3D interfacial debonding during microbond testing: Advantages of local strain recording

The microbond (MB) test is the most widely adopted micromechanical test to characterize fibre matrix interfaces but typically lacks reliability and output for determining multi-parameter interface models. In the current research, the MB test is enhanced by incorporating Fibre Bragg Grating (FBG) sensors for local fibre strain monitoring. Strain-force data is used to analyse and validate the type and paramter values of a cohesive zone modelling (CZM) basis in the three-dimensional interface damage model. For the prepared epoxy resin droplets, that are used as a benchmark case, a bi-linear CZM traction-separation law is fitted for each droplet. The results confirm the selection of maximum FBG strain, force-strain profile with the two primary peaks in the force-strain derivative, and the peak force to be valid for proper interface characterization. The analysis of the performed tests clearly reveal the droplet fracture process to consist of four distinct stages. Only after the first stage, interfacial crack propagation independent of the point on perimeter is achieved. Full debonding occurs during the fourth stage.