Date of Award


Degree Type


Degree Name


Degree Program



Mechanical Engineering

Major Professor

Schilling, Paul

Second Advisor

Verges, Melody

Third Advisor

Herrington, Paul


Graphite/epoxy composite laminates are widely used in the aerospace industry. However the industry cannot take full advantage of the superior strength and stiffness of composite materials until their failure mechanisms can be thoroughly understood by engineers. Recognizing the importance of such understanding, the current study was undertaken to determine the microcracking fracture toughness in composite laminates using the energy release rate criteria. Three materials of specific interest in the aerospace industry – IM7/977-2, IM7/5555 and IM7/5276-1 – were analyzed. To evaluate the microcracking fracture toughness, displacement controlled static tensile tests were performed. Microcrack density (the number of microcracks per unit length) was measured as a function of applied stress. The data were analyzed to obtain the microcracking fracture toughness (Gm) for each material system. The value of Gm can be used to predict the microcracking behavior of composite laminates made from the corresponding material.


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