Present paper describes application of four points bending tests to investigate fatigue and fracture of Al-Al_2O_3-CrC coating. The crystallographic and morphological texture was characterized and the fracture resistance was measured. CrC nanoparticles improve fracture resistance of aluminum oxide coating. CrC nanoparticles produced by the pyrolitic deposition technique effectively heal pores and defects of aluminum oxide coating. It results in high fracture resistance. The experiments showed that in all cases, the detection of an acoustic signal corresponded to the appearance of a circular cracks seen on the surface; in a very few cases, examination of the surface after detection of a signal revealed the presence of two ring cracks. The number of healed defects and the effectiveness of the individual healing determine the degree of toughening associated with crack healing. Micromechanical models using arrays of internal or surface cracks have been developed. The models provide mechanics of deformation and failure for the coating. This micromechanical model gives a reasonable explanation for the observed fatigue crack growth. Based on these theoretical findings it would appear that the technique has a great potential for studying of the fatigue properties of coatings based on oxide ceramics and chrome carbide nanoparticles.

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Present paper describes the use of Hertzian indentation with rheological models as a method for determining the fracture of multi-layered brittle coatings. The advantage of the method revealed here is that the only quantity to be measured is a deformation or a fracture load. By measuring this minimum load an accurate estimate of fracture may easily be made with application of rheological modeling. Use of rheological models for strain-deformation modeling has enabled accurate estimates to be made of the minimum loads necessary to propagate cracks by Hertzian indentation. At present the analysis only applies for the case where the sphere and the substrate are made of the same material. However, the analysis is comprehensive in that it can be applied to sphere/substrate systems with any values of mechanical properties represented by combination of plasticity, viscosity and elasticity of given materials. The only other requirement is that the surface should be coarsely polished and a sphere of relatively small radius (less than 5 millimeters) should be used. Two further points are worthy of note. Because the only quantity that must be measured is a fracture load, it is possible that this method of determining fracture can be automated with equipment and software. Also, the existence of an absolute minimum fracture load, for a given sphere size, suggests that the Hertzian indentation test could find use as a localized proof-test technique.

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Fatigue crack nucleation and initiation at particles or defects in materials have been the interest of many researchers over the past twenty years. This is because the understanding of these phenomena would provide a better understanding of production of new fatigue resistance materials. In this study a test was developed to test the fatigue properties and to allow microscopic observation of fatigue crack nucleation and initiation in sintered steel. The fatigue test was based on plate bending which gives balanced biaxial tension where an optical finished polished specimens were tested. The results of the experimentation showed that there were mixed mode of crack nucleation and initiation such that most cracks initiated at the interface of particles and matrix especially at high stress levels. Cracks were also observed to initiate at voids and beneath the surface. Quenched specimens and tempered between temperatures ranges of 300℃ and 600℃ showed a similar behaviour of crack initiation mechanism. The significant difference between the as received and tempered specimen was the number of cycles to failure due to differences in material hardness and internal defects. The results of the experimentation are discussed in the light of possible micro crack toughening at the crack tip and presence of residual stresses due to temperature changes. It is believed that some effects of residual stresses at the surface and beneath play a major role in the nucleation and initiation and thus the fatigue behaviour of sintered steel.

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The use of Three-dimensional Photoelasticity is shown for the identification of qualitative real physics characteristics of a stress distribution in a crankshaft crank. This crank is a machine element of complex geometry and loading, and the experimental technique is a tool for mainly qualitative validation of the stress state obtained through a numerical model. An experimental model was used to visualize and to identify the internal general state of stresses as well as the points of stress concentration. This is performed through photoelastic results of immediate characterization, namely the pattern of isochromatic and isoclinic fringes, as well as the distribution of tangential stresses along lines inside the model. The quantification of the internal stress state was accomplished through the technique of Finite Elements, using an analogous numerical model, whose real physics analogy was demonstrated (validated using the data of the experimental model (from the numerical results only shear stresses are shown in comparison to the photoelastic results).

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In this study, the interaction between plasticity and creep deformation is observed from both macro and microscopic point of view using Type 304 stainless steel at room temperature. The experiments conducted in this study are as follows: (1) subsequent creep after tension-compression cyclic preloading with a constant strain amplitude under a constant strain rate; (2) subsequent torsional creep after cyclic torsional preloading with a constant strain amplitude under a constant strain rate; (3) subsequent stress relaxation tests after tension-compression cyclic preloading with a constant strain amplitude under a constant strain rate; (4) tension-compression cyclic loading with the change of the strain rate. These experimental results show that the subsequent time-dependent deformations are depending on the number of cycles of the preloading even though the stress-strain curves of the preloading are almost same. To verify the difference from microscopic point of view transmission electron microscope (TEM) observations are conducted. The dislocation structures observed are clearly different due to the number of cycle of the preloading.

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This paper looks at active control of the swept shock wave/turbulent boundary layer interaction using smart flap actuators. The actuators are manufactured by bonding piezoelectric material to an inert substrate to control the mass transfer rate through a plenum chamber. The cavity provides communication of signals across the shock, allowing rapid thickening of the boundary layer approaching the shock, which splits into a series of weaker shocks forming a lambda shock foot, reducing wave drag. The design is a trade-off between allowing sufficient mass transfer for control and suppressing deflection to create active control. Active control allows optimum control of the interaction, as it would be capable of positioning the control region around the original shock position and unimorph tip deflection, hence control mass transfer rates. The actuators are modelled using classical composite material mechanics theory, as well as a finite element-modelling program (ANSYS 6.0).

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The thermomechanical properties of polyurethane-shape memory polymer (SMP) foams were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam after compressive deformation at high temperature, stress decreases and the deformed shape is fixed. By heating the shape-fixed foam under no-load, the original shape is recovered. The ratio of shape fixity is 100% and that of shape recovery 98%. (2) Recovery stress increases by heating under constraint of the fixed shape. Recovery stress is about 80% of the applied maximum stress. (3) The shape deformed at high temperature is maintained for six months under no-load at T_g-60K without depending on maximum strain, and the original shape is recovered by heating thereafter. (4) If the deformed shape is kept at high temperature, new-shape forming appears. Applications of SMP are introduced.

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In the authors' series study on ultrasonic nondestructive evaluation method, velocity changes of transverse waves propagating in a polycrystalline aggregate under simple and pure shear states showed the same change tendency as the development of plastic deformation. However, although no velocity changes of longitudinal wave under simple shear state were concluded, the velocity changes under pure shear state were clearly observed for both experimental and numerical results, regardless of the same stress and strain state of the two cases. Therefore, in this paper the effects of microstructural behavior on transverse and longitudinal wave velocity changes under simple and pure shear states are studied via finite element polycrystal model (FEPM). From the fact that the texture developments under simple and pure shear states are roughly the same and similar to the transverse wave velocity changes under both shear states, it is concluded that transverse wave velocity depends upon texture development mainly. On the other hand, the multiplicative amount of cross slip under pure shear state is larger than that under simple shear state and this means that the point defects induced by cross slip are much easier to introduce under pure shear state than under simple shear state, therefore we conclude that the longitudinal wave velocity depends heavily upon point defects induced by cross slip. Furthermore, longitudinal wave propagation properties under pure shear state were studied at different specimen surface morphologies. Concerned with the longitudinal wave velocity changes, the experimental results were apparently categorized into two types: (i) simple decreasing change tendency at polished surface state, and (ii) chaotic change tendencies at unpolished surface state. Therefore, from the viewpoint of longitudinal wave velocity changes showing a sensitive response to the point defects, the effects of surface roughness and crystal orientation on the amount of cross slip under pure shear state are analyzed via FEPM. The results indicate that the crystal orientation causes much more influence on the amount of cross slip than what the surface roughness does. This means that crystal orientation at the surface due to machining is responsible for the phenomenon of variety of longitudinal wave velocity change tendencies at unpolished surface state. However, the distribution of crystal orientation at the surface tends to be uniformed and its peculiarity due to machining tends to be vanished when the specimen is polished, this results in the simple decreasing change tendency of longitudinal wave velocity.

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A fatigue-test machine for alternating bending of a wire under strain-controlled conditions was developed. Bending-fatigue tests on a TiNi shape-memory alloy wire were then performed for various strain ratios. The results obtained can be summarized as follows. (1) The fatigue life curves under alternating bending and pulsating bending, as expressed by the relationship between maximum strain and the number of cycles to failure, systematically follow the order of strain ratio. (2) The larger the strain ratio, the longer the fatigue life. (3) The fatigue life under rotating bending is shorter than that under alternating bending. (4) The increase in temperature during cyclic bending becomes larger in the order: rotating bending, alternating bending, pulsating bending. The fatigue life decreases in proportion to the increase in temperature. (5) The fatigue limit of strain for alternating bending, pulsating bending and rotating bending is in the region of R-phase transformation.

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Three point bending tests were carried out on honeycomb sandwich curved panels which were made from an aluminum alloy and had radii of curvatures of 200, 300 and 400mm. Major conclusions obtained in this study are summarized as follows: 1) A bending strength of curved panels was about 10% higher than that of a flat panel regardless of the radius of curvature. 2) A flexural rigidity of the curved panel was decreased with the decrease in the radius of curvature. 3) An effect of a deformation of core on the bending property of curved panel became small with the decrease in the radius of curvature.

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Aluminum-based metal matrix composites (Al MMCs) are attractive materials that can be used in various industrial fields. Their unique characteristic is the combination of lightweight, excellent ductility of the aluminum matrix and high strength, high stiffness and high temperature capability of the reinforcements. Processing conditions are proven being closely related to the properties of the composites. In this study, Al MMCs reinforced with stainless steel fiber (SSF) were fabricated under different processing conditions. Properties, such as density and tensile strength, as well as microstructures of the composites were investigated. The effect of fabrication parameters on the microstructures and properties of the composites, and the effect of secondary treatment of rotary swaging were discussed. The experimental results reveal that interfacial reaction tends to occur at temperatures higher than about 450℃, and forms an apparent reaction products layer between the matrix and SSF. The interfacial reaction layer, which is regarded as a mixture of various intermetallic compounds, exhibits high hardness and brittle feature resulting in the composites with low ductility.

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Even though high damping rubber (HDR) is used in various fields such as vibration isolation and seismic isolation, few studies have been conducted to investigate thermo-mechanical behaviors. Besides, modeling on thermo-mechanical coupling is not available. This paper presents experimental investigations of temperature dependency behavior of HDR material and its thermo-mechanical constitutive modeling. The use of infrared thermographs to measure temperature field in HDR under cyclic shear is presented. Changes of mechanical properties of HDR are investigated with respect to frequency of loading and rubber body temperature. Based on the results of rubber material tests, a temperature dependent constitutive model for HDR is proposed, which combines elasto-plastic body with strain dependent isotropic hardening law and hyperelastic body with damage model. Temperature dependent parameters, which can express rate dependent hardening, yielding and thermal softening are introduced to the model. The proposed constitutive model can express both temperature dependent and frequency dependent behavior of HDR. Finally, the energy balance equation is constructed to evaluate average surface temperature of the material. The modeling results agree well with the experimental ones.

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The hydrogen behavior in fatigue and sustained-load cracks growth of a γ-TiAl intermetallic compounds has been studied by means of hydrogen microprint technique. Hydrogen was introduced to a specimen by cathodic charging technique, and then metal-hydride on the charged specimen surface were removed by electropolishing. For the hydrogen microprint technique, specimen surface was covered with collodion and photographic emulsion before pre-cracking. The hydrogen accumulated region was well visualized by the hydrogen microprint technique. It was found that the duration time is the important factor on the hydrogen accumulation behaviour in the fatigue crack growth. In sustained-load crack growth, it was proven that large amount of hydrogen was accumulated in the high stress field at the crack tip. Also it was confirmed that hydrogen content was dependent on the hydrostatic stress.

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MUSIC is a high-resolution signal-processing algorithm for the direction and location finding using the received signals sampled by the array receiver having several sensors. The MUSIC has been conventionally applied to signal sources located in the far field. We are now proposing a new MUSIC algorithm that is able to highly resolve and make precise estimating for the location finding of short-range sources. The new MUSIC will be used in the diagnosis of the machine and for non-destructive testing, etc. This paper will describe the details and differences between the conventional and the proposed MUSIC, and show these performances for the location finding of the simulated signal sources. Results of the numerical and experimental simulations were included to support our examination, and it is clear that the proposed MUSIC was able to precisely resolve and highly estimate the short-range sources.

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Strain gages made of copper plating foil are devised for measuring the elastic surface stress of machine parts in operation. The elastic stress is measured by observing slip bands in the bonded foil. Calibration studied by cyclic tension test and cyclic torsion test with various stress ratios and different stress waveforms are performed on round steel bars with plating foil. It is verified that the relation between the threshold stress for the first appearance of slip bands and the number of cycles is not affected by the stress ratios and stress waveforms. Using a computer image-processing system, the density of slip bands in a microscopic image of the bonded foil is analyzed automatically and quantitatively. Under various stress ratios, the relation between the stress amplitude and the density of slip bands for a constant number of cycles is examined. In order to examine the accuracy of this method, the peak stresses in grooved shafts under cyclic tension test are obtained using the present method. The results are compared with those derived from the design formulas by Roark and Young. It is confirmed that this method provides an accurate calibration value for measuring the cyclic stress.

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The fatigue crack propagation test was carried out in order to clarify the effect of humidity on the characteristics of fatigue crack propagation in spherical graphite cast iron. Spherical graphite cast iron (FCD450) was used as a specimen. Then, two kinds of heat treatments were conducted to the material. One was an austemper ductile cast iron (ADI), the other was a quenching and tempering treatment (QT). And, as cast material (As-cast) was added, and with these three materials fatigue clack propagation test was carried out. The experiment conformed to ASTM. Stress ratio R was 0.1, and specimen used was 1CT type, 12.5mm thick. The test was carried out at room temperature and under four or five kinds of humidity, 0,20,40,60,80%. The relationship between the characteristics of fatigue crack propagation and the crack closure produced on fracture surface was investigated. The obtained results were as follows. (1) In the low ΔK region, since the oxide-induced crack closure is generated, the propagation speed lowered, and ΔK_<th> increased. (2) In high ΔK region of QT and ADI, the fatigue crack propagation rate was accelerated by the effect of humidity. (3) ΔK_<th> of As-cast and QT were increased with the rise in humidity. (4) ΔK_<th> of the ADI was highest in the humidity 40% atmosphere. However, the factor of decreasing ΔK_<th> over the 40% couldn't be clarified.

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A hybrid moire -finite element (FE) analysis was used to determine the crack tip opening angle (CTOA) along a tunneling crack front in a single-edged notch, three-point bend (SENB) specimen. The specimen was machined from a ductile 2024-T351 aluminum plate of 8.1 mm thickness and was prefatigued to an initial crack length to width ratio of α_0/W &ap; 0.45. The specimen was then subjected to stable crack growth of Δα &ap; 0.5 to 5.5 mm, after which the specimen was post-fatigued to mark the final crack front and loaded to failure. A quarter segment of the SENB specimen was modeled with a truncated 3-D elastic-plastic finite element (FE) model. Measured surface displacements, which were obtained by moire analysis, and stable crack growth were prescribed on the FE model. CTOA was obtained from the computed crack opening displacement, approximately 1 mm behind, and normal to the crack front. The good agreement between the measured and computed surface CTOA indicated the accuracy of this procedure.

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In order to toughen brittle materials, shotblasting process at room temperature was performed, followed by annealing at high temperature. During annealing, fine cracks, which were introduced by shotblasting process, disappeared and dislocation cells were formed. Brittle materials were toughened by the crack propagation prevention effect of dislocation cells. Toughness was evaluated by measuring fracture toughness value K_<IC>, and It was 1.4 to 4 times the rate of an improvement of the fracture toughness K_<IC> after toughening process.

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The time-temperature dependent flexural strength of honeycomb sandwich (SW) composite panel with Nomex^<TM> honeycomb core and satin-woven glass fiber/epoxy face sheets was studied as well as glass fiber reinforced plastic (GFRP) laminate of face sheet. The three-point bending with constant strain rate (CSR) was employed. The experiment results show that the SW panel indicates time-temperature dependent behavior. Relevant experiments of dynamic test and CSR flexural test of GFRP laminate of face sheet were performed and compared, the time-temperature characteristics are consistent. Failure mechanism of SW panel was analyzed by fractograph and FEM analysis.

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A method for automatic measurement of principal-stress directions in the entire field of a model is developed based on the results of photoelastic experiments. This method uses a set of color photoelastic images, which is obtained by rotating polaroids in dark-field polariscopes. Second, a set of monochrome photoelastic images is obtained by dividing the sum of light intensities at the same point in the red, green and blue images at the same rotation angle of polaroids by the sum of the maximum light intensities in each set of red, green and blue images. Lastly, the principal-stress directions are obtained by applying the generalized phase-shift method to a set of monochrome photoelastic images. The proposed method is applied to a circular disk subjected to a concentrated load. Results show that the principal-stress directions obtained by this method are in good agreement with the theoretically determined directions.

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Boat propellers are damaged frequently and are replaced by new propellers once in every six months. The reasons for the damage in propellers used in Pilot boats are explored. A method for increasing the life of the propellers is proposed viz., improving the composition of the propeller material. Aluminium bronze materials are found to have better properties compared to the existing propeller materials. Three new alloys of Aluminium bronze have been developed to find a better material for extending the service life of the propellers. The preliminary results of mechanical properties evaluation clearly reveals that these alloys are alternative to the existing Copper-Tin-Zinc-Lead alloys. The alloy with Ni/Fe=1.1 (with a chemical composition of Cu 80.31%, Al 9.52%, Ni 4.87%, Fe 4.4% and Mn 0.9%) has been found to have better mechanical properties compared to other two alloys. This may be attributed to the possible formation of optimum morphology and volume fraction of intermetallics phases in copper matrix.

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Cavitation impacts by high-speed water jet can be used to modify the residual stress in materials as a water shot peening method. High level of compressive residual stress has been generated under the surface of materials by using water cavitation technique. In the present paper, a helical gear of SCR420H steel was processed by water peening process after heat treatment. The residual stresses on the tooth surface of the gear and at various depths under the tooth surface were measured by X-ray diffraction method. The area of peening zone, level of introduced residual stress, depth of compresive stress layer and effect of peening time were invesgated. By comparing the residual stresses of the tooth before and after water peening, the effectiveness of water peening process was verified for a quenched gear.

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The unique performances of Shape Memory Alloy Composite(SMAC), such as compressive residual stress in matrix and deformation of composite(deformation ability), are derived by the interaction of the mechanical properties between the SMA fibers and matrix. Therefore, if the control of unique performances is tried for SMAC, it is necessary to grasp the change of unique performance due to combination of materials. In the present paper, firstly, systematization of change of unique performance due to combination of materials(fiber volume fraction and young's modulus of matrix) is analytically tried. Secondary, for some SMACs having a combination of materials, deformation ability under thermo-loading is experimentally measured using digital image correlation method. Also, compressive residual stress in matrix is qualitatively observed using photoelastic method. Temperature distribution on surface of composite is measured by infrared radiation thermometry method.

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The relationship between surface strain behavior and the state of a subsurface delamination for a thermal-barrier-coated (TBC) material was described in this paper. Tension-compression fatigue tests were carried out at high temperatures (893K and 833K) and room temperature for ZrO_2-8Y_2O_3-sprayed and Al_2O_3-sprayed type 304 stainless steel specimens. Surface strain behavior during the fatigue test was measured using a laser speckle strain gauge. It was found that a substrate strain was fully reflected on a surface strain unless a subsurface delamination was initiated, while a surface strain was found to decrease when a subsurface delamination was initiated. All the surface strain behaviors were classified in five patterns, and they were related to the state of a subsurface delamination. The number of cycles to delamination was decided by the surface strain behavior. It was found that the fatigue fracture life was long when the fatigue delamination life was long for the specimen with a high strength bond-coating, while the fatigue fracture life was found to be short when the fatigue delamination life was long for the specimen with a low strength bond-coating. It was concluded that the bond-coating with high strength and high adhesive strength was effective in improving the fatigue fracture life of a thermal-barrier-coated material due to the restriction of a crack initiation into the substrate.

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The integration of passive sensors like gratings into the surface of micro systems is a convenient way to measure system parameters under long term conditions. In this paper a new approach is proposed. The first diffraction order of a specimen grating under load is investigated by means of Digital Holography. The sensitivity of this technique is discussed theoretically and an experimental setup is presented implementing this method. Finally, experimental investigations are shown which prove the Digital Holography to be able to measure displacements of a surface grating under load. To demonstrate the feasibility of this technique for use in reliability testing of polymeric micro components, the surface gratings were directly implemented into a PMMA substrate using an excimer laser.

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Nowadays, 316L stainless steels are mostly used in high temperature structures because of their superior high-temperature strength and ductility. The materials in high temperature structures are subjected to combined creep-fatigue damage. It is very important to predict the fatigue life of materials under creep-fatigue condition in order to use the materials safely and efficiently at high temperature. In this research, we could quantify the effect of tensile hold time on the fatigue life of 316L stainless steels through creep-fatigue tests with a tensile strain-hold wave form. In these tests, the creep loading and fatigue loading were repeated alternately. A new creep-fatigue life prediction model is formulated with the linear damage summation rule. When the sum of the fatigue damage and creep damage is equal to unity, the failure of materials occurs. Then the fatigue damage component was derived from the cycles ratio and the creep damage component was formulated as a function of the amount of stress relaxation. A new purposed creep-fatigue life prediction model was more accurate than classical life prediction methods (Time fraction rule, ductility exhaustion rule).

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A functional concrete, named "Life-Controllable-Smart" concrete, was developed on the basis of the composite technology. The material, which is a concrete containing the PET blocks improved in microwave heatability as the aggregate, can be easily and safely on demand by irradiating 2.45 GHz microwave. The breakability, heatability, workability and strength were investigated to improve the total performance of the LCS concrete. It is evident that when thermal expansion coefficient α_r of the filler is the same, fracture property of LCS concrete would be almost wholly dependent upon bulk modulus K_r of the filler. It is clear that as resin content V_f increases, temperature at break point descends drastically and results of fracture experiment were almost the same as those of the numerical analysis. Finally, it is confirmed that the decomposing property, execution property and strength are within the allowable limits of practical utilization, and satisfactory results are obtained concerning material development

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A circular notched round bar specimen produces multi-axial stress field when uni-axial stress is applied in the axial direction. This stress field is produced at practical component structure. Therefore the characterization of creep crack growth rate under this condition is important for practical use. For a circular notched specimen of creep ductile material, a creep crack grows in brittle manner. In this paper, a creep brittle material such as 12Cr ferritic heat resistant steel was noticed. High temperature creep crack growth tests were conducted for a circular notched specimen for 12Cr ferritic heat resistant steel. Q^* parameter which predicts creep crack growth rate is derived for this specimen. On the basis of this Q^* parameter, the algorithm of predicting the life of creep crack growth is proposed.

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Plastic gears have recently been used for power transmission. So, it becomes very important to evaluate time dependent stresses around tooth roots of plastic gears, finally. It should, owever, be pointed out that an effective and reliable technique for the purpose has not yet been proposed. The authors discuss a new technique developed by combination of the elliptically polarized white light photoviscoelastic (EPWLP) technique and the color digital correlation technique to perform tooth root stress analysis on a rotating plastic gear. The experimental results show good qualitative agreement with those by FEM viscoelastic analysis.

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Phase-shifting digital holography is a suitable method for measuring very small displacement. An optical system which can measure surface displacement was built and the validity was verified for a fixed disk under a concentrated load perpendicularly to the surface at its center. To obtain the components of 3D strain, the components of displacement obtained by holography have to be differentiated spatially. The authors adopted the minimum spanning tree technique for the process to get continuous distribution of displacement. The results showed a good agreement between theoretical and experimental analyses.

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A specific experimental method, the split Hopkinson pressure bar (SHPB) technique is used to determine the dynamic material properties under the impact compressive loading condition with strain-rate of the order of 10^3/s〜10^4/s. The dynamic deformation behavior of rubber materials widely used for the isolation of vibration from varying structures under dynamic loading is determined by using the Split Hopkinson Pressure Bar technique. The relationships between the stresses at transition points of rubber materials and the strain rate are found to be bi-linear. However, an interesting relationship between the strains at transition points of rubber materials and the strain rate, which needs further investigation, is noted.

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We investigated a method to evaluate fatigue damage of steels with optical method by detecting surface change caused by fatigue. In the earlier stage of fatigue in a low-carbon steel, slipbands appear on the specimen surface and then density of the slipbands increases with progress of fatigue damage. When a laser illuminates surface of the fatigued steel, light intensity distribution of the diffusion pattern of the reflected light changes with the change of surface properties caused by slipbands. Using this method, we are able to detect fatigue damage before crack initiation by observing diffusion pattern change during fatigue test. In this study, we investigated relation between change of surface properties and diffusion pattern. We also investigated a method to estimate fatigue life of the object material by observing change of the diffusion patterns during fatigue loading.

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Polymeric flexible films are candidate materials for the fabrication of inflatable structures, which is a key technology in constructing space facilities. These materials are also central to the design of future artificial satellites and solar panels for space stations. These space-based structural members have to hold a certain amount of tensile load in severe environments irradiated by atomic oxygen and radiation. The effects of radiation on polymeric film have been studied, but the damage resulting from processes under tensile force have not been fully elucidated. To investigate this phenomenon, we conduct space experiments that expose PEEK sheets under tensile stress to a real space environment utilizing the International Space Station's Russian Service Module, and carry out ground control experiments that irradiate single and combined atomic oxygen, ultraviolet ray, and electron beam to the same materials. This report introduces an outline of these experiments and presents results of pilot irradiation tests carried out before the regular ground control experiments.

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This article describes fatigue crack growth experiments to investigate the degradation of the durability of polymers due to fluid environments. The degradating effect of media causing stress cracking can be observed on the fracture surfaces of tested samples by scanning electron microscopy. Strategies to improve environmental stress cracking like changes in molecular weight, orientation, toughening with rubber particles of different sizes are discussed. Fatigue crack growth experiments can be employed as a very fast and effective screening method.

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The analysis of the effect of the temperature history on the morphology, and the shear relaxation behavior of two commercial PA6 material (BS400N, and NS4A1) is presented. The material was first brought into the molten state and then solidified along the two distinct temperature histories, simulating the conditions during the manufacturing process, such as injection molding, or extrusion. Morphological analysis, using the optical microscope with polarized light, revealed significantly different structure in the two groups of specimens. The shear relaxation experiments, performed at six different temperatures, were used to characterize the mechanical properties of these specimens. The time-temperature superposition principle was used to construct the master curves, which determine the long/time behavior of the materials. Comparison of the master curves showed that the mechanical properties of PA may vary, depending on temperature history during the manufacturing, close to 80% in strength, and more than 1000 times in long-time behavior!

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In this work, the effect of transverse fiber distribution on the elastic-viscoplastic behavior of long fiber-reinforced laminates is studied using a homogenization theory. To this end, a basic cell with random fiber distribution is arranged point-symmetrically with respect to the cell boundary facet centers. The basic cell is also arranged Y-periodically. By means of the standard deviation of fiber distribution and the radial distribution function, it is demonstrated that the point-symmetric arrangement can enhance the randomness of fiber distribution than the Y-periodic arrangement. Then, by assuming the point-symmetry based fiber distribution as the transverse fiber array in laminae, the in-plane elastic-viscoplastic deformation of CFRP laminates is analyzed using the homogenization theory of nonlinear time-dependent composites. Comparative analysis is further performed by assuming the perfectly periodic, hexagonal fiber distribution in laminae. It is thus shown that the transverse randomness of fiber distribution has negligible influence on the macroscopic elastic-viscoplastic behavior of laminates, whereas the microscopic distribution of stress in laminae is markedly affected by the fiber distribution. It is also shown that the results of analysis agree very well with the corresponding experimental results.

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The neutron diffraction method was applied to measure the loading stresses in a monolithic aluminum alloy (Al2024) and an aluminum alloy reinforced with silicon carbide particles (SiCp/Al2024). Under uniaxial loading, the longitudinal and transverse strains were measured by the time of flight (TOF) method. The lattice strains obtained from several diffraction lines were determined. The strain in the longitudinal direction increased proportionally to the applied stress, while the transverse strain decreased with applied stress. The elastic constants measured by the neutron method was compared with the value predicted by the kroener model. For the results of monolithic aluminum alloy, the peak intensity of more than 300 counts was required to determine the lattice strain with sufficient reliability. The intensity of Al200 diffraction was high enough to determine the lattice strain in both longitudinal and transverse directions. The elastic constants agreed well with the predicted values. For the composite, the loading stresses in each constituent phase of the aluminum alloy and the silicon carbide particles were measured. Diffractions from SiC102, SiC110 and Al200 were suitable for the determination of the lattice strain. The measured strain were compared with the values predicted by the inclusion models. The measured results close to the predicted values. The macro stress calculated by the rule of mixture agreed very well with applied stress.

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To investigate the fatigue properties of aluminum alloy die castings , fatigue tests were conducted on five types of aluminum alloy die castings. The fatigue strengths were evaluated by using the stair case method for small sample size (JSME Standard S02-1994 14S-N testing method ) and √<area> parameter model using the statistics of extreme values of casting defects. The main results obtained are as follows: (1) For ADC10, ADC12, and D10FM, the origin of fatigue crack is casting defect caused by various die casting methods. While for ADC24Z and AC4C, the origin of fatigue crack is the base matrix. (2) In the case of ADC10, ADC12, and D10FM, the square root of casting defect area (√<area>) follows the statistics of extreme values, and the fracture surface at around the fatigue crack initiation portions were Mode I fracture surface. The fatigue limits predicted by the √<area> parameter model are in good agreement with the fatigue limits from the 14S-N testing method. (3) In the case of ADC24Z , the fatigue fractures were caused by Mode I cracks. (4) In the case of AC4C, the fatigue fractures were caused by Mode II cracks. (5) The extra-long fatigue strength(10^7-10^9 cycles)of AC4C-T6 decreased along with the increase in the number of cycles, while the extra-long fatigue strength(10^7-10^9 cycles) of ADC10-T5did not decrease along with the increase of the number of cycles.

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Fatigue crack propagation behavior and stress-induced martensitic transformation behavior in two types of TiNi were investigated: One is TiNi with shape memory effect, FML4, the other is superelastic TiNi, FML6, at room temperature. In addition to the observation of fatigue cracks by optical and scanning electron microscopes, the crystallographic orientation image microscope was utilized to investigate the distribution of martensitic phase around the crack. Particular emphasis was placed on the effect of the stress-induced martensitic transformation measured by neutron and X-ray diffraction in a smooth and notched specimens. The results show that the crack propagation rate, da/dN, in FML4 was smaller than that in FML6 when compared at the same stress intensity range, ΔK. In the range over da/dN of 1x10^<-9> m/cycle, the value was about 1/5 of that in FML6. The threshold value of ΔK was also higher in FML4. Even when da/dN is compared at the same effective stress intensity range, ΔK_<eff>, the difference remains remarkable and the threshold value of ΔK_<eff> in FML4 was found to be larger. The difference of the phase surrounding the fatigue crack was found to be a dominant factor for difference between FML4 and FML6. Based on the result of EBSP measurement, the residual martensitic phase was hardly found at the crack tip and crack wake in FML6. The distribution of the stress-induced martensitic phase at notch root was measured in FML4 and found to be the effective method to measure the stress-induced martensitic phase at a crack tip.

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A C-Cr bearing steel (JIS SUJ2) was fatigued with the ultrasonic fatigue-testing machine (20kHz) in laboratory air. In the very long-life regime, the decline of fatigue limit was seen. The origins of crack initiation were mostly internal inclusions. However, even when the specimen broke in a long life region, some cracks were initiated from specimen surface. Fracture surface were observed with a scanning electron microscope (SEM). The fish-eyes were observed in the specimens broken from the internal inclusions. The fracture surface could be divided into three regions. The first region surrounding inclusion was a facet area. The crack propagation in the facet region was Stage A and the crack propagation outside the facet region was Stage B. When the fatigue cracks reached the specimen surface, the fatigue cracks propagated as surface cracks.The crack propagation rate in each region was estimated to be a power function of the stress intensity range. Fatigue life was calculated by integrating with the crack propagation laws determined from the data obtained for the rotating bending. The predicted fatigue life agrees with the experimental result.

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Aspherical mirrors are being widely used in modern optoelectronic instruments. Hence measurement of optical aspherical surfaces is necessary. Phase shifting interferometry is the current method for measuring aspherical mirror and has many advantages, but it is marred by a few inaccuracies due to the vibration and mechanical movement of the phase shifter itself. This paper presents a novel aspherical optical surface measurement instrument based on the fringe projection. In this system, phase shifting is done electronically and thus errors due to the vibration and mechanical movement of the phase shifter itself are eliminated. The shifting operation is easy and rapid, and can be controlled precisely. A practical example confirms the predictions of the proposed method.

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This study has investigated the usefulness of waste plastics for nitriding of ferrous materials. Namely, after ferrous materials were heated in the waste melamine plastic powder and then cooled down, their surface and surface layers were analyzed. As a result, it was found that their nitriding took place regardless of their type. Therefore, this method can be used as a technique to improve the fatigue and wear resistance of machine's components.

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Fatigue crack propagation tests of poled and non-poled PZT specimens were performed under mechanical loads with and without superposition of electric fields. The crack length was evaluated from the change of compliance of the specimen. For specimens which were poled in the longitudinal direction (PL specimens) perpendicular to the crack plane, the crack propagation rate for the case of open circuit was faster than that for the case of short circuit. The application of a negative or positive electric field accelerated the crack propagation rate and the amount of acceleration was larger for the case of the negative field. The relation between the crack propagation rate and the stress intensity factor (SIF) can be divided into three regions. In Region I, the crack propagation rate decreases with increasing SIF, and then turn to increase in Region III. In Region II, the propagation rate is nearly constant. The mechanisms of crack propagation in PZT under cyclic loading was discussed on the basis of microscopic observation.

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Microscopic buckling and macroscopic instability of periodic cellular solids under uniaxial, as well as biaxial, compression are studied. To this end, a general framework of microscopic bifurcation and post-bifurcation analysis is established on the basis of an updated Lagrangian type, two-scale theory. Using the framework, cell aggregates of an elastoplastic honeycomb subject to in-plane compression are analyzed. We thus demonstrate the dependence of microscopic bifurcation on periodic length, the inherent multiplicity of long-wave microscopic bifurcation, the localizations of microscopic buckling in a cell row and in deltaic areas, and the change into an asymmetric, long-wave mode under equi-biaxial compression.

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Ecological and economic aspects induced to the evolution of tyre patches, that could increase the work-life of the heavy duty tyres. This technical solution permits to repair, with an important reliability, different broken wires of the tyre wall. The tyre repair is an extremely delicate and accurate process, that needs careful analysis. With this work, the behaviour of some tyre patches, that have the task to compensate for the lack of structural integrity has been analysed. The possibility to follow the tyre's deformations, due to everyday working on the road stresses, of two kinds of patches has been evaluated. In particular, the thermo -mechanical behaviour has been highlighted, by means of an IR camera, that revealed extremely sensitive to the thermal superficial gradient induced by hysteresis' phenomena.

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Fatigue tests of vulcanized natural rubber were conducted under displacement-controlled conditions. The specimens were of three types: smooth specimen, specimen with an artificial surface defect of 0.2mm in diameter, and specimen with an artificial through-thickness defect of 2mm in length. In smooth specimens, a fatigue crack started from natural defects of about 0.15mm in size, and grew as an internal crack, and then became a through-thickness crack. The spring constant of the specimen decreased slowly in the range of about 80% of the total life (Stage A), followed by a rapid decrease (Stage B). The transition from Stage A to B took place when a crack penetrated through the thickness. The rate of fatigue crack propagation is expressed as a second-power function of the J-integral range both for surface cracks and through-thickness cracks. The J-integral was evaluated from the crack-center opening displacement. Fracture surfaces for three types of specimens were observed by scanning electron microscope (SEM). In smooth specimens and specimens with an artificial surface defect, fatigue cracks propagated in the shape of a concentric circle centering on natural or artificial defects. Fracture surfaces neighboring natural or artificial defects were very flat. After a crack penetrated through the thickness, the fracture surface became rough as the crack propagated. In specimens with an artificial through-thickness, the same tendency was also obtained.

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The fatigue properties at about 10^7 cycles are not enough to issue long life of structural components. Therefore, the fatigue properties up to 10^9 cycles were essential. However, very long times and much efforts are necessary to examine the fatigue test in order to evaluate the S-N curve up to 10^9 cycles by the conventional fatigue testing at low frequency of 5〜70Hz. The examination of an ultrasonic fatigue test by high frequency is very shorten fatigue testing time. In this study, the ultrasonic fatigue testing was used for some engineering steels. This high speed test by ultrasonic was conducted by the resonance of the test pieces. Temperature of test pieces rose in fatigue testing. In order to solve the problem of temperature rise of test pieces, intermittent ultrasonic loading method was applied to the fatigue test of some engineering steels. Applicability of ultrasonic fatigue testing was examined by comparing S-N curve and crack propagation behavior between the conventional rotating bending and the ultrasonic fatigue test. In S-N curve, crack initiation life was shorter fort the ultrasonic than fort conventional method at low frequency. On the other hand, the crack propagation behavior, the same tendency was obtained for two fatigue tests. In-situ observation of specimens surface was conducted.

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For the shape memory alloy, three types of tests were conducted. The first is the tensile test, the second is the S-N fatigue tests and the final was the crack propagation tests. These testing temperature is room temperature in air, two fatigue tests was performed under three types of the stress ratio and maximum stresses. The used material was the Ti-Ni alloy with shape memory effects. As the results of tensile tests, the stress-strain curves were the typical curves of Ti-Ni SMA. The transformation stress, σ_T, is 150 MPa. Young's modulus were E_A=28.5 GPa in the austenite phase and E_M=13.4 GPa in the martensitic dominant region. As the results of the S-N fatigue tests, the fatigue limit was 153 MPa. The relationship between σ_<max> and N was divided into three regions: Region I, II and III. Region I is the low cycle region above 200 MPa. Region III is below the fatigue limit. Region II is the transitional region from Region I to Region III, this region is 153 MPa or more and is 200 or less, corresponding to the transformed region from austenite to the martensitic phase Final tests were the fatigue crack propagation tests. Regardless of stress ratios and maximum stresses, crack was slowly extended from crack initiation to about 200μm, because of the compression residual stress by stress-induced martensitic transformation. In the stable crack propagation region, the relationships between the crack propagation rate, da/dN, and stress intensity range, ΔK plotted on log-log coordinates was straight, da/dN can be expressed by power function of ΔK. Regardless of stress ratio, these relationships between da/dN and ΔK for same maximum stress were in good agreement. When the maximum stress was varied, the slopes of da/dN-ΔK for same stress ratio were different in three maximum stresses. The fracture surface was observed by Field emission scanning electron microscope (FE-SEM) and fracture-surface form was discussed.

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