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Abstract:
This paper presents a digital image processing based finite element method for the two-dimensional mechanical analysis of geo-materials by actually taking into account their material inhomogeneities and microstructures. The proposed method incorporates the theories and techniques of digital image processing, the principles of geometry vectorization and the techniques of automatic finite element mesh generation into the conventional finite element methods. Digital image techniques are used to acquire the inhomogeneous distributions of geo-materials including soils,rocks, asphalt concrete and cement concrete in digital format. Digital
image processing algorithms are developed to identify and classify the main homogeneous material types and their distribution structures that form the inhomogeneity of a geomaterial in the image. The vectorized digital images are used as inputs for finite element mesh generations using automatic mesh generation techniques. Lastly, the conventional finite element methods are
employed to carry out the computation and analysis of geomechanical problems by taking into account the actual internal inho-mogeneity of the geomaterial. Using asphalt concrete as an example, the paper gives a detailed explanation of the proposed digital image processing based finite element method.
*Introduction
Digital image processing (DIP) is the term applied to convert video pictures into a digital form, and apply various mathematical algorithms to extract significant information from the picture. This information may be characteristics of cracks on a material surface, the microstructure of inhomogeneous soils and rocks and other man-made geo-materials, texture of sea ice or the
angularties and shapes of granular materials. While digital image processing has been widely used in a range of engineering topics in recent years, a literature survey indicates that the incorporation of digital image pro-cessing into computational geomechanical methods
such as finite element methods (FEM) is very limited .This paper is intended to present an innovative digital image processing based finite element method for the mechanical analysis of geomaterials by taking into account their actual inhomogeneities and micro-structures. It is noted that the DIP based FEM pro-posed in this paper is for two-dimensional finite element analysis. Using the stereoscopic logical alternation principle, it is believed that the proposed method can be
extended to three-dimensional finite element analysis .
*Digital images and discrete function
microstructure of a geomaterial. A cylindrical asphalt concrete (AC) sample is used for the illustration. In general, field cores or laboratory pre-pared AC or rock samples can be cut with a circular masonry saw into multiple vertical or horizontal plane cross-sections. The fresh cross-sections are then photo-graphed with eithe a conventional came a o a digital camera. A scale is placed beneath the section fo DIP
scaling and calibration. If a conventional camera is used, the photographs can be digitized using a scanner and digital image stored in a desktop computer.The digital image consists of a rectangula a ray of image elements or pixels. Each pixel is the intersection area of any horizontal scanning line with the vertical scanning line. These lines all have an equal width h.At each pixel, the image brightness is sensed and assigned with an integer value that is named as the gray level.For the mostly used 56 gray images and binary images,their gray levels have the integer interval from 0 to 55 and from 0 to 1 respectively. As a result, the digital image can be expressed as a discrete function f(i,j)in the i and j Cartesian coordinate system below.Digital image