Fiber-reinforced polymer matrix composites are fractured by accumulation of microscopic damage in fiber length scale. Therefore, accurate prediction of microscopic crack initiation is extremely important to predict failure of composite structures. In this study, multiscale modeling approach that consists of a macroscopic scale analysis and a microscopic scale analysis is proposed, and is applied to tensile testing of unidirectional off-axis specimens of carbon fiber reinforced plastic (CFRP) to predict their failure strain. On a macroscopic analysis, off-axis specimen is modeled as a homogeneous body, and 3D finite element analyses (FEA) are performed using an anisotropic elastoplastic constitutive law to obtain accurate deformation field under off-axis loading. On a microscopic scale, 3D periodic unit cell (PUC) analyses are conducted by applying strain history obtained from macroscopic FEA to predict initial cracking strain. Two failure criteria are employed for matrix resin in PUC analysis. The first is the dilatational energy density criterion for brittle failure, and the second is the ductile damage growth law for ductile failure. In order to validate the accuracy of proposed multiscale approach, predicted results are compared with the experimental results.

抄録全体を表示

This paper describes a simulation method for predicting tensile strength of unidirectional fiber-reinforced epoxy matrix composites using a spring element model (SEM).The strengths predicted with SEM are compared with experimentally-obtained data to demonstrate the potential of the SEM. It is found that by utilizing the bimodal Weibull distribution for estimation of fiber strength distribution, the strengths predicted with the SEM are in a reasonable agreement with those acquired by resin-impregnated strand tensile tests. We then also showed that the improvement in the fiber strength distribution in the short gauge length is needed as well as the strength distribution in long gauge length to enhance the tensile strength of the composites.

抄録全体を表示

The positive use of carbon fiber reinforced plastics (CFRP) contributes to the low carbon society because the weight saving of their structures achieves the fuel-saving. Recently, the plain woven CFRP laminates are used for structure of ship and automobile. In the laminating process of the plain woven CFRP laminates, the relative gap of the crimp position between the periodical fiber undulations occurs. However, the relationship between this gap and the mechanical properties has not been clarified enough. In this study, therefore, the effect of the relative gap of the crimp position between the periodical fiber undulation on tensile strength and microscopic damages of plain woven CFRP laminates was investigated experimentally and numerically. As the result, the tensile strength of CFRP laminates with staggered sequence of the crimp gap was lower than that with symmetry sequence. These tensile strengths were also related with mode I type transverse crack density occurring.

抄録全体を表示

Generally, the repair effectiveness of damages, such as delamination and transverse cracks, in fiber reinforced plastics has been evaluated based on the mechanical properties of specimens which include the repaired region. However, to discuss its effectiveness in detail, we should extract the repaired region from laminates. In this study, we tried to evaluate the effectiveness of repair using thermal fusion bonding (TFB) on the delamination generated by out-of-plane impact in carbon fiber reinforced polyamide 6 cross-ply laminate. Interlaminar shear test using double-notched specimen was also carried out to evaluate interlaminar shear strength at the region of repaired delamination, directly. As a result, the mechanical properties of region of repaired delamination was not recovered completely, while the delamination was closed geometrically by TFB in certain condition and the reflected wave from the crack in ultrasonic inspection was disappeared. In addition, it was possible to evaluate the shear strength in the region of repaired delamination by using interlaminar shear test using double-notched specimen.

抄録全体を表示

In this work, we describe the development of carbon fiber reinforced plastics (CFRP) using a polyaniline (PANI) -based electrically conductive thermoset matrix to enhance its electrical properties. The conductive thermosetting resin uses dodecylbenzenesulfonic acid (DBSA) and p-toluenesulfonic acid (PTSA) as dopants and divinylvenzene (DVB) as the crosslinking polymer. The thermal and electrical properties of the PANI-based thermosetting resin are characterized as part of the work. The developed resin is utilized to fabricate CFRP by a prepreg-based hot press method. This paper reports on the electrical properties of the fabricated CFRPs, which exhibit excellent electrical conductivity in the thickness direction. Finally, the electromagnetic shielding properties of the developed CFRP are demonstrated and compared to traditional CFRP.

抄録全体を表示

This paper simulates dispersion behavior of several types of graphene in epoxy resin. In general, mechanical properties of graphene composites are improved in range of low fraction of the graphene content ; however, the mechanical properties with high fraction of the graphene content decrease due to aggregation of the nano-filler. It is an important issue how the graphene disperses in polymer matrix. The present study numerically simulates the dispersion of graphene, graphene oxide and aminated graphene in the epoxy resin by means of molecular dynamics (MD). Before that, molecular orbital (MO) method is employed to estimate the electrostatic potential of graphene and aminated graphene in order to give some information how the graphene themselves aggregate. MO results in that aminated graphene is expected to disperse by electrostatic repulsion between the functional groups. A dissipative particle dynamics (DPD) is then employed to demonstrate how each graphene disperse. For the result, aminated graphene disperses in epoxy resin, because the graphene-graphene interaction is much less significant. This study calculates a relationship between goodness of dispersion and amine-functionalize ratio.

抄録全体を表示

The biocompatible materials composed of hydroxyapatite (HAp) particles and poly-lactic acid (PLA) are one of the most promising candidates as scaffold materials for bone regeneration, owing to the bone-conductivity of HAp and the biodegradability of PLA. However, the poor fracture properties, mainly caused by the weak interface, are one of the factors limiting their practical application. In this study, we tried the “hybrid” interface control in HAp/ PLA composite materials using both pectin and chitosan as the surface treatment polymers in consideration with the biological affinity. Here, photo-dissociable protective groups, which can be eliminated from the protection site by the irradiation of ultraviolet rays, were applied into carboxyl groups of pectin, in order to avoid the direct chemical reaction between pectin and chitosan. In order to evaluate the effect of the hybrid interface control on fracture properties of HAp/PLA composite materials, tensile tests for un-modified and hybrid-interface-controlled HAp/PLA composite materials were carried out, followed by the observation of fracture morphologies and surfaces. Finally, the effect of the hybrid interface control on the fracture behavior of HAp/PLA composite materials was discussed from the viewpoint of the interfacial mesoscopic structures.

抄録全体を表示

Carbon fiber reinforced plastic (CFRP) is widely used for many structures because of its high strength and rigidity characteristics. However, impact damage such as in-flight lightning strike decreases the strength of the material. In the case of metallic materials, there is only a low possibility of serious damage resulting from lightning strike, but impact damage accumulation may occur in CFRP, and damage minimization measures are important. We have investigated possibility to measure the impact force during lightning by using optical fiber sensor. As the results, a gap voltage of several hundred volts results in lightning damage, and a crater forms along the current flow direction. We found that the lightning trace depended on the direction of the carbon fibers and not on the direction of current flow. The optical fiber sensor was able to measure the pressure from the lightning strike when the applied voltage was several hundred volts.

抄録全体を表示