Applying and Improving Non-Linear Ultrasonic Techniques for Robust Inspection of Concrete and Polymer Composite Materials

Abstract

Increasing the service life and therefore the efficiency of a structure can be achieved by implementing Non-Destructive Testing and Evaluation (NDT&E) techniques. Detecting defects is not always possible when using Linear Ultrasonic (LU) techniques especially at the early stages of damage formation. In this dissertation a new Non-Linear Ultrasonic (NLU) technique for monitoring progression of curing in concrete specimens, estimating strength of concrete specimens, detecting defect initiation and progression in composite plates is presented. Additionally, an experimental verification of an acoustic source localization technique in composite plates is also presented. Reviewing the literature shows that there is a need for a new NLU technique that is able to detect and monitor defects in structures reliably and consistently. The Sideband Peak Count-Index (SPC-I) technique is proposed as a new NLU technique that can overcome challenges faced by other conventional NLU techniques. In Concrete cylinder specimens it was found that the SPC-I exhibits clear distinction among various concrete specimens at different stages of curing. LU parameters, however, do not show such consistency. Therefore, the SPC-I technique provides an easy and effective way for monitoring the degree of concrete curing. Additionally, it was found that the SPC-I technique is a good estimator of concrete strength that can be used alongside traditional LU techniques. For composite plate specimens it is observed that the SPC-I NLU parameter can monitor the early stage of damage progression better than the LU parameters while some LU parameter is more effective than the NLU parameter for monitoring the advanced stages of damage. Therefore, a combination of LU and NLU analyses is ideal for the holistic monitoring of the composite panels from the crack nucleation stage to the structural failure stage. Recommendations for further research to aid in the development of the SPC-I are discussed.