Damage Diagnosis in Composite Materials under Applied Load with Guided Waves-based SHM

Structural health monitoring (SHM) of composite structures provides an approach for fully utilizing the benefits of composite materials while providing a strategy for monitoring their complex damage mechanics in real-time. Application of SHM requires not only the ability to localize, classify, and quantify damage in a structure, but also to compensate for changing environmental and operational conditions. This work will focus on one such problem, specifically identifying the presence of delamination in composites while the material is under applied load. An experimental series was conducted testing composite coupons under tension-tension fatigue in order to cause damage to gradually propagate through the samples. Guided wave signals, propagated through the composite samples using piezoelectric transducers, and verification X-ray images were collected at progressive stages and different applied load levels during testing. By analyzing ultrasonic signal changes from the SHM system when experiencing effects from varying levels of damage severity and applied load the goal is to identify delamination in a signal propagation path. Signal features extracted from the guided wave data, such as amplitude, velocity, and energy content, are used to identify delamination. Utilizing combinations of signal features as prediction variables for statistical modeling, decision trees are grown to create a multi-layer model which uses these signal changes in order to predict delamination regardless of the operational effects also influencing the guided wave SHM system