A Concept of Thermographic Method for Non-Destructive Testing of Polymeric Composite Structures Using Self-Heating Effect.

Andrzej Katunin

doi:10.3390/s18010074

Abstract

Traditional techniques of active thermography require an external source of energy used for excitation, usually in the form of high power lamps or ultrasonic devices. In this paper, the author presents an alternative approach based on the self-heating effect observable in polymer-based structures during cyclic loading. The presented approach is based on, firstly, determination of bending resonance frequencies of a tested structure, and then, on excitation of a structure with a multi-harmonic signal constructed from the harmonics with frequencies of determined resonances. Following this, heating-up of a tested structure occurs in the location of stress concentration and mechanical energy dissipation due to the viscoelastic response of a structure. By applying multi-harmonic signal, one ensures coverage of the structure by such heated regions. The concept is verified experimentally on artificially damaged composite specimens. The results demonstrate the presented approach and indicate its potential, especially when traditional methods of excitation with an external structure for thermographic inspection cannot be applied.

Highlights

Due to wide applicability of polymer-matrix composites (PMCs) for manufacturing elements with high load bearing capacity, primarily in aircraft, aerospace, automotive and marine industries, the knowledge about their actual structural condition becomes crucial for their proper operation and estimation of their residual life
In the case when the tested specimen was excited by the harmonic signal with its first natural frequency (Figure 3a), the temperature increase coincides with the maximal magnitudes of vibration on this mode
In the second case (Figure 3b), when the tested specimen was loaded with its second natural frequency, the damage locations were observable in the regions of the highest vibration magnitudes for this modal shape

Summary

Introduction

Due to wide applicability of polymer-matrix composites (PMCs) for manufacturing elements with high load bearing capacity, primarily in aircraft, aerospace, automotive and marine industries, the knowledge about their actual structural condition becomes crucial for their proper operation and estimation of their residual life. Among the various NDT methods applied to PMCs, including ultrasonic testing, eddy current testing, vibration-based testing, shearography, X-ray computed tomography testing, etc., a group of thermographic methods can be considered as one of the most widespread NDT methods. This is due to several advantages contributing by these methods, such as high speed of testing, and comparatively high sensitivity to particular types of flaws and damage as well as high resolution. In NDT studies, the IRT methods are usually limited to the active ones. The comprehensive overview of the simplest IRT methods used for NDT purposes, namely pulsed ones, can be found in [2]

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