The current work presents the manufacturing, poling, testing and validation of a fully 4D printed strip with two integrated piezopolymer (PVDF) elements with printed electrodes. The configuration is designed based on the pitch and catch concept, where each PVDF can perform either as actuator or sensor for wave-based structural health monitoring (SHM) applications. The whole system is additively manufactured using a multi-material printer and three different materials: (1) ABS (acrylonitrile butadiene styrene) for the host beam, (2) PVDF for the piezoelectric elements and (3) silver conductive ink or conductive epoxy for the electrodes. After the fabrication, contact poling is performed in order to increase the PVDFs piezoelectric properties. In contact poling, a high electric field is applied through-the-thickness on each piezopolymer for a specific time period. The poling efficiency is evaluated through vibration testing, where the piezoelectric constants of each PVDF are approximated using inverse numerical modeling. After successful poling, impact tests and guided wave propagation experiments manifest the capacity of the printed PVDF elements to be used as sensors and actuators. The experimental results manifest the great potential of such 4D printed structural systems in SHM applications.

This presentation will report the research progress of ultrasonic guided wave based structural health monitoring for composite structures from Active Materials and Intelligent Structures (AMIS) Lab at Shanghai Jiao Tong University. Both linear and nonlinear ultrasonic guided wave techniques will be covered. In the first part of the presentation, advanced modeling strategies for heterogeneous, anisotropic materials will be delivered, such as the Semi-Analytical Finite Element (SAFE) method and Local Interaction Simulation Approach (LISA). The AMIS SAFE-DISPERSION software and AMIS LISA code can obtain accurate simulation results of dispersion curves and transient dynamic wavefields in a very efficient manner. The second part of the presentation will focus on case studies of utilizing linear and nonlinear ultrasonic guided wave tomography and wave-path interactions for impact damage imaging from sensor array signals. Thereafter, novel Piezoelectric Composite Frequency Steerable Acoustic Transducers (PC-FSAT) will be introduced for generating and receiving directional guided wave signals for structural sensing applications. Furthermore, a self-sensing piezoelectric composite material will be showcased for creating structural self-awareness through guided wave and high frequency vibration actuation and sensing. Both numerical and experimental demonstrations will be presented.

Rivetless structural bonding is a key technology for increasing the structural efficiency of composite aircraft. Structural bonding provides a more uniform load distribution than mechanical fastening, resulting in higher composite joint strength at a reduced weight. However, the certification of rivetless structural bonds is challenging due to their more complex design, their inability to retard damage within the adhesive layer, and concerns regarding their long-term durability. As a result, it is state-of-the-art to certify safety-critical composite joints using well-established mechanical fastening processes, despite their weight penalty. Therefore, there is a need for a rivetless structural bond design that is lightweight and complies with the strict certification requirements.
Increasing damage tolerance through design features and monitoring the bondline integrity are two options defined by aviation authorities to obtain certification. The multifunctional bondline combines both approaches because they complement each other well. In particular, monitoring the structural health of the bondline can be simplified due to the damage tolerance feature. Since the damage tolerance feature arrests damage at defined positions and maintains limit load capacity after arrest, the idea is to reduce the requirements for the structural health monitoring (SHM) system.

Cracked-lap shear specimens equipped with multifunctional disbond arrest features (MDAFs) illustrate the feasibility of the multifunctional bondline approach. The MDAFs consist of fibre Bragg grating sensors or miniaturised strain gauges for damage monitoring and thermoplastic surface-toughening elements for damage arrest. As damage alters the load transfer across the bondline, comparing strains measured near the damage front to those in an undamaged region enables detection. The minimal distance between the two measurement points is the minimum load-transfer length---the distance required to complete 95 % of the load redistribution in structural bonds. Therefore, a two-staged MDAF design consisting of two surface toughening elements with integrated sensors, positioned slightly further apart than the estimated minimum load-transfer length, was tested.

The results demonstrate that the two-stage MDAFs reliably arrest damage and enable damage detection by comparing the strain values obtained at both stages. For the given setup, comparing the strain differences to a threshold suffices as a damage criterion. Even though this criterion requires adjustments for the application in more complex systems, the results confirm that it is feasible to reduce the requirements of the SHM system by combining it with a disbond arrest function. Instead of tracking damage initiation and providing precise damage localisation and residual strength estimates, the SHM system is only required to identify the event of arrested damage by the MDAF. The residual strength can then be determined from the remaining undamaged bondline regions. Therefore, the complexity of the SHM system can be reduced in terms of both the number of installed sensors and the damage-detection algorithms.

Structural health monitoring (SHM) based on ultrasonic guided waves is a novel technology using permanently attached actuator and sensor networks, data acquisition and data evaluation systems to enable in-service inspection of aircraft structures.

A modular and decentralized SHM system is presented that can be adapted to various aircraft application scenarios. The central element of the SHM system is a robust sensor array based on piezocomposite technology that can be efficiently integrated into the manufacturing process of CFRP structures (via co-bonding). The sensor array consists of integrated piezoceramic transducers, electrical cables and integrated electronic components. The decentralized system architecture of the individual electronic components reduces the installation and cabling effort during the assembly of aircraft structures as well as the system weight.

The aeroelastic response of thin-walled cantilever plates in axial flow has gained considerable attention for small-scale wind energy harvesting, as these structures can develop self-sustained oscillations within specific wind-speed ranges. Inverted cantilevers and T-shaped cantilevers with tip masses are particularly promising, since their large-amplitude limit-cycle oscillations may be driven by vortex-induced vibration or rotational flutter, depending on geometry and mass distribution (see Figure). Despite their potential for continuous power generation, the long-term structural durability of such harvesters under repeated large deformation remains insufficiently studied. In particular, fatigue accumulation in thin plates with high modal curvature can restrict the usable wind-speed range and strongly influence geometric design choices.

This study presents a unified computational framework for evaluating the fatigue performance of thin-walled cantilevered aeroelastic harvesters across a wide range of flow conditions. High-fidelity coupled fluid–structure interaction simulations are performed using a previously validated two-dimensional partitioned solver that combines an adaptive Vortex Particle Method with a geometrically nonlinear corotational beam formulation. This approach captures the motion-dependent aerodynamic forces, nonlinear stiffness effects, and transitions from stable behaviour to self-excited oscillations that govern both power output and fatigue loading.

Two systems are examined: inverted cantilevers, which exhibit vortex-induced flapping within a narrow operational band, and T-shaped cantilevers with tip masses, which undergo rotational flutter and maintain oscillations across a broader range of wind speeds. For each configuration, time-resolved internal force signals extracted at critical locations are processed using rainflow counting to evaluate stress ranges, mean stresses, and accumulated fatigue damage. The results show that the T-shaped design offers a wider harvesting bandwidth but may experience higher fatigue at elevated wind speeds due to increasing rotational amplitudes. In contrast, the inverted cantilever operates only within its limited VIV-driven range.

Based on these findings, a fatigue-informed design strategy is proposed in which key geometric parameters, such as vertical plate height, cantilever thickness, and tip mass, are adjusted to maintain fatigue damage rates below a prescribed threshold for the prevailing wind conditions. This enables the tailoring of harvesters to specific environments, allowing either low-wind activation with minimal fatigue penalty or sustained operation over extended wind-speed ranges while keeping stress cycles within acceptable limits. Overall, the study demonstrates the value of integrating fatigue assessment into the design of aeroelastic energy harvesters. By combining high-resolution FSI simulations with cycle-based fatigue evaluation, the proposed framework supports the development of durable, wind-speed-specific harvesters capable of delivering reliable power for long-term autonomous sensing applications.