Increase In Critical Length Research Articles

Research on the dynamic buckling of functionally graded material plates under conditions of one edge fixed and three edges simply supported

Based on the strain assumption and linear mixing rate of Vogit, the physical property parameter expression of functionally graded material plates is obtained. According to the theory of small deformation and Hamilton principle, the dynamic buckling governing equation of functionally graded material plates under longitudinal load is obtained. Using the method of trial function, the analytical expression of critical load and the buckling solution of the functionally graded material plate under conditions of one edge fixed and three edges simply supported is obtained. The analytical expression of critical load is numerically calculated by METLAB. The influence of geometric size, gradient index, modal order and material composition on critical load is discussed. The results show that the critical buckling load decreases exponentially with the increase of critical length, decreases with the increase of gradient index k, increases with the increase of modal order, and the elastic modulus of constituent materials has significant effect on the critical load. The higher-order buckling modes of functionally graded material plates are prone to occur under the condition of high longitudinal load.

Simulation Study for Temperature-Dependence of Tensile Strength of Continuous and Discontinuous Unidirectionally Fiber-Reinforced Metal Matrix Composites

To describe the feature that the tensile strength of unidirectional discontinuous fiber (whisker)-reinforced aluminum matrix composites decreases with increasing temperature more than that of continuous fiber-reinforced ones, a calculation of the critical length and stress concentration factor affected by the temperature-dependence of mechanical property of matrix, and a Monte Carlo simulation, were carried out. The reduction in strength of both continuous and discontinuous fiber-composites at high temperatures could be attributed to the predominancy of the effect of the matrix-softening-induced increase in critical length over the effect of the decrease in stress concentration arising from the existence of fiber-ends and fiber-breakages. The larger reduction in strength of discontinuous fiber-composites at high temperatures than that of the continuous ones could be explained from the view-point of the larger reduction in the stress carrying capacity of fibers and easier fiber-pull-out.

Temperature-dependence mechanism of tensile strength of Si-Ti-C-0 Fiber-Aluminum matrix composites

The mechanism for the temperature dependence of the tensile strength of unidirectional hybrid type Si-Ti-C-O (Tyranno) fiber-reinforced aluminum matrix composite, in which SiC-particles are dispersed in the matrix, is discussed, focusing on the temperature dependencies of the stress concentration arising from broken fibers and critical length and their influences on the composite strength, by means of a shear-lag analysis and a Monte Carlo simulation. The main results are summarized as follows. The softening of the matrix at high temperatures raises the composite strength from the point of decrease in stress concentration, but on the other hand, it also reduces strength from the point of increase in critical length, which reduces the stress-carrying capacity of broken fibers over a long distance. The reason why the measured strength of composite decreased with increasing temperature could be attributed to the predominacy of the latter effect over the former one. The results of the simulation indicated that the hybridization of the composites improved room-temperature and high-temperature strengths through the strengthening of the matrix.

Ｓｉ‐Ｔｉ‐Ｃ‐Ｏ繊維強化アルミニウム基複合材料の引張強さの温度依存性

Tensile strength at temperatures between room temperature and 773K of the unidirectional Si-Ti-C-O fiber (Tyranno fiber) reinforced aluminum matrix composite produced by a squeeze casting method was investigated. The longitudinal strength decreased gradually with increasing temperature up to 673K, but then a rapid decrease was observed at the higher temperature. The transverse strength decreased larger than longitudinal one with increasing temperature. A drop of strength was observed at about 500 and also at 673K. In order to understand the temperature dependence of composite strength, temperature-dependence of matrix yield stress in the composite was deduced from thermal expansion curve. Using thus deduced matrix yield stress and temperature dependence of shear modulus of matrix taken from a literature, the stress concentration factor in the fibers adjacent to broken fibers and the critical length of broken fibers in the composite, which are representative strength-determining factors, were calculated for various temperatures by means of the shear lag analysis. The stress concentration factor decreased slightly, while the critical length increased much with increasing temperature. From the calculation, the decrease in longitudinal strength with increasing temperature could be attributed to the increase in critical length due to the softening of matrix. The reduction in transverse strength was caused directly by the softening of matrix.