Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: www.elsevier.com/locate/tws Full length article Experimental testing and numerical analysis of FDM multi-cell inserts and hybrid structures Stefan Tabacu a, ⁎ ,1 ,Cătălin Ducu b,1 a Automotive Department; Faculty of Mechanics and Technology, University of Pitesti, 1, Târgu din Vale, 110040 Pitesti, Romania b Manufacturing Department, Faculty of Mechanics and Technology, University of Pitesti, 1, Târgu din Vale, 110040 Pitesti, Romania ARTICLE INFO Keywords: Fused deposition modelling Sample testing Axial crushing Multi-cell structures Hybrid structures ABSTRACT Modern transportation systems require light materials with an increased level of protection thus thin walled structures are in the focus of structural engineers. The latest developments in the field of manufacturing pro- cesses allow the use of Rapid Prototyping technologies for custom safety devices and Additive Manufacturing is a candidate that already captured some attention. In this work Fused Deposition Modelling method was used to manufacture samples for material characterization and multi-cell insert designed as safety devices and the material is ABS. Traction tests were performed and some SEM images complete the specimens’ analysis. From this analysis, in order to define a simple material model for numerical analysis, a stacking configuration -45°/0°/ 45°/90° was selected. A model for material damage is also presented in this paper. Circular structures with rectangular multi-cell were manufactured and tested in compression. In order to improve the performances a hybrid structure was investigated. Aluminium tubes were added in order to enhance the performances of the printed structures. For each step of the experimental work a numerical companion is presented. Modelling techniques and parameters are presented and discussed in this paper. By adding the aluminium tube there is an increase in the performances of the structure. A progressive profile for the crushing force is obtained. By ad- justing the support (outer aluminium tube) and designing multi-cell insert, structures for safety enhancement can be developed. 1. Introduction Modern transportation systems require an increased level of pro- tection thus, due to the increased number of add-on devices fitted on board the mass of the supporting structure should be as low as possible but at the same time it must provide the maximum level of protection during a collision. As a consequence, thin walled structures are in the focus of structural engineers especially when crashworthiness is ad- dressed. These structures demonstrate a high energy absorption capa- city for a relatively reduced mass, thus being a reliable solution when the total mass of the construction is critical. The modern analysis of thin walled structures with circular section has a strong background in work of Abramowicz and Jones [1], Hsu and Jones [2], Wierzbicki et al. [3] and Reid [4], while the structures with a rectangular cross-section were investigated by Abramowicz and Jones [5] and Wierzbicki and Abra- mowicz [6]. In order to improve the structural performance，multi-cell structures were designed and studied by Alavi Nia and Parsapour [7], Costas et al. [8], Jusuf et al. [9] Qiu et al. [10] and Zhang and Zhang [11–13]. A recent review paper of Baroutaji et al. [14] outlines the findings in field of thin-walled structures designed as energy absorbing devices. The use of multi-cell structure is an effective method to in- crease the energy absorption while keeping a reduced mass of the fin- ished part. These structures can be manufactured by extrusion or, for research purposes, by cutting from a solid block. This work is focused on the investigation of circular multi-cell structures, previously in- vestigated by developing a theoretical model for the evaluation of the crushing force [11,15]. The latest developments in the field of manu- facturing processes allow the use of Rapid Prototyping technologies for custom safety devices. Rapid Prototyping includes sets of technologies used to produce complex parts [16] in limited series. The parts can be used for design and functional analysis and in some cases as structural components, like multi-cell structures that are in the focus of the pre- sent study. The performances of the finished parts are however de- pendent on the technology employed for the manufacturing process [17–19]. Among Rapid Prototyping technologies is Additive Manufacturing which consists in building parts layer by layer. Due to the relatively simplicity of the equipment, 3D Printers are widely used as Rapid https://doi.org/10.1016/j.tws.2018.04.009 Received 26 November 2017; Received in revised form 6 April 2018; Accepted 10 April 2018 ⁎ Corresponding author. 1 web page: http://www.upit.ro E-mail addresses: stefan.tabacu@upit.ro, stefan.tabacu@gmail.com (S. Tabacu), catalin.ducu@upit.ro, catalinducu@yahoo.com (C. Ducu). Thin-Walled Structures 129 (2018) 197–212 0263-8231/ © 2018 Elsevier Ltd. All rights reserved. T