In this work, we propose a constitutive model to describe the behavior of Piezoelectric Fiber Reinforced Composite (PFRC) material consisting of elasto-plastic matrix reinforced by strong elastic piezoelectric fibers. Computational efficiency is achieved using analytical solutions for elastic stifness matrix derived from Variational Asymptotic Methods (VAM). This is extended to provide Structural Health Monitoring (SHM) based on plasticity induced degradation of flapping frequency of PFRC. Overall this work provides an effective mathematical tool that can be used for structural self-health monitoring of plasticity induced flapping degradation of PFRC flapping wing MAVs. The developed tool can be re-calibrated to also provide SHM for other forms of failures like fatigue, matrix cracking etc.
Flapping wing Micro Air Vehicles (MAVs) are a class of bio-inspired autonomous flying robots that have stringent weight and size restrictions, making them attractive for many military as well as civilian applications. In this work, a novel material is proposed for both the structure and the flapping actuator of the MAV. The said material is a kind of piezoelectric fiber composite, called Macro Fiber Composite (MFC). MFC is made by combining piezoelectric fibers in epoxy-based polymer materials and electroded in an inter-digitated manner. The focus of this paper is to address the challenge of designing suitable power electronics for this piezocomposite actuator. The requirements of a light weight, high voltage (-500V to 1500V) drive circuit drawing power from low voltage sources, such as on-board batteries, are addressed. The paper presents the detailed design and simulation of such a drive circuit for MAV applications. The designed circuit first generates a DC voltage of 1500V from 5V DC by using a voltage multiplier and a fly back converter. This high voltage DC signal is then converted to a high voltage AC signal (in the required range of -500V to 1500V AC) by using a H-bridge inverter circuit. PWM signals are used for proper amplitude control of the output signal. The designed circuit is simulated in MATLAB Simulink and the desired results are obtained. The entire design is done to meet the stringent weight requirement of MAV and the circuit can effectively drive the piezoelectric composite actuator.
This paper deals with the evaluation of the component‐laminate load‐carrying capacity, i.e., to calculate the loads that cause the failure of the individual layers and the component‐laminate as a whole in four‐bar mechanism. The component‐laminate load‐carrying capacity is evaluated using the Tsai‐Wu‐Hahn failure criterion for various layups. The reserve factor of each ply in the component‐laminate is calculated by using the maximum resultant force and the maximum resultant moment occurring at different time steps at the joints of the mechanism. Here, all component bars of the mechanism are made of fiber reinforced laminates and have thin rectangular cross‐sections. They could, in general, be pre‐twisted and/or possess initial curvature, either by design or by defect. They are linked to each other by means of revolute joints. We restrict ourselves to linear materials with small strains within each elastic body (beam). Each component of the mechanism is modeled as a beam based on geometrically nonlinear 3‐D elasticity theory. The component problems are thus split into 2‐D analyses of reference beam cross‐sections and nonlinear 1‐D analyses along the three beam reference curves. For the thin rectangular cross‐sections considered here, the 2‐D cross‐sectional nonlinearity is also overwhelming. This can be perceived from the fact that such sections constitute a limiting case between thin‐walled open and closed sections, thus inviting the nonlinear phenomena observed in both. The strong elastic couplings of anisotropic composite laminates complicate the model further. However, a powerful mathematical tool called the Variational Asymptotic Method (VAM) not only enables such a dimensional reduction, but also provides asymptotically correct analytical solutions to the nonlinear cross‐sectional analysis. Such closed‐form solutions are used here in conjunction with numerical techniques for the rest of the problem to predict more quickly and accurately than would otherwise be possible. Local 3‐D stress, strain and displacement fields for representative sections in the component‐bars are recovered, based on the stress resultants from the 1‐D global beam analysis. A numerical example is presented which illustrates the failure of each component‐laminate and the mechanism as a whole.
Apart from the inherent anomalous behaviour under tensile and compressive structures, auxetic structures have shown improved energy absorption characteristics that are of prime interest to various fields of study. This is further exemplified by additive manufacturing (AM) techniques and polymer composites to tailor the shape, geometry and form of these structures. Consequently, this paper aims to characterise the in-plane compressive behaviour and negative Poisson’s ratio (NPR) of the most prominent auxetic structures fabricated additively used polymer nanocomposite materials. The study incorporates the use of glycol-modified polyethylene terephthalate (PETG) and nanocomposites of PETG filled with organically modified montmorillonite (OMMT) nanoclay particles to produce auxetic structures fabricated through fused filament fabrication (FFF). Different structures such as hexagonal re-entrant honeycomb structures, peanut-shaped honeycombs, chiral honeycomb structures and missing rib structures are characterised for their compressive performance through experimental approaches involving mechanical testing and digital image correlation (DIC). Different parameters such as the peak crushing strength, average crushing strength, NPR, specific energy absorption (SEA), and crush force efficiency (CFE) of these structures are evaluated at different strain rates/loading rates for varying concentrations of nanoclay and PETG. It is observed that higher loadings of nanoclay particles lower the compressive strength of the structures. Additionally, the NPR decreases with increasing strain rates and is also influenced by the composition and the resultant stiffness. Moreover, the geometrical parameters of the structure largely influence its strain energy absorption. The results have shown that such material-structure combinations can produce structures of high-performance capabilities suitable for aerospace applications.
The goal of the current study is to determine how the mechanical performance of hybrid composites is impacted by the fibre composition, layering arrangement and sequencing. Hand-layup approach was used to create four distinct hybrid composites with five lamina comprising varied stacking sequences of jute/coir/carbon fibres. The skin layers only encapsulate bio-fibres orientated horizontally. CJKJC, CKJKC, CJCJC and CKCKC were the stacking sequences, with C, J and K representing carbon fibre mat, jute fibres (unidirectional) and coir fibres (unidirectional). The fibres in the core layer were oriented perpendicular to the enclosing adjacent plies and they may be jute/coir fibres depending on the stacking sequence. Stress vs. strain curves shows that all the proposed composites fail suddenly exhibiting a linear trend except for the sample with a significant concentration of coir fibres. Jute fibre layers added strength and energy-absorbing capability to the composites, whereas coir fibre layers added strain and toughness. It is found from the present study that incorporating the fibres of carbon in the core and skin enhances the mechanical properties compared to its counterparts. The fractography of the proposed composites are studied using scanning electron microscope.
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