For the [±θ]_S and [θ]_4 (θ=15, 30, 45, 60, 75°) CFRP laminates, Microscopic damage behavior in off-axis ply under tensile loading was investigated. Growth of matrix cracks were observed by optical microscopy, by soft X-ray radiography and by replica method. It is confirmed that damages in each angle-ply laminate progress and that crack growth behavior in unidirectional laminate was corresponding to in angle-ply laminates.

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It is difficult to analyze the Filament Winding Pipe(FW Pipe) because fiber are complicatedly woound and FW Pipe is not lamina structure. In this study, the method to evaluate strengths and flexual rigidities of FW Pipes with several winding angles established with using Finite Element Method(FEM). Furthermore results of FEM analyzes were compared with result of three-point bending tests. As the result, both results of FEM analyses and experiments are quantitatively agreement with eath other. And it was found that flexual rigidity of FW Pipes small winding angle was became large value.

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Tensile-tensile fatigue tests were conducted on carbon fiber reinforced high temperature matrix, bismaleimide cross-ply laminates to clarify the effect of 90° ply thickness on the transverse crack behavior. First cracking cycles were larger in laminates with thinner 90°plies, and transverse crack density became smaller in laminates with thicker 90°plies. The method to predict the transverse crack density was derived based on Nairn's method. Predictions were compared with experimental results to evaluate the effectiveness of the present analysis. Prediction of first cracking cycles based on the fracture mechanics is found to be necessary for quantitative evaluation of transverse cracking.

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Objective of this study is to clarify the crack-propagation properties of corrosion-resistant GFRP laminates under various acid stress environments, an effect of the constituents on fracture and the threshold properties of the crack propagation of woven C-glass cloth/vinylester laminates. This experiment is performed under descending load in HCl solution, in water and in air, and the crack-propagation behavior is depicted on the da/dt-K_I diagram. The crack-propagation rate in water is largely enhanced in comparison with that in the air and it is nearly as promoted as that in the acid solution. Then, the interfacial crack propagation behavior is investigated to confirm the role of the warp and weft fiber strand, using unidirectional specimens. As a result, it is suggested that the fiber bridging is observed, when the crack progress along the fiber direction.

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This study is about the characteristic of creep behavior of carbon fiber reinforced PEEK, superior to various mechanical character (ex. heat endurance). In this study, non-crystallized material was made by heat treatment to remove the influence of crystallinity and used for researching the influence of physical aging on creep characteristic. It became obvious that Arrhenius reciprocation law of time-temperature accomplished on the creep behavior at various temperatures to long time side, and that activation energy changed when physical aging treatment affected on the slope figure of shift factor.

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The Single fiber fragmentation test is carried out to examine the microscopic degradation process of the inner fiber surrounded by matrix resin and the interface under acid stress environment. The single fiber model composite specimen of C-glass fiber/Vinylester resin system is immersed in environmental solution under constant loading before the fragmentation test. Average strength of the fiber and maximum interfacial shear strength are obtained by the Weibull scale parameter and the Cox's interfacial stress transfer model, respectively. It is noted that the diffsion phenomenon in polymer materials is generally accelerated by the applied stress, the present results indicate the influence of water diffusion. The fiber strength lowered with the immersion time, at the same time also lowered with the applied stress. It is considered that the dterioration of the fiber strength is due to the exist of the inherent flaw on the fiber surface originally covered with the surface treatment agent. These hydrophilic coupling agent is affected by the diffusive water. Thus, it is considered that these phenomenon make the apparent strength of the fiber. On the other hand, the interfacial shear strength are affected by the immersion time, however, it is independent of the applied stress. The experimental data indicates the affect of water diffusion into the interface through the matrix as the fiber strength. Some factors to govern the deterioration in the interfacial shear strength can be estimated. According to the Cox's model, the deterioration of the interfacial strength is explained by the variation of the matrix elastic properties.

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Static tension fatigue test and pulsating tension fatigue test were carried out using the FW・RP cylindrical test specimen in which fiber orientation angle and wall thickness changed. And, surface temperature until it destroyed the specimen was measured. The effect of fiber orientation angle and wall thickness on fatigue strength was examined from these experimental results. The results showed that there was the effect of fiber orientation angle at the fatigue strength and that there is the relation in specimen life and temperature rise.

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Recently, shape memory polymer as one of functional materials has received much attention and its mechanical properties have been investigated. Shape memory polymer of polyurethane series has the glass transition temperature (Tg) around the room temperature. Based on the large change in modulus of elasticity above and below Tg, the material has excellent shape memory property. In this study, for the wider applications in the fields of industry, medical treatment, welfare and daily life, the glass fiber reinforced shape memory polymer was developed. The specimens with different fiber weight fractions, which are SMP bulk, 10wt%, 20wt%, and 30wt%, were prepared, and their mechanical properties and stress-strain-temperature relations were investigated experimentally. Then, the influence of fiber weight fraction on the shape memory effect was evaluated. It was found that mechanical properties and the shape memory effect of the developed materials heavily depend on both temperature change and the fiber weight fraction

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Transverse-compressive and interlaminar shear tests on a epoxy GFRP laminate, which had plain woven glass fiber, were conducted over a temperature range from R.T. to 200℃. Moreover, fatigue tests under compressive and compressive/shear loading were performed over a wide range from 10^2 to 10^7 cycles at R.T. and 150℃. The transverse-compressive and interlaminar shear strengths decreased with increasing temperature. The interlaminar shear strength was about one tenth of transverse-compressive one. The obtained fatigue S-N curves were approximately linear for all test conditions. The fatigue strengths of compressive and compressive/shear tests were arranged well using maximum shear stress than principal stress.

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It was well known that crystallization on the thermoplastic resin resisted the progress of viscoelastic deformation But there are a few reports for the effect of crystallization on viscoelastic deformation on polymers and also few report on fiber reinforced plastics(FRP). In this report, for CFRP of Polyimide, the effects of not only the fiber volume fraction but also crystallization on bending creep behavior were researched because creep behavior in viscoelasticity is the most important design factor. The time-temperature dependence of creep behavior on some kind of fiber volume fraction and the resistance of crystallization on creep were confirmed.

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Vapor grown carbon fiber (VGCF) is a new kind of carbon fiber, which has outstanding properties such as high mechanical strength and electrical conductivity. We studied injection molding of polystyrene (PS) including VGCF as a filler and compared with the composites molded under the same conditions in which conventional carbon fillers were filled. As a result, the volume resistivity of VGCF/PS composite was 2.1 × 10^3 Ω・cm when the VGCF concentration was 6.7 volume percent. The resistivity was significantly lower than that of the composites which conventional carbon fillers were filled. The volume resistivity of CB/PS composite linearly dropped, whereas that of VGCF/PS composite dropped significantly between 3 and 4 volume percent and after which it linearly dropped. In addition, the resistivity of the composite decreased when the flow velocity during injection process was slow. The mechanical properties of the composites were almost constant in the VGCF concentration range from 0 to 12 volume percent.

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When FBG sensors are applied to detection of transverse cracks in CFRP laminates, there is the possibility that the resin coating of the optical fibers will deteriorate the sensitivity of the sensors. Hence, in this study, the strain transfer from the 0° ply to the core of the optical fiber was calculated by a theory developed from the shear-lag model. As a result, it was found that the variation of axial strain in the core of a polyimide-coated FBG sensor was smaller than that of an uncoated FBG sensor. Nevertheless, the reflection spectra of the coated and uncoated FBG sensors calculated from the strain distributions were almost the same. This result shows that the coating of the optical fiber does not deteriorate the sensitivity of the FBG sensor for the detection of transverse cracks.

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In the fracture process of the s.f.c, the number of AE events is in a good agreement with the number of fiber breakage, and the sources of AE signals are the failure modes at fiber breakages. Using the proposed time-frequency method of wavelet transform (WT) for AE signals processing, the micro failure modes at a fiber breakage and the microfracture mechanism, such as the sequence of each failure mode and their interaction, are made clearer. These give that the both processing methods of AE signals, FFT and WT, are powerful to identify the micro failure modes and elucidate the microfracture mechanisms in composite materials.

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The authors have applied newly developed small-diameter Fiber Bragg Grating(FBG) sensors, whose cladding was 40μm in diameter, for the detection of transverse cracks in Carbon Fiber Reinforced Plastic(CFRP) quasi-isotropic laminates. Loading/unloading test was carried out, and reflection spectra from the FBG sensor were measured at various tensile strain. When transverse cracks occured in the laminate, the shape of reflection spectrum was drastically distorted, and the Full Width at Quarter Maximum(FWQM) increased in proportion to the transeverse crack density in the 90° ply. This change in the form of the spectrum could be confirmed by the theoretical calculation.

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When strain is measured with the center wavelength of an FBG sensor, the accuracy can be decreased by large temperature change. In this research, a device using single FBG sensor was studied to measure both strain and temperature simultaneously. The device named "Laminate Patch" is a laminate of 90° plies of CFRP and an epoxy plate including an FBG sensor. When temperature decreases, the cross section of the optical fiber is deformed because of the thermal residual stress. The deformation causes the birefringence and widens the reflection spectrum. It is expected that, therefore, the spectrum width has specific relation to the temperature change. Experimental results showed that the FWQM changed in proportion to the temperature change and the strain. Therefore, it was revealed that strain and temperature can be calculated from the center wavelength and the FWQM.

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Thin, ring-shape disks are used as the standard specimens in spin tests. To investigate the deformation/failure behaviors of the specimen under centrifugal loading, stress analysis of the rotating disk is necessary. Although there are many analyses about isotropic or cylindrical anisotropic rotating disks, no closed-form solution is found for rotating rings with Cartesian anisotropy. In this paper, an approximate analyzing approach based on Ritz's method is proposed to analyze the deformation characteristics of a cubic anisotropic ring under centrifugal loading. Approximate expressions of displacement components are proposed, which contain 15 unknown coefficients. The potential energy of the disk is calculated. By using variation theory, the unknown coefficients are solved and the disk's deformation behavior becomes known. Analytical results from present approach are compared to FEM's. It is found that the displacement results from both analyses agree very well, with error less than 1%. The major stress component results agree well with each other, too.

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Spacecraft structures in low earth orbit (LEO) encounter a degradation problem caused by atomic oxygen in the space environment. This study presents an experiment of impact degradation on the ground. The experiment was carried out in a vacuum space chamber. Atomic oxygen produced at a plasma torch was accelerated fluid dynamically with Argon working gas. As the target materials several carbon-based materials (graphite, C/C composite and Si-C.C.) were employed. The degradation was analyzed in the aspect of macroscopic mass loss per unit area and the microscopic degradation modes'. The temperature effect is investigated. The comparison among the target materials is developed. The mass loss per unit area depends on the temperature of material surface. The eroded surfaces of materials were observed with SEM. In case of C/C composite, the matrix region erodes more than carbon fiber, however, this effect is more pronounced in normal oxidation at ambient atmosphere. The mass loss of Si-C.C. is less than that of corresponding C/C composite and only the C/C composite region erodes deeply with almost no erosion in Si and SiC regions.

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The reason that the ductile fracture surface bears the fractal characteristics is investigated. The dimple shape covering the ductile surface is assumed to the sinusoidal curve and the dimple size distribution density function is considered to be able to describe by the power of the dimple size. The connection of the exponent of the power law, α, and the fractal dimension of the surface profile, D , is described in the form of D = α/2. The validity of this formula is evaluated with the comparison of the experimentally obtained fractal dimension.

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The fracture modes, i.e., brittle and ductile, are studied comparing the criteria in macroscopic and microscopic aspects. As the macroscopic criterion, the critical stress intensity factor is used. As the microscopic criterion, the idea of fractal is applied to the profile of fracture surface. In the experiment, the three points bending fracture of a cracked specimen of mild steel is employed. The relationship between the measured macroscopic criterion and microscopic criterion is discussed.

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In this study, the effect of loading rate on the strength and the absorbed energy of paper foam board was examined by a series of dynamic and quasi-static compression tests. For comparison, polystyrene foam board was also tested. In dynamic compression tests, a polyvinyl chloride (PVC) tube instead of an ordinary metal bar was used for the measurements of the load applied to the specimens, in order to relieve the impedance mismatch between stress bars and specimens. The absorbed energy up to a strain of 60 % in compression tests of paper foam board is about 1.3 times greater than that of polystyrene foam board. It was also found that the absorbed energy obtained from dynamic tests for paper foam board was about twice comparing with quasi-static results.

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The fracture experiments of C/C composites and Si-C/C are conducted up to the elevated temperature. The each test specimen material is composed in 6 layers with 0°/90°. Two kinds of orientation is used. One is that the fiber direction is perpendicular to the tensile axis and the other is 45°. The fracture modes of each case is discussed focusing the mechanism.

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One of the factors to make an ultra high vacuum apparatus is to reduce the gas permeation through the welded joint. In order to clarify the contribution of surface conditions and the diffusion in specimen, the hydrogen gas permeation through the stainless steel with variation in thickness is investigated. As a result, the significant difference is observed in the tendency of the gas permeation rate in transient process and the value of the permeation rate at the steady state. The results suggest the surface condition have the large effect to the gas permeation rate. The analysis of these results might lead to the clarification of the effect of the diffusion through the bulk material and the surface conditions to the gas permeation phenomena through the welded joint of the stainless steel.

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AZ61 magnesium alloy plate with 4mm thickness was butt welded using a high voltage electron beam welder. Effects of both welding speed and post weld heat treatment on the microstructure and mechanical properties of electron beam welded joints were investigated. The arcing phenomenon tended to appear with welding speed is under 250mm/min. Independent of the welding speed, the remarkably fine crystal grains were observed in the fusion zone, though after post weld heat treatment those were become coarse. The tensile strength of the welded joints showed almost same value as that of the base metal regardless of the welding speed. The elongation of as welded joints was inferior to that of the base metal. But it increased with after post weld heat treatment. The highest elongation could be obtained with T6 heat treated welded joints.

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Dissimilar joint of steel and aluminum alloy was produced by YAG laser welding. Maximum tensile shear strength was about 86 % of tensile strength of aluminum alloy. About 10 μm thickness intermetallic layer was observed at the interface of the joint. Temperature distribution was calculated by BEM (Boundary Element Method) analysis combined with the results of temperature measuring test. According to BEM analysis, maximum temperature at the interface was between melting point of aluminum and steel. Diffusion occurred during laser welding between solid state steel and liquid state aluminum to produce thin intermetallic layer

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AZ31 magnesium alloy plates 6 mm and 8 mm in thickness were butt welded using an AC TIG welding machine. Effects of welding conditions on mechanical properties of welded joints were examined. In case of the double square groove butt welded joint using 6 mm thickness plate, the good bead was obtained with surface current of 120A/over and penetration current of 120A /less. And the highest tensile strength of welded joint showed with surface current of 140A and penetration current of 120A, this value is 92% of the base metal. The.double-V groove butt welded joints of plate thickness of 8 mm with filler wire, it is obtained enough penetration with both surface and penetration current of over 150A. The maximum joint efficiency of welded joint with both surface and penetration current of 150A showed 95% of the base metal.

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Experiments clarify effect of operating parameters on mechanical properties using conventional friction welding machine equipped sliding stage. 5052 and 2017 aluminum alloys rod of 20 mm diameter was used as the coating consumable. The substrate material was used 5052 aluminum alloy plate with a width of 50 mm, length of 150 mm, and thickness of 5 mm. In case of the 5052 alloy rod, the soften area of the coating layer was observed on the near the bonding interface of substrate material side, and the maximum tensile strength showed about 85% of 5052 alloy plate regardless of the friction pressure. In case of the 2017 alloy rod, both tensile strength and elongation of deposited specimen showed higher value to 5052 alloy plate. It is not recognized that the coated material was fallen from substrate material by the tensile test.

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A6061 aluminum alloy was joined using the friction welding process to clarify mechanical properties related with welding parameters. Taguchi method was applied to find the major factors for friction welding. Parameters are selected rotational speed, friction upset distance, friction pressure, upset pressure and upset time for this purpose. Furthermore, it is carried out to evaluate microstructure of friction welded joints and hardness distribution. Following results were obtained; (1) rotational speed and friction upset distance are significant influence on mechanical properties from the analyzed results of Taguchi method. (2) the joint strength reaches to 87% of tensile strength of base metal under the optimum friction welding condition. (3) higher heat input rate is resulted in higher tensile strength.

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5052 aluminum alloy thin plate with 0.6 mm in thickness was friction welded by friction heat between specimen and tool. The rotational tools with 6 mm, 10 mm and 15 mm in diameter were used. Both microstructure and tensile shear strength of friction spot welded joint were investigated. The appearance of friction spot welded joint showed similar to a resistance spot welding. Both nugget and deformation of weld interface were not observed in the friction spot welded joints. The tensile shear load of welded joint using tool of 6 mm increased with increasing of friction pressure independent of rotational speed. In case of using 10 mm tool, effect of rotational speed on the tensile shear load became smaller at friction pressure of 30 MPa, but tensile shear load decreased with increasing of rotational speed at friction pressure 40 MPa. The highest tensile shear load of welded joint using tool of 15 mm was obtained at rotational speed of 10.8 s^<-1>. The tensile tested specimens which showed high tensile shear strength were shown like a plug type rupture.

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Pure copper to pure aluminum were friction welded using a N/C controlled brake type friction welding machine. The intermetallic compound was analyzed with X-ray diffraction system after welded joint breaks compulsory at weld interface. A stratified compound layer was observed at the weld interface. In case of before heat treatment, a θ phase(CuAl_2) was observed on the aluminum side, and both θ phase and γ_2 phase(Cu_9Al_4) were recognized on the cupper side. The hardness of θ phase and γ_2 showed HK536 and HK736, respectively. The thickness of compound layer became thicker with increasing of heating time. The tensile strength of welded joint showed same value to that of the aluminum base metal before heat treatment and decreased with increasing of heating time. The minimum tensile strength of welded joint was obtained at heating temperature of 808K and heating time of 300min and was 25% to that of welded joint before heat treatment. The impact value of welded joint increased with increasing heating time.

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Effect of the corrosion environment on the fatigue strength of AZ31 magnesium alloy/SUS304 stainless steel of friction welded joints, which were welded by a N/C controlled friction welding machine, has been investigated. The fatigue tests were conduced by Ono's rotary bending tester for smoothed specimen. The fatigue strength of welded joint, which was tested in air, was lower than that of the based metal irrespective of the number of cycles to failure, and the fatigue limit was 75% of the base metal. In case of immerse joint in salt water for 8 hours, number of cycle to failure was increasing with decreasing of applied stress, and the fatigue limit obtained 36% to that of the base metal. The fatigue strength of welded joint, which was tested under corrosion environment, decreased almost lineally with the increase of the number of cycles to failure and fatigue limit was not recognized. All the welded joints were fractured near the weld interface under corrosion environment.

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5052 aluminum alloy sheet of 5 mm in thickness was welded by Friction Stir Welding (FSW). Effect of shape of probe on the mechanical properties of joint was investigated. The welding defect was observed on the advancing side independent of the shape of probe, and it was increasing with increased welding speed. Regardless of the shape of probe and welding speed, the soften area was observed on heat affected zone. The width of soften area became narrower with increasing of the welding speed. Both maximum tensile strength and elongation of welded joint was obtained using a Type D tool. The maximum tensile strength of the joint was 94% and elongation was 68% to those of the base metal. The joints which used Type C and D tools were fractured at the boundary of heat affected zone and stirring part of the retreating side, but joints using Type A and B tools were fractured at stirring part.

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For development of the friction welding with smaller change in shapes, the prediction of plastic flow behavior during the friction welding process is required. Plastic flow behavior of aluminium alloy with the temperature distribution was numerically analyzed dynamically. The plastic flow behavior was calculated with the finite element method for the elasto-plastic material. The change of temperature distribution was analyzed with unsteady state heat conduction equation. The analysis was conducted with various welding parameters, including the friction pressure, friction time and the speed of rotation. The results of the numerical analysis were compared with the experimental results obtained by the friction welding with the same parameters.

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Effects of brake timing on the mechanical properties of welded joints of 5052 aluminum alloy, which were made by using a numerical controlled brake type friction welding machine, were investigated. The total loss of welded joint became shorter with decrease of brake timing. The highest tensile strength of welded joint was 240.8 MPa, joint efficiency was 93.2%, at brake timing of 0 second. The tensile strength of welded joints under conditions of brake timing from -0.1 to 0.2 seconds showed almost same value, and they were fractured at the heat affected zone. The highest elongation of welded joint was obtained when braking time 0.2 seconds. The welded joints, exceed the elongation of 14%, were fractured at the soften area. But welded joints, elongation under 5%, were fractured at the weld interface.

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It is difficult to match phases at the particular position of a rotation side and a fixed side using a conventional friction welding machine. Because the rotating spindle does not control the exact stop position. Development of positioning control friction welding meets to be solved difficulties as stop at the specified position during duration of braking. This positioning control friction welding was installed servo motor positioning without hydraulic brake system. Characteristic flash formation is different from ordinary friction welding. Severe metal flow was observed at the vicinity of weld interface in case of positioning control. The sever plastic metal flow was caused in brake stage, and the amount of twist angle was depended on rotation speed and stopping period. Friction and forge pressure effect little on the amount of twist angle.

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The friction stir forming process uses the friction heat generated between a rotating tool and the material being forged. Trials with friction stir forming of various aluminum alloys were carried out on a modified milling machine. The results of friction stir forming 6061, 20l7, 2024, and 7075 alloys were discussed in terms of forgeability.

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The objective of this study is to develop a new method of mechanical fastening using friction stir forming technique. Trials with friction stir cladding were carried out on a modified milling machine. Carbon steel plate with internal thread has been successfully clad with aluminum alloy by friction stir technique.

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AZ31 magnesium alloy plate with 6.4 mm thickness was friction stir welded using a N/C controlled vertical type milling machine. The impact properties of FSW joint was investigated by the instrumented Charpy impact tester and SEM. Regardless of the welding conditions, the impact strength of FSW joint showed higher value than that of the base metal. FSW joint with welding feed of 0.2 mm/s was shown the highest value regardless of the rotational speed. The crack generational energy of FSW joint was higher than that of the base metal. All the impact tested FSW joints showed a ductile fracture on which dimples were found.

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5052 aluminum alloy plate with 5 mm in thickness was friction stir welded using a universal milling machine. Effect of push angle on mechanical properties of FSW joint was investigated. The burr was observed on the retreating side without push angle, but it disappeared with push angle. Both the vertical and feed force in which welding process showed higher value in case of with push angle, but the horizontal force with push angle was smaller than to that of without push angle. The tensile strength of FSW joint with push angle increases with increasing of the push angle. Regardless of the rotational speed and feed, the tensile strength of FSW joint with push angle was obtained about 120% to that of the joint without push angle. The elongation of FSW joint showed a similar tendency of the tensile strength.

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Trials with friction stir welding of SiC whisker reinforced aluminum composites were carried out on a modified milling machine. The results of friction stir welding 6061+16%SiC whisker composites were discussed in terms of weld ability and weld strength.

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Trials with measurement of tool temperature during friction stir welding of 6061-T6 aluminum alloy were carried out on a modified milling machine. It was seen that the temperature of the tool tip achieved a maximum of approximately 800K and the temperature of the shoulder were around 700K.

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This study was carried out to aim development of new system to recycling waste cans of aluminum using friction extrusion to solve social requirement. The principle is characterized that rotating rod is applied axial load onto the scraped aluminum, which is filled in a cartridge with extruding nozzle. As this process is defined as the solid phase technique, frictional heat and pressure generate relative motion to plastized metal without an external heat source such as furnace heat. Scrap material is extruded into wire form through the cartridge nozzle after continuous generation of the plastized metal flow. The result shows rotation speed of rod and frictional pressure give a significant effect on amount of extruding products and material temperature reaches 829K in processing, which is below melting point of aluminum

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An apparatus for the welding of fine particles using a tungsten microprobe was constructed. The welding is carried out as follows. When the voltage is applied to the probe in contact with the particle, the particle is weakly welded on the substrate by the electrical discharge between the particle and the substrate. On the other hand, tough welding is obtained by the elctrical discharge from the probe placed about 20-50μm above the particle. In this paper, the apparatus and the merits or features of the welding procedure are introduced, and the effects of pre-heating for welding are discussed.

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