Strain-rate sensitivity analysis of microwave processed polypropylene-carbon nanotube composites

Abstract

The study investigates the strain rate sensitivity of microwave-processed polypropylene nanocomposites containing a 10% volume fraction of multi-walled carbon nanotubes (MWCNTs), synthesized using a domestic microwave applicator (DMA). Through experimental analysis under various loading conditions including tensile, flexural, and multistep relaxation loads, the mechanical strength of these nanocomposites is assessed alongside destructive testing and scanning electron microscopy (SEM) results. Mathematical models are proposed to elucidate the mechanical response under different strain rate loadings. The nanocomposite exhibits elastoplastic behavior, with maximum elongation observed at a strain rate of 3 mm/min. During uniaxial tension tests, the ultimate strength increases significantly from 5.74 MPa at 1.52 mm/min to 13.8 MPa and 15.7 MPa at 1 mm/min and 2 mm/min respectively during multistep relaxation tests. The true stress-true strain curve follows a power law of strain hardening under high strain rate tensile tests. Flexural tests reveal maximum flexural strength and modulus at a strain rate of 1.25 mm/min, with elongation peaking at 1.50 mm/min. Mechanical properties, including modulus and ultimate strength, show an increasing trend with strain rate until a limiting value is reached, beyond which thermal softening occurs. SEM fractography illustrates the random and spatial distribution of CNTs at low strain rates, whereas agglomeration and CNT pull-out are observed at higher strain rates. This comprehensive analysis sheds light on the intricate mechanical behavior of microwave-processed polypropylene nanocomposites, offering insights into their potential applications and optimization strategies.