“The Lamborghini promise is to ensure that the carbon fiber repair is 100 percent the same quality as the original part,” says Casper Steenbergen, head of composite repair for the high-end automaker. Lamborghini’s team of repair specialists – called “flying doctors” – travel to dealerships to assess damage and perform repairs. The company modeled its flying doctor program after a similar strategy used by Boeing, says Steenbergen. “The aircraft manufacturer has been working with traveling specialists for some time and has developed a system for execution of carbon fiber repair work using extremely compact equipment,” he says.
Some repairs first require the core to be rebuilt matching the specifications from the original core, such as balsa or foam in the case of wind turbine blades. “We use foam in prescored sheets to make it easy to pack anywhere from 100 x 100 millimeters to several square meters for a major repair,” says Kanaby. The core is later vacuum packed to ensure a complete bond.
The decision to use wet layup or a prepreg repair for the skin depends on the composite material and the original part design. Matching the direction of the composite fibers to each ply of the original design is most critical to duplicating the fiber axial load capability in the structure.
According to Henry Elliot, an instructor at the IYRS School of Technology and Trades, wet layups for skin repair remain the most common method for laminate skin marine applications. “We do see prepregs being used more often now for racing boat repair,” said Elliot. “But prepreg must be used in an environment where temperature, humidity and contaminants can be controlled.”
With wind turbine repair, the environment dictates wet layup. “Prepregs require storage in a cool place to control curing. Since wind turbine repair usually takes place outside in warm weather, we use wet layups 99 percent of the time,” says Kanaby. “Fibers are oriented at 45 degrees in one direction and 45 degrees in the opposite direction for biaxial strength for the skins while unidirectional is used in the structure.”
Dorworth summarizes the complex process of making and bonding repairs: “Once the edges of the damaged part have been tapered or scarfed to accept the repair, a series of replacement plies are cut to size. The fiber material is wetted with a laminating resin that will bond to the existing structure. Alternately, prepreg material, which is already pre-impregnated with just enough resin to bind the fibers together, will require an adhesive interface to bond the laminate. Systematically orienting the direction of the fibers in each repair ply to match the original axis of the corresponding original ply ensures the repair can efficiently transfer loads back into the structure.”