CFRP repair: Aventador
Automobili Lamborghini SpA (Sant'Agata Bolognese, Italy) uses several types of carbon fiber composites on its new Aventador LP700-4 supercar, but one type of repair that might be performed on a prepreg part would go as follows.
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Automobili Lamborghini SpA (Sant'Agata Bolognese, Italy) uses several types of carbon fiber composites on its new Aventador LP700-4 supercar, but one type of repair that might be performed on a prepreg part would go as follows. Before the Flying Doctor arrives (see “Automotive CFRP: Repair or replace?” under “Editor’s Picks,” at top right) the body shop where the vehicle was taken would strip the car down so that bare carbon components would be ready. Upon arrival, the Flying Doctor would begin the repair process by making a template. This involves affixing a clear plastic film over the damaged area (here, the part is a rocker panel) and drawing progressively larger concentric ovals on the film outside the damaged area. These markings will later be used as the cut lines for prepreg plies that will be used in the patch.
Fiber in the damaged area (including a sufficient margin so the patch has solid material to which it can adhere) is cut from the part, and the surface of the remaining material is roughened up with sandpaper to improve bonding. The technician then creates a backing piece that is slightly larger than the hole where damaged material was removed. In the case of a rocker panel, the piece is cut from prepreg using one of the concentric ovals previously marked on the clear film as a template. Next, two holes are drilled away from the edges of the backing piece and a wire is fed through them that is used for maneuvering the backing piece into place. Then the piece is slipped into the opening, moved into position, and bonded in place with paste adhesive. When the backing plate is firmly bonded in place, the wire is removed and the patching begins.
The technician uses the marked-up clear film to cut five (or more, depending on the hole size) successively smaller ovals out of prepreg (starting with the largest marking first and then trimming the template down for each subsequent layer). The fiber alignment is alternated on successive plies. Starting with the smallest patch (which is slightly larger than the hole), the technician proceeds to lay up the patch, moving from smallest to largest ply. Next, the patched section of the part is vacuum bagged, air is evacuated and a heater blanket is applied to cure the resin in the prepreg. When crosslinking is complete, a portable ultrasound unit is used to scan the part to ensure patch integrity (e.g., that trapped air hasn’t left any voids).
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