Mutual dependence of experimental and data analysis features in characterization of fiber-matrix interface via microdroplets

The accurate determination of interfacial strength in composites poses a significant challenge, a critical factor yet often complex due to the multitude of unknowns that affect the microbond (MB) test. This complexity arises not only from different individual parameters, but also from the combined effects of these parameters interdepending with each other. This study presents a thorough analysis of the MB test, carried out through numerous finite element simulations that take into account a wide range of parameters. This was achieved in the context of an experimentally validated reference test. In this study, 624 different numerical simulations were performed, each using a unique set of parameters defined for this investigation. The study demonstrates that even minor modifications to features such as a change in droplet behavior (change in ductility - simulated via different material models), the normalized error can range from -2.5% to 20.6% and -10% to 80%, for peak force (F-max) and force-displacement area ((F -(delta)(area)), respectively. The negative percent values indicate lower magnitudes than the reference experimental data, while positive values suggest higher predicted magnitudes. In addition, residual stresses are identified as the second strongest in terms of mutual interaction and a key feature that interacts with other parameters. The results also show that typical comparisons using F-max and (F -(delta)(area) are inadequate and misleading, suggesting the use of critical stress and critical energy release rate for more accurate qualitative comparisons about the interface. In this work, the interdependencies between the selected features are investigated with the reasoning based on the interfacial crack propagation and associated dissipative phenomena of the droplet.

Automated summary

The accurate determination of interfacial strength in composites is a significant challenge due to the complexity of the microbond (MB) test. This study provides a thorough analysis of the MB test through finite element simulations and identifies residual stresses as an important factor affecting the results.