Electro-mechanical Behavior of Graphene–Polystyrene Composites Under Dynamic Loading

An experimental investigation was conducted to understand the electro-mechanical response of graphene reinforced polystyrene (PS) composites under static and dynamic loading. Graphene/PS composites were fabricated using a solution mixing approach followed by hot-pressing. Absolute resistance values were measured with a high-resolution four-point probe method for both quasi-static and dynamic loading. A modified split Hopkinson (Kolsky) pressure bar apparatus, capable of simultaneous mechanical and electrical characterization, was developed and implemented to investigate the dynamic electro-mechanical response of the composites. In addition to measuring the change in electrical resistance as well as the dynamic constitutive behavior, real-time surface damage and global deformation was captured using high-speed photography. The real-time damage was correlated to both stress–strain and percent change in resistance profiles. The experimental findings indicate that the bulk resistance of the composite increased significantly due to the brittle nature of the PS matrix and the presence of relative agglomerations of graphene platelets which resulted in micro-crack formations. Scanning electron microscopy imaging gives further insight into the various damage mechanisms that occur within the composites subjected to a static or dynamic load. The results show that the change in transport properties can provide further insight into the micro-structural evolution of composite materials during loading

Sensitivity and dynamic electrical response of CNT-reinforced nanocomposites

A series of dynamic compressive experiments were performed to experimentally investigate the electrical response of multi-wall carbon nanotube (CNT)-reinforced epoxy nanocomposites subjected to split Hopkinson pressure bar (SHPB) loading. Low-resistance CNT/epoxy specimens were fabricated using a combination of shear mixing and ultrasonication. Utilizing the CNT network within, the electrical resistance of the nanocomposite was monitored using a high-resolution four-point probe method during each compressive loading event. In addition, real-time deformation images were captured using high-speed photography. The percent change in resistance was correlated to both strain and real-time damage. The results were then compared to previous work conducted by the authors (quasi-static and drop weight impact) in order to elucidate the strain rate sensitivity on the electrical behavior of the material. Furthermore, the percent change in conductivity was determined using a Taylor expansion model to investigate the electrical response based on both dimensional change as well as resistivity change during mechanical loading within the elastic regime. Experimental findings indicate that the electrical resistance is a function of both the strain and deformation mechanisms induced by the loading. The bulk electrical resistance of the nanocomposites exhibited an overall decrease of 40-65% and 115-120% during quasi-static/drop weight and SHPB experiments, respectively. © 2012 Springer Science+Business Media, LLC

Dynamic Thermo-mechanical Response of Hastelloy X to Shock Wave Loading

A comprehensive series of experiments were conducted to study the dynamic response of rectangular Hastelloy X plates at room and elevated temperatures when subjected to shock wave loading. A shock tube apparatus, capable of testing materials at temperatures up to 900 °C, was developed and utilized to generate the shock loading. Propane gas was used as the heating source to effectively provide an extreme thermal environment. The heating system is both robust and capable of providing uniform heating during shock loading. A cooling system was also implemented to prevent the shock tube from reaching high temperatures. High-speed photography coupled with the optical technique of Digital Image Correlation (DIC) was used to obtain the real-time 3D deformation of the Hastelloy X plates under shock wave loading. To eliminate the influence of thermal radiation at high temperatures, the DIC technique was used in conjunction with bandpass optical filters and a high-intensity light source to obtain the full-field deformation. In addition, a high-speed camera was utilized to record the side-view deformation images and this information was used to validate the data obtained from the high temperature 3D stereovision DIC technique. The results showed that uniform heating of the specimen was consistently achieved with the designed heating system. For the same applied incident pressure, the highest impulse was imparted to the specimen at room temperature. As a consequence of temperature-dependent material properties, the specimen demonstrated an increasing trend in back-face (nozzle side) deflection and in-plane strain with increasing temperature. © 2013 Society for Experimental Mechanics

Electrical behavior of carbon nanotube reinforced epoxy under compression

An experimental investigation was conducted to study the effect of quasi-static and dynamic compressive loading on the electrical response of multi-wall carbon nanotube (MWCNT) reinforced epoxy nanocomposites. An In-situ polymerization process using both a shear mixer and an ultrasonic processor were employed to fabricate the nanocomposite material. The fabrication process parameters and the optimum weight fraction of MWCNTs for generating a well-dispersed percolation network were first determined. Absolute resistance values were measured with a high-resolution four-point probe method for both quasi-static and dynamic loading. In addition to measuring the percentage change in electrical resistance, real-time damage was captured using high-speed photography. The real-time damage was correlated to both load and percentage change in resistance profiles. The experimental findings indicate that the bulk electrical resistance of the nanocomposites under both quasi-static and dynamic loading conditions initially decreased between 40%-60% during compression and then increased as damage initiated and propagated

Electrical Response of Carbon Nanotube Reinforced Nanocomposites Under Static and Dynamic Loading

An experimental investigation was conducted to study the effect of quasi-static and dynamic compressive loading on the electrical response of multi-wall carbon nanotube (MWCNT) reinforced epoxy nanocomposites. An in-situ polymerization process using both a shear mixer and an ultrasonic processor were employed to fabricate the nanocomposite material. The fabrication process parameters and the optimum weight fraction of MWCNTs for generating a well-dispersed percolation network were first determined. Absolute resistance values were measured with a high-resolution four-point probe method for both quasi-static and dynamic loading. In addition to measuring the percentage change in electrical resistance, real-time damage was captured using high-speed photography. The real-time damage was correlated to both load and percentage change in resistance profiles. The experimental findings indicate that the bulk electrical resistance of the nanocomposites under both quasi-static and dynamic loading conditions initially decreased between 40%-60% during compression and then increased as damage initiated and propagated. © 2011 Society for Experimental Mechanics

Electrical response of graphene reinforced composites under static and dynamic loading

An experimental investigation was conducted to understand the electro-mechanical response of graphene reinforced polystyrene composites under static and dynamic loading. Graphene-polystyrene composites were fabricated using a solution mixing approach followed by hot-pressing. Absolute resistance values were measured with a highresolution four-point probe method for both quasi-static and dynamic loading. A modified split Hopkinson (Kolsky) pressure bar apparatus, capable of simultaneous mechanical and electrical characterization, was developed and implemented to investigate the dynamic electro-mechanical response of the composites. In addition to measuring the change in electrical resistance as well as the dynamic constitutive behavior, real-time damage was captured using high-speed photography. The real-time damage was correlated to both stress-strain and percent change in resistance profiles

Tailoring of electro-mechanical properties of graphene reinforced templated composites

A capillary-driven particle level templating technique was utilized to disperse graphite nanoplatelets (GNPs) within a polystyrene matrix to form multi-functional composites that possess tailored electro-mechanical properties. Utilizing capillary interactions, highly segregated composites were formed via a melt processing procedure. Since the graphene particles only resided at the boundary between the polymer matrix particles, the composites possess tremendous electrical conductivity but poor mechanical strength. To improve the mechanical properties of the composite, the graphene networks in the specimen were deformed by shear. An experimental investigation was conducted to understand the effect of graphene content as well as shearing on the mechanical strength and electrical conductivity of the composites. The experimental results show that both the mechanical and electrical properties of the composites can be altered using this very simple technique and therefore easily be intelligently optimized for desired applications

Massive electrical conductivity enhancement of multilayer graphene/polystyrene composites using a nonconductive filler

We report a massive increase in the electrical conductivity of a multilayer graphene (MLG)/polystyrene composite following the addition of nonconducting silica nanoparticles. The nonconducting filler acts as a highly effective dispersion aid, preventing the sheetlike MLG from restacking or agglomerating during the solvent casting process used to fabricate the composite. The enhanced dispersion of the MLG leads to orders of magnitude enhancement in electrical conductivity compared to samples without this filler