Crashworthiness Design and Multi-Objective Optimization of Bionic Thin-Walled Hybrid Tube Structures

Thin-walled structures are widely used in cars due to their lightweight construction and energy-absorbing properties.However,issues such as high initial stress and lowenergy-absorbing efficiency arise.This study proposes a novel energy-absorbing structure inwhich a straight tube is combinedwith a conical tube and a bamboo-inspired bulkhead structure is introduced.This configuration allows the conical tube to flip outward first and then fold together with the straight tube.This deformation mode absorbs more energy and less peak force than the conical tube sinking and flipping inward.Through finite element numerical simulation,the specific energy absorption capacity of the structure is increased by 26%compared to that of a regular circular cross-section tube.Finally,the impact resistance of the bionic straight tapered tube structure is further improved through multi-objective optimization,promoting the engineering application and lightweight design of hybrid cross-section tubes.

奇异鞍点问题的NESS迭代法半收敛性分析

最近一些学者对于非奇异鞍点问题提出了一种新的外推移位分裂(NESS)预处理,并研究了NESS迭代方法的收敛性以及NESS预处理矩阵的谱分布。本研究进一步将NESS迭代方法用于求解奇异的鞍点问题,给出NESS迭代法在(1,1)块子矩阵是对称正定情况下的半收敛性分析。最后通过数值实验,验证了在适当参数下NESS迭代法求解奇异鞍点问题的可行性和有效性。

Static strength and crashworthiness analysis of a train cowcatcher at a running speed of 160 km/h

The cowcatcher is one of the unique devices at the front end of the train, which can remove obstacles on the track by crashing before the vehicle body to ensure the safety of the train. When a collision accident happens, the cowcatcher serves as the first energy-absorbing structure to dissipate and guide the collision energy. The design of the existing cowcatcher of multiple units generally focuses on the good ability to remove obstacles, while the secondary function, the crashworthiness of orderly deformation under collision, still needs further research. In this study, a finite element model of structural static load and collision analysis was established under standard EN 15227, with the cowcatcher for 160 km/h train as the prototype. Then the solution and simulation process was accomplished under the environment of ANSYS and LS-DYNA. The analysis results showed that the structural static strength of the current cowcatcher met the requirements of the standard EN 15227, and the longitudinal stiffness was evenly distributed. When removing the obstacles with low mass, the impact force was small and the structure would not produce obvious deformation;when removing the obstacles with large mass, the impact force was large and the shear fracture might occur at the connection of the cowcatcher.

Simulation and Analysis of Crashworthiness of Fuel Tank for Helicopters

Crashworthiness requirement of fuel tanks is one of the important requirements in helicopter designs. The relations among the protection frame, textile layer and rubber layer of the fuel tank are introduced. Two appropriate FE models are established, one is for an uncovered helicopter fuel tank without protection frame, and the other is for fuel tank with protection frame. The dynamic responses of the two types of fuel tanks impinging on the ground with velocities of 17.3 m/s are numerically simulated for the purpose of analyzing energy-absorbing capabilities of the textile layer and protection frame. The feasibility of the current crashworthiness design of the fuel tank is examined though comparing the dynamic response behaviors of the two fuel tanks.

Crashworthiness design of density-graded cellular metals

Crashworthiness of cellular metals with a linear density gradient was analyzed by using cell-based finite element models and shock models. Mechanisms of energy absorption and deformation of graded cellular metals were explored by shock wave propagation analysis. Results show that a positive density gradient is a good choice for protecting the impacting object because it can meet the crashworthiness requirements of high energy absorption, stable impact resistance and low peak stress.

Crashworthiness Analysis on Alternative Square Honeycomb Structure under Axial Loading

Hexagonal metal honeycomb is widely used in energy absorption field for its special construction. However, many other metal honeycomb structures also show good energy absorption characteristics. Currently, most of the researches focus on hexagonal honeycomb, while few are performed into different honeycomb structures. Therefore, a new alternative square honeycomb is developed to expand the non-hexagonal metal honeycomb applications in the energy absorption fields with the aim of designing low mass and low volume energy absorbers. The finite element model of alternative square honeycomb is built to analyze its specific energy absorption property. As the diversity of honeycomb structure, the parameterized metal honeycomb finite element analysis program is conducted based on PCL language. That program can automatically create finite element model. Numerical results show that with the same foil thickness and cell length of metal honeycomb, the alternative square has better specific energy absorption than hexagonal honeycomb. Using response surface method, the mathematical formulas of honeycomb crashworthiness properties are obtained and optimization is done to get the maximum specific energy absorption property honeycomb. Optimal results demonstrate that to absorb same energy, alternative square honeycomb can save 10% volume of buffer structure than hexagonal honeycomb can do. This research is significant in providing technical support in the extended application of different honeycomb used as crashworthiness structures, and is absolutely essential in low volume and low mass energy absorber design.

Design optimization of the S-frame to improve crashworthiness

In this paper, the S-frames, the front side rail structures of automobile, were investigated for crashworthihess. Various cross-sections including regular polygon, nonconvex polygon and multi-cell with inner stiffener sections were investigated in terms of energy absorption of S-frames. It was determined through extensive numerical simulation that a multi-celI S-frame with double vertical internal stiffeners can absorb more energy than the other configurations. Shape optimization was also carried out to improve energy absorption of the S-frame with a rectangular section. The center composite design of experiment and the sequential response surface method （SRSM） were adopted to construct the approximate design sub-problem, which was then solved by the feasible direction method. An innovative double S- frame was obtained from the optimal result. The optimum configuration of the S-frame was crushed numerically and more plastic hinges as well as shear zones were observed during the crush process. The energy absorption efficiency of the structure with the optimal configuration was improved compared to the initial configuration.

Crashworthiness assessment of thin-walled double bottom tanker: A variety of ship grounding incidents

This study addresses the issue of ship accidental grounding as an impact phenomenon,with the assumption that an interaction of its structure with the oceanic seabed(obstruction),idealized as rock topology,is capable of initiating a so-called hard ground scenario.This occurrence variation was considered by performing two main instances,encompassing raking and stranding,often experienced by oil/chemical tankers as thin-walled structures.In addition,a failure criterion was implemented on the structural geometry,in order to define its ultimate limit and possible damage,during interaction with the obstructions.Subsequently,the analysis results were compiled to assess structural crashworthiness as well as progressive failure of the double bottom part of the tanker,where energy criterion indicated the raking to be more destructive.Meanwhile,detailed observation of the failure sequence indicated the stranding to have successfully breached the inner bottom shell.

Crashworthiness of innovative hexagonal honeycomb-like structures subjected to out-of-plane compression

Seeking for innovative structures with higher mechanical performance is a continuous target in railway vehicle crashworthiness design.In the present study,three types of hexagonal reinforced honeycomb-like structures were developed and analyzed subjected to out-of-plane compression,namely triangular honeycomb(TH),double honeycomb(DH)and full inside honeycomb(FH).Theoretical formulas of average force and specific energy absorption(SEA)were constructed based on the energy minimization principle.To validate,corresponding numerical simulations were carried out by explicit finite element method.Good agreement has been observed between them.The results show that all these honeycomb-like structures maintain the same collapsed stages as conventional honeycomb;cell reinforcement can significantly promote the performance,both in the average force and SEA;full inside honeycomb performs better than the general,triangular and double schemes in average force;meanwhile,its SEA is close to that of double scheme;toroidal surface can dissipate higher plastic energy,so more toroidal surfaces should be considered in design of thin-walled structure.These achievements pave a way for designing high-performance cellular energy absorption devices.

Crashworthiness Design and Multi-Objective Optimization for Bio-Inspired Hierarchical Thin-Walled Structures

Thin-walled structures have been used in many fields due to their superior mechanical properties.In this paper,two types of hierarchical multi-cell tubes,inspired by the self-similarity of Pinus sylvestris,are proposed to enhance structural energy absorption performance.The finite element models of the hierarchical structures are established to validate the crashworthiness performance under axial dynamic load.The theoreticalmodel of themean crushing force is also derived based on the simplified super folded element theory.The finite element results demonstrate that the energy absorption characteristics and deformation mode of the bionic hierarchical thin-walled tubes are further improved with the increase of hierarchical sub-structures.It can be also obtained that the energy absorption performance of corner self-similar tubes is better than edge self-similar tubes.Furthermore,multiobjective optimization of the hierarchical tubes is constructed by employing the response surface method and genetic algorithm,and the corresponding Pareto front diagram is obtained.This research provides a new idea for the crashworthiness design of thin-walled structures.

Optimizing crashworthiness design of square honeycomb structure

To provide theoretical basis for square honeycombs used as crashworthy structures, energy-absorption properties of metal square honeycombs and the size optimization were performed. Specific energy absorption(SEA) was defined as the energy absorbed by the honeycomb structure per unit volume. This parameter was often used for determining the crashworthiness of thin-walled structures. In order to find the most optimized metal square honeycomb structure with the maximum SEA and the lowest peak stress, the cell length and the foil thickness of the metal honeycombs were optimized, with a low peak stress and a high SEA set as the two primary objectives. The pre-processing software Patran was used to build FE models, and the explicit solver LS-DYNA was employed to perform the crashworthiness analyses. The results show that the square honeycomb exhibits good energy absorption performance in some cases. The geometry is effective using 16.8% less buffer structure volume than the hexagonal honeycombs with a peak stress limitation of 1.21 MPa.

Impact of Crash Environments on Crashworthiness of Fuselage Section

In order to study the crash resistance of the civil aircraft structure in different crash environments,two environmental models of soft soil and water are established to analyze the dynamic response of the fuselage section subjected to the vertical at the impact velocity of 7 m/s.Simulation results show that the soft crash environment can have a certain cushioning effect on the structure crash,but it will prolong the crash time and change the energy absorption mode.This work suggests that soft environment may not be suitable for forced landing.

Vehicle Crashworthiness Simulation Based on Virtual Design of Auto-body

Vehicle crashworthiness simulation is the main component of the virtual auto-body design. One developing commercial vehicle was simulated on crashworthiness by the non-linear finite element method. The bumper crashworthiness at the speed of 8 km/h was analyzed and valuated. On the other hand, the deformation of the auto-body, the movement of the steering wheel and the dynamic responses of the occupant at the initial velocity of 50 km/h were studied. The results appear that the design of the vehicle could be improved on structure and material. Finally, the frontal longitudinal beam, the main energy-absorbing part of the auto-body, was optimized on structure. Simulation results also show that applying new material, such as high strength steel, and new manufacture techniques, such as tailor-welded blanks could improve the crashworthiness of the vehicle greatly.

Crashworthiness design and experimental validation of a novel collision post structure for subway cab cars

This paper proposes a novel collision post structure designed to improve the crashworthiness of subway cab cars.The structure provides two innovative features:1)a simpler connection between the post and the car roof,which gives a more reasonable load transfer path to reduce the stress concentration at the joint;and 2)a stiffness induction design that provides an ideal deformation model to protect the safe space of the cab cars.The novel collision post structure was evaluated with finite element analysis,and a prototype cab car was mechanically tested.The results demonstrate that the deformation response was stable and agreed well with the expected ideal mode.The maximum load was 874.17 kN and the responses remained well above the elastic design load of 334 kN as required by the design specification.In addition,there was no significant tearing failure during the whole test process.Therefore,the novel collision post structure proposed has met the requirements specified in new standard to improve the crashworthiness of subway cab cars.Finally,the energy absorption efficiency and light weight design highlights were also summarized and discussed.

Effect of stiffeners on crashworthiness of square aluminium columns considering damage evolution

Combining the optimization and FEM technology,crashworthiness of aluminum extrusions was studied for an automobile safety plan.The effects of longitudinal stiffeners on the crushing of stiffened square columns were studied considering the damage evolution.The numerical analysis was carried out by ABAQUS software.Subsequently,the collapse behavior of aluminum extrusion damage was validated by comparing against solution published in literature.Finally,in order to find more efficient and lighter crush absorber and achieving minimum peak crushing force,response surface methodology(RSM) has been applied for optimizing the aluminum extrusion tube.

Crashworthiness of extruded magnesium thin-walled square tubes

Axial compression tests were conducted on AZ31 B magnesium and A6063 aluminum thin-walled square tubes with varied lengths and induced features at different compression rates. In compression, the magnesium tubes exhibited a "local buckling and fracture" mode, with three fracture patterns, i.e."horizontal","double-oblique", and "spiral" fractures. In general, the magnesium tube showed an inferior crashworthiness to the aluminum square tube. In addition, the effects of L/W ratio, strain rate and induced features on the crashworthiness of thin-walled square tubes were investigated. With an increase in the L/W ratio(L and W represent the tube length and width, respectively) from 1 to 4, the maximal force and global specific energy absorption decreased in a power-law trend for the magnesium tubes,while they remained approximately constant for the aluminum tubes. Furthermore, as the compression rate increased from 5×10-5 to 10 m/s, the primary crashworthiness parameters of the magnesium tubes increased in an approximately exponential manner,while for the aluminum tubes,they changed slightly. Finally,the involved induced features were proven to be not an effective method to improve the specific energy absorption of magnesium tubes, thus, more trigger types,locations,and sizes will be evaluated in future to improve the energy-absorption ability.

Crashworthiness of double-cell conical tubes with different cross sections subjected to dynamic axial and oblique loads

Thin-walled tubes are increasingly used in automobile industries to improve structural safety.The present work deals with the collapse behavior of double-cell conical tubes subjected to dynamic axial and oblique loads.Crashworthiness of these tubes having different sections(e.g.,circular,square,hexagonal,octagonal,decagonal)was numerically investigated by using an experimentally validated finite element model generated in LS-DYNA.Geometry of these tubes was then optimized by decreasing the cross section dimensions at the distal end while the weight remained unchanged.Octagonal conical tube was finally found to be more preferable to the others as a collision energy absorber.In addition,square and circular tubes showed diamond deformation mode,while the other tubes collapsed in concertina mode.A decision making method called TOPSIS was finally implemented on the numerical results to select the most efficient energy absorber.

Crashworthiness optimization design of foam-filled tapered decagonal structures subjected to axial and oblique impacts

In this research,crashworthiness of polyurethane foam-filled tapered decagonal structures with different ratios of a/b=0,0.25,0.5,0.75 and 1 was evaluated under axial and oblique impacts.These new designed structures contained inner and outer tapered tubes,and four stiffening plates connected them together.The parameter a/b corresponds to the inner tube side length to the outer tube one.In addition,the space between the inner and outer tubes was filled with polyurethane foam.After validating the finite element model generated in LS-DYNA using the results of experimental tests,crashworthiness indicators of SEA(specific energy absorption)and Fmax(peak crushing force)were obtained for the studied structures.Based on the TOPSIS calculations,the semi-foam filled decagonal structure with the ratio of a/b=0.5 demonstrated the best crashworthiness capability among the studied ratios of a/b.Finally,optimum thicknesses(t1(thickness of the outer tube),t2(thickness of the inner tube),t3(thickness of the stiffening plates))of the selected decagonal structure were obtained by adopting RBF(radial basis function)neural network and genetic algorithm.

Contrastive analysis and crashworthiness optimization of two composite thin-walled structures

For the safety protection of passengers when train crashes occur, special structures are crucially needed as a kind of indispensable energy absorbing device. With the help of the structures, crash kinetic-energy can be completely absorbed or dissipated for the aim of safety. Two composite structures(circumscribed circle structure and inscribed circle structure) were constructed. In addition, comparison and optimization of the crashworthy characteristic of the two structures were carried out based on the method of explicit finite element analysis(FEA) and Kriging surrogate model. According to the result of Kriging surrogate model, conclusions can be safely drawn that the specific energy absorption(SEA) and ratio of specific energy absorption to initial peak force(REAF) of circumscribed circle structure are lager than those of inscribed circle structure under the same design parameters. In other words, circumscribed circle structure has better performances with higher energy-absorbing ability and lower initial peak force. Besides, error analysis was adopted and the result of which indicates that the Kriging surrogate model has high nonlinear fitting precision. What is more, the SEA and REAF optimum values of the two structures have been obtained through analysis, and the crushing results have been illustrated when the two structures reach optimum SEA and REAF.

Laminate Tailoring of Composite Tubular Structures to Improve Crashworthiness Design at Off-Axis Loading

This paper presents experimental and numerical investigation on the parameters effecting energy absorption capability of composite tubular structures at oblique loading to improve crashworthiness performance. Various inclined angles of 5°, 10°, 20° and 30° were selected for the study of off-axis loading. The results indicate that by increasing the lateral inclination angle the mean crushing force and also energy absorption capability of all tested sections decreased. From design perspective, it is necessary to investigate the parameters effecting this phenomenon. The off-axis loading effect that causes significant reduction in energy absorption was investigated and the effected parameters were improved to increase energy absorption capability. To establish this study, 10° off-axis loading was chosen to illustrate the obtained improvement in energy absorption capability. Five cases were studied with combinations of ply-orientation and flat trimming with 45° chamfer. This method was applied to the integrated 10° off-axis loading and the final results showed significant improvement in energy absorption capability of composite absorbers. Finite element model (FEM) was developed to simulate the crushing process of axial and off-axis composite section in LS-DYNA and the results were in good agreement with the experimental data.