ABSTRACT
Shear thickening fluids (STFs) are a unique type of fluids that can quickly transform into a solid-like state when subjected to forces (rate dependent). These fluids are created by dispersing micro and nanoparticles within a medium. When the force is removed, they return to their original liquid state. Shear thickening fluids can absorb a significant amount of impact energy, making them useful for reducing vibrations and serving as a damper. This study provides a comprehensive and brief overview of existing literature on shear thickening fluids, including their properties, classification, and the rheological mechanisms behind the shear thickening behaviour. It also examines the use of these fluids in various applications, such as improving resistance to stabs and spikes, protecting against low- and high-velocity impacts, and as a new medium for energy dissipation in industries such as battery safety, vibration control and adaptive structures. Lastly, this work reviews the promising combination of STFs with cork. Given the sustainability of cork and its energy absorption capacity, cork-STF composites are a promising solution for various impact-absorbing applications. Overall, the paper underscores the versatility and potential of STFs, and advocates for further research and exploration.
ABSTRACT
In this study, we investigate the role of adding shear thickening fluids (STFs) and multi-functional shear thickening fluids (M-STFs) to the core of a sandwich-structured composite made of aluminum facesheets and XPS foam cores with different geometries on force attenuation performance. Six different core designs were machined, and all designs had the same space for adding STFs and M-STFs. STF with 40 wt% SiO2 in PEG 400 was selected and fabricated. M-STFs were made by adding multi-walled carbon nanotubes (MWCNTs) up to 1.5 wt%. The effects of MWCNTs on the rheological and electrical properties of the STF were investigated. The force attenuation tests were performed with an impact drop tower test system at three different heights with 5, 10, and 15 J energy levels. According to the results, V6_STF (with 16 holes with a diameter of 6 mm) and H6_STF (with 16 rectangular cubic column with cross-sections of 6 × 6 mm) designed sandwich structures showed better performance in terms of force attenuation compared with the other samples. Next, these two sandwich structures were filled again with M-STF (0.5 wt% MWCNT), and the force attenuation performance of the structures showed an improvement further, and the H6_STF_CNT sample improved by 24.8% compared to the clean sandwich structure sample. These results demonstrate the potential of STFs and M-STFs in strengthening the force attenuation performance of sandwich structures with XPS foam cores, mainly when used with appropriate core geometry.
ABSTRACT
In this study, we fabricated an intelligent material, shear stiffening polymer (SSP), and reinforced it with carbon nanotube (CNT) fillers to obtain intelligent mechanical and electrical properties. The SSP was enhanced with multi-functional behavior, such as electrical conductivity and stiffening texture. Various amounts of CNT fillers were distributed in this intelligent polymer up to a loading rate of 3.5 wt%. The mechanical and electrical aspects of the materials were investigated. Regarding the mechanical properties, dynamic mechanical analysis was carried out, as well as conducting shape stability and free-fall tests. Viscoelastic behavior was investigated in the dynamic mechanical analysis, whereas cold-flowing and dynamic stiffening responses were studied in shape stability and free-fall tests, respectively. On the other hand, electrical resistance measurements were carried out to understand the conductive behavior of the polymers of the electrical properties. Based on these results, CNT fillers enhance the elastic nature of the SSP while initiating the stiffening behavior at lower frequencies. Moreover, CNT fillers provide higher shape stability, hindering the cold flow in the material. Lastly, SSP gained an electrically conductive nature from the CNT fillers.
ABSTRACT
This study aimed to analyze the influence of the thermal treatment of shear thickening fluids, STFs, on their viscosity. For this purpose, shear thickening fluids based on polypropylene glycols PPG400 and PPG1000 and Aerosil®200 were developed. The shear thickening behavior of obtained fluids was confirmed by using a parallel-plate rheometer. Next, thermogravimetric (TG) analyses were used to characterized thermal stability and weight loss of the STFs at a constant temperature. Finally, the thermal treatment of the STFs obtained was provided using the apparatus developed for this purpose. The received STFs exhibited a very high maximum viscosity up to 15 kPa. The rheology of the STFs measured after thermal treatment indicated that the proposed method allowed the development of STFs with a very high maximum viscosity. The maximum viscosity of the STFs increased twofold when thermal treatment of the STFs at elevated temperature for 210 min was performed. TG confirmed the convergence of the weight loss in the apparatus. Our results show that controlling the thermal treatment of STFs allows STFs to be obtained with high viscosity and a dilatation jump of the STFs by degradation of the liquid matrix.
ABSTRACT
Shear thickening fluids (STFs) are innovative materials that can find applications in smart body armor. However, the usage of STFs is limited by the aging of these materials. This work aims to analyze the influence of UV radiation on the aging process of STFs. The investigation was done experimentally, and artificial aging was applied to investigate the impact of UV radiation on the properties of STFs. The shear-thickening properties of obtained STFs were confirmed by viscosity measurements. The STFs based on PPG425, PPG2700, and KE-P10 exhibited a very high maximum viscosity of up to 580.7 Pa·s and 3313 Pa·s for the STF425 and STF2700, respectively. The aging of the obtained STFs caused the liquid matrix degradation, causing damage to the STFs and their change from liquid into solid. Furthermore, the FT-IR, 1H NMR, and 13C NMR spectroscopies were used for the confirmation of the breakdown of STFs. The FT-IR spectroscopy revealed the appearance of carbonyl groups in STFs after aging. Moreover, 1H NMR and 13C NMR spectroscopy confirmed the formation of the typical groups containing carbonyl groups. Our results demonstrate that STFs are UV light-sensitive and may lose their properties during storage.
