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Intricate lattice structures can be fabricated by the selective laser melting method, which decreases the production limitations effectively and significantly provides more design freedom. In the present work, additive manufacturing and topological optimization are integrated to develop a novel body- and edge-centered 12 vertices lattice structure with modified triangular prismatic strut pattern (MTP-lattice). Finite element models of MTP-lattice were first established in PAM-CRASH and then experimentally verified via compressive test. The validated finite element models were then employed to investigate the novel MTP-lattice’s energy absorption and mechanical behavior under axial and offset loading. The results show that topology-optimized MTP-lattice has a superior energy absorption performance compared with competing unit cells. Besides, its mechanical performance is greatly influenced by the strut pattern and shape parameters. Furthermore, the deformation evolution from the overall structure to the strut level during the entire compression process was analyzed. The observations illustrate that the MTP-lattice exhibits a steady deformation mode with optimal shape parameters, which appears to have a promising prospect for the application of crashworthy components. The research results provide excellent guidance for the application of novel lightweight energy-absorbing lattice.

Multi-wall profile as one of the most widely approaches can enhance the crashworthiness properties in thin-walled tubular structures. In actual application process as energy absorbers, there may be...

The progress of additive manufacturing (AM) technique broadens the conceivement and adoption of new types of lattice structures effectively. A new lattice structure, drawing on inspiration from nature, was developed and manufactured via selective laser melting (SLM) to explore the effects of printing parameters on densification and mechanical performance. Compressive experiments were conducted by universal testing machine and Split Hopkinson Pressure Bar (SHPB) system to assess energy absorption and collapse behaviour of bio-inspired structures subjected to static and dynamic load. Each deformation evolution was captured and the digital image correlation (DIC) method was adopted to analyze the strain distribution in the compressive process. The observations reveal that the bio-inspired structure possesses a steady deformation mode under static and dynamic loading, which exhibits a promising prospect for impact resistant applications. Furthermore, energy absorption of this bio-inspired structure displayed some sensitiveness to the rate of strain. Finally, finite element analysis based on Johnson-Cook constitutive model was performed as well to simulate the static and dynamic response of the bio-inspired structure. The finite element outcomes remarkably coincide with the outcomes of experiments.

Lumped parameter modeling (LPM) combined with optimization techniques is an efficient approach for parametric configuration design of energy absorption to improve crashworthiness performance during train collision. This work proposed a simplified model by introducing a bar element to consider the influence of the carbody in a collision process. The optimization method is applied to calibrate the equivalent parameters of the bar element. Bar elements with calibrated parameters are adopted in establishing a one-dimensional (1D) model for the train crash. Subsequently, a novel crash energy management (CEM) mode with functionally graded energy (FGE) configuration is introduced to the train crash model for improving crashworthiness performance. The influence of parameters in graded function on interfacial force and peak acceleration is investigated and optimal design parameters are obtained by Nondominated Sorting Genetic Algorithm (NSGA-II). It is concluded that considering the behavior of the carbody can improve the accuracy of LPM in predicting the longitudinal response, and the gradient CEM is a potential energy configuration mode to improve the crashworthiness of the train in a collision.

Self-similar structures with hierarchy become novel configuration by presenting higher energy absorption efficiency and better crashworthiness performance, however, its performance is hard to increase continually via expanding hierarchy. In this work, a novel multi-cell hierarchical hexagon honeycomb structure (HHHS) was obtained by changing the topological connection, of which structure is ruled by a length coefficient defined as the ratio of 1st and 2nd hexagon honeycomb. The effect of wall thickness and length coefficient on structural energy performance was numerically investigated using finite element model validated by experiments. The optimization problem was established via surrogate model and solved using Non-dominated Sorting Genetic Algorithm (NSGA-II) to increase specific energy absorption (SEA) and decrease peak crushing force (PCF) of the HHHS for seeking superior crashworthiness. It is indicated that there is an optimal ratio between two level sub-structure, which is beneficial to enhance the crashworthy performance due to the interaction effect of adjacent folded element. The HHHS with optimal geometrical parameters presents remarkable enhancement and energy absorbing potential, which can be selected for energy absorption in consideration of a balance between better crashworthiness and preparation cost.

The lattice structure manufactured by additive manufacturing has geometric defects, which makes geometric shapes different from initial design. This research aims to incorporate stochastic geometric defects into the strut elements of a lattice structure to enhance predictive capabilities of simulation and analyze the influence of difference defects on mechanical properties. Here, X-ray computed tomography (CT) was used to extract the shape and distribution of process-induced defects. The X-ray CT images showed more geometric defects in horizontal struts than diagonal struts or vertical struts. Then, the geometric defects which are strut thickness variation and strut waviness were statistically quantified and considered into the ideal finite element model (FEM) to create the statistical FEM. Comparing the ideal FEM with the statistical FEM, it turns out that the statistical FEM was closer to experimental results. In addition, influence of different geometric defects in different struts on mechanical properties of the lattices were investigated. It indicated that strut thickness variation had more significant effect than strut waviness and thickness variation of diagonal strut had the greatest influence in difference direction.

The implementation of graded thicknesses in structural designs is an efficient strategy for improving the energy absorption performance of thin-walled columns. In this study, the mechanical responses of square columns with double-surfaced gradients under axial crushing forces were analytically and numerically investigated. A mathematical expression for the mean crushing force on a novel tube design is derived according to the super folding element method by introducing two novel parameters: the average thickness of the efficient energy absorbing region (EEAR) and global average thickness. The analytical predictions show good agreement with the simulation results that were obtained using the nonlinear finite element program ANSYS/LS-DYNA. The results demonstrate that a greater coefficient of average thickness of the EEAR versus global average thickness improves the energy absorption efficiency. However, increasing this coefficient largely depends on the sectional material distribution law. To explore the effects of this law on crushing responses, three different material distribution types were investigated. A significant improvement in specific energy absorption (approximately 30%) was obtained for a double-surfaced column with an optimized material distribution type compared to that of a square column with a uniform thickness.

Multi-cell design and graded thickness are two efficient strategies for improving the mechanical behaviors of metallic thin-walled tubes. This paper combines these two strategies to present a novel multi-cell structure with a double surface gradient (DSG) and to address the energy absorption characteristics of the new tube subjected to axial compression. A mathematical formulation for the mean load was derived through theoretical analysis of the multi-cell structure's folding mechanism, and two vital parameters were proposed. Afterwards, comprehensive numerical simulations were conducted to validate the formulation and to investigate effects of the DSG on the mechanical properties. The results demonstrated that the combination of the DSG strategy and the multi-cell structure led to a greater energy absorption capacity. Finally, the key factor of the DSG design in promoting the energy absorption efficiency was analyzed. To achieve a higher promotion, an approach of rationalizing the sectional material distribution of the DSG tube was attempted and proven valid. All these achievements shed a light on the multi-cell and graded thickness effects on mechanical properties.

In this paper, energy-absorbing structures at the front end of the subway trains are studied through size optimization and topology optimization. To maximize the energy absorption and minimize peak impact force, the size optimization is conducted by optimization software iSIGHT and collision simulation software PAM-CRASH. Moreover, the topology optimization of energy-absorbing device is obtained by software OptiStruct. The results indicate that combining the two aforementioned optimization techniques is capable to improve the crashworthiness of the energy-absorbing structures and the passive safety of the subway train.