Ageing and mechanical failure of fiber reinforced polymers

2015-06-10Fiber reinforced polymers (FRPs) have been widely used in the aerospace industry for decades. However, the use of FRPs in civilian infrastructure applications is increasing, particularly in applications such as high-voltage transmission lines, wind turbine blades, and off-shore oil platforms. In such applications, long-term environmental ageing is a major concern because these structures, unlike aircraft, are expected to provide decades of service with minimal inspection or maintenance. This presents a major challenge for FRPs because ageing has complex effects on mechanical performance, making it difficult to forecast property retention and predict component lifetime. The overriding focus of the present work is to determine the effects of different types of ageing on the mechanical behavior of FRPs. Two FRP systems are considered, each with distinct matrix chemistry and intended service applications. The first system is a polydicyclopentadiene (pDCPD) resin with intrinsic hydrophobicity and exceptionally low viscosity, attributes that are suitable for fabrication of large parts and humid service conditions, such as wind turbine blades and components for oil and gas production. The second system is a unidirectional (UD) composite rod intended as the load-bearing core for high voltage power transmission lines (overhead conductors). ❧ For the first system, pDCPD is an attractive candidate resin for potential use in corrosive environments because of its intrinsic hydrophobicity, which imparts resistance to ageing in humid environments. We first investigate the hygrothermal ageing behavior of pDCPD composites and effects on mechanical behavior, including the fatigue behavior. Next, we investigate the thermal oxidation ageing of pDCPD resins and composites to determine effects on mechanical behavior. By investigating the ageing behavior and resulting degradation in mechanical properties, the water diffusion mechanism, salt corrosion behavior, and oxidized layer evolution of pDCPD composites are better understood. These insights provide a basis for lifetime predictions based on ageing rules and the composite can be optimized to achieve improved performance. ❧ For the second system, UD FRPs have high strength in the longitudinal direction, but low transverse strength, often resulting in premature damage initiation. The study here investigates the transverse compression behavior of UD FRPs using both experimental and finite element simulation. The investigation provides a basis for optimizing the rod design and improving the characteristics of this new product