Gao Xiguang

Numerical Simulation of Dynamic Response of Fiber Reinforced Ceramic Matrix Composite Beam with Matrix Cracks Using Multiscale Modeling

Abstract A multiscale method for simulating the dynamic response of ceramic matrix composite (CMC) with matrix cracks is developed. At the global level, the finite element method is employed to simulate the dynamic response of a CMC beam. While at the local level, the multiscale mechanical method is used to estimate the stress/strain response of the material. A distributed computing system is developed to speed up the simulation. The simulation of dynamic response of a Nicalon/CAS-II beam being subjected to harmonic loading is performed as a numerical example. The results show that both the stress/strain responses under tension and compressive loading are nonlinear. These conditions result in a different response compared with that of elastic beam, such as: 1) the displacement response is not symmetric about the axis of time; 2) in the condition of small external load, the response at first order natural frequency is limited within a finite range; 3) decreasing the matrix crack space will increase the displacement response of the beam.

A temperature-dependent constitutive model for fiber-reinforced ceramic matrix composites and structural stress analysis

A temperature-dependent constitutive model based on the continuum damage mechanics (CDM) theory is developed to model the stress/strain behavior of C/SiC composites. A formulation of Helmholtz free energy with initial modulus and tangent modulus is proposed to describe the bilinear constitutive behavior of such materials. The Lagrange interpolation is used to describe the relations between material parameters and temperature. The effect of temperature is introduced into the theoretical framework of continuum damage mechanics. The constitutive model is applied to predict the stress/strain curves of two-dimensional woven C/SiC composite at room and elevated temperatures. Good agreement was found between the experimental data generated and the results predicted by the continuum damage mechanics model. This demonstrates that the methods developed in this paper are effective. The numerical analysis of two-dimensional woven C/SiC laminate with a hole shows that the temperature effect will reduce stress concentration near this hole.

A Quadrilateral Element-based Method for Calculation of Multi-scale Temperature Field

In the analysis of functionally graded materials (FGMs), the uncoupled approach is used broadly, which is based on homogenized material property and ignores the effect of local micro-structural interaction. The higher-order theory for FGMs (HOTFGM) is a coupled approach that explicitly takes the effect of micro-structural gradation and the local interaction of the spatially variable inclusion phase into account. Based on the HOTFGM, this article presents a quadrilateral element-based method for the calculation of multi-scale temperature field (QTF). In this method, the discrete cells are quadrilateral including rectangular while the surface-averaged quantities are the primary variables which replace the coefficients employed in the temperature function. In contrast with the HOTFGM, this method improves the efficiency, eliminates the restriction of being rectangular cells and expands the solution scale. The presented results illustrate the efficiency of the QTF and its advantages in analyzing FGMs.