AMT Seminar: Thin-ply composites - pushing the boundaries of design and performance of aerospace composite structures
In the seminar series in aerospace manufacturing technologies, we are presenting invited speakers with selected topics in the field of novel manufacturing technologies. The upcoming seminar talk will be given by Dr. Joël Cugnoni from EPFL/ HEIG-VD
In recent years, important progress has been made in the development of composite laminates using thinner pre-impregnated plies down to about 20 micrometers instead of ~200 micrometers for traditional composites. The motivation for this trend towards the development of thin-ply composites is not only to allow the production of thinner and lighter laminates for lightweight structures, but also to provide enhanced effective design space for laminate optimization as well as improved strength and damage resistance thanks to positive size effects.
The first prime benefit of using thinner plies in a given structure, i.e. at of a constant laminate thickness, is the ability to use a larger number of ply orientations to achieve an optimal solution as the laminate design space is naturally extended. This fact is particularly important for already thin laminates in which only two or three fiber orientations can be selected with standard ply thickness to satisfy design constraints, such as laminate symmetry and minimum fraction of fibers at 90°. The second benefit is that thin-ply composites present a very significant performance advantage over traditional composites due to positive ply size effects with decreasing ply thickness. Indeed, it has been shown that multi-axial laminates made of thin-ply composites can reach an ultimate strength and first ply failure corresponding to 100% , of the ultimate strain of the fibre. This outstanding property of thin ply composites is related to the delay or near suppression of transverse cracking of off-axis plies leading to an equally suppressed delamination crack growth until fibre failure is reached.
In this seminar, an overview of experimental characterization of the mechanics of thin-ply composites will be presented to highlight the main performance advantages and drawbacks of this new class of composites [1,2]. To understand those mechanisms, a multiscale model of transverse cracking in thin-ply laminates has been developed recently in our team and provides important insight on the cause of the observed experimental scaling of in-situ strength of thin-ply quasi-isotropic laminates [3,4]. Finally, two applications examples on the use of thin-ply composites in aeronautic structures will be presented, using automation and optimized design for manufacturing.
 Amacher R., Cugnoni J., Botsis J., Sorensen L., Smith W., Dransfeld C (2014) Thin-Ply composites: Experimental characterization and modeling of size-effects, Composite Science and Technology, 101, 121-132, doi:10.1016/j.compscitech.2014.06.027
 Cugnoni J., Amacher R., Kohler S. et al., Towards aerospace grade thin-ply composites: Effect of ply thickness, fibre, matrix and interlayer toughening on strength and damage tolerance, Composite Science and Technology, 2018, 168, pp467-477, https://doi.org/10.1016/j.compscitech.2018.08.037
 Transverse cracking in the bulk and at the free edge of thin-ply composites : experiments and multiscale modelling, Kohler S., Cugnoni J., Amacher R. , Botsis J., Journal of Composites : Part A, under review
 Sebastien Kohler, J. Botsis and J. Cugnoni (Dirs) Multiscale characterization and modeling of thin-ply composite size effects, 2014, PhD EPFL Thesis 9132 (2019), dx.doi.org/10.5075/epfl-thesis-9132
Joël Cugnoni has been Associate Professor at the University of Applied Sciences, Yverdon (HEIG-VD), since 2018. He received his PhD in 2004 on the Identification of constitutive properties of composites shells based on modal response at Ecole polytechnique fédérale de Lausanne EPFL. His main research interest lies in the computational and experimental solid mechanics of composites, but he also made relevant engineering contributions in the field such as the design optimization of the composite structure of the ATLAS SCT detector for the CERN-Large Hadron Colider experiment. In 2006 he became Associate Researcher at the Laboratory of Applied Mechanics & Reliability (LMAF) at EPFL, additionally he has being appointed Associate Professor at the University of Applied Sciences Western Switzerland (HES-SO) in Yverdon in August 2018.