Presenter Information

C L. Leung, Rockwell International

Location

La Jolla, CA

Start Date

1979 12:00 AM

Description

The absorption of moisture into fibrous polymeric meterials has been recognized as one of the major mechanisms in the strength degradation of such materials as reported by several workshops (1-3) and publications (4-7). The objective of the work reported here is to use nondestructive evaluation (NDE) techniques to determine the moisture content (profile) within a composite by measuring the w~isture diffusion rate and then subjecting the data to a statistical estimation analysis. This reveals the location of structural degradation and provides a sensitive inspection method for the serviceability of composites. Hydrothermal aging effects on cured graphite-epoxy composites were determined using: (1) acoustic attenuation, αL, (2) ultrasonic velocity, cL, and (3) thickness measurements of the composites. Results showed that while ultrasonic acoustic properties, sample thickness and moisture diffusion profiles are highly sensitive to structural degradation, ultrasonic inspection becomes insensitive in areas of extensive internal damage, probably due to high acoustic attenuation which results in loss of signals. Moisture diffusion analysis (MDA), in this case, becomes highly sensitive as a quantitative detection tool. Presently, analytical methods are developed to quantify the depth profile of moisture penetration in graphite-epoxy composites. Measurement of effusion kinetics over a range of time intervals followed by application of statistical estimation theory enables the depth concentration of moisture at initial time t=0 to be calculated. For a particular model in which the sample is assumed to be exposed to periodically changing environments, the model predicts large fluctuations in moisture concentration near the surfaces while the interior concentration is relatively constant.

Book Title

Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE

Chapter

7. NDE for Advanced Materials

Pages

278-284

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Moisture Diffusion Analysis for Composite Microdamage

La Jolla, CA

The absorption of moisture into fibrous polymeric meterials has been recognized as one of the major mechanisms in the strength degradation of such materials as reported by several workshops (1-3) and publications (4-7). The objective of the work reported here is to use nondestructive evaluation (NDE) techniques to determine the moisture content (profile) within a composite by measuring the w~isture diffusion rate and then subjecting the data to a statistical estimation analysis. This reveals the location of structural degradation and provides a sensitive inspection method for the serviceability of composites. Hydrothermal aging effects on cured graphite-epoxy composites were determined using: (1) acoustic attenuation, αL, (2) ultrasonic velocity, cL, and (3) thickness measurements of the composites. Results showed that while ultrasonic acoustic properties, sample thickness and moisture diffusion profiles are highly sensitive to structural degradation, ultrasonic inspection becomes insensitive in areas of extensive internal damage, probably due to high acoustic attenuation which results in loss of signals. Moisture diffusion analysis (MDA), in this case, becomes highly sensitive as a quantitative detection tool. Presently, analytical methods are developed to quantify the depth profile of moisture penetration in graphite-epoxy composites. Measurement of effusion kinetics over a range of time intervals followed by application of statistical estimation theory enables the depth concentration of moisture at initial time t=0 to be calculated. For a particular model in which the sample is assumed to be exposed to periodically changing environments, the model predicts large fluctuations in moisture concentration near the surfaces while the interior concentration is relatively constant.