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Influence of textile grid forms on tensile mechanical behaviors of carbon textile-reinforced composites with polyethylene (PE) short fibers

100%

Wu Z. , Deng M. , Tian T. , Dong Z. , Sun Y. , Zhang W.

tom Vol. 23, no. 2

art. no. e103, 2023

Textile-reinforced composite (TRC) is a new material composed of finely grained cement-based concrete and textile grids, which can be a substitute for fiber-reinforced polymer (FRP) in strengthening applications. The diversity of the textile grid results in a difference in bond behaviors at the textile-matrix interface, which influences the tensile properties of TRC. Several researchers have investigated the tensile behaviors of TRC, mainly concentrating on the matrix strength, the content of short synthetic fibers, and the number of textile grids; discussions on the textile grid geometry, especially the coupling effect between the textile grid form and matrix category, remained limited. Therefore, this paper focuses on the effects of three carbon textile grids on the tensile behavior of TRC through a uniaxial tensile test; the design parameters also include the textile reinforcement ratio and matrix category. Twenty-seven groups of tensile samples were manufactured to investigate the effect of each variable on the crack distribution, failure pattern, stress-strain curve and characteristic parameter. The test results showed that flattening the roving diameter and especially thinning the coating depth ameliorated the matrix-to-textile permeability, and consequently improved the tensile mechanical properties of TRC. The enhancement level of tensile strength by increasing the textile reinforcement ratio was lower than that by optimizing textile grid form. In terms of different textile grid forms, the effect of the matrix category on the tensile performance of TRC showed significant differences. Finally, an analytical model is presented to forecast the stress-strain behavior of TRC with textile rupture failure.

Termomechaniczne aspekty przemiany fazowej w stopie TiNi z pamięcią kształtu indukowanej naprężeniem

67%

Pieczyska E.

tom R. 55, nr 11

958-961

W pracy przedstawiono wyniki badań sprzężeń termodynamicznych zachodzących podczas indukowanej naprężeniami przemiany fazowej w stopach TiNi z pamięcią kształtu. Wykazano, że przemiana martenzytyczna wprost i odwrotna, zachodząca podczas pseudosprężystego odkształcania tych stopów, ma charakter niejednorodny. Makroskopowo rozwija się w zlokalizowanych cienkich pasmach, podobnych do pasm Lüdersa, w dwóch prawie prostopadłych kierunkach, co udokumentowano stosując metodę badań w podczerwieni oraz fotografując relief na powierzchni próbki.

Experimental investigations of thermomechanical couplings related to stress-induced martensite transformation in shape memory alloy (SMA) are presented in the paper. TiNi shape memory alloy specimens were subjected to uniaxial tensile tests carried out with various strain rates on an MTS testing machine (Fig. 1). The tem-perature changes, accompanying the process of stress-induced martensite transformation were recorded with use of a thermovision camera. It was shown that the martensite forward and reverse transformation, related to the SMA pseudo-elastic behavior, can occur and develop in inhomogeneous way in Lüders-like bands [3-5]. Nucleation and development of the phase transformation fronts in the SMA recorded by infrared camera were studied. Narrow bands of considerably higher temperature corresponding to the martensitic phase, starting from the central part of the specimen and developing towards the specimen grips, were recorded. Next, the upswing region was observed, manifested by the more advanced and more homogeneous stage of the phase transformation, accompanied by the more uniform temperature distribution. The inclined bands of heterogeneous temperature distribution were observed also during the unloading process of the SMA, while the reverse transformation accompanied by the temperature decrease took place [14]. The martensite transformation heterogeneity was confirmed by infrared technique and by photographs of the SMA specimen surface relief (Fig. 2). Thermomechanical aspects of the exothermic martensitic forward and the endothermic reverse transformations for various strain rates were analyzed.