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A novel structure resembling plant stems, termed bio-inspired fractal plant stems multi-cellular circular tubes (BFPMC), was developed by incorporating fractal plant stem characteristics into smaller circular tubes within larger ones. The crashworthiness of this structure under axial impact was investigated using a validated LS-DYNA finite element model. The energy absorption performance of BFPMC tubes, varying in the number of branches, fractal orders, and inner circular diameters, was numerically studied. The numerical findings reveal a 19.27% increase in specific energy absorption (SEA) for BFPMC with $D_i=30$mm compared to $D_i=0$mm, indicating that filling a single circular tube can enhance the structure’s impact resistance. Subsequently, structural parameters conducive to excellent energy absorption characteristics were determined for various combinations of a number of branches, fractal order, and inner circle diameter parameters. These results offer valuable insights for designing multi-cellular double tubes with high energy absorption efficiency.

To enhance the crashworthiness of thin-walled structures, this study proposes a self-similar nested hierarchical hexagonal tube. This innovative design incorporates the hierarchical technique into the structural configuration of hexagonal thin-walled tubes. Numerical analysis, conducted using a validated finite element model, reveals that the proposed self-similar nested hierarchical hexagonal tube (SNHHT) significantly enhances energy absorption compared to traditional hexagonal tubes, maintaining consistent wall thickness and mass conditions. Particularly noteworthy is the improvement in energy absorption indexes under the same mass condition, with SNHHT-4 demonstrating enhancements of up to 76.45% and 86.84% in energy absorption and crushing force efficiency, respectively, while concurrently achieving a 4.11% reduction in initial peak crash force. Subsequently, a parametric study exploring wall thickness, shape factor, and various rib thicknesses was performed to investigate structural crashworthiness. Finally, employing the simplified super-folded element method, the theoretical formulation of mean crushing force was derived, and its accuracy was validated through numerical simulations.

Single-cell arched beams show excellent energy absorption performances under transverse loads. However, the fabrication of arched beams with a perfect arc segment is relatively tricky and expensive by casting or additive manufacturing technology. In this paper, a simple three-point bending method is proposed for the fabrication of single- or multi-cell arched beams. Although indentation or concave is formed in the central region of arched beams during fabrication, the beams show even better energy absorption performances than the perfect arched beams. Static and dynamic three-point bending tests of the fabricated arched beams are first carried out, and numerical simulations of the fabrication process and the subsequent bending collapse are then performed. The influences of the fabrication factors on the performances of the arched beams are investigated. Arched beams with tube fillers and multi-cell sections can be easily fabricated by the proposed method, and the crashworthiness performances of these fabricated arched beams are significantly improved. In addition, the multi-cell arched beams fabricated by the present method exhibit excellent performances and outperform the arched beams with a perfect arc segment.

Crashworthiness research has attracted significant attention, focusing on evaluating deformation behavior and selecting composite material components that act as energy-absorbing devices. Among the available composite materials, carbon fibers can absorb high energy during a crash. This paper presents the initial concept of the design application of a carbon fiber Belleville spring. The proposed design of the mechanism is directed to reduce the extent of the impact. An analytical approach is followed to calculate the energy absorbed during a crash. The parametric study is conducted for a different range of load $22250\le F\le 27000$N to predict which spring material absorbs maximum energy. The impact on the occupant side is minimum by the finite element approach. A brief overview of the spring’s energy absorption capability is provided through Ansys, and a correlation is proposed, which helps predict the value of Energy for different loads.

In this paper, a virtual testing model (VTM) for the Korean high speed train (KHST) is developed to meet several design purposes, and an improved collision safety assessment method is also suggested. Although twisting, buckling, zigzagging, chain reactions, overriding and derailment have long been recognized as the important elements that can affect the safety of passengers in the event of a collision, the means by which such behaviors can be predicted have been restricted. To address this, a VTM, supported by the technological advancements of numerical analysis software and high-performance computers, was developed to simulate and evaluate such behaviors. The VTM for KHST was modeled using finite elements, in order to obtain such collision behaviors. In addition, the VTM was simulated in a variety of accident scenarios, and the results were analyzed and compared with the results obtained using other modeling techniques. Since factors such as the deformation of individual members, serial collisions and twisting of the train body were incorporated into the VTM, this simulation provides more practical collision responses than other modeling techniques. This shows that it can predict more nonlinear collision behaviors, giving it a wider range of applications.

In this paper, the strain rate effect of energy absorption members in rolling stock is studied using the virtual testing model (VTM) for Korean high speed train (KHST). The VTM of KHST was simulated for two different strain rate conditions. The VTM is composed of FE models for structures, and nonlinear spring/damper models for dynamic components. To simplify numerical model for the full rake KHST, the first three units consist of full flexible multi-body dynamic models, and the remainder does 1-D spring/damper/mass models. To evaluate the strain rate effect of KHST, the crash simulation was performed under the accident scenario for a collision with a rigid mass of 15 tons at 110kph. The numerical results show that the overall crash response of the train is not largely affected as much as expected, but individual components have some different deformations according to strain rate. The deformation of the front end structure without strain rate effect is larger than that with it. However, the deformation of the rear end structure without strain rate effect is smaller than that with it. Finally, the intrusion of the driver's cabin is overestimated for no strain rate effect when compared to the case with it.

A study about the response of motorcycle helmets to impacts is described in this paper and possible ways to improve current designs are discussed. Firstly, a simple unidimensional model of helmet is analyzed and the main parameters that affect its response are pointed out. Subsequently, the generation and testing of the Finite Element model of a commercially available helmet are described and numerical results are compared to experimental results. Finally, the FE modeled is used to compare different design configurations.

This paper deals with the crashworthiness of an aluminum crash box for an auto-body with the various shapes of cross section such as a rectangle, a hexagon and an octagon. First, crash boxes with various cross sections were tested with numerical simulation to obtain the energy absorption capacity and the mean load. In case of the simple axial crush, the octagon shape shows higher mean load and energy absorption than the other two shapes. Secondly, the crash boxes were assembled to a simplified auto-body model for the overall crashworthiness. The model consists of a bumper, crash boxes, front side members and a sub-frame representing the behavior of a full car at the low speed impact. The analysis result shows that the rectangular cross section shows the best performance as a crash box which deforms prior to the front side member. The hexagonal and octagonal cross sections undergo torsion and local buckling as the width of cross section decreases while the rectangular cross section does not. The simulation result of the rectangular crash box was verified with the experimental result. The simulation result shows close tendency in the deformed shape and the load–displacement curve to the experimental result.

This paper deals with a regression model for light weight and crashworthiness enhancement design of automotive parts in frontal car crash. The ULSAB-AVC model is employed for the crash analysis and effective parts are selected based on the amount of energy absorption during the crash behavior. Finite element analyses are carried out for designated design cases in order to investigate the crashworthiness and weight according to the material and thickness of main energy absorption parts. Based on simulations results, a regression analysis is performed to construct a regression model utilized for light weight and crashworthiness enhancement design of automotive parts. An example for weight reduction of main energy absorption parts demonstrates the validity of a regression model constructed.

This paper introduces the jig set for the crash test and the crash test results of shear bolts which are designed to fail at train crash conditions. The tension and shear bolts are attached to Light Collision Safety Devices(LCSD) as a mechanical fuse when tension and shear bolts reach their failure load designed. The kinetic energy due to the crash is absorbed by the secondary energy absorbing device after LCSD are detached from the main body by the fracture of shear bolts. A single shear bolt was designed to fail at the load of 250 kN. The jig set designed to convert a compressive loading to a shear loading was installed to the high speed crash tester for dynamic shear tests. Two strain gauges were attached at the parallel section of the jig set to measure the load responses acting on the shear bolts. Crash tests were performed with a carrier whose mass was 250 kg and the initial speed of the carrier was 9 m/sec. From the quasi-static and dynamic experiments as well as the numerical analysis, the capacity of the shear bolts were accurately predicted for the crashworthiness design.

In this paper, we fabricate human DNA and polar bear inspired thin-walled tube that tends to reduce the strength of decelerating force during impact, while escalating the amount of energy absorbed. The crashworthiness performance under axial impact is investigated using experimental analysis and non-linear finite element analysis (FEA). The investigation is conducted in three phases; the first phase consists of the design and fabrication of a novel bio-inspired tube (BIT) motivated by the most stable human DNA. Twelve BITs are created by filling cylindrical tubes into different positions of the BIT, which was inspired by the microstructural of polar bear hair. The second phase comprises the nonlinear FEA of energy-absorbed ability for different BITs under axial impact loading using LS-DYNA software, and then validated by the Simplified Super Folding Element (SSFE) theorem. In the third phase, Radial Basis Function (RBF) meta-models and Non-dominated Sorting Genetic Algorithm II (NSGA-II) are used for the multi-objective optimization design of BIT-11. The numerical simulation results are compared with the experimental results to confirm the crash behavior and energy absorption (EA) characteristics of the optimal structure over a base one. Based on the results, the suited configuration with required performance in crashworthiness is suggested, which should be incorporated into automobiles for safety consideration of passengers during an impact. The results show an increment of 49% in Specific Energy Absorption (SEA), suggesting the better choice of a particular tube over the base tube.

For a honeycomb structure used for absorbing crash energy and protecting the safety of human or instruments, the bigger the specific energy absorption (SEA) is, the more popular it would be when the peak crushing stress (σ_p) was retained small enough. In order to improve the energy absorption capacity, crashworthiness optimization for honeycomb structures with various cell specifications are studied in this paper. Detailed numerical models are established for those honeycomb structures by using an explicit finite element method code LS-DYNA. The numerical simulation results are then used as the design samples for constructing metamodels. The optimal Latin hypercube design (OLHD) method is employed for the selection of sampling design points in the design space, and the polynomial functions, radial basis functions (RBF), Kriging, multivariate adaptive regression splines (MARS), and support vector regression (SVR) are utilized to formulate the two optimal objectives SEA and σ_p. It is found that the polynomial function is the most efficient in constructing the crashworthiness metamodels of honeycombs among the above-mentioned methods. Then, the polynomial function models of SEA and σ_p are chosen as the surrogate models in the crashworthiness optimization. In order to further validate the polynomial function models, the polynomial function models of SEA and σ_p are compared with the analytical solutions based on Wierzbicki's theory and Kunimoto and Yamada's theory, respectively. An excellent correlation has been established. As such, the multi-objective particle swarm optimization algorithm (MOPSOA) is applied to obtain the Pareto front of SEA with σ_p of the honeycomb structures with various cell specifications, which has resulted in a range of optimal designs of honeycomb structures by the multi-objective optimization.

Cross-sectional shapes and dimensions of concrete guardrails directly influence climbing angles and directions of a car when a collision between concrete guardrail and car occurs. At the same time, contacting and climbing angles and directions influence the peak crushing force and the peak acceleration of a car body during a collision. Therefore, cross-sectional shapes and dimensions of concrete guardrails can influence the severity of injuries sustained when a collision between concrete guardrail and car occurs. In this study, the passive safety of a car body is considered in optimizing the cross-sectional dimensions of a New Jersey (NJ) concrete guardrail based on numerical simulations and surrogate model techniques. Optimal Latin hypercube design is used to get sampling points, and multi-island genetic algorithm is utilized to obtain the optimal size of NJ concrete guardrail in the optimization process. After simulating the collision between car and optimal NJ shaped guardrail, the results show that the peak acceleration of optimal results reduces significantly by 28% compared with the initial value, and the peak interface force decreases from 378.6 kN to 241.5 kN.

Foam-filled thin-walled structure has been widely used in vehicle engineering due to its highly efficient energy absorption capacity and lightweight. Unlike the existing foam-filled thin-walled structures, a new foam-filled structure, i.e., functionally graded foam-filled graded-thickness tube (FGFGT), which had graded foam density along the transverse direction and graded wall thickness along the longitudinal direction, was first studied in this paper. Two FGFGTs with different gradient distributions subjected to lateral impact were investigated using nonlinear finite element code through LS-DYNA. According to the parametric sensitivity analysis, we found that the two design parameters $n_1$ and $n_2$, which controlled the gradient distributions of the foam density and the tube wall thickness, significantly affected the crashworthiness of the two FGFGTs. In order to seek for the optimal design parameters, two FGFGTs were both optimized using a meta-model-based multi-objective optimization method which employed the Kriging modeling technique as well as the nondominated sorting genetic algorithm II. In the optimization process, we aimed to improve the specific energy absorption and to reduce the peak crushing force simultaneously. The optimization results showed that the FGFGT had even better crashworthiness than the traditional uniform foam-filled tube with the same weight. Moreover, the graded wall thickness and graded foam density can make the design of the FGFGT flexible. Due to these advantages, the FGFGT was an excellent energy absorber and had potential use as the side impact absorber in vehicle body.

Thin-walled structures are used in automotive industry due to their excellent lightweight and crashworthiness properties. This paper proposes a vertex fractal multi-cell hexagonal structure to develop a novel lightweight energy absorber. Experimental analysis and numerical modeling are performed to investigate the crashworthiness of the fractal multi-cell hexagonal structures. The numerical results indicate that fractal configurations and geometrical parameters of the fractal hexagonal structure have significant effect on the crashworthiness. In addition, the multi-objective design optimization is performed to seek the optimal crashworthiness parameters and explore the optimal crashworthiness of the fractal hexagonal structure. The results show that the fractal multi-cell hexagonal structure outperforms non-fractal hexagonal structure.

In this paper, a new interval multi-objective optimization (MOO) method integrating with the multidimensional parallelepiped (MP) interval model has been proposed to handle the uncertain problems with dependent interval variables. The MP interval model is integrated to depict the uncertain domain of the problem, where the uncertainties are described by marginal intervals and the degree of the dependencies among the interval variables is described by correlation coefficients. Then an efficient multi-objective iterative algorithm combining the micro multi-objective genetic algorithm (MOGA) with an approximate optimization method is formulated. Three numerical examples are presented to demonstrate the efficiency of the proposed approach.

Since lightweight and energy-absorbing materials have an effective role in occupant safety during accidents, the use of hybrid aluminum–composite tubes and their optimum designs are of great importance in the crashworthiness. In this study, finite element simulation and multi-objective optimization of a hybrid aluminum–composite tube are performed under axial crushing to investigate the effect of metal volume fraction (MVF) on the objective functions, the specific energy absorption and the peak force. Besides, the effects of annealing and tempering of ductile aluminum alloys (Al-6061) as the base metal of hybrid tubes are investigated. The optimum values of the objective functions are obtained at $\mathrm{\text{MVF}}\cong 0.5$ (the same thickness of aluminum and composite). Also, annealing of ductile aluminum alloys has a negative effect on the objective functions. As a guideline for the design of fiber metal laminates under crushing, it is suggested to use tempered Al-6061 and increase the thickness of composite material so that $\mathrm{\text{MVF}}<0.5$.

A study is made to investigate the compression behavior of different nested tube systems made of mild steel under lateral compression. The nested tube systems including stacked groups of circular, rectangular and square tubes are built for application in narrow compressive zones. The deformation mode of these systems is observed and their lateral compression behavior are identified. The desirable stepwise energy absorption is obtained by designing the nested tube system. The load response revealed that there is no appearance of the peak compressive load in the case of a circular-circular tube (CCT) system, while a circular-rectangular tube (CRT) system offers bigger peak compressive load compared with that of a circular-square tube (CST). The energy absorptions of CCT and CRT systems are smallest and greatest, respectively. This study also estimates the energy absorption capacity of these system. By implementing the “plastic hinge line” concept of the modified simplified super folding element (MSSFE) theory and superposition principle, the analytical models predicting compressive load of the nested tube systems are introduced. The analytical investigations are compared with the data obtained from tests on these systems. Excellent correlation is observed between the theoretical and experimental data.

In this paper, the energy absorption behavior of a novel multibody circular tube is investigated based on the experimental and numerical methods. To achieve the best design for the segments, the bell-end circular tubes, a multi-objective optimization technique was implemented using Python and MATLAB with four various objective functions such as absorbed energy, mass, peak crush force, and average crush force. Moreover, an arrangement of these bell-end tubes as a multibody structure would decrease the total length, obtain less capacity usage, and have better crashworthiness characteristics. The results elucidate an enormous decrease in the peak crush force and an increase in specific absorbed energy in comparison with the thin-walled circular tubes having the same mass. Finally, the energy absorption behavior of the optimal multibody circular tube was tested and compared to the obtained numerical results in single and double forms.

A thin-walled tube with a predesigned spiral structure, named as the sinusoidal spiral tube (SST), was proposed to improve the energy absorption performance of the traditional circular straight tube and sinusoidal corrugation tube (SCT). A prototype of the SST was fabricated through additive manufacturing and its mechanical properties were tested. The numerical results were consistent with the tests. The effect of geometric features involving amplitude and pitch on energy absorption has been investigated through a series of numerical simulations. The results showed that there are six representative deformation modes and these modes transformed clearly under the action of amplitude and number of turns. On the other hand, the initial peak force was significantly reduced by 53.57–85.34% compared to the straight tube. The stability of plateau force was greatly improved by the spiral structure. The specific energy absorption increased by more than 15% compared to the SCTs under pinned–pinned and fixed–fixed boundary conditions, attributed to the transformation of the deformation mode and the increased number of folded lobes in the straight part. Last but not least, a theoretical model was proposed to predict the mean crushing force of the novel structure under free–free boundary conditions. It showed a good agreement with the numerical results.