FAUSST – bridging the gap between steel and fibre reinforced materials

For a variety of applications, such as shipbuilding or automotive, a variety of materials is used in order to meet certain design constraints or certification limitations. Within ship building for international waters, different design codes are distinguished for civil and naval use. While the SOLAS (safety of life at seas) ship code and the HSC (high speed craft) code have strict regulation in the use of composite materials, some naval rules enable such materials already leading to ship designs e.g. the Visby or Zumwalt class. However, the joining of multi-material structures remains challenging from a technical and regulative point of view. Composite materials aboard of ships has a variety of benefits, such as weight reduction, fuel reduction, increased corrosion resistance and the ability to use different innovative design solutions. Nevertheless, these benefits have to be pondered against the higher material and process costs. Moreover, strict design rules according to naval requirements, e.g. shock resistance, impact, etc. need to be met for the materials as well as their joints. The presented developments focus on one of the process challenges needed, being the joining of a steel structure and a composite material. Within the shipbuilding industry the preferred joining mechanism is welding, whereas other procedures such as bonding or riveting are complex in several manners, e.g. approval. To overcome this challenge FAUSST, a joint based on a hybrid knitted fabric, has been developed. This fabric is composed of steel and glass fibres in a way that a transition element is created, thereby effectively bridging both materials. It can be welded on one side to a metallic structure and integrated on the other side into a FRP. Depending on the design of the transition element loads of up to 240 kN per meter joint can be transferred in the presented design with an overlap length of only 10 mm. This transition element, therefore, may lead to more sophisticated designs using composite materials