Application of Acoustic Emission to Study Debond Growth inudCo-cured/Co-bonded Composite Structures under Fatigue Loading

摘要

Increasing use of fibre-reinforced composite materials for primary and secondary componentsudin aircraft construction has resulted in the development of lightweight and efficient structures.udThe major emphasis is now towards realization of such structures at reduced cost. In order toudachieve this, newer concepts in design and manufacturing of structural composites are beingudexplored. One such concept is to make components with integral construction through co-curingudand co-bonding. Through this approach, one can integrate a number of sub-componentsudto realize assemblies in a single cure. Adhesive bonding is one of the most widely usedudprocesses for joining two structural members. Adhesive bonding is preferred to mechanicaludfastening in view of the better structural stiffness that can be achieved. However, the quality ofudbonding depends on a number of parameters and is very sensitive to the quality of the bondingudsurfaces. In view of this, it may be extremely difficult and impractical to expect the same degreeudof bond quality over the bonded region, especially with large aircraft structural components.udHence, we invariably end up with variations in the bond quality. There is a concern from theuddesigners as well as the certifying agencies with regard to these bond quality variations on itsudlong-tem structural performance. With this background, Advanced Composites Division, NAL,udhas projected a test programme to understand how the structure with inherent good bonds,udpoor bonds and debonds would behave and to what extent the presence of defects would reflectudon the structural integrity. It is essential that the growth of debonds, debond initiation at poorlyudbonded regions are monitored in real-time to assess the structural integrity. Among theudconventional Non-destructive Evaluation (NDE) techniques, Acoustic Emission (AE) isudprobably the only technique that would provide this information. In this paper, we describe theudapplication of AE technique to monitor defect initiation and growth of debonds during fatigueudcycling in co-cured/co-bonded structural components such as flaps for a civilian aircraft. Thisudprovides useful information towards establishing damage tolerance of a co-cured/co-bondedudcomposite structure.