Issue 7

C. Colombo et alii, Frattura ed Integrità Strutturale, 7 (2009) 65-72 ; DOI: 10.3221/IGF-ESIS.07.05 71 Figure 9 : A fatigue broken specimen near the gripping zone. Also in this case SEM observations have been performed on run-out specimens to evaluate the fatigue damage. Pictures showing SEM images after 10 millions cycles are reported in Fig. 10, that refers to longitudinal sections: the presence of arrested cracks can be noted. On the basis of the analysis of SEM observation a quantitative estimation of the fatigue damage was made by counting the number of different defects in the layer that form the pultruded material. The results are shown in Tab. 3 and evidence that debonding (crack between matrix and fibers) in the Mat layer is the main responsible of the fatigue damage of this material (a) (b) Figure 10 : SEM images of the fatigue specimens: (a) Mat, (b) Roving. Mat Roving Volumat Debonding 67 25 60 Fiber Cracks 30 15 8 Matrix cracks 5 0 0 Table 3 : Defect count in the fatigued run-out specimens C ONCLUSIONS he static and fatigue behaviour of a pultruded glass-fiber reinforced composite material used in structural applications was investigated. On the basis of the tests executed it was possible to determine quantitative data that can be applied for the design of structural parts manufactured with this material. The fatigue tests allowed to determine that the material has a fatigue limit that can be used for designing long life-span parts subjected to time variable loading. The SEM observation allowed to evidence the evolution of static and fatigue damage. In particular, as regards this latter one, it was possible to assess that fatigue damage take place mainly in the Mat layer and that it mainly consists in T