Fracture Energy of Steel Fiber-Reinforced Concrete
Steel fiber-reinforced concrete (SFRC) is a cementitious material reinforced with discrete fibers. The energy absorption capacity is the main material property benefited by fiber reinforcement. Closed-loop servo-controlled equipment should be used to evaluate this property. The tests should be carried out using displacement control in order to obtain the postpeak force- displacement relationship (tensile strain-softening branch). To assess the fracture energy of SFRC, three-point bending tests were carried out using displacement control. Series of notched beams reinforced with 30, 60, and 90 kg/m3 of hooked-end steel fibers were tested. Besides the energy dissipated in fracturing the concrete, the energy determined from the force-displacement relationship can also include the energy absorbed during nonlinear behavior of concrete in compression. Ductile materials, such as concrete reinforced with a high content of fibers, develop large deflections before exhausting their energy absorption capacity. In these cases, the "fixed" points of the bar supporting the displacement transducer may not remain fixed, adding an extra deflection into the control displacement transducer and thus leading to incorrect evaluation of the fracture energy. These factors are analyzed in the present work in order to assess the suitability of the specimen dimensions and the test procedures for evaluating the fracture energy of SFRC.
Acta Polytechnica
The unique properties of nanotextiles based on poly(vinyl-alcohol) (PVA) manufactured using the electrospinning method have been known and exploited for many years. Recently, the enrichment of nanofiber textiles with nanoparticles, such as ions or nanodiamond particles (NDP), has become a popular way to modify the textile mechanical, chemical and physical properties of the textile. The aim of our study is to investigate the macromechanical properties of PVA nanotextiles enriched with NDP, silver (Ag) and copper (Cu) ions. Nanofiber textiles of various surface weights were prepared from a 16% PVA solution, while glyoxal and phosphoric acid were used as cross-linking agents. The copper and silver ions were diluted in an aqueous solution and NDP were dispersed into the fibers by ultrasound homogenization. All but one of the sets of samples were exposed to a temperature of 140 °C for 10 minutes. The samples without thermal stabilization exhibited significantly lower elastic stiffness and tensile strength. Moreover, the results of tensile testing indicate that the addition of dispersed nanoparticles has a minor effect on the mechanical properties of the textiles and contributes rather to their reinforcement. However, the lack of thermal stabilization results in a poor interconnection of individual nanofiber layers, and the non-stabilized textiles exhibit lower elastic stiffness and reduced tensile strength.
Liquid state 1H high field NMR in food analysis.
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