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1. Experimental Study on Fiber Attrition of Long Glass Fiber-Reinforced Thermoplastics under Controlled Conditions in a Couette Flow

   Goris, S. (May 2017, Annual technical conference and exhibition - Society of Plastics Engineers)

   Fiber attrition of long glass fiber-reinforced polypropylene in a Couette Flow was studied to obtain a fundamental understanding of the physics in fiber breakage. The developed experimental setup of the Couette rheometer in combination with the developed fiber length measurement technique is able to provide repeatable, accurate and robust data sets to quantify the fiber length reduction during the processing of fiber-filled materials. This article summarizes the first results of an ongoing experimental study on fiber breakage at the Polymer Engineering Center at the University of Wisconsin- Madison. The impact of fiber concentration, initial fiber length, residence time, melt temperature and processing speed was quantified and studied. The proposed procedure aims to isolate the effect of process variables on fiber breakage. Even for the gentlest processing conditions, the results indicate that the residual fiber length after processing is less than 50% of the initial fiber length. For the most severe processing conditions, the results suggest a reduction to less than 10% of the initial fiber length, which highlights the challenges that fiber breakage poses for processing of long glass fiber-reinforced thermoplastics. 

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2. A Calmodulin-Like Gene (GbCML7) for Fiber Strength and Yield Improvement Identified by Resequencing Core Accessions of a Pedigree in Gossypium barbadense

   https://doi.org/10.3389/fpls.2021.815648  

   Zhao, Nan; Wang, Weiran; Jiang, Kaiyun; Grover, Corrinne E.; Cheng, Cheng; Pan, Zhuanxia; Zhao, Cunpeng; Zhu, Jiahui; Li, Dan; Wang, Meng; et al (February 2022, Frontiers in Plant Science)

   Sea Island cotton ( Gossypium barbadense ) is world-renowned for its superior natural fiber. Although fiber strength is one of the most important fiber quality traits, genes contributing to fiber strength are poorly understood. Production of sea island cotton also is inextricably linked to improving its relatively low yield, thus enhancing the importance of joint improvement of both fiber quality and yield. We used genomic variation to uncover the genetic evidence of trait improvement resulting from pedigree breeding of Sea Island cotton. This pedigree was aimed at improving fiber strength and yielded an elite cultivar, XH35. Using a combination of genome-wide association study (GWAS) and selection screens, we detected 82 putative fiber-strength-related genes. Expression analysis confirmed a calmodulin-like gene, GbCML7 , which enhanced fiber strength in a specific haplotype. This gene is a major-effect gene, which interacts with a minor-effect gene, GbTUA3 , facilitating the enhancement of fiber strength in a synergistic fashion. Moreover, GbCML7 participates in the cooperative improvement of fiber strength, fiber length, and fiber uniformity, though a slight compromise exists between the first two of these traits and the latter. Importantly, GbCML7 is shown to boost yield in some backgrounds by increasing multiple yield components to varying degrees, especially boll number. Our work provides valuable genomic evidence and a key genetic factor for the joint improvement of fiber quality and yield in Sea Island cotton. 

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3. A Comparative Study of Pellet-Based Extrusion Deposition of Short, Long, and Continuous Carbon Fiber-Reinforced Polymer Composites for Large-Scale Additive Manufacturing

   https://doi.org/10.1115/1.4049646  

   Pappas, John M.; Thakur, Aditya R.; Leu, Ming C.; Dong, Xiangyang (July 2021, Journal of Manufacturing Science and Engineering)

   null (Ed.)

   Abstract Pellet-based extrusion deposition of carbon fiber-reinforced composites at high material deposition rates has recently gained much attention due to its applications in large-scale additive manufacturing. The mechanical and physical properties of large-volume components largely depend on their reinforcing fiber length. However, very few studies have been done thus far to have a direct comparison of additively fabricated composites reinforced with different carbon fiber lengths. In this study, a new additive manufacturing (AM) approach to fabricate long fiber-reinforced polymer (LFRP) was first proposed. A pellet-based extrusion deposition method was implemented, which directly used thermoplastic pellets and continuous fiber tows as feedstock materials. Discontinuous long carbon fibers, with an average fiber length of 20.1 mm, were successfully incorporated into printed LFRP samples. The printed LFRP samples were compared with short fiber-reinforced polymer (SFRP) and continuous fiber-reinforced polymer (CFRP) counterparts through mechanical tests and microstructural analyses. The carbon fiber dispersion, distribution of carbon fiber length and orientation, and fiber wetting were studied. As expected, a steady increase in flexural strength was observed with increasing fiber length. The carbon fibers were highly oriented along the printing direction. A more uniformly distributed discontinuous fiber reinforcement was found within printed SFRP and LFRP samples. Due to decreased fiber impregnation time and lowered impregnation rate, the printed CFRP samples showed a lower degree of impregnation and worse fiber wetting conditions. The feasibility of the proposed AM methods was further demonstrated by fabricating large-volume components with complex geometries. 

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4. Background-penalty-free waveguide enhancement of CARS signal in air-filled anti-resonance hollow-core fiber

   https://doi.org/10.1364/OL.461614  

   Bahari, Aysan; Sower, Kyle; Wang, Kai; Han, Zehua; Florence, James; Wang, Yingying; Gao, Shoufei; Howard Lee, Ho Wai; Scully, Marlan; Zheltikov, Aleksei; et al (January 2022, Optics Letters)

   We study coherent anti-Stokes Raman spectroscopy in air-filled anti-resonance hollow-core photonic crystal fiber, otherwise known as “revolver” fiber. We compare the vibrational coherent anti-Stokes Raman signal of N 2 , at ∼2331 cm −1 , generated in ambient air (no fiber present), with the one generated in a 2.96 cm of a revolver fiber. We show a ∼170 times enhancement for the signal produced in the fiber, due to an increased interaction path. Remarkably, the N 2 signal obtained in the revolver fiber shows near-zero non-resonant background, due to near-zero overlap between the laser field and the fiber cladding. Through our study, we find that the revolver fiber properties make it an ideal candidate for the coherent Raman spectroscopy signal enhancement. 

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5. Interpreting Acoustic Energy Emission in SiC/SiC Minicomposites through Modeling of Fracture Surface Areas.

   Swaminathan, B.; McCarthy, N.R.; Almansour, A.S.; Sevener, K.; Musaffar, A.K.; Pollock, T.; Kiser, J.D.; Daly, S. (January 2021, Journal of the European Ceramic Society)

   null (Ed.)

   The relationship between acoustic emission (AE) and damage source areas in SiC/SiC minicomposites was modeled using insights from tensile testing in-scanning electron microscope (SEM). Damage up to matrix crack saturation was bounded by: (1) AE generated by matrix cracking (lower bound) and (2) AE generated by matrix cracking, and fiber debonding and sliding in crack wakes (upper bound). While fiber debonding and sliding exhibit lower strain energy release rates than matrix cracking and fiber breakage, they contribute significant damage area and likely produce AE. Fiber breaks beyond matrix crack saturation were modeled by two conditions: (i) only fiber breaks generated AE; and (ii) fiber breaks occurred simultaneously with fiber sliding to generate AE. While fiber breaks are considered the dominant late-stage mechanism, our modeling indicates that other mechanisms are active, a finding that is supported by experimental in-SEM observations of matrix cracking in conjunction with fiber failure at rupture. 

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