Effect of Moderate Magnetic Annealing on the Microstructure, Quasi-Static, and Viscoelastic Mechanical Behavior of a Structural Epoxy

In this study, the effect of moderate magnetic fields on the microstructure of a structural epoxy system was investigated. The changes in the microstructure have been quantitatively investigated using wide angle X-ray diffraction (WAXD) and pole figure analysis. The mechanical properties (modulus, hardness, and strain rate sensitivity parameter) of the epoxy system annealed in the magnetic field were probed with the aid of instrumented nanoindentation, and the results are compared to the reference epoxy sample. To further examine the creep response of the magnetically annealed and reference samples, short 45 min duration creep tests were carried out. An equivalent to the macroscale creep compliance was calculated using the aforementioned nanocreep data. Using the continuous contact compliance (CCC) analysis, the phase lag angle, tan (δ), between the displacement and applied force in an oscillatory nanoindentation test was measured for both neat and magnetically annealed systems through which the effect of low magnetic fields on the viscoelastic properties of the epoxy was invoked. The comparison of the creep strain rate sensitivity parameter, A/d(0), from short term(80 s), creep tests and the creep compliance J(t) from the long term (2700 s) creep tests with the tan (δ) suggests that former parameter is a more useful comparative creep parameter than the creep compliance. The results of this investigation reveal that for the epoxy system cured under low magnetic fields both the quasi-static and viscoelastic mechanical properties have been improved.