Semester

Fall

Date of Graduation

1998

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Industrial and Managements Systems Engineering

Committee Chair

Ever J. Barbero.

Abstract

While it is widely recognized that failure occurs as a result of damage accumulation, characterization of composite material behavior is currently limited to obtaining the elastic properties and the strength values. With such information, it is not possible to assess the remaining life of a structural component or to estimate the likelihood of failure as a function of the time in service. The present investigation concerns the development of a continuum damage mechanics (CDM) formulation for polymer-matrix composites assuming the damage accumulates in the matrix, fiber, and fiber-matrix interphase regions. A local approach was taken by dividing the analysis of damage in the three phases. The phases may be initially isotropic but become orthotropic as a result of damage. The damage evolution in each phase is orthotropic without any a priori imposition of preferential orientation for the damage or orthotropy of the degraded material properties. Orthotropic damage is represented by a second order symmetric tensor. The development of the degraded constitutive equations is carried out using an equivalent fourth order tensor. Great effort was invested in developing a physically and mathematically consistent representation of damage evolution, which implied significant development of tensor analysis. The identification of material constants is based on accepted simple models of fiber and matrix behavior, thus minimizing the amount of testing required.

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