Selection of hybrid composite configuration
During last decades, the partial substitution of traditional composites (especially fibreglass, more recently also carbon fibre composites) with vegetable fibres (especially flax and hemp) has been often proposed in the literature, also by some of the proposers, therefore obtaining hybrid composite materials.
The main difficulty in this process is in the achievement of a sound fibre-matrix interface, with performance/weight ratio comparable with the original composites, although this would of course depend on the application. Another difficulty, which is partially related to the above, lies in the fact that hybrid composites would need to be resistant to water absorption (a problem non existent in traditional composites).
Both these issues are minimised by the selection of a suitable vegetable fibre material and in the production of an adapted hybrid configuration. Testing would be required, comparing different configurations (all with the same amount of synthetic and vegetable fibre, but distributed in different way across the laminate), especially as regards tensile characteristics and water absorption.
Experimental testing (both static and dynamic) on samples of the selected configuration
Once the hybrid configuration has been selected, a number of tests on normalised samples would need to be performed, which would concern both static (especially tensile, flexural and interlaminar shear strength) properties and dynamic properties (both due to service, hence performing fatigue tests, and to accidental events, hence performing falling weight impact tests, both to induce damage and to assess penetration loads).
This entire testing database would also be able to allow assessment of the damage morphology of the hybrid composites proposed, by comparing it with previous data available in the literature.