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Proceedings Paper

Composite cure monitoring with Bragg grating sensors
Author(s): Kerry T. Slattery; Kelli Corona-Bittick; Donald James Dorr
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Paper Abstract

Residual stress is induced in fiber composite materials during the cure process because the thermal expansion coefficient of the fiber is generally much lower than that of the polymer matrix. The two materials are 'locked' together at the cure temperature. Then, as they cool, the matrix attempts to contract more than the fiber leading to tension in the matrix and compression in the fiber. This can lead to the formation of microcracks parallel to the fibers in thick composite piles or yarns. The magnitude of residual stress can be reduced by modifying the cure cycle; however, optimizing the cure cycle requires a complete understanding of the state of cure throughout the composite. This is a complex problem -- especially in thick composites. Pilot studies have been performed placing Bragg gratin sensors in glass fabric preforms and monitoring the response of the grating during resin infusion and cure. The typical response shows the initial thermal expansion of the Bragg grating, a rapid contraction of the grating as the resin gels, slower contraction during cure, and thermal contraction at the composite thermal expansion coefficient during cool down. This data is then sued with micromechanical models of the fiber/matrix interaction during cure to establish material parameters for cure simulation. Once verified, these cure simulation methods will be used to optimize tooling design and cure cycles in composite components.

Paper Details

Date Published: 15 March 1998
PDF: 8 pages
Proc. SPIE 3399, Process Control and Sensors for Manufacturing, (15 March 1998); doi: 10.1117/12.302543
Show Author Affiliations
Kerry T. Slattery, Duke and Associates (United States)
Kelli Corona-Bittick, Production Products (United States)
Donald James Dorr, Duke and Associates (United States)


Published in SPIE Proceedings Vol. 3399:
Process Control and Sensors for Manufacturing
Richard H. Bossi; David M. Pepper, Editor(s)

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