Issue 46

C. Bellini et alii, Frattura ed Integrità Strutturale, 46 (2018) 319-331; DOI: 10.3221/IGF-ESIS.46.29 330 C ONCLUSIONS n this paper a design methodology of a mould for manufacturing isogrid structure made of composite material was defined and evaluated through structural tests. In fact, some issue can arise during the production of this kind of parts, that are induced by a bad-designed process, in terms of parameters and tools. A particularly delicate area is located where the ribs intersect each other, because in that zones the material compaction is more uneven, dangerous residual tensions can arise and the non-uniformly distributed load caused by build-up can make cure induced deformation and damage initiation arise. In this work, a methodology involving some solutions for the abovementioned issues is proposed. In particular, the mould grooves presented a variable depth to guarantee a correct compaction, since in the intersection points three times the material quantity was present than in the other parts. Another parameter to be taken into consideration was the tape stratification sequence, as it could influence the quality of the part. In order to evaluate the suitability of the design methodology for the manufacturing of lattice structures, some structures of this type were produced and tested. In particular, the geometry dimensions were taken from a previous work; however, for the analysis carried out in this work, in order to highlight the rib properties, as the material compaction, only a sector equal to one fifth of the structure was manufactured and the lattice structure was produced without the skin. For assessing the quality of a produced lattice structure, both qualitative and quantitative experimental tests were carried out. A visual inspection was suitable to highlight in qualitative manner the stratification induced defects and the rib compaction, while calcination tests and interlaminar shear strength tests were adopted to define in a quantitative manner the compaction degree and the quality of the ribs. The first adopted stratification sequence was found not suitable since it induced some defects in the head and at the base of the structure. To design a new groove profile was deemed necessary as the rib compaction degree was found uneven. In this work a preliminary process design optimization was carried out in order to remove the presence of defects. A new stratification sequence was successfully introduced, in fact the void spaces in the head trajectories disappeared, and an acceptable compaction level was obtained in the intersection point. However, some issues were still present in the transition points, so making use of a more advanced design tool will be necessary. A CKNOWLEDGEMENTS his work was conducted under the R&D project in implementation of Asse I – Research, Innovation and Strengthening of the productive basis of the POR FERS Lazio 2007–2013 (CO-RESEARCH). Special thanks to ‘‘Tecnologie Avanzate s.r.l.” and Eng. R. Aricò for their support in this work. R EFERENCES [1] Frulloni, E., Kenny, J.M., Conti, P. and Torre, L. (2007). Experimental study and finite element analysis of the elastic instability of composite lattice structures for aeronautic applications, Compos. Struct., 78(4), pp. 519–528. DOI: 10.1016/j.compstruct.2005.11.013. [2] Dawood, S.D.S., Inayatullah, O.B. and Samin, R.B. (2015). Computational study of the effect of using open isogrids on the natural frequencies of a small satellite structure, Acta Astronaut., 106, pp. 120–138. DOI: 10.1016/j.actaastro.2014.10.039. [3] Totaro, G. (2015). Optimal design concepts for flat isogrid and anisogrid lattice panels longitudinally compressed, Compos. Struct., 129, pp. 101–110. DOI: 10.1016/j.compstruct.2015.03.067. [4] Zheng, Q., Jiang, D., Huang, C., Shang, X. and Ju, S. (2015). Analysis of failure loads and optimal design of composite lattice cylinder under axial compression, Compos. Struct., 131, pp. 885–894. DOI: 10.1016/j.compstruct.2015.06.047. [5] Totaro, G. (2012). Local buckling modelling of isogrid and anisogrid lattice cylindrical shells with triangular cells, Compos. Struct., 94, pp. 446–452. DOI: 10.1016/j.compstruct.2011.08.002. [6] Totaro, G. (2013). Local buckling modelling of isogrid and anisogrid lattice cylindrical shells with hexagonal cells, Compos. Struct., 95, pp. 403–410. DOI: 10.1016/j.compstruct.2012.07.011. [7] Totaro, G., De Nicola, F. and Caramuta, P. (2013). Local buckling modelling of anisogrid lattice structures with hexagonal cells: An experimental verification, Compos. Struct., 106, pp. 734–74. I T