Semester

Spring

Date of Graduation

2004

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Julio F. Davalos.

Abstract

The focus of this dissertation is on developing efficient modeling techniques to study facesheet-core interface delamination in honeycomb fiber-reinforced polymer (HFRP) sandwich panels. Delamination problems are usually treated from a fracture mechanics point of view. However, interface delamination is generally very complex in nature and difficult to solve, because it involves not only geometric and material discontinuities, but also the inherently coupled Mode I, II and III fracture in layered material systems attributed to the well-known oscillatory singularity nature of the stress and displacement field in the vicinity of the delamination crack tip. One of the key issues in this research is to determine the best way to characterize interface delamination within the framework of continuum mechanics rather than using ad hoc methods just to facilitate numerical implementations, such as springs across a crack in the finite element method.;The usual requirement of defining an initial crack and assuming self-similar progression of a crack, make traditional fracture mechanics approaches inefficient for modeling interface delamination. To circumvent these difficulties, five most relevant nonlinear crack models are reviewed and compared. It is concluded that by unifying strength-based crack initiation and fracture-based crack progression, the cohesive crack modeling approach has distinct advantages compared to other global methods.;In this study, a cohesive zone model (CZM) with linear-exponential irreversible softening traction-separation law, satisfying empirical mixed-mode fracture criteria, is proposed to represent progressive damage occurring within the interface during the fracture process. The CZM is implemented as a cohesive interface element through a user-defined element subroutine within the general purpose finite element code ABAQUS. The framework and formulation of a three dimensional interface element are presented. Two sets of parameters are required for application of the developed interface element, namely, interfacial strength and fracture toughness. (Abstract shortened by UMI.).

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