Issue 30

P. Corigliano et alii, Frattura ed Integrità Strutturale, 30 (2014) 304-310; DOI: 10.3221/IGF-ESIS.30.37 307 Experimental Tests and DIC analysis Displacement controlled tests at R=-1 (u x =±1.2 mm) were performed, where x is the vertical direction. The images of the specimen during the tests were acquired and processed by means of the ARAMIS system using the DIC technique. The experimental set-up is shown in Fig. 7. Fig. 8 shows the values of force and displacement, measured in two cycles. It can be noted that the imposed displacement is symmetric, while the measured force has different absolute values at maximum F max and mininum F min loads, due to the structural weakness under compressive load caused by axial misalignment and due to the presence of residual stresses caused by the welding process. Furthermore, the value of F min is not in correspondence of the minimum displacement value, in fact as shown by fig 9, the specimen deforms in a way that bending (buckling) arises causing a diminution of the load. This behavior is also confirmed by the DIC analysis, shown in Fig. 10 and 11, which illustrate the strain in the x–direction ε x (vertical longitudinal direction) at F max and F min , respectively. Fig. 10 shows a difference in terms of ε x from the left side (about 1%) to the right side (about 0.5%), which means that not only tensile stresses are occurring, but there is also a bending component. This effect is increased under compressive loads in Fig. 11, which exhibits negative and positive strains respectively of +1.2 and -1.2%. The DIC results, shown in Fig. 10 and 11, illustrate that large strains occur close to the notch and they become even larger along the base material. Figure 7 : Experimental setup. Figure 8 : Imposed displacement and measured force. Figure 9 : Deformed specimen at F min . Figure 10 : ε x at F max (u x = 1.2 mm). Figure 11 : ε x at F min (u x =-1.2 mm). Finite Element Analysis and Comparison to DIC results ANSYS software was used for a nonlinear FE analysis of the cruciform welded joint. The mesh elements of the 3D FE model are of type solid186. Fig. 12 shows the local geometry used in the FE model for the welds and the notches, with a notch radius of 1 mm. The minimum size of the element is 0.018 mm in the radial direction, 0.018 mm in the