Graduate Studies


Date of this Version



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Engineering Mechanics, Under the Supervision of Professor Anthony Bunsell and Professor Mehrdad Negahban. Lincoln, Nebraska: April 2012

Copyright (c) 2012 Jared C. Miller


A composite consisting of a polyphthalamide (PA-6T + PA-6I) matrix reinforced with short glass fibers is studied after aging the material in humid air and immersed in water at varying temperatures. The goal of this study is to create a functioning finite element analysis (FEA) model of the material under elastic loading during and after aging of the material under certain temperatures and humid/moist conditions.

Experiments were performed by Laurent Maze of Ecole Nationale Supérieure des Mines in Paris, France. The resulting data was analyzed by this author to determine physical properties and apply them to an FEA model. The following results come from this analysis.

The material was found to follow a Fickian absorption model with diffusivity and saturation mass gain both dependent on temperature and humidity conditions.

Results from tensile testing of the aged composite samples at different temperatures combined with information from a thermal sweep in DMA indicates that the Young’s modulus of the composite and its matrix may follow a sigmoidal behavior with temperature. A sigmoidal function is proposed to model this behavior.

Finding the orientation tensor of the reinforcing fibers allows us to subtract the effects of the fiber and find the matrix properties of the composite through the Lielens/Mori-Tanaka method. Orientation tensors were found that indicates the fibers are primarily aligned in the direction of the injection-flow of the material. The Young’s modulus of the matrix was found to follow a sigmoidal function similar to the Young’s modulus of the composite.

The results and analysis in this report were then applied in a custom Lielens/Mori Tanaka finite element analysis of the composite material for a plate sample. It was shown that one can find the effective stiffness tensor at each node in a meshed model of this material after aging, given temperature and water concentration boundary conditions.