Truly integrated carbon nanotubes (CNT) in oxide ceramics for micro-strain sensing applications

Oxide ceramic matrix composites (OCMC), particularly those reinforced with fibers, have shown promising properties for structural health monitoring applications in high-temperature environments. Despite their enhanced mechanical and unique dielectric properties, exposure to high temperatures and humidity adversely affects the impact resistance of OCMC, leading to structural deformations. Recent advances in strain sensor technology have introduced novel solutions for monitoring OCMC structural deformations, including the use of carbon nanotubes in nanocomposites for ultra-stretchable and skin-mountable strain sensors. These sensors have demonstrated excellent performance in strain sensing applications. However, because these nanocomposite sensors are mounted on the surface of OCMC structures, their sensitivity to strain is limited due to poor load transfer between the structures and the strain sensors. In this work, multi-walled carbon nanotubes (MWCNTs) were embedded within the OCMC, allowing the oxide ceramic structures to function as strain sensors. In MWCNT/OCMC composites, MWCNTs form a electrically conductive network within the ceramic matrix. Under strain, changes in these conductive network lead to variations in resistance, which depend on the applied strain. Unlike traditional surface-mounted sensors, which suffer from weak load transfer, embedding MWCNTs directly inside the ceramic structure enhances sensitivity and ensures stable electrical behavior under repeated strain cycles. For efficient and homogeneous incorporation of CNTs into oxide ceramic composites, the solution mixing approach was employed. This versatile method involves dispersing nanoscale fillers within a liquid solution for nanocomposite synthesis. An MWCNT/OCMC-based specimen structure was fabricated using ceramic injection molding with dimensions of 79.6 × 9 . 9 × 3 mm 3 (length × width × thickness). Microstructural analysis of MWCNT/OCMC using scanning electron microscopy confirmed the homogeneous and efficient integration of MWCNTs into the oxide ceramic composites. To assess the properties of MWCNTs after integration within the OCMC, FTIR and Raman spectroscopy analyses were conducted. Furthermore, the homogeneity of MWCNT distribution in OCMC was analyzed using four-point resistance measurements at different positions along the specimen. Results showed that the deviation in bulk resistivity was less than 17% of the minimum resistivity measured across the specimen. The developed MWCNT/OCMC structure was tested as a strain sensor by measuring electrical resistance during a four-point flexural test within a strain range of 0–380 μ ɛ at a strain rate of 190 μ ɛ /min. The results showed that the gauge factors (GF) were 7.99 and 2.12 in the strain ranges of 0–160 μ ɛ and 160–380 μ ɛ , respectively. Additionally, the sensor exhibited considerably less hysteresis after ten cycles of tensile strain. • Homogeneous Integration of Multi-Walled Carbon Nanotubes in Oxide Ceramic Composites for Strain Sensing Applications. • Integrating the strain Sensing Performance of MWCNT/OCMC Composite Structures.