Multiscale Modeling Methods for Analysis of Failure Modes in Foldcore Sandwich Panels
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Multiscale Modeling Methods for Analysis of Failure Modes in Foldcore Sandwich Panels R. Sturm 1 & P. Schatrow 1 & Y. Klett 2
# Springer Science+Business Media Dordrecht 2015
Abstract The paper presents an homogenised core model suitable for use in the analysis of fuselage sandwich panels with folded composite cores under combined loading conditions. Within a multiscale numerical design process a failure criterion was derived for describing the macroscopic behaviour of folded cores under combined loading using a detailed foldcore micromodel. The multiscale modelling method was validated by simulation of combined compression/bending failure of foldcore sandwich panels. Keywords Computational modelling . Damage mechanics . Sandwich . Multiscale
1 Introduction Sandwich structures consisting of thin stiff facesheets and a thick, low density core exhibit excellent stiffness-to-weight ratio and are investigated for novel light weight fuselage concepts. Currently the application of sandwich structures in transport aircraft is limited to secondary structures, since further understanding is required in the field of manufacturing, repair, vulnerability and safety before sandwich design can be applied for primary structures. Folded cores are currently investigated for future fuselage applications since the open cellular design of foldcore cells would solve the problem of humidity accumulation of closed cellular sandwich cores such as honeycombs [1–3]. Foldcore is a comparably novel core concept and can be produced out of different materials [4]. The manufacturing of foldcores is described in detail by Klett [5]. Homogenised core models and core micromodels can be used for core characterisation [6]. Different modelling techniques can be found in the literature for cellular core structures made out of Aramid paper. Impact resistance against high velocity impact loads
* R. Sturm [email protected] 1
Institute of Structures and Design, German Aerospace Center (DLR), Pfaffenwaldring 38-40, 70569 Stuttgart, Germany
2
Institute of Aircraft Design, University of Stuttgart, Stuttgart, Germany
and a corresponding micro model simulation strategy were developed [7, 8] and applied to predict the impact damage [9, 10]. Firstly, cellular core structures can be modelled using an homogenised model in a solid element representation [7, 11]. Using a detailed shell representation of the folded core micro-geometry the instability failure can be simulated in more detail. Hereby Aramid paper can be modelled using an idealised elastic–plastic material description [8]. The detailed composition of the Aramid paper is addressed in the multi-layered material description developed in the CELPACT project [7]. For novel fuselage concepts safety regulations require an equivalent crashworthiness compared to the conventional metal fuselage design. Brittle failure mechanisms of CFRP structures make the verification of equivalent crashworthiness for CFRP fuselage concepts challenging since conventional metal fuselages absorb a significant portion of the
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