Abstract. This paper addresses the modeling of certain rate-dependent mechanisms which contribute to hysteresis inherent to piezoelectric materials operating at low frequencies. While quasistatic models are suitable for initial material characterization in some applications, the reduction in coercive field and polarization values which occur as frequencies increase must be accommodated to achieve the full capabilities of the materials. The model employed here quantifies the hysteresis in two steps. In the first, anhysteretic polarization switching is modeled through the application of Boltzmann principles to balance the electrostatic and thermal energy. Hysteresis is then incorporated through the quantification of energy required to translate and bend domain walls pinned at inclusions inherent to the materials. The performance of the model is illustrated through a fit to low frequency data (0.1 Hz -1 Hz) from a PZT5A wafer.
We investigated the chemical, mechanical and geometrical properties of basalt fibers from three different commercial manufacturers and compared the results with those from an industry standard glass fiber. The chemical composition of the fibers was investigated by X-ray fluorescence spectrometry, which showed that basalt and glass fibers have a similar elemental composition, with the main difference being variations in the concentrations of primary elements. A significant correlation between the ceramic content of basalt and its tensile properties was demonstrated, with a primary dependence on the Al2O3 content. Single fiber tensile tests at various lengths and two-way ANOVA revealed that the tensile strength and modulus were highly dependent on fiber length, with a minor dependence on the manufacturer. The results showed that basalt has a higher tensile strength, but a comparable modulus, to E-Glass. Considerable improvements in the quality of manufacturing basalt fibers over a three-year period were demonstrated through geometrical analysis, showing a reduction in the standard deviation of the fiber diameter from 1.33 to 0.61, comparable with that of glass fibers at 0.67. Testing of single basalt fibers with diameters of 13 and 17 µm indicated that the tensile strength and modulus were independent of diameter after an improvement in the consistency of fiber diameter, in line with that of glass fibers.
Typical soft armor systems are constructed of multiple layers of a single fabric type. This empirical research sought to begin optimization of these systems through hybridization, sequencing dissimilar armor fabrics to maximize their ballistic protective performance, by first investigating single plies with a spectrum of properties to determine their behavior and response to impact. Eight individual plain weave fabrics with varying yarns and thread counts were manufactured from para-aramid and ultra-high molecular weight polyethylene (UHMWPE) yarns and physical and ballistic characterizations were conducted. The ballistic impact tests established the specific energy absorption (SEA) of each fabric across a range of impact velocities (340–620 m·s–1) and the transverse displacement wave velocity across the rear of the fabric was found using digital image correlation. Low cover factor ( Cfab) fabrics (0.74–0.84) consistently showed faster transverse wave speed than the high Cfab fabrics (0.84–0.96) for any given yarn type. The relative SEA of the fabrics varied dependent on both the impact velocity and number of plies impacted. It was found that lower Cfab fabrics had the highest SEA, critical velocity and transverse wave velocity. UHMWPE fabrics were not considered suitable for a woven hybrid system as they had a significantly lower SEA compared to all the para-aramid fabrics. Results indicate that a hybrid system, when considered as a theoretical spaced system, would benefit from higher Cfab fabrics as rearward layers. However, transverse wave results suggest the lower response of these fabrics may inhibit lower Cfab fabrics at the front of a combined hybridized system.
In this study, the effect of fibre sizing on the modification of basalt fibres in preparation for use with a polypropylene matrix (PP) was investigated. Fibres were coated by the manufacturer with a standard available epoxy (EP) sizing and four experimental PP focused sizings (PPs1-4). Fibre with no sizing was produced to act as a control. The surface topography of sized fibre was analysed by SEM and AFM, indicating that PP sized fibres displayed a more inhomogeneous coating of the fibre. Furthermore, PP sizing resulted in an increase in AFM measured roughness by ~360%, translating to a 12.5% increase in surface area, over both unsized and EP fibres. Scratching of the fibre surface revealed, that in general, the coating thickness of PP was ~ 30nm thicker than EP sizing despite the same application parameters. XPS revealed that the sizing in all cases adhered to the fibre surface with an increase in potential reactive sites present on PP sized fibres. Analysis of fibre surface energy showed that the overall surface energy of fibres remained similar but the use of PP focused sizing resulted in a decrease of the polar component. Overall, this investigation shows that sizing has a significant effect on the fibre's surface: changing its topography and chemistry and hence, has an evident potential for increased mechanical and chemical bonding. This was further confirmed by single fibre fragmentation testing which highlighted that sizings PPs2-4 increase the interfacial shear strength by up to 117% compared to non-sized fibres.
This work studied the effects of adding short basalt fibers (BFs) and multiwalled carbon nanotubes (MWCNTs), both separately and in combination, on the mechanical properties, fracture toughness, and electrical conductivity of an epoxy polymer. The surfaces of the short BFs were either treated using a silane coupling agent or further functionalized by atmospheric plasma to enhance the adhesion between the BFs and the epoxy. The results of a single fiber fragmentation test demonstrated a significantly improved BF/epoxy adhesion upon applying the plasma treatment to the BFs. This resulted in better mechanical properties and fracture toughness of the composites containing the plasma-activated BFs. The improved BF/epoxy adhesion also affected the hybrid toughening performance of the BFs and MWCNTs. In particular, synergistic toughening effects were observed when the plasma-activated BFs/ MWCNTs hybrid modifiers were used, while only additive toughening effects occurred for the silane-sized BFs/MWCNTs hybrid modifiers. This work demonstrated a potential to develop strong, tough, and electrically conductive epoxy composites by adding hybrid BF/MWCNT modifiers.
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