Integrating PZT-based WP and EMI techniques with multi-criteria analysis for monitoring and assessment of mechanical properties of structural adhesives under curing

Structural adhesives are commonly employed as bonding agents in FRP strengthening systems. Measuring and assessing the mechanical properties of adhesives during the curing process is essential, as these properties directly influence the overall effectiveness of the strengthening system. This study investigated the development of mechanical properties in structural adhesives at various curing times using two PZT-based monitoring techniques, specifically wave propagation (WP) and electromechanical impedance (EMI) techniques. Two types of structural adhesives and two distinct curing temperatures (ambient temperature and mild temperature) were selected for examination. Throughout the adhesive curing process, both methods were utilized for monitoring. Subsequently, tensile tests were conducted to obtain the mechanical properties at different curing durations. The results demonstrate that monitoring indicators from both PZT-based techniques effectively captured the enhancement in adhesive performance during the curing process. Moreover, the tensile strength of the Sika and Carbon adhesives reached stability at ambient temperature after five and three days, respectively, while elevated temperatures accelerated the curing process. Furthermore, two Multi-Criteria Decision Making (MCDM) methods were employed to select monitoring indicators with the least deviation and the closest correlations with mechanical properties. These indicators have the potential to predict mechanical properties, potentially reducing the need for tensile tests.