plate is stimulated by sinusoidal voltage of 100kHz. Damage in the plate is simulated by mass loading at different locations. Measurement of the charges created by the piezoelectric AFC element during the stimulation provides the technical basis for detection of changes in the composite plate.

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This paper presents a mathematical model to predict the resistance change in CFRP cross-ply laminates subjected to tensile loading and temperature change. The proposed piezoresistance model offers a one-dimensional constitutive equation, which describes the relation among the resistance change, mechanical strain and temperature change. The strain distribution in the laminate with transverse cracking is given on the basis of a shear lag analysis including the thermal strain. The residual resistance change was expressed as a function of transverse crack density and temperature. The resistance change-mechanical strain curves were measured for various transverse crack densities at each temperature to obtain the gage factors and residual resistance change together with the residual strain. It was found that the residual resistance change increases with increasing transverse crack density and temperature although the transverse crack density becomes smaller at high temperatures.

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CFRP laminates are adopted for fuel tank structures of next generation space rockets or automobiles using fuel cells. The matrix cracks may cause fuel leak or triggers of fatigue damages. This requires monitoring system of the matrix crack density. Authors have developed an electrical resistance change method for monitoring of a delamination crack of CFRP laminates. The reinforcement fibers are used as self-sensing system. In the present study, the electric potential method is adopted for the matrix crack density monitoring. FEM analyses are performed to investigate the possibility of matrix crack density using multiple electrodes mounted on the specimen single surface. The FEM analyses reveals that the matrix crack density increases electrical resistance at the target segment between electrodes. Experimental confirmations are also performed here. Material used here is carbon/epoxy prepreg produced from Mitsubishi Rayon Co. Ltd. The prepreg is stacked to make three types of laminates. Specimens of 245 mm x 15 mm were cut from each laminate. Eight electrodes were mounted on the specimen single surface by using silver paste after polishing the specimen surface with sand paper. The outermost couple of the electrodes were used to apply electrical current, and the inner other electrodes were used to measure electric voltage changes. The slope of electrical resistance during reloading was the appropriate tool for the detection of the matrix crack density. As a result, the proposed method is shown to be effective for the matrix crack density monitoring.

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Since damage occurring in laminated composites is usually difficult to detect by means of visual inspection, laminated composites are not reliable enough for primary structures. In order to improve the reliability of laminated composite structures, an in-service automatic system of damage identification is desirable. Todoroki et al. has proposed the damage identification method for graphite/epoxy laminates using the electrical resistance change method (ERCM) and confirmed its applicability for beams and thin plate-type specimens. In this method, multiple electrodes are mounted on the surface of laminates to measure those electrical resistance changes. Damage to the laminate such as delaminations can be detected by measuring the electrical resistance changes caused by damage creation. The ERCM has yet to be investigated for thick laminates, although thick laminates has been used practically in structures such as the primary structure of commercial aircrafts. In this study, in order to evaluate the capability of the ERCM for thick graphite/epoxy laminates, measuring method for the ERCM are analytically investigated with FEM. The delamination is focused as a typical damage of laminated composites. To simulate the actual delamination by FEM, indentation tests and the detailed observations of damage are experimentally performed. In order to improve the detecting capability of ERCM for thick laminates, two kinds of measuring method is compared analytically and its applicability was confirmed.

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Carbon fiber reinforced plastic (CFRP) laminates, used at the beginning in aerospace structure, are now widely used in various fields. It is, however, very sensitive to an impact which causes delaminations in the laminate. Since the delamination reduces the mechanical property of the laminate with difficulty of visual inspection, nondestructive inspection (NDI) is required to maintain the structural reliability of the CFRP structure. Eddy current method, which is often used for metallic materials, can be applied to CFRP laminate due to conductivity of carbon fibers. The advantages of the method are short scanning time, low cost and portability. The method has been studied to be applied to the CFRP laminate. Strong electric anisotropy and inhomogenity of the laminates, however, makes simple application of the method difficult. Since delamination is in-plane damage in the thin laminate, conventional eddy current method has problem for making current-loop which should be disturbed by the damage to be detected. In this paper, eddy current method with conventional probe was firstly applied to CFRP fabric and cross-ply laminate to clear the problem of the method. For the fabric laminate, the damage location was successfully detected. For the cross-ply laminates, it was difficult to detect the location. The large scatter of response signal was observed due to the strong anisotropy of cross-ply laminate. To resolve the problem, a new probe for electrically anisotropic CFRP laminate is introduced. The new probe is made of two coils put side-by-side and induces uniform electric current that is stronger than the electric current induced by a conventional probe. It is applied to the cross-ply laminate. The new probe is arranged perpendicular to the scanning direction and move straight along specimens with fiber breakages and a delamination; the applicability of the new probe is shown experimentally.

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This research is about the selection index for selecting a standard data group for damage diagnosis via the statistical diagnosis method. The method presented can diagnose the soundness of the structure from data that will be acquired after a setup. The method presented detects structural failures with the statistical method that judges the equivalence of two data groups. One of these is called the standard data group, which is acquired when a structure is intact. The other is called the diagnosis data group, which is acquired when a structure is in operation. Therefore, the method presented does not require complicated modeling or information about the damaged condition of structures. However, for the in-service structure, two or more normal states exist. Therefore, it is necessary to prepare two or more standard data groups and to choose the suitable group for the present condition. Then, the two or more standard data groups is called reference data group. In the present study, the selection index for selecting the groups is proposed, and an improvement of the index is carried out.

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The present study is about an automatic diagnostic method for the structural health monitoring. In this study, a new diagnostic method applicable to existing structures from the present moment is proposed. In the proposed method, structural condition is diagnosed without information about damaged condition. The proposed method statistically diagnoses structural condition by means of investigating the change of a response surface. The response surface is calculated as a regression model of relationship between multiple sensors. The shape of the response surface is changed reflecting the change of the structural condition. In this method, the change of the response surface is statistically investigated with the F-test. In the F-test, the threshold of normal or damaged condition is decided with only theoretical F-probability distribution. This theoretical F-distribution is easily calculated using the response surface parameters. Therefore, diagnosis is conducted by means of only intact data used for the reference data. This means the proposed method doesn't require information about the damaged condition. Since the SI-F method is able to detect the damage in the structure by judging the deviation from the normal state, it is important to avoid the false positive detection for raising the reliability of the structure. In the present study, relationship between the condition of the false detection and the shape of the response surface is clarified. And several numerical simulations were carried out to declare the optimal condition of the damage detection for the structural health monitoring using the SI-F method.

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In general, the reflective signal of fiber Bragg grating (FBG) sensors has the shape of a single sharp peak. This signal shape can be broadened or split by non-axisymmetric stress or strain gradient applied to the grating region. Because of this signal distortion, researches have reported the difficulties in using embedded FBG sensors for the strain measurement of the composite structures. In this study, the small diameter FBG sensor (40 μm in diameter) which was recently developed for embedded applications was tested in a quasi-static indentation. Both cylindrical and spherical indentors are used to give different stress conditions to the sensor embedded in a thin composite plate. A normal diameter FBG sensor (125 μm in diameter) was also tested in the same conditions for comparison. The results of indentation tests using the spherical indentor were analyzed using simplified finite element models to estimate stress distributions in each FBG sensor. The difference in the spectral behaviors of two FBG sensors was explained using finite element analysis.

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This Paper proposes the determination method of creep exponent and coefficient from indentation creep testing. Extensive finite element analyses were performed for simulating the indentation creep, and stress states under the indenter was analyzed. An equation was developed which relates the indentation creep strain rate to the indentation stress based on the theory of plasticity taking account of the stress multiaxiality under the indenter. The equation theoretically demonstrated that the creep exponent obtained from the indentation creep testing agrees with that in uniaxial tensile creep testing. The equation also proposed the determination method of the creep coefficient from the indentation creep testing. An experimental apparatus for performing the indentation creep testing was developed and the creep exponent and coefficient obtained in the indentation tests agreed with those in the uniaxial creep in the creep datasheet. The validity of the proposed method was also verified by an extensive creep finite analysis.

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The pressure sensitivity behavior of polymeric solids is studied by depth sensing indentation. The proposed analysis expands the scope of previous methodologies that deal with the determination of plastic properties by depth sensing indentation available in literature [1-3]. Two indenter geometries were used: Berkovich and spherical indentation. An inverse problem type algorithm was developed to determine the properties of materials assuming they display a pressure dependant perfectly plastic behaviour. The stability of this algorithm is investigated to identify the extent to which this algorithm can be applied effectively. An experimental example of the application of the methodology was successfully carried out on PMMA.

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Composite materials have been widely applied in a variety of engineering and industrial fields over the past two decades. In order to reduce maintenance costs and to avoid potential catastrophic failure, it is essential to detect damage to these composite structures at the earliest possible stage. Evolutionary approaches, such as genetic algorithms and simulated annealing, have attracted considerable attention as a means of solving a range of combinatorial optimization problems. Accordingly, the current study applies a hybrid evolutionary approach to detect damage in a simply supported equal-sided sector of a spherical laminate shell on the basis of natural frequency and mode shape data obtained from modal testing. The simulations consider two different damage scenarios, namely single-point damage and multiple-point damage. Furthermore, to simulate the measurement errors inherent in experimental modal testing, the simulations consider three specific error conditions, i.e. no error (the ideal case), a maximum 5% error in both the natural frequency and the mode shape data, and a maximum 5% error in the natural frequency data and a maximum 10% error in the mode shape data. The simulation results indicate that the algorithm successfully detects both the location and the extent of the damage in both damage scenarios irrespective of the magnitude of the errors assigned to the natural frequency and mode shape data.

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We propose and verify a simple, convenient, and low cost method to inversely measure arbitrary strain distributions by applying a genetic algorithm approach to analyze the reflection intensity spectra of two fiber Bragg gratings (FBGs). The proposed method involves bonding one uniform FBG and one chirped FBG to the same location of the structure of interest such that they both encounter the same strain field. The arbitrary strain distribution within the fiber gratings is then determined inversely from the two Bragg intensity spectra by means of a genetic algorithm population-based optimization process. Also, we include the reflection power attenuation factors into the genetic algorithm and make this approach more useful in practical. Several strain distributions along the fiber Bragg gratings are reconstructed numerically. The proposed measurement method is suitable for many smart structure-monitoring applications.

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The demands on machining accuracy have been increasing lately and therefore research of thermal behavior of machine tool structures is crucial for successful manufacturing. Generated heat diffuses into the structure of the machine tool components, this process is affected by heat sinks such as heat transfer on the surfaces and cooling systems. Meanwhile the heat warms up the structure of the machine tool and thermal dilatation deforms the structure, which subsequently affects machining accuracy in a negative way. Different systems are used to eliminate the thermal error, but their efficiency corresponds to the quality of the thermal machine tool model. The key problems of machine tool thermal error reduction are not in the thermal model itself, but in the fast, or even real-time, identification of the heat sources and the heat transfer coefficients on the surfaces. The identification process represents inverse heat conduction problem (IHCP), where the temperatures of the structure are the input parameters. This paper brings up a new solution of such IHCP, which enables a real-time identification of the heat transfer coefficient. The solution is founded on an analytical description of the heat transfer in a thin plate. The identification method is tested on a finite element model and experimentally.

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A material mixing method to obtain an optimal topology for a structure made of several materials in static problems has been developed based on Evolutionary Structural Optimization (ESO). We extended the material mixing method to a structure with the multiple thermal criteria of thermal flux and thermal stress. To examine the validity of the method, it was applied to a printed circuit board (PCB) substrate. The overall efficiency of material usage in PCB substrate was measured in terms of the combination of thermal stress levels and heat flux densities by using a combination strategy with weighting factors. Pareto optimal topology solution having multiple thermal criteria was obtained. The effects of weighting factors for thermal stress and heat flux criteria as well as mechanical boundary conditions on optimal topologies were investigated. It is found that as the weighting factor for heat flux density is getting larger, the size of holes at the center portion become larger in proportion to the weighting factor in order to dissipate thermal energy much efficiently. The thermal stress on the clamped four sides is larger than that on the two sides clamped. It was verified that the suggested material mixing method works very well for topology optimization of a PCB substrate for various mechanical boundary conditions with multiple thermal criteria.

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Injection molded bulk-shape Poly (L-lactide) (PLLA) specimens were hydrolyzed in the phosphate buffered solution and the mechanical properties were evaluated after the hydrolysis tests. In order to evaluated the effect of crystallinity on the hydrolysis, specimens were annealed with 70 and 130℃ for 24 h. Hydrolysis tests were conducted with soaking the specimens in the phosphate buffered solution (pH 7.4) in an incubator where temperature was kept as 37℃. Vickers hardness was not influenced by hydrolysis until 30 days. Tensile tests results, however, indicated the strength reduction with hydrolysis. From the appearance inspection, whitened regions were observed at the inner of the specimen. These results indicated the bulk erosion with accelerated inside erosion occurred.

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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 small 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 (S_0-mode, A_0-mode) and a Shear Horizontal (SH) -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 components detection using the trial EMAT could also provide useful information on the damage to any structures or any materials.

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Korean high-speed trains with the maximum speed of 300 km/h have started revenue services since April 2004. A large portion of the "Kyung-Bu" line is comprised of tunnels or bridges, which may cause excessive noise in a vehicle. During the process of the site acceptance test it was unable to satisfy some of the requirements for the noise test. Hence, the test procedure for the interior noise measurement of KTX trains are reviewed and investigated with the reference of international standards. The vibration generated by the trains propagates into the structure of the tunnel and the vehicle and it can be radiated as noise inside the vehicle interior. This noise can usually be heard as low frequency structure-borne noise. Measurement of the noise and vibration inside the Korea Train Express (KTX) vehicle confirmed that the noise comprises of frequencies below 250 Hz with a couple of broad peaks. In this study the analysis has been presented to reveal the cause of the excessive noise level and the correlation between the vehicle interior noise and the vibration of the tunnel structure. A remarkable aspect of the frequency spectra is the peak in the low frequency region. The acceleration level of the sleeper in a ballasted track is much higher because it's motion is relatively free compared to that of a slab track. Finally, a reduction method of interior noise of KTX in tunnels. The study was also intended to investigate fluctuation of pressure in a tunnel as one of interactions between a vehicle and a tunnel. To from a test vehicle with the existing mud-flap and another one with the new one. It was shown that mud-flap used in this study reduced the interior noise of KTX vehicle effectively while it is running on slab bed in a tunnel.

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In the present study, the application of nondestructive evaluation to determine the characteristics of creep damage in P92 alloy was investigated. Generally, as the hold time of static load increases, the degradation of material becomes more severe with the reduction of service life. Therefore, the creep-fatigue strength and life of high-pressure vessel such as main steam pipe at high temperature is very important in power plants. Backscattering ultrasound signals were analyzed from the creep-fatigue specimens where both static and cyclic loads had been applied simultaneously. Testing temperature was 873K and a constant load level at a stress ratio of R=0.1 was applied to the CT specimen. Various trapezoidal creep-fatigue loading wave shapes with hold times ranging from 0 to 1000 s at the maximum loads were employed. The results obtained by bulk wave of focused ultrasound were compared and analyzed with the experimental parameters. The relation between parameter, the RMS level of backscattering signals and the area fraction of cavity in creep-fatigue damage zone was investigated, where the life of the damaged specimen was evaluated.

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Acousto-ultrasonic technique that combined ultrasonic and acoustic emission tests was used to evaluate the corrosion damage of pipe in this study. The experimental equipment was established to improve the corrosion process of carbon steel pipe. The internal conditions of the carbon steel pipe were under 473K temperature and 10Mpa pressure, and acousto-ultrasonic technique was used to inspect the degree of corrosion. Ultrasonic bulk waves are limited by poor time resolution when used in the measurement of corrosion depth in thin wall structures because the corroded surfaces cause unclear echo signal edges. Therefore, in this study, the ultrasonic guided waves were generated in the pipe due to its thickness, and mode conversion of the guided wave is subsequently occurred due to the implications of the corrosion on the pipe. To analyze only the mode for evaluation of the corrosion has a limitation because of the variation of defects by corrosion. In order to overcome this problem the analysis by many parameters can be possible by using the acoustic emission technique. In this study, the corroded pipe for a period of time (three and six months) was tested by acousto-ultrasonic technique, and AE parametric features were compared. The features of energy, count, rise time and amplitude were useful to measure the degree of corrosion inside the carbon steel pipe under 473K temperatures and 10Mpa pressures.

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