Micro-CT Based 3D Morphological Analysis And Performance Study Of Porous Metal Fiber Sintered Sheet

Porous metal fiber sintered sheet(PMFSS), as a new kind of functional material, has been widely applied in various industrial applications. Such as energy absorption, filter and separation, fuel cell, etc. The quantatively description of its micro structure and the understanding of the relationship between strucuture and its performance are of great importance to the optimization of its fabrication processes and finally improve its performance. PMFSS was produced by the solid-state sintering of copper fibers fabricated using the multi-tooth cutting method. To further explore its microstructure, X-ray micro-tomography technique(Micro-CT) was employed to obtain 3D internal structural images. Based on which the skeleton extraction method was employed to perform various morphology explorations. The fracture behavior of PMFSS was explored taking into account the morphological data. Moreover, an active design modeling method was also explored which can fit the actual structure features well. The transport properties of the material were explored using numerical methods. The relationship between the structure and corresponding performances was analyzed as well. Our work provides promising methods for the structure descriptions, active design modeling and performance studies which could contribute to the structural optimization of PMFSS. This work was arranged in following orders: 1. Morphology study of PMFSS based on skeleton extraction and segmentationThe 3D image of PMFSS was obtained using Micro-CT devices, which provides the access to the inter structure exploration of the 3d network. The 3d image was later abstracted into skeleton representation using skeleton extraction algorithm based on distance transform method which was later improved by introducing the scale axis transform method. The initial skeleton was later divided into skeleton segments through multi-step skeleton pruning and segmentation, from which various morphology statistics data involving fiber segments type, length, orientation, tortuosity and radius were summarized. These morphology characteristics provide reliable information for the performance studies and active design modeling of PMFSS. 2. Fracture energy prediction of PMFSSAs there was certain deviation between available fracture energy predition method and the experimental measurement, the fracture energy of PMFSS was studied based on the modified prediction version taking into account the morphological statistics data, the theory of max shear force criterion and the elongation of single fiber measured during tensile test. The efficacy of the modified method was verified through comparsion with the previous version and experimental results. Moreover, the possible cause of error was analyzed and the fracture behavior in different stages was analyzed quantitatively. 3. Deterimination of representative volume element and active desgin modeling of PMFSSTo analyze the impact of representative volume element(RVE) size on local geometrical characters(porosity and specifically surface) and finally determine its proper size, a group of 3D sub-images were analyzed and compared. The proper RVE size was determined by standard deviation criterion. To achieve the active design modeling of PMFSS, the fiber segment orientation was converted into fiber orientation by length weighted method. The active design modeling of fiber networks was achieved using a fiber distribution controllable model. According to which the porosity, tortuosity and orientation can be controlled and fitted to the actual structure. Finally, the active design representative unit was established. 4. Numerical study of transport properties of PMFSSThe transport properties of PMFSS were deeply coupled with its microstructures, especially the pore size of the network in the void phase. In this work, the pore phase was characterized using the maximal ball method, and its tortuosity was measured using fast marching method. The transport properties were finally analyzed using lattice Boltzmann method and finite volume element respectively, both methods agreed well on transverse permeability. Based on CT data, using lattice Boltzmann method, the transverse permeability of PMFSS was studied. The impact of simulation domain size and resolution of 3D image on the numerical results were discussed. The reliability of the simulated results was verified through comparing with analytical models. And the linear relationship between square pore size and permeability was verified and quantitatively deterimined. Moreover, using the active desgin model, the permeability was studied through finite volume method as well, and both of the transverse and parallel permeability were studied. Pressure drop vs velocity curves were recorded, permeability was obtained and simulated data was compared with experimental measurements and analytical models, through which the reliability of the active design modeling method was verified. Finally, the impacts of flow directions and fiber orientations on simulated permeability were discussed as well.