As a piezoelectric polymer, poly (vinylidene fluoride) (PVDF) is attractive in energy conversion applications between electrical and mechanical forms because of its low cost, high flexibility, and biocompatibility. The piezoelectricity of electrospun PVDF polymer is due to changes in the crystalline structure (e.g., creating the β‐phase) during the electrospinning process. This research focuses on two approaches for investigation of β Phase formation: (1) addition of LiCl in different concentrations (0.001, 0.00133, 0.002, 0.004 wt%) as inorganic salt to the polymer solution, (2) increasing tension along the fiber axis by increasing the collector drum speed during the aligning process. Performances of these structures were evaluated by using X‐ray diffraction (XRD), Fourier Transform Infrared (FTIR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). A one‐step nano‐generator and cost‐effective package based on electrospun nanofibers was presented to measure output voltages as a performance factor. Results show that the addition of LiCl leads to β Phase formation in the crystalline structure, decreasing fiber diameter to 65 nm, and increment in the work of rupture and piezoelectric output. Moreover, the results show that increasing collector drum speed causes the alignment of β‐crystallites along the fiber axis and subsequently no considerable effect on the formation of β‐phases and output voltage. POLYM. ENG. SCI., 56:61–70, 2016. © 2015 Society of Plastics Engineers

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In this article, a new method for temperature compensation on the basis of artificial neural networks (ANNs) in impedance-based structural health monitoring (ISHM) has been introduced. ISHM using piezoelectric wafer active sensors (PWAS) has been extensively developed to provide detection of fault in structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. Any change in structure leads to changes in mechanical impedance of structure. The electrical impedance of PWAS can sense this change by the electromechanical coupling effect of PWAS. Therefore, the difference in this electrical impedance for undamaged and damaged structures can be considered as a damage index to detect the damage in structure. Since physical and mechanical properties of structure also PWAS materials are temperature dependent, so this electrical impedance of PWAS will be affected by temperature changes. Consequently, the variation in environmental or service temperatures can be detected erroneously as damage in ISHM method. In this article, a new method using ANN based on radial basis function (RBF) has been proposed and developed to compensate the temperature effect on the damage index. A steel plate and gas pipe with bolted joints are considered as two case studies for the performance evaluation of the proposed fault detection methodology. Results confirm that the proposed method using the ANN can be effectively utilized to compensate temperature variation for damage detection in different structures.

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In the recent years, the piezoelectric wafer active sensors (PWASs) are increasing as a measurement tool in structural health monitoring techniques. In impedance-based structural health monitoring (ISHM) method, the electrical impedance of a PWAS bonded to the structure is measured and served as a defect detection index of the structure. The principle of this method is based on the electromechanical coupling effect of PWAS materials. As any change in the structure will lead to a change in mechanical impedance of structure, the electrical impedance of PWAS could sense this change by the electromechanical coupling effect of PWAS. Since the physical and mechanical properties of PWAS materials are temperature-dependent, so the electrical impedance of PWAS will change with varying temperature. Consequently, the changes in environmental or service temperatures could be detected in ISHM method as a defect. In this article, in order to consider the temperature dependency of PWAS material properties, a temperature-dependent model is developed for a PWAS bonded to an Euler Bernoulli cantilever beam. An aluminum (alloy 2024) beam was examined experimentally by ISHM method in order to validate the proposed model. The comparison of theoretical and experimental results demonstrates a good improvement in ISHM modeling where temperature variation is present.