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• The paper investigates rib-based reinforcement strategies for improving structural integrity of form-found shell structures. • The study introduces diverse stiffening patterns for shell structures, designed with geometric, biomimetic, and optimization-derived methodologies. • The paper demonstrates through mechanical testing and numerical simulations that these patterns significantly improve stiffness and buckling resistance of form-found shells. • The study validates that integrating form-finding with targeted rib-based reinforcements can lead to sustainable and structurally resilient solutions. This paper investigates innovative approaches for enhancing the structural integrity of form-found shell structures with a focus on rib-based reinforcements. It discusses the significance of ribs in enhancing stability and addressing the sensitivity of form-found structures to various loads. Traditional methods such as increasing shell thickness or introducing supports often compromise efficiency and aesthetics. A more intelligent approach involves reinforcing the shell with ribs and advanced materials. Diverse rib patterns are presented, including geometric, biomimetic, and topological optimization-inspired designs, each adhering to a 50 % volume constraint, when compared to the original shell. Physical testing and numerical simulations demonstrate that these rib patterns significantly increase stiffness and buckling resistance. The findings presented in the paper suggest that combining form-finding methodologies with well-designed rib patterns can create sustainable and resilient structures, contributing to a reduction in both the consumption of materials and the environmental impact of these structures. [ABSTRACT FROM AUTHOR]

Thin films may experience wrinkling instability when two clamped ends are stretched uniaxially. For a fiber-reinforced anisotropic thin film, the wrinkling distributions and evolutions can be significantly affected by the fiber orientation and the anisotropic parameters. In this paper, we study the stretch-induced wrinkling of anisotropic thin films based on a uniformly-valid asymptotic plate equation for anisotropic materials derived from the three-dimensional field equations. A numerical model is established in COMSOL Multiphysics by virtue of the weak form of plate equations and by employing the Holzapfel–Gasser–Ogden model. The effects of fiber orientations and anisotropic parameters on wrinkling evolutions are unraveled from various case studies. In particular, we find that there exists a critical fiber orientation interval where the usual isola-center bifurcation will give way to the pitchfork bifurcation, and the associated amplitude against strain curve presents an N shape. A phase diagram for different bifurcation types is characterized as well. Our numerical model is validated by three-dimensional numerical simulations. It is expected that the results in this paper will offer useful insight into pattern formation in anisotropic soft materials. • The wrinkling responses of anisotropic parameters and fiber orientation are analyzed. • Stretch-induced wrinkling could be an N-shaped pitchfork bifurcation. • A phase diagram for different bifurcation types is provided. • The numerical model is validated by 3D numerical simulations. [ABSTRACT FROM AUTHOR]

• The effectiveness of thin-walled cellular beams manufactured by RFSSW was developed. • A parameterized finite element model (FEM) of the cellular beam was developed. • Results of numerical simulations and experimental tests were compared. • A parametric FEM model of the cellular beam was developed in the ADINA system. • The numerical model was used to analyze beams with different cross-sections. The paper presents analyses of thin-walled I-beams constructed from 6061-T6 aluminum alloy using refill friction stir spot welding (RFSSW). A parametrized finite element model of the reference cellular beam was developed, and the results from numerical simulations and experiments were compared. Subsequently, the validated numerical model was utilized to conduct an in-depth analysis of three additional beams featuring distinct cross-sections. To assess the weld behavior, experiments were conducted on samples composed of two sheets connected by two spot welds. The outcomes of these investigations underscore the suitability of RFSSW as a method for constructing thin-walled structures in civil engineering applications. [ABSTRACT FROM AUTHOR]

In this paper, we compare the failure behaviors of CFRP single and double (S–D) lap joints and analyze the effects of hygrothermal aging on these joints through a comprehensive experiment and simulation. Firstly, we analyze and compare the degradation pattern of the residual strength of S–D​ lap joints under three hygrothermal environments, and reveal the aging mechanism in conjunction with the macro/fine-view failure surfaces of the joints. Secondly, we elucidate the probability distribution of joint aging failure using the two-parameter Weibull distribution. Finally, we develop a finite element model to simulate the failure process of the cohesive behavior, and compare not only the bending moment and contact stress distribution of the two joints, but also analyze the damage condition of the CFRP matrix/fiber. We define environmental degradation factors to express the failure behavior of lap joints after aging. Through the above analysis methods, we find that hygrothermal aging can seriously damage the CFRP and adhesive properties. The mechanical performance of DLJs is significantly superior to that of SLJs, and they also exhibit better reliability. Therefore, DLJs can be substituted for SLJs in some application scenarios. Additionally, our paper provides new insights into the selection of an appropriate lap bonding method. • This paper evaluates the aging durability of single and double lap joints from multiple perspectives. • The failure behavior of single and double lap joints is comprehensively compared by numerical simulations. • This paper provides some new insights into the selection of an appropriate lap bonding method. [ABSTRACT FROM AUTHOR]

• Bio-inspired hierarchical multi-cell circular tubes with various numbers of ribs were developed. • The mean crushing force, energy absorption and specific energy absorption (SEA) of all three types of tubes proposed increase with wall thickness. • The hierarchical tubes with four ribs have the highest SEA at each hierarchical order. • Theoretically predicted mean crushing forces agree well with the corresponding simulated ones. Bio-inspired and hierarchical concepts are demonstrated to be effective in enhancing the compressive performance of tubes. The bio-inspired hierarchical multi-cell circular (BHMC) tubes with different numbers of ribs were investigated in this paper. The effects of hierarchical order, tube mass, the number of ribs, outer circle tube and inner structure with non-uniform thicknesses were explored. The results show that the SEA of BHMC tubes with four, five and six ribs (i.e. BHMC-R4, BHMC-R5 and BHMC-R6) is greater than that of conventional hollow circular tube with the same mass. The SEA of the third order of BHMC tube with four ribs (i.e. BHMC-R4–3) is approximately twice that of conventional hollow circular tube with the same mass. As the tube mass increases, the SEA of BHMC-R4, BHMC-R5 and BHMC-R6 tubes increases. Moreover, BHMC-R4 tubes with different hierarchical orders present the highest SEA among BHMC-R4, BHMC-R5 and BHMC-R6 tubes. In addition, theoretical models were proposed and their predictions of plateau forces aligned well with those obtained through numerical simulations. [ABSTRACT FROM AUTHOR]

• The lever-type IA mechanism is introduced in the sandwich plate for the first time. • The IA-MSP exhibits a lower bandgap compared with LR-type sandwich plate. • The effectiveness of the IA-MSP in attenuating low-frequency vibration is studied. • A simplified and intuitive formulation by using a factor of lever ratio is proposed. • The IA-MSP demonstrates remarkable performance in the realm of lightweight design. The utilization of sandwich plate structures is widespread across diverse engineering fields owing to their advantageous high stiffness-to-weight ratio properties. However, these lightweight and thin-walled structures commonly encounter challenges related to inadequate vibration performance in the low-frequency range, imposing significant limitations on their applications. This paper thereby presents a design for a metamaterial sandwich plate that incorporates lever-type inertial amplified resonators (IA-MSP) to achieve a low-frequency bandgap and effective vibration attenuation capability. The bandgap characteristics and vibration behavior of the IA-MSP are comprehensively studied through an integrated approach involving theoretical analysis, numerical simulations, and experimental studies. The dynamic model of the IA-MSP is mathematically formulated, theoretically elucidating the underlying inertial amplification mechanism within the proposed metamaterial sandwich plates. The investigation on vibration transmission is conducted to analyze the vibration attenuation performance of the IA-MSP, utilizing both numerical simulations and experimental methods. The findings reveal that lever-type resonators amplify the mass motion, thereby enhancing the effective mass of the system and leading to a reduction in the frequency associated with the coupled mode of the bandgap. This amplification facilitates the attainment of a low-frequency bandgap without the need for utilizing the inclusion of additional centralized mass or heavy local resonators. By altering the lever ratio R of the lever-type inertial amplified resonators, precise fine-tuning and optimization of the low-frequency bandgaps are achievable. Compared with traditional metamaterial sandwich plates with local resonators (LR-MSP) featuring identical geometrical and material characteristics, the proposed IA-MSP characterized by an R -value of 2 exhibits boundary frequencies that are half of those observed in the LR-MSP. With an increase in the lever ratio R of the IA-MSP, a noticeable trend emerges a decrease in the lower boundary frequency, accompanied by a corresponding shift of the bandgap towards lower frequencies. The present study's outcomes are anticipated to hold significant promise in the realm of sandwich plate design, with a specific focus on furnishing vibration attenuation capabilities at lower frequencies. [ABSTRACT FROM AUTHOR]

• The flexural buckling behaviour of austenitic stainless steel semi-oval hollow section columns was studied. • Twelve pin-ended column tests were conducted. • FE models were developed to validate against the test results and then adopted to conduct parametric studies. • The codified buckling curves were evaluated and led to an overall good level of design accuracy. Semi-oval hollow section is an innovative cross-section profile and consists of one semi-circular flange, one flat flange and two flat webs. While the semi-circular flange (exposed to fluid or wind) offers a low level of hydrodynamic or aerodynamic drag, the flat elements facilitate connections with other members. The flexural buckling behaviour and resistances of austenitic stainless steel semi-oval hollow section columns are investigated in this paper. An experimental programme was firstly conducted on two austenitic stainless steel semi-oval hollow sections, with six column specimens of varying member lengths adopted for each cross-section, and included tensile coupon tests, initial geometric imperfection measurements and pin-ended column tests. Both 'C'-shaped flexural buckling (with failure specimens bowing towards semi-circular flanges) and 'reverse C'-shaped flexural buckling (with failure specimens bowing towards flat flanges) were observed upon testing. The experimental programme was accompanied by a numerical modelling programme, with finite element models developed to simulate the test results and then adopted to conduct parametric studies to generate further numerical data. On the basis of the test and numerical data, the relevant buckling curves for austenitic stainless steel circular hollow section columns, as provided in the European code, American specification and Australian/New Zealand standard, were evaluated for their applicability to austenitic stainless steel semi-oval hollow section columns. The evaluation results generally revealed that the codified buckling curves led to overall accurate and consistent flexural buckling resistance predictions when used for austenitic stainless steel semi-oval hollow section columns. [ABSTRACT FROM AUTHOR]

• Proper quantification of joint rotational stiffness (JRS) of a flight intersection joint (FIJ) influences the dynamic characteristics of a flight vehicle. • JRS of an FIJ is often determined experimentally due to the lack of a right predictive model. • An analytical model is proposed to evaluate the JRS of a radial-type FIJ when subjected to an external bending moment. • Numerical analyses and experiments are performed on six different FIJ configurations. • JRS and moment-rotation behavior predicted by the proposed model are correlated with both experimental and numerical analyses. • Further, the effect of joint clearances on the behavior of FIJ is investigated through the present model. Joint rotational stiffness (JRS) of a flight intersection joint (FIJ) and its accurate quantification play an essential role in studying the dynamic modal characteristics of a flight vehicle. This JRS of a FIJ is mostly determined through elaborate experiments due to the non-availability of a reliable predictive model. Therefore, in this paper, an analytical model is proposed to evaluate JRS of a radial type FIJ when subjected to external bending moment. In this model, at first, the tensile and compressive part of the FIJ section is identified by determining the neutral axis position. The respective part's contributing stiffness is then estimated by employing a spring-mass model. Later, the JRS expression is derived from the moment equilibrium condition and expressed as a function of the stiffness of the tensile and compressive part and neutral axis position. Subsequently, finite element analysis (FEA) is conducted with different numbers of screws, followed by detailed experimental investigations. The proposed analytical model is validated with the results from FEA and experiments for different screw configurations of FIJ. Further, the proposed model is extended to account for the effect of joint clearances on the JRS and the corresponding moment-rotation characteristics of the FIJ. [Display omitted] [ABSTRACT FROM AUTHOR]

• A new modular building and its all-bolt internal sleeve connection joints are introduced. • The mechanical properties of the all-bolt internal sleeve joints are investigated by tests. • The FE model that can accurately simulate the joints' mechanical properties is established using a reasonable simulation technique. • The test-validated FE model carried out the parametric analysis of the all-bolt inner sleeve joints. • The properties of the gap and inner sleeves' properties are critical to the mechanical properties of the joints. In response to the contradiction between the insufficient number and unreasonable distribution of stadiums in cities and the increasing demand of people for fitness, the authors propose movable modular gymnasiums. This gymnasium takes advantage of the modular building, which can be quickly built, dismantled, and reassembled to fully utilize the temporary empty land in the city to meet the fitness demand of the people. However, the box modules bear a huge roof load, which puts higher demands on the performance of the modular units and their connecting joints. This study proposes a novel joint using an inner sleeve and bolted connections. The proposed connection uses an inner sleeve and bolts to connect the upper and lower columns of the modular unit to give it a higher bearing capacity. Bolts connect the lower unit's ceiling beam and the upper unit's floor beam to provide a better overall performance of the modular unit. The authors conducted experimental studies of 2 full-scale models and 24 finite-element parametric analyses. The results show that the welding quality determines the beam-ward bearing capacity of the joints, while it has little effect on the column-ward bearing capacity. In practical engineering, the authors suggest that the initial stiffness of the joints does not consider the contribution of the inner sleeve. The setting of stiffening ribs forces the inner sleeve to deform and force, improving the joints' mechanical properties, with the initial stiffness in the column direction increase of 25 %, the initial stiffness in the beam direction increase of 31 %, and a bearing capacity in the beam direction increase of 38 %. The design thickness of the inner sleeve and stiffening ribs should be close to the wall thickness of the modular beam and column. The results of this paper contribute to the development of fitness for the whole population and the expansion of the application of modular buildings. [Display omitted] [ABSTRACT FROM AUTHOR]

Aluminium alloy has recently become popular in New Zealand's construction sector as a sustainable building material. However, in roll-formed aluminium alloy (RFA) channel beams, particularly those having web holes, cripples at points of concentrated or localised loading. In this paper, end-two-flange (ETF) web crippling behaviour of RFA unlipped channels having web holes was investigated using experimental tests, numerical simulations and a deep learning model referred as deep belief network (DBN). A total of 1080 data points was generated to train the DBN, using a finite element (FE) model that was validated using 30 new experimental results reported in this paper. Compared to the test data, the DBN predictions were conservative by around 6%. Using the DBN predictions, a comprehensive parametric study was undertaken which used the validated FE model in order to explore the effects of hole size, hole location, section thickness, and bearing plate on the web crippling strength of RFA channels having web holes. Web crippling strengths obtained from the DBN, tests and finite element analysis (FEA) were utilised to evaluate the performance of current design specifications from the American Iron and Steel Institute (AISI), Australian/New Zealand Standards (AS/NZS 1664; AS/NZS 4600:2018) and Eurocode (CEN 2006, 2007). It is shown that the current design rules are not reliable to predict the web crippling strength of RFA unlipped channels with web holes. As a consequence of the parametric analysis, new web crippling strength and web crippling strength reduction factor formulae for perforated RFA unlipped channels were proposed. A reliability analysis was then conducted, which confirmed that the proposed equations are capable of predicting the ETF web crippling strength of perforated RFA unlipped channels. • ETF web crippling behaviour of roll-formed aluminium alloy channels was studied experimentally and numerically. • Finite element analysis was conducted and validated against test results. • A deep-learning model was developed to predict the web crippling strength. • A parametric study was conducted to investigate the effects of different parameters. • New design equations were proposed for web crippling strength of roll-formed aluminium alloy channels. [ABSTRACT FROM AUTHOR]

• The structural performance of G550 high strength CFS lipped channel section columns was studied. • 10 axial compression tests on G550 high strength CFS lipped channel section columns were conducted. • FE models were developed and validated against test results and then used to perform parametric studies. • The current design methods were evaluated for their applicability to G550 high strength CFS lipped channel section columns. This paper presents the experimental and numerical investigations into the structural performance and strengths of G550 high strength cold-formed steel (CFS) lipped channel section columns failing by interactive buckling. A testing program was first conducted, comprising material testing, measurements of initial local, distortional and global geometric imperfections and ten pin-ended column tests. The interaction between different buckling modes was observed and discussed for all the examined specimens upon testing. A numerical modeling program was subsequently performed, where numerical models were created and verified with reference to the test results and afterwards utilized to conduct parametric analysis to produce more numerical data over an extensive spectrum of cross-section geometries and effective member lengths. The effective width method (EWM) codified in the European code and direct strength method (DSM) specified in American and Australian standards were evaluated, based on the combined set of numerical and test data, for their suitability to G550 high strength CFS lipped channel section columns susceptible to interactive buckling. The evaluation results indicated that (i) the EWM yielded scattered and conservative ultimate strengths for columns with small and intermediate slenderness ratios, but relatively accurate results for those of large slenderness ratios and (ii) the DSM led to more consistent and accurate strength predictions for G550 high strength CFS lipped channel section columns failing by interactive buckling, though a number of strength predictions were on the unsafe side. [ABSTRACT FROM AUTHOR]

In order to facilitate the replacement of damaged components and prevent the weak-story mechanism of frame structure after strong earthquakes, a novel assembled self-centering buckling-restrained brace (ASC-BRB) is proposed in this paper. The proposed bracing system is comprised of the buckling-restrained brace (BRB) system and the self-centering (SC) system. The SC system consists of two sets of steel strands and one group of disc springs stacked in series to achieve the goal of large deformability and post-hardening behavior. The detailed configuration, fundamental working mechanism, and restoring force model of the ASC-BRB are first presented. Different from SC systems with bilinear elastic behavior of existing SC-BRBs, the SC system of ASC-BRB exhibits trilinear elastic behavior due to its special configuration. Then, quasi-static tests are conducted to validate the effectiveness of the proposed ASC-BRB. The experimental results indicate that the ASC-BRB has a flag-shaped hysteretic response with excellent self-centering capability, stable energy dissipation capability, and appreciable deformation capacity with a maximum ductility coefficient of 25.58. More importantly, the specimen can exhibit the anticipated post-hardening behavior. The refined numerical model of ASC-BRB is established and verified by the experimental results, which can effectively analyze the mechanical behavior of the main components of ASC-BRB, making up for the deficiency of the tests. According to the problems discovered in the tests and numerical analyses, an improved configuration of the ASC-BRB is proposed and validated by the numerical simulation of the BRB system before and after improvement. The numerical results indicate that the improved BRB system exhibits more stable hysteretic behavior, and the stress levels of the inner and outer tubes become much lower after replacing 1-shaped cores with steel angle cores. • An innovative assembled self-centering buckling restrained brace (ASC-BRB) with high post-yield stiffness was proposed. • Experimental results indicated that the proposed ASC-BRB exhibited stable hysteretic behavior, appreciable self-centering capability, large deformability, and prominent post-hardening behavior. • The theoretical restoring force model of the ASC-BRB coincided well with the experimental hysteretic curve. • The refined numerical model could effectively analyze the mechanical behavior of the main components of the ASC-BRB. • An improved configuration of the ASC-BRB was proposed and validated by the numerical simulation. [ABSTRACT FROM AUTHOR]

When materials are in tension or in compression, their mechanical properties are essentially different, however, in existing studies it is generally ignored because of the complexity of the analysis. In this paper, a theoretical study of the problem of axisymmetric large deformation of thin shallow shells with different moduli in tension and compression (bimodular thin shallow shells) under uniformly vertical loading is presented. Based on the Föppl–von Kármán equations of flexible thin plates, the governing equation of the axisymmetric large deformation of bimodular thin shallow shells are established by introducing an appropriate curvature modification term from thin shallow shells and a bending stiffness term from bimodular plates. By selecting the central deflection as a perturbation parameter, the perturbation solution of the axisymmetric large deformation problem is derived using the perturbation method. The applications of variation method as well as the implementation of numerical simulation verify, from the theoretical and numerical perspectives, the correctness of the perturbation solution obtained. This study shows that the introduction of different moduli in tension and compression not only affects the relationship of loads vs. central deflection, but also affects the critical values of the rise-thickness ratio of bimodular thin shallow shells when the snapping phenomenon occurs. In particular, the bimodular effect may accelerate or slow down the occurrence of the snapping phenomenon of thin shallow spherical shells, according to the relative magnitude of tensile and compressive moduli. The work presented here will be helpful to analyze the mechanical response of heavily loaded thin shallow shells with obvious bimodular effect. • A set of governing equation for bimodular thin shallow shells is first established. • The perturbation method is first used to solve the governing equations. • The variation method and numerical simulation validate the perturbation solution. • The bimodular effect will influence the relationship of loads vs. central deflection. • The bimodular effect will accelerate or slow down the snapping phenomenon. [ABSTRACT FROM AUTHOR]

Prismatic or conical frusta are used as crash boxes, absorbing the energy of impact loads in collision, due to their advantages in comparison with circular or parallelepiped tubes (decrease of peak crushing force and stabilization of crushing process). The paper presents results of experimental research into crashworthiness performance and energy absorption effectiveness of thin-walled prismatic frusta of square base, produced from two face to face steel channel sections, joint using the riveting technique. Hollow and filled with polypropylene foam specimens were tested on drop hammer tower. On the basis of impact tests load–deformation characteristics were determined, represented by load-shortening diagrams. Selected crashworthiness indicators (Peak Crushing Force, Crash Load Efficiency, Stroke Efficiency and Total Efficiency) were calculated. Experimental load-shortening diagrams and experimental values of crashworthiness indicators were compared with the results of numerical FE simulations. Validation of the FE model was performed, which was the main objective of the study. FE model and results of the parametric analysis into energy absorption effectiveness of examined frusta was presented in Part 1 of this study: Crashworthiness performance of thin-walled hollow and foam-filled prismatic frusta — FEM parametric study. [ABSTRACT FROM AUTHOR]

Multi-cell tube have been proven to have better energy absorption performance than conventional thin-walled tube. The mean crushing load and wavelength of multi-cell tube were investigated in this paper. Numerical simulation was carried out firstly and the numerical values of mean crushing loads were employed to validate two existing theories. The numerical wavelengths of walls in multi-cell tube were compared with natural wavelengths and good agreement was achieved. A theory aimed at predicting the mean crushing load of uniform and non-uniform multi-cell tube was developed and verified to have high prediction accuracy. • Comparison between two existing theories which aim to predict the mean crushing load of multi-cell tube is carried out. • A concept of "natural wavelength" is proposed. • The wavelengths of walls in a multi-cell tube are proven to be very close to their natural wavelengths. • A theoretical method to predict the mean crushing load of uniform, especially non-uniform multi-cell tube is developed. [ABSTRACT FROM AUTHOR]

Hierarchical structures and gradient structures have become research hotspots due to their excellent crashworthiness. However, hierarchical gradient structures that combine hierarchical structures and gradient structures are rarely reported. Inspired by the gradient distribution of biological structure vascular bundles and the excellent energy absorption capacity of hierarchical structures, this paper innovatively combines hierarchical structures and gradient structures to propose a new type of bioinspired hierarchical gradient multicell tube (BHGMT). Crashworthiness studies have shown that the high-order BHGMT has a much better crashworthiness than the low-order BHGMT. The specific energy absorption of the 4th order BHGMT under the same mass is 216.26% that of the 0th order BHGMT. A comparison with other existing hierarchical structures under the same mass conditions shows that the proposed hierarchical gradient structure also has better crashworthiness. Subsequently, the systematic development of the influence of structural parameters such as hierarchy, section thickness, and crisscross rib thickness on the parameterization of BHGMT was carried out. Finally, theoretical research on the mean crushing force of the 3rd order BHGMT was carried out, and the theoretical solution was shown to be in agreement with the numerical simulation results. • Bioinspired hierarchical gradient multicell tubes are proposed to enhance crashworthiness. • Introduction of hierarchical gradients can effectively improve various crashworthiness indicators. • The influence of different crisscross ribs thickness on crashworthiness is studied. • A theoretical model is proposed to predict the mean crushing force of bioinspired hierarchical gradient multicell tubes. [ABSTRACT FROM AUTHOR]

Beetle elytron plate (BEP) is a new type of sandwich structure inspired by the internal architecture of beetle elytra and characterised by trabeculae in the core to achieve higher load bearing capacity compared to the basic conventional honeycomb sandwich plate. This paper investigates elastic–plastic buckling behaviour of the compressive skin of BEP with flexible core. The development is based on adapting existing solutions for relevant structures through the following three transformation steps: (1) obtaining the elastic–plastic buckling stresses of BEP with simple and fixed supports by extending respective solutions for conventional sandwich plate; (2) modifying the elastic buckling stress solution for conventional sandwich plate with flexible core to BEP with flexible core through replacement of deformation shape functions; (3) assuming that the interpolation function between simple and fixed supports for BEP with flexible core for elastic buckling stresses is applicable to elastic–plastic buckling stresses. Despite complexity of the problem and simplification in the above mentioned transformation steps, the proposed analytical method is shown to be quite accurate by comparison against numerical simulation results using a validated ABAQUS model for a variety of BEP geometries (such as trabecular diameter, slenderness values of the compressive skin and the core layer) and different material properties as represented by Ramberg–Osgood model covering the entire spectrum of elastic buckling to plastic behaviour, with the maximum difference between the proposed analytical model and numerical simulation results being 7%. • Extension from elastic to elastic-plastic buckling load of beetle elytron plate (BEP) with simple & fixed supports. • New analytical method for elastic-plastic buckling load of the compressive skin of BEP with flexible trabecular core. • Validation of new analytical methods by validated numerical models. [ABSTRACT FROM AUTHOR]

This paper presents a novel chiral column to enhance the crashworthiness of the multicell energy absorber. The crashworthiness of the chiral column is conducted by experimental investigation, numerical simulation and theoretical analysis. Firstly, quasi-static crushing tests of three chiral columns are performed, and the anti-tetrachiral column (ATC) has more outstanding energy absorption (EA) than the standalone structure. In addition, the connection type of the ATC is investigated by numerical simulation. Results indicate that the ATC with connection has the best EA and crushing force efficiency. Furthermore, the parametric analysis is carried out to investigate the influence of node diameter D , node center distance L and wall thickness t on the crashworthiness. It is found that the increase of D increases the PCF of the ATC, but L has little effect on the PCF. In addition, the wall thickness t i of internal chiral structure has a greater effect on crashworthiness than the wall thickness t o of external square tube. Lastly, an equivalent replacement method is used to theoretically predict the membrane energy, and the theoretical model of the mean crushing force is efficiently obtained by Simplified Super Folding Element. • Chiral column is proposed to enhance the crashworthiness of energy absorbers. • The synergistic behavior between the internal chiral column and the square tube promotes the energy absorption. • The node diameter has a critical effect on the deformation and energy absorption of chiral column. • The equivalent replacement method can well predict the membrane energy of the internal chiral structure. [ABSTRACT FROM AUTHOR]

This paper aims to assess the effect of dent defects on the collapse pressure of sandwich pipes under external pressure. A new pipe-making process is proposed, and its ability to resist external loads is investigated. The result shows that the collapse pressure of the sandwich pipe is 76.46%–99.95% higher than that of a single-wall pipe in the same dent defect, and the buckling propagation pressure is 100% higher than the sum of the inner and outer pipes. Otherwise, the influence of the dent on the sandwich pipe is weakened. The pipe consists of two steel pipes and a polypropylene pipe bonded together by one-millimetre thick epoxy resin to form a sandwich pipe. Seven specimens with varying degrees of defects were investigated to obtain their collapse pressure, where four specimens are sandwich pipes. Additionally, a numerical model was established and validated, and systematic parametric studies were carried out to supplement the test results. The experimental and numerical results show that the collapse pressure of the sandwich pipe is significantly influenced by the dent defect. Based on the parametric study, the main parameters that affect the collapse pressure of sandwich pipes are obtained. The relationship between the collapse pressure and the geometry of the sandwich pipes was analysed. The research shows that dent defects have a significant effect on the collapse pressure of sandwich pipes and that reducing the thickness-to-ratio of the inner pipe and the friction between layers is an effective method to improve the collapse pressure of defective sandwich pipes. • A new manufacturing method for the sandwich pipe is proposed and the polypropylene pipe is chosen as the core layer. • 7 collapse tests of pipes subjected to external pressure have been carried out. • The effect of dent defects on the collapse pressure of sandwich pipe under external pressure was experimentally investigated. • The difference of the cross-section and collapse and buckling propagation of the sandwich pipe are analysed. • A numerical simulation method was proposed. [ABSTRACT FROM AUTHOR]

Fuel tanks, as core fuel components of many types of mechanical equipment, are highly vulnerable to strong dynamic loads, such as those from explosions and fragments. In this paper, two types of polyurea materials (AMMT-53 and AMMT-55) were designed to enhance the damage resistance of fuel tanks. The mechanical parameters and performance differences of the two polyurea materials were first obtained. On this basis, a series of experiments study on fuel tanks coated with different thicknesses polyurea subjected to a combination of blast waves and fragments were performed. The results showed that these two types of polyurea materials had different protective abilities. The AMMT-53 polyurea could effectively reduce the perforation rate but could not prevent the liquid leakage, while the AMMT-55 polyurea could not significantly reduce the perforation rate, but the self-healing property could effectively prevent the leakage of liquid. The whole process of the shock wave and the fragments acting on the fuel tank was revealed by numerical simulations. From the change of the fragment velocity, the strength of the shock wave in the liquid, and the energy change of the polyurea layer, it was proven that the coated polyurea layers had good protective effects on the fuel tank. • Two types of polyurea with different material properties were characterized. • The experiment of polyurea coated fuel tank under impact was carried out. • Four typical damage degrees of polyurea coated fuel tank were obtained. • The energy absorption mechanism of polyurea coated fuel tank was revealed. [ABSTRACT FROM AUTHOR]