Issue 45

L.M. Viespoli et alii, Frattura ed Integrità Strutturale, 45 (2018) 121-134; DOI: 10.3221/IGF-ESIS.45.10 129 Figure 2 : Coarse mapped mesh realized for the extraction of the reference stresses to be extrapolated at the weld toe as Structural Hot Spot Stress. The model is composed of 4 nodes SHELL181 elements. In figure, the first principal stress after model solution, for nominal stress of 160 MPa. In correspondence of the weld there is a clear increase in stress, but far from the singularity a 3D refined mesh could represent. S TRAIN E NERGY D ENSITY A PPROACH he aim of the use of this method is to provide an improvement in the accuracy of the assessment. It combines the theory related to the study of notches in fracture mechanics with the advantage of a relatively fast solution due to the possibility of the use of a very coarse mesh. This is due to the fact that the averaged SED has very low sensibility to the refinement of the discretization. A 3D FEM model has been realized writing an APDL code, discretizing the geometry with a coarse mesh of non-linear Solid186 elements. Taking advantage of the double symmetry of the joint, only a quarter of it has in effect been modelled, in order to reduce the resources needed for the solution. The nominal stress has then been applied on the free end of the main plate in form of a negative pressure (traction load). The control volume of radius R=0.28mm is placed at the weld toe, this being the crack initiation spot for this structural detail. The solution of the model for a unit nominal stress gives a Strain Energy on the critical volume equal to:    SENE Nmm 7 2.01266 10  Over a volume of:    VOLU mm 1 3 0.215503 10  The resulting Averaged Strain Energy Density is:      SENE W Nmm mm VOLU 6 3 9.33938 10  / Once solved the model for a certain load, it is simple to obtain the SED for any other load imposed to the specimen, simply considering that the SED has a quadratic variation with the stress imposed. This property is used to compute the values in Tab. 5 without newly solving the model. That is: T