Abstract:
The effects of environment on the interfacial bond strength of carbon fiber tow embedded in epoxy resin are being studied through accelerated aging experiments and pull-out tests (PT). The goal is to examine the synergistic effects of hot, cold, wet, dry and stressed environment on interfacial bond strength (IFBS) of carbon/epoxy composites in order to forecast life of composites in severe environments. The PT specimens were prepared by embedding a fixed length of a carbon fiber tow in uncured epoxy. The interfacial debonding between resin and fiber tow is the targeted mode of failure. A spring loaded frame was designed for applying a preset load to multiple PT specimens. All the PT specimens including the frames with the stressed specimens were subjected to accelerated environmental aging conditions for different time intervals. The moisture absorption and desorption data were recorded. The PT tests were then carried out by pulling the carbon fiber tow from the cylindrical resin, mounted in a screw driven MTS testing machine. Average IFBS of approximately 21.5 MPa was observed for the unaged control sample. The hot/wet/stressed (70ºC/3% moisture/2 lb) specimens show a significant degradation (-29.03 %) in bond strength after 176 days of aging time. The degradation due to moisture is seen to be more critical under the influence of temperatures (50°C, 70°C). In order to obtain the maximum interfacial shear strength for various embedded lengths and environmental aging parameters, a numerical analysis has been carried out using a 3D finite element model (FEM). A FEM analysis was done using cohesive elements at the fiber/matrix interface in order to study the environmental aging effects at the interface. The predicted bond strength from the numerical analysis was compared with the experimental data. A reasonable agreement was observed between experimental data and Finite Element Analysis (FEA).
