Characteristics of carbon fiber based strain sensors for structural-health monitoring of textile-reinforced thermoplastic composites depending on the textile technological integration process
“…Previous examinations made by the authors showed that CF is suitable as an in situ strain gage for the structural and strain monitoring of fiber-reinforced plastic components. 16–19 Figure 3.Measurement principle of carbon fiber (CF)-based textile strain gages (a) and method for the determination of specific sensor values (b).…”
This contribution will introduce carbon-reinforced concrete components (so-called carbon concrete composites, or C3) with sensor functionalities for innovative building envelopes. For a continuous in situ structural monitoring, these textile-reinforced concrete components are equipped with textile sensor networks consisting of resistive carbon fiber sensors (CFSs), which are integrated into the carbon fiber non-crimp fabrics of the concrete reinforcement by multiaxial warp-knitting. The in situ CFSs, consisting of 1 k or 50 k carbon fiber roving with added staple fiber/multifilament dielectric cladding, are later integral to the load-distributing elements of the concrete component, and elongations within these are easy to record with good correlation to ohmic resistance changes. Gage factors of k = 0.52–1.23 at linearity deviations of ALin = 4.0–8.7% are feasible. This allows a monitoring of C3 building envelopes for structural mechanical changes caused by physical changes within the component through mechanical or thermal loads or deformation and cracks.
“…Previous examinations made by the authors showed that CF is suitable as an in situ strain gage for the structural and strain monitoring of fiber-reinforced plastic components. 16–19 Figure 3.Measurement principle of carbon fiber (CF)-based textile strain gages (a) and method for the determination of specific sensor values (b).…”
This contribution will introduce carbon-reinforced concrete components (so-called carbon concrete composites, or C3) with sensor functionalities for innovative building envelopes. For a continuous in situ structural monitoring, these textile-reinforced concrete components are equipped with textile sensor networks consisting of resistive carbon fiber sensors (CFSs), which are integrated into the carbon fiber non-crimp fabrics of the concrete reinforcement by multiaxial warp-knitting. The in situ CFSs, consisting of 1 k or 50 k carbon fiber roving with added staple fiber/multifilament dielectric cladding, are later integral to the load-distributing elements of the concrete component, and elongations within these are easy to record with good correlation to ohmic resistance changes. Gage factors of k = 0.52–1.23 at linearity deviations of ALin = 4.0–8.7% are feasible. This allows a monitoring of C3 building envelopes for structural mechanical changes caused by physical changes within the component through mechanical or thermal loads or deformation and cracks.
“…The type of carbon fibers used in the current research were carbon fiber tows or rovings which were based on a commercially available Toray T300b. The choice of Toray T300b was based on its performance in the literature [ 20 , 21 , 25 , 27 ]. Each roving contains a bundle of long strand of fibers.…”
Carbon fiber-based materials possess excellent mechanical properties and show linear piezoresistive behavior, which make them good candidate materials for strain measurements. They have the potential to be used as sensors for various applications such as damage detection, stress analysis and monitoring of manufacturing processes and quality. In this paper, carbon fiber sensors are prepared to perform reliable strain measurements. Both experimental and computational studies were carried out on commercially available carbon fibers in order to understand the response of the carbon fiber sensors due to changes in the axial strain. Effects of parameters such as diameter, length, and epoxy-hardener ratio are discussed. The developed numerical model was calibrated using laboratory-based experimental data. The results of the current study show that sensors with shorter lengths have relatively better sensitivity. This is due to the fact short fibers have low initial resistance, which will increase the change of resistance over initial resistance. Carbon fibers with low number of filaments exhibit linear behavior while nonlinear behavior due to transverse resistance is significant in fibers with large number of filaments. This study will allow researchers to predict the behavior of the carbon fiber sensor in real life and it will serve as a basis for designing carbon fiber sensors to be used in different applications.
“…In case of strain measurement for example it is the electrical resistance of the used sensor material. In contrast to CF, which shows good electrical conductivity, GF is an isolator. Therefore, an electroconductive sizing, using CNTs, is applied on the GF to realize electrical conductivity .…”
In this comparative study two sensor yarns, such as carbon filament yarns and carbon nanotube coated glass filament yarns are analyzed regarding their electrical property changes during textile manufacturing into multi-layer weft knitted structures as well as during compression molding into a composite plate due to the different electro-mechanical behavior, various sensitivities, and changing ways of acting as an in-situ sensor: yarns act either as a conductive fiber itself (carbon) or as an electrical conductive sizing (CNT-coated glass). Both sensor yarns under investigation have to be considered differently with regard to changes in the electrical conductivity due to mechanical loading during textile processing and possible healing of cracks during compression molding.
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