Multi-label classification algorithms for composite materials under infrared thermography testing

The key idea in this paper is to propose multi-labels classification algorithms to handle benchmark thermal datasets that are practically associated with different data characteristics and have only one health condition (damaged composite materials). A suggested alternative approach for extracting the statistical contents from the thermal images, is also employed. This approach offers comparable advantages for classifying multi-labelled datasets over more complex methods. Overall scored accuracy of different methods utilised in this approach showed that Random Forest algorithm has a clear higher performance over the others. This investigation is very unique as there has been no similar work published so far. Finally, the results demonstrated in this work provide a new perspective on the inspection of composite materials using Infrared Pulsed Thermography

Function-oriented in-line quality assurance of hybrid sheet molding compound

Die Verwendung von faserverstärkten Kunststoffen (FVK) nimmt weltweit stetig zu. Die Kombination von diskontinuierlichem Sheet Molding Compound (DiCo-SMC) und kontinuierlichem SMC (Co-SMC) in einer neuen, hybriden Materialklasse (CoDiCo-SMC) verspricht günstige Herstellungskosten bei gleichzeitig hoher lokaler Steifigkeit und Festigkeit zu erreichen. Allerdings gefährden auftretende Fertigungsabweichungen die Funktionserfüllung der gefertigten Bauteile. Die resultierende Forderung nach fehlerfreien FVK-Bauteilen gilt neben den hohen Preisen für Rohmaterialien als ein weiterer Kostentreiber. Mithilfe des Ansatzes einer bauteilindividuellen, funktionsorientierten In-line-Qualitätssicherung soll im Rahmen dieser Arbeit Abhilfe geschaffen werden. Für diese Art der Qualitätssicherung werden In-line-Messergebnisse in Funktionsmodelle integriert. Metamodelle der Funktionsmodelle beschleunigen die Funktionsbewertung und ermöglichen eine Funktionsaussage innerhalb der Zykluszeit in der Produktion. In der vorliegenden Arbeit wurde die bauteilindividuelle, funktionsorientierte In-line-Qualitäts-sicherung exemplarisch für die neue Werkstoffklasse CoDiCo-SMC umgesetzt. Zur Quantifizierung von drei relevanten Fertigungsabweichungen (lokale Glasfaseranteile, Pose des Co-SMC Patches, Delamination) wurden drei verschiedene Messtechniken eingesetzt. Die Terahertz-Spektroskopie wurde zum ersten Mal zur In-line-Messung lokaler Glasfaseranteile in DiCo-SMC eingesetzt. Die Puls-Phasen-Thermografie wurde zur Quantifizierung der Delamination und eine Industriekamera zur Messung der Pose des Co-SMC Patches genutzt. Für jede Messtechnik wurde die Messunsicherheit gemäß des „Guide to the expression of uncertainty in measurement“ (GUM) quantifiziert. Die Messergebnisse wurden in einem parametrierten Finite-Elemente-Modell (FE) weiterverarbeitet und zu einer Funktionsprädiktion aggregiert. Mit Hilfe der Messergebnisse und der modellierten Funktion konnten über diese Input-Output-Beziehungen Metamodelle trainiert werden. In dieser Arbeit wird die prädizierte Bauteilfunktion ebenfalls als Messergebnis verstanden. Daher wurden die Mess-unsicherheiten sowohl der FE-Modelle als auch der Metamodelle bestimmt. Der vorgeschlagene Ansatz wurde anhand von zwei exemplarischen Prüfkörpern validiert. Die Ergebnisse zeigen, dass insbesondere die Messung der lokalen Glasfaseranteile und der Pose des Co-SMC Patches Rückschlüsse auf die bauteilspezifische Steifigkeit zulassen. Allerdings muss aufgrund der ermittelten Messunsicherheiten derzeit noch auf eine industrielle Anwendung verzichtet werden. Die Nutzung bauteilspezifischer Funktionsinformationen nach der Fertigung ermöglicht es, gängige Sicherheitsfaktoren in der Dimensionierung von FVK-Bauteilen zu reduzieren

Nondestructive Testing in Composite Materials

In this era of technological progress and given the need for welfare and safety, everything that is manufactured and maintained must comply with such needs. We would all like to live in a safe house that will not collapse on us. We would all like to walk on a safe road and never see a chasm open in front of us. We would all like to cross a bridge and reach the other side safely. We all would like to feel safe and secure when taking a plane, ship, train, or using any equipment. All this may be possible with the adoption of adequate manufacturing processes, with non-destructive inspection of final parts and monitoring during the in-service life of components. Above all, maintenance should be imperative. This requires effective non-destructive testing techniques and procedures. This Special Issue is a collection of some of the latest research in these areas, aiming to highlight new ideas and ways to deal with challenging issues worldwide. Different types of materials and structures are considered, different non-destructive testing techniques are employed with new approaches for data treatment proposed as well as numerical simulations. This can serve as food for thought for the community involved in the inspection of materials and structures as well as condition monitoring

Recent advances in active infrared thermography for non-destructive testing of aerospace components

Active infrared thermography is a fast and accurate non-destructive evaluation technique that is of particular relevance to the aerospace industry for the inspection of aircraft and helicopters’ primary and secondary structures, aero-engine parts, spacecraft components and its subsystems. This review provides an exhaustive summary of most recent active thermographic methods used for aerospace applications according to their physical principle and thermal excitation sources. Besides traditional optically stimulated thermography, which uses external optical radiation such as flashes, heaters and laser systems, novel hybrid thermographic techniques are also investigated. These include ultrasonic stimulated thermography, which uses ultrasonic waves and the local damage resonance effect to enhance the reliability and sensitivity to micro-cracks, eddy current stimulated thermography, which uses cost-effective eddy current excitation to generate induction heating, and microwave thermography, which uses electromagnetic radiation at the microwave frequency bands to provide rapid detection of cracks and delamination. All these techniques are here analysed and numerous examples are provided for different damage scenarios and aerospace components in order to identify the strength and limitations of each thermographic technique. Moreover, alternative strategies to current external thermal excitation sources, here named as material-based thermography methods, are examined in this paper. These novel thermographic techniques rely on thermoresistive internal heating and offer a fast, low power, accurate and reliable assessment of damage in aerospace composites

Multi-layer carbon fiber reinforced plastic characterization and reconstruction using eddy current pulsed thermography

Ph. D. Thesis.Carbon fibre composite materials are widely used in high-value, high-profit applications, such as aerospace manufacturing and shipbuilding – due to their low density, high mechanical strength, and flexibility. Existing NDT techniques such as eddy current testing suffers from electrical anisotropy in CFRP (carbon fibre reinforced plastics). Ultrasonic is limited by substantial attenuation of signal caused by the multilayer structure. The eddy current pulsed thermography has previously been applied for composites NDE (non-destructive evaluation)such as impact damage, which has the ability for quick and accurate QNDE(quantitative non-destructive evaluation) inspection but can be challenging for detection and evaluation of sub-surface defects, e.g., delamination and debonding in multiple layer structures. Developing QNDE solutions using eddy current thermography for addressing subsurface defects evaluation in multi-layer and anisotropic CFRP is urgently required. This thesis proposes the application of eddy current pulsed thermography (ECPT) and ECPuCT (eddy current pulse compression thermography) for tackling the challenges of anisotropic properties and the multi-layer structure of CFRP using feature-based and reconstruction-based QNDE and material characterisation. The major merit for eddy current heating CFRP is the volumetric heating nature enabling subsurface defect detectability. Therefore, the thesis proposes the investigation of different ECPT and their features for QNDE of various defects, including delamination and debonding. Based on the proposed systems and QNDE approach, three case studies are implemented for delamination QNDE, debonding QNDE, conductivity estimation and orientation inverse reconstruction using the two different ECPT systems and features, e.g., a pulse compression approach to increase the capability of the current ECPT system, the feature-based QNDE approach for defect detection and quantification, and reconstruction-based approach for conductivity estimation and inversion. The three case studies include 1) investigation of delamination with different depths in terms of delamination location, and depth quantification using K-PCA, proposed temporal feature-crossing point feature and ECPuCT system; 2) investigation of debonding with different electrical and thermal properties in terms of non-uniform heating pattern removal and properties QNDE using PLS approaches, impulse response based feature