Strain Sensor For Structural Health Monitoring Research Articles

Strain-Detecting properties of hybrid PE and steel fibers reinforced cement composite (Hy-FRCC) with Multi-Walled carbon nanotube (MWCNT) under repeated compression

This experimental research investigates the feasibility of using hybrid polyethylene (PE) and steel fibers reinforced cement composite (Hy-FRCC) with multi-walled carbon nanotube (MWCNT) as strain sensors. Smart construction material presented in the study is a new type of multifunctional cement composite with both structural material and self-sensing functionalities. The effect of MWCNT dosage (1 and 2% by weight of cement) and the magnitude of repeated compressive stress on the strain-detecting function and elastic modulus was studied. The history of applied compressive loading consists of five successive levels (30, 50, 60, 70 and 80% of compressive strength) of stress amplitude to evaluate the repeated strain-sensing ability of Hy-FRCC. Test results revealed that the incorporation of MWCNT within 2% has little effect on the compressive strength of Hy-FRCC at curing ages of 28-day while under repeated compression, MWCNT is effective to decrease the reduction of the elastic modulus in the Hy-FRCC. Piezoresistivity experiments indicated that the change in resistivity of Hy-FRCC-2 (with 2% MWCNT) specimen can simulate the changes in the measured strain during repeated compressive loading at increasing stress amplitudes up to 80% of compressive strength. It is found that the Hy-FRCC-2 mixture proposed in the present study is likely to be used as strain-sensors for structural health monitoring (SHM) of civil infrastructures.

Characteristics of carbon fiber based strain sensors for structural-health monitoring of textile-reinforced thermoplastic composites depending on the textile technological integration process

The paper presents an effective online measurement technology for non-destructive and continuous monitoring of endless glass fiber reinforced thermoplastic (FRTP) composite structures using the numerous possibilities of textile process technologies for the design and one-step integration of one- and two-dimensional sensor structures based on piezo-resistive exPAN carbon filament yarn (CFY) in textile reinforced structures.The focus of this paper is directed at the analysis of such textile technological integrated sensors as an integral part of the textile reinforcement and their usability for in situ monitoring of local and/or global mechanical loading conditions in difficult or inaccessible areas within short distance of the structural load-bearing layers of FRTP's. If the adhesion of the carbon filament yarn sensor (CFYS) to the surrounding FRTP is sufficient enough, a change in geometry and thereby in resistivity of the carbon filaments can be measured by any mechanical load of the sensor-carrying FRTP component.The advantages and disadvantages of the tailored fiber placement (TFP), flat knitting and weaving textile processes for creating sensor structures will be shown, wherein the mentioned variety of interlacing techniques are used.The effects of the used textile manufacturing processes on the sensory properties are being compared. Furthermore, the effects of the integrated CFY on the mechanical properties of the basic structure are quantified. Sensor structures with minimal influence on the composite structure can be derived from it as well as sensors that enable a selective reinforcement of the composite structure. The textile integration provides a routing of one CFY through several layers of reinforcement. Thus, a damage-free and reproducible production of more complex, 3-dimensional, textile-based sensor networks is feasible in one step.

A carbon nanotube strain sensor for structural health monitoring

A carbon nanotube polymer material was used to form a piezoresistive strain sensor forstructural health monitoring applications. The polymer improves the interfacial bondingbetween the nanotubes. Previous single walled carbon nanotube buckypaper sensorsproduced distorted strain measurements because the van der Waals attraction force allowedaxial slipping of the smooth surfaces of the nanotubes. The polymer sensor uses largermulti-walled carbon nanotubes which improve the strain transfer, repeatability andlinearity of the sensor. An electrical model of the nanotube strain sensor was derived basedon electrochemical impedance spectroscopy and strain testing. The model is useful fordesigning nanotube sensor systems. A biomimetic artificial neuron was developedby extending the length of the sensor. The neuron is a long continuous strainsensor that has a low cost, is simple to install and is lightweight. The neuron has alow bandwidth and adequate strain sensitivity. The neuron sensor is particularlyuseful for detecting large strains and cracking, and can reduce the number ofchannels of data acquisition needed for the health monitoring of large structures.