Stitching is used to reduce incomplete infusion of T-joint core (dry-core) and reinforce T-joint structure. However, it might cause new types of flaws, especially micro-sized flaws. In this paper, a new micro-laser line thermography (micro-LLT) is presented. X-ray micro-computed tomography (micro-CT) was used to validate the infrared results. The micro-LLT and micro-CT inspection are compared. Then, a finite element analysis (FEA) is performed. The geometrical model needed for finite element discretization was developed from micro-CT measurements. The model is validated for the experimental results. Finally a comparison of the experiments and simulation is conducted. The infrared experimental phenomenon and results are explained based on the FEA results
Determining fiber length distribution in fiber reinforced polymer components is a crucial step in quality assurance, since fiber length has a strong influence on overall strength, stiffness, and stability of the material. The approximate fiber length distribution is usually determined early in the development process, as conventional methods require a destruction of the sample component. In this paper, a novel, automatic, and nondestructive approach for the determination of fiber length distribution in fiber reinforced polymers is presented. For this purpose, high-resolution computed tomography is used as imaging method together with subsequent image analysis for evaluation. The image analysis consists of an iterative process where single fibers are detected automatically in each iteration step after having applied image enhancement algorithms. Subsequently, a model-based approach is used together with a priori information in order to guide a fiber tracing and segmentation process. Thereby, the length of the segmented fibers can be calculated and a length distribution can be deduced. The performance and the robustness of the segmentation method is demonstrated by applying it to artificially generated test data and selected real components.
In this article, quantitative evaluation of optical thermographic techniques relative to the non-destructive inspection of aluminum foam material is studied. For this purpose, a set of aluminum foam specimens with flat-bottom holes (FBH) was inspected by both optical lock-in thermography (LT) and pulsed thermography (PT). Probability of detection (PoD) analysis, as a quantitative method to estimate the capability and reliability of a particular inspection technique, was studied and compared for both optical LT and PT inspection results
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. In this paper, microscopic inspection, ultrasonic c-scan, pulsed thermography, vibrothermography and laser spot thermography are used to investigate the internal flaws in a stitched T-joint CFRP. Then, a new micro-laser line thermography is proposed. Micro-CT is used to validate the infrared results. A comparison between micro-laser line thermography and micro-CT is performed. As a conclusion, micro-laser line thermography can detect the internal submillimeter defects. However, the depth and the size of defects can affect the detection results. The micro-porosities with a diameter of less than 54 µm are not detected in the micro-laser line thermography results. Micro-laser line thermography can detect the micro-porosity (a diameter of 0.162 mm) from the depth of 90 µm. However, it cannot detect the internal micro-porosity (a diameter of 0.216 mm) from the depth of 0.18 mm. The potential causes are given. Finally a comparative study is conducted.
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.
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