A B S T R A C TComposites are known to be vulnerable to out-of-plane loading such as impact. Investigating the residual properties of the laminate as a function of damage detection is the main purpose of impact damage tolerance design in aeronautics. As a good alternative to experimental campaigns, numerical approaches would lead to saving of time. The model developed in Institut Clément Ader over the last years enables representation of behavior of composite laminates subjected to low velocity/low energy impactincluding permanent indentation and Compression After Impact. Damage such as permanent indentation, fiber failures, matrix cracks and delamination are taken into consideration at each step thanks to a discrete ply modelling. The work presented here deals with the use of this model to make a composite laminate design optimization according to impact damage tolerance design. A method to improve optimization by reducing computation time is also proposed, based on a "best candidates" selection.

The development and certification of aeronautical composite structures is still largely based on the pyramid of tests. This approach is extremely costly in terms of number of tests, especially at the level of coupons. Moreover, these tests are highly conservative, under uniaxial loading, and do not represent the actual behavior at structure scale. To overcome these drawbacks, a new methodology has been developed at the Institut Cl� ement Ader, which uses a complex loading test rig for technological specimens. This research focuses on the combined loading after impact of CFRP plates and highlights a specific behavior quite different from the usual CAI (Compression After Impact) response at the scale of coupons. In particular, compression, shear and combined shear/compression loadings were applied to large Carbon Fiber Reinforced Plastics (CFRP) laminated plates and the interaction of the impact damage with the post-buckling behavior has been investigated.

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Laser‐based powder bed fusion (LPBF) is attractive to build complex parts in spite of the low machinability of Inconel 625. The LPBF microstructures and tensile properties are well documented in literature. But fatigue properties and impact of the LPBF intrinsic defects and microstructures on the crack initiation and propagation mechanisms are uncommon. Low and high‐cycle fatigue tests at room and service temperature presented in this paper prove that the LPBF defects shorten the crack initiation stage. After annealing heat treatment, the microstructure adapts to the defects, and the fatigue response becomes similar to a free defect material. The fatigue life of as‐built Inconel 625 is lower than 50% of its monotonic yield tensile strength (YTS) while the annealed material reaches 100% of its YTS. The propagation rate is slowed by the homogeneous annealed microstructure and improved ductility resulting from removal of dislocation cells and changes in grain morphology.

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