Issue 7

C. Colombo et alii, Frattura ed Integrità Strutturale, 7 (2009) 65-72; DOI: 10.3221/IGF-ESIS.07.05 66 composites under flexural loading is investigated, while [9] describes the tensile fatigue performances of pultruded reinforced polymers profiles, with particular emphasis on the effect of the specimens shape on the fatigue strength and endurance. In the same paper some results obtained from fatigue tests up to 10 million cycles are reported, but the results number is limited and does not allow the determination of a fatigue limit. In [10] the rotating bending fatigue strength of a pultruded glass fiber reinforced composite is investigated. In [11] the residual fatigue strength of a pultruded composite after damage occurred due to impact of a external object is considered. Other papers focus their attention on pultruded composite application in fatigue loaded parts. In [12] the fatigue performance of a cellular FRP bridge deck adhesively bolted to steel girders is investigated, while in [13] the fatigue strength of a pultruded I-shaped post for railway noise barriers is considered and analyzed by means of ad-hoc experimental tests. From the analysis of references, it is clear that the designer cannot found sufficient data and knowledge for a safe and reliable application of pultruded materials for structural applications where a long life (many millions of cycles) is required. Only a couple of papers report data for such a long endurance and the number of specimens under investigations is limited and further research is needed, both for obtaining quantitative data and to know much about the failure mechanisms by changing the load amplitude. This paper intends to give a contribution in this field. A glass fiber reinforced composite obtained by pultrusion and used for box shaped beams used in civil infrastructures (i.e.: noise barriers, [6]) is considered and experimentally analyzed. Its static behaviour is investigated by means of tensile tests while the observations at the scanning electronic microscope allowed to investigate the damage mechanism involved in the static failure. Then the fatigue behaviour of the material was investigated by means of axial tests (R=-1) long up to 10 million cycles. The results showed a narrow scatter and allowed to determine the S-N curve and to assess the existence of the fatigue limit. By means of the SEM analysis it was moreover possible to understand how fatigue damage develops in the different layers of materials. M ATERIAL he material is a glass-fiber reinforced composite obtained by pultrusion. The matrix is made of equally distributed polyester not saturated resins commercially called Leguval W 24 GA and Synolite 0175-N-1. The global volumic mass of the matrix is about 1,3 g/cm 3 . The E glass fibers have a ultimate tensile strength of 1800 MPa, an elastic modulus of 76 GPa and a volumic mass of 2.53 g/cm 3 . In Fig. 1 it is shown the section from which the specimens were cut: these latter were obtained from the longer side. In the same figure it is shown the the lay-up of the material and different layers can be observed: their composition is described in Tab. 1. It can be noted that most of glass fibers (84%) are unidirectional (Roving) while the remaining part (16%) is randomly distributed. Sontara is a thin layer used on the surface to prevent surface damage due to impacts or to the aggressive environment effects. Reemay is a surface writing. Both Sontara and Reemay does not modify mass and mechanical characteristics of the material. Figure 1 : Section of the pultruded bar from which the specimens were cut. T