Characterization of Flexible Adhesive for Composite Bolted/Bonded Joint

Student: Gyu Hyeong Lim, Master Student

Supervisor: Prof. Larry Lessard

Sponsors: Bombardier Aerospace, L-3 Communication, Delastek, National Research Council

This project investigates the joining of composite materials using a simultaneously bolted and bonded joint, otherwise known as a hybrid joint. There is a clear benefit for combining the bolt and bond: mechanical efficiency of the bond and the fatigue resistance of the bolt.  However, due the considerable stiffness of common industrial adhesives, the bond tends to carry most of the load.  In order to improve the joint efficiency, it is advantageous to implement a more flexible adhesive to hybrid joints. Preliminary finite element analysis also shows that the flexible adhesive alleviates the stress concentration inside the bond.

My work concerns characterization of flexible adhesive. Initially, tensile tests are performed to obtain the nonlinear stress/strain response, Poisson’s ratio, and the failure properties. Biaxial tests follow in an attempt to capture the yielding of the flexible adhesive under various biaxial loadings. Lastly, the adhesive is tested under cyclic loading to capture the post-yielding properties. Digital Image Correlation is actively employed for the measurement of large deformation.

Optional study performs testing for hybrid joint under cyclic loading, in order to investigate how repeated yielding of adhesive affects the joint performance. This testing is a representation of an aircraft in service carrying out repeating flights.