Effects of Environmental Degradation on Flexural Failure Strength of Fiber Reinforced Composites |
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Authors: | T Nakamura R P Singh P Vaddadi |
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Institution: | (1) Department of Mechanical Engineering, State University of New York at Stony Brook, NY 11794, USA |
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Abstract: | Fiber-reinforced composite laminates are often used in harsh environments that may affect their long-term durability as well
as residual strength. In general, environmental degradation is observed as matrix cracking and erosion that leads to deterioration
of matrix-dominated properties. In this work, cross-ply laminates of carbon fiber reinforced epoxy were subjected to environmental
degradation using controlled ultraviolet radiation (UV) and moisture condensation and the post-exposure mechanical properties
were evaluated through elastic modulus and failure strength measurements. Additionally, both degraded and undegraded were
subjected to cyclic fatigue loading to investigate possible synergistic effects between environmental degradation and mechanical
fatigue. Experimental results show that the degradation results in reduced failure strength. Greater effects of degradation
are observed when the materials are tested under flexural as opposed to uniaxial loading. Based on strength measurements and
scanning electron microscopy, we identified various damage modes resulting from exposure to UV radiation and moisture condensation,
and cyclic loading. The principal mechanisms that lead to reduction in mechanical properties are the loss of fiber confinement
due to matrix erosion, due to UV radiation and moisture condensation, and weakened/cracked ply interfaces due to mechanical
fatigue. An empirical relationship was established to quantify the specific influence of different damage mechanisms and to
clarify the effects of various degradation conditions. |
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Keywords: | Composites Environmental degradation UV radiation Moisture Fatigue Residual strength |
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