Creep compliance characterization of vapor-grown carbon nanofiber/vinyl ester nanocomposites using a central composite design of experiments
The effects of vapor-grown carbon nanofiber (VGCNF) weight fraction, applied stress, and temperature on the viscoelastic response (creep compliance) of VGCNF/vinyl ester (VE) nanocomposites were studied using a central composite design (CCD). The nanocomposite test articles were fabricated by high shear mixing, casting, curing, and postcuring in an open face mold under a nitrogen environment. Short-term creep/creep recovery experiments were conducted at prescribed combinations of temperatures (23.8 - 69.2 C), applied stresses (30.2 - 49.8 MPa), and VGCNF weight fractions (0.00 - 1.00 parts of VGCNF per hundred parts of resin, phr) determined from the CCD. The response surface model (RSM) for predicting the creep compliance was developed using the least squares method and an analysis of variance procedure. The response surface estimates indicate that increasing the VGCNF weight fraction marginally increases the creep resistance of the VGCNF/VE nanocomposite at low temperatures (i.e., 23.8 - 46.5 C). However, increasing the VGCNF weight fraction for temperatures greater than 50 C decreased the creep resistance of these nanocomposites. The latter response may be due to a decrease in the nanofiber-to-matrix adhesion as the temperature is increased. The creep compliance RSM revealed the interactions between the VGCNF weight fraction, stress, and temperature on the creep behavior of thermoset polymer nanocomposites. 2012 AIAA.