Ballere, Ludovic (2008) Damage tolerance of impacted curve composite structures : scale effects. PhD thesis Mécanique, LAMEFIP, ENSAM 2008ENAM0010 p.209.

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Abstract

During its life, a composite structure can be damaged locally although this deterioration may not be visible to the naked eye. It is necessary, in the stage of design, to appreciate the criticality of such a damage. Nevertheless, tests needed to estimate this criticality are often very expensive, especially in the case of large-size parts. The use of small-scale models can be an alternative to this problem. That implies the use, even the development, of scaling methods making it possible to extrapolate the behaviour of the reduced structure to that of the real structure. The objective of this research work, realized in collaboration between the laboratory LAMEFIP-ENSAM-ParisTech and SNECMA Propulsion Solide SAFRAN Group, is to establish a methodology that would potentially free the compagny from a heavy experimental study on structures (filament wound vessels) at the real scale. From tests, carried out on structures at smaller scales and from the model established in this work, it will be possible to predict the residual behaviour under internal pressure of a structure at the real scale when it is damaged by impact. Curved panels were used for the establishment of this methodology since they are less expensive than filament wound vessels - even at reduced scale -. Initially, a damage tolerance study, consisting of damage initiation by impacts, ultrasonic and microscopic inspections of the damage and quasi-static tensile tests until rupture, was carried out on two sclaes of specimens, based on experimental designs. Through this study, it was possible to highlight the existence of many scale effects, mainly due to the thickness and the curvature of the specimens. Then, a progressive damage model of the layers and the interface was established and implemented in a finite element code and fine tuned with respect to the response surfaces experimentally determined. This numerical modeling establishes the methodology allowing the scaling of structures. Then, this methodology was applied to the case of filament wound vessels. Numerical results match with data of an experimental study carried out on scaled vessels and show the need for taking into account the damage of the interface for the prediction of the residual behaviour of pre-impacted curved structures.

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