Moisture driven crack growth in natural fibre materials

Natural fiber materials are made of a complex network of self organised hard and soft constituents structured by multiple physico-chemical interactions conferring them their unique properties. These fiber-based structures are more and more looked at as the new generation of lightweight materials with tailored properties, suitable for many applications such as packaging, medicine and insulation.

However, one of the key issues arising in the development of these applications relates to the detrimental effects of moisture on the mechanical properties of such materials which appear to be very susceptible to water. Not only does water dissolve the bonds between the fibers reducing the stiffness of the material, but it also induces local stress due to fiber expansion and twisting.

The goal of this project is to get knowledge of the fundamental physical mechanisms leading to the initiation and growth of cracks in natural fiber materials exposed to aggressive moisture environment and mechanical load, and to quantify the detrimental effects of moisture driven microscopic fractures on the structural integrity of these materials. In this project, the focus is on slowly growing fractures, including moisture transport, using a discrete modeling approach with high spatial resolution, complemented with experimental observations (µ tomography) to understand the complex deformation mechanisms. Important microstructural features are determined, like pore size and distribution, or fiber geometry, and an effort is made to link them to the material's moisture driven fracture mechanism.

The success of the project is expected to represent a breakthrough in the design of renewable fiber materials, particularly through providing crucial parameters such as critical loads at different moisture levels, or beneficial fiber distributions to obtain higher fracture toughness against moisture changes.