Foundation for the Research, Development and Application of Composite Materials (FIDAMC), Avda. Rita Levi Montalcini 29, Tecnogetafe, 28906 Getafe, Spain.
Institut für Polymerwerkstoffe und Kunststofftechnik TU Clausthal, Agricolastraße 6, 38678 Clausthal-Zellerfeld, Germany.
Sensors (Basel). 2023 May 16;23(10):4784. doi: 10.3390/s23104784.
Piezoceramic transducers (PCTs) bonded to carbon fiber-reinforced plastic (CFRP) composite structures must be durable as well as remain properly bonded to the structure in order to provide reliable data for accurate guided-wave-based structural health monitoring (SHM) of aeronautical components. The current method of bonding transducers to composite structures through epoxy adhesives faces some shortcomings, such as difficult reparability, lack of weldability, longer curing cycles, and shorter shelf life. To overcome these shortcomings, a new efficient procedure for bonding the transducers to thermoplastic (TP) composite structures was developed by utilizing TP adhesive films. Application-suitable TP films (TPFs) were identified and characterized through standard differential scanning calorimetry (DSC) and single lap shear (SLS) tests to study their melting behavior and bonding strength, respectively. Special PCTs called acousto-ultrasonic composite transducers (AUCTs) were bonded to high-performance TP composites (carbon fiber Poly-Ether-Ether-Ketone) coupons with a reference adhesive (Loctite EA 9695) and the selected TPFs. The integrity and durability of the bonded AUCTs in aeronautical operational environmental conditions (AOEC) were assessed in accordance to the standard Radio Technical Commission for Aeronautics DO-160. The AOEC tests performed were operating low and high temperatures, thermal cycling, hot-wet, and fluid susceptibility tests. The health and bonding quality of the AUCTs were evaluated by the electro-mechanical impedance (EMI) spectroscopy method and ultrasonic inspections. The AUCT defects were created artificially and their influence on the susceptance spectra (SS) was measured to compare them with the AOEC-tested AUCTs. The results show that a small change occurred in the SS characteristics of the bonded AUCTs in all of the adhesive cases after the AOEC tests. After comparing the changes in SS characteristics of simulated defects with that of the AOEC-tested AUCTs, the change is relatively smaller and therefore it can be concluded that no serious degradation of the AUCT or the adhesive layer has occurred. It was observed that the most critical tests among the AOEC tests are the fluid susceptibility tests, which can cause the biggest change in the SS characteristics. Comparing the performance of the AUCTs bonded with the reference adhesive and the selected TPFs in the AOEC tests, it was seen that some of the TPFs, e.g., Pontacol 22.100 outperforms the reference adhesive, while the other TPFs have similar performance to that of the reference adhesive. Therefore, in conclusion, the AUCTs bonded with the selected TPFs can withstand the operational and environmental conditions of an aircraft structure, and hence, the proposed procedure is easily installed, reparable, and a more reliable method of bonding sensors to aircraft structures.
压电陶瓷换能器（PCTs）与碳纤维增强塑料（CFRP）复合材料结构结合必须具有耐用性，并且能够正确地与结构结合，以便为航空部件的基于导波的精确结构健康监测（SHM）提供可靠的数据。目前通过环氧树脂胶粘剂将换能器粘结到复合材料结构的方法存在一些缺点，例如难以修复、缺乏可焊接性、更长的固化周期和更短的保质期。为了克服这些缺点，通过利用热塑性（TP）胶粘剂薄膜开发了一种将换能器粘结到热塑性复合材料（TP）结构的新的高效方法。通过标准差示扫描量热法（DSC）和单搭接剪切（SLS）试验分别对应用合适的 TP 薄膜（TPF）进行了识别和特性研究，以分别研究其熔融行为和粘结强度。将特殊的超声复合换能器（AUCT）与高性能 TP 复合材料（碳纤维聚醚醚酮）试件结合，使用参考胶粘剂（Loctite EA 9695）和所选 TPF。根据航空无线电技术委员会 DO-160 标准，评估了在航空操作环境条件（AOEC）下粘结的 AUCT 的完整性和耐用性。进行了 AOEC 测试，包括工作低温和高温、热循环、湿热和流体敏感性测试。通过机电阻抗（EMI）光谱法和超声波检查评估 AUCT 的健康状况和粘结质量。通过人工制造 AUCT 缺陷，并测量它们对电纳谱（SS）的影响，将其与经过 AOEC 测试的 AUCT 进行比较。结果表明，在所有胶粘剂情况下，AOEC 测试后，粘结 AUCT 的 SS 特性仅发生了微小变化。在比较模拟缺陷的 SS 特性变化与经过 AOEC 测试的 AUCT 的 SS 特性变化之后，可以得出这样的结论，即 AUCT 或胶粘层没有发生严重的退化。观察到 AOEC 测试中最关键的测试是流体敏感性测试，因为它会导致 SS 特性发生最大变化。在 AOEC 测试中比较粘结有参考胶粘剂和所选 TPF 的 AUCT 的性能时，发现某些 TPF，例如 Pontacol 22.100，优于参考胶粘剂，而其他 TPF 的性能与参考胶粘剂相似。因此，总之，粘结有所选 TPF 的 AUCT 可以承受飞机结构的操作和环境条件，因此，所提出的方法易于安装、可修复，并且是将传感器粘结到飞机结构的更可靠的方法。
