Abstract
X-ray based computed microtomography is a non-destructive, well established tool for a three-dimensional characterization of open-cell metallic foams. Macroscopic physical and chemical properties of these materials stay in close relation to their micro-structure parameters. The purpose of the paper is to present two types of thresholding methods so-called global and local thresholding for evaluating the structural parameters of open-cell metal foams based on X-ray microtomography data. Two different methods were chosen: automatic Otsu thresholding (global) and adaptive (mean of minimal and maximal grey values of grayscales within a selected radius). The key parameters of aluminum and nickel-chromium foams fine structure calculated using Otsu and locally thresholded images were significantly different. The proper image segmentation is the key point in metallic foam morphometry. The influence of a radius of the image processing region on the results obtained is discussed for the local thresholding method. Examples of the images artifacts generated by local thresholding method to demonstrate possible results misinterpretation are also given. The optimization of local thresholding parameter (radius of the image processing region) was presented.
Highlights
Physical and chemical properties of the foams as well as their desired technological and biological applications are closely related to their structural and morphological parameters
Solid foams may be manufactured from many different materials like metals or their alloys (Al, Ni, Cu, kanthal, NiCr), ceramics (Al2O3, ZrO2, SiC, mullite, cordierite etc.), plastics, glass or carbon [1,2,3,4,5]
Recemat BV, the nickel-chromium foam manufacturer denotes the number of pores per inch while ERG Aerospace Corporation for aluminum foams specifies the number of windows per inch
Summary
Physical and chemical properties of the foams as well as their desired technological and biological applications are closely related to their structural and morphological parameters. To achieve the detailed knowledge of these parameters different research methods like magnetic resonance imaging (MRI), optical analysis and Xray computed microtomography (micro-CT), are used. The last method is becoming increasingly popular in the area of foam analysis [6,7,8,9,10,11,12]. The general principle of this method is based on detecting differences of linear attenuation coefficient of X-rays passing through a sample. In this paper all results have been obtained using desktop type micro-CT with X-ray tube. The sample is scanned at different angles and the intensity of transmitted X-rays is detected. X-ray projection yields a set of grey level cross-sectional images of the sample but to obtain whole quantitative sample characterization in 3D space, as e.g. shape, volume, porosity, an
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