Abstract
Self-healing is an essential property of smart concrete structures. In contrast to other structural metals, shape memory alloys (SMAs) offer two unique effects: shape memory effects, and superelastic effects. Composites composed of SMA wires and conventional cements can overcome the mechanical weaknesses associated with tensile fractures in conventional concretes. Under specialized environments, the material interface between the cementitious component and the SMA materials plays an important role in achieving the enhanced mechanical performance and robustness of the SMA/cement interface. This material interface is traditionally evaluated in terms of mechanical aspects, i.e., strain–stress characteristics. However, the current work attempts to simultaneously characterize the mechanical load-displacement relationships synchronized with impedance spectroscopy as a function of displacement. Frequency-dependent impedance spectroscopy is tested as an in situ monitoring tool for structural variations in smart composites composed of non-conducting cementitious materials and conducting metals. The artificial geometry change in the SMA wires is associated with an improved anchoring action that is compatible with the smallest variation in resistance compared with prismatic SMA wires embedded into a cement matrix. The significant increase in resistance is interpreted to be associated with the slip of the SMA fibers following the elastic deformation and the debonding of the SMA fiber/matrix.
Highlights
Shape memory alloys (SMAs) provide two useful forms depending on their polymorphism as a function of temperature and external stress: a shape memory form, and a superelastic form.The shape memory form is a prescribed shape from heating, and the superelastic form allows a phase transformation from austenite to martensite by increasing the external stress with no temperature change [1,2]
Mechanical Characterization of the NiTi shape memory alloys (SMAs) Fibers Embedded into the Cement Mortar
Mechanical force-displacement behaviors associated theofpullout behaviors behaviors of the Ni/Ti wires embedded into the cement-based matrix, inwith terms the geometric ofshapes the Ni/Ti wires embedded into the cement-based matrix, in terms of the geometric shapes applied to the ends of the SMA fibers
Summary
Shape memory alloys (SMAs) provide two useful forms depending on their polymorphism as a function of temperature and external stress: a shape memory form, and a superelastic form. Shape memory alloys are of increasing academic/industrial interest due to their diverse benefits, such as self-healing functions and the ability to enhance the mechanical strength and robustness of cement-based materials [6,7]. The current work uses Ni/Ti-based shape memory alloy fibers, which have high tensile strength and bending strength, in contrast to conventional steel fibers. The current work placed its main emphasis on the electrical self-sensing features that can be integrated with the self-healing function of the SMA materials using the shape memory effects through heating in smart concrete structures. This work investigated the pullout resistances of artificially deformed SMA fibers embedded in cement mortar systems based on mechanical and electrical characteristics. The mechanical contact between the SMA wires and the cement-based materials affects the electrical conduction that forms between the two metal electrodes
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