Speaker
Description
It is well known that during the service life advanced polymer composites may be exposed not only to complex mechanical loading but also to harsh environmental conditions. In applications such as aeronautics, automotive, wind turbine blades, composites undergo frequent exposure to sub-zero and even cryogenic temperatures. This may lead to initiation of micro-damage in composites and premature failure of structures. To anticipate these events, one needs to understand the behavior of composites and be able to predict degradation of mechanical properties in sub-zero environment.
In the current work, the mechanical properties and damage initiation/accumulation in woven glass fiber-reinforced epoxy (GF/EP) composites were studied at room temperature as well at temperatures below zero. To evaluate influence of sub-zero environment on mechanical performance of GF/EP laminates two types of test campaigns were carried out: 1) long term exposure of material to liquid nitrogen environment followed by tensile tests at room temperature; 2) tensile tests in sub-zero environment of unconditioned specimens. The quasi-static tensile tests were performed to measure elastic modulus of the composites while loading-unloading experiments were performed to monitor initiation (and accumulation) of micro-damage and its influence on the stiffness of GF/EP laminates.
The results on cryogenic damage and fracture in the laminates are discussed with focus on degradation of properties of GF/EP composites crucial for their use in structural applications: strength, stiffness, damping. The evaluation of different epoxy system formulations with respect to the damage initiation and tolerance in low temperature conditions is carried out. To analyze and demonstrate damage tolerance of GF/EP subjected/tested at different environments, the predictions of stiffness degradation with respect to the induced damage is done by means of analytical modeling.
