Issue 46

C. Bellini et alii, Frattura ed Integrità Strutturale, 46 (2018) 319-331; DOI: 10.3221/IGF-ESIS.46.29 324 Finally, the number of tape layers N S was determined as: rib S C P N P  (4) Using the abovementioned relations and the material properties reported in Tab. 1, a N S equal to 20 was fixed for the structure under investigation. To determine the tape stratification sequence, a first one is that shown in the following. Considering the mould portion placed on a two-dimensional plane and numbering all the starting points trajectories as reported in Fig. 6, a first sequence is described in Tab. 2. To better clarify the meaning of this table, some sequence steps will be explained in the following; for example, the first step describes the first helical trajectory to be executed, from point 0 up to point 6, to lay down the tape in the groove, above the mould. The second step indicates the return trajectory of the tape, which adhered to the rear of the mould from point 6 to 8; for this reason, it is defined as “below”. This choice was necessary to ensure continuity of tension and trajectory to the tape. Following the proposed sequence consisting of 18 step, all the helical ribs were stratified at first and then the circumferential ones were added, thus ensuring the adhesion of the tape on the bottom of the grooves to guarantee an even consolidation in the intersection points. Figure 6 : First stratification sequence scheme. Step Trajectory Position Step Trajectory Position Step Trajectory Position 1 0-6 Above 7 10-7 Above 13 10-4 Above 2 6-8 Below 8 7-6-8-7 Below 14 4-9 Below 3 8-2 Above 9 7-4 Above 15 9-5 Above 4 2-1 Below 10 4-10 Below 16 5-11 Below 5 1-4 Above 11 10-1 Above 17 11-3 Above 6 4-10 Below 12 1-2-10 Below 18 3-0 Below Table 2 : First stratification sequence. Manufacturing of lattice structure After the machining and the surface treatment of the mould, the GFRP tape was deposited in the mould grooves. For the ribs deposition, the mould was mounted on a turntable, by using a special equipment, and the prepreg tape was laid down by hand in the mould grooves following the sequence described in the previous paragraph. The limits and difficulties of a manual deposition were those of not being able to obtain a high repeatability. Therefore, problems such as having a constant tape tensioning, being able to have perfectly overlapping layers and avoiding neck-in and twist of the tape are