Composites are due to their high stiffness and strength combined with low weight, indispensable in structures as wind turbine blades and aircrafts structures. Composites are also frequently used in other applications with demand to strength, light weight and environmental stability as marine structures and pipes. Nevertheless, composites still suffer from being vulnerable to production imperfections and damages from for instance impacts. To increase the use of composites in larger constructions, they need to provide a low life cycle cost based on low-cost high throughput production and low need for maintenance. Production of still larger parts at low cost, increase the probability of production imperfections. To mitigate the effects of this, and to reduce the need for costly maintenance and repairs, composites should be made more damage tolerant. Damage tolerant in this context meaning that cracks originating from production imperfections or extreme loadings will not develop to a critical scale.
The overall objective of DACOMAT has been to develop more damage tolerant and damage predictable low cost laminated composite materials, aimed for use in large load carrying constructions like bridges, buildings, wind-turbine blades and off-shore structures. In addition, advanced materials and structural modelling, and structural health monitoring methods to enable detection and assessment of damages has been developed.
DACOMAT represents a radical new way of thinking for composite materials by changing the philosophy from "As strong as possible to avoid any cracks" to "Cracks can be tolerated but they should be controlled and stabilised through optimal fracture mechanical material design".
DACOMAT has focused on laminated glass fibre composites build layer by layer. The interface between the layers/lamina are “weak zones” and are vulnerable to cracks along the interface, so called delamination. In DACAMONT the resistance to delamination, technically called interlaminar fracture resistance, has been significantly improved.
Technically, the approach has been to utilize the concept of interlaminar fibre bridging and close parallel cracks. When a crack forms between two lamina, fibres can remain anchored in both crack surfaces. This is fibre bridging. As the crack grows the fibres are strained and gradually pulled out until they fail. This requires energy and increase the interlaminar fracture toughness. In addition, if close parallel cracks in adjacent interfaces are formed and advances simultaneously the fracture resistance will add up to nearly the sum of the fracture resistance of both cracks.
