Co-authors​ :

 Juan-Manuel GARCIA (FRANCE), Jules LUCO (FRANCE), François-Henri LEROY , Cédric JULIEN , François-Xavier IRISARRI (FRANCE) 

In the aerospace industry, since its beginnings until nowadays, there is a strong need for materials and structures with exceptionally high stiffness and strength and low density. Truss structures are a very good example of this. Recently, architected structures have found interesting application for aircraft structures [1]. Indeed, these structures consist of slender bars working under tensile or compression loadings that are assembled in lattices using different joining techniques, for instance, welds or bolts. In the case of the latter, under specific loading conditions, joints may experience slight displacements and rotations, resulting in a non-linear macroscopic response and posing challenges for modelling their behaviour. Because of their high stiffness, observing and measuring the displacements and rotations of these structures, particularly through optical means, can be challenging. To the best of our knowledge, only few studies investigates the characterization and modelling of the mechanical behaviour of architected composite structures.
In this work, the mechanical behaviour of an ultra-light architected composite structure is assessed through mechanical tests instrumented with optical cameras. The base elements are made of a polymer matrix reinforced with continuous carbon fibres using the Tailored Fibre Placement (TFP) process and assembled using PA66 bolts to form octet-truss structures. The unit cell is cubic with 120 mm side. Mechanical tests are performed on different structures composed of one or several octet cells, up to 9x2x1 cells, in x, y and z direction respectively. Tensile, bending and torsion test are performed on a specific test bench with an electric actuator. The tests are instrumented with optical cameras and linear variable differential transformers. For the out-of-plane bending tests, the load-displacement curves highlighted non-linear macroscopic responses. The displacements and rotations of the joints and bars are successfully observed through a novel technique of motion amplification based on an algorithm of large displacement optical flow with deep matching. Digital image stereo correlation is also performed on different planes of the octet-pattern. The non-linear mechanical response of the structure is related to the rotation and displacements at the joints. We propose a discussion on the strategies required for numerical simulations of these structures.