Carbon nanotube/polymer-based composites have led to studies that enable the realization of low-cost, high-sensitivity piezoresistive strain sensors. This study investigated the characteristics of piezoresistive multi-walled carbon nanotube (MWCNT)/epoxy composite strain sensors subjected to tensile and compressive loads in one direction at relatively small amounts of strain. A patterned sensor was designed to overcome the disadvantage of the load direction sensitivity differences in the existing sensors. The dispersion state of the MWCNTs in the epoxy polymer matrix with the proposed dispersion process was verified by scanning electron microscopy. An MWCNT/epoxy patterned strain sensor and a patch-type strain sensor were directly attached to an acrylic cantilever beam on the opposite side of a commercial metallic strain gauge. The proposed patterned sensor had gauge factors of 2.52 in the tension direction and 2.47 in the compression direction. The measured gauge factor difference for the patterned sensor was less than that for the conventional patch-type sensor. Moreover, the free-vibration frequency response characteristics were compared with those of metal strain gauges to verify the proposed patch-type sensor. The designed drive circuit compensated for the disadvantages due to the high drive voltage, and it was confirmed that the proposed sensor had higher sensitivity than the metallic strain gauge. In addition, the hysteresis of the temperature characteristics of the proposed sensor is presented to show its temperature range. It was verified that the patterned sensor developed through various studies could be applied as a strain sensor for structural health monitoring.

The objective of this paper is to study the performance of piezoelectric materials on a piezoelectric paint sensor. The paper begins by presenting a fabrication method for a paint sensor with piezoelectric properties using piezoelectric materials. The paint sensor is composed of piezoelectric powder and epoxy resin in a 1:1 weight ratio. Five different piezoelectric materials, including three soft-type and two hard-type materials, were used and their piezoelectric properties compared in paint sensors and ceramic sensors. The paint sensors were cured using a steel mold for producing a uniform specimen size of 20 × 10 × 0.2 mm ³ , and an electrode was made on the upper and lower sides using silver paste. Poling treatment was then successfully performed at room temperature (20 °C) under a 4 kV mm ⁻¹ electric field for 30 min in order to activate the paint specimen as a sensor. Impact signals were monitored by measuring output voltage from the paint sensor in relation to impact force. The sensor’s piezoelectric properties were then calculated using normalized piezoelectric properties. In addition, five different piezoelectric ceramic sensors were fabricated and their d ₃₃ value measured to compare the sensitivity of paint sensors. As a result, Pb(Ni _1/3 Nb _2/3 )O ₃ -Pb(Zr, Ti)O ₃ (PNN-PZT) powder showed higher sensitivity and higher piezoelectric properties than other piezoelectric materials in both paint and ceramic sensors.

In this study, we propose a method to estimate structural deformation and failure by using displacement-strain transformation matrices, i.e., strain-to-displacement transformation (SDT) and displacement-to-strain transformation (DST). The proposed SDT method can be used to estimate the complete structural deformation where it is not possible to apply deformation measurement sensors, and the DST method can be used for to estimate structural failures where strain and stress sensors cannot be applied. We applied the SDT matrix to a 1D beam, a 2D plate, rotating structures and real wind turbine blades, and successfully estimated the deformation in the structures. However, certain difficulties were encountered while estimating the displacement of brittle material such as an alumina beam. The study aims at estimating the displacement and stress to predict the failure of the structure. We also explored applying the method to multi-material structures such as a two-beam bonded structure. In the study, we used alumina–aluminum bonded structures because alumina is bonded to the substrate to protect the structure from heat in many cases. Finally, we present the results of the displacement and failure estimation for the alumina–aluminum structure.