Non-destructive testing procedure for porosity determination in carbon fibre reinforced plastics using pulsed thermography

Mayr, G.; Gresslehner, K. H.; Hendorfer, G.

doi:10.1080/17686733.2017.1326078

Cited by 7 publications

(6 citation statements)

References 20 publications

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“…Due to the large scattering of the thermal diffusion times estimated by TSR, where the experimental log-log thermogram is fitted by a logarithmic polynomial of degree n=9 [30], no quantitative porosity estimation was possible, as also concluded by Mayr et al [6]. For all TSR evaluations, the measurement data T meas was not truncated and the full A-scan representation of the virtual wave, where the amplitude of the virtual waves is plotted versus the thermal diffusion time t d for the steps # = [7,11,15,19,23] temporal data (Fo = 0.05 -Fo = 1) was used for evaluation. Despite the doubled diffusion process through the material in reflection configuration the standard deviation of the estimated thermal diffusion time, carried out by the VWC, is also less than 4 % and therefore more accurate than the stateof-the-art method TSR.…”

Section: Results For Validation Of the Methodsmentioning

confidence: 91%

“…8b) are shown for five different steps # = [7,11,15,19,23], as these steps cover nearly the entire range of the step wedge. for five different steps # = [7,11,15,19,23]. The measurement parameters are given in Table 3 The comparison of the measured temperature values T meas (for only one pixel each step) to the regularized temperatures T ADMM reg show good agreement and demonstrate the filter effect due to regularization.…”

Section: Results For Validation Of the Methodsmentioning

confidence: 99%

“…averaged pore shape and orientation) have to be known to allow the prediction of the effective thermal diffusivity [6]. Based on effective medium theories (EMT), a sophisticated model was introduced by Mayr et al [7]. This model enables the estimation of porosity in CFRP without the knowledge of the actual sample thickness, therefore the apparent thermal diffusivity is introduced and expressed as a quadratic model.…”

Section: Introductionmentioning

confidence: 99%

“…Reflection configuration (z = 0) Estimated diffusion time t d for five different steps # =[7,11,15,19,23], in comparison with state-of-the-art methods for transmission (LDF) and reflection configuration (TSR) ity α, was determined based on VWC results. The fitting parameters in transmission and reflection configuration are nearly equal and correspond to literature based values for non-porous CFRP (Φ=0).…”

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confidence: 99%

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Photothermal Porosity Estimation in CFRP by the Time-of-Flight of Virtual Waves

et al. 2020

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Porosity is an unavoidable defect in carbon fiber reinforced polymers and has noticeable effects on mechanical properties since gas filled voids weaken the epoxy matrix. Pulsed thermography is advantageous because it is a non-contacting, non-destructive and fast photothermal testing method that allows the estimation of material parameters. Using the Virtual Wave Concept for thermography data, ultrasonic evaluation methods are applicable. In this work, the pulse-echo method for Time-of-Flight measurements is used, whereby the determined Time-of-Flight is directly related to the thermal diffusion time of the examined material. We introduce a signal-to-noise dependent approach, the optimum evaluation time, for evaluating only relevant time ranges which contain information of heat diffusion. After the validation of the method for heterogeneous materials, effective medium theories can be used for quantitative porosity estimation from the estimated diffusion time. This model-based approach for porosity estimation delivers more accurate results for transmission and reflection configuration measurements compared to thermographic state-of-the-art methods. The results are validated by X-ray computed tomography reference measurements on a wide range of different porous carbon fiber reinforced plastic specimens with different number of plies and varying porosity contents.

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Section: Results For Validation Of the Methodsmentioning

confidence: 91%

Section: Results For Validation Of the Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Photothermal Porosity Estimation in CFRP by the Time-of-Flight of Virtual Waves

et al. 2020

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“…Due to the resolution of these methods, they will only respond to volume-average void content, rather than providing the information about the location, size and morphology of each void that is needed in this study. [9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

A parametric study of segmentation thresholds for X-ray CT porosity characterisation in composite materials

Tretiak

Smith

2019

Composites Part A: Applied Science and Manufacturing

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Porosity in composites is a critical manufacturing defect that leads to a reduction of mechanical performance. Non-destructive testing (NDT) techniques are used to inspect composites after manufacture to identify defects and to help assess their impact on mechanical performance. Micro X-ray computed tomography is a promising NDT technique which provides information about pore location, size and morphology. To identify and characterise voids, an image 'segmentation' must be applied to the full CT dataset, which is simply a rule-based decision about whether a voxel is inside a pore or not. This work uses a simple model to analyse and compare the effectiveness of previously accepted threshold methods for segmentation across a range of material and porosity parameters. A new CT-segmentation thresholding method is proposed and evaluated for characterising voids in a wider range of composites.The sources of uncertainties are investigated and recommendations are made to minimise these uncertainties.

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