In-plane impact response of symmetrically embedded chiral honeycomb structures

Honeycomb sandwich structures have wide range of applications in the aircraft, automobile, and satellite sectors due to their superior properties such as high specific strength, stiffness, energy absorption, and high impact strength. In this study, mechanical characteristics such as compression, three-point bending, and in-plane impact properties of 3D woven honeycomb composites produced from Kevlar and glass fiber were investigated. The focus of this research is to compare the mechanical performance of woven honeycomb composites developed from these two fibers with similar cell structures. The results revealed that Kevlar fiber honeycomb composite shows higher peak load and energy absorption for flatwise and edgewise compression while in three-point bending and in-plane impact, glass fiber honeycomb composite shows higher peak load, and impact energy absorption. The deformations shown in all the mechanical properties give the ductile behavior for Kevlar fiber and brittle behavior for glass fiber composite. The findings of the study suggest that the failure modes are mostly determined by the nature of the material itself.

Thin-walled tubes are widely used as energy absorption devices in automobiles, designed to protect the costly structures and people inside during an impact event through plastic deformation. They show excellent performance under axial loading in terms of weight efficiency, stroke distance and total energy absorption, but also have the disadvantage that the crushing force is not uniform during deformation process, especially with the existence of a high initial peak force. Recently, pattern design on tubular structures has received increasing attention. It has been found that, if the surface of a tube is pre-folded according to an origami pattern, the collapse mode of the tube can be altered, leading to changes in energy absorption performance. In this paper, we present a series of origami patterned tubes with a kite-shape pattern that is constructed by joining two pieces of Miura-ori. First of all, the geometry of the pattern is presented. We develop a theoretical model to predict the energy absorption associated with the axial crushing of the patterned tubes and derive a mathematical formula to calculate the mean crushing force accordingly. Secondly, a family of origami tubes with various profiles are designed, and their performances subjected to quasi-static axial crushing are numerically investigated. A parametric study is also conducted to establish the relationship between the pre-folded angle of the pattern and the initial peak force as well as the mean crushing force. Numerical results show that introducing patterns to thin-walled tubes offers three advantages in comparison with conventional tubes, i.e., a lower initial peak force, a more uniform crushing load, and a stable and repeatable collapse mode. A 36.0% increase in specific energy absorption and 67.2% reduction in initial peak force is achieved in the optimum case. The new origami patterned tubes show great promise as energy absorption devices.

Thin-walled structures serve as energy-absorbing components in the automotive industry. This study proposes a novel double-section circular tube (DSCT) with dual-variable attributes consisting of outer and inner circular structures. The crashworthiness of DSCT is investigated. The existing experiment is employed to correlate the base DSCT computer model, followed by an investigation of the effect of changing length and diameter. Initial peak force (IPF), energy absorption (EA), specific energy absorption (SEA), and mean crushing force (MCF) serve as crashworthiness evaluation indicators. Results indicate that the DSCT with a short outer structure illustrates an 18.12% higher EA and MCF than the corresponding THST. Besides, the DSCT with a shorter inner structure demonstrates a superior EA, SEA, and MCF than the corresponding DSCT with a shorter outer structure. The DSCT, whose diameter of the inner structure is 70 mm, can be a superior energy absorption candidate for EA and MCF. The results provide reliable guidance for designing a novel bi-tubular device.

Carbon fibre composite tubes have high strength to weight ratios and outstanding performance under axial crushing. In this paper, square CFRP tubes and aluminium sheet-wrapped CFRP tubes were impacted by a drop mass to investigate the effect of loading velocity on the energy absorption of CFRP/aluminium tubes. A comparison of the quasi-static and dynamic crushing behaviours of tubes was made in terms of deformation mode, peak crushing force, mean crushing force, energy absorption and specific energy absorption. The influence of the number of aluminium layers that wrapped square CFRP tubes on the crushing performance of tubes under axial impact was also examined. Experimental results manifested similar deformation modes of tubes in both quasi-static and dynamic tests. The dynamic peak crushing force was higher than the quasi-static counterpart, while mean crushing force, energy absorption and specific energy absorption were lower in dynamic tests than those in quasi-static tests. The mean crushing force and energy absorption decreased with the crushing velocity and increased with the number of aluminium layers. The impact stroke (when the force starts to drop) decreased with the number of aluminium layers.

Most natural materials have rotational and hierarchical properties, so they can show excellent mechanical properties such as shear resistance and impact resistance. In order to further improve the energy absorption characteristics of vibration absorbing structures, a new type of honeycomb structure with integral rotation and group rotation is designed and characterized. The effects of the geometrical parameters of rotation Angle on the impact deformation mode, stress response curve and energy absorption characteristics of the honeycomb structure are studied through numerical simulation and experimental design. The results show that the overall honeycomb performance of 15° is better than that of 0°, the specific energy absorption is the results show that the overall honeycomb performance of 15° is better than that of 0°, the specific energy absorption is increased by 6%, the bearing capacity is increased by 320 N, and the crushing force efficiency is increased by 2%. Compared with the whole cell and the group cell, the specific absorption energy increased by 35%, 73% and 71%. The results of this paper provide a new insight into the impact performance of monolithic and grouped rotating honeycomb structures, which is helpful for the results of this paper provide a new insight into the impact performance of monolithic and grouped rotating honeycomb structures, which is helpful for the optimization of crashworthiness structural design.

Compression property and energy absorption capacity of 4D-printed deformable honeycomb structure

Introducing origami with outstanding flexibility into thin-walled tubes can enhance their energy absorption performance. This paper first proposes a cutting and folding-based design route of thin-walled origami tubes which enables geometry gradients such as uniform, tapered, hourglass-shaped, and ellipsoidal shapes. Subsequently, the finite element model of the proposed tube is established and verified through comparisons with experimental results. Numerical simulation results demonstrate that the quasi-static energy absorption capability of the graded thin-walled origami tubes is closely related to the folding angle, the total number of layers, and shapes. Compared with the conventional octagonal tubes (COT), the initial peak force in the proposed origami tube experiences a dramatic reduction, reaching a maximum decrement of 70.75%, while achieving a 39.96% boost in specific energy absorption (SEA). Moreover, the incorporation of gradient shapes within the origami tubes facilitates a more predictable and controlled collapse pattern, leading to an enhanced energy-absorbing efficiency than conventional uniform origami tubes. This study provides new insights into the design of thin-walled tubes that balance energy absorption and shape.

Crashworthiness unit cell design investigation for energy absorption analysis

A crash box design is developed to enhance the crash box’s abilities to absorb crash energy. Previous research has developed the crash box by adding filler material. Adding the filling material to the crash box will increase energy absorption. Aluminum honeycomb has a combination of lightweight mass and an ability to absorb crash energy. The addition of filler material to the crash box will also reduce the possibility of global bending in the crash box. The method of study is a computer simulation using ANSYS Academic software ver 18.1. This research used circular, square and hexagonal cross-section variations, which reached the same cross-sectional area design. Geometry model for the crash box and honeycomb filler is defined as crash box thickness (tc) 1.6 mm, honeycomb filler thickness (t) 0.5 mm for single layer and 1 mm for double layer and crash box length (l) 120 mm. The materials used were AA6063-T6 for crash boxes and AA3003 for honeycomb fillers. The test model consisted of two types, namely frontal load and oblique load test. The impactor velocity (v) is set to 15 m/s. The impactor and the fixed support are modeled as a rigid body, while the crash box is assumed as an elastic body. Observations were done by using the characteristics of deformation pattern and the absorption amount of produced energy due to the given loading model. Based on the deformation pattern results, it can be found that in the crash box model with square and hexagon honeycomb filler, the occurred deformation pattern was concertina, while the crash box with circular honeycomb filler was the mixed mode in the frontal load test. Regarding the oblique loads, the crash box remains to collapse the global bending on all models. Simulation results with the frontal load test model found that the crash box with circle-shaped honeycomb has the highest energy absorption while the crash box with hexagonal honeycomb filler has the highest Specific Energy Absorption (SEA). In the oblique load test, it was found that the crash box with hexagonal honeycomb filler has the highest energy absorption and SEA. By comparing the hexagonal crash box model with and without honeycomb filler, it is noted that the hexagonal crash box with honeycomb filler has higher Crash Force Efficiency

With advances in 3D printing technology, now honeycomb structures can be made with virtually unlimited unit cell geometries and cell arrangements giving a wide range of possible mechanical properties. However, studies on such structures have been mainly limited to the hexagonal honeycombs with little work done on other cell geometries. This paper investigates the effect of unit cell geometry on the in-plane compressive response and energy absorption behaviour of honeycombs using full-scale non-linear numerical simulations. Nine types of honeycombs are designed from different unit cell shapes, but having the same relative density. Finite element analysis is used to simulate the honeycombs’ behaviour under uniaxial compression loading. The results showed that unit cell geometry and cell arrangement affect the honeycombs’ compressive response significantly and provide different energy absorption characteristics. This comparison study shows that the honeycombs in which the deformation mode is dominated by bending of cell edges present a lower stiffness (effective modulus) and compressive strength, but a smoother plateau stress. The honeycombs having their deformation mode dominated by plastic buckling present a higher stiffness with less stable and undulated plateau stress. The results of this study provide more understanding in predicting the global behaviour of honeycomb structures and their energy absorption characteristic through their micro-topology. The effect of cell shape and its arrangement on the selection of honeycombs for energy absorption application is discussed and a methodology is proposed to balance the energy absorption with maximum transmitted stress, which is crucial for energy-absorbing design of structures.

The concept of both hierarchy and gradient are incorporated into thin-walled hexagonal tubes for a configuration with optimum crashworthiness and energy absorption. Graded hierarchical hexagonal (GHH) tubes are developed by replacing the corners of an original hexagonal tube with a series of micro hexagonal cells. The total net cross-sectional area as well as the mass are kept the same for all the GHH tubes. The axial crushing behavior of the GHH tubes is investigated in terms of deformation modes, crushing forces and energy absorption. Theoretical solutions are also derived to predict the mean crushing forces (MCFs) of the GHH tubes. Two deformation modes have been identified, a locally layer-by-layer folding deformation (Mode-L) and a globally buckling-like deformation (Mode-G). The hierarchical and graded parameters have significant but quite different influences on the crushing behavior of GHH tubes. The MCF and the specific energy absorption (SEA) can be significantly improved with reasonably hierarchical and graded arrangements, while the initial peak force (PF) remains almost constant.

Axial and lateral crushing responses of aluminum honeycombs filled with EPP foam

Thin-walled tubes are generally used as impact energy absorber in various application due to their ease of fabrication and installation, high energy absorption capacity and long stroke. However, the main drawback of plain tube is the high initial peak force. A concentric plunger in the form of tapered block is proposed to overcome this shortcoming while at the same time, improving the impact performance. Static and dynamic axial crushing were performed to determine the initial peak force (IPF), crush force efficiency (CFE) and specific energy absorption (SEA) for the concentric plunger with various taper angles. It was found that the concentric plunger affected the tube impact response. Comparison with plain circular tube was carried out and it was found that the concentric plunger improved the impact response of the tube especially in term of initial peak force.

The bipolar plate (BPP) is a crucial component of proton exchange membrane fuel cells (PEMFC). However, the weight of BPPs can account for around 80% of a PEMFC stack, posing a hindrance to the commercialization of PEMFCs. Therefore, the lightweight design of BPPs should be considered as a priority. Honeycomb sandwich structures meet some requirements for bipolar plates, such as high mechanical strength and lightweight. Animals and plants in nature provide many excellent structures with characteristics such as low density and high energy absorption capacity. In this work, inspired by the microstructures of the Cybister elytra, a novel bio-inspired vertical honeycomb sandwich (BVHS) structure was designed and manufactured by laser powder bed fusion (LPBF) for the application of lightweight BPPs. Compared with the conventional vertical honeycomb sandwich (CVHS) structure formed by LPBF under the same process parameters setting, the introduction of fractal thin walls enabled self-supporting and thus improved LPBF formability. In addition, the BVHS structure exhibited superior energy absorption (EA) capability and bending properties. It is worth noting that, compared with the CVHS structure, the specific energy absorption (SEA) and specific bending strength of the BVHS structure increased by 56.99% and 46.91%, respectively. Finite element analysis (FEA) was employed to study stress distributions in structures during bending and analyze the influence mechanism of the fractal feature on the mechanical properties of BVHS structures. The electrical conductivity of structures were also studied in this work, the BVHS structures were slightly lower than the CVHS structure. FEA was also conducted to analyze the current flow direction and current density distribution of BVHS structures under a constant voltage, illustrating the influence mechanism of fractal angles on electrical conductivity properties. Finally, in order to solve the problem of trapped powder inside the enclosed unit cells, a droplet-shaped powder outlet was designed for LPBF-processed components. The number of powder outlets was optimized based on bending properties. Results of this work could provide guidelines for the design of lightweight BPPs with high mechanical strength and high electrical conductivity.

Mechanical behavior of composited structure filled with tandem honeycombs