Combined shear/compression structural testing of asymmetric sandwich structures

Asymmetric sandwich technology can be applied in the design of lightweight, non-pressurized aeronautical structures such as those of helicopters. A test rig of asymmetric sandwich structures subjected to compression/shear loads was designed, validated, and set up. It conforms to the standard certification procedure for composite aeronautical structures set out in the “test pyramid”, a multiscale approach. The static tests until failure showed asymmetric sandwich structures to be extremely resistant, which, in the case of the tested specimen shape, were characterized by the absence of buckling and failure compressive strains up to 10,000 μ strains. Specimens impacted with perforation damage were also tested, enabling the original phenomenon of crack propagation to be observed step-by-step. The results of the completed tests thus enable the concept to be validated, and justify the possibility of creating a much larger machine to overcome the drawbacks linked to the use of small specimens

Bi-level optimization of blended composite panels

Two approaches are examined for finding the best stacking sequence of laminated composite wing structures with blending and manufacturing constraints: smeared stiffness-based method and lamination parameter-based method. In the first method, the material volume is the objective function at the global level and the stack shuffling to satisfy blending and manufacturing constraints is performed at the local level. The other method introduced in this paper is to use lamination parameters and numbers of plies of the pre-defined angles (0, 90, 45 and -45 degrees) as design variables with buckling, strength and ply percentage constraints while minimizing the material volume in the top level optimization run. Given lamination parameters from the top level optimization as targets for the local level, optimal stacking sequence is determined to satisfy the global blending requirements. On a benchmark problem of an 18-panel wing box, the results from these two approaches are compared to published results to demonstrate their potential