Understanding the response and damage evolution of structures subjected to multiple impact events is essential for designing resilient structures capable of withstanding complex loading scenarios, such as impacts from hail, gravel or foreign object debris. This article presents the development and characterization of a novel test bench, the “Compressed air multi-cannon”, designed specifically for studying the multi-impact behavior of composite materials. This test bench offers advantages over traditional impact testing methods by enabling controlled and adjustable impact parameters, including number of impacts, spatial and temporal lag, energy, angle and impactor dimensions. The primary objective of this work is to provide a detailed description of the test bench design, construction, and validation procedures. Key components such as the pressurized air system, projectile launch mechanism, target mounting arrangement, and data acquisition system are discussed. Experimental methodologies for assessing multi-impact response, specimen preparation, instrumentation, and data analysis techniques are outlined. Through a series of single-impact and multi-impact tests, distinctive damage mechanisms and energy absorption characteristics were observed in composite structures, revealing significant differences in how composites respond under single- and multi-impact conditions. It was found that the single-impact configuration remains particularly critical compared to multi-impact configurations with a high number of impacts. However, further testing is required to determine whether this result holds true under varying impact parameters, highlighting the unique value of this machine for exploring new, realistic questions in the literature.

Comportement aux multi-impacts des structures composites : approche expérimentale et numérique: Les matériaux composites sont largement utilisés dans le domaine des transports en raison de leurs propriétés mécaniques spécifiques élevées. Cependant, au cours de leur cycle de vie, ils peuvent subir une dégradation significative de leurs propriétés mécaniques lorsqu'ils sont soumis à des chargements d'impacts. Les dommages induits par des impacts se manifestent sous différentes formes telles que la rupture des fibres, la fissuration matricielle, la décohésion fibres/matrice et le délaminage. L'étude du comportement aux impacts des structures composites a suscité une attention importante dans la littérature. Cependant, ces études se rapportent généralement au cas d'un seul impact ou d'impacts répétés. Peu de travaux se sont intéressés au cas d'impacts multiples, même s'ils sont plus proches des conditions réelles de service, comme dans les cas de chute de grêlons ou de projection d'objets externes tels que les gravillons présents sur les routes, les impacts d'oiseaux, etc. Dans cette thèse, nous présentons des méthodes expérimentales et numériques robustes pour le suivi in-situ et post-mortem des endommagements suite aux différents cas d'impacts possibles : mono-impact, impacts répétés, séquentiels, simultanés, etc. Ce travail a consisté dans un premier temps à développer un banc d'essai unique « canon à air comprimé ». Ensuite, un dialogue (essais expérimentaux-calculs numériques) a été assuré afin de mieux comprendre les phénomènes en jeu dans les cas de multi-impacts, pour finalement atteindre les performances maximales des matériaux composites.

This study addresses real-world scenarios such as impacts from hailstones, gravel, or external debris, where multiple simultaneous impacts occur on composite structures. The effects of multiple impacts are analyzed in terms of time lag between impacts, energy levels, and the relative positions of the impacts. Quasi-simultaneous impacts with varying energies are performed, and their results are compared in terms of energy dissipation, delaminated area, and material response. It is observed that, beyond a certain distance between impacts, two simultaneous impacts become equivalent to two mono-impacts. Additionally, a specific energy threshold per projectile exists beyond which the effect of multiple impacts becomes negligible. The findings highlight that the parameter time interval between impacts is the most significant factor in multi-impact studies, unlike in mono-impact scenarios where this parameter does not exist. The study underscores the importance of impact energy, the number of simultaneous impacts and their positions in the evolution of delamination and damage in composite materials. This article provides experimental data on simultaneous multi-impacts that researchers could use to validate their models using a high-complexity problem.