Durability of Bonded Joints for Low and LO Repair of High Performance Composite Structures

The objective of SBIR Phase I project has been successfully accomplished, beyond the proof-of-concept study. The achievements include: (1) developed an innovative M-integral method; (2) developed and validated 2-D environmentally induced degradationmodels; (3) implemented autoadaptive mesh technology in composite bonded joints, especially in the region of stress concentrations; (4) demonstrated the validity and applicability of the algorithms by comparing with experimental results for the double-lapshear specimen; and (5) developed a prototype software BondJoint. The goal of the Phase II project is to provide a complete design solution to predict the long-term lifetime durability of composite structures with bonded joints under realistic service environments including cyclic moisture, cyclic temperature, andcyclic mechanical loading. To achieve this objective, the following innovative tasks have been identified and will be carried out: (1) identification of failure initiation site from corners by the use of M-integral for extraction of generalized stressintensity factors; (2) comprehensive failure criteria coupled brittle and ductile materials together; (3) crack growth (damage) simulation algorithm enabling to trace arbitrary crack growth path; (4) comprehensive degradation models with time-dependent andcoupled diffusion-reaction characteristics fro three materials systems, FM-300, PMR-15, and BMI; (5) Windows NT based software promises a wide applicability; and (6) flexible software structure to accommodate the user-defined failure criteria. A simulationdesign tool, BondJoint, will be generated to perform accurate durability, damage, and design evaluations and to predict accurately the long-term lifetime durability of bonded joint under realistic service conditions for repair of current aircrafts and fornext generation aircraft fleet.