“Finite-Element” Displacement Fields Analysis from Digital Images: Application to Portevin–Le Châtelier Bands

Abstract

A new methodology is proposed to estimate displacement fields from pairs of images (reference and strained) that evaluates continuous displacement fields. This approach is specialized to a finite-element decomposition, therefore providing a natural interface with a numerical modeling of the mechanical behavior used for identification purposes. The method is illustrated with the analysis of Portevin-Le Châtelier bands in an aluminum alloy sample subjected to a tensile test. A significant progress with respect to classical digital image correlation techniques is observed in terms of spatial resolution and uncertainty.

Experimental analysis and mathematical modeling of fracture in RC elements with any aspect ratio

“…The experimental study presented in this paper differs from the aforementioned references in the use of digital image correlation (DIC), see for instance [18]. This method allows for the classification and quantification of the different failure mechanisms in a much better way than the classic procedures, which are either local or performed by visual inspection.…”

“…Next, further pictures are taken during the experiment while the chosen external forces are applied. A computer program [18] processes first the reference digital image; the program divides this photo into small portions that may be imagined as small "finger prints" and identifies each of them. Then, the program analyses the following picture, looks for the same "finger prints" and determines their new position in the picture.…”

Investigation of Strain Measurements using Digital Image Correlation with a Finite Element Method

“…The SSD correlation function is defined as [11] ( 5) where is the grayscale intensity value at point of the reference image, and is the grayscale intensity value at point of the deformed image. After neglecting the high-order terms, the first-order Taylor expansions of yields (6) where g x and g y are the first-order derivatives of grayscale intensities, and in this study they are calculated by central difference of neighboring points in the x and y directions, respectively.…”

“…Xiang [10] used the moving least-squares (MLS) method to smooth the displacement field followed by a numerical differentiation of the smoothed displacement field to get the strain fields. Different from above pointwise algorithms, the Q4-DIC developed by Besnard [11] and the finite element method proposed by Sun [12] can be classified as a continuum method, in which the surface deformation of the sample is measured throughout the entire image area. These techniques ensure the displacement continuity among pixel points.…”

On the fracture locus of AA7075-T651

“…For the shear test, local strains at the fracture location are extracted by DIC using the postprocessor Correli (Besnard et al [12]. Black dots are painted on the white background of the specimen to obtain a speckle pattern.…”