Lock-In Thermographic Stress Analysis of notched and unnotched specimen under alternating loads

Urbanek, Ralf; Bär, Jürgen

doi:10.1016/j.prostr.2017.07.170

Cited by 8 publications

(9 citation statements)

References 7 publications

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“…The DFT analysis of the temperature signal results in a dissection of the measured signal for each pixel in a sum of sinusiodal waves according to equation (2). In contrast to the common evaluation with a simple sinusoidal fit, beside the thermoelastic response, values for the amplitude and the phase shift for the dissipative 2 fL-part and the higher harmonic frequencies up to the Nyquist frequency are achieved.…”

Section: Dft Analysis Of the Thermoelastic Effectmentioning

confidence: 99%

“…Unfortunately, because of the not ideal emissivity of the coating, the temperature amplitude measured by thermography is smaller than the theoretical values. When the thermal emissivity of the coating is unknown, a thermoelastic constant KE including the emissivity of the specimen surface can be determined by calibrating the system with defined stress amplitudes [2].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Dft Analysis Of the Thermoelastic Effectmentioning

confidence: 99%

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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“…The emissivity of the coating has to be taken into account for a correct determination of elastic stresses out of the measured temperature amplitude. When the thermal emissivity of the coating is unknown, a thermoelastic constant K c including the emissivity of the paint can be determined by calibrating the system with defined stress amplitudes [6]. In this case, Kc replaces the constant K0 in Eq.…”

Section: Introductionmentioning

confidence: 99%

“…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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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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Detection of short cracks in riveted connections using Lock‐In‐Thermography

Sieber¹,

Urbanek²,

Bär³

2021

ce papers

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Although many riveted bridge structures made of old structural steel from the 19th and early 20th centuries are still in use today, there is usually no need to replace them. When assessing these steel structures with regard to necessary refurbishment or strengthening measures, engineers need information about the remaining fatigue lifetime in particular. Often no sufficient remaining fatigue life can be determined based on normative S‐N‐curve assessment. An initiation of fatigue cracks has to be assumed. These cracks occur primarily at the edge of the rivet holes. In the early phase of crack growth below the rivet head, the crack cannot be found in a visual inspection of the structure. For this reason, the remaining cyclic lifetime based on fracture mechanics is determined assuming a start length of the crack beyond the rivet head. This paper reports investigations using thermoelastic stimulated Lock‐In‐Thermography as a NDT method for detection of hidden cracks in riveted joints. The results have shown that cracks below rivet heads can be detected. This is possible despite the presence of a corrosion protection coating. The detectable crack length depends mainly on the level of stress and the loading frequency.

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Lock-In Thermographic Stress Analysis of notched and unnotched specimen under alternating loads

Cited by 8 publications

References 7 publications

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

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

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

Detection of short cracks in riveted connections using Lock‐In‐Thermography

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