Deformation Behavior of a Polygonal Tube under Oblique Impact Loading

Abstract

Aluminum tubes are energy-efficient absorbing components and are widely used for framework and reinforcement materials of structures. The effects of the axial length and crosssectional shape on the deformation behavior were investigated. Regarding the axial length, it has changed only to a certain length, and there are few studies on it. This paper deals with the influence of axial length. Also, when an impact is actually applied to the square tube, the impact in the oblique direction must also be taken into consideration. Therefore, the deformation behavior was analyzed by applying impact to the square tube from various angles other than the axial direction. An analysis of the dynamic deformation process of the polygonal tube was made using a finite element method. The results show that the load reached the peak immediately after the weight hit the square tube, then declined gently. The same tendency was obtained even if the axial length was changed. However, as the axial length became longer, the displacement taken to reach the peak load increased. As for the impact in the oblique direction, the peak load was small as compared with the axial direction. The deformation of square tube did not buckle in whole but only partially at any length. Introduction Square tubes have been used for framework and reinforcement members of structures.There are many studies on circular tubes, and deformation behaviors have been studied by static and dynamic compression tests [1]. Previous studies have shown that square tubes have a role of absorbing impact energy by crushing under pressure in the axial direction at the time of a collision [2]. Aluminum alloy has a Young’s modulus that is one-third that of commonly used steel materials, giving it the disadvantage of low rigidity. In addition, the whole buckles become large when thickness is increased, and causing axial compression deformation, which cannot effectively absorb collision energy[3].The tubular bodies with polygonal tubes and cellular cross sections have been studied as a means to effectively absorb energy [4]. Additionally, an influence of axial length on dynamic axially compressed aluminum tubes is being considered [57].It is known that elastic deformation occurs in the entire square tube prior to plastic deformation when the square tube deforms. Since this is periodic and wavy, it seems that the axial length will have a large influence. In a previous study, deformation behaviors up to 500 mm in length have been considered [8]. The purpose of this paper is to discuss, the deformation behavior of dynamic axial compression of an aluminum square tube of axial lengths of 500 mm, 750mm and 1000 mm. Also, when an impact is applied to the tube, the impact in the oblique direction must also be taken into consideration. Therefore, for comparison with the axial compression, deformation behavior of aluminum square tube under oblique impact loading was considered. Explosion Shock Waves and High Strain Rate Phenomena Materials Research Forum LLC Materials Research Proceedings 13 (2019) 41-46 https://doi.org/10.21741/9781644900338-7 42 Numerical Analysis Analytical method. The analysis is conducted by non-linear structure analysis program (Marc 2018) and pre-post processor (Mentat 2018). An example of analytical model is shown in Fig. 1. The specimen is an aluminum tube (A6063-T5). Material properties are shown in Table 1. Concerning axial length l, the square tubes (l = 500 mm, 750 mm and 1000 mm) are discretized at 20000, 30000, 40000 bilinear four-node shell elements, respectively. For the analysis in the oblique direction, an angle of θ= 10 degrees was given between the weight and the impact edge of the square tube. Schematic diagram of the analysis model is shown in Fig. 2. Fig. 1 Analytical model of square tube (l = 500mm). Fig. 2 Impact angle of weight (θ= 10 deg). The nodes on the edge of the tube are fixed with the exception of in the axial direction of the impact edge. The weight (80 × 80 × 20 mm, 15 kg) is an un-discretized three-dimensional, eightnode, first-order, isoparametric element. The deformed tube is regarded as an isotropic material following von-Mises yield condition, and the flow stress-strain relationship is shown in Equation (1) because the effect of the strain rate of the aluminum is smaller than that of other materials like iron, etc [9]. X Y Z θ Aluminum Weigh