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Cellulose nanofibers (CNF) have recently attracted attention as one of the reinforcements for composite materials. However, the same as other nanofibers, CNFs can be easily agglomerated and the nano-level defibration is necessary to obtain their outstanding properties in polymer matrices. To overcome this issue, two major defibration methods, chemical and mechanical defibration have been considered. The chemically-defibrated CNF is expensive and so prevents the practical realization of CNF as general-purpose products. Therefore, the mechanical defibration method by a clean low-cost water jet was focused on. Mechanically-defibrated CNF reinforced epoxy resin matrix (Epoxy-CNF) composite was fabricated via mechanical mixing and the variation of their tensile and flexural properties with different CNF volume fractions was evaluated. The tensile and flexural moduli of the epoxy resin were increased by CNF addition, while the fracture elongation was decreased. The calculated ultimate tensile strength (UTS) and ultimate flexural strength (UFS) of the Epoxy-CNF composites, using the aspect ratio of the agglomerated CNF clusters, indicated the validity of the random dispersion model considering the agglomerated CNF as one whole fiber. It seems that epoxy resin is enhanced by the mechanical interaction when the CNF volume fraction is higher than 0.37 vol.%. [ABSTRACT FROM AUTHOR]

This paper investigates the fatigue failure and electrical resistance behaviors of carbon nanotube-based polymer composites at cryogenic temperatures. Tension–tension fatigue tests were performed on carbon nanotube /polycarbonate composites at room temperature and liquid nitrogen temperature (77 K), and the electrical resistance of the specimens was monitored during the tests. Based on the obtained results, the dependence of the mechanical and electrical responses of the nanocomposites on the temperature and the nanotube content was studied. Microscopic examinations were also carried out on the specimen fracture surfaces, and the failure mechanisms of the nanocomposites were discussed. [ABSTRACT FROM AUTHOR]

This paper studies the flexural stiffness controllability of hybrid layered beams with woven carbon fiber reinforced polymer composite and shape memory polymer layers. The temperature of the shape memory polymer layer was controlled using electrical resistive heating of the woven carbon fiber reinforced polymer layers. Flexure tests were then conducted on the layered cantilever beams, and the temperature dependence of the beam flexural stiffness was examined. A three-dimensional finite element analysis was also performed to predict the flexural response of the layered beams, and a good correlation was observed between the predicted and measured results for the flexural stiffness. In addition, the deformation states in the layered beams were determined numerically and discussed in detail. [ABSTRACT FROM AUTHOR]

This work deals with the delamination growth behavior in woven glass fiber reinforced polymer (GFRP) composite laminates under mixed-mode I/III fatigue loading at cryogenic temperatures. Fatigue delamination tests were carried out with eight-point bending plate (8PBP) specimens at room temperature, liquid nitrogen temperature (77 K), and liquid helium temperature (4 K), and the delamination growth rate data were expressed in terms of the energy release rate range during fatigue loading. The energy release rate was calculated using the three-dimensional finite element method. Moreover, the fracture surface characteristics of the woven GFRP laminates under mixed-mode I/III fatigue loading were examined by scanning electron microscopy (SEM). [ABSTRACT FROM AUTHOR]

This article investigates the interlaminar shear behavior and damage detection of woven carbon fiber reinforced polymer composite laminates at cryogenic temperatures. Short beam shear tests were performed at room temperature and liquid hydrogen temperature (20 K), and the temperature dependence of the apparent interlaminar shear strength was examined. The electrical resistance of the composite specimens was also monitored during the tests. A detailed observation of the tested specimens was made to assess the damage, and the relationship between the damage and the electrical resistance was discussed. In addition, the stress, strain and current density distributions in the short beam shear specimens were determined by the finite element method. The numerical results were used to better understand and explain the experimental findings. [ABSTRACT FROM PUBLISHER]

In this article, we investigate the strength characteristics of woven glass fiber reinforced polymer composite laminates subjected to tensile fatigue loading at cryogenic temperatures using the open hole specimens. Tension–tension fatigue tests were conducted on the open hole specimens of the woven glass fiber reinforced polymer laminates at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K), and microscopic observations of damage around the hole were made on failed specimens. A numerical procedure based on the finite element method was then applied to evaluate the fatigue strength of the unnotched woven glass fiber reinforced polymer laminates using the experimentally applied load and the length of the hole edge damage zone. The obtained results were compared with the existing experimental data from the unnotched specimens. It was demonstrated that the presented combined numerical–experimental method was effective for the determination of the fatigue properties of the woven glass fiber reinforced polymer laminates at cryogenic temperatures. [ABSTRACT FROM AUTHOR]