Publications Details
Damage Tolerance Assessment of Bonded Composite Doubler Repairs for Commercial Aircraft Applications
One of the concerns surrounding composite doubler technology pertains to long-term survivability, especially in the presence of non-optimum installations. This test program demonstrated the damage-tolerance capabilities of bonded composite doublers. The fatigue and strength tests quantified the structural response and crack-abatement capabilities of boron-epoxy doublers in the presence of worst-case flaw scenarios. The engineered flaws included cracks in the parent material, disbonds in the adhesive layer, and impact damage to the composite laminate. Environmental conditions representing temperature and humidity exposure were also included in the coupon tests. Large strains immediately adjacent to the doubler flaws emphasize the fact that relatively large disbond or delamination flaws (up to 100 diameter) in the composite doubler have only localized effects on strain and minimal effect on the overall doubler performance (i.e., undesirable strain relief over disbond but favorable load transfer immediately next to disbond). This statement is made relative to the inspection requirement that result in the detection of disbonds/delaminations of 0.5 '' diameter or greater. The point at which disbonds become detrimental depends upon the size and location of the disbond and the strain field around the doubler. This study did not attempt to determine a "flaw size vs. effect" relation. Rather, it used flaws that were twice as large as the detectable limit to demonstrate the ability of composite doublers to tolerate potential damage.