In quest of methods for measuring 3D mechanical properties of composites

Assessing 3D shear stress–strain properties of composites using Digital Image Correlation and finite element analysis based optimization

“…It is worth noting that the previous method developed by the authors in Ref. [4] was based on the measurement of the maximum shear strain only and therefore required a significant number of DIC measurements for complete assessment of the nonlinear shear stressestrain material response.…”

“…1, allowing for DIC measurement in all three material planes, is different from the design used in Ref. [4] to determine only interlaminar material properties.…”

“…The confidence margin output parameter available in the DIC software Vic-3D is calculated from the covariance matrix of the correlation function [14] and is used in this work to estimate s j in equation (4). Weighted residuals used in the definition of the objective function allow reducing the sensitivity of the optimization algorithm to measurement noise, since the contribution of noisy data points with high variance is scaled down by the inverse of their variance.…”

“…Earlier techniques, including a shortbeam shear (SBS) method allowing for measuring most of the 3D stressestrain constitutive relations [5,6], fell short of capturing nonlinear interlaminar shear properties in the 2e3 principal material plane. Most recent results, published in Composites Science and Technology [4], include the ability to characterize shear stressestrain curves until material failure in both 1e3 and 2e3 interlaminar material planes based on a small rectangular plate torsion (plate-twist) specimen using DIC based deformation measurements. For reference, 1 indicates the fiber direction; 2 the inply transverse direction; and 3 the laminate thickness direction.…”

“…For reference, 1 indicates the fiber direction; 2 the inply transverse direction; and 3 the laminate thickness direction. The ability of unidirectional small-plate torsion specimens to simultaneously exhibit large shear strains in all principal material planes, including 2e3 interlaminar shear, advanced the state-ofthe-art for measuring 3D mechanical properties of composites in a single experiment [4]. The interlaminar shear stressestrain relations were obtained through coupling DIC-based strain data with FEM-based stresses, using a stress-updating procedure where material properties in the FEM were updated until the change in the maximum FEM-based shear stress became negligible.…”