Issue 41

S. Beretta et alii, Frattura ed Integrità Strutturale, 41 (2017) 269-276; DOI: 10.3221/IGF-ESIS.41.36 270 still requires attention even though the rich literature growing in the last decades [3-5]. In fact, real crack tip displacement fields are affected by several factors that cannot be easily controlled during DIC displacement measurements. Crack tip plasticity, crack closure, correlation parameters (field of view, subset size) have shown to profoundly influence the SIF calculation. In order to clarify and to provide a guideline on the SIF measurements, in this work we analyze the displacement field calculated according finite element (FE) simulations of two typical cracked body geometries: the center cracked tension (CCT) and single-edge notched tension (SENT) specimens. Starting from the displacement fields obtained from the FE simulations, this work shows the comparison with the SIF predicted by the numerical analyses focusing specifically on the parameters that are required to be properly set to obtain an accurate SIF measurement during DIC measurements. The methodology was successively experimentally implemented for the measurement of the opening stress for a crack propagating in a SENT specimen. Figure 1 : Geometries considered in this study: Center Cracked Tension (CCT) and Single-Edge Notched Tension (SENT) specimens. The regressions of the displacement fields in front of the crack tip are based on the Williams expansion [6]. The Williams expansion is herein written for the displacements v in the direction perpendicular to the crack surfaces in three different versions based on the number of terms involved:                               2 sin 1 2cos cos 2 2 2 2 I v K r v k Ar B (1)                                            2 sin 1 2cos sin 3sin cos 2 2 2 2 8 I v K r T v k r k Ar B (2)                                                                           2 3/2 13 sin 1 2cos sin 3sin 2 2 2 2 8 1 3 3 sin sin cos 2 2 2 2 2 I v K r T v k r k r A k Ar B (3) The terms A and B account the contributions of the specimen rotation and translation on the displacement field.