Energy Absorbing Structures Research Articles

Dynamic crushing analysis of a circular honeycomb with leaf vein branched characteristic

For further improving the mechanical properties of the traditional honeycomb structure, a new excellent energy absorption structure named as the leaf vein branched honeycomb (LVBH) is proposed based on lotus leaf vein branched structure. The in-plane dynamic crushing of LVBH is numerically studied by LS-DYNA. Meanwhile, the crushing behavior of the regular circular honeycomb is carried out for comparison. The introduction of leaf vein branched characteristics affects the local deformation zone and the deformation mechanism of LVBHs can be classified into three categories: quasi-static mode, transition mode and dynamic mode. The mode classification map is further given. The comparison indicates that LVBH has better energy absorption performance with 79.94% higher specific energy absorption per unit mass (SEAm) than regular circular honeycomb (RCH). Following that, the influence of microstructure, relative density and crushing velocity on the energy absorbing characteristics of LVBH is systematically studied. The LVBHs with moderate structural parameters exhibit better mechanical properties. The quasi-static plateau stress depends upon the unit-cell configuration. Based on one-dimensional shock theory, the empirical equations of dynamic plateau stress for LVBHs with different relative densities are given by using least-square fitting. Furthermore, the numerical results show that the part of the outer-circle and branch-vein cell walls have higher energy absorption efficiency. The specific energy absorption per unit mass(SEAm)of LVBH can increase by 12.4% through the thickness matching between main-vein and the branch-vein cell walls. The results of this study will be helpful to design a novel honeycomb structure with better energy absorption ability.

Design optimization of a novel bio-inspired 3D porous structure for crashworthiness

Porous structure is widely used in automobile, aerospace and other industrial fields due to its lightweight and high energy absorption capacity. In this study, a novel porous structure, i.e. hierarchical three-dimensional porous (H3DP) structure inspired by the bone in nature is created based on the primitive triply periodic minimal surface sheet structure, which is a basic three-dimensional periodic porous structure consist of triply periodic minimal surfaces. The numerical simulation for the axial crushing of the H3DP structures is carried out using the nonlinear finite element code through LS-DYNA. For accuracy of the numerical results, the finite element model is validated by the experiment performed for H3DP structures which are manufactured by selective laser melting technology using a EOS M290 machine. The numerical results showed that this novel bio-inspired H3DP structure had excellent energy absorption capacity. However, the crashworthiness of the H3DP structure is affected by design parameters such as wall thickness, ribs thickness, number of inner ribs and distance between the inner and outer walls. In order to obtain the optimal design of the H3DP structure with the best crashworthiness, a multi-objective optimization is implemented employing the Kriging (KRG) surrogate modeling method and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). According to the crashworthiness comparison of the H3DP structure and the traditional energy absorbed structures, it is found that the H3DP structure had relatively higher energy absorption capacity than the primitive sheet structure as well as lots of previous traditional materials or structures in nature and engineering. Thus, the H3DP structure can be used as a good energy absorbing structure and had good application prospect in the field of impact engineering.

Study on the crashworthiness of bio-inspired multi-cell tube under axial impact

In recent years, thin-walled energy-absorbing structures have attracted more and more attention due to their excellent structural mechanical properties. In this article, one new kind of multi-cell bionic intersecting thin-walled tube inspired by the structure of the pine cone was designed. In order to fully study the crashworthiness of this new multi-cell tube under axial impact, the effectiveness of the simulation analysis is verified by the verification test of the circular thin-walled tube. Then, the crashworthiness of the circular tube and a series of multi-cell tubes were compared by means of simulation analysis. The simulation results show that the new multi-cell tube can effectively improve the efficiency of energy absorption, specific energy absorption, and crushing force efficiency under the premise of sacrificing part of the peak load. Finally, the response surface method was used to find the optimal design parameters. Response surface model (RSM) was used to represent specific energy absorption (SEA), peak force (PF), crushing force efficiency (CFE), and mass (M). Optimisation results show that the overall impact performance of the three-cell bionic tube under the axial impact load is better than that of the ordinary circular tube and several other multi-cell tubes. Therefore, the three-cell bionic tube can be used as an excellent absorption structure of collision energy under axial impact.

Crashworthiness performance of corrugation- reinforced multicell tubular structures

Improving the crashworthiness performance of thin-walled tubes is of vital significance for vehicle safety because thin-walled tubes are the most common and economical energy absorption structures. To this end, a new structural design method combining multicorrugation and multicell configurations was proposed in this study. Triangular, circular and square corrugation reinforced multicell tubes (CRMTs) were designed with this method. Finite element simulation validated by quasi-static compression experiments was adopted to investigate the crashworthiness performances of the CRMTs. The integrated entropy TOPSIS method was used to select the best of the proposed tubes. The results showed that the circular CRMT with a 3-order cell number (C-C-3) performed the best of the proposed CRMTs. Then, multiobjective optimization incorporating the integrated entropy TOPSIS method was conducted to search for the optimum geometric parameters of C-C-3. After optimization, the SEA increased by 2.39% and the CFE increased by 7.69%. In conclusion, the design combining the multicorrugation and multicell configurations can dramatically improve the crashworthiness of thin-walled tubes; therefore, the proposed structures can be used for energy absorption in the automobile and train industries.

Bio-inspired protective structures for marine applications

Materials and structures for marine applications are often required to combine high mechanical performance with lightness, but traditional solutions are not always adequate to the scope. The application of biomimetic science could provide innovative and efficient solutions, whose research is the aim of the present paper. In the current work, bamboo samples were subjected to impact both on the outside and on the inside surface. It was found that the impact strength is correlated to the third power of thickness and that the softer inside layers may act as an energy absorbing structure, which enhance impact resistance. Impact tests were also performed on specimens whose outside surface had been abraded and on whole cylindrical sections. The role of graded and hierarchical structure in impact response, suggested some guidelines for bio-inspired structures design. Four bamboo-inspired structures were designed, based on the idea of combining corrugated panels with different geometrical characteristics to resemble bamboo graded and hierarchical structure. These structures were made using 3D printing and tested in compression. The best performance was obtained by the structure which more closely replicates bamboo’s hierarchy. Structure performance could be predicted with reasonable accuracy using buckling theory.

Experimental and numerical investigation of out-of-plane crushing behaviour of aluminium honeycomb material

The bio-inspired honeycomb designs due to its efficient distribution of material in space exhibit excellent mechanical properties like high out-of-plane compression and shear strength, good bending stiffness along with low density, leading to high strength to weight ratio which makes it suitable for variety of applications, especially as energy absorption structures in automotive, aerospace, defense and transportation industries. This paper involves studying the crushing behavior of an aluminium honeycomb material under out-of-plane compressive load, using experimental quasi-static testing. Furthermore, a non-linear Finite Element Analysis (FEA) simulation is performed using Altair® Radioss™ 13.0 to predict the deformation characteristics of the specimen during the test. The results obtained using FEA are then compared with the experimentally obtained load deflection curves to validate accuracy of the model. Three models-full scale, half scale and single cell- have been used with appropriate boundary conditions to simulate the crushing process, which have been compared with each other on the basis of accuracy and computational expense.

Phenomenological investigation on crash characteristics of thin layered CFRP-steel laminates

Most energy absorbing structures in automotive applications consist of metals. Those are characterised by high absolute energy absorption (EA) values yet low mass-specific energy absorption (SEA m ). In contrast carbon fibre reinforced polymers (CFRP) reach higher SEA m values. The difference however is not a direct consequence of the density, weight specific stiffness or strength. Instead, the failure progression and hence the energy dissipation characteristics of metallic and CFRP structures are different. Whether a combination of the two material types leads to an increase or decrease of the SEA depends on the crash characteristics of the laminate which supposedly depends on the lay-up. The present paper reports on an experimental investigation on the crash behaviour of omega-shaped fibre-metal laminates (FML) composed of unidirectional CFRP prepreg layers and steel-foils under compressive axial loads. A potential of the tested hybrid laminates is proven by an increase of the mass-specific energy absorption value (SEA m ) of 58%, compared to CFRP.

Improving the Buffer Energy Absorption Characteristics of Movable Lander-Numerical and Experimental Studies.

To improve the soft-landing crash performance of the movable lander (ML), this study presents an investigation of a newly designed gradual energy-absorbing structure subjected to impact loads using an ML for theoretical calculation and numerical simulations. In this work, we present a novel computational approach to optimizing the energy absorption (EA) of the ML. Our framework takes as inputting the geometrical parameter (GP) as well as EA. The finite element model of the HB1, HB2, and HB3 was established and effectively verified using numerical simulation and experimental data. The relationship between the GP of the buffer material and the EA was obtained through static experiment and impact experiment, and the cushioning performance of the lander was optimized according to the ML load mass, contact speed, and EA function. According to the optimization results, we chose an outer diameter of 240 mm, an inner diameter of 50 mm, heights of HB1 = 140 mm, HB2 = 110 mm, and HB3 = 225 as the collocation, and completed the numerical simulation of three different cases. By comparing the results of theoretical calculation and numerical simulation experiments, it can be found that the overload response rates of the main body in 4 type landing, 2-2 type landing, and 1-2-1 type landing are 4.72 G, 2.61 G, and 2.33 G, respectively. It also laid the foundation for the theoretical and methodological research of the ML and manned lander in the future.

Experimental study on the crashworthiness of bio-inspired aluminum foam-filled tubes under axial compression loading

As a lightweight and efficient energy-absorbing structure, thin-walled filled structure is widely used in various fields. This paper proposed four types of bio-inspired foam-filled thin-walled structures based on two typical straw structures (Cornstalk and Reed): bionic foam core with a central hole, 4 square holes, 4 taper holes and 2 nodes, respectively. The energy absorption capacity and deformation mode of bionic structures were studied by dynamic drop hammer and quasi-static compression. The results showed that 9 of 12 bionic samples had higher energy absorption capacity than the corresponding fully-filled samples. Different bionic features have different effects on the deformation of thin-walled tube, and the bionic features with the best overall performance are the 4 Square Holes and 4 Taper Holes design. It is noted that the bionic method can improve energy absorption capacity and affect the deformation mode of the thin-walled tubes under certain conditions.

Crashworthiness performance of green composite energy absorbing structure with embedded sensing device providing cleaner environment for sustainable maintenance

In this study, bio-degradable green composite energy absorbing structure with embedded self–sensing device is proposed as a viable alternative to the conventional synthetic ones without sensing device. The goal of the study is to introduce the promising potentials of integrating a low-cost self sensing device into green composite energy absorbing structure so as to achieve green high performance capabilities. At first, a comparative analysis of the mechanical strength of green composites and their synthetic counterparts is given according to results obtained from previous works. It is shown that by mixing appropriate amount of reinforcing agents with green composites, the mechanical strength is improved significantly and the reinforced green composite material can, therefore, be used to fabricate highly efficient energy absorbers for crashworthiness application. In the latter part of the study, a self–sensing device, made from carbon nanotubes, collects information and tracks the performance of the green energy absorbing structure as well as its extent to environmental friendliness, is proposed. Finally, the synergistic role of the green composite energy absorber with the embedded self–sensing device is presented. The result of the proposed structure promises higher green performance capabilities over their conventional natural and synthetic counterparts without sensing device. It is found that the overall green performance capabilities resulted in increased crashworthiness performance, improved fuel economy, better environmental friendliness, efficient sustainable maintenance and the enhancement of human lives.

Theoretical development and multi-objective optimisation of a double-tapered rectangular tube with diaphragms

A double-tapered rectangular tube with diaphragms (DTRTD) for energy absorbance in railway vehicles is proposed. The mean crushing force (MCF) of DTRTD was derived. The code LS-DYNA3D (971) was used to build a finite element model, validated using a quasi-static test. The experiment results and numerical simulation indicate the accuracy of the theoretical prediction for the MCF of DTRTD and the regularity and stability of the collapse pattern of this energy-absorbing structure (EAS). To explore the effects of the thickness of different EAS parts on the crashworthiness indexes and obtain the optimal designs, the design of experiment (DOE) and a surrogate model were employed for a parameter study and multi-objective optimisation (MOO). The specific energy absorption (SEA) and crush force efficiency (CFE) cannot reach the optimal values concurrently. Nonetheless, all designs from the Pareto front of MOO significantly improve the crashworthiness of EAS because of the larger SEA and CFE.

Study on the crashworthiness of windowed multi-cell square tubes under axial and oblique impact

Abstract The crumpling of aluminium alloy AA6060 T4 thin-walled tubes when subjected to axial and oblique impact is often experienced in collisions. Tubes with holes (so-called windows) and multi-cell tubes are efficient in terms of the structure's energy absorption. This paper proposes a combination of rectangular windows and multi-cell square tubes to improve the structure's crashworthiness. The advantages of the introduction of windows into the structure can diminish the initial peak collapsing load. This can also improve the crashworthiness performance and the mechanism of a folding formation. However, this introduction causes cracks in the tube and thus reduces the plastic zone area of the fold. The decrease in the plastic zone area and the cracks reduce the tube's energy absorption capacity. The specific energy absorption (SEA) and mean collapsing load (Pmcl) of WMCT-I and WMCT-III under axial impact is higher by about 20% and 16% compared to those of MCT-I and MCT-III, respectively. Relating to MCT-II having a wall-to-corner (WTC) one, the tube with holes does not improve in either case of axial and oblique impact. Extensive theoretical solutions are proposed to predict the mean collapsing loads of the windowed multi-cell tubes. The results of the theoretical predictions are compared to those of the numerical simulation. The Multi-Criteria Decision Making (MCDM) method is applied to select the better structure for the energy absorber application.

The multi-objective structural optimisation design to improve the crashworthiness of a multi-cell structure for high-speed train

This article addresses the energy absorption and crashworthiness optimisation of a multi-cell energy-absorbing structure which is composed of orthohexagonal tubes and connecting column under dynamic impact loading. In this work, a finite element model was established and effectively verified using experimental data. To explore the effects of each structural part length parameters on crashworthiness characteristics such as the specific energy absorption (SEA) and the impacting force efficiency (IFE). The influence of design variables on the impact response is evaluated based on the parametric study of surrogate model. The results show that side lengths at different locations have different effects on SEA and IFE. The characteristics and trends of different variables are different. In addition, based on the surrogate models, to maximise the SEA and IFE under the constraint of design space, multi-objective optimisation design was carried out using multi-objective genetic algorithm. The optimised structure has significant improvement in SEA, IFE and space.

Crashworthiness of CFRP/aluminum alloy hybrid tubes under quasi-static axial crushing

Carbon fiber reinforced plastic (CFRP)/aluminum alloy hybrid tubes is a lightweight and energy absorption structure in the automobile design. In this paper, simulations and tests are conducted to study the crashworthiness of the hybrid tubes under the quasi-static axial crushing. According to the research on the effect of cross section shapes on the crashworthiness, it can be found that the specific energy absorption (SEA) and the crushing force efficiency (CFE) of the circle cross section are the largest. For the CFRP/aluminum alloy hybrid tubes with the circle cross section, the finite element analysis (FEA) model under the quasi-static axial crushing are built, and the specimens for tests are manufactured. The affecting factors on the crashworthiness are studied including the length, the thickness ratio of the aluminum alloy to the CFRP (tm/tc), the layer number, the fiber direction and the proportion of the axial fibers to the circumferential fibers. The load–displacement curves and the crashworthiness indicators of the different affecting factors are obtained, and how the factors affect the crashworthiness are discussed. In addition, the process of the quasi-static axial crushing, the failure modes and the energy absorption mechanisms are analyzed. This study provides a reference for the application of the CFRP/aluminum alloy hybrid tubes in the automobile lightweight and crashworthiness design.

Numerical Prediction on the Crashworthiness of Circular and Square Thin-Walled Tubes with Polymeric Auxetic Foam Core

This present research numerically investigates the energy absorption capability of auxetic foam-filled tubes when loaded statically. Accordingly, numerical simulations were performed to quantify the influence of tubes’ parameters such as wall thickness, diameter and width on the energy absorption responses and deformation modes of auxetic foam-filled circular and square tubes using validated FE models. The results reveal that the progressive collapse and deformation mode of auxetic foam-filled circular tube are pronouncedly affected by varying the tube width, so that the number of lobes created decreases as the tube width increases. Moreover, it was found that the absorbed energy by auxetic foam-filled square tube shows more dependence on the tube wall thickness variations than on the tube width. Nonetheless, increasing the width of filled tube makes the structure heavier without considerably affecting the absorbed energy, which is undesirable in design of energy absorbing structures. The primary outcome of this research is a design guideline for the use of auxetic foam as a core for an energy absorber device where impact loading is expected.

Study on Crush Tube Geometric Cross sections and Topology for Axial Crashworthiness

Crush tubes are used as crash impact energy absorbing structure (EAS) and are located in the frontal compartment of road vehicles. Ideal crashworthiness of an EAS mandates that the equivalent decelerations due to impact forces should to be ≤ 20g; and crush force and stroke efficiencies should tend to unity. It is understood from the literature that no single geometric cross-section shape exhibits a near-ideal crashworthiness; and most EAS members exhibit a high initial peak crush force which is detrimental to the occupant safety, and moderate stroke and crush force efficiencies leading to a compromise in the total energy absorbed. In this paper, finite element analysis (FEA) methodology is formulated and experimentally validated for axial crush of a crush tube of SS304 material with circular cross section. Subsequently, plastic deformation phenomenon and folding patterns in relation to crush force behaviour of crush tubes with various basic cross-sections of polygonal geometric shapes from triangle to octagon and circle are extensively studied through FEA. Further, two new geometric cross-section profiles with combination of basic shapes are proposed to combine the merits of different basic shapes. The crashworthiness of all basic cross-sections including the two proposed cross-section profiles is assessed based on standard parameters. The proposed new geometries may form a basis for the development of new EAS configurations for enhanced crashworthiness.

Recent research development of energy-absorption structure and application for railway vehicles

As the application of energy-absorption structure reaches an unprecedented scale in both academia and industry, a reflection upon the state-of-the-art developments in the crashworthiness design and structural optimization, becomes vital for successfully shaping the future energy-absorption structure. Physical impacting test and numerical simulation are the main methods to study the crashworthiness of railway vehicles at present. The end collision deformation area of the train can generally be divided into two kinds of structural design forms: integral absorbing structure design form and specific energy absorbing structure design form, and different energy-absorption structures introduced in this article can be equipped on different railway vehicles, so as to meet the balance of crashworthiness and economy. In pursuit of improving the capacity of energy dissipation in energy-absorption structures, studies are increasingly investigating multistage energy absorption systems, searching breakthrough when the energy dissipation capacity of the energy-absorption structure reaches its limit. In order to minimize injuries, a self-protective posture for occupants is also studied. Despite the abundance of energy-absorption structure research methods to-date, the problems of analysis and prediction during impact are still scarce, which is constituting one of many key challenges for the future.

Supportless Lattice Structures for Energy Absorption Fabricated by Fused Deposition Modeling.

Additively manufactured cellular structures represent a promising engineering design concept for making customized products where user-specific mechanical properties are required. One of the major challenges in the additive manufacturing (AM) process is removal of unwanted support structures from the lattice. The support structure consumes extra material, printing time, and energy for manufacturing. Postprinting, it needs extensive postprocessing work to remove it from the lattice structure chemically or mechanically. In the case of flexible materials such as thermoplastic polyurethane (TPU), removing the support structure from the lattice is very difficult with the material extrusion process. In this article, a new type of a shell-shaped lattice structure inspired by sea urchin (SU) morphology is designed. This lattice can be additively manufactured by material extrusion processes such as fused deposition modeling (FDM) without requiring any support structures. The mechanical properties of the proposed structure, such as stiffness and energy absorption during loading and unloading, have been evaluated as they are important for cushioning. The compressive results indicate that the stiffness property is almost twice as high compared with the benchmarked, bending-dominated, body-centered cubic (BCC) lattice structure of the same relative density and ethylene vinyl acetate (EVA) foam. Energy absorption is almost equal to the BCC lattice and 20% better than EVA foam. Last, a predictive model on stiffness behavior and energy return was developed to facilitate a systematic way to select optimal densities of the SU lattice structure for energy-absorbing applications. Visual inspection has also revealed that there is no sagging or failure of the lattice, which reduced the manufacturing time and postprocessing time, saving a significant amount of material without compromising on quality. Supportless lattice printing was also validated by printing the specimen with a different FDM printer and TPU filament. A possible application for supportless lattice structures can be for AM of customized shoe midsoles at low cost, ski boots, tires, automotive crush boxes, or any other energy-absorbing structures.

Crashworthy design and energy absorption mechanisms for helicopter structures: A systematic literature review

Helicopters are versatile aircraft that can perform numerous missions such as ground surveillance, rescue missions, air ambulance, fire-fighting etc. However, helicopter crashes sometimes occur owing to technical failures or human errors. Accordingly, the crashworthy design of helicopters has always remained a top priority to prevent catastrophic structural failure and significant casualties. The crashworthy performance of helicopters can be immensely improved with well-designed energy absorption materials or structures. This paper presents a systematic literature review on crashworthy design and energy absorption mechanisms for helicopter structures. Firstly, the historical development of aircraft crashworthiness investigation at various periods over the past few decades is presented. Then, some typical energy absorbing components such as rings, tubes, honeycombs, corrugated structures and emerging energy absorbers are introduced to act as the major structural elements for the crashworthy design of helicopters. After that, an emphasis is placed on the dynamic behavior and energy absorption of typical helicopter structures such as the landing gear, subfloor, full-scale airframe, helicopter crashworthy seats, fuel tank and helicopter blade. In addition, representative helicopter crash scenarios such as bird strike, water impact and the impact response and injury of the occupants are described. Finally, the crashworthy evaluation criteria of helicopter structures are summarized in this paper. This article is intended as a comprehensive literature review of crashworthy design and impact protection of helicopter structures.

Transverse compressive characteristics of fiber reinforced cementitious composites tubes

Abstract Fibre reinforced cementitious composites (FRCC) hollow tube is a kind of promising high-toughness energy absorption structure. As this structure absorbs energy via the transverse deformation of tube, it is necessary to investigate the transverse compressive behavior and failure mode of the FRCC tubes. In this study, the transverse compressive response of cementitious composites tubes reinforced by Polyvinyl alcohol (PVA) fiber and ultra-high molecular weight polyethylene (PE) fibre, respectively, has been experimentally investigated, numerically simulated and dimensionally analyzed. According to the transverse compression tests, the FRCC tubes failed with four-hinge fracture. The FRCC tubes presented ductile fracture while the plain cement-based material (P0) tube presented brittle fracture. The numerical simulation based on extended finite element method (XFEM) has a good agreement with the experimental measurements, and both the crack development at the hinges and stress distribution on the crack section are predicted. The fibre reinforcements remarkably enhanced the mechanical properties of tubes, including the transverse force resistance and deformation capacity. The peak force and maximum energy absorption of FRCC tube is 2 times and 60 times higher than those of P0 tube, respectively. The dimensional analysis suggested that the specific energy absorption per unit volume was principally dominated by the ratio of tube thickness to average radius, whereas the stroke efficiency was governed by the ratio of tube thickness to average radius and the ratio of average radius to tube length. This work provides a guidance for developing FRCC tubes with high specific energy absorption, and is expected to widen the applicability of FRCC tubes in protection engineering.