Henrique Fernandes

Comparative study on submillimeter flaws in stitched T-joint carbon fiber reinforced polymer by infrared thermography, microcomputed tomography, ultrasonic c-scan and microscopic inspection

Abstract. Stitching is used to reduce dry-core (incomplete infusion of T-joint core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography, and laser spot thermography are used to investigate the internal flaws in a stitched T-joint carbon fiber-reinforced polymer (CFRP) matrix composites. Then, a new microlaser line thermography is proposed. Microcomputed tomography (microCT) is used to validate the infrared results. A comparison between microlaser line thermography and microCT is performed. It was concluded that microlaser line thermography can detect the internal submillimeter defects. However, the depth and size of the defects can affect the detection results. The microporosities with a diameter of less than 54  μm are not detected in the microlaser line thermography results. Microlaser line thermography can detect the microporosity (a diameter of 0.162 mm) from a depth of 90  μm. However, it cannot detect the internal microporosity (a diameter of 0.216 mm) from a depth of 0.18 mm. The potential causes are given. Finally, a comparative study is conducted.

Pulsed micro-laser line thermography on submillimeter porosity in carbon fiber reinforced polymer composites: Experimental and numerical analyses for the capability of detection

In this article, pulsed micro-laser line thermography (pulsed micro-LLT) was used to detect the submillimeter porosities in a 3D preformed carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to verify the thermographic results. Then, finite element analysis was performed on the corresponding models on the basis of the experimental results. The same infrared image processing techniques were used for the experimental and simulation results for comparative purposes. Finally, a comparison of experimental and simulation postprocessing results was conducted. In addition, an analysis of probability of detection was performed to evaluate the detection capability of pulsed micro-LLT on submillimeter porosity.

Optical and Mechanical Excitation Thermography for Impact Response in Basalt-Carbon Hybrid Fiber-Reinforced Composite Laminates

In this paper, optical and mechanical excitation thermography was used to investigate basalt-fiber-reinforced polymer, carbon-fiber-reinforced polymer, and basalt-carbon fiber hybrid specimens subjected to impact loading. Interestingly, two different hybrid structures including sandwich-like and intercalated stacking sequence were used. Pulsed phase thermography, principal component thermography, and partial least-squares thermography (PLST) were used to process the thermographic data. X-ray computed tomography was used for validation. In addition, signal-to-noise ratio analysis was used as a means of quantitatively comparing the thermographic results. Of particular interest, the depth information linked to Loadings in PLST was estimated for the first time. Finally, a reference was provided for taking advantage of different hybrids in view of special industrial applications.

Comparative study of microlaser excitation thermography and microultrasonic excitation thermography on submillimeter porosity in carbon fiber reinforced polymer composites

Abstract. Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it may cause new types of flaws, especially submillimeter flaws. Thermographic approaches including microvibrothermography, microlaser line thermography, and microlaser spot thermography on the basis of pulsed and lock-in techniques were proposed. These techniques are used to detect the submillimeter porosities in a stitched T-joint carbon fiber reinforced polymer composite specimen. X-ray microcomputed tomography was used to validate the thermographic results. Finally an experimental comparison of microlaser excitation thermography and microultrasonic excitation thermography was conducted.

Quantitative Evaluation of Pulsed Thermography, Lock-in Thermography and Vibrothermography on Foreign Object Defect (FOD) in CFRP.

In this article, optical excitation thermographic techniques, including pulsed thermography and lock-in thermography, were used to detect foreign object defect (FOD) and delamination in CFRP. Then, vibrothermography as an ultrasonic excitation technique was used to detect these defects for the comparative purposes. Different image processing methods, including cold image subtraction (CIS), principal component thermography (PCT), thermographic signal reconstruction (TSR) and Fourier transform (FT), were performed. Finally, a comparison of optical excitation thermography and vibrothermography was conducted, and a thermographic probability of detection was given.

Carbon fiber composites inspection and defect characterization using active infrared thermography: numerical simulations and experimental results

Composite materials are widely used in the aeronautic industry. One of the reasons is because they have strength and stiffness comparable to metals, with the added advantage of significant weight reduction. Infrared thermography (IT) is a safe nondestructive testing technique that has a fast inspection rate. In active IT, an external heat source is used to stimulate the material being inspected in order to generate a thermal contrast between the feature of interest and the background. In this paper, carbon-fiber-reinforced polymers are inspected using IT. More specifically, carbon/PEEK (polyether ether ketone) laminates with square Kapton inserts of different sizes and at different depths are tested with three different IT techniques: pulsed thermography, vibrothermography, and line scan thermography. The finite element method is used to simulate the pulsed thermography experiment. Numerical results displayed a very good agreement with experimental results.

Fiber orientation assessment on surface and beneath surface of carbon fiber reinforced composites using active infrared thermography

Fiber orientation in composite materials is an important feature since the material’s strength and stiffness are related to the fiber orientation. In this paper, non-destructive infrared thermography is used to assess fiber orientation of carbon/PEEK (Polyether ether ketone) laminates on the surface and subsurface of the material. Specifically, a noncontact laser lock-in thermography (LLT) technique is used for fiber orientation measurement in composite materials. LLT utilizes a modulated continuous wave (CW) laser as a heat source for lock-in thermography instead of commonly used flash and halogen lamps. Experimental results show that fiber orientation on the first (surface) and second layers of the laminate can be successfully measured using this technique.

Suspicious event recognition using infrared imagery

The societys concern about safety is growing every day and with it the demand for intelligent surveillance systems with the minimal human intervention possible. In this work we identify suspicious events that could take place in a parking lot based on infrared imagery. The object segmentation process is performed using a dynamic background-subtraction technique which robustly adapts detection to illumination changes. Segmented objects are tracked by a two phase function: prediction and correction. During the tracking process the objects are classified into two categories: Person and Vehicles, based on features like size, velocity and temperature. With the objects correctly segmented and classified using features like velocity and time stood in one spot, it is possible to identify suspicious events occurring in the monitored area. Experimental results are presented to demonstrate the effectiveness of the proposed technique to recognize suspicious events.

Machine Learning and Infrared Thermography for Fiber Orientation Assessment on Randomly-Oriented Strands Parts

The use of fiber reinforced materials such as randomly-oriented strands has grown in recent years, especially for manufacturing of aerospace composite structures. This growth is mainly due to their advantageous properties: they are lighter and more resistant to corrosion when compared to metals and are more easily shaped than continuous fiber composites. The resistance and stiffness of these materials are directly related to their fiber orientation. Thus, efficient approaches to assess their fiber orientation are in demand. In this paper, a non-destructive evaluation method is applied to assess the fiber orientation on laminates reinforced with randomly-oriented strands. More specifically, a method called pulsed thermal ellipsometry combined with an artificial neural network, a machine learning technique, is used in order to estimate the fiber orientation on the surface of inspected parts. Results showed that the method can be potentially used to inspect large areas with good accuracy and speed.

Numerical and experimental analyses for natural and non-natural impacted composites via thermographic inspection, ultrasonic C-scan and terahertz imaging

In this paper, thermographic inspections, ultrasonic C-scan and terahertz imaging were used to detect damages caused by impacts in natural, non-natural and hybrid composites. In particular, different hybrid structures were used. In some samples, numerical simulations were performed to predict the damage. A comparison of the results based on experimental and simulated experiments were afterwards conducted with the aim to explore the inspection capability of each technique.