Analysis of the nonlinear behavior of inserts in sandwich structures : application to an innovative sizing method

The insert sizing for sandwich structures is usually made using the methods proposed in the “Insert design handbook” of the ESA and the “Military handbook 23A”. These analytical methods based in the in the research carried by Ericksen in 1953 could lead to errors of the pull-out allowable load prediction in the range of ±20 % for some cases.In this thesis, the principal failure modes of inserts are investigated; the core shear damage of the Nomex honeycomb core, and the potting failure. A detailed analysis of the shear postbuckling of the Nomex honeycomb core is made, allowing to propose a two variables damage model. Then, the obtained results are used to develop an insert virtual model that is validated through comparison with pull-out tests, and then used to draw failure mode maps of inserts. Using this method, the admissible pull-out load of inserts can be estimated more precisely. This method could be an alternative to using the analytical methods for the insert sizing. The resulting charts could be given to engineers as a tool for the insert sizing which could reduce the insert’s design-validation time.