Delamination of reinforced polymer materials is one of the catastrophic and an unsolved mystery for composite structures. Very often, a composite structure under shear loading experiences an interlayer fracture. Among many of the fracture modes, crack initiation due to the failure of the matrix is very common. The polymer matrix is weaker in mechanical properties than the fibers and shows inferior shear performance under different loading conditions. In this study, epoxy layers under shear loading have been analyzed by cohesive contact generated by the finite element method by ABAQUS. The development of stress and failure features have been identified by existing cohesive zone theories. A comparative analysis has been performed for composite structures fabricated with neat epoxy and epoxy modified with electrospun carbon nanofiber. The qualitative study indicates composites structure fabricated from nanomaterial modified matrix may show different cohesive zone. Therefore, composite materials reinforced with an additional phase in the matrix may exhibit different delamination mechanics under short beam shear loading. A detailed analysis of the cohesive contact parameters has been introduced and to characterize the delamination behavior in the matrix layer in between the interlaminar region has been discussed. The current study indicates a change in the cohesive zone is necessary for better representation of nanofiber modified epoxy contact than the conventional epoxy layer analysis.
Relative motion between surfaces of mechanical parts causes surface wear and damage. The degradation to the surfaces has been monitored using vibration characteristics as well as acoustic emissions generated during the relative surface movements. In particular, acoustic emission signals were found to be sensitive to some of the microscopic processes occurring at the frictional interface. In this study, friction between two surfaces was monitored experimentally under controlled conditions. Relative velocity, contact pressure, and surface roughness values were varied in the experiments. Friction related acoustic emission signals were recorded and analyzed to understand the relationship between the signals generated and the physical processes giving rise to these signals. Information related to the stick-slip movements during cyclic motion, in the experiments, was observed from the signals. Features of the waveforms were found to reveal the conditions existing at the friction interface. In particular, the changes in the surface roughness and contact pressure were readily observed from the acoustic emission signals.
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