The experimental and numerical analysis of the ballistic performance of elastomer matrix Kevlar composites

In this paper, the behavior of high-velocity impact of Kevlar fabric and elastomer composites was investigated both experimentally and numerically. The experimental tests were performed by a gas gun device and hemispherical projectiles at different velocities, ranging from 122 m/s to 152 m/s for 2- and 4-layer samples. The penetration resistance of these composites during impact was determined using ABAQUS/Explicit. The present study's novelty lies in choosing the finite element model for Kevlar fabric and elastomer matrix in composites with nonlinear behavior to estimate the damage mechanism in the impact zone. For this purpose, the material model of the formable was used to define the damage criteria for Kevlar, and the material model of the VUMAT was used to consider the non-linear behavior and damage evolution of elastomer matrix with one of the damage criteria. Then, the dynamic behavior of the laminate was studied by a Split Hopkinson Pressure Bar. The effect of the number of layers, the shape of the projectile, the energy absorption and failure mechanisms were studied. The verification of this numerical model with experimental observations showed good agreement. The results reveal that elastomeric composites can cause to increase energy absorption and reduce the damaged area

Development of a Lorentz force drive system for a torsional paddle microresonator using Focused Ion Beam machining

This thesis focuses on the concept, design, fabrication and characterisation of a torsional micro paddle resonator. The ultimate intention is to use the device for rapid detection of anthrax bacteria. A comprehensive research was carried out to review the state of the art in MEMS based mass sensing. Various driving and detection strategies were investigated and discussed. Based on evidence from literature, a novel approach was adopted to realise a device with improved functionality and overcome currently existing drawbacks. The working principle of the proposed device is based on electromagnetic actuation and monitoring of the shift in resonance frequency of a micro paddle. The design of the paddle was optimised using theoretical and finite element methods. Dual beam Focused Ion Beam (FIB) machining techniques were used to fabricate the prototype devices. The chosen substrate is a LPCVD 200 nm thick silicon nitride membrane. Prior to milling the substrate, the sputtering rate of silicon nitride was validated experimentally to ensure machining stability. Different actuating pattern designs were fabricated to generate torque including micro spiral coil, micro dual loop, and single conductive track on the micro paddle. The geometry was finalised for a defined working condition of 1 MHz resonance frequency. Important fabrication parameters were discussed and damage prevention issues were investigated. The sensitivity to the added mass was experimentally characterised and found to be 2.35 fg/Hz. To characterise the asymmetrical paddle resonator, piezoelectric excitation was applied to the device and a laser Doppler vibrometer was used to record the resonant frequency. Resonant frequencies of 0.841 and 0.818 MHz were detected by testing the device in an air medium and a quality factor of about 300 was calculated by applying a Lorentzian curve fit to collected data

Experimental investigation of quasi-static behavior of composite and fiber metal laminate panels modified by graphene nanoplatelets

The current study investigated the influence of incorporation of graphene nanoplatelets (GNPs) on quasi-static behavior of composite and fiber metal laminate (FML) panels. The unmodified and modified composite specimens and FML panels with 2/1 configuration were fabricated using a hand lay-up method and investigated through a quasi-static punch and indentation testing. The two sets of tests were conducted with a flat-ended indenter and the loading conditions were the same for all samples, except support spans which were varied. Following experimental testing, possible damages at the punch region were closely investigated and localized and global damages were observed. The results revealed that adding 0.2 wt% GNPs improved the strength and fracture toughness of specimens by delaying the failure modes. On the contrary, GNPs made the bonding between the aluminum and composite interface to weaken