It is well known that 3D printed parts prepared by fused deposition modeling (FDM) exhibit large anisotropy of mechanical properties. In this article, poly(lactic acid; PLA)/carbon fiber (CF) composites with different built orientations (X, Y, Z) were prepared by FDM. The effects of printing temperature, speed, orientations, and layer thickness on the mechanical properties of the composites were systematically investigated. The mechanical properties of PLA/CF composites show more significant anisotropy. The orientation of the fibers along the printing direction is displayed by scanning electron microscopy. Printing parameters bring almost no effect on mechanical properties of the X‐construct oriented specimen, and bring obvious effect on those of the Y‐construct oriented specimen and Z‐construct oriented specimen. According to the analysis, carbon fiber can amplify this anisotropy from layer fashion, and the key factors from printing parameters are porosity and bond strength between fuses. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48786.
The hydroxylate carbon nanotubes (CNTs) were grafted by chemical method on the surface of the oxidized carbon fibers (CF) to improve the mechanical and tribological properties of polyimide (PI). The microstructure and fracture surface of the polyimide composites indicated that CF-CNTs hybrid as a multiscale reinforcement can distribute into the PI matrix homogeneously. Tribo-tests further showed that CF-CNTs hybrid had a better effect on hardness increment, impact strength enhancement, friction reduction, and wear resistance. Compared to the neat PI, the friction coefficient and wear rate of CF-CNTs/PI composite deceased by 23.2 and 55.9%, respectively. In particular, the loading capacity and high speed resistance of CF-CNTs/PI composite were greatly improved. The corresponding wear mechanisms were also discussed by observing the worn surface of the PI composites.
High-performance polymer-based frictional materials have become increasingly important to improve the mechanical output properties of ultrasonic motors. This study discussed the friction and wear behavior of 2 dominating frictional materials of polymer composites for ultrasonic motors, polyimide (PI), and polytetrafluoroethylene (PTFE) filled by aramid fibers (AF) and molybdenum disulfide (MoS 2 ). To explore the wear mechanisms, the tribo-pair contact stress was theoretically characterized, and the interface temperature rise was numerically predicted. The predictions showed that the flash temperature on asperity tips could reach the glass transition temperature of the polymer materials. The experimental results indicated that the contact stress and sliding speed have a small effect on the friction of the PI composite but influence considerably the friction of the PTFE composite. A higher contact stress brings about a higher specific wear rate, but a higher sliding speed reduces the wear rate. Compared with AF/MoS 2 /PTFE, the AF/MoS 2 /PI has much better tribological performance under high loads and speeds. KEYWORDS friction and wear, polyimide, polytetrafluoroethylene, temperature, ultrasonic motors 1 | INTRODUCTION An ultrasonic motor (USM) is driven by the frictional force between its stator and rotor. Such motors have been extensively used in medical apparatus, precision positioning devices, and aerospace structures because of their fast response capacity, high torque at low speed, and self-locking without the application of external power. 1 However, there are also drawbacks which have hindered the development of USMs, including their low transfer efficiency, poor mechanical output stability, and short service life in harsh environments. To improve the performance of USMs, better frictional materials of ultralow wear rate and stable friction are required because their properties determine directly the output characteristics and service life of USMs in complex, harsh environments. Some frictional materials have been tested for USMs, 2-6 including rubber, resin, metal coatings, alloys, and ceramic composites. It was found that most of them cannot meet the requirements due to, eg, severe wear, short service life, and high noise. Polymer-based frictional materials, however, have been found to be applicable to travelling wave USMs for their excellent wear resistance, low noise, suitable hardness, and thermal stability. For instance, Rehhein and Wallaschek 7 studied the friction and wear behavior of PI composites and found that the inclusion of carbon fibers could improve the wear resistance of PI sliding against steel. Ishii et al 8 established a method to predict the service life of USMs with a carbon-fiber-reinforced polymer as the frictional material. Qu et al 3-5,9,10 investigated the tribological properties of polytetrafluoroethylene (PTFE), phenolic resin, and Ekonol composites in different environments and proposed a method for selecting frictional materials incorporating operation conditions. Ding et al ...
This article reports on a novel route to develop ethylene-propylene-diene rubber (EPDM)/montmorillonite nanocomposites Modification of the MMT was carried out with maleic anhydride (MA), which acts as the intercalation agent for MMT and the vulcanizing agent for EPDM matrix, as well as the compatibilizer for the EPDM and MMT phases. The effect of MA-modified MMT in nanocomposites was investigated by focusing on three major aspects: structural analysis, thermal properties, and material properties. The d-spacings of both the MA modified MMT and exfoliated nanocomposites were investigated by X-ray diffraction (XRD), and the morphology of these nanocomposites was examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Dynamic mechanical analysis confirms the constraint effect of exfoliated MMT layers on EPDM chains, which benefited the increased storage modulus, increased glass transition temperature. Thermogravimetric analysis indicates that there is some enhancement in degradation behavior between the nanocomposites and EPDM matrix. The nanocomposites exhibit great improvement in tensile strength and modulus, as well as elongation-at-break. The effects of MA addition on the formation of nano-metric reinforcement and on the mechanical properties of nanocomposites are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.