Prepreg material is temperature sensitive. Excessively  high temperatures cause the material to begin curing, and  excessively low temperatures make the material difficult  to handle. For repairs on aircraft in very cold or very hot  climates, the area should be protected by a tent around the  repair area. Prepare the prepreg repair plies in a controlled- temperature environment and bring them to the repair area  immediately before using them.  been referred to as a combination of metal bonding and  conventional on-aircraft composite bonded repair. Boron  prepreg tape with an epoxy resin is most often used for this  application. In the co-bonding process, one of the detail parts is precured  with the mating part being cured simultaneously with the  adhesive. Film adhesive is often used to improve peel  strength. Co-curing is a process wherein two parts are simultaneously  cured. The interface between the two parts may or may not  have an adhesive layer. Co-curing often results in poor panel  surface quality, which is prevented by using a secondary  surfacing material co-cured in the standard cure cycle or  a subsequent fill-and-fair operation. Co-cured skins may  also have poorer mechanical properties, requiring the use of  reduced design values. A typical co-cure application is the simultaneous cure of a  stiffener and a skin. Adhesive film is frequently placed into  the interface between the stiffener and the skin to increase  fatigue and peel resistance. Principal advantages derived  from the co-cure process are excellent fit between bonded  components and guaranteed surface cleanliness. Secondary bonding utilizes precured composite detail parts,  and uses a layer of adhesive to bond two precured composite  parts. Honeycomb sandwich assemblies commonly use  a secondary bonding process to ensure optimal structural  performance. Laminates co-cured over honeycomb core may  have distorted plies that have dipped into the core cells. As  a result, compressive stiffness and strength can be reduced  as much as 10 and 20 percent, respectively. Precured laminates undergoing secondary bonding usually  have a thin nylon or fiberglass peel ply cured onto the  bonding surfaces. While the peel ply sometimes hampers  nondestructive inspection of the precured laminate, it has  been found to be the most effective means of ensuring  surface cleanliness prior to bonding. When the peel ply is  stripped away, a pristine surface becomes available. Light  scuff sanding removes high resin peak impressions produced  by the peel ply weave which, if they fracture, create cracks  in the bondline. Composite materials can be used to structurally repair, restore,  or enhance aluminum, steel, and titanium components.  Bonded composite doublers have the ability to slow or stop  fatigue crack growth, replace lost structural area due to  corrosion grind-outs, and structurally enhance areas with  small and negative margins. This technology has often  Read the SRM and determine the correct repair material,  number of plies required for the repair, and the ply  orientation. Dry the part, remove the damage, and taper  sand the edges of damaged area. Use a piece of thin plastic,  and trace the size of each repair ply from the damaged area.  Indicate the ply orientation of each ply on the trace sheet.  Copy the repair ply information to a piece of repair material  that is large enough to cut all plies. Impregnate the repair  material with resin, place a piece of transparent release film  over the fabric, cut out the plies, and lay up the plies in the  damaged area. The plies are usually placed using the smallest  ply first taper layup sequence, but an alternative method is to  use the largest ply first layup sequence. In this sequence, the  first layer of reinforcing fabric completely covers the work  area, followed by successively smaller layers, and then is  finished with an extra outer layer or two extending over the  patch and onto the sound laminate for some distance. Both  methods are illustrated in  Figures 7-46  and  7-47 . Figure 7-46.  Repair layup process. Co-bonding Co-curing Secondary Bonding 7-28 Warp P EXTRA 0 P2 45 P3 0 P1 0 F.P. Ply locating template Taper sanded repair Repair plies Part zero direction Layup Process (Typical Laminated Wet Layup) Layup Techniques