Issue 33

C. Bagni et alii, Frattura ed Integrità Strutturale, 33 (2015) 105-110; DOI: 10.3221/IGF-ESIS.33.14 109 directly be taken equal to the average inter-aggregate distance, the results generated by testing the un-notched specimens being used to determine a suitable value for the reference strength. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch A Un-notched Material Endurance Limit  0,MAX =3.3 MPa L/2=2.9 mm Linear-elastic stress-distance curve (K t =4.32) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch B Un-notched Material Endurance Limit  0,MAX =5.1 MPa L/2=2.9 mm Linear-elastic stress-distance curve (K t =4.32) Figure 3 : Critical distance L determined for Batch A and Batch B according to the PM. 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch A Un-notched Blunt Intermediate Sharp Un-notched Material Endurance Limit  0,MAX =3.3 MPa Error= +20% Error= -20% l =2.05 mm 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch B Un-notched Blunt Intermediate Sharp Un-notched Material Endurance Limit  0,MAX =5.1 MPa Error= +20% Error= -20% l =2.05 mm Figure 4 : Accuracy of GE applied by taking l = 2.05 mm, Eq. (6) . 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch A Un-notched Blunt Intermediate Sharp Un-notched Material Endurance Limit  GE0,MAX =2.8 MPa Error= +20% Error= -20% l =4.0 mm 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 5 10 15 20  y,max [MPa] Distance, x [mm] Linear-elastic stress fields - Batch B Un-notched Blunt Intermediate Sharp Un-notched Material Endurance Limit  GE0,MAX =4.3 MPa Error= +20% Error= -20% l =4.0 mm Figure 5 : Accuracy of GE applied by taking l equal to the average inter-aggregate distance ( l = 4 mm). The charts reported in Fig. 5 show the linear-elastic gradient-enriched stress-distance curves plotted, at the endurance limit, under the maximum loading in the cycle. According to this figure, the reference strength,  GE0,MAX , determined from the results generated by testing the un-notched specimens was equal to 2.8 MPa for Batch A and to 4.3 for Batch B. These diagrams clearly prove that the use of the gradient-enriched notch tip stresses determined by taking l equal to the average