Combining two types of reinforcement fiber in a common matrix may lead to different failure modes such as micro-cracks between the layers when the structure is subjected to lower stress levels. Real-time damage detection should be integrated into the hybrid composite structure to provide structural integrity and mitigate this problem. This paper outlines the working mechanisms and the fabrication of an integrated capacitive sensor in an intra-ply hybrid composite (2 × 2 twill weave). Uniaxial tensile and flexural tests were conducted to characterize the proposed sensor and provide self-sensing functionality (smart structure). The sensitivity and repeatability of the capacitive sensor were measured to be around 1.3 and 185 µΔC/Co, respectively. The results illustrate that onset of damage between layers can be detected by in situ monitoring. It can be seen that the initial damage was detected at the turning point where the relative change in capacitance begins to reduce while the load increases. Finite element modeling was also constructed to analyze the test results and explain the reasons behind the turning point. It was shown that the carbon yarns experienced high transverse shear stress (τxz) in the crimp region, leading to inter-fiber cracks.

Hybrid composite material has been widely used in many engineering applications (e.g., for automobiles)and has several advantages over conventional fibre-reinforced composite materials, such as high strength-to-weight ratio and low cost. However, combining two kinds of reinforcement fibre within a common matrix may lead to different failure modes, such as delamination between the layers and fragmentation when the structure is subjected to high loads. To avoid this problem, real-time damage detection should be integrated into the hybrid composite structures for structural integrity. This paper outlines the working mechanisms and the initial fabrication of an integrated capacitive sensor into the intra-ply hybrid composite. The tensile test was conducted to perform the basic characterization of the proposed sensor and provide self-sensing functionality (smart structure). The results illustrate that damage between layers can be detected by in-situ monitoring. It is shown that the initial damage was detected at the turning point where the relative change in capacitance begins to decrease and when the axial tensile force increases. In addition, the developed smart material has shown a linear sensitivity toward crosshead displacement up to the turning point, and applying the monitoring is useful in self-sensing for hybrid composites.