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Auxetic materials are attracting increasing interest due to their extraordinary or even abnormal mechanical properties. Different from the traditional truss-lattice structures, this paper proposes a series of novel auxetic plate-lattice structures with an excellent auxetic effect. Utilizing a dual-materials glue-free assembly design involving hyperelastic and plastic materials, these plate-lattices exhibit numerous advantages such as disassembly, assembly, replacement, recyclability, reusability, excellent energy absorption, high specific stiffness, and impact resistance performances. Quasi-static/dynamic tests and simulations are conducted to assess mechanical properties, including elastic constants, deformation modes, and mechanical responses. Simultaneously, the effect of the principal geometric parameter, concave angle, on the structural response was analyzed with various impact velocities. Findings suggest that the concave angle influences the structural elastic constants under compressive loading. The stress–strain response exhibits a distinct dual-plateau phenomenon. Taking the A65 (concave angle is 65°) configuration as an example, the stress on the second plateau is approximately 2.7 times that of the first plateau, significantly enhancing the structure's energy absorption capability. Under dynamic impact loadings, different configurations and varying impact velocities affect the structure's energy absorption performance. This paper introduces a series of assemblable plate-lattice structures with an auxetic effect, offering design insights and guidance tailored to the convenient transportation, unconventional structures, and rapid assembly needs of lightweight, impact-resistant mechanical metamaterials. [ABSTRACT FROM AUTHOR]

Additive manufactured lattice structures offer great potential for impact resistance applications. They exhibit excellent energy absorption characteristics during the elasto-plastic deformation process, providing protection to internal devices. However, the mechanical response of lattice structures undergoes substantial variations during the deformation process, thereby imposing limitations on their energy absorption behavior. This study introduces a novel twist design to modify the energy absorption behavior of rectangular and hollow cylindrical lattice structures. Powder bed fusion was used to fabricate the twisted lattice structures. The study employed a combination of compressive simulations and experimental investigations to systematically explore the impact of the twist angle on the peak crushing force, energy absorption, and crash load efficiency of the structures. Adjusting the twist angle results in a reduction of the peak crushing force and a transition towards a stable loading profile during the deformation process. Moreover, the crash load efficiency is also reduced. The twist design concept presented in this paper provides insight into designing and optimizing lattice structures for energy absorption applications. [ABSTRACT FROM AUTHOR]

Auxetic mechanical metamaterials contract or expand laterally when subjected to compressive or tensile load in the axial direction and offer potential benefits in areas such as flexible electronics, aerospace, and soft actuators. Nevertheless, when metamaterials are fabricated using conventional methods, their configurations and properties are fixed, which prohibits adaptation to the specific geometric requirements of their application environment. This limits their further development. This paper proposes an auxetic mechanical metamaterial with a negative Poisson's ratio and energy absorption capability. Compression specimens are fabricated with LCD photo-curable printing technology. The deformation mechanism and in-plane compression characteristics are examined through experimental and numerical simulation methods. The influence of unit cell geometrical control parameters on Poisson's ratio and energy absorption are also explored. The results indicate the dominant deformation mechanism of metamaterial during in-plane compression is bending deformation. The negative Poisson's ratio behavior is more pronounced when compressing along the X direction than along the Y direction, and the specimens also exhibit energy absorption capacity. In addition, the metamaterials prepared by 4D printing technology can be transformed from one configuration to another under external stimuli stimulation and force, and exhibit different mechanical properties, realizing programmable and reconfigurable, further expanding their application range. [ABSTRACT FROM AUTHOR]

The fiber-reinforced polymer (FRP) composites have been widely used as bullet-proof materials due to their low specific gravity, high specific strength and stiffness, and excellent impact resistance. A comprehensive understanding of the energy absorption of the FRP composites during impact and penetration and accurate prediction of the ballistic limits of the FRP composites may provide valuable guidance for designing bullet-proof composites. In this review paper, various analytical and numerical research on the ballistic limits of FRP composites are outlined. Besides, the influences of various factors such as component properties and microstructure of FRP composites and impactor characteristics on the ballistic limits of FRP composites are discussed. We focus on introducing new methods and ideas that provide guidance for the design of advanced bullet-proof composites. [ABSTRACT FROM AUTHOR]

• A novel meta -honeycomb was obtained and fabricated, which reversed the energy absorption method of traditional materials. • The enhanced bandgap property was established by multi-resonator. • The dynamic response of the meta -honeycombs was measured under the impact and blast loads. • The optimization of the meta -honeycomb was verified by coupling different resonators. Conventional honeycomb materials are difficult to resist multiple blast because the enormous energy generated by the explosion would cause plastic deformation of the material, which weakens the strength of the structure. In this paper, a novel meta -honeycomb is designed by adding local resonance system to hierarchical cells, which is based on the multi-resonator-enhanced bandgap property, to withstand multiple blast. This meta -honeycomb reverses the energy absorption mode of traditional honeycomb materials; that is, the energy absorption by plastic deformation of the material becomes the reflection of the stress wave through the equivalent negative mass property generated by the local resonance system, which significantly reduces the deformation of the material and the reaction force at the support under impact loads. In particular, for the secondary explosion loading, the maximum deformation of the meta -honeycomb is reduced by 74% compared with the traditional hierarchical honeycomb. Furthermore, it is demonstrated that the design of meta -honeycomb can be optimized by coupling the bandgap generated by the negative mass property, thereby improving the energy absorption efficiency. This research result provides a new concept for the design of blast-proof materials, which has a high potential for a wide range of engineering applications. [ABSTRACT FROM AUTHOR]

Arched structures have increased in importance over the last few years due to their high efficiency in bearing loads. This paper introduces arched ribs to the classical re-entrant honeycomb (RH) as reinforced structures, and then its energy absorption is improved by simultaneously utilizing the reinforced structures and the auxetic deformation of RHs. Herein, the in-plane crashing response of reinforced RHs (RRH) under different impact velocities is investigated with finite element methods verified against the quasi-static compression experiment of 3D-printed RRH specimens. By introducing arched structures, the deformation of RHs becomes more stable and regular, and two plateau stresses are produced in the stress-strain curves of RRHs. Benefiting from the stacking deformation of RRHs and pure compression characteristic of catenary arches, the second plateau stress of all-reinforced RHs (ARH) is 3.8 times higher than the first one. Two plateau stresses of ARHs are derivated theoretically with a relative error of less than 7 %. Furthermore, a parametric study is performed to explore the effect of impact velocities, thicknesses, and the height of arched ribs on the crashing response of RRHs. The present investigation paves a new way toward strengthening the energy absorption of conventional honeycombs. [ABSTRACT FROM AUTHOR]

• An innovative 3D auxetic structure (3D CATS) was proposed based on the coupling connection of the tube and auxetic units. • The force responses exhibit multiple stages, and the tube and auxetic units played different roles during different stages. • The interaction between the auxetic units and the tube completely changes the deformation modes of the tube. • The SEA of the structure was significantly superior to most existing 2D and 3D auxetic structures. • Two sets of parameters were introduced to vary the compression displacement and force in the plateau stage. In this paper, a novel 3D composite auxetic tubular structure (3D CATS) connected by a thin-walled (TW) circular tube was proposed, and two sets of parameters h 1 , h 2 , and β , n were introduced to construct structural families with various geometries and mechanical properties. The mechanical responses of the 3D CATS were preliminarily explored through the quasi-static experiment. The good agreement between the experimental results and the finite element (FE) simulation verified the accuracy of the FE model. Subsequently, the coupling mechanism between the tube and auxetic units was revealed by analyzing the deformation modes and force responses. The results indicated that the deformation of auxetic units caused more plastic hinges in the tube to enhance the contact force seriously. Then, the 3D CATS was proved to exhibit better specific energy absorption (SEA) compared with other auxetic structures. Furthermore, the influence of h 1 , h 2 , and β , n on the responses was also discussed. The results showed that h 1 , h 2 can change the compression displacement points and forces, while β , n can adjust the stiffness and forces. The results can provide an important reference for the design and study of variable mechanical properties for innovative 3D auxetic structures with enhanced performance. [ABSTRACT FROM AUTHOR]

This study investigated negative stiffness (NS) mechanical metamaterials, which are potential in the energy absorption field. However, critical drawback of low specific energy absorption in traditional NS mechanical metamaterials limits them to be applied. In this paper, a reusable continuous carbon fiber reinforced polymer (CFRP) composite NS mechanical metamaterial was proposed and fabricated. A combination of compression tests and numerical simulations have been carried out to gain a comprehensive understanding of the structural quasi-static mechanical properties. Repeatability of the metamaterial was then verified by cyclic compression. The results of quasi-static test show that the metamaterial has excellent reusability characteristics and good energy absorption capability. In addition, the effect of the structural parameters on the mechanical properties was revealed using the experimentally verified numerical model. Moreover, by dint of the numerical model, the effect of stacking sequence of the metamaterial on the mechanical properties was also investigated, and the correctness of the curved beams adopted 0° stacking sequence in this paper was proved. Finally, plate-impact tests were performed to investigate the cushion performance of this metamaterial. The metamaterial structure shows good impact resistance without the occurrence of any plastic deformation. The research has guiding significance for the design of impact-resistant metamaterials. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a comparison of behavior and energy absorption of neat Kevlar fabric and polymer matrix composites under high velocity impact loading. Two types of matrices including rubber and thermoset (epoxy) matrices were used in order to study the effect of a hard and brittle matrix compared with the soft and flexible matrix on energy absorption of the composite. Moreover, two types of rubber matrix with high hardness (HH) and low hardness (LH) were used in this study to investigate the effect of rubber matrix formulation on impact resistance of composites. Ballistic impact tests were performed by firing a 10 mm hemispherical projectile onto neat fabric and composites in a velocity range of 30–150 m/s for two- and four-layer samples. Results show that the matrix affects the ballistic performance of composites significantly. Rubber matrix enhances the energy absorption of the fabric by keeping composite flexibility. Increase the number of layers for Kevlar/rubber composite results in better ballistic performance. On the contrary, the thermoset matrix leads to an inflexible composite that restricts the fabric deformation and has a negative effect on the fabric's ballistic performance. Finally, damage mechanisms were discussed in detail for each sample. [ABSTRACT FROM AUTHOR]

Abstract A novel carbon fiber reinforced plastics-aluminum alloy (CFRP/AA6061) hybrid tube with five-cell-rounder-corner (C5C) profile was presented in this paper. Different from the available hybrid tubes, the novel structure consisted of a C5C-profile aluminum alloy tube wrapped by CFRP cloths. Numerical simulations and experiments of the C5C hybrid tubes subjected to axial compression were performed. The parameters of modelling CFRP and modelling the interface between CFRP and AA6061 tube were validated. Two multi-objective optimizations aiming to obtain the optimal dimensions of the C5C profile and the optimal angles of the CFRP plies were conducted. The energy absorption and the peak force of the C5C hybrid tube were compared with that of the tubes with common profiles. The effect of wrapping on the energy absorption and the peak force was discussed. The results showed that the novel hybrid tube had excellent energy absorption performance. It could avoid the unstable cracking and early cracking that often occurred to the tubes with common profiles. The specific energy absorption (SEA) of the C5C CFRP/AA6061 tube was 16.7% larger than the SEA sum of the constituent tubes. Wrapping could produce a coupling amplification effect and CFRP/Al hybrid tubular structures manufactured by wrapping were promising materials in light weighting. [ABSTRACT FROM AUTHOR]

Abstract Recently, auxetic honeycombs have attracted considerable attention for their excellent mechanical properties, especially the potential applications for energy absorption. In this paper, a novel re-entrant auxetic honeycomb is proposed and named as re-entrant star-shaped honeycomb (RSH), with the in-plane impact responses explored theoretically and numerically. Three types of microstructural deformation modes are observed under different impact velocities, including low-velocity mode, medium-velocity mode and high-velocity mode. Moreover, a deformation map is summarized to illustrate the effects of the impact velocity and the relative density on the deformation modes. Two typical plateau stress regions are detected under low-velocity impact loading, and the second plateau stress is almost twice higher than the first one. The transverse contraction of the RSH mainly occurs at the first plateau region, which is different for the classical re-entrant honeycomb (RH). In addition, the absorbed energy of the RSH decreases slightly and then increases with the impact velocity. The results of the finite element simulations suggest that the RSH shows more excellent impact resistance, compared with the RH and SSH with same cell wall thickness. Furthermore, the effects of the cell wall thickness and the impact velocity on the crushing strength of the RSH are discussed, and the theoretical results are in good agreement with the finite element simulations. [ABSTRACT FROM AUTHOR]

Abstract In this paper, Energy absorption characteristics of tapered multi-cell tubes improved by foams are studied. For the energy absorption process, a theoretical formulation is developed to represent the mean crush load of the foam-filled tubes considering a combination of mean crush loads due to non-filled tube, the foam-filler, and a frictional resistance between them (interaction effects). The formulation is based on the assumptions including equivalent segmented non-tapered single-cell tubes as well as a parallel resisting force of the contributors (non-filled tubes, foam-filler, and interaction effects). Moreover, an extensive numerical analysis on the crushing of the foam-filled tapered multi-cell tubes, with a taper angle ranging from 0 to 7 degrees, a wall thickness ranging from 0.25 to 3 mm, and a cell number ranging from 11 to 10 × 10, is conducted to evaluate the effects of side wall tapering, cross section's division into multiple cells and wall thickness enlargement on the crashworthiness characteristics. Analyses indicate that there are significant enhancements in the energy absorption behavior of the foam-filled tubes with respect to the non-filled ones. As a special case, the force-displacement results obtained in the numerical simulation are verified against those experimentally observed and reported in the literature for a foam-filled non-tapered single-cell tube. [ABSTRACT FROM AUTHOR]

• This paper presents the superior energy absorption capacity of hollow-cylindrical-joint hierarchical honeycomb composite tubes under axial quasi-static crushing. • The fiber orientation (α) has a significant effect on the energy-absorbing characteristics of these structures and specific energy absorption (SEA) tend to initially decrease and then increase with increasing α. • The SEA of the biomimetic multi-cell tubes can be significantly enhanced by employing different fiber orientations. • The highest SEA value measured on these structures, 77.3 J/g, is more than double measured on a traditional circular tube (34.9 J/g). This paper investigates the superior energy-absorbing characteristics of hollow-cylindrical-joint hierarchical honeycomb composite tubes under axial quasi-static crushing. Biomimetic multi-cell tubes (BMCTs), inspired by the forewing of a beetle, were manufactured using the vacuum bag moulding method. Quasi-static compression tests were conducted to characterize the force–displacement response, the progression of failure, the crashworthiness characteristics, and the corresponding energy absorbing mechanisms. The experimental results show that the fiber orientation (α) has a significant effect on the energy-absorbing characteristics of these structures. The crush load efficiency (CLE) and specific energy absorption (SEA) tend to initially decrease and then increase with increasing α. It has also shown that the SEA of the BMCTs can be significantly affected by employing different fiber orientations. The highest SEA value measured on these structures, 77.3 J/g, is more than double of 34.9 J/g measured on the single circular tube counterpart. The energy-absorbing capacity of the composite structures is devisable and can be enhanced by integrated biomimetic design. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bio-inspired "photonic micropillar pattern" (PMP) honeycomb is proposed for enegy absorption. • The PMP honeycomb has remarkable mechanical robustness with crashworthiness indicators comprehensively improved. • The SEA of the PMP honeycomb is significantly increased by 70% compared with that of the conventional hexagonal honeycomb. • The PMP honeycomb has a self-constrained mechanism to achieve a layer-by-layer collapse mode with Poisson's ratio close to zero. • The PMP honeycomb has a self-adaptability for impact valocities to achieve more stable deformation mode. Beetle's elytra provide elaborate microstructural designs to achieve functional synergies in face of external environments. Natural design strategies can provide effective solutions to the long-standing challenges about how to design an energy absorbing structure with comprehensively improved mechanical properties. Inspired by the pattern of the micropillars distributed in photonic structures of beetle's elytra, this paper proposes a bio-inspired "photonic micropillar pattern" (PMP) honeycomb with robust crashworthiness, self-constrain, self-adaptability, and enhanced energy absorption capacity as an alternative material to the conventional single hexagonal-celled (SHC) honeycomb. The computational and experimental results both show that all in-plane crashworthiness indicators of the PMP honeycomb have been significantly improved compared with that of the SHC honeycomb. Subsequently, the collapse and energy absorption mechanisms of the PMP honeycomb are revealed by the analytical model established in this study. Based on numerical simulations and precisely theoretical predictions, the effects of the relative density, cell wall angle, impact velocity and thickness distribution on the in-plane crashworthiness performance of the PMP honeycomb are analyzed and discussed. This study creates a possibility for future excavation of advanced energy-absorbing structures with multifunctional synergies. [ABSTRACT FROM AUTHOR]

Lattice materials possess broad application potential in many engineering fields due to their excellent mechanical properties. In this paper, a thorough investigation is carried out for the lattice materials with the generalized body-centered cubic (BCC) cell geometry. The investigated geometry variations include (1) adding additional reinforcement bars along several cell edges, and (2) offsetting the central vertex of the cubic cell that the oblique beams connect. The influences of the cell geometry on the stiffness, the Poisson's ratio, the energy absorption capacity and the deformation pattern of the generalized cubic lattice are ascertained through extensive theoretical and finite element (FE) numerical analyses. The results indicate that adding reinforcement bars along the loading direction can effectively enhance the stiffness and strength, but does not significantly change the deformation pattern as depicted by the shape of shear bands. The additional bars perpendicular to the loading direction can largely influence the Poisson's ratio, making it possible to approach unity. It is found that a modified BCC lattice with properly offset central cell vertices achieves an optimal energy absorption capacity that is about 2.26 times of traditional BCC lattice. This work could provide a comprehensive reference for the mechanical properties of the most generalized BCC lattice materials. [ABSTRACT FROM AUTHOR]

This paper is concerned with sandwich foam tubes (SFTs), a recent type of sandwich structure containing metal syntactic foam (MSF). To create these structures, MSF is cast between thin-walled aluminium tubes in a single-step counter-gravity infiltration casting technique. Their mechanical properties and deformation mechanism are studied using quasi-static compression tests. For comparison, uniform MSFs and foam filled tube (FFT) structures are manufactured and tested alongside the SFTs. The deformation of the SFTs and FFTs is controlled by the symmetrical buckling of the tubes. A significant interaction effect between MSF and tubes is observed, i.e. the compressive strength of these structures exceeds the sum of their constituents. As a result, the specific energy absorption of the SFTs and FFTs increased compared with MSF samples. [ABSTRACT FROM AUTHOR]

Self-similar hierarchical structures are widely observed in nature, and have been credited with superior mechanical properties. In this paper, a novel self-similar hierarchical hexagonal columns (HHC) is proposed to improve structural crashworthiness performance. The self-similar hierarchical hexagonal columns are constructed by iteratively adding sub-hexagons at the corners of primary hexagon. To investigate the crashworthiness of HHC, the nonlinear finite element model is first developed and validated against experimental data obtained from 1 st order HHC. Numerical investigations of 1 st and 2 nd order hierarchical hexagonal columns with different hierarchical levels are performed to compare with 0 th order HHC, the results show that 1 st and 2 nd order hierarchical hexagonal columns improve the energy absorption and crush force efficiency by governing the material distribution, especially, 2 nd order HHC exhibits significant advantage for energy absorption. In addition, parametric designs of 2 nd order HHC are carried out to explore crashworthiness effect on hierarchical size ratio, cell wall thickness and impact velocity. The significant effects on both specific energy absorption (SEA) and the peak crushing force (PCF) are observed. The findings of this study offer a new route of designing novel crashworthiness structure with highly energy absorption capacity. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental work carried out to fabricate and characterise the in-situ foam filled tubes (FFTs) made of aluminium alloys prepared by powder metallurgy method, using aluminium alloy tubes with extremely thin walls (∼0.6 mm). The fabrication procedure demonstrates that thin-walled tubes with extremely thin walls can support temperatures near to its melting temperature (∼700 °C) required to form a closed-cell aluminium alloy foam, consequently in-situ filling the tube. The mechanical performance of fabricated structures was evaluated using uniaxial compressive tests and infrared thermography. Results demonstrate that the benefits of the manufacturing process and its product, the FFTs (composite structures). Additionally, they reveal that this is a cost-effective solution to prepare efficient energy absorbing lightweight structures, allowing to adjust the weight and levels of the energy absorption, simultaneously. The results demonstrate that the promising in-situ FFTs with thinner outer tubes axially deform in an efficient mixed mode, showing superior energy absorption capability compared to the empty thin-walled tubes. [ABSTRACT FROM AUTHOR]

Discontinuous unidirectional fiber-reinforced composites are shown to possibly exhibit pseudo-ductile failure that is lacking in continuous fiber composites. The aim of this paper is to use a discontinuous and interdigitated design strategy which mimicks the nacre structure to improve the specific energy absorption (SEA) of a carbon/expoxy composite tube. Quasi-static axial compressive experiment is combined with a digital image correlation system to analyze the failure process of the specimens. Four kinds of tubular specimens which are based on different ply cut intervals and distributions are fabricated and crushed. The load-crushed displacement curves and the SEA values are obtained showing that circular shaped continuous ply cuts result is the highest fluctuation of the compressive force. Moreover, the tubes with helical and nacre mimicking ply cut structures result in a flatter load-crushed displacement curve. This work demonstrates that in a crush process, unidirectional composites with a well-designed discontinuity at the ply level can improve the SEA over 51% as compared to the unidirectional continuous tubes. [ABSTRACT FROM AUTHOR]

Auxetic warp-knitted spacer fabric is known for its excellent mechanical properties, shear-resistance, cushioning property, energy absorbing abilities, therefore draws more and more attention to this kind of fabrics. In order to study the impact resistance and energy absorption ability of auxetic warp-knitted spacer fabrics under low-velocity impact, falling weight impact tests are adopted in this paper and influence relations of energy absorption and impact resistance to auxetic performance and initial impact energy are analyzed. Results show that the larger absolute value of negative Poisson’s ratio is, the better energy absorption ability and impact resistance could be obtained, and the initial impact energy has little influence on the overall energy absorption of fabrics under low-velocity impact. [ABSTRACT FROM AUTHOR]

This paper proposes novel re-entrant honeycombs (NREH), which are designed as the support ribs of the re-entrant honeycomb subunit in an asymmetrical form to further improve its mechanical properties. First, three types of NREH composed of asymmetric subunits are compared. The σ m and specific energy absorption (SEA) of the three NREHs are not much different during in-plane impact, while the Poisson's ratio of NREH-3 is smaller than that of the other NREHs. Analyze the performance of NREH-3 by analyzing the change of angle θ. It was found that in the y-direction, the SEA of NREH-3-80 is 41.46% higher than that of NREH-3-60, and the Poisson's ratio is almost unchanged. On x-direction, the energy absorption performance is not significantly improved. Analysis of NREH-3′s sensitivity to impact velocity revealed that NREH-3-60, NREH-3-70, and NREH-3-80 are greatly affected by impact velocity. As the velocity increases, their deformation models significantly change, while other structures remain constant. An analysis of the influence of NREH-3 on wall thickness showed that the SEA of NREH-3 is significantly improved with increasing wall thickness and that Poisson's ratio did not significantly change, indicating that appropriately increasing the wall thickness effectively improves the impact resistance of the honeycomb structure. [ABSTRACT FROM AUTHOR]

In this paper, a novel design for the interlocking ceramic/PE composite laminates is proposed, and numerical simulations are performed to investigate the penetration resistance and mechanism of the structures. The FE model is first validated by the existing experimental tests, and the influences of the interlocking angle, impact velocity, contacting position and the penetration angles on the deformation features as well as the mechanics are detailly investigated. Results show that the deformation of the ceramic/PE laminates expands to the far away regions due to the interlocking effect. The Mises stress distribution regions in the cores are varied with the variation of the inclined angle of ceramic cells. The residual velocity of the bullet remains almost constant when the inclination angle is relatively small, while it significantly increased as the angle further raises. In the present work, the highest specific energy absorption is achieved at θ = 12.5° due to interlocking effect and the lower structural mass. [ABSTRACT FROM AUTHOR]

Multi-cell and foam-filled structures have shown outstanding crashworthiness capacities. As a result, foam-filled twelve right angles thin-walled structures (FTRATS), an integrator of them, can be excellent energy absorber candidates in the vehicle body structure. This paper presents a new methodology to investigate the crashworthiness potential of a series of novel FTRATS with different topological distributions. The base computer FTRATS model was correlated using existing experiments based on a single core thin-walled square tube filled with foam, then followed by a dynamic response evaluation of 32 FTRATS configurations, with the purpose of finding the lowest peak crushing force (PCF) and maximum displacement (Dmax), the highest specific energy absorption (SEA) and crash load efficiency (CLE). As the results were initially inconclusive, a complex proportional assessment (COPRAS) method was used to extract the configuration with the highest potential, suggesting that the five-cell FTRATS filled with foam at its periphery showed superior crashworthiness properties. This selection was followed by an optimization using adaptive multi-population genetic algorithm methods based on response surfaces methodology, kriging model and Optimal Latin hypercube design. The solution obtained generated a stable collapse, increased the CLE (63.94 %), lowered PCF (38.83%) and increased SEA (38.86%). This new and innovative process has shown that coupling COPRAS and optimisation lead to an unbiased and efficient method to study and optimize FTRATS structures. [ABSTRACT FROM AUTHOR]

To obtain a structure with excellent energy-absorbing ability, based on the traditional star-shaped honeycomb (SSH), a crossed star-shaped honeycomb (CSSH) was designed via evolving the horizontal and vertical walls of the honeycomb into crossed inclined walls. In this paper, the Poisson's ratio and Young's modulus of honeycomb under axial load are theoretically deduced, and a method is proposed to evaluate the deformation stability of honeycomb with the maximum deviation of unilateral horizontal strain (MDUHS). Numerical simulation is employed to verify the theoretical solution, and the in-plane mechanical properties and deformation behavior of CSSH are investigated in detail. The numerical simulation method in Abaqus software was verified by using quasi-static crush test data of 3D printed CSSH specimens. It is found that by changing the inclined angle θ 2 , CSSH can evolve into a positive Poisson's ratio(PPR), zero Poisson's ratio(ZPR), or negative Poisson's ratio structure(NPR), and Young's modulus is very sensitive to the difference between the opened angle θ 1 and the inclined angle θ 2 ; increasing θ 1 or decreasing θ 2 not only significantly improves the energy absorption capacity of the honeycomb but also facilitates the generation of a more pronounced double plateau region on the stress-strain curve; by changing the length of the crossed inclined wall, three improved CSSHs(ICSSH) can be obtained. Among them, by adjusting the length of the crossed inclined wall in the horizontal direction, the structure with the superior energy absorption capacity can be obtained. The structure with excellent deformation stability can be obtained through adjusting the length of the crossed inclined wall in the vertical direction. Results show that the performance of CSSH is better than that of SSH, with a specific energy absorption (SEA) of 245% higher than that of SSH. This work is expected to guide the design of new auxetic honeycombs with better energy absorption properties, and can also provide a reference for the optimization of honeycombs. [ABSTRACT FROM AUTHOR]

This paper investigates the energy-absorbing characteristics of a lightweight honeycomb core containing embedded carbon fibre reinforced plastic (CFRP) tubes. Initial tests are undertaken on the plain aluminum honeycomb material in order to characterize its specific energy absorption (SEA) capability and to identify the prevailing failure mechanisms. Tests are then conducted on honeycomb cores reinforced with increasing numbers of composite tubes in order to establish the influence of varying the density of the tubular array on the measured SEA. Finally, a series of drop-weight impact tests are conducted in order to characterize the dynamic response of these materials and assess their overall rate-sensitivity. Tests on the plain aluminum honeycomb cores resulted in the characteristic plastic wrinkling of the cell walls, yielding an average value of SEA of 14 kJ/kg. Embedding CFRP tubes into the honeycomb served to greatly enhance the energy-absorbing properties of the core, with quasi-static values of SEA reaching as high as 105 kJ/kg. An examination of the failed samples indicated that the previously-observed wrinkling mode of failure was largely absent, with the composite tubes being reduced to fine debris. Increasing the areal density of tubes in the honeycomb to relatively high values proved to be counterproductive, due to unwanted interactions between the individual tubes. Dynamic tests on the tube-reinforced honeycombs yielded SEA values that exceeded the quasi-static results with values reaching 112 kJ/kg for a moderately-reinforced core. Given the simplicity of the preparation process, it is believed that these lightweight structures represent an attractive cost-effective energy-absorbing material for use in dynamic applications. [ABSTRACT FROM AUTHOR]

In this paper, a prospective simulation method for composite crushing under axial crash loading is presented. To this end carbon fibre-reinforced plastic (CFRP) circular crash tubes are investigated in drop tower tests. Flat specimen tests are performed to determine calibration parameters and are used for efficient re-parameterization of a transversally isotropic material card used in finite element (FE) simulation. An existing material card for CFRP based on basic tension and compression tests is used as a starting point and only a small set of material parameters is numerically reasonable adjusted to account for crushing. Once calibrated by means of flat specimens the material model is able to cover a variety of different composite layups and specimen geometries, e.g. tube specimens. Therefore, numerical simulation of drop tower testing is carried out and results show good agreement between numerical and experimental results. In addition to these tests, it can be shown that the presented approach is leading to equally good results when the material and geometry of the specimens are changed to a glass fibre-reinforced plastic (GFRP) tube structure. [ABSTRACT FROM AUTHOR]

Composites with auxetic effect have been drawing more attention in recent years due to their unique features and wide applications. In this study, a kind of novel multilayer orthogonal structural composite with auxetic effect was fabricated for energy absorption and impact resistance. Non-auxetic composite with the same raw materials but with different reinforcement structure was also fabricated for comparison in order to better understand the effect of reinforced structure on the deformation mechanism and mechanical responses of the composites. Since the quasi-static compressive properties and Poisson’s ratio effect of composites had been investigated previously, this paper only focused on the study of the low-velocity drop-weight impact tests of composites under impact energies from 7.25 J to 65.25 J. It was shown that both auxetic and non-auxetic composites were strain rate sensitive from 34.23 s −1 to 111.48 s −1 , but they exhibited totally different mechanical responses due to different deformation and damage mechanism. Pull out tests demonstrated that strong interfacial bonding between the reinforcements and matrix could ensure the desired deformation of structural reinforcements and auxetic effect of the composite. It was also concluded that the auxetic composite had better energy absorption performance in medium strain range. [ABSTRACT FROM AUTHOR]

Obligatory standards are dictated to vehicle manufacturers for decreasing the high number of road dead tolls in rollover crashes; at the same time demands to produce light-weight vehicles have increased substantially to reduce the toxic gases emission. This paper presents a new design of the roof strengthening configuration in which sandwich material has been used. This type of configuration improves the energy-absorption capacity of the vehicle roof system and dissipates impact energy in a controlled manner. In reality, carrying out roof crush test is not cost effective, thus numerical analysis of vehicle roof crush test has been performed according to standard FMVSS 216 test. Sandwich structures with unidirectional carbon/epoxy composite face-sheets and Expanded Polypropylene (EPP) foam core have been used to model different configurations for vehicle roof structure. The effects of increasing the foam core density and face-sheets thickness on the energy absorption and strength-to-weight ratio (SWR) of vehicle roof structure have been investigated. Results revealed that, the optimized sandwich solution type 6 with the face-sheets thickness of 0.8 mm and foam core of 70 kg/m 3 density reduces the vehicle roof panel mass by 68% while it has almost the same structural performance with the steel solution having equal value of SWR. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the mechanical properties of thermosetting polyurethane (TSPU) and thermoplastic polyurethane (TPU) under quasi-static and low velocity impact (LVI) loading. Hollow glass microspheres were added at different volume percentages to the TSPU to decrease the density and to investigate the effect on the mechanical properties. Incorporating the fillers leads to the development of a stepwise graded foam, which has been shown to yield more constant plateau stress levels under dynamic loading. The work was extended to investigate reinforcing the TSPU and the TPU matrix with carbon fibre reinforced plastic (CFRP) tubes, providing a higher load-bearing capacity under static loading. Reinforcing the syntactic TSPU resulted in a 47.7% increase in specific energy absorption (SEA), with the average value reaching 56.28 kJ/kg. The specific compressive strength for the reinforced TSPU was also improved under quasi-static loading, where a 65% increase was observed, relative to the unreinforced TSPU. For the reinforced TPU significant improvements were seen under dynamic loading conditions, relative to the unreinforced TPU, with increases in plateau stress levels of 629% and 452% at strain levels of 25% and 50%, respectively. [ABSTRACT FROM AUTHOR]

This paper studies the low-velocity impact properties of foam-filled composite lattice sandwich beams. The effects of transverse and longitudinal lattice-web spacing, lattice-web thickness, foam density, foam thickness, impact height and impact position on the impact resistance of the sandwich beam were investigated. Experimental results showed that the failure modes of the sandwich beams mainly included buckling of lattice web, skin fiber fracture, interfacial delamination between skin and foam, shear failure of foam, foam indention, and foam crushing. With the reduction of the longitudinal lattice-web spacing, the maximum impact force increased by 136.92%, and the maximum vertical displacement decreased by 51.46% for the simply supported specimen. With the increase of the web thickness, the maximum impact force of the specimen increased by 33.40% for the specimen on the rigid support. Furthermore, a numerical model was built and parametric analysis (skin thickness, foam density, and boundary conditions) on the properties of the sandwich beam was also conducted. Parametric analysis showed that the energy absorbed by the foam of the specimen on the rigid support was 110.39% more than that of the simply supported specimen. [ABSTRACT FROM AUTHOR]

Porous/multi-cell structures are widely used in practical engineering due to their excellent energy absorption capacity and lightweight. In recent decades, as an important member of porous structures, lattice structure is found to have extremely excellent energy absorption capacity per unit mass. It has become a hot spot in the research of porous structures for energy absorption properties. There are more and more studies on energy absorption characteristics of lattice structures in the world. This paper reviews and discusses the research work on the energy absorption characteristics of lattice structures in recent years. Firstly, the performance evaluation indexes and loading conditions for energy absorption of the lattice structures are summarized. Then, the lattice structures in the current research literature are classified, and the lattice structures are divided into 2D lattice structure and 3D lattice structure. The 2D lattice structures are divided into general structure, auxetic structure and hierarchical structure, while the 3D lattice structures are divided into truss-based, plate-based, shell-based and hierarchical 3D lattice structure. Furthermore, the energy absorption properties of different types of 2D and 3D lattice structures are introduced in detail. Then, the fabrication process and the engineering application for energy absorption of the lattice structures are introduced. Finally, the future research direction of energy absorption of lattice structure is predicted. Therefore, this work provides a useful platform for researchers and engineers to design energy absorbed lattice structures, and provides a basis for developing new excellent energy absorbed lattice structures. [ABSTRACT FROM AUTHOR]

This paper aims to explore the off-center low-velocity impact response and damage characteristics of carbon fiber reinforced aluminum laminate (CARALL). Progressive damage finite element models of CARALL considering the stiffness degradation and damage evolution of carbon fiber reinforced plastic (CFRP) were established using a user subroutine and verified by off-center impact tests with different impact energies. The motion propagation, damage, and spatial distribution of dynamic responses of CARALL impacted in different locations are studied. The results indicate that increase in impact distance from center dissipates more energy due to the more severe damage and failure of CFRP, while the off-center impact have a negative effect on the plastic energy absorption of metal compared with center impact. A quantitative expression is proposed to describe the spatial distribution of the maximum transverse displacement. [ABSTRACT FROM AUTHOR]

• A novel elliptical anti-chiral (EAC) honeycomb structure is proposed by replacing the straight cell walls of the criss-cross anti-chiral (CAC) honeycomb with elliptical cell walls. • Both numerical and experimental results reveal the existence of a plateau stage and an enhancement stage in the stress–strain curves of the EAC honeycomb. • Larger semi-axis length ratio results in larger plateau stress and densification strain, while smaller semi-axis length ratio means larger initial peak stress and plateau strain. • The empirical formulas of critical impact velocity and plateau stress are further derived. Honeycombs with anti-chiral (AC) unit cells are found to have auxetic properties and enhanced energy absorption capacities than regular hexagonal honeycombs. To further improve the energy absorption capacity, by replacing the straight cell walls of the criss-cross anti-chiral (CAC) honeycomb with elliptical cell walls, a novel elliptical anti-chiral (EAC) honeycomb is proposed in this paper. The in-plane crushing response of the EAC honeycomb is investigated numerically under different impact velocities. The numerical modeling method in ABAQUS software is validated by the compression test data of 3D-printed EAC honeycomb specimens. Both experimental and numerical results reveal that the EAC honeycomb has a plateau stage and an enhancement stage in the stress–strain curve. The empirical formulas of critical impact velocity and plateau stress are further derived, which is in good agreement with the numerical simulation results. The parameter analysis further shows that the microstructural parameters have a great influence on the crushing strength of the EAC honeycomb. Under the same impact velocity, larger semi-axis length ratio results in larger plateau stress and densification strain, while smaller semi-axis length ratio means larger initial peak stress and plateau strain. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation into the behaviour of braided CFRP tubes subjected to quasi-static and dynamic axial crushing. Tubes of six different geometries, with round, rectangular or square cross-sections, with 2–4 plies of triaxial braids, were tested. Two types of square tubes were also tested with a plug initiator. Comparisons were made by examining the failure modes, load-displacement curves, specific energy absorption (SEA), and the ratio of the peak load to the average progressive crush load. When tested without a plug initiator, the crush characteristics of these tubes differed significantly under the two loading rates. Under quasi-static crush, tubes showed a greater tendency to fail in an unstable manner, characterized by global buckling, folding of the walls and crushing at both ends of the tube. Therefore, quasi-static crush testing should be used with caution when evaluating dynamic response of a structure. In dynamic testing, seven out of the eight configurations failed in a stable manner, with damage initiating at the bottom and propagating up the length of the tube in a splaying type failure mode. The smaller square and the round tubes performed the best, displaying higher SEA and lower load ratio values. [ABSTRACT FROM AUTHOR]

The aim of this paper is to evaluate the quasi-static and dynamic compressive crush performance of integral-skin closed-cell aluminium alloy foam with and without radial constraints. The foam specimens were prepared by the powder compact foaming method. The behaviour under different loading conditions (loading velocity and radial constraints) has been determined by an extensive experimental program. The results show a significant increase in the collapse stress of the integral-skin closed-cell aluminium foam under quasi-static loading when radial constraints are applied. The radial constraint induces a significant strain hardening of the foam, where the densification occurs at lower strains, consequently enhancing the energy absorption per unit volume of the deformed foam. The strain hardening is also sensitive to the foam density, increasing with the density. [ABSTRACT FROM AUTHOR]

The oblique lateral collapse of the metal/composite hybrid beams is a critical mechanism for the kinetic energy dissipation. However, the deformation features and energy absorption mechanism of such beams is not clear. This paper presents numerical and theoretical studies on the oblique lateral collapse of aluminum/CFRP (Al/CFRP) hybrid beams. The finite element model for the A/CFRP beams subjected to oblique lateral loads is first established, and its accuracy is validated by comparing the numerical results with the existing experiments. The influences of the Al thickness, CFRP layer number, loading angle and the friction coefficient on the oblique collapse responses are then explored by means of the finite element method. Finally, analytical studies are carried out to further explore the energy dissipated by the plastic hinge of the Al part, the flattening of CFRP section and the fracture of CFRP layers. Results show that increasing the Al thickness can significantly improve the total energy absorption and specific energy absorption (SEA), while the variation of the CFRP layer numbers has minor influences on the SEA due to the mass increase and the fiber breakage. The decrease of the load angle results in a higher crushing force level, while the friction coefficient has minor effects on the force responses. The analytical results compare well with the numerical results, and the errors of the energy absorption between them is no more than 12.3% in the analyses. The present work provides an effective alternative to evaluate the crashworthiness performance of metal/composite beams under oblique lateral loads. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of cumulative damage on the energy absorption capability of plain-woven fabric systems. The cumulative damage was generated by creating pre-damaged holes, aiming to simulate the post-impacted sample targets. Ballistic impact tests were performed to characterize the ballistic protection of the pre-damaged and undamaged systems, and FE simulation was used to study the underlying mechanisms of energy dissipation. The results showed that the pre-damaged systems appear to be less protective than the undamaged system in most cases. The ballistic performance of the fabrics is more sensitive to the pre-damaged holes that are located on the primary yarns than that on the secondary yarns. When the primary yarns are broken, the holes are detrimental to the evolution of the transverse deflection but are beneficial in increasing the amount of energy dissipated by frictional sliding during the yarn pull-out process. Angle-plying the constituent layers of multi-ply panels is found to be useful in minimizing property degradation. It was also determined that the angle-plied systems absorb less energy than the aligned system regardless of the existence of the pre-damaged holes. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of two distinct techniques to improve energy absorption capability of an accordion cellular structure with close-to-zero Poisson's ratio. For this purpose, fiber-reinforcement and foam-filling methods were employed to address the material enhancement and to obtain light and tough structures with high specific energy absorption. Employing an innovated additive manufacturing based on material extrusion process, specimens of glass fiber-reinforced PLA were produced in both in-plane directions to compare with the un-reinforced counterpart. In continue, some of the 3D printed samples were strengthened by means of polyurethane foam in their hollow structure. The quasi-static compressive tests showed that the initial stiffness, collapse stress, and plateau stress were enhanced significantly in the presence of both fiber-reinforcement and foam-filling. The energy absorption behavior of the enhanced cellular structure was then simulated via finite element method and a good-agreement between experimental and numerical results was observed. Afterwards, an analytical model was proposed to validate the observed elastic stiffness of the compressive samples. In comparison with the relevant cellular configurations, it was also demonstrated that the fiber-reinforced PLA accordion cellular structures, as well as the foam-filled ones, exhibited not only a greater specific energy absorption but also presented a lower density. [ABSTRACT FROM AUTHOR]

This paper proposes a novel nested corrugated-elliptical tube (NCET) system as an energy absorber. The crushing characteristics of the NCET are investigated under lateral load through quasi-static experiments and finite element analysis. The NCET shows a low initial stiffness and stable deformation process, and a dual-plateau force displacement curve with a high energy absorption is generated in the experimental crushing process. Furthermore, the crushing characteristic of the dual-plateau stages makes the NCET exhibit a greater specific energy absorption (SEA) and lower initial peak crushing force (IPCF) than that of the single-walled tube and typical nested energy absorbers. The influence of the wave crest N , amplitude A and wall thickness t on the crushing behavior of the NCET is numerically investigated to further understand the crushing mechanism of the NCET under a lateral load. The result shows that the wall-thickness t is the most sensitive to the SEA and IPCF. Moreover, the wave crest N and amplitude A have a large influence on the deformation mode and the IPCF of the NCET. This study provides a novel corrugated nested design method to promote mechanical properties of an energy absorber under a lateral load. [ABSTRACT FROM AUTHOR]

This paper presents results of an experimental study on the processing and mechanical characterisation of plain and in-situ carbon-steel bar reinforced cylindrical Al-alloy foams. The reinforcement is incorporated into the foam-structure during the foaming-process which is based on the powder metallurgy method. Some key technical issues concerning the manufacturing procedure are discussed. A technical solution to design moulds to prepare high-quality foam parts with longer lengths is proposed. This has been achieved by constructing moulds with varied mould-wall thickness. Such an approach enabled to control the foaming-process and subsequent the foam-filling in different regions of the mould cavity. A series of plain and in-situ reinforced foams with two different lengths (150 and 200 mm) and the same diameter (25 mm) were fabricated. Uniaxial compressive and three-point bending behaviour was studied, exploring their deformation and failure mechanisms. The results demonstrate that the carbon-steel bar increases the compressive behaviour of the foams but does not significantly influence their bending behaviour in terms of peak load. Under bending loads, the stress–strain curves are shifted along the strain axis in comparison to the plain foams. The deformation and failure mode of both specimens under compressive and bending loads is similar. The results indicate the potential of reinforced materials. [ABSTRACT FROM AUTHOR]

In this paper, two different types of unstiffened and lozenge grid-stiffened E-glass/epoxy composite cylindrical shells are experimentally investigated under lateral compression. The composite shells are compressed in two different loading conditions; between two rigid flat platens and between a rigid flat platen and a rigid cylindrical indenter which is aligned perpendicular to the shell axis. The effects of the grid stiffeners on the stiffness, contact force and energy absorption capacity of the composite cylindrical shells are investigated in the two mentioned loading conditions. Incorporation of grid stiffeners in the composite cylindrical shells leads to an increase in the structural stiffness, contact force and energy absorbing capacity in both loading conditions. Furthermore, it is observed that the effect of the stiffeners on the structural stiffness is dominant in the elastic deformation stage of the compression processes. The results show that stiffening the composite cylindrical shells with lozenge grid stiffeners can increase the specific energy absorption almost twice in comparison with the unstiffened composite shells; and among all of the specimens, the grid-stiffened structures compressed between two rigid flat platens have the highest specific energy absorption, while the unstiffened structures compressed by the cylindrical indenter have the least capacity to absorb energy. [ABSTRACT FROM AUTHOR]

Foam-filled circular composite tube has been widely used in safety design of automobile, space craft recovery and so on due to its advantage of high energy absorption, light weight and anti-corrosion. But the axial crush behavior and energy absorption capability of foam-filled composite tubes are threatened by elevated and high temperatures. In practice, the effects of high temperatures cannot be ignored because composites and foam are sensitive to temperature. In this paper, an experimental investigation was carried out to evaluate the effectiveness of energy absorption of foam-filled circular glass fiber reinforced plastic (GFRP) tube under elevated and high temperatures. The temperature range was from 20 °C to 110 °C, covered the glass transition temperature (92 °C). In the meantime, the effects of high environmental temperatures on failure mode, crush force efficiency, energy ductility coefficient and specific energy absorption were also studied. The test results demonstrated that the axial crush behavior and energy absorption capacity of foam-filled GFRP tubes were determined by the environmental temperature. The foam-filled GFRP tubes can achieve top crashworthiness performance when the environmental temperature was less than 70 °C. [ABSTRACT FROM AUTHOR]

Several natural fibres such as hemp, flax, sisal, kenaf and jute have been used in different industrial applications. Recently, natural fibres have drawn the interest of researchers, engineers and scientists as substitute reinforcements for fibre reinforced polymer (FRP) composites tubes. Due to their fairly good mechanical properties, low cost, high specific strength, environmentally-friendliness and bio-degradability, ease of fabrication, and good structural rigidity, these materials can be used in an extensive range of applications, including aerospace and the automotive industry. Previous studies focused on how to introduce the natural fibres into industrial applications and the replacement of synthetic fibres with natural fibre materials. The tensile properties of natural fibre reinforce polymers are mainly influenced by mechanical properties such as tensile properties, flexural properties, and impact strength are strongly affected by fibre content. Furthermore, the overall tensile and flexural properties of natural fibre-reinforced polymer hybrid composites are highly dependent on the aspect ratio, moisture absorption. The geometric designs such as geometry and shapes and triggering and non-triggering and filled and non-filled was found that significantly affected the crashworthiness parameters and specific energy absorption of natural fibre reinforced polymer composite tubes. Furthermore, the compressed data, which is based on the maximum values, reported in the literature, it can be observed that the woven flax fabric circular tube exhibits high energy absorption capability and CFE. This result contributes to the increased ability to use natural fibres in vehicle manufacture and thus increases the sustainability of this industrial sector. This paper presents an overview of the developments made in the area of natural fibres reinforced composites, in terms of their physical and mechanical properties, and crashworthiness properties. Several uncertainties affecting the experimental results were discussed. [ABSTRACT FROM AUTHOR]

A 3D intralaminar continuum damage mechanics based material model, combining damage mode interaction and material nonlinearity, was developed to predict the damage response of composite structures undergoing crush loading. This model captures the structural response without the need for calibration of experimentally determined material parameters. When used in the design of energy absorbing composite structures, it can reduce the dependence on physical testing. This paper validates this model against experimental data obtained from the literature and in-house testing. Results show that the model can predict the force response of the crushed composite structures with good accuracy. The simulated energy absorption in each test case was within 12% of the experimental value. Post-crush deformation and the damage morphologies, such as ply splitting, splaying and breakage, were also accurately reproduced. This study establishes the capability of this damage model for predicting the responses of composite structures under crushing loads. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the uniaxial-compressive crush performance of thin-walled structures filled with Advanced Pore Morphology (APM) foam elements, exploring their deformation and failure mechanisms. The APM-foam elements are integral-skin closed-cell foams of near spherical shape fabricated through the Powder-Compacting-Foaming method by heating precursor in a continuous belt furnace. Two lightweight structures using the APM-foam elements were assembled, tested and evaluated: (i) Al-alloy tube filled with non-bonded APM-foam elements and (ii) Al-alloy tube filled with polyamide-bonded APM-foam elements. Non-bonded APM-foam filled tubes were prepared by pouring the APM-foam elements into an empty Al-alloy tube (without any bonding). Polyamide-bonded APM foam filled tubes were prepared by pouring the APM-foam elements coated with polyamide into an empty Al-alloy tube and then submitted to a heat treatment curing the polyamide. The axial crush performance of the APM foam filled tubes was compared to that of the empty tubes (with and without heat treatment) and tubes filled with conventional closed-cell foam. The results show a significant influence of the adhesive bonding on the compressive behaviour of polyamide-bonded APM foam filled tubes, which exhibit controlled deformation behaviour without appearance of cracks and show superior specific energy absorption per mass unit. [ABSTRACT FROM AUTHOR]

The foam-filled thin-walled composite structures have proven an ideal energy absorber in automotive engineering for its extraordinary energy absorption ability and lightweight features. Unlike existing uniform foam and thickness (UFT) structure, this paper introduces functionally graded foam (FGF) to fill into functionally graded thickness (FGT) thin-walled structure, named as double functionally graded (DFG) tube, where different configurations of foam and wall thickness gradients are taken into account. To systematically explore the crashworthiness of DFG structures, first, experimental results were performed to validate finite element (FE) models. Second, a comparison of crashworthiness was carried out for (1) four different DFG structures, (2) four single functionally-graded (SFG) structures and (3) one traditional UFT structure. The results showed that the DFG structures have better energy absorption capacity than the SFG and UFT structures, especially with a convex gradient configuration. In addition, the specific energy absorption (SEA) values of these four DFG structures are fairly close to each other, while their loading responses highly depend on the combination of gradients. Of these DFG structures, Ascending–Ascending configuration exhibits best overall crashworthiness characteristics. Finally, parametric studies were performed and the results indicated that widening the ranges of foam density and tube wall thickness can improve the energy absorption of the Ascending–Ascending DFG structures without increasing the initial peak load. Therefore, the DFG structure of Ascending–Ascending gradient is recommended for a potential absorber. [ABSTRACT FROM AUTHOR]

This paper details the theory and implementation of a composite damage model, addressing damage within a ply (intralaminar) and delamination (interlaminar), for the simulation of crushing of laminated composite structures. It includes a more accurate determination of the characteristic length to achieve mesh objectivity in capturing intralaminar damage consisting of matrix cracking and fibre failure, a load-history dependent material response, an isotropic hardening nonlinear matrix response, as well as a more physically-based interactive matrix-dominated damage mechanism. The developed damage model requires a set of material parameters obtained from a combination of standard and non-standard material characterisation tests. The fidelity of the model mitigates the need to manipulate, or “calibrate”, the input data to achieve good agreement with experimental results. The intralaminar damage model was implemented as a VUMAT subroutine, and used in conjunction with an existing interlaminar damage model, in Abaqus/Explicit. This approach was validated through the simulation of the crushing of a cross-ply composite tube with a tulip-shaped trigger, loaded in uniaxial compression. Despite the complexity of the chosen geometry, excellent correlation was achieved with experimental results. [ABSTRACT FROM AUTHOR]

Composites in automotive structures show great promise to further improve vehicle crashworthiness. However, designing automotive structures for crash with advanced composite materials is challenging. The large amount of design parameters for laminated composites, the complex non-linear material behavior and the discontinuous design space in vehicle design, such for crashworthiness, are the main contributors to this challenge. In this paper, we propose a new design strategy to address this and integrate advanced laminated composite materials in automotive design for crashworthiness. First a computationally efficient physical surrogate is introduced to predict the structural validity of the design options and filter the design space. Secondly a method is introduced which uses Sobol decomposition to derive a design parameter importance hierarchy. Thirdly the physical surrogate is used to derive parameter bounds to increase robustness. A typical S-rail benchmark has been developed to confirm the usefulness of the proposed method. Finally the method provides for a reduced and robust design space which may help to decrease early development time. [ABSTRACT FROM AUTHOR]

In this paper, the plastic behavior of a clamped rectangular sandwich tube with metal foam core is studied by analytical and numerical methods. Using the yield criterion, the analytical solution for plastic behavior of a rectangular metal foam core sandwich tube under transverse loading is derived. The numerical calculation is conducted, analytical results are compared with numerical ones. Analytical and numerical results are verified by each other. Finally, the influences of the punch width, loading position, foam strength, and tube-wall thickness on large deflection of the sandwich tubes are discussed based on the analytical model. It is shown the load and plastic energy increase with the increase of punch width, the metal-foam strength and tube-wall thickness, loading position moving from the center to the sides. [ABSTRACT FROM AUTHOR]

• Discretely assembled composite self-locked energy absorption systems were proposed. • The effect of deformation mechanism on mechanical response of the tube was revealed. • The analytical solution of the crushing force of the tube was derived and verified. • The parametric study of multiple-tube system in dynamic condition was carried out. • The functionally graded design of the proposed systems was explored and summarized. Impact accidents cause great damage to lives and devices due to strong destructiveness and weak predictability, and accordingly, flexibility and modifiability are essential in the design of novel impact-resistant structures. To achieve this goal, two newly-designed energy absorption systems were proposed in this paper, which could be discretely assembled without boundary constraints. Quasi-static experiments and finite element method (FEM) simulations were carried out to reveal the deformation mechanism and test the usability, based on which the analytical solutions of the crushing force of the models were established adopting plastic hinge analysis and energy method. Parametric study of multiple-tube systems was conducted to reveal the effects of foam porosity and inner tube parameters on dynamic response, and the optimal design was summarized, achieving the energy absorption efficiency of 39%. The functionally graded design of composite self-locked (CSL) systems was explored, and it was proven that the system with positive stiffness gradient was optimal. [ABSTRACT FROM AUTHOR]