This paper reviews the numerical simulation of initial damage in a transverse ply of CFRP laminates. Especially, we recently studied the effect of fiber arrangement on transverse tensile failure in unidirectional CFRP with a strong fiber-matrix interface using a unit-cell model that includes a continuum damage mechanics model. The simulated results indicated that tensile strength is lower when neighboring fibers are arrayed parallel to the loading direction than with other fiber arrangements. A shear band occurs between neighboring fibers, and the damage in the matrix propagates around the shear band when the interfacial normal stress (INS) is sufficiently high. This work is briefly introduced with the other literatures.

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The advanced accelerated testing methodology(ATM-2)for the long-term life prediction of CFRP laminates exposed to an actual loading having general stress and temperature history is proposed based on the accelerated testing methodology(ATM-1)established for the long-term life prediction of CFRP laminates exposed to a fixed stress history such as static, creep or fatigue loadings at a constant temperature. The most important condition for ATM-1 is the fact that the same time-temperature superposition principle to be held for the viscoelastic behavior of matrix resin holds for the static, creep and fatigue strengths of CFRP laminates. Furthermore, three conditions as the basis of ATM-2 are introduced with the scientific bases. The long-term fatigue strength of CFRP laminates under an actual loading is formulated based on the three conditions. The viscoelastic coefficients of matrix resin, which perform an important role for the time and temperature dependence of long-term life of CFRP laminates, are also formulated based on the time-temperature superposition principle. The applicability of ATM-2 is demonstrated by predicting the long-term fatigue strengths of typical four directions of unidirectional CFRP laminates.

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Foam core sandwich panel structures are an excellent structural concept to realize full potential capabilities of composite materials owing to its high strength to weight and stiffness to weight ratio together with suitable formability for integral structures. However, degradation of strength due to the interfacial crack initiated from the damaged area is one of serious problems of this concept. Authors proposed the interfacial crack suppression method named the crack arrester. This concept is to install materials with higher stiffness on the crack propagation path and induce the redistribution of load between foam core area near the crack tip and the leading edge of the crack arrester in order to decrease energy release rate at the crack tip less than the interfacial fracture toughness. Crack suppression effect of the crack arrester were analytically estimated and experimentally validated under mixed mode of mode I and mode II, and mode III loading conditions. As for the analyses, it was confirmed that the energy release rates at crack tip decreased as crack tip approached the leading edge of the arrester under constant loadings. In the experimental validation, fracture toughness tests were conducted and apparent fracture toughness increased as crack tip approached the leading edge of the arrester. Based on the acquired apparent fracture toughness derived from test data, a crack onset estimation method was proposed and a crack onset diagram was prepared in order to apply this concept to structural design.

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Effects of the fiber/matrix interfacial properties on the tensile strength of unidirectional Tyranno ZMI fiber reinforced epoxy matrix composites are investigated experimentally. The interfacial properties are evaluated by using the fragmentation test and the single fiber tension test. Tensile tests on the unidirectional composites are also performed to clarify the relation between the interfacial properties and the composite strength. Both fibers with and without sizing treatment are used to discuss the effect of difference in the interfacial properties. Preliminary results of the Monte Carlo simulation prediction of the composite strength are shown for further discussion of the effect of the interfacial properties on the composite strength.

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In this paper, a composite material based on epoxy matrix reinforced with glass-fibre non-crimp fabric was evaluated. The multi-axial E-glass reinforcement textile has a mass per unit area of 972±5 % g/m2 and a [0°,+45°, 90°, .45°] stacking sequence. The layers are stitched together with a polyester (PES) multifil binding yarn. Epoxy system chosen was constituted of resin D.E.R331 from Dow Company, which is a liquid resin of low viscosity and high content of epoxy groups. Samples were cut from several laminas having each of the four plies of unidirectional fibers' orientations (0°, ±45°, 90°) parallel to sample length in order to test the effect of the polyester knit yarn on the damage initiation and propagation. To evaluate the mechanical properties of NCF, the three S-S diagrams at different textiles' orientations (0°, 45°and 90°) were compared. Samples at 0°exhibited better mechanical properties, on the other hand, 90°shown higher deformation. Higher Young's modulus and bending strength was shown for 0°composites while results for 45°and 90°were not very dissimilar. For all samples, discontinuities on the curves appeared when a significant crack emerged. Materials at 90°were observed to have more serrations on its curve due to the higher crack density due to the reinforced textile geometry.To evaluate the crack initiation and propagation, Acoustic Emission (AE) Technique was applied during bending tests. Cumulative AE Energy was increased at the decrease point in load on each material. With Projected Wavelet Transform Analysis, the major frequencies of all AE waves were calculated. As the result of frequency analysis, the discriminative frequency was determined with the observation by the optical microscope. Considering with the all of the data suggested that the stress concentration by the outer layer and the PES stitch caused the crack initiation and propagation.

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Mirrors of satellite are one of the heaviest parts in the satellite. The maximum weight of the satellite is determined by the launch capacity of the rocket. Of course, the weight of the main mirror is limited but larger mirror enable higher resolution observation. A specific stiffness of the mirror material is hence a key factor. Since carbon fiber reinforced polymeric composite material(CFRP)is superior to not only the specific stiffness also in.plane thermal stability, it may be suitable to use as mirror. Before applying CFRP to the mirror, several problems should be solved ; one of them is long.term reliability of mirror surface accuracy. It is reported that there exist a “print. through” problem for CFRP mirror surface. To address this problem, a lot of works regarding surface coating treatment have been done for the mean time. However, the long.term assurance of the surface roughness has not been discussed nevertheless the mechanical property of CFRP is inherently time.dependent. There is a possibility that the time.dependent deformation of the material deteriorates the mirror surface accuracy. The deformation induced by physical ageing, dewater and internal stress relaxation of the matrix may change the surface accuracy. A deformation induced by temperature change is another problem. In this paper, time and temperature dependence of the surface accuracy is studied for CFRP sandwich mirror. The effect of different surface treatment on the surface accuracy is also investigated.

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Even though carbon fiber reinforced plastic (CFRP) has remarkable mechanical properties, invisible or barely visible damage significantly degrades the strength of CFRP, restricting design space of CFRP aircraft structures. In this context, several structural health monitoring (SHM) technologies have been developed. If detected damage can be repaired by using rapid cure CFRP patch immediately after its occurrence, CFRP structures can be designed to tolerate larger damage, and thus more lightweight and adaptable aircraft structures may be realized. However, damage size, position, and type estimated by SHM systems are not absolutely accurate. Hence, this study experimentally and numerically investigated effects of the uncertainty about detected-damage information on the strength of repaired parts. Simulated impact or lightning damage was introduced in strip specimens, and tensile tests were conducted using them after repairing. It was shown that the strength requirement of the repaired part can be fulfilled by deciding the size of the CFRP repair patch in consideration of the uncertainty about the damage information. Furthermore, required capability of an impact damage detection system combined with the rapid repair method was identified.

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Mechanical properties and dimensional accuracy of FRP parts depend on molding process. In this study, a simulation method considering molding process to predict those of FRP parts has been developed. In this paper, new parameters of the simulation method to predict the stiffness and the strength of a co-cured honeycomb sandwich structure were proposed. The new parameters were acquired experimentally by evaluating the proportions of the strength and stiffness of a CFRP faceskin/aluminum honeycomb sandwich panels molded by co-cure to those of them molded by pre-cure. In addition, the relationships between the dimple depths of the CFRP faceskins and the strength of the aluminum honeycomb sandwich panels were investigated experimentally to prepare the parameters more efficiently.

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Tensile loading simulation of a nano-sized pillar-shaped polycrystalline thin film which has a preferred orientation in a specific direction was conducted, and effect of grain size on deformation behavior was examined by the molecular dynamics analysis. The model which was constructed by 2-dimensional Voronoi tessellation consisting of a columnar aggregate of cubic crystals with fiber texture whose axis was ＜110＞,＜100＞ and ＜111＞ direction perpendicular to the film surface. The uniaxial displacement was applied to the models to obtain the deformation behavior of thin film. In the stress.strain relationship, the average atomistic stress increases monotonously with increasing applied strain. After taking a maximum value, the average stress decreases moderately with applied strain. The 0.2% offset stress increases with decreasing grain size following by Hall-Petch relation if the grain is larger than15nm. However, the offset stress decreases with decreasing grain size following by inverse Hall-Petch relation if the grain is smaller than15nm. The transgranular strain increases with increasing applied strain. However, when the stress.strain relationship becomes nonlinear, the transgranular strain decreases with applied strain.

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In this study, various foaming conditions for a surface layer foaming process by means of a batch type forming process were examined, where saturation times and saturation temperatures of surface layer-foamed plastics thus formed were measured. While, the change of inner structures (cell sizes and foaming depth) with respect to saturation times and saturation temperatures observed. Thus, investigations were made as to the effect of these factors on the inner structures, as well as impact absorption characteristics of surface layer-foamed plastics and their light diffusion characteristics. As a result, following matters were clarified. The forming process of surface layer. foamed plastics has been established, where foaming depth and cell diameter are controllable. The knowledge on the effectiveness in impact absorption characteristics and optical characteristics of surface layer-foamed plastics were obtained.

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