Issue 35

R. Sepe et alii, Frattura ed Integrità Strutturale, 35 (2015) 534-550; DOI: 10.3221/IGF-ESIS.35.59 539 the panel was statically tested with loading condition T1. Then the fatigue test is continued and other 12˙708 cycles were applied and then the demonstrator broke down definitively at the middle-lower bay, near the third frame (Fig. 8). Figure 6 : Frame failure at 164˙292 cycles. Figure 7 : Frame failure at 164˙292 cycles (detail). Figure 8 : Final failure at 177000 cycles. FE ANALYSIS eometric nonlinear finite element analyses were conducted to predict the strain and stress distributions for the several test condition. The analyses were carried out by using a commercially available finite element code (ANSYS). The panel was modeled using two-dimensional four-nodes shell elements (SHELL 181) with each node having six degrees of freedom for each node. A global view of the finite element model is shown in Fig. 9, which consists of 64432 elements and 205664 nodes; here different colors of shell elements are associated to different thicknesses. Four-noded shell elements were used throughout to model skin, frames, stringer clips, stringers, and load attachment doublers. The presence of the rivets was taken into account defining the proper number and location of constraint points (CP). The analysis has been performed in geometric non linear condition (large displacements), while the material has been considered in linear elastic hypothesis with Young modulus equal to 72500 MPa for Al 2024-T3 aluminium alloy and 71016 MPa for Al 7075-T6 51 aluminium alloy, and Poisson’s ratio is equal to 0.33 for both materials. Stress stiffening capability is included. G