Fatigue crack growth in unidirectional titanium matrix composites: A wear-based approach to modeling

Geoffrey Tabor Ward, Purdue University

Abstract

The topic of fiber bridging in continuous fiber composite materials has received a great deal of attention in the recent literature. When an intact reinforcing fiber bridges a matrix crack, the stress in that fiber at the matrix crack face increases. As the distance from the crack face increases along the fiber, the additional load is transferred from the fiber back to the matrix through a shear stress at the fiber/matrix interface. A common approach to modeling the fiber bridging problem has been to assume that this shear stress has a constant value over some slip region. In doing so, this value is typically found as a curve-fitting parameter with which to match experimental data. This value has been found to be inconsistent. A modified bridging model is proposed, wherein the actual shear stress value is not necessary, due to an assumption that the stresses are transferred between the fiber and matrix from a Coulomb friction standpoint. While this approach in itself is not unique, an additional effect of fiber surface roughness has been included. A wear model is incorporated that decreases the amplitude of fiber surface roughness due to cyclic loading of the interface. Interface fatigue tests have been performed as a means to determine the unknown parameters within the wear model. The combined Coulomb friction and wear models have been applied to a discrete composite model formulation in order to predict the history-dependent crack growth rates and crack opening displacement profiles for a titanium matrix composite. The results show good correlation with existing experimental data, especially at relatively high crack growth rates.

Degree

Ph.D.

Advisors

Hillberry, Purdue University.

Subject Area

Mechanical engineering|Aerospace materials

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