Towards Criteria Characterizing the Metrological Performance of Full-field Measurement Techniques

Abstract

Users of full-field measurement methods like Digital Image Correlation (DIC) often aim to perform measurements with the best trade-off between spatial resolution, bias and measurement resolution. Whenever two full-field methods are compared, it is essential that these criteria are taken into consideration. Recently a metrological efficiency indicator for full-field measurements has been proposed and discussed. This indicator combines measurement resolution and spatial resolution. It has been shown to be invariant to the subset size in the case of Local DIC. The goal of this article is to discuss a method, which determines both the spatial and the measurement resolutions for a given bias for two different DIC methods, in order to obtain the metrological efficiency indicator for each of these methods. The benefit of this indicator is that it

On the Optimal Pattern for Displacement Field Measurement: Random Speckle and DIC, or Checkerboard and LSA?

“…This curve can be considered as an intrinsic signature of a given technique when applied to a pair of reference and deformed images. In addition, if, as expected, the product σ u × d is really constant [18], considering a logarithmic scale for both quantities, as in [34], should lead to a straight line of slope -1 in the σ u -d plane. This enables us to easily visually observe whether this property (the fact that σ u × d is constant) is satisfied or not.…”

“…Inspired from recent studies on the metrological performance of various full-field measurement techniques [18,34], the procedure employed here consists in fixing the bias λ to the same value for both techniques, and then in examining how the measurement resolution σ u evolves as the spatial resolution d progressively changes. This latter quantity increases with the subset size 2M + 1 (DIC), and with (LSA).…”

Towards Material Testing 2.0. A review of test design for identification of constitutive parameters from full‐field measurements

“…Another interesting conclusion of this second step is that quadratic matching functions (instead of bilinear ones) and steps of one pixel between successive subsets should systematically be used, leading to lower values of C 3 . The superiority of the quadratic shape functions has been documented in previous works, [136,137] while step size has, regrettably, not been the focus of much attention in the past. It is worth noting that the orientation of the fibres in OAUIT has also been optimized with this type of approach in the particular case of wood, see Kretschmann et al [96] In the same spirit as in the preceding study, a refinement of the work presented in Wang et al [121] on orthotropic polymeric foams (and discussed in the preceding section) tested with an Arcan fixture was proposed in Wang et al [64] The experimental device is shown in Figure 10.…”

Comparing several spectral methods used to extract displacement fields from checkerboard images

“…However this result does not take into account the spatial resolution of the different techniques. As suggested in [9], this quantity, denoted by d, can be estimated by considering the cross-section of the displacement field returned by a given technique along its horizontal line of symmetry, and by finding the period of the sinusoidal vertical displacement such that a bias λ equal to 10% is observed, see Section 3.1 and [26,9,37] for instance. Figure 16 shows σ u as a function of d for WGPA and various settings (fives possibilities for Z f , six values for k), along with the same quantity obtained with LSA performed with and without deconvolution.…”

“…This is the price to pay to obtain a measurement defined nearly pixelwise, without any influence of the actual displacement that occurs at the surrounding pixels. In recent studies on LSA and DIC [39,37], it is proposed to assess the compromise between spatial resolution and displacement resolution by considering the product between these two quantities. The reason is that this product has been demonstrated (respectively observed) to be constant for LSA (respectively for DIC) in [38] (respectively [39]).…”