The enhancement of mechanical damping and stiffness trade-off using unidirectional carbon fiber reinforced polymer composite interleaved with recycled carbon fiber and short virgin aramid fiber non-woven mats

  • Cephas Yaw ATTAHU

Student thesis: PhD Thesis


It is possible to suppress unwanted mechanical vibrations without sacrificing stiffness; however, it is difficult when recycled carbon fibers (rCFs) are utilized. The characteristics of these rCFs have slightly deteriorated. Carbon fiber reinforced polymer composites (CFRPs) are increasingly used in various applications. This builds up in waste generated during the manufacture of raw carbon fibers and prepregs and during the end-of-life of their products. Fibers from these wastes are recovered primarily due to environmental and regulatory regulations. The strength of the recovered fibers was only slightly degraded compared to their new counterparts, according to many authors. To manufacture composite laminates that include the rCFs for structural applications, the developed composite laminate should meet a trade-off between mechanical damping and stiffness. To determine whether a material meets this trade-off, it must be able to escape what is known as the Ashby limit for mechanical damping/stiffness trade-off. To manufacture the composite laminates, a papermaking method was utilized to convert all involving fibers into 60 g⁄m^2 non-woven mats and the non-woven mats (mats) were either sized with titanate coupling agent-L12 or not, depending on the investigating factors. Before being used for interleaving, the mats were sandwiched between two layers of 125 g⁄m^2 resin films. The composite laminates were then made using a vacuum-assisted compression molding technique. To get around the Ashby limit, the author looked at the impacts of titanate coupling agent-L12 on the mats; the number of interleaved rCFs mats; their placements; and the influence of rCF lengths and combinations, kinds, and micro-hybridization with short virgin aramid fibers (vAFs). The limit (Ashby limit for mechanical damping/stiffness trade-off) was eluded by escaping to the curve's far right-hand corner (the best route for mechanical damping/stiffness trade-off). In the figure of merit, the best laminate [Unidirectional CFRP with a 100% (T700 + M46J) (3 mm + 6 mm) (in the percentage ratios of 75:25 due to manufacturing limitations) recycled carbon fiber non-woven mat] (herein referred to as Laminate T) was 54.2 percent better than the control sample (herein referred to as Laminate A). A reproducibility test was conducted for the best laminate because manufacturing processes could influence the results. There were no significant differences in the mean flexural modulus values measured for the composite laminates and only minor variances in the standard deviation values for the individual laminates. These findings were not surprising given the challenges of producing consistent, homogenous non-woven mats. Also, the test samples were cut from various portions of the laminates; thus, the results were not unexpected. Additionally, a composite made of non-woven mats was designed to analyze the dynamic behavior utilizing free and forced vibrations (modal and harmonic analyses, respectively). This allowed for a direct evaluation of the non-woven mats' dynamic performance. There was excellent agreement between the numerical (FEA) and the theoretical natural frequencies when the natural frequencies were analyzed using both theoretical and FEA approaches. The effects of rCFs and short virgin aramid fibers (vAFs) hybridization as well as the influence of fiber volume fraction and combination of fiber lengths (using only rCFs), were investigated. The damping capacities of the composite laminates were evaluated using the amplitude-frequency plot for the two simulated modes. The specific stiffness values of the various composites were utilized to comprehend the effects of the parameters more clearly under investigation, and it was determined that increasing the specific stiffness of the non-woven mat composites might enhance their dynamic performance.
Date of AwardOct 2022
Original languageEnglish
Awarding Institution
  • University of Nottingham
SupervisorJian Yang (Supervisor), Kok Wong (Supervisor) & Chung Ket Thein (Supervisor)


  • recycled carbon fiber
  • aramid fiber
  • non-woven mats
  • structural damping polymer composites
  • mechanical damping
  • mechanical properties
  • dynamic mechanical analysis
  • vacuum-assisted compression molding
  • figure of merit

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