Harmonious developments of electrical and mechanical performances are crucial for stretchable sensors in structural health monitoring (SHM) of flexible aircraft such as aerostats and morphing aircrafts. In this study, we prepared a highly durable ternary conductive nanocomposite made of polydimethylsiloxane (PDMS), carbon black (CB) and multi-walled carbon nanotubes (MWCNTs) to fabricate stretchable strain sensors. The nanocomposite has excellent electrical and mechanical properties by intensively optimizing the weight percentage of conducting fillers as well as the ratio of PDMS pre-polymer and curing agent. It was found that the nanocomposite with homogeneous hybrid filler of 1.75 wt % CB and 3 wt % MWCNTs exhibits a highly strain sensitive characteristics of good linearity, high gauge factor (GF ~ 12.25) and excellent durability over 10⁵ stretching-releasing cycles under a tensile strain up to 25% when the PDMS was prepared at the ratio of 12.5:1. A strain measurement of crack detection for the aerostats surface was also employed, demonstrating a great potential of such ternary nanocomposite used as stretchable strain sensor in SHM.

Aircraft smart skin technology requires the integration of large-scale, lightweight, and integrative sensor networks with aircraft structural skin, but it is difficult to directly manufacture such sensor networks in a large-scale, low-cost, reliable, and simple way. To study this issue, a design and manufacturing method of a stretchable and large-scale guided wave sensor network is proposed in this article. The key principle of the method is to design and manufacture the guided wave sensor network in a limited scale and expand it in a large-scale for aircraft smart skin of structural health monitoring. To ensure the excellent stretchability of the network, the design method of a serpentine-based fractal island-interconnect structure combined with the flexible printed circuit manufacturing process is proposed. The whole manufacturing process of the guided wave sensor network is realized by the mature flexible printed circuit process and the piezoelectric transducers (referred to as PZTs) are integrated with the network by reflow soldering which is compatible with the flexible printed circuit process, which greatly reduce manufacturing costs, simplify manufacturing process, and improve the yield and stability of the network. The guided wave sensor network can be uniaxially stretched to 500% of its original size and work well when fully expanded to cover 2500% of its original area. The test results of guided wave response show that the PZTs on the network can excite and receive guided wave signal normally. In addition, the network is placed on the surface of a carbon fiber composite laminate with stiffeners and the validation results show that the network can be applied to both active and passive guided wave–based structural health monitoring of composite structures, including damage imaging and impact imaging.

Through the integration of advanced sensors, actuators, and micro-processors, aircraft smart skin technology can improve the structural performance of aircraft and make them self-perception, self-diagnosis, self-adaptation, self-learning, and self-repair. Aircraft smart skin for structural health monitoring (SHM) is an important type of aircraft smart skin and has received extensive attention in recent years. Large-scale, lightweight, and low-power consumption are three key problems hindering the realization and engineering applications of aircraft smart skin for SHM. In view of these problems and restrictions of practical aircraft onboard applications, this article reviews the current research progress on aircraft smart skin for SHM, introduces their design, materials, manufacturing process, and monitoring principles in detail, and discusses how they study above problems from these aspects. Finally, perspectives are proposed on the opportunities and future developments of aircraft smart skin for SHM.

Due to the growing use of composite materials in aircraft structures, Aircraft Smart Composite Skins (ASCSs) which have the capability of impact monitoring for large-scale composite structures need to be developed. However, the impact of an aircraft composite structure is a random transient event that needs to be monitored on-line continuously. Therefore, the sensor network of an ASCS and the corresponding impact monitoring system which needs to be installed on the aircraft as an on-board device must meet the requirements of light weight, low power consumption and high reliability. To achieve this point, an Impact Region Monitor (IRM) based on piezoelectric sensors and guided wave has been proposed and developed. It converts the impact response signals output from piezoelectric sensors into Characteristic Digital Sequences (CDSs), and then uses a simple but efficient impact region localization algorithm to achieve impact monitoring with light weight and low power consumption. However, due to the large number of sensors of ASCS, the realization of lightweight sensor network is still a key problem to realize an applicable ASCS for on-line and continuous impact monitoring. In this paper, three kinds of lightweight piezoelectric sensor networks including continuous series sensor network, continuous parallel sensor network and continuous heterogeneous sensor network are proposed. They can greatly reduce the lead wires of the piezoelectric sensors of ASCS and they can also greatly reduce the monitoring channels of the IRM. Furthermore, the impact region localization methods, which are based on the CDSs and the lightweight sensor networks, are proposed as well so that the lightweight sensor networks can be applied to on-line and continuous impact monitoring of ASCS with a large number of piezoelectric sensors. The lightweight piezoelectric sensor networks and the corresponding impact region localization methods are validated on the composite wing box of an unmanned aerial vehicle. The accuracy rate of impact region localization is higher than 92%.