ABSTRACT
Fatigue properties of polyetheretherketone (PEEK) and multiwall carbon nanotube (CNT) reinforced PEEK were investigated with the ultrasonic fatigue testing method. Lifetimes were measured in the high and very high cycle fatigue regime at resonance frequency 19 kHz and load ratio R = -1. Pulse-pause loading served to avoid specimen self-heating and led to effective cycling frequencies in the range from several hundred Hz to about two kHz. Stress amplitude for 50 % fracture probability at 109 cycles is 21.2 ± 4.3 MPa for unreinforced PEEK (22 % of its tensile strength) and 33.5 ± 3.5 MPa for CNT reinforced PEEK (33 % of its tensile strength). Servohydraulic fatigue tests at 22 Hz with CNT reinforced PEEK delivered fatigue lifetimes comparable to ultrasonic tests, i.e. no frequency effect and no influence of load versus displacement control was observed. Keeping specimen temperature far below the glass transition temperature, ultrasonic fatigue testing of a high temperature resistant plastic was successfully implemented.
ABSTRACT
A hybrid functional nanomaterial was synthesized by functionalizing carbon nanofibers (CNF) with polyhedral oligomeric silsesquioxane (POSS). The reaction between CNF and the amine group of ocataminophenyl POSS was achieved using carbodiimide chemistry. The CNF-POSS hybrids were designed to increase the reactivity of CNF without affecting its inherent properties. The reactive amine groups of CNF-POSS were further modified with an oligomer of polyimide polymer to improve the interaction with the polymer matrix, thus forming a nanocomposite with enhanced multifunctional properties. Functionalization was characterized using thermal gravimetric analysis (TGA), x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).