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A stochastic model based on Markov process is proposed to estimate the number of fiber-break points of a unidirectional fiber-reinforced composite. This model relies on the assumption that each sta...

In ceramics matrix composites (CMCs), fiber-matrix interfacial debonding and sliding are the main toughening mechanisms. An interfacial debonding and sliding problem was formulated in this study, using the constrained conditional finite-element method (CC-FEM). In this formulation, the equivalence of nodal displacements at the interface and the equilibrium of contact forces are assumed as constrained conditions in which Coulomb’s law of friction is taken into account. As a distinguished advantage, numerical solutions are obtainable by a single calculation without an iterative algorism. We earlier treated a case in which fibers were oriented along the loading direction. In actual CMCs, however, fibers are not necessarily oriented along the loading direction. The fiber diameter also fluctuates along the axis. In this study, therefore, the off-axial interfacial debonding and sliding problem based on CC-FEM was formulated. Its validity was discussed by comparison with ANSYS. In both cases of on-axis and off-a...

Natural fiber-reinforced green composites are increasingly being used in various industries. Generally speaking, the cross sections of natural fibers are not circular. Moreover, they show wide variation in their cross-sectional area. Nevertheless, the tensile properties of natural fibers are often evaluated on the assumption of a circular cross-sectional shape. Therefore, we proposed a new method to calculate the natural fiber cross-sectional area by measuring their projection widths to estimate the proper tensile properties. This method was used to investigate the effects of cross-sectional area variation on tensile properties. Additionally, to estimate the proper Weibull parameters of natural fibers apart from the cross-sectional area variation, we proposed a strength distribution function that incorporates cross-sectional area variation, based on a Weibull distribution. Finally, we formulated a strength distribution function of natural fibers that includes the cross-sectional area variation.

Nowadays, utilisation of biodegradable materials has become necessary in order to maintain global environmental and ecological balance. Fully biodegradable nano 'Green' textile composites have been prepared from cellulose nanofibers reinforced corn starch resin and ramie fabric. Nanofibers having dimensions of approximately 1 μm long and 20–30 nm in diameter are used in the study. The nanofibers were incorporated in corn starch resin via ball mill mixing using ceramic balls. Textile composites were fabricated by pasting the reinforced resin onto the ramie fabric and by hot compression molding technique. Interactions at the fiber–matrix interface and the compatibility between cellulose and corn starch resin molecules will affect the properties of the system. The well dispersed cellulose nanofibers contribute higher interfacial area and good fiber networking within the matrix resin. This will lead to better barrier properties. Sorption characteristics of water, oil and diesel in the textile composites were ...

Environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding. As appropriate matrices for injection molding and press molding, polypropylene (PP) and polycaprolactone-cornstarch (PCL-C) were selected, as a typical recyclable resin and biodegradable resin, respectively. The mechanical properties of BF/PP composites were investigated in view of fiber mass fraction and injection molding conditions. And the mechanical properties and the biodegradation of BF/PCL composites were also evaluated. In the case of injection molding, the flexural modulus increased with an increase in fiber mass fraction, and the mechanical properties decreased with an increase in cylinder temperature due to the thermal degradation of BF. The optimum conditions increasing the flexural properties and the impact strength were 90°C mold temperature, 30 s injection interval, and in the range of 165 to 185°C cylinde...

We propose a stochastic process analysis for predicting the strength and reliability of a unidirectional fiber-reinforced ceramic matrix composite. The analysis is based on a Markov process, in which it is assumed that a state of damage in the composite is developed with each fiber breakage. When the Weibull distribution is used to describe the strength distribution of the fiber, the probability of being in each state can be solved analytically in a closed form. Using the solutions of the probabilities, a discussion about damage tolerance of the composites is quantitatively developed, from the viewpoint of materials reliability engineering. To compare the proposed stochastic process analysis with previously proposed strength models in the basis of classical bundle theory, we obtained the expected value and variance in the composite stress from solutions of the probabilities of being in the states. The expected value and variance both consist of two terms, equivalent to the effects of both bundle structure...

A Monte-Carlo simulation model based on 3D-finite element analysis was developed to clarify the effect of interfacial shear strength (IFSS) on tensile strength of a unidirectional composite with fibers placed in a hexagonal array. The simulation model comprises fiber, matrix and interface elements; thereby, fiber breaks, matrix fractures and interfacial debondings during loading can be predicted individually. Tensile fracture processes and strengths of a boron/epoxy composite were simulated at various IFSSs. Results show that as IFSS decreases, stress concentration factors to intact fibers adjacent to a broken fiber element decrease because of occurrences of interfacial debonding. However, since interfacial debonding also reduces load carrying capacity in broken fibers, composite strength is reduced in all fiber volume fractions. On the other hand, a large IFSS causes many matrix fractures at once; therefore, it induces low composite strength. Thus, intermediate IFSSs increase tensile strength of the comp...