Date on Master's Thesis/Doctoral Dissertation

8-2005

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Mechanical Engineering

Committee Chair

Bradshaw, Roger D.

Subject

Computer vision--Industrial application; Imaging systems; Strains and stresses--Measurement; Quality control--Automation; Aluminum films--Research

Abstract

Aluminum fiber metal laminates (AFMLs) are a promising new type of fiber metal laminate that consists of aluminum foils interleaved with layers of a graphite fiber-polymer matrix composite (PMC) material. AFMLs combine the attractive features of aluminum with the advantages of traditional graphite polymer-matrix composite. There are a number of anticipated benefits of such a material including weight reduction, improved bearing capability and high conductivity for lightning strike protection. The presence of the fiber-reinforced composite also provides a method to arrest cracks in the aluminum layers via fiber bridging. In order to understand crack initiation and growth in AFML specimens, this study considers the tensions-tension fatigue response of 39 AFML specimens at five different stress levels and three different specimen configurations. The specimens and support for the project was provided by The Boeing Company (Structures Damage and Technology Group). Several methods of crack investigation were considered for this study; it was determined that visual inspection through digital photography at evenly spaced intervals throughout the test provided the best method for the characterization of crack initiation and growth. Visual analysis of the specimen images was performed. This led to precise estimates of the cycles to crack initiation as well as crack length versus cycle count throughout each experiment. The results clearly demonstrated reduced crack growth rates throughout each experiment, which is likely attributed to fiber bridging. Crack growth versus cycles for various experiments were well represented by a single reference curve with appropriate cycle count scale factors. This demonstrates that linear elastic fracture mechanics appears to govern the crack growth response. This project demonstrates the value of visual imaging to monitor crack initiation and growth in AFMLs and offers a potential method to better understanding the phenomenon in future studies.

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