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Proceedings Paper

Millimeter-wave nondestructive evaluation of glass fiber/epoxy composites subjected to impact fatigue
Author(s): Donald W. Radford; Stoyan I. Ganchev; Nasser Qaddoumi; Guy Beauregard; Reza Zoughi
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Paper Abstract

The useful life of a glass fiber/epoxy composite subjected to impact fatigue loading is an important issue in the future design of numerous industrial components. Lifetime predictions have been a problem particularly due to the difficulties encountered in monitoring damage accumulation in composites. It is hypothesized that there is a build up of micro damage, such as matrix micro-cracks and micro-delaminations, even though there is no apparent change in material compliance. A critical level is finally reached at which time the properties of the composite begin to fall and compliance change is evident. In this study the apparent compliance change and the type of damage accumulation is investigated. To measure the compliance change, a test unit was developed that uses a dynamic load measuring system. The load cell measures the load throughout each impact pulse and the compliance and energy absorbed by the specimen is then related to the recorded curve. Initially no change in the impact pulse was apparent; however, after a finite number of cycles the peak load and area under each impact pulse drop, indicating an increase in compliance. Unfortunately, the impact load does not provide information on the form and degree of damage. Thus, millimeter wave nondestructive investigation is used, in conjunction with impact fatigue tests, to examine microstructural aspects of damage initiation and growth. The millimeter wave scanning technique results in detectable damage growth throughout the impact fatigue test. Damage size and growth patterns specific to composites are obvious, and after significant damage can be related to the observable macro damage. Continued development of these investigative techniques promises to enhance the ability of detecting defects and damage growth in fiber reinforced composite materials as well as improving the understanding of impact fatigue initiation in these complex materials.

Paper Details

Date Published: 14 September 1994
PDF: 6 pages
Proc. SPIE 2275, Advanced Microwave and Millimeter-Wave Detectors, (14 September 1994); doi: 10.1117/12.186723
Show Author Affiliations
Donald W. Radford, Colorado State Univ. (United States)
Stoyan I. Ganchev, Colorado State Univ. (United States)
Nasser Qaddoumi, Colorado State Univ. (United States)
Guy Beauregard, Colorado State Univ. (United States)
Reza Zoughi, Colorado State Univ. (United States)

Published in SPIE Proceedings Vol. 2275:
Advanced Microwave and Millimeter-Wave Detectors
Satish S. Udpa; Hsiu C. Han, Editor(s)

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