Peel-ply method

An alternative pre-treatment for composites is the tear (peel) ply method. A fabric is incorporated in the composite near the surface. The fabric is pulled away just prior to bonding, exposing a clean surface, provided there is no contamination from the fabric... 

Typhoon Applications in this aircraft show the use of structural adhesives to bond carbon composite adherends together. The composite adherends use a peel ply method of pretreatment prior to bonding, with the actual areas to be bonded then being abraded (by hand). This is followed by a solvent wash. 

One surface preparation method that is unique for composites employs a peel or tear ply.77 Utilization of the peel ply is illustrated in Fig. 16.5. With this technique, a closely woven nylon or polyester cloth is incorporated as the outer layer of the composite during its production layup. This outer ply is then torn or peeled away just before bonding. The tearing or peeling process fractures the resin matrix coating and exposes a clean, fresh, roughened surface for the adhesive. This method is fast and eliminates the need for solvent cleaning and mechanical abrasion. 

Composite components are pretreated using peel ply techniques and FR-HiTEMP has devised their own patented method for the pretreatment of high chrome steel. 

The primary desired method of load transfer through an adhesive bonded joint is by shear. This means that the design mnst avoid peel, cleavage, and normal tensile stresses. One practical apphcation of a method avoiding other than shear stresses is the nse of a rivet bonded construction (Fig. 4.35). The direction of the fibers in the onter ply of the composite (against the adhesive) should not be 90° to the expected load path. 

---