Abstract
It is well-known that fiber reinforced composites made from glass-fibers are susceptible to both ageing effects and failure under constant loads (creep-rupture), particularly when exposed to water environments. There are very few experimental studies, however, which have dealt explicitly with the effect of exposure period (ageing) on the resulting creep-rupture response. Understanding this effect is particularly important when dealing with applications which are either delayed in entering full service or are being re-commissioned after some period of dormancy. In the current study, a preliminary examination is made to determine the influence of pre-conditioning period on the resulting time-to-failure curves for a glass-fiber reinforced epoxy system exposed to a water environment. Moisture absorption behavior and resulting failure characteristics are presented.
Fiber reinforced polymer (FRP) composites are seeing increased application in the infrastructure sector for both new construction and rehabilitation due to their reduced weight and ease of installation. For large structural applications, glass-fiber composites are being considered due to its relative lower cost compared to alternative fiber systems. One of the major issues, however, is understanding and quantifying the durability of these material systems under long-term environmental exposure. While the effect of environment on the mechanical durability of fiber composites has been extensively studied, a number of questions still remain.
From the literature, two degradation modes have been identified in glass-fiber composites: 1) ageing [1-3], and 2) creep-rupture (CR) [4-6]. Both are associated with a decrease in mechanical strength over time with exposure to a given environment. The former occurs without the application of applied stress to the material (ageing), while the latter is associated with damage under constant loads (CR). For both damage modes, the level of degradation is a function of the specific composite material system (matrix and fiber), the fiber interfacial properties, and the exposure environment (chemistry and temperature).
Ageing of composite materials is most often evaluated by performing simple tensile tests (monotonic loading conditions) on samples which have been pre-exposed to particular service environments. While this method is simple, inexpensive and provides a direct measure of residual strength with exposure time, it is unclear whether the results are a sufficient measure of long-term durability. For applications where the material is also subjected to sustained loading conditions (in conjunction with exposure), creep-rupture testing is most commonly employed. The main disadvantage with these tests is increased cost and complexity.
In general, strength loss in glass-fiber reinforced polymers is increased by exposure to aqueous solutions and elevated temperatures [1-6]. Under immersion conditions, most glassfiber composites will absorb water leading to degradation of the polymer matrix or to the fibermatrix interface. When superimposed loads are applied during immersion, further degradation of mechanical strength occurs due to stress corrosion cracking of the glass fibers [4-6]. The interaction between these two degradation mechanisms, however, is not fully understood.
The objective of this study is to investigate the effect of moisture pre-conditioning (ageing) on the resulting creep-rupture behavior of a glass-fiber polyester composite system.
Author:
Wolodko, J. and Petersen, R.
Publisher:
NACE International Corrosion Conference
Year Published:
2007
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