Novel data processing modalities for thermal non-destructive testing and evaluation of composite materials

Abstract

Non-Destructive Testing and Evaluation (NDT&E) is a testing and analyzing technique adopted for the inspection of materials without impairing their future usefulness and in-service applicability. NDT&E is also reckoned by the term non-destructive examination (NDE) or non-destructive inspection (NDI). Among various NDT&E modalities, active Infrared non-destructive testing (IRNDT), also known as Active Infrared Thermography (AIRT) has emerged as a proficient technique due to its fast, remote and wide-area inspection of a vast variety of materials under test. The pulse compression favorable Frequency Modulated Thermal Wave Imaging (FMTWI) technique has attained immense acceptance over its conventional pulse and modulation based thermography counterparts due to its better defect detection sensitivity and resolution. The proposed FMTWI is a non-stationary modulated thermographic technique that probes a wide range of frequencies over a limited span of time into the specimen under test to locate all the defects present at different depth locations. Furthermore, pulse compression via matched filtering post processing approach has been incorporated to facilitate enhanced defect detection. In addition to this, several novel data processing approaches like Time Domain Phase (TDP), Frequency Domain Phase (FDP), Differential Filtering and Background Subtraction have been adopted so as to improvise the depth resolution of defects located at various spatial dimensions. The detailed inspection reliability analysis for an AIRT modality is one of the most critical aspects of the generalized industrial inspection procedure. The Probability of Detection (PoD) curves are the widely accepted criterion for ensuring AIRT/IRNDT reliability, and are expressed as a parametric function of defect parameter. Each and every experiment of active AIRT (pulse compression favorable FMTWI) ought to be well designed in order to generate an extensive valid source data set. The continuous signal response PoD model usually works on diverse inspection results generated due to distinct heating and data processing modalities. The aspect ratio (diameter/depth) of any defect located deep inside the specimen under test (composite polymers) is framed according to our experimental experiences to ensure that it is from non-detectable to minimum detectable aspect ratio and larger. The main objective of the thesis is to introduce novel data processing modalities in order to perform quantification of the pulse compression favorable FMTWI for defect estimation via generation of the Probability of Detection (PoD) curves. In the first stage, a linkage is established between various existing active thermographic techniques such as pulse, modulated and FMTWI techniques and in the next stage, we investigated several data post processing modalities and have considered different attributes as statistical figures of merit to achieve a better probabilistic defect characterization. Additionally, constructed PoD curves for Pulse Compression based aperiodic thermal wave imaging (PCTWI) techniques are compared with other traditional AIRT techniques.