Title page for ETD etd-032299-161945

Type of Document Dissertation
Author Mahieux, Celine Agnes
Author's Email Address cmahieux@vt.edu
URN etd-032299-161945
Title A Systematic Stiffness-Temperature Model for Polymers and Applications to the Prediction of Composite Behavior
Degree PhD
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Reifsnider, Kenneth L. Committee Chair
Case, Scott W. Committee Member
Kampe, Stephen L. Committee Member
Lesko, John Jack Committee Member
Marand, Hervé L. Committee Member
  • statistical model
  • life prediction
  • composites
  • elevated temperatures
  • bending
  • polymer matrix composites
  • fatigue
  • thermally activated switches
  • cryogenic temperatures
  • polymers
  • stiffness
  • temperature
Date of Defense 1999-02-26
Availability unrestricted
Polymer matrix composites (PMC’s) are now being used more and more extensively and over wider ranges of service conditions. Large changes in pressure, chemical environment or temperature influence the mechanical response of such composites. In the present effort, we focus on temperature, a parameter of primary interest in almost all engineering applications. In order to design composite structures without having to perform extensive experiments (virtual design), the necessity of establishing theoretical models that relate the macroscopic response of the structure to the microscopic properties of the constituents arises. In the first part of the present work, a new stiffness versus temperature model is established. The model is validated using data from the literature. The influence of the different polymer’s properties (Molecular weight, crystallinity, and filler content) on the model are studied by performing experiments on different grades of four polymers PMMA, PEEK, PPS, and PB. This statistical model is proven to be applicable to very different polymers (elastomers, thermoplastics, crystalline, amorphous, cross-linked, linear, filled, unfilled…) over wide temperature ranges (from the glassy state to the flow region). The most attractive feature of the proposed model is the capability to enable a description of the polymer’s mechanical behavior within and across the property transition regions.

In order to validate the feasibility of using the model to predict the mechanical response of polymer matrix composites, the stiffness-temperature model is used in various micromechanical models (rule of mixtures, compression models for the life prediction of unidirectional PMC’s in end-loaded bending…). The model is also inserted in the MRLife prediction code to predict the remaining strength and life of unidirectional PMC’s in fatigue bending. End-loaded fatigue experiments were performed. A good correlation between theoretical and experimental results is observed. Finally, the model is used in the Classical Lamination Theory; some laminates were found to exhibit stress reversals with temperature and behaved like thermally activated mechanical switches.

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