This paper presents an investigation into the damage monitoring and displacement behavior of carbon fiber reinforced plastic (CFRP) laminates at low velocity impact tests. Instrumented drop weight impact tests are conducted for CFRP laminates. Optical fiber sensor is able to detect elastic wave from 0.1Hz to several MHz. For damage monitoring and displacement behavior sensing, the optical fiber sensor was bonded on the CFRP. Optical fiber sensor is able to detect damage and displacement behavior at the same time. Moreover, it was found that optical fiber sensor signal correspond to the impact damage detected by NDI test (C-Scan) and cross-section observation.
We have constructed an optical setup which can measure strain at a sampling rate up to an order of megahertz. The system consists of broadband light source, fiber Bragg grating (FBG) sensor, dielectric multilayered optical filter and photodetector. The Bragg wavelength of FBG varies with strain applied to the FBG. The Bragg wavelength is converted to light intensity with an optical filter. Intensity of light transmitted through and reflected from the optical filter was measured using photodetectors. Strain can be evaluated from the ratio of the difference to the sum of the two photodetector outputs. Strain of a thin stainless-steel cantilever beam during free vibration was measured with an FBG sensor and a resistive strain gauge. Experimental results demonstrate that the FBG-based optical system is capable of strain measurement with a higher S/N ratio compared to conventional strain gauges.
The validity of usage of a cruciform specimen as an experimental evaluation method of composite interfacial strength is discussed. To avoid the stress singularity at the free edge, the cruciform specimen method has been proposed to evaluate the interfacial tensile strength. In the present study, the validity of the method is discussed both experimentally and analytically. Moreover, to discuss the relation between the normal and shear stresses when debonding occurs, a specimen in which the angle between the fiber and loading directions is different from the original cruciform specimen method is considered. In experiments, a model composite system, SUS 304 wire/epoxy, is used to make debonding detection easy. In analytical approach, finite element method (FEM) is used to analyze stress distribution in the cruciform specimens and to design the cruciform specimen shape.
In multiaxial stitched CFRP laminates, it is thought that the existences of knitting fibers in between layers and gaps between carbon fiber bundles etc., which are configurations different from conventional unidirectional and woven laminates, significantly affect the interlayer fracture properties. Besides, objective large-scale structures are affected by environment such as variable temperature and humid, thus the interlayer fracture properties might become more complicated. In this study, Mode I and Mode II interlaminar fracture toughness and the crack growth property under fatigue, thermal and water environments of multiaxial stitched CFRP laminates for innovative marine composites were investigated.
The prediction of long-term fatigue life of innovative CFRP laminates for marine use under temperature and water environments were performed by our developed accelerated testing methodology based on the timetemperature superposition principle(TTSP).
Three kinds of CFRP laminates employed were conventional plain fabric T 300 carbon fibers/vinylester, flat yarn plain fabric T 700 carbon fibers/vinylester and multi-axial knitted T 700 carbon fibers/vinylester for marine use. These CFRP laminates were prepared under three water absorption conditions of Dry, Wet and Wet+Dry after molding. The three-point bending constant strain rate(CSR)tests for three kinds of CFRP laminates at three conditions of water absorption were carried out at various temperatures and strain rates. Furthermore, the three-point bending fatigue tests for these specimens were carried out at various temperatures and frequencies.
The flexural CSR and fatigue strengths of these CFRP laminates strongly depend on water absorption as well as time and temperature. The mater curves of fatigue strength as well as CSR strength for these CFRP laminates at these conditions are constructed by using the test data based on TTSP. It is possible to predict the long term fatigue life for these CFRP laminates under an arbitrary temperature and water absorption conditions by using the master curves.
It is important to reveal distribution of properties within VARTM products in order to achieve accurate production. In this study, fiber volume fraction and mechanical property of VARTM products were evaluated. Consequently, fiber volume fraction and bending strength showed lower value near resin inlet region, and apparent distribution of such properties were shown. To modify distribution of properties within VARTM products, the effects of permeability and resin viscosity were evaluated. Permeability was changed by rotating of fabric alignment, and fiber volume fraction was increased. However resin viscosity was reduced by adding styrene monomer to vinylester resin, and fiber volume fraction was modified, mechanical properties were reduced.
This paper addresses experimental evaluation for the following three cases to realize practical material recycling of special plastics. First, the influence of different plastic contamination for matrix plastics was examined. As a result, when polypropylene (PP) more than 1%got mixed with flame-retardant-polystyrene (FRPS), elongation and IZOD strength of FRPS decreased markedly, and importance of exclusion of PP was elucidated. Second, the case of different additives in the same plastics was examined. Then, it was found that the mechanical properties of material recycling plastics was not almost changed. However, we pointed out that the establishment of sorting and collection system of the plastics for used additive becomes important. Third, the case of contamination of painting pieces was examined. As a result, it was suggested that practical use became restricted because of the defects on the molding surface.
Carbon fiber reinforced silicon oxycarbide ceramic matrix composite was prepared. Ceramic matrix was derived from phenylsilsesquioxane organic inorganic hybrid pyrolyzed at 1000-1700℃.The difference in fracture behavior between single fiber composite and fiber bundle composite, optimum heat treatment temperature and the interface of fiber/matrix were investigated. The reaction between fiber/matrix occurred by heat treatment above 1300℃, which was confirmed by the damaged fiber in single fiber composite. On the other hand, the fiber efficiency in fiber bundle composites treated at 1500℃ showed the maximum value. This suggests that the modified layer on carbon fiber, which was formed by the reaction of fiber/matrix, affect the fracture behavior, resulting in the lower interfacial shear strength between matrix and modified layer.
Montmorillonites (Mt's) modified by boronic acid derivatives were filled in poly (vinyl alcohol)(PVA), and the microstructure and mechanical properties of PVA/Mt nanocomposites were investigated. Two types of boronic acid were used : 4-aminophenylboronic acid (4AP) and 4-aminomethylphenylboronic acid (4AMP). It was confirmed by the X-ray diffraction that the interlayer spacing of the Mt modified by 4AP (4APMt) was extended to 16.04Åwhile the spacing of unmodified Mt was 12.26Å. By 4phr filling the 4APMt, the tensile modulus (2.7GPa) and tensile
strength (67MPa) of PVA have increased to 3.6GPa and 97MPa, respectively. The 4APMt-filled PVA has also exhibited the increase of storage moduli over the wide range of temperature, the enhancement of glass transition temperature, and the lower tanδ value at peak temperature. And the 4APMt-filled PVA has also showed remarkably lower water absorption property compared with PVA matrix and 4AMPMt-filled PVA. These properties are considered due to the uniform dispersion of 4APMt's in the PVA matrix and the exfoliated and/or intercalated microstructures of 4APMt's confirmed by the transmission electron microscopy. These results suggest the strong bond (monodiol complex) formation between the 4APMt and PVA matrix.