Issue 28

D. Gentile et alii, Frattura ed Integrità Strutturale, 28 (2014) 42-50; DOI: 10.3221/IGF-ESIS.28.05 46 Therefore, provided the pipe reference radius (inner, outer or thickness average), the crack opening angle  , and the maximumCOD at the center of the crack for the in axis configuration, Eqn. 1 provides the equation of the COD in the 3D space. Figure 4 : HCM for the generic off-center crack configuration. R ESULTSANDDISCUSSION n Fig. 5 the comparison of the measured and calculated COD profile for the centered crack configuration and two different pipe thicknesses is shown. Here, experimental data could be obtained only for half of the crack length since in the centered crack configuration the crack length was exceeding the DIC cameras window. However, it was possible tomeasure the COD beyond the point for which themaximum opening occurs to confirm the symmetry of the COD profile. ThemaximumCODwas measured for the centered crack configuration also for 2  =90° and for the three pipe thicknesses. These results have been used to validate available solutions based on FEM such as those reported in the GE-EPRI. It was found that in some cases, these solutions donot agreewell with present experimental results. TheHCM assumes that, given themaximumCOD for the center crack, the COD distribution for the off-center crack configuration is givenby                   1 2 2 2 2 0 2 / cos cos sin sin tan              (1.1) This solutionoverestimates the effectivemaximumopening for givenoff-axis angle. It has been found that applying the following correction usually leads tomuch better agreement between theHCM andFEM results,   0 0 0 * cos /      where  0 is a factor that depends on the amplitude of the applied bending and crack length and it is equal to the ratioof half crack angle   and the off center angle  forwhich there is half closure of the crack. This correction is appliedonly for half crack angle greater than 45°. In Fig. 7-Fig. 11 the comparison of the HCM and the measured COD profile for the off-axis configuration is shown. In all the cases, the agreement is very good indicating that theHCM is accurate enough to predict the effectivemodification of theCODprofilewith the increasing off-axis angle even for very large cracks. InTab. 2, the comparison between themeasured COD and calculated values determinedwithGE-EPRI solution for the centered crack configuration, [6] is given. It is interesting to note that for smaller thickness and shorter crack length, the difference is larger. A possible explanation is that GE-EPRI numerical simulation were performed using shell elements which do not correctly take into account 3D effects and rotation of the through-thickness crack faces. Much better agreement is foundwhen using 3D finite elementmodels as shown inby the author in [10]. I