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The low-velocity impact properties and the optimal hybrid ratio range for improving the property of hybrid composites are studied, and the application of hybrid composites in automobile engine hoods is discussed in this paper. The low-velocity impact properties of the hybrid composite material are simulated under different stacking sequences and hybrid ratios by finite element simulation, and the accuracy of the finite element model (FEM) is verified through experiments. Increasing the proportion of carbon fiber (CF) in the hybrid layer and placing the basalt fiber (BF) on the compression side can improve the energy absorption capacity under low-velocity impact loads. CF/BF hybrid composite hoods are optimized based on the steel hood and the low-velocity impact performance of the hybrid composite. The BCCC layer absorbs the most energy under low-velocity impact loads. Compared with CFRP, the energy absorbed under 10 J and 20 J impact energy is increased by 26.1% and 14.2%, respectively. Through the low-velocity impact properties of hybrid composites, we found that placing BF on the side of the load and keep the ratio below 50%, while increasing the proportion of CF in the hybrid laminate can significantly improve the property of the hybrid laminate. The results show that the stiffness and modal properties of the hybrid composite can meet the design index requirements, and the pedestrian protection capability of the hood will also increase with the increase in the proportion of BF. [ABSTRACT FROM AUTHOR]

The oblique collision happening in vehicle accidents poses a huge threat to passive safety, which causes great difficulties in the design of energy absorption (EA) structures and the prediction of EA capacity due to its highly nonlinear deformation characteristics. This study aims to establish a theoretical prediction model for the compression performance of Carbon Fiber Reinforced Polymer (CFRP)/Al hybrid tube considering the loading angle. First, a high‐precision FE model was established to obtain the influence laws of tube diameter, Al thickness, and CFRP thickness on the crashworthiness of CFRP/Al hybrid tubes, laying the foundation for subsequent theoretical model validation. Second, by summarizing the deformation modes of hybrid tubes generated by various parameter combinations, a modified global origami deformation assumption was proposed under multi‐angle compression conditions, and the key terms in energy composition are extracted based on the initial and final states of folding elements. Third, a theoretical model for predicting the mean crushing forces (MCFs) of hybrid tubes was established by revealing the correlation mechanism between energy composition terms and loading angle. Finally, the theoretical prediction model was validated by experiment and simulation results and the application premise was given. Results showed that the theoretical prediction model was proved to be of high accuracy, as the average absolute prediction errors of MCF under axial, 10°, 20°, and 30° compression conditions were 6.54%, 4.63%, 3.72%, and 3.93%, respectively. This study provides valuable guidance for the forward design and development of multi‐material hybrid structures facing complex crushing conditions. Highlights: An analytical model of the hybrid circular tubes considering compression angle is newly proposed.Deformation mode and axial crushing response are analyzed by experiments.The major energy dissipation mechanism for hybrid circular tubes is explicitly derived.The Al thickness has the most significant impact on energy absorption.The recommendations for the design and development of hybrid tube are provided. [ABSTRACT FROM AUTHOR]

Facing serious environmental degradation and its resulting of climate warming, how to conserve energy and reduce emissions becomes a serious issue for government supervisors and modern vehicle enterprises. Reducing the mass of a vehicle is one of the most effective ways to reduce emissions and improve fuel utilization, essential to persist the low-carbon and sustainable-development bases in industrial production processes. When it comes to the selection of lightweight material for a car body in the processes of vehicle production, it is essential to comprehensively evaluate multiple relevant attributes in order to select the optimal material from several alternatives. Thus, it can be seen as a multicriterion decision-making (MCDM) problem. However, it is difficult to consider both the uncertainty of the expert's preference and the imprecision of the attribute estimate. Considering this, this paper uses the method integrating grey relational analysis (GRA) with analytic hierarchy process (AHP) to solve the problem of lightweight material selection for a car body. The AHP method is used to determine the weight of each attribute, and the GRA method is to select the optimal material among several alternatives. Finally, a case study is applied to verify the practicability of the proposed approach. The result shows that the proposed multicriterion decision method provides a precise and objective foundation for making decisions about the material selection issue. [ABSTRACT FROM AUTHOR]

• The influence law between IPCF and tubular parameters is clarified. • A universal multi-cell cross-section characterization scheme is proposed. • The mapping mechanism between IPCF and multi-cell configuration is revealed. • The generalization ability of the prediction model is validated. Accurately predicting the initial peak crushing force (IPCF) of the CFRP/metal hybrid structure is of great significance for the high-efficiency energy absorption of energy-absorbing elements and ordered deformation of combined energy-absorbing devices. Due to the significant differences in material properties between CFRP and metal and the high complexity of cross-sectional shape, a combined method of machine learning and mechanism analysis is proposed for predicting the IPCF of CFRP/Al hybrid energy-absorbing tube. First, a high-precision finite element model validated by the axial and oblique experiments is conducted to generate the dataset for predictive analysis. Second, a sample space through the design of experiment (DOE) is established for data fitting between structural parameters and IPCF based on traditional response surface model (RSM). It is found that traditional RSM method can successfully predict the IPCF of the single-cell hybrid tube, but cannot effectively predict the IPCF of the multi-cell tube due to the strong coupling effect between inner and outer plates. To address the issue of the lack of accurate correspondence between structural parameters and IPCFs in multi-cell hybrid tube, the indicator of relative density is proposed to characterize complex cross-sectional features. Surprisingly, there is a strong correlation between relative density and IPCF where multi-cell tubes with the same relative density have almost the same IPCF. Third, different artificial neural networks (ANN) are trained by a pre-simulated IPCF database of CFRP/Al hybrid energy-absorbing tube depending on the parameter characterization scheme based on mechanism analysis. In order to enhance the network's performance, the optimal configuration parameters of the neural network, including the number of layers and nodes, are ascertained through a combination of K-fold cross-validation and the Grid Search method. As a result, compared with the traditional RSM and Kriging model, the IPCF of CFRP/Al hybrid energy-absorbing tube can be predicted in small samples with high accuracy using the optimal ANN model. Finally, Through the comparative analysis of the IPCF of hybrid tubes with reported multi-cell configurations, it is found that the prediction model proposed in this paper has good generalization ability, which can be used to predict more complex types of multi-cell tube configurations. The present study offers important suggestions for the overall control of multi-materials hybrid energy-absorbing tube and the ordered deformation of combined energy-absorbing devices. [Display omitted] [ABSTRACT FROM AUTHOR]

• The material functional properties of multi-materials hybrid tube are described. • The bending instability mechanism of multi-cell hybrid tube is revealed. • The necessity of position gradient thickness winding is demonstrated. • A reasonable design strategy is given for variable thickness hybrid multi-cell tube. In order to fully utilize the energy absorption potential of hybrid structure composed of multiple materials, a variable thickness Carbon Fiber Reinforced Plastic/ aluminum (CFRP/Al) hybrid multi-cell tube is proposed, with a focus on the design strategies of variable thickness filament winding and multi-cell layout. First, based on the validated finite element (FE) model, a comparative study of different tube configurations is implemented to clarify the advantages and disadvantages of multi-cell hybrid tube. By analyzing the energy absorption contribution of two component materials and local structures, the bending instability mechanism of multi-cell hybrid tube at large angles is revealed to emphasize the necessity of variable thickness filament winding. It is found that multi-cell Al tube is the key factor to induce structural instability, and CFRP with positive gradient thickness distribution is beneficial to restrain the bending instability of hybrid multi-cell tube. Second, in order to better describe the influence mechanism of the design parameters, two comprehensive crashworthiness performance indicators for multi-angle compression conditions are proposed, namely comprehensive specific energy absorption and energy absorption stability. Then, a detailed parametric study is performed to explore the influence mechanism of the variable thickness winding parameters and multi-cell cross-section parameters on the comprehensive energy absorption capacity of the hybrid tube under multi-angle compression conditions. Finally, an application recommendation for the variable thickness CFRP/Al hybrid multi-cell tube is given to provide a reasonable design strategy. Furthermore, a comparative analysis of crashworthiness between the suggested CFRP/Al hybrid tube and reported typical energy-absorbing structures is carried out to reveal the superiority of the variable thickness CFRP/Al hybrid multi-cell tube in the energy absorption stability. This research provides valuable guidelines and suggestions for the crashworthiness design of multi-material hybrid structures facing complex loading conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

Three-dimensional in-plane progressive damage model was developed for carbon/basalt fibre interlayer hybrid composites in this study, and cohesive element model was employed to simulate interlaminar damage. Numerical simulation of low-velocity progressive impact damage of hybrid composite laminate was carried out, and its accuracy was verified by physical impact test, with the maximum error of the maximum contact force, maximum displacement and energy absorption not exceeding 6.1% and the maximum error in damage area size within 4.8%. The effects of lay-up structure and angle on the impact properties of hybrid laminate were investigated through simulation. Finally, real number coding strategy was proposed for the parametric representation of the lay-up material and angle of each layer. Multi-objective optimization of hybrid laminate based on Kriging surrogate model and hybrid algorithm composed of elitist non-dominated sorting genetic (NSGA2) algorithm and multi-objective particle swarm (MPSO) algorithm was conducted. The optimal trade-off solution was selected from the Pareto solutions using technique for ordering preferences by similarity to ideal solution (TOPSIS) coupled with principal component analysis (PCA) methods. The coefficient of variance between peak force and maximum displacement of the optimized laminate was 49.3%, 44.9% and 31.4% lower than those of the pure CFRP laminate, pure BFRP laminate, and hybrid laminate before optimization, respectively, indicating that the balance degree of impact displacement and force has been substantially improved. The progressive impact damage simulation and parametric optimization design methodology proposed in this study provide useful guidance for the design of hybrid composite laminate. [ABSTRACT FROM AUTHOR]

Poly(lactic acid) (PLA) is an emerging plastic that has insufficient properties (e.g., it is too brittle) for widespread commercial use. Previous research results have shown that the strength and toughness of basalt fiber reinforced PLA composites (PLA/BF) still need to be improved. To address this limitation, this study aimed to obtain an effective compatibilizer for PLA/BF. Melt-blending of poly(butylene adipate-co-terephthalate) (PBAT) with PLA in the presence of 4,4′-methylene diphenyl diisocyanate (MDI: 0.5 wt% of the total resin) afforded PLA/PBAT-MDI triblock copolymers. The triblock copolymers were melt-blended to improve the interfacial adhesion of PLA/BF and thus obtain excellent performance of the PLA-ternary polymers. This work presents the first investigation on the effects of PLA/PBAT-MDI triblock copolymers as compatibilizers for PLA/BF blends. The resultant mechanics, the morphology, interface, crystallinity, and thermal stability of the PLA-bio polymers were comprehensively examined via standard characterization techniques. The crystallinity of the PLA-ternary polymers was as high as 43.6%, 1.44× that of PLA/BF, and 163.5% higher than that of pure PLA. The stored energy of the PLA-ternary polymers reached 20,306.2 MPa, 5.5× than that of PLA/BF, and 18.6× of pure PLA. Moreover, the fatigue life of the PLA-ternary polymers was substantially improved, 5.85× than that of PLA/PBAT-MDI triblock copolymers. Thus, the PLA/PBAT-MDI triblock copolymers are compatibilizers that improve the mechanical properties of PLA/BF. [ABSTRACT FROM AUTHOR]

• A novel self-similar hierarchical honeycomb is proposed by adding smaller hexagons in the center and the vertex position of the hexagonal honeycomb. • The energy absorption mechanism of the proposed honeycomb is investigated by FEM, which is validated by theoretical results and experimental results. • Two typical plateau stress regions are found under quasi-static compression, and the second plateau stress is over three times higher than the first one. • The presented honeycomb is proved to absorb much more energy than the conventional HH and the vertex-based hierarchical structure with the same masses. In order to enhance the energy absorption capacity of the honeycomb structure, a novel self-similar hierarchical honeycomb is proposed by adding smaller hexagons in the center and the vertex position of the hexagonal honeycomb (HH), and therefore named as center-vertex honeycomb (CVH). An analytical model is built to investigate the in-plane crushing responses of the newly proposed honeycomb, which is in good agreement with the simulation and experimental results. The in-plane quasi-static compression characteristics and energy absorption capabilities of CVH are investigated systematically by finite element method and are compared with that of HH and other hierarchical honeycombs. Two plateau stress regions in the stress–strain curves of CVH are found under the quasi-static compression, and the second plateau stress is over three times higher than the first one. In order to understand the strengthening mechanism clearly, stable unicellular deformation and global modes are revealed. Two typical plateau stress are deduced theoretically based on the collapse modes to achieve performance prediction, which are respectively decided by the hexagonal structures located on both sides and the six vertexes of the representative unit cell. The results show that CVH can absorb much more energy than HH and the vertex-based hierarchical structure with the same masses under quasi-static compression. Furthermore, a parametric study is performed to explore the influence of the impact velocity, the order number, and the wall thickness on the plateau stress, specific energy absorption, and collapse deformation modes of CVH. It can be concluded that CVH is a better choice for energy absorption. The present study provides significant suggestions and guidance for the design-oriented multi-stage energy absorbing reinforced honeycomb structure with special functions. [Display omitted] [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of laser assisted treating metal surface on the strength of polymer-metal hybrid. The oxide film on the metal surface was removed by caustic soda and nitric acid solution. After that, the metal surface was treated by fiber laser, and the hot pressing connection between polymer and metal was completed by plate vulcanizing machine. And then, the tensile strength was obtained by using universal testing machine. The effect of different laser power, different scanning line width and different scanning speed on the bonding strength of polymer-metal hybrid was investigated. The correlation between the characteristics of metal surface and the bonding strength of polymer-metal hybrid was analyzed based on the micro structure morphology and scanning electron microscope (SEM). The results show that the bonding strength of polymer-metal hybrid increases first and then decreases with the increase of laser power. With the increase of scanning line width, the strength of polymer-metal hybrid increases. When the scanning speed is 500 mm/s, the strength of polymer-metal hybrid is the lowest. Based on the experiment, a simplified model is established and analyzed. Through using ABAQUS to conduct the numerical simulations, the results are consistent with the theoretical analysis and experimental data. [ABSTRACT FROM AUTHOR]

The effect of basalt fiber (BF) content on the properties of BF-reinforced polylactic acid (PLA) composites was investigated. Composites with 10, 20, 30, 40, 50, and 60 wt% BF were fabricated. The results revealed that (1) the mechanical properties improved with increasing BF content. The maximum tensile strength and modulus of the composites (i.e. 140 and 5050 MPa, respectively) occurred at a BF content of 50%. The maximum flexural strength, that is, 159.5 MPa was two times larger than that of the pure PLA and was obtained at a BF content of 40%. However, the mechanical properties deteriorated at BF contents >50%. (2) BF can stop storage modulus loss and are effective in improving the crystallinity, as revealed by dynamic mechanical analysis and differential scanning calorimetry measurements. The crystallinity improved from 34.6% to 54.6% with BF addition. (3) After the accelerated aging test, pure PLA was too weak for testing. However, high values of the tensile modulus (i.e. 60% that of the nonaged samples) were maintained by the BF-reinforced PLA. This resulted possibly from the high crystallinity of the PLA composites. Therefore, suitable amounts of BF as reinforcements can yield improvements in the performance of PLA composites. [ABSTRACT FROM AUTHOR]

• The novel structure with a bidirectional gradient distribution is proposed. • The longitudinal gradient design can increase the energy absorption. • The lateral gradient design can enhance the stability of crashworthiness. • Equal gradient layer design shows excellent energy absorption capacity. Oblique impact loading conditions strongly influence the crashworthiness of energy-absorbing structures. In the present work, inspired by the distribution characteristics of spider webs, a bidirectional gradient configuration of cell wall thickness was introduced to enhance the crashworthiness of lattice structures based on the functional similarity of longitudinal gradient distribution and lateral gradient distribution. A comparative study of different gradient configurations was carried out using the finite element (FE) simulations. It was found that the longitudinal gradient distribution was beneficial to improve the comprehensive energy absorption capacity of the lattice structure, especially under small-angle impact conditions. With the increase of impact angle, the effect of the lateral gradient distribution on the stability of energy absorption became more prominent. In comparison to the uniform structure and the single gradient structure, the lattice structure with the positive longitudinal gradient and the negative lateral gradient distribution exhibited great potential in enhancing the energy absorption capacity and reducing the peak crushing force. A detailed parametric study was executed to explore the effects of the gradient layer number and the gradient thickness increment of the bidirectional gradient distribution on the comprehensive energy absorption capacity and energy absorption stability of the structure under multi-angle impact conditions. The findings of this research provide valuable guidelines to design bio-inspired lattice structures subjected to complex loading conditions. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three kinds of bionic bamboo tubes (BBT) are introduced in this paper. • Explore the crashworthiness of different structural configurations under multi-angle compression loads. • Explore the effect of the cross-section feature and the gradient distribution feature on crashworthiness. • Reveal the superiority of BBT structure in energy absorption capacity for multiple load cases. A bamboo bio-inspired method is developed to enhance the energy absorption capacity of thin-walled tube for multiple load cases. Based on the simplified double-ring cross-section feature and the gradient distribution feature of bamboo knots, three kinds of bionic bamboo tubes (BBT-I, BBT-II, BBT-III) are introduced in this paper. A comparative study on the BBT-I, BBT-II, BBT-III, and hollow circle tube is performed to explore the crashworthiness of different structural configurations under multi-angle compression loads based on the validated simulation model. The corresponding prediction formulas of mechanical properties are deduced. The BBT structures show great potential in enhancing the specific energy absorption compared with the hollow tube, and the BBT-II and BBT-III structures show remarkable energy absorption effects under large-angle cases. A detailed parametric research is carried out to explore the effect of the cross-section feature and the gradient distribution feature on the specific energy absorption, peak crushing force, and collapse deformation patterns of BBTs. Furthermore, a crashworthiness comparison of BBT and typical multi-cell structures is carried out to reveal the superiority of BBT structure in energy absorption capacity for multiple load cases. This study provides valuable suggestions and guidelines for developing the bio-inspired multi-cell structure under multiple loading cases. [Display omitted] [ABSTRACT FROM AUTHOR]

• The representative unit cell (RVE) of CVH is divided into three sub-regions with independent thickness parameters according to the position of the hexagon. • The influence of different thickness distributions on the performance of CVH is investigated to explore the conditions for the emergence of dual-platform features. • Four key design parameters of the whole energy absorption process are extracted, which are derived theoretically based on the stable deformation modes. • A detailed parametric design strategy of the CVH specimen is proposed based on the theoretical analysis, which can regulate the energy absorption curve to the required range. The center-vertex honeycomb (CVH) structure based on the self-similar hierarchical evolution of the hexagonal honeycomb (HH) is introduced in this paper. The CVH structure has stable deformation modes, excellent energy absorption performance, and multi-platform features, and can be applied to multi-stage energy absorption devices with special requirements, such as energy-absorbing components of vehicles and trains. In this study, the multi-stage energy absorption characteristics of CVH under the in-plane quasi-static compression load are investigated numerically and theoretically, which is verified by the experimental test. The representative unit cell (RVE) of CVH is divided into three sub-regions with independent thickness parameters according to the position of the hexagon. The effects of different thickness distributions on the performance of CVH are investigated to explore the conditions for the emergence of dual-platform features. Then, the four key design parameters of the whole energy absorption process are extracted, which are derived theoretically based on the stable deformation modes. Further, a detailed parametric design strategy of the CVH specimen is proposed based on the specific engineering requirements. The design results proved that the proposed design strategy is reliable and accurate, which provides valuable suggestions and guidelines for the regulation of the energy absorption process of relevant structures for specific engineering needs. [Display omitted] [ABSTRACT FROM AUTHOR]