Issue 7

C. Colombo et alii, Frattura ed Integrità Strutturale, 7 (2009) 65-72; DOI: 10.3221/IGF-ESIS.07.05 70 to 80 MPa, the endurance passes from around 550.000 cycles to more than 10 millions cycles (run-out tests). It can be deduced that this material has a fatigue limit and, according to the stair case method, its value was calculated as 90 MPa. Figure 7 : Damage evolution for increasing stress values (transversal section): (a) Mat 200 MPa, (b) Mat 340 MPa, (c) Roving 200 MPa, (d) Roving 340 MPa. Figure 8 : Experimentally determined S-N curve of the pultruded material. ( ○ : broken specimens; ● : fatigue limit; __ maximum likelihood estimation for the mean, --- confidence limits for the model at 95%) Most of the failures happened near the gripping zone, like in Fig. 9; this denotes a probable influence of the gripping system onto the obtained results and it is in agreement with the results reported in [9] where the influence of the specimens shape was analysed and where it is found that this kind of specimens gives the lowest fatigue strength.