Long-Term Residual Stress Monitoring via Surface Acoustic Waves Using Piezoelectric Patch Transducers

Residual stresses play a crucial role in the maintenance and longevity of engineering structures. However, continuous monitoring of these stresses remains a challenge due to cost, implementation complexity, and reliability concerns. The present contribution proposes a novel method for continuous long-term residual stress monitoring by tracking the effect of residual stress changes on the propagation velocity of surface acoustic waves (SAWs) due to the acoustoelastic effect via a fixed setup of piezoelectric patch transducers (PETs). The applicability of patch transducers to stress measurement using SAW was experimentally validated using tensile and bending tests on 25CrMo4 (1.7218) steel specimens. The tensile tests exhibited a consistent decrease in wave velocity with increasing stress, enabling straightforward determination of the acoustoelastic coefficient (AEC). The bending tests confirmed the method’s applicability, highlighting the need for multiple excitation frequencies to improve reliability and detect inconsistencies. Finally, it is briefly outlined how to separate residual and load stresses during long-term measurements. The results demonstrate that this approach provides a cost-effective solution for continuous monitoring of residual stresses in metallic materials, offering potential applications in structural health monitoring and predictive maintenance.