Influence of motion compensation on lock-In thermographic investigations of fatigue crack propagation

Urbanek, Ralf; Bär, Jürgen

doi:10.1016/j.engfracmech.2017.03.043

Cited by 16 publications

(17 citation statements)

References 22 publications

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“…In case of the long crack the stress state in front of the crack tip is influenced by the limited specimen width. The influence of limited specimen width is already known in presence of deep notches [13]. This additional bending stress reduces the sum of principal stresses with increasing crack length, which reduces the temperature changes at the crack tip, although the stress intensity in the loading direction is constant.…”

Section: Discussionmentioning

confidence: 96%

“…Urbanek and Bär [12,13] extended the approach to higher harmonic frequencies up to the Nyquist frequency, resulting in additional D1 and D2 modes:…”

Section: Introductionmentioning

confidence: 99%

“…In all approaches, the noise of the temperature measurement is suppressed, leading to a good temperature resolution of about 1.6 mK in the resulting amplitude images [12,13]. The Lock-In Thermography is suitable for the investigation of dynamic processes, for example in crack propagation experiments.…”

Section: Introductionmentioning

confidence: 99%

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Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography

Bär

Urbanek²

2019

Frattura Ed Integrità Strutturale

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Lock-In thermography can be used to investigate elastic stresses and dissipative effects in dynamic processes like crack propagation. The evaluation normally is performed with a Discrete Fourier Transformation resulting in E-and D-Amplitude and phase images. The E-Amplitude images give information about the stress distribution, the D-Amplitude is connected with dissipated energies. The observed changes in the E-amplitude values can be attributed to a change in the stress state at the crack tip due to bending of the specimen caused by the propagating crack. In the crack propagation experiments the maximum value of the D-Mode in the area in front of the crack tip was found to be constant. The appearance of higher harmonic modes in the evaluation raises the question if the Discrete Fourier Transformation is the appropriate method for a quantitative evaluation of dissipative effects. Experiments performed on flat specimens show that the temperature change due to dissipative effects could not be described with a sine wave with the double loading frequency. Therefore, a quantitative determination of dissipated energies using the Discrete Fourier Transformation is impossible. For a quantitative determination of dissipated energies a new evaluation method has to be developed.

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Section: Discussionmentioning

confidence: 96%

“…Urbanek and Bär [12,13] extended the approach to higher harmonic frequencies up to the Nyquist frequency, resulting in additional D1 and D2 modes:…”

Section: Introductionmentioning

confidence: 99%

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Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography

Bär

Urbanek²

2019

Frattura Ed Integrità Strutturale

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“…This clearly indicates that the higher harmonic frequencies are coupled with plastic deformation and it is not sufficient to describe the dissipated energies only with the 2 fL-part. When the rigid body motion of the specimen is not negligible, the evaluation should be combined with a motion compensation technique previously used by Urbanek and Bär [2,5]. This compensation technique requires sharp gradients, for example the border of the painted area.…”

Section: Dft Analysis Of the Thermoelastic Effectmentioning

confidence: 99%

“…This part is known as the so-called D-Mode and is assigned to dissipative energies. Urbanek and Bär [5] showed that in case of plastic deformation additionally amplitudes at higher harmonic frequencies appear, whose entities are currently unclear. The resulting complete DFT evaluation is given by equation 2:…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Thermo-Elastic Behavior of a High-alloyed Steel by Fourier Transformation based Lock-In-Thermography

Urbanek¹,

Bär²

2018

Proceedings of the 2018 International Conference on Quantitative InfraRed Thermography

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For the measurement of elastic stresses with Thermographic Stress Analysis a precise knowledge of the thermoelastic behavior also under consideration of plasticity and strain hardening is necessary. The influence of the coating and the specimen motion have been evaluated. The evaluation of the thermographic measurements was performed with a common sinus fit and a signal dissection with a discrete Fourier transformation (DFT). The distortion of the thermal response by plastic deformation is a known fact also the accompanying high harmonic parts in the DFT. The distortion of the thermal signal has been evaluated by using the Total Harmonic Distortion ratio.

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Infrared Image Processing to Guide the Identification of Damage and Dissipative Mechanisms in 3D Layer-to-Layer Woven Composites

et al. 2022

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This article discusses techniques that aim at facilitating the identification of dissipative mechanisms activated in woven composites under cyclic loadings. The focus is put on the post-processing of thermal measurements acquired during heat build-up experiments, as these are usually used to identify the dissipation sources. The importance of motion compensation pre-processing is demonstrated as it is shown that the latter enhances the quality of the evaluated thermoelastic and dissipation fields. Two specific post-processing techniques are presented in this article. The first one analyzes temperature or thermoelastic fields and searches to detect thermal events associated with the creation of cracks. The second one is based on a Fourier decomposition of thermal fields and aims at highlighting an increased contribution of friction as a dissipation source.

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Influence of motion compensation on lock-In thermographic investigations of fatigue crack propagation

Cited by 16 publications

References 22 publications

Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography

Determination of dissipated Energy in Fatigue Crack Propagation Experiments with Lock-In Thermography

Evaluation of the Thermo-Elastic Behavior of a High-alloyed Steel by Fourier Transformation based Lock-In-Thermography

Infrared Image Processing to Guide the Identification of Damage and Dissipative Mechanisms in 3D Layer-to-Layer Woven Composites

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