Editorial for the Special Issue on Carbon Fiber Composites, Volume II

Fibers with lengths much larger than their widths have been developed over centuries because of their unique properties [1,2,3,4]. Therefore, these fibers have been extensively applied in different fields, including wearable electronics, energy storage, sports, and environmental protection [5,6,7,8]. Many materials, such as polymers, metals, and metal oxides, can be made into fibers using various approaches [9,10,11,12]. Among these materials, carbon fibers (CFs), which contain mostly carbon atoms, have attracted tremendous interest since their discovery in the 1860s because of their mechanical properties, chemical resistance, and electrical/thermal conductivities [13,14,15,16]. Additionally, CF-derived composites are lighter in weight and provide superior performance compared with other fibers because of their high strength-to-weight ratio. As such, these CF-derived composites show promise for developing next-generation composites for various practical applications [17,18,19,20,21,22].

This Special Issue includes papers reporting studies related to the development of approaches to improve the structure and processing design of CF-derived composites [23,24,25], analyses of these composites from both experimental and computational aspects [26,27,28,29], and the various applications of CF-derived composites (i.e., catalysts, sensors, and risers for deep-water) [30,31,32]. Çelik et al. investigated the effects of line processing parameters on the properties of a carbon fiber epoxy composite, finding that fiber straightness plays a critical role in mechanical performance [33]. The influence of the notch shape and size on carbon-fiber-reinforced epoxy was explored by Cao et al. [34], in which the samples with/without notches were tested for comparison. The features of the failure were identified and compared among these specimens. Khozeimeh et al. found that carbon-fiber-reinforced polymer (CFRP) in a manipulator’s structure enhanced the static and vibrational properties of the manipulator, increasing its loading capacity [35]. Some other factors may also affect the final properties of CFRPs, such as stacking sequence and overall thicknesses. Wu et al. studied the effects of the pores generated during the fabrication process on the residual stresses in a composite [36], and the results were experimentally analyzed. In addition to the above-discussed experimental methods, modeling was performed to understand the working mechanisms of CFRPs. For instance, Burgani et al. developed a finite-element model to explain the increase in load-bearing capacity achieved with the use of CFRPs, which was validated with experimental data [37].

Some composite systems other than CFRPs have been studied. Tanaka et al. [38] grafted carbon nanotubes (CNTs) via chemical vapor deposition onto CFs using Ni as the catalyst. Li et al. tuned the intensities of electrochemical anodic oxidation to optimize the surface modification of CFs to increase the loading of catalyst particles and enable CNTs to be uniformly distributed on CFs [39].

Recycled CFs have received considerable interest, and the corresponding supply chain has been well established because of the relatively low cost of and legislation on CFs. For example, Vaidya et al. [40] developed a practical approach to recycle CFs with thermoplastic resins (i.e., polyethylene, polyamide 66, and polyethylene terephthalate). The corresponding mechanical properties of the resultant composites were further explored. The proposed approach could benefit the design of sustainable composites.

In summary, this Special Issue collects studies on different CF composites, including those on the design of their structure, failure analyses, and applications. These studies provide new insights into the fundamental understanding of CF composite systems, which benefit their future design and accelerate their practical application.