Applying the genetic algorithm for determination electrospinning parameters of poly vinylidene fluoride (PVDF) nano fibers: theoretical & experimental analysis

Poly Vinylidene Fluoride (PVDF) because of its piezoelectric properties has been applied in different applications such as smart textiles, medical application and membranes for energy harvesting. It was declared that nanofibres diameters and electrospinning parameters could be enhanced the piezoelectric properties of these materials. The main objective of this paper is applying the Genetic Algorithm (GA) to determine the optimum condition of solution parameters and processing conditions based on the desired diameter size of PVDF fibers to produce the fibers without any structural faults. In this method, The Fitness function was determined by a simple analytical model presented by Fridrikh. Toward approving the GA results the experimental tests were done. the effect of four parameters such as flow rate of the polymer solution, electrospinning voltage, electrospinning distance and polymer concentration on the fiber formation and fiber diameter size of electrospun PVDF fibers have been explored by Scanning Electron Microscopy (SEM) to attest the accuracy of the model. Assessment of experimental and theoretical results show that electrospinning parameters determined by GA method leads to achieve desire fiber diameters. Because of time and energy consuming of electrospinning process, the GA method may be useful to achieve desired fiber diameter by determining electrospinning parameters for polymers prior to fiber production

Fatigue Damage Identification and Remaining Useful Life Estimation of Composite Structures using Piezo Wafer Active Transducers

The prediction of fatigue damage accumulation is a crucial element in the estimation of the Remaining Useful Life of composite structures subjected to cyclic loading. In this paper, two Glass-Fibre Reinforced Plastics, a thin strip and a thick beam, are subjected to fatigue load while being monitored with Piezo Wafer Active Sensors. Two distinct methods, one based on Electro-Mechanical Impedance Spectroscopy (EMIS) and one based on the Reconstruction Algorithm for Probabilistic Identification of Damage (RAPID), are employed. Both methods are mostly used for damage detection, yet not for damage accumulation monitoring. The results presented in this paper show that damage accumulation can be followed during fatigue loading of the test objects. The trends shown in the damage accumulation graphs give an indication of the damage accumulation, and even a change in the damage evolution stage, yet a complete RUL estimation is not possible without further analysis of the experiments, possibly assisted by numerical modelling

Demodulation-derived damage metrics for nonlinear wave modulation-based health monitoring of structures

Nonlinear wave modulation (NWM) is a promising technique for structural health monitoring and contact-type damage detection. In NWM, the severity of the damage is proportional to the intensity of the modulation. Spectral analysis is often employed to calculate the Modulation Index (MI), and the damage intensity. According to some recent studies, damage metrics obtained by demodulation of the sensory signal can provide more information about the damage than spectral MIs. The Hilbert Transform (HT), Synchronous Demodulation (SD), Short-Time Fourier Transform (STFT), and more recently, In-Phase/Quadrature Homodyne Separation (IQHS) have been used to demodulate the sensory signal and extract effective damage metrics in the NWM technique. The objective of this work is to investigate demodulation methods to obtain reliable amplitude and frequency modulation damage indicators. The drawbacks of the HT and original IQHS methods are discussed, and a Modified-IQHS (M-IQHS) method is proposed to address them. The M-IQHS is validated analytically and experimentally, with the latter taking place in a sandwich panel setup with a loose bolt as the damage, and the results are compared to their HT and original IQHS-derived counterparts. The results show that the M-IQHS can improve NWM damage detection by providing precise modulation metrics for any range of pump frequency, including ultrasonics. It can also provide information about the MI distribution for signals with multiple sidebands. Furthermore, of the demodulation algorithms developed for NWM so far, M-IQHS is the most noise-resistant.</p

Effect of vacancy defects on transport properties of

The effect of vacancy defects on electrons transport behavior of the alpha-armchair graphyne nanoribbons has been studied by density-functional tight-binding and non-equilibrium Green’s function methods. Three different widths of the nanoribbons with 6, 7 and 8 atoms and four types of vacancy defects contain one, two, three and four missing atoms were selected in this study. In relaxed structures, the structural changes around the defects are observed. Some of the free hands form new atomic chains containing 6 or 7 atoms. Comparing with perfect devices, the current decreases at the defective devices with 8 atoms width, whereas, it increases for devices with 6 atoms width. By calculating the density of states, transmission spectrums and molecular energy spectrums for devices with 6-atoms widths, there is a resonance state for DDOS and T(E) peaks in the QV device, while the peak of the density of states and transmission spectrums does not match in the SV1 device. Also, the results show that HOMO-LUMO gap energy in the SV1 device is much more than the perfect and QV devices. For devices with 8 atoms width, the transmission spectrums are reduced for all defects due to the lower density of the energy level of molecular energy. However, the orbital distribution of LUMO state in the device with the defect is localized but for the perfect structure, both the LUMO and the HOMO orbital distribution are quite delocalized

Nanofibers-based piezoelectric energy harvester for self-powered wearable technologies

The demands for wearable technologies continue to grow and novel approaches for powering these devices are being enabled by the advent of new energy materials and novel manufacturing strategies. In addition, decreasing the energy consumption of portable electronic devices has created a huge demand for the development of cost-effective and environment friendly alternate energy sources. Energy harvesting materials including piezoelectric polymer with its special properties make this demand possible. Herein, we develop a flexible and lightweight nanogenerator package based on polyvinyledene fluoride (PVDF)/LiCl electrospun nanofibers. The piezoelectric performance of the developed nanogenator is investigated to evaluate effect of the thickness of the as-spun mat on the output voltage using a vibration and impact test. It is found that the output voltage increases from 1.3 V to 5 V by adding LiCl as additive into the spinning solution compared with pure PVDF. The prepared PVDF/LiCl nanogenerator is able to generate voltage and current output of 3 V and 0.5 µA with a power density output of 0.3 µW cm−2 at the frequency of 200 Hz. It is found also that the developed nanogenerator can be utilized as a sensor to measure temperature changes from 30◦C to 90◦C under static pressure. The developed electrospun temperature sensor showed sensitivity of 0.16%/◦C under 100 Pa pressure and 0.06%/◦C under 220 Pa pressure. The obtained results suggested the developed energy harvesting textiles have promising applications for various wearable self-powered electrical devices and systems

Compressibility Behaviour of Warp Knitted Spacer Fabrics Based on Elastic Curved Bar Theory

Nowadays, the mechanical characterization of 3-D spacer fabrics has attracted the interest of many textile researchers. These Spacer fabrics present special mechanical and physical characteristics compared to conventional textiles due to their wonderful porous 3-D structures. These fabrics, produced by warp knitting method, have extensive application in automobile, locomotive, aerospace, building and other industries. In these applications, the compressibility behaviour plays a significant role in the fabric structural stability. This compressibility behaviour could be affected by different knitting parameters such as density of pile yarn, fabric thickness, texture design etc. The aim of this paper is to introduce and develop an appropriate elastic theoretical model to predict the compressibility behaviour of warp knitted spacer fabric (WKSF). Three theoretical models are proposed, based on modelling pile yarns as the curved bars and are improved in three steps: a) with same curvatures in weft and warp directions (model A), b) curved bar for warp direction and cantilever bar for weft direction (model B), and c) curved bars with two different curvatures in weft and warp directions considering the curvature variations under loading (model C: improved model). The results obtained by the proposed models have been compared with previous model based on simply cantilever bars theory in literature. The results show that the simulation data obtained by the model C are closer to the experimental results comparing to the models A and B. Model C based on different weave parameters could better predict the elastic compressibility behaviour of this kind of WKSF in order to compare with previous models

Theoretical expression of compressibility behaviour of warp knitted spacer fabrics

Nowadays, 3-D spacer fabrics characteristics become a highly interested concept for textile researchers. These products have extensive application in automobile, locomotive, aerospace, building and other industries. Several techniques could be applied to produce spacer fabrics using woven, weft and warp knitting technology. Warp knitting is the most commonly used technology for production of spacer fabrics. Spacer fabrics present special characteristics compared to conventional textiles due to their wonderful porous 3-D structures. The compression resistance is a distinct feature beneficial for the structural stability of spacer fabrics, and it is proper to fulfil permanent or instant loading and recovery requirements. The goal of this research is to develop an theoretical model to predict the compressibility behaviour of warp knitted spacer fabric and compare it with experimental data. All required samples were produced on two needle bars Rachel warp knitting machine with different thickness, stitch densities and texture designs. The basic theory is based on modelling pile yarns as curve bar. The theoretical results related to the assumption of pile yarn as curve bar are closer to the experimental results of these spacer fabrics comparing to the previous theoretical models in literature