The challenge
Polymer composite materials are increasingly being used in offshore and marine industries for subsea structures, shipping and wind or tidal turbine blades. While these materials are lighter weight and more corrosion resistant than steel, for example, they still undergo environmental degradation over time. It is critical to understand the long-term behaviour of these composites to ensure:
- The design accurately reflects the application and material behaviour
- They are the most cost-effective material choice
- There are sufficient safety margins for the mechanical properties
- The durable lifetime of the material in use can be predicted
The solution
Moisture diffusion in composites can cause the mechanical properties of composite components to deteriorate. Although salt water has been shown to diffuse into composites more slowly than water, it has a similar effects on the composite properties. In a marine environment salt water is the primary degradation agent, particularly for submerged components, so understanding the degradation process is vital.
NPL can investigate the moisture diffusion by using elevated temperatures or pressure to accelerate the ageing of polymer composite specimens when immersed in water. The specialist procedure uses both water baths and autoclaves to simulate and monitor the degradation of polymer composites in a marine environment. We use four-point bend flexure, Fourier transform infra-red spectroscopy, dynamic mechanical analysis and microscopy to understand the microstructural behaviour and mechanical property changes.
Testing of aged specimens has shown that the increase in moisture content over time causes changes in material behaviour with a decrease in the glass transition temperature. It also changes the flexural strength and failure mechanism. Results also show that the application of pressure does not affect the rate of diffusion; particularly important for consideration in subsea applications.
The impact
NPL’s wide range of test techniques can be carried out at different temperatures, pressures and conditions, which means that we can use to understand and predict long-term material, and subsequently component, performance. Working in a range of environments using test coupons allows companies to work with us to predict component performance.
Bespoke, specialised mechanical testing is important for understanding the durability of polymer composites. We have applied our expertise to determine the lifetime of marine components so that companies can:
- Use composite materials with confidence
- Predict the life of the material in a particular environment
- Plan maintenance, inspection and upgrade reliably
This means new, lighter materials can be used with confidence, and ultimately save money.