Mechanical degradation estimation of thermosets by peak shift assessment: General approach using infrared spectroscopy. (14th April 2021)

• Record Type: Journal Article
• Authors: Doblies, Audrius; Feiler, Christian; Würger, Tim; Schill, Eduard; Meißner, Robert H.; Fiedler, Bodo
• Is Part Of: Polymer. Volume 221(2021)
• Publication Date: 2021-04-14
• Subjects: Non-destructive testing -- FTIR -- Plasticity -- Structural health monitoring; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2021.123585
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Until now, detecting weak spots in composite structures remains a key challenge in the aviation industry. The correct assessment of the load-bearing capability after structural overloading or the occurrence of barely-visible damages is particularly important to maintain structural integrity. Nonetheless, a reliable and overarching non-destructive inspection method to estimate the residual mechanical properties while covering all major damage scenarios has not been found yet. Several non-destructive techniques have been proposed to approach these challenges and are already in place for specific damage cases. However, each technique has its sources of information and therefore, limitations in practice due to a lack of generalisation. In this work, we present a concept and approach to gain access to the residual mechanical properties of a thermosetting polymer solely based on its inherent material state independent from its life-cycle history. Therefore, the material state is obtained by combining Fourier-transformed infrared spectroscopy with feature extraction algorithms based on Gaussian peak fitting. As proof of concept, tensile, creep, and cyclic tests are conducted to demonstrate this approach's advantage. A complementary theoretical investigation using quantum chemical calculations is employed to support the experimental work by identifying the investigated polymer's characteristic vibrational modes and predicting their evolution during the experiments. The results show that the quantification of molecular changes can estimate the material state and that the method is suitable to improve the understanding of the degradation processes and severity. This publication shall particularly serve as the basis for further research to study the interaction between molecular forces and material properties. Graphical abstract: Image 1 Highlights: Thermosetting polymers can undergo significant plastic deformation at certain conditions. Infrared spectroscopy peak-shifts can be applied to estimate the molecular stress distribution of thermosetting polymers. Feature extraction algorithms contribute to discover correlations with material properties and predict future behavior. Quantum chemical calculations enable an estimation of characteristic vibrational modes and a prediction of their evolution.