Contents lists available at ScienceDirect Thin-Walled Structures journal homepage: www.elsevier.com/locate/tws Full length article Axial splitting of conical frusta: Experimental and numerical study and crashworthiness optimization Seyed Mohammad Elahi, Jafar Rouzegar ⁎ , Hasan Assaee Department of Mechanical and Aerospace Engineering, Shiraz University of Technology, P.O. Box 71555-313, Shiraz, Iran ARTICLE INFO Keywords: Axial compression Energy absorber Finite element method Design of experiments Optimization Thin-walled structure ABSTRACT This paper investigates the axial splitting process of thin-walled conical aluminum frusta, experimentally and numerically. The specimens were prepared using the spinning method and some edge slits were created at the specified locations. The specimens were axially compressed between a rigid plate on top and a rigid conical die at the bottom using Zwick universal testing machine. Some key parameters of energy absorbers such as specific absorbed energy (SAE), non-dimensional load-carrying capacity (NLC) and undulation of load-carrying capacity (ULC) were extracted from the load-displacement diagrams. Effects of different parameters such as specimen wall semi-apical angle, die semi-apical angle, number, and length of initial slits were studied on the energy absorption capability of specimens. The numerical analyses were performed by finite element method using Abaqus/Implicit software package. The surface-based cohesive behavior technique which works only with im- plicit solver was employed for cracks propagation. The numerical simulations were compared with experiments and good agreements were found between numerical and experimental results. To find the optimum energy absorber parameters, the design of experiments (DOE) method was employed. Using the existing data and ap- plying the Taguchi technique, the optimal specimens with best SAE, ULC, and NLC were found. To check the efficiency of the DOE approach, these specimens were fabricated and tested and it was observed that the tested specimens had the best SAE, ULC, and NLC among all specimens. So, the excellent performance of DOE technique in present application was proved. 1. Introduction Energy absorbers are systems that can partially convert the kinetic energy of impacts into other forms of energies. Thin-walled structures such as cylindrical tubes and conical shells are common energy absor- bers that the researchers have paid considerable attention to their collapse behavior in the last decades. Among different energy absorp- tion methods, axial splitting is an efficient mechanism of energy dis- sipation due to its relatively constant force over a long stroke [1]. Stronge et al. [2] examined the splitting of square tubes compressed axially on a die and they found that the energy is dissipated by fracture and plastic deformation of metal tubes. Lu et al. [3] experimentally studied tearing energy of square aluminum and mild steel tubes under splitting process. They also determined the bending energy considering rigid-perfectly-plastic material behavior. Huang et al. [4] investigated the energy absorption capacity of square metal tubes in axial splitting. Pyramid shaped dies with various semi-angles were used and the square tubes were pushed slowly against them. Also, they studied splitting behavior of circular metal tubes by compressing the specimens on to conical dies with various semi-angles [5]. The effects of different parameters such as tube dimensions, semi-angle of the die and friction coefficient were investigated on the results. Bheemineni et al. [6] stu- died the tearing behavior of circular metal tubes under axial com- pression. The numerical simulations were carried out using ANSYS/LS- DYNA software. Yuen et al. [7] studied splitting process of circular tubes under blast load. Effect of length of cut on mean cutting load, cutting force efficiency and peak cutting load was investigated. Ni- knejad et al. [8] presented some theoretical relations for prediction of axial force of circular metal tubes during the splitting process. They investigated the effects of wall thickness and inner radius of the tubes, number, and length of initial slits, and die semi-angle on the results, experimentally. Tanaskovic et al. [9] combined shrinking and splitting processes to increase energy absorption characteristics of circular tubes. The efficiency of presented energy absorber was approximately 60% higher than absorbers with only shrinking. Li et al. [10] performed experimental and numerical studies on new energy absorber which combines expanding and splitting processes to enhance the energy absorption capability of circular metal tubes. A finite element model for https://doi.org/10.1016/j.tws.2018.03.005 Received 26 October 2017; Received in revised form 3 February 2018; Accepted 6 March 2018 ⁎ Corresponding author. E-mail address: rouzegar@sutech.ac.ir (J. Rouzegar). Thin-Walled Structures 127 (2018) 604–616 0263-8231/ © 2018 Elsevier Ltd. All rights reserved. T