The project aimed to create an integrated structural health monitoring (SHM) system for composite aircraft structures, combining vibration‑based monitoring with acoustic emission (AE) and acoustic ultrasonics (AU). The core technical outcome was a laboratory prototype that could be applied to a real door‑frame structure and validated under mechanical loading. The system architecture was defined in the first milestone, with a robust actuator‑sensor module that measures strain, acceleration, and temperature and includes on‑board data preprocessing and communication electronics. This module was designed to be compatible with all SHM modalities, thereby reducing wiring complexity and overall system weight.

Modal analysis of the door‑frame structure was performed to identify natural frequencies and mode shapes. Four damage‑relevant frequencies were highlighted, and the system’s ability to detect changes in modal parameters was demonstrated. Load steps of 0, 0.4, 0.6, and 0.75 (presumably fractions of the ultimate load) were applied, and the resulting modal shifts were recorded. The dust‑spread diagram and failure images of the upper stringer adhesive provided visual confirmation of damage initiation and progression. The integrated SHM system successfully detected and localized damage at these load levels, confirming the reliability of the combined acoustic and modal approach.

The acoustic subsystem employed AE to capture high‑frequency stress waves generated by crack initiation and growth, while AU provided continuous monitoring of the structure’s acoustic response. The vibration subsystem used accelerometers positioned as shown in the sensor layout to capture modal responses. Data fusion algorithms were developed to correlate AE events with modal changes, enabling precise damage localization and progression assessment. The software for data evaluation was completed in the final milestone and demonstrated real‑time monitoring capabilities.

Collaboration was carried out by a consortium of the University of Siegen, the University of Bochum, and Wölfel Engineering GmbH + Co. KG. The project began in early 2020, but the COVID‑19 pandemic caused significant delays in hardware procurement and on‑site work. Despite these challenges, the partners maintained close communication, with the University of Siegen’s Mechanical Engineering department taking over the SHM subproject from Bochum after Professor Peter Kraemer’s appointment. Wölfel Engineering provided the funding support, receiving a grant of 65 % of the 600 k € self‑costs, and contributed to the development of the actuator‑sensor module and the integration of the system on the test structure.

The project’s milestones included concept development, system identification of the test object, laboratory installation of the test system, software development for data analysis, and validation of the vibration‑based subsystem through simulation and laboratory experiments. The final outcome is a validated SHM prototype that demonstrates reliable damage detection and localization in a composite door‑frame structure, paving the way for predictive maintenance strategies that can extend inspection intervals and reduce maintenance costs in aviation.