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Evaluation of internal defects generated in machine milled carbon fiber reinforced plastic using X-ray computed tomography
摘要： In this study, X-ray computed tomography (X-ray CT) was used to investigate internal defects generated on machine milled carbon fiber reinforced plastics (CFRP). Internal defects such as cracks, fractures, and deformation of the carbon fibers, which are invisible from the surface, were observed using the X-ray CT method. Defects were generated based on the machining method and direction of the fibers. A large number of defects were generated when using the conventional cut method along 45°, 90°, and the climb cut method along 90°. Few internal defects were observed when using the climb cut method along 45°; however, the machined surface was very rough. The mechanism for these phenomena was investigated by studying surface observations and cutting force, in addition to X-ray CT imaging. These results indicate that X-ray CT is a powerful tool for visualizing internal defects in CFRP, which differ significantly based on the direction of the fiber and machining method used.
关键词： Carbon fiber reinforced plastics,Surface roughness,Milling,Internal defect,X-ray computed tomography
更新于2025-09-16 10:30:52
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An investigation into the effect of gradients on the manufacturing fidelity of triply periodic minimal surface structures with graded density fabricated by selective laser melting
摘要： Triply periodic minimal surfaces (TPMSs) have attracted increasing attention for their high manufacturability, biocompatibility, and mechanical properties. In this work, graded Gyroid cellular structures (GCSs) with varying gradient directions were mathematically designed and manufactured via selective laser melting (SLM). The effect of gradients on manufacturing fidelity, i.e. degree of conformity between the manufactured part and engineering design, of these structures was investigated using X-ray computed tomography (CT). The results indicate that relative density and volume fraction of as-built GCSs are higher than those specified in the engineering design due to strut diameters being larger than specification and the presence of bonded powder particles. Manufacturing fidelity is shown to depend on the geometry of the struts in these structures, including inclination angle of struts, relative density, and density gradient direction. Bonded powder particles were particularly present at the upper inner walls of sphere-like pores, where inclination angles are low and as a result there is a lack of support and non-ideal transfer of heat from the melt pool. Decreasing density along the building direction reduces the occurrence of bonded powder particles and increases manufacturing fidelity. The empirical findings in this study provide insight into the effects of part geometry on the quality of its manufacture by SLM. Results are used to establish guidelines for optimal design of cellular structures.
关键词： Graded cellular structure,Gyroid,Selective laser melting,Triply periodic minimal surface,X-ray computed tomography
更新于2025-09-12 10:27:22
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On the occurrence of weld bead porosity during laser vacuum welding of high pressure aluminium die castings
摘要： Due to porosity and incomplete fusion, aluminium high pressure die castings are materials that are known to be difficult to weld. Hereby porosity is mainly caused by hydrogen which is trapped within the weld bead during solidification as a result of insufficient degassing. To enhance degassing and to reduce the influence of surrounding air, laser vacuum welding was applied within the current study. The main goal was to investigate the occurrence of porosity during laser beam welding of aluminium high pressure die castings. To reach this aim, die casting plates were laser welded at varied ambient pressure and investigated by x-ray computed tomography. The analysis of the welds focuses on the size, position, amount and shape of the detected defects depending on the ambient pressure during welding. The results showed a dependency of the occurrence of porosity and the ambient pressure whilst welding.
关键词： Aluminium die castings,Laser vacuum welding,Aluminium,X-ray computed tomography,Laser welding,Porosity
更新于2025-09-12 10:27:22
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Combined Infrared Thermography, X-ray Radiography, and Computed Tomography for Ink Drying Studies
摘要： This work describes the comparison of drying behavior of ink deposited on two substrates used commonly in polymer electrolyte fuel cells (PEFCs): microporous layer (MPL) and Nafion. For the same drying conditions and ink composition, ink deposited onto the MPL dried faster and also formed cracks faster. During drying, ink deposited on the MPL had more cracks and smaller intercrack spacing compared to ink deposited on Nafion. Smaller intercrack spacing for ink on the MPL substrate is explained by the higher critical stress predicted by the model. A novel combination of infrared (IR) thermography, X-ray radiography, and computed tomography (CT) is used to characterize ink drying behavior. X-ray radiography with fast temporal resolution showed the existence of skin on the top of drying film that formed due to slow convective ink transport within the film and fast evaporative drying. From X-ray CT, detailed three-dimensional data was obtained on crack morphology within the drying film and was correlated to temperature profiles obtained with IR-thermography. The formation of a Y-crack in the film deposited on the MPL was correlated to the defect within the MPL substrate. The combination of three techniques is a unique probe to capture the temporal, thermal, and morphological evolution of drying ink.
关键词： IR thermography,fuel cells,evaporation,X-ray computed tomography,X-ray radiography,ink drying
更新于2025-09-10 09:29:36
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Evaluation of the Internal Structure of the Multilayer Ceramic Mould for Precision Casting Critical Parts of Aircraft Engines by X-ray Computed Tomography
摘要： The aim of the study was to present the possibilities of X-ray computed tomography to evaluate the internal discontinuities in multilayer ceramic moulds for precision casting critical parts of aircraft engines. Study for determination of internal discontinuities such as: porosity, micro-cracks and delamination at the ceramic moulds was carried out using the method of X-ray computed tomography. Using this method allowed to obtain a 3D virtual model of the ceramic form and, consequently, the measurement of porosity and thickness both the first layer and the constructional layer in the multilayer ceramic mould. The results are presented possibilities of computer tomography as a tool for microanalysis 3D, identify internal discontinuities and measurement of geometrical size for assessing the quality of ceramic mold in relation to the research of its technological structure.
关键词： Precision casting,Ceramic shell moulds,X-ray computed tomography
更新于2025-09-10 09:29:36
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Study of Size Effect on Microstructure and Mechanical Properties of AlSi10Mg Samples Made by Selective Laser Melting
摘要： The macroscopic mechanical performance of additive manufactured structures is essential for the design and application of multiscale microlattice structure. Performance is affected by microstructure and geometrical imperfection, which are strongly influenced by the size of the struts in selective laser melting (SLM) lattice structures. In this paper, the effect of size on microstructure, geometrical imperfection, and mechanical properties was systemically studied by conducting experimental tests. A series of AlSi10Mg rod-shaped samples with various diameters were fabricated using SLM. The uniaxial tensile test results show that with the decrease in build diameter, strength and Young’s modulus of strut decreased by 30% more than the stable state. The main reasons for this degradation were investigated through microscopic observation and micro X-ray computed tomography (μ-CT). In contrast with large-sized strut, the inherent porosity (1.87%) and section geometrical deviation (3%) of ponysize strut is greater because of the effect of thermal transform and hydrogen evolution, and the grain size is 0.5 μm. The discrepancy in microstructure, geometrical imperfection, and mechanical properties induced by size effect should be considered for the design and evaluation of SLM-fabricated complex structures.
关键词： selective laser melting,size effect,microstructure,X-ray computed tomography,mechanical properties
更新于2025-09-09 09:28:46
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Reconstructing granular particles from X-ray computed tomography using the TWS machine learning tool and the level set method
摘要： X-ray computed tomography (CT) has emerged as the most prevalent technique to obtain three-dimensional morphological information of granular geomaterials. A key challenge in using the X-ray CT technique is to faithfully reconstruct particle morphology based on the discretized pixel information of CT images. In this work, a novel framework based on the machine learning technique and the level set method is proposed to segment CT images and reconstruct particles of granular geomaterials. Within this framework, a feature-based machine learning technique termed Trainable Weka Segmentation is utilized for CT image segmentation, i.e., to classify material phases and to segregate particles in contact. This is a fundamentally different approach in that it predicts segmentation results based on a trained classifier model that implicitly includes image features and regression functions. Subsequently, an edge-based level set method is applied to approach an accurate characterization of the particle shape. The proposed framework is applied to reconstruct three-dimensional realistic particle shapes of the Mojave Mars Simulant. Quantitative accuracy analysis shows that the proposed framework exhibits superior performance over the conventional watershed-based method in terms of both the pixel-based classification accuracy and the particle-based segmentation accuracy. Using the reconstructed realistic particles, the particle-size distribution is obtained and validated against experiment sieve analysis. Quantitative morphology analysis is also performed, showing promising potentials of the proposed framework in characterizing granular geomaterials.
关键词： Machine learning,Shape reconstruction,3D particle morphology,X-ray computed tomography,Level set
更新于2025-09-09 09:28:46