Carbon nanotubes commonly known as CNT, have outstanding properties and an extensive collection of applications. That is why these have gathered considerable attention recently. Researchers across the world have worked tirelessly over the last decade to produce CNT fiber, which has emerged as a distinct novel part of the carbon fiber family unit. The study of CNT both experimentally and theoretically has increased extensively because of its exceptional mixture of electrical, mechanical, thermal, chemical properties [1]. Synergistic improvement in composite characteristics at small volume fractions is due to the inclusion of CNT in polymer matrices. Many studies and researches have been done regarding the mechanical properties of the interface between CNT and matrix. Because of the outstanding properties of CNTs, these are planned to be used as field-effect transistor (FET) materials, nanoscale wire materials, electron emission sources, chemical sensors, optical communication switches, high strength composites, and thermal devices. CNTs acquire high tensile modulus and strength. Strong composites can be designed and fabricated by using the CNTs as reinforcing filler and thus can be used to develop and produce strong composites. The mechanical strength of the composites can decrease due to defective CNTs. Some of the defects are Stone-Wales (SW) and vacancy defects. The outcome of the mechanical properties is important to analyze when any of the parameters are mean to vary. On varying the input values of parameters, the mechanical properties of SWCNT-PP nanocomposites can be affected considerably. This study will be focused on analyzing this impact. Many researchers have been interested in the influence of strain rates on the mechanical behavior of several nanocomposites in recent years. It was found that strain rate has enhanced the mechanical properties. Thus strain rate is one of the key factors that play a vital role to enhance the mechanical property of nanocomposites. In past studies, the SWCNT/PP nanocomposites have not been investigated by varying the strain rate. In this study, the influence of compressive strain rate on SWCNT/PP nanocomposites has been examined.
Parvaneh and Shariati [2] examined the influence of SW defects and vacancy defects on Young’s modulus of SWCNT. A structural mechanics model was constructed to investigate Young’s modulus. The tension test was reported as the best method for measuring Young’s modulus of CNT. It was concluded that when CNTs are sufficiently large, imperfections have a negligible effect. Jacob et al. [3] reviewed the impact of strain rate on the mechanical properties. It was observed that many researchers have looked into the effect of variable loading rate on the tensile, compressive, shear, and flexural properties of fiber-reinforced nanocomposites, with a range of conflicting explanations and conclusions. Saxena and Lal [4] investigated the effects on the mechanical properties of SWCNT produced by SW defects and vacancy defects. The vacancy and SW defects ranged from 1 to 4 and their relative positions and orientations were varied. The investigation reported that vacancy defects have reduced the tensile strength and strain more than the SW defects. Yang et al. [5] studied the effect of SW defect on the characteristics of SWCNT/PP composites using the molecular dynamics (MD) simulation technique. A (15,0) zigzag CNT with several defects i.e. 0, 5, 10, 15 were studied. The strain rate was put as 0.0001/ps. The outer strain was amplified up to 2% in all defects cases. It was seen that Young’s modulus of SWCNTs decreased when the number of SW defects rises. As the number of SW defects increases, the interfacial bonding becomes stronger, improving the transverse Young’s modulus and two shear moduli.
Sharma et al. [6] investigated the consequence of SW and vacancy defects on Young’s modulus of CNTs and their nanocomposites. The impact of varying the diameter of faulty SWCNTs on their Young’s modulus was also investigated using MD modeling. The study showed that as the diameter and the number of defects in armchair SWCNT were increased, the elastic moduli were gradually degraded. The moduli of SWCNTs having SW defects declined at a faster rate than the moduli of CNTs with vacancy defects as the number of defects was increased. It was deduced that the presence of SW or vacancy defects in an SWCNT system degrades the mechanical characteristics of the structure. It was also found that in contrast to SWCNTs with SW defects, the percentage rise in different moduli with increasing volume fraction (Vf) was larger for SWCNTs having vacancy flaws. Li et al. [7] examined the results of temperature, strain rate, and molecule length on the deformation of graphene/polyethylene composites. It was seen that the host molecules migrated more easily at higher temperatures to suit the strain during deformation. It was observed that the nanocomposite model’s atoms were more stress-free to meet the strain when the strain rate was lower.
Zhang et al. [8] investigated the impact of strain rate and temperature on the interfacial property of glass fiber reinforced PP nanocomposites by MD simulation. Since at higher strain rates atoms do not have enough time, interfacial strength was improved as the strain rate was increased. It was found that with the increase of strain rate the yield stress and elastic modulus were increased. The study suggested that the atoms were less stress-free at greater strain rates, requiring more fracture energies for the ultimate fracture, resulting in higher interfacial strength at the glass fiber-PP interface. Khan et al. [9] used functionalized MWCNTs and hydroxyapatite nano-rods reinforced with PP for bio-medical applications. Schossig et al. [10] observed the consequence of strain rate on mechanical properties of reinforced polyolefins. High-speed tensile tests were performed on glass-fiber reinforced thermoplastic materials. PP and polybutene-1 having the weight percentage (%wt) 0, 20, 30, and 40 of glass fiber were used. The results of the tests revealed that the glass fiber reinforced polypropylene (GFRPP) and polybutene-1 (PB-1) exhibit a positive strain rate dependent relative nature as well. In contrast to low strain rates, high strain rates resulted in a stronger increase in tensile strength. It was reported that PP materials have superior strength levels than PB-1 materials. Fitoussi et al. [11] examined the influence of the strain rate on the mechanical properties of a discontinuous glass fiber reinforced ethylene-propylene copolymer matrix nanocomposite. A 50 percent increase in Young’s modulus with the increase in strain rate was observed. A substantial rise in the damaging stress and strain thresholds was observed.
Notta-Cuvier et al. [12] studied the influence of strain rate and heterogeneous fiber orientation on the mechanical behavior of short-glass fiber reinforced PP. The composite’s tensile macroscopic behavior was investigated in a quasi-static and dynamic range from 1 mm/min to 1 m/s at various angles of loading concerning the injection flow direction and variable displacement rates. It was observed that tensile strength and stiffness increased with the increment in strain rate. Cui et al. [13] studied the impact of strain rates on mechanical characteristics and failure behavior of long glass fiber reinforced (LGFR) thermoplastic composites. At high strain rates, the increase in ultimate strength and breakage strain of LGFR-PPs was due to improvements in interfacial bonding characteristics and energy amalgamation capacity. Kim et al. [14] investigated the strain rate-dependent mechanical behavior of glass fiber reinforced polypropylene nanocomposites. Zhang et al. [15] investigated the impact of strain rate and temperature on the interfacial property of glass fiber reinforced PP nanocomposites by MD simulation. It was reported that the interfacial strength of the glass fiber-PP interface reduced when PP molecules shifted more easily to adjust tensile strain.
From the literature, it could be seen that inadequate work has been done to analyze the effect of compressive strain rate on mechanical properties of SWCNT reinforced PP nanocomposites. MD simulation can provide useful atomistic insights into the compressive behavior of SWCNT/PP composites. The effect of SW and vacancy defective CNTs on the mechanical properties of PP composites have also been predicted using MD simulation. The results obtained from this study could be useful for the researchers designing PP based materials for compression loading to be used for bio-medical applications.