•Two types of new classes of hierarchical circular tubes (HCTs) are constructed.•Two deformation patterns are identified, which have different crushing behavior of the HCTs.•The mean crushing force ...and the specific energy absorption can be significantly improved by choosing suitable hierarchical configurations.•Partial hierarch performs better than the fully compacted one in improving the crashworthiness of the tubes.
In this numerical study by means of finite element modeling, the concept of hierarchy is incorporated into thin-walled circular tubes for a configuration with optimum energy absorption. Hierarchical circular tubes (HCTs) are constructed by replacing the wall of an initially single-cell circular tube (SCT) with a series of small tubes placed next to each other (Fully packed, HCT-F) or at a distance apart (partially packed, HCT-P); the total net cross-sectional area and hence the mass is kept the same. The behavior of these new classes of hierarchical tubes under axial crushing is investigated in terms of deformation modes, crushing forces and energy absorption. Two deformation modes are identified and they have different crushing behavior of the HCTs. The initial peak force (PF) remains almost constant after micro-cell tubes are hierarchically introduced, but the mean crushing force (MCF) and hence the specific energy absorption (SEA) can be significantly improved by choosing suitable configurations. It is also demonstrated that partial hierarchy performs better in enhancing the crushing performance of the tubes compared with the full hierarchy.
•A novel tube known as the kirigami crash box that is designed by kirigami approach, is proposed to improve the crashworthiness of the tubular structures.•The results indicate that the ideal ...extensional mode is successfully triggered with a 39.7% reduction of initial peak force and 33.9% increase of mean crushing force comparing to conventional square tube.•The superiority of energy absorption for kirigami crash box subjected to dynamic loading is more significant comparing to quasi-static axial crushing.
Thin-walled tubes are extensively employed as energy absorption devices. The extensional mode (EM) of collapse in thin-walled square tube is desirable in terms of energy absorption while facing impact loading. In this paper, a novel tube known as the kirigami crash box (KCB) that is designed by kirigami approach, is proposed to improve the crashworthiness of the tubular structures by collapsing in EM. The experimental and numerical results show that kirigami pattern in KCB serves as both geometric imperfection to reduce the initial peak force Fmax and mode inducer to trigger the desired EM while collapsing. Numerical simulation indicates that the ideal EM is successfully triggered with a 39.7% reduction of initial peak force Fmax and 33.9% increase of mean crushing force Fm comparing to conventional square tube (N-CST). Parametric study shows that the collapse mode of KCBs deformed in EM is independent of aspect ratio b/t within the range of b/t ≤ 81.3, while for CST, the corresponding range is b/t ≤ 7.5. KCB inclines to collapse in EM when the dihedral angle θ or the number of modules M decrease. The Fmax, Fm and CFEs of KCBs with identical M increase with the increasing θ. Whereas, the effect of M on energy absorption is relatively less important while θ remains the same. Moreover, the superiority of energy absorption for KCB subjected to dynamic loading is more significant comparing to quasi-static axial crushing.
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•A novel dual-sub-fold Miura foldcore is proposed by introducing sub-fold into the cell walls of conventional Miura foldcore.•The improvement in initial peak force and average force ...are demonstrated in novel Miura compared to the conventional Miura.•The novel Miura are found to exhibit a predictable and stable deformation mode for a wide range of geometric parameters.
A modified Miura foldcore geometry was developed by introducing sub-folds into the cell walls of a conventional Miura foldcore. Similar to other sub-fold Miura foldcores, stable plastic hinge lines were generated at sub-fold sites under the guidance of the sub-folds and transformed into traveling hinge lines or stationary hinge lines in the subsequent crushing process. Therefore, in comparison to the conventional foldcore, the dual-sub-fold Miura foldcore exhibited a higher average crushing force with an improvement of 60.8 % in the optimum case. The dual-sub-fold Miura foldcore exhibited relatively lower stiffness at the sub-fold sites, effectively reducing the initial peak crushing force. This reduction in peak crushing force reached a maximum decrease of 70 %. Moreover, this dual-sub-fold foldcore was glued to two parallel rigid plates (top and bottom), making it more suitable for engineering applications. The parametric study indicated that the dual-sub-fold Miura foldcore exhibited predictable and stable deformation modes. It was found that the average crushing force could be effectively enhanced by reducing the core folding angle, elevating the sub-fold position, decreasing the sub-fold size, and elongating the foldcore. The theoretical model for predicting the energy absorption performance of the foldcore was also established.
This paper aims to explore the failure modes and crashworthiness characteristics of double hat shaped tubes made of weave carbon fiber reinforced plastic (CFRP) subjected to quasi-static axial ...crushing and transverse bending. Experimental investigations were carried out into three different thicknesses of the composite tubes fabricated by the bladder molding process. Three distinct failure modes, classified as progressive end crushing (I), unstable local buckling (II) and mid-length collapse (III), were observed in the axial crushing tests, whereas only one similar progressive collapse mode was observed in transverse bending tests. It is shown that the thickness is a critical parameter affecting the failure mode and energy absorption capability, leading to the increase in the peak load and specific energy absorption (SEA) during the tests. The SEA of the tested double hat shaped tubes under axial crushing ranges from 60 to 90J/g, which is marginally higher than that of regular sectional CFRP tubes but over 2 times of that of conventional metallic tubes. By comparison, the load bearing and energy absorption capabilities of the tubes under transverse bending are much lower than those of the axially compressed tubes (less than 10% and 1%, respectively).
A novel thin-walled tube, named as origami crash box, is recognized as a promising energy absorption device. Experimental results reveal that unintentional imperfection could trigger the symmetric ...mode with low mean crushing force rather than a high-performance mode, known as complete diamond mode. Therefore, the imperfection-sensitivity of origami crash boxes is investigated in this paper. Appropriate geometric imperfection which is regarded as a substitution of the real defect is introduced into finite element models to trigger the symmetric mode. Numerical simulation shows that the specific energy absorption SEA declines with the increase in imperfection amplitudeAi. And a critical value of ratio Ai/t that is just able to trigger the symmetric mode is obtained. A detailed parametric analysis indicates that a suitable geometry is beneficial to improve the compliance of origami crash box, leading to stable collapse behavior with higher performance in terms of energy absorption. Moreover, a bulkhead reinforced origami crash box is proposed as a low imperfection-sensitivity energy absorption device. And an optimal wall thickness ratio t1/t is obtained through numerical analysis.
•Appropriate geometric imperfection could successfully trigger the symmetric mode.•SEA declines with the increase in imperfection amplitude.•Lower dihedral angle ϑ and higher ratio b/t improve the compliance of origami crash box.•A bulkhead reinforced tube is proposed as an imperfection insensitivity structure.
Carbon fiber reinforced polymers (CFRP) has been increasingly applied in automobile industry for vehicle body lightweight and safety performance improvement. However, design of CFRP components ...especially for crushing structures is still highly ambiguous. The present study aims to study the deformation behaviour and energy absorption of the hat shaped CFRP structures and optimize the section shape. Two types of hat shaped CFRP structures with various thicknesses and ply orientation were tested under axial quasi-static crushing. The results show that the Type II hat shaped structure presents a stable progressive crushing mode and better energy absorbing ability as compared with the Type I hat shaped structure. Then, a finite element model was developed using the multi-layer shell element method, and was validated by the axial crushing test results. Finally, the section shape of the Type II CFRP structure was optimized through the surrogate model of radial basis function and global response surface method, and the influences of the section shape on crushing behaviours and energy absorbing abilities were analysed.
•Propose a novel multicell structure with axially-varying thickness (AVT).•Conduct the quasi-static compression experimental test of AVT nine-cell and five-cell tubes.•Compare the crashworthiness of ...uniform thickness (UT) and AVT columns numerically.•Derive an analytical expression of the mean crushing force for AVT multicell tubes.
Multicell columns have becoming increasingly attractive in crashworthiness applications due to their high efficiency of material utilization. Meanwhile, an urgent need exists to develop new structures to achieve the aim of light weight without sacrificing crashworthiness. A novel multicell column with axially-varying thickness (AVT) is proposed in this study. Quasi-static crushing tests were firstly performed experimentally to investigate crushing behaviors. Subsequently, corresponding numerical simulation models were built, validated, and used to conduct a parametric study. Finally, analytical equations for the mean crushing force for AVT multicell columns were derived and used to assess the crashworthiness of multicell columns according to SFE (super folding element) method. The numerical results agreed well with experimental results in terms of deformation mode and crushing forces, and the theoretical predictions were validated by the experimental results. It was concluded that the thickness gradient of AVT multicell columns could effectively reduce the initial peak crushing force while maintaining energy absorption capacity over a long crushing distance. From this perspective, the AVT multicell columns demonstrated competitive advantages over uniform columns as energy absorbers. Moreover, the analytical prediction could be a powerful tool for designing crashworthy structures.
•Bionic design was introduced to increase the axial energy absorption for thin-walled tube inspired by bamboo structure.•The three types of bionic specimens were prepared by 3D printed and ...machined.•Bionic specimens under axial impact were tested by the drop weight test.•Eight of fourteen bionic specimens can increase the SEA compare with circular tube.•Bionic design provided a new guideline for the structural design of thin-walled tube.
We report an experimental study on three new types of tubes inspired by the cross-section and nodes of bamboo with the aim of improving the crashworthiness of three types of cylindrical metal tubes: Bionic Tubes of Variable Thickness (BTVTs), Bionic Tubes with Rib (BTRs), and Bionic Tubes with Bamboo Cross-section (BTBCs), respectively. The EA capacity and deformation modes of the bionic tubes and a cylindrical tube were experimentally investigated in this study by drop-weight test. The drop test results revealed that 8 of the 14 bionic specimens exhibited greater SEA than the CT. And these results indicate that the bionic method can improve crashworthiness and affect the deformation mode under certain conditions. Different bionic feature have different effects on the deformation of thin-walled tube. Further research is required to optimize the bionic cross-section, rib, and thickness for the new types of tubes.
•Multicellular structure and gradient thickness design were combined to achieve ideal energy absorption (IEA).•Multicellular tubes with different cell densities and material distribution principles ...were tested under axial compression.•High energy absorption performance of multicellular tubes with modified gradient thickness (MGT) was confirmed by experiment and simulation.•Its performance potential was further explored through parameter allocation.•Comparison of the structural efficiency of various energy absorbers revealed the MGT multicellular structure to be feasible to approach IEA with controllable cost.
Energy absorption of traditional tubular energy absorbers is restricted by the low structure efficiency, which makes the mean crushing force of the structure usually much lower than its yield strength. The combination of a multicellular design and a gradient-thickness strategy significantly improves the energy-absorption ability of thin-walled energy absorbers while reducing weight. Gradient-thickness multicellular tubes (GTMT) were studied in this paper to demonstrate this advantage. Mechanical performances of GTMT with two material-distribution principles, sample gradient thickness (SGT) and modified gradient thickness (MGT), were investigated experimentally and numerically, primarily in terms of folding behaviors, energy-absorption ability, and load-carrying capacity undulation. Wire-cut electrical discharge machining technology was used to create a series of aluminum alloy specimens that were then compressed under quasistatic loading conditions.
Following that, finite element method was used to run detailed numerical simulations. The effect of geometric configuration was determined after conducting parametric studies with different cell density and thickness gradient coefficients. The results showed that, compared to a traditional multicellular tube, a gradient-thickness one with MGT material distribution can improve structural efficiency with a stable loading history. Increases in cell density and thickness gradient coefficient have positive effects on energy-absorption ability; however, excessively high parameter values will lead to global bending deformation and weaken the mean crushing force. Therefore, reasonable parameter matching is vital. The result shows that when the cell density reached 9 × 9 and the thickness gradient coefficient reached 1.4, the mean crushing force was 98.16% of the full-plastic strength of the matrix, and there was no irregular deformation, indicating that ideal energy absorption is almost achieved. These achievements pave a way for achieving ideal energy absorption.
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Adopting multi-cell sections and composite wrapping are two effective approaches to improve the crashworthiness performance of thin-walled tubes. The axial crushing of single-cell and multi-cell ...aluminum/carbon fiber reinforced plastic (Al/CFRP) hybrid tubes is investigated in this paper. Quasi-static and dynamic experimental tests are performed for CFRP, Al and Al/CFRP tubes with single-cell, double-cell or quadruple-cell sections. The influences of Al wall thickness and the number of composite layers and sectional cells on the crushing response and energy absorption characteristics of the tubes are analyzed. Results show that the increase of all these factors can improve the load bearing and energy absorption capability of the tubes. The enhancement effect of composite wrapping for the Al/CFRP hybrid tubes is determined by the relative strength/weakness on the energy absorption efficiency of Al and CFRP. The interaction effect between the Al and CFRP on energy absorption of various sections is also investigated and the results show that the interaction effect decreases with the increase of the number of the sectional cells, while it is enhanced by increasing the number of CFRP layers.
