Full length articleCrashworthiness analysis and optimization of a cutting-style energy absorbing structure for subway vehicles
Graphical abstract
Introduction
The safety of passengers after railway collision accidents has always been a hot spot of attention because the casualties and severe loss of property are unbearable. For example, on July 12, 2008, a serious railway collision accident occurred in Los Angeles that killed at least 26 people, and more than 130 people were injured. A similar collision occurred in Wenzhou, China, on July 23, 2011, killing 40 people and wounding at least 200 people. Therefore, substantial investigations have focused on the crashworthiness design and the optimization of energy absorption structures.
Several investigations have addressed the crashworthiness design and optimization of energy absorption structure using numerical simulations and experiments. Thin-walled structures are widely used in civil engineering, shipbuilding, and other industries because of their low cost, high strength-weight ratio, and progressive deformation under an axial crushing load during crashworthiness analysis [1], [2]. Jones [3] studied the effectiveness of thin-walled structure with different section shapes under static and dynamic axial loadings by adopting an energy-absorbing effectiveness factor. Based on the response surface method, Liu [4] optimized the cross-sectional dimensions of thin-walled structures to maximize the specific energy absorption and presented efficient, simplified models that obtained optimum results of a certain accuracy. Nia and Hamedani [5] compared various section shapes of thin-walled tubes and concluded that pyramidal and conical tubes can lower the peak force, whereas the circular tube absorbs the most energy. Hosseinipour and Daneshi [6] found that grooves on the tubes can stabilize the deformation pattern to lower the deceleration pulse.
Furthermore, cellular material, as filler material for hollow tubes, has attractive mechanical properties for improving the crashworthiness and is widely used in automotive, military, and other industrial applications [7]. Several studies [8], [9], [10], [11], [12], [13], [14] showed that aluminum foams have good energy absorption under both quasi-static and dynamic loading conditions. Paz et al. [15] found that the honeycomb-filled tube showed an improved energy absorption over the hollow tube by performing tests with a hollow tube and a honeycomb filled tube. Regarding aluminum honeycomb sandwich panels, Paik et al. [16] concluded that the aluminum honeycomb core has excellent properties with respect to the weight savings and fabrication costs based on a series of strength tests performed on an aluminum honeycomb-cored sandwich panel specimen. Santosa et al. [17] found that aluminum foam filling provided better crash behavior than aluminum honeycomb filling. Bi et al. [18] showed that the foam-filled tube has a significantly larger crushing force than the hollow tube. Generally, there is a large, undesirable, initial peak force, followed by fluctuation in the force-displacement curve [19]. Peng et al. [20] focused on the study of the combination of thin-walled metal composite structures and aluminum honeycomb structures and found that as the thickness or honeycomb yield strength increases, the initial peak impact force and average crashing force increase. However, most studies have only focused on the parameter optimization of the thin-walled structure and the aluminum honeycomb structures or composite structures. There are few studies on the cutting-style energy absorbing structure, which works on the principle that the plastic deformation of cutting chips, the tearing of the metal tube, and the friction force between knives and carved metal will consume the impact energy. Another essential advantage of this structure is its strong stability because the energy absorption tube can works as a guide rail.
In this paper, a finite element model of the proposed structure was established and validated by a full-scale impact experiment in the same constraint conditions. The cutting depth, the cutting edge angle and the chip central angle were set as the design parameters. Based on the validated simulation model, the influence of the design parameters on the crashworthiness performance was studied. In this work, several indicators, including the energy absorption (EA), the peak cutting force (), and the average cutting force (), are defined as the crashworthiness indicators to systematically evaluate the crashworthiness of the cutting-style energy absorbing structure.
Section snippets
Geometrical description
The energy-absorbing structure in this paper is fixed at the front end of the underframe of the subway. There are four parts of the structure, as illustrated in Fig. 1. The energy absorption tube, with an outside diameter of 195 mm and inside diameter of 171 mm, consists of tube A (axis length of 694 mm) and tube B (axis length of 185 mm). The energy absorption tube absorbs energy when carved by the knives and works as a guide rail, which can guarantee that all the knives bear the average force and
Validation of the finite element (FE) model
To validate the accuracy of the developed FE model, a full-scale experiment was conducted under the same boundary conditions as the simulation. The experiment specimen had a cutting depth of 3 mm, a cutting edge angle of 15° and a chip central angle of 20°. The results of the experiment and simulation are represented by the force-time history curve and deformation series. Fig. 7 and Fig. 8 display the comparison of the impact behaviors between the experiment and corresponding simulation in terms
Definition of the optimization problem
In general, the EA and the peak cutting force () are key indicators. As an energy-absorbing component, the cutting-style energy absorbing structure is expected to absorb as much crash energy as possible to reduce the severe injury of the occupants. Meanwhile, the of the structure may reflect the severity of the collision, which is also highly related to the severity of occupant injury. Thus, in this paper, we select the maximum EA and the minimum as the objective optimization function.
Conclusion
In this study, the crashing behavior of cutting-style energy absorbing structure with different values of design parameters are comprehensively investigated and optimized. An finite element model was established using nonlinear FE code LS-DYNA. To validate the accuracy of the FE model, a full scaled dynamic impact experiment was conducted and the accuracy of the FE model was demonstrated by analyzing the date of experiment and numerical simulation, which are essentially agreed with each other.
Acknowledgments
The authors would like to thank the financial support of the National Nature Science Foundation of China (514005517, U1334208), the Natural Science Foundation of Hunan (2015jj3155) and Strategic Leading Science and Technology Project of Central South University (ZLXD2017002).
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