In the present study, CFRTP using thermoplastic polyimide resin as matrix was molded through a variety of molding processes to clarify the relationship between molding conditions and resin impregnation to a fiber bundle and an effect of resin impregnation behavior on the mechanical properties. The specimens were prepared using micro-braiding, film stacking and powder methods to evaluate impregnation behavior. From a cross-sectional observation and the rate of impregnation, excessive high pressure reduced impregnation and low molding pressure was enough to complete resin impregnation into the fiber bundle. In the case of the low molding pressure load, the shape of voids is changed according to molding temperature.

Purpose of this study is to investigate fracture mechanisms and influence on mechanical properties of shoulder part of composite pressure vessels subjected to impact load experimentally and analytically. CFRP laminates simulated as shoulder part of composite pressure vessels were made through FW method and subjected to out-of-plane impact load. Static tensile and tensile fatigue tests were conducted on the impacted specimens. Impact damage was inspected with cross-sectioning and X-ray photograph. Finite element analysis that simulates the experimental impact test was also conducted. The experimental result showed that the impact load induced matrix crack, delamination, and splitting. Tensile strength and tensile fatigue characteristic were degraded by impact loading application. From the result of finite element analysis, dominant stress component for initiation of damage on back-face of laminate was suggested.

Adhesive jointed CFRP will contributes to further light weight of aircraft. But weak bonds including kissing bonds prevent adhesive joint from being introduced in a primary structural member for aircraft because weak bonds is difficult to detect using conventional ultrasonic detection. Although a number of nondestructive technique (NDT) were studied to detect weak-bonds, more simple NDT is required in industry. In this study, we use acoustic emission (AE) method for CFRP single-lap jointed specimen to investigate influence of weak bonds on elastic waves under a low stress. Elastic waves revealed the weak bond distributed stress concentration sites in the inner adhesive region. And bonded zone fractured suddenly after wide-area generation of waves.

Stress rupture and fatigue properties of carbon fibers are not well-evaluated, since matrix fracture is dominant to those properties of carbon fiber reinforced plastics (CFRP). The reason is stress concentration around the gripping portion of specimen. In this study, we focused on the adhesion of tab on unidirectional CFRP in order to examine test methodology. Effect of hardener for epoxy resin on the tab adhesive was investigated through measurement of acoustic emission (AE) which generated during static tensile test of unidirectional CFRP. In order to measurethe AE from tab bonding region, AE from central portion of specimen is removed by using AE sensor in midportion of specimen as guard sensor. Polymercaptan, modified polyamine, polythiol and N-(3-dimethylaminopropyl)-1,3-propylenediamine were used as hardener. Tensile strengths and elastic modulus were compared with different hardeners. Comparison of generation time and analysis of frequency of AE which generated in tab region were conducted to investigate adhesion. As a result, effect of hardener on mechanical properties and adhesion in static tensile test was little.

The purpose of this study is to manufacture carbon fiber reinforced thermoplastic composites for aerospace and automotive applications. In order to accomplish this purpose, we produced carbon fiber pre-impregnated resin filament for FDM 3D printer. Moreover, we developed an FDM 3D printer that incorporates a mechanism to amputate continuous carbon fibers. We conducted a tensile test and bending test of an acrylonitrile butadiene styrene (ABS) specimen and a carbon fiber reinforced thermoplastic (CFRTP) specimen to evaluate dynamic characteristics of CFRTP shaped by FDM 3D printer. As a result, the tensile strength and modulus of longitudinal elasticity of the CFRTP specimen were found to be 4 and 4.8 times higher than those of the ABS specimen, respectively. The bending strength and bending modulus of longitudinal elasticity of the CFRTP specimen were found to be 2.9 and 5.1 times higher than those of the ABS specimen, respectively. We conducted cross-sectional observation of CFRTP specimen wherein resin-rich and resin non-impregnated spheres were observed. However, these values were lower than the theoretical values calculated from the law of mixtures. By examining the evidence, lower dynamic characteristics were concluded to result from the presence of the aforementioned spheres.

In order to suppress damage in bolted joints of CFRP (Carbon Fiber Reinforced Plastics), it is considered to insert titanium foils between CFRP plies. However, interfacial delamination between CFRP and titanium foil occurs easily. In this study, effect of different surface treatments for titanium foils on bearing damage behavior in CFRP/titanium foil composite laminate joints is investigated. Hydrogen peroxide solution and NMT (Nano Molding Technology) are adopted for surface treatments of titanium foils. NMT forms microasperity on surface of titanium foils. Bearing tests are carried out on the CFRP/Titanium foil laminates using their bolted joints. During static tests, load-displacement responses are recorded in order to examine the damage behavior of jointed specimens. Specimens are observed by means of microscope after crosshead displacement reached 7mm to assess internal damage. Cross-sectional images show that interfacial delamination between CFRP and titanium foil is more difficult to occur by adopting NMT as surface treatments compared to hydrogen peroxide solution. It is concluded that titanium foils with surface treatment by NMT are more effective to suppress bearing damage than by hydrogen peroxide solution.

During VaRTM (Vacuum assisted Resin Transfer Molding) a distribution medium which is incorporated on fiber preform as a surface layer is used to shorten impregnation time of resin by increasing the flow rate of resin and is removed after molding. In this study, the distribution medium is replaced by a thermoplastic polyamide mesh, and the mesh is still remained in the fiber preform after VaRTM process. The mesh is expected to improve not only the resin flow but also interlaminar toughness in the composite laminates after molding. Multipoint measurements for resin flow during VaRTM process are carried out by using embedded fiber optic sensors. It is confirmed that the polyamide mesh inserted in the fiber preform increased the flow rate during the impregnation of resin. ENF tests using with specimens which have bonded doubler plates to both top and bottom surfaces are carried out. The crack length can be predicted by a simple beam theory. ENF tests have been found that GIIC are improved by inserting the polyamide mesh. From these results it is shown that improvements in both resin flow and interlaminar toughness can be achieved by the single action of inserting the polyamide mesh.

We estimate effects of ply thickness on mechanical properties and damage evolution of CFRP angle-ply laminates under various tensile loading. It should be noted that the laminate thickness is almost the same, but the ply thickness are quite different. Monotonic tensile tests, cyclic loading-unloading tensile tests and stress relaxation tensile tests are performed on [(±θ)₁₂]_s (t-0.05 prepreg×48plies, t-0.05 ply thickness), [(±θ)₄]_s (t-0.15prepreg×16plies, t-0.15 ply thickness) and [(+θ)₄/(-θ)₄]_s （t-0.15prepreg ×16plies, t-0.6 ply thickness）T700SC/2500 carbon/epoxy laminates with various fiber directions (θ=30, 40, 45, 50 and 67.5°) at 1.0 mm/min crosshead speed. Laminates with thin ply thickness showed high strength and fracture strain. From SEM observation, t-0.6 laminates exhibit brittle fracture, however delamination occurred in each interlaminar interface in thin ply thickness (t-0.05, t-0.15) laminates. In stress relaxation tests, laminates exhibit nonlinear response and then stress relaxation behavior appears. In addition, it is considered that each angle-ply laminate have rate dependence in comparison with monotonic tensile test results at 0.1mm/min crosshead speed. Also damage evolution can be determined by cyclic loading-unloading tensile tests. We use mesoscale damage model to investigate damage evolution in CFRP laminates. From damage observation and damage evolution analysis, it is considered that thin ply thickness laminate can accumulate damage in specimen until high stress state.

Effects of nucleating agent on the crystal nucleation of poly lactic acid (PLA) were investigated by adding two kinds of nucleating agent into PLA. The induction period and crystallization rate of PLA were investigated by optical polarizing microscope observation on a hot stage. The crystallization temperature, melting temperature and crystallization time were investigated on non-isothermal process and isothermal process via DSC, respectively. The induction period, crystallization temperature and crystallization time depended on combination of nucleating agent. Furthermore, it was found that these properties also depended on the concentration of nucleating agent. The crystallization rate and melting temperature of PLA were not affected by nucleating agent.

In this study we aim to estimate damage in materials which is used in antenna's radial ribs of new radio astronomy satellite. The materials are carbon fiber reinforced plastics (CFRP) because of their high-specific strength. In space environment, cyclic temperature change is loaded on a structure due to sunshine and eclipse. As a result, severe thermal stress occurs and causes damages in CFRP. The purpose of this study is to evaluate thermal fatigue effects on microscopic damage progress in CFRP. We also conducted finite element analyses to discuss the mechanism of damage behavior.

Application of CFRP is spreading from aircrafts to automobiles. The energy reduction in the manufacturing process of CFRP is strongly requested with the increase of CFRP production volume. So, the Vacuum Assisted Resin Transfer Molding (VaRTM) is becoming the mainstream from Autoclave Molding as the manufacturing method of CFRP. However, even in VaRTM, the interfacial strength between carbon fiber and resin must be improved. It is difficult to control the resin flow to fill all the space in CFRP, therefore, the void is remained slightly on the interfacial surface. Recently, the design of CFRP with optimal arrangement of carbon fiber distribution is progressing including curved line as well as straight. It is possible to weave carbon fiber in any shape, however, using VaRTM, the flow of the resin is deteriorated and CFRP becomes inhomogeneous. In this study, the manufacturing method of CFRP by using electrodeposition was developed. CFRP was manufactured with immersing the woven carbon sheet in the epoxy electrodeposition solution. Electrodeposition conditions were investigated and the tension test was conducted on the CFRP.

The energy absorption mechanism on progressive crushing of injection molded fiber reinforced thermoplastics (FRTP) have been investigated with triggered coupon specimens. These materials consist of glass fiber and polyamide 6,6. Progressive crushing tests were carried out at -30, 23 and 90°C. The energy absorption performances on progressive crushing were constant independently of the temperature nevertheless the impact compressive strength decreased as the temperature rises. In the observation of fracture surface, matrix was stretched in the direction of shear. Furthermore, in the observation of fracture morphology using high speed camera, plural crack were formed during crushing. According to the above results, it was suggested that mode I/II fracture toughness affect the energy absorption performance.

The effects of environment temperature on initiation and propagation of transverse crack in cross-ply carbon fiber reinforced thermoplastic (CFRTP) laminates have been investigated. Static tensile tests for the cross-ply laminates and the 90° unidirectional laminates were carried out at room temperature and high temperature (366K). The transverse cracks were observed by soft X-ray photography. In consequence, the tensile strength and the failure strain in the cross-ply laminates and the 90° unidirectional laminates at 366K decreased compared to the values at room temperature. It was also found that the behavior of initiation and propagation of the transverse cracks in the cross-ply laminates was changed due to the environment temperature. Fiber-matrix interfacial fracture on the fracture surface of the 90° unidirectional laminates was observed in some areas at high temperature whereas matrix fracture was observed at room temperature. Therefore, it was suggested that the interface strength between polymer and fiber was decreased at high temperature.

Among engineering polymers, polycarbonate (PC) has been widely used as structural components in various industries. This study investigated the molecular structural mechanism during tensile deformation behavior by using molecular dynamics (MD) simulation. In this simulation, coarse grain method was employed to reduce the number of atom and molecule. This study creates relatively large model with 16 nm cubic size, including polymerization degree of 100 and the number of molecular chains of 200. During uni-axial tensile deformation, the material undergoes elastic deformation, and then plastic deformation. The deformation mechanism at molecular structural level was investigated, especially changes of the bond length, bond angle and torsion angle of molecular chains are quantitatively examined. It is found that their potential energy significantly changes with respected to the applied tensile strain. Based on the variation of potential energy, we will discuss mechanism of yield onset and plastic deformation.

High speed turbo machineries experience severe vibrations such as resonance or self-excited whirl of bearings. Utilizing O-rings as supporters of bearing is promising way to suppress these oscillations. But the prediction of dynamic properties of the O-rings is hard because of its non-linearity. In this paper, we measured the shear viscoelasticity of O-ring material for high frequency up to 1 [kHz]. The properties for each frequency were modeled as 3-element model and the FEM dynamic analysis was conducted. As a result, we could calculate the dynamic properties of O-rings without actual measurement.

Physical aging, and its long-term effect upon stiffness, strength and creep compliance, is an important phenomenon that needs to be well understood and modelled for the safe use of polymers and polymer matrix composites when applied in engineering structures. It is well known that many material properties, such as density, elastic modulus, yield stress, indentation hardness and elongation, are affected by physical aging. Many research efforts on accelerated physical aging of polymeric materials have been carried out experimentally. However, analytical information about the examination of physical aging by molecular dynamics simulation is very limited. In this study, we focused on the movement of polymer chains into a slow and gradual approach to equilibrium. The stabilization of polymers by using Molecular Dynamics Simulation was analyzed.

To reduce axial forging load in upsetting process, application of torsion die motion was proposed. In the proposed upsetting process, one-way torsional moment was simultaneously superposed with axial forging load during upsetting process. In this study, a cylindrical workpiece was twisted around the z-axis with a maximum rate of 0.05 rad/s (0.5 rpm) and a maximum angle of 1.5π rad (270°) during upsetting with an axial compression speed of 0.1 mm/s. It was found that the axial forging load of the workpiece was reduced by approximately 5-40% in the forging conditions where torsion angle/axial stroke and angle were larger than approximately 0.26 rad/mm and π/180 rad (1°), respectively.

Recently, earthquakes frequently occur in Japan. It is desired to promote seismic isolation technology of building. It has been found that composite material filled with low rigidity material to high rigidity material has energy absorbing capacity. However, it must have higher energy absorption capacity in order to respond to a large scale earthquake. Therefore, a new energy absorbing device with cells was proposed. Two-layer circular tubes were used as the cells in order to equip energy absorbing capacity themselves. It is known from previous studies that has been found to be a Hysteresis occurs and it absorb the energy by friction that is generated between the outer layer and the inner layer. It is effective when inside shape of inner layer is floral pattern. In this study, we examined forming method of two layer circular tube and investigated effect of punch speed on formability of two-layer circular tube. In addition, the inner shape of the inner circular tube is also considered the case of floral pattern. As a result, fast punch speed is better formability than slow one. In addition, floral pattern is better formability and functionality than round.

Aims of the study are to evaluate valuation of stress quantitatively due to difference of die shape patterns and to configure evaluation criteria for reducing trouble by analyzing formability at the time of processing product. In forward extrusion at same reduction rate of area, we analyzed stress condition due to each different angle and considered effect of taper angle when material is flowed in. As a result, there were two deformation patterns which are material flow and shear deformation. It was revealed that a boundary taper angles which switch material flow to shear deformation between 45° and 60°.

To improve forming accuracy in press working, a new structure die-set with a link mechanism has been developed. The reduction rate by the link mechanism was set to 1/6. Annealed A1050 pure aluminum wires with a diameter of 1.0 mm was employed for workpiece. The wires were upset with flat dies. Dispersions of bottom dead point and thickness of formed workpieces were compared with by using die-sets with and without link mechanism. The dispersion of strokes of a servo press was about 10 μm, however, that of upper plate of the developed die-set was about 30 μm due to allowance. That of middle plate was about 6 μm and the dispersion was reduced. Difference between the objective thickness and thickness of formed wire without link mechanism was about 11μm, however, that with link mechanism was about 1 μm and the forming accuracy was improved. Dispersions of the thickness of formed wire with link mechanism became half of that without link mechanism.