Crashworthiness unit cell design investigation for energy absorption analysis

Effect of metal foam with two-dimensional porosity gradient on melting behavior in a rectangular cavity

Forced convective heat transfer performance of foam-like structures – comparison of the Weaire-Phelan and the Kelvin structures with real metal foam

Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)

Open-cell metal foams have been investigated extensively as a potential heat exchanger in many applications due to their unique microstructures, made of interconnected pore-ligament constructions. Many studies have proved their excellent heat transfer performances. However, excessive pressure drop becomes one of its major drawbacks. In addition, fluid flow structures induced by the metal foam are always associated with various instabilities. For established thermohydraulics properties of the metal foam heat exchangers in clean and fouled conditions, more experimental works are called for. Until recently, the fouled condition has received relatively little attention among researchers. It is understandable as there are still many unsolved issues in the clean condition due to various geometrical considerations such as annulus pipe, duct, baffle, porous sandwich, including the trade-off analyses between pressure drop and thermal performances for both fully and partially filled configurations at different operating conditions.This present study conducted a series of experiments to investigate the thermohydraulic properties of (1) a metal foam-filled annulus and (2) a partially filled channel with metal foam. The latter configuration was also subjected to a fouled condition to gain insight of underlying mechanisms of particle transport and deposition processes in the metal foam structure. The experiments were conducted using Particle Image Velocimetry (PIV), Laser Doppler Anemometry (LDA), Hot-Wire Anemometry (HWA), Phantom high-speed camera and infrared radiation (IR) camera, depending on the experimental purposes. The PIV measurement provides instantaneous whole flow-field velocity, and the LDA and HWA offer local flow velocity in non-porous regions. The investigation of flow behaviours inside the porous structure of the metal foam was conducted based on the temperature distributions from the IR images. Meanwhile, in-situ observation of particles movement and deposition was performed using the high-speed camera, where the particle trajectories in a region of interest (ROI) could be determined.The result shows that the pressure drop of the metal foam-filled annulus is increasing with the airflow rates (20, 85, and 150 SLPM) and foam length. However, a significant amount of heat transfer takes place only in the first half of the foam, suggesting a need for an effective length for this kind of metal foam heat exchanger. For a certain case, for example, 20 PPI at 20 SLPM, a longer metal foam than 0.05 to 0.06 m would be unnecessary since it will only increase the pressure drop. The temperature distributions inside the porous structure are non-linear with a developed flow could be only seen at the lower half of the annulus of 20 PPI at 150 SLPM.For the partially filled channel, a part of the incoming airflows would enter the porous structure of the metal foam block, while the rest is going into the free stream region (a non-porous region that located on the top of the foam block). The free stream velocity is increasing with the blockage ratio (a ratio of foam height to channel height) and a formation of recirculation zone could be seen at the downstream region of a high enough blockage ratio. Interestingly, this phenomenon did not occur with the low pore density, e.g., 10 PPI foam but the 30 PPI foam and solid block. The flow inside the foam block also tends to leave into the free stream region through the fluid/foam interface for a certain foam length, pore density and blockage ratio. While the pressure drop is expected to be increased with the pore density in a fully filled channel, it is not necessarily always true for the partially filled channel. The fluctuating velocity and changes of the flow direction at the interface, as well as the formation of a recirculation zone would affect the total pressure drop and resistance coefficient.Furthermore, the metal foam causes a higher pressure drop than the solid block of the same size, indicating the substantial effects of porous structure on the total pressure drop. Our proposed friction factor model for the partially filled channel agrees with the experimental data with ±16% deviation. The result from the fouling experiment shows that the particle size has a significant influence on the particle transport and deposition processes. The large particles tend to keep their inertia, while the fine particles would follow the fluid streamlines. For the high blockage ratio, more particles tend to deposit on the frontal area of the foam block and the deposition is building up in the upstream region. When the blockage ratio is low, more deposited particles could be observed on the top surface of the foam block. As expected, the deposition causes an increase in the pressure drop performance. However, fluctuated pressure drop values could be seen at the beginning of the fouling process before reaching a similar value over time, regardless of pore density.

In view of the deficiency of the existing research on the energy absorption characteristics of composite multi-cell structures, a kind of multicellular filling structure (MFS) was proposed, which was filled by some single small-size CFRP tubes (SCT) into large-size CFRP tubes. The quasi-static compression tests of SCT and MFS were carried out, which included full stroke compression and multi-staged compression, then the failure mode and energy absorption characteristics were analyzed. The results show that the failure mode of the outermost CFRP tube of MFS is similar to SCTs, and there is no obvious difference between full stroke compression and multi-staged compression, but the radial deformation of the outermost tube is obvious due to the compression of the inner tube and debris. Compared with the full stroke compression process, the total energy absorption of SCT and MFS is more when they are multi-staged compressed. In this study, the maximum specific energy absorption (SEA) of SCT is 86.0 J/g and the minimum SEA is 59.3 J/g. While, due to the low SEA of the outermost tube of filled structures, the SEA of the MFS is between 69.8 J/g and 75.9 J/g, which is less than the maximum SEA of SCT. The SEA of the MFS is higher than that of SCT with appropriate external constraint and internal carbon tube number by further research.

Thin-wall columns or tubular beams play an important role on passenger safety in frontal and real collisions by absorbing crushing energy of a vehicle. A tubular beam with a large specific energy (the ratio of energy absorption to mass) and a large crushing force is the most desirable for its better safety performance and less weight. Due to the complexity of crash, obtaining such designs has been a challenge to the trial-and-error approach using physical experiments. To this end, finite element simulation combined with optimization methodologies has provided a viable means to meet the challenge. In this study, the singlecell hexagonal columns filled with aluminum foams are optimized for crashworthiness (maximum specific energy absorption) with respect to section geometries, tube thickness, and foam densities. Existing literature shows that the interaction between aluminum foam and a tube structure causes the combined structure to have more energy absorption than that if both are separated. It was also observed from experiments that the stress-strain behaviors of aluminum foams depend on their densities. To this end, the best tube design is obtained by simultaneously designing the tube structure and selecting foam densities. The optimization work is performed using the object-oriented optimization framework HiPPO, with the aid of metamodeling and finite element crash simulations.

Effect of foam geometry on heat absorption characteristics of PCM-metal foam composite thermal energy storage systems

Lattice structures and thin-walled tubes are two types of energy-absorbers widely studied and applied in engineering practice. In this study, a new type of lattice-structure filled thin-walled tube (LFT) was proposed by combining these two energy absorbers and designed via a new explainable data mining method. In this new type of LFT, a BCC-Z (Body- centred cubic unit cell with vertical struts) lattice structure was filled into a square thin-walled tube. Then, the new LFT was parameterized by five design variables, that is, the number of layers in the longitudinal direction (n), number of cells in the transverse direction (m), rod diameter (d), tube thickness (t) and height difference between tube and lattice structures (h). Using Latin hypercubic sampling algorithm, 150 design cases were generated. Numerical models were then developed to simulate their crush behavior, and the simulation dataset was used for data mining. The results showed that (1) Filling the BBC-Z lattice structure into a thin-walled tube can significantly improve the energy absorption (EA) capacity of the structure. (2) SEA (Specific Energy Absorption) of LFT significantly increased by increasing the rod diameter d, number of cells in the transverse direction m and number of layers in longitudinal direction n. (3) The decision trees generated in the data mining process indicated that the rod diameter d of the lattice structure is the key design variable that has most significant impact on EA, followed by m and n. (4) The design rules to build LFTs with high EA efficiency (SEA ≥ 16 kJ/kg and CFE (Crush Force Efficiency)≥45%), high total EA (SEA ≥ 16 kJ/kg and EA ≥ 6 kJ) and lightweight (SEA ≥ 16 kJ/kg and Mass ≤ 0.45 kg) were obtained from decision trees. The ideal configurations of LFT corresponding to these three objectives are: d > 2 mm, n > 2 and m > 3 for high EA efficiency; d > 2 mm, n > 2 and m > 3 for high total EA; and d > 2 mm, n > 2, m ≤ 4 and t ≤ 1.7 mm for lightweight.

Different failure modes occur in textile‐reinforced composite under applied loads. Fracture mechanism of braided composites are closely related to the geometry of braids. In the present study, fracture mechanism of glass/epoxy braided composite cylinders is investigated under tensile loads. For this purpose, glass/epoxy braided composites were fabricated using braids with braiding angles of 30°, 45°, and 57° to find the role of fiber path on the fracture mechanism. To determine the fiber path, helixes on the cylinders with aforementioned angles was considered and analyzed. New fixtures (jaws) were designed and manufactured for tensile testing of cylindrical composites. Tensile tests were carried out on the prepared samples to evaluate the failure modes of composites. The SEM micrographs of samples are provided after tensile test. Various failure modes were observed regarding the angle of the braid. Fiber breakage, matrix fracture, and debonding are the dominant modes that occur in braided composites proportional to the angle of braids. Fiber breakage is the dominant mode in the 30° angle braid reinforced composite, while the dominant failure mode in the 57° angle braid reinforced composite is matrix fracture. In composites with a braid angle of 45°, a combination of fracture modes occurred. In addition, energy absorption as well as specific energy absorption (SEA) of braided composite cylinders were also investigated and obtained from load–displacement curves. The results showed that the reinforced composite with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.Highlights Fiber breakage is the dominant mode at the 30° angle braid reinforced composite. The dominant failure mode at the 57° angle braid reinforced composite is matrix fracture. In composites with the braid angle of 45°, a combination of fracture modes occurred. The composite reinforced with a braid angle of 30° absorbs the lowest amount of energy (21.5 J) and also the lowest amount of specific energy (5375 J/kg). The maximum absorbed energy (67.7 J) and the maximum SEA (9675 J/kg) were observed in the reinforced composite with a braid angle of 45°.

Honeycomb structures have garnered significant attention from researchers due to their lightweight characteristics and excellent energy absorption capabilities. This article presents the concept of an embedded symmetric chiral honeycomb (ESCH), which is developed based on a symmetric chiral honeycomb (SCH). The design rationale for this structure involves filling the symmetric chiral honeycomb with a chiral configuration in order to create a centrally embedded chiral honeycomb. To investigate the energy absorption and deformation behavior of the proposed honeycomb structure, we employed the commercial software Abaqus/Explicit for numerical simulations. To ensure the accuracy of the finite element model, we first fabricated corresponding honeycomb samples using 3D printing technology and subsequently validated the finite element model’s accuracy through quasi-static tests. The results of the numerical simulations indicate that the ESCH exhibits superior load-carrying capacity and energy absorption performance compared to the SCH. For identical mass conditions, the specific energy absorption and average stress of the ESCH are found to be 49.6% greater than those of the SCH, while the initial peak force is 166.98% lower. In terms of deformation behavior, the ESCH demonstrates greater stability than the SCH and more effectively exhibits the negative Poisson’s ratio effect. Additionally, to investigate the influence of various parameters on the honeycomb structure, we analyzed the dynamic response of the in-plane impact force of the ESCH at varying impact velocities and wall thicknesses. In conclusion, the embedded symmetric chiral honeycomb structure effectively enhances the mechanical properties of chiral honeycombs and demonstrates improved deformation characteristics.

Energy absorption behaviour of an aluminium foam-filled circular-triangular nested tube energy absorber under impact loading

This research deals with experimental and numerical axial quasi-static crash tests on end-capped cylindrical and conical tubes. Axial quasi-static crush tests have been generated for end-capped cylindrical and conical tubes. Furthermore, in order to gain more detailed knowledge about the crash process, finite element (FE) simulations of the experiments have been performed. The explicit FE code Abaqus/explicit was used and the results have been validated by experimental data. The elastic–plastic material model was used for the aluminium tubes. In terms of finding more efficient (higher energy absorption) and lighter crash absorbers particularly, the energy absorption, E, and specific energy absorption, SEA, have been considered. The influences of geometrical parameters of the tubes on their collapse response have also been investigated. Finally, a multiobjective optimisation method is used to find the tube geometry which has the maximum energy absorption and specific energy absorption.

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.

Mechanical properties of auxetic circular and square tubes filled with aluminum foam

This study explores the effect of auxetic unit cell geometry and wall thickness on the energy absorption performance of sandwich composites under quasi-static and low-velocity impact (LVI) loading. Four auxetic geometries reentrant, arrowhead, starshaped, and kiteshaped were 3D-printed using ABS material and first evaluated through quasi-static compression tests with three wall thicknesses (0.44, 0.62, and 0.80 mm). Results showed that thinner-walled specimens exhibited higher initial peak forces but more brittle collapse, while thicker-walled designs provided smoother force responses. The arrowhead geometry with 0.44 mm wall thickness exhibited the highest peak crushing force (6.413 kN) while 0.44 mm starshaped geometry showed the maximum specific energy absorption (SEA) value of 6.226 J/g. Based on these results, representative auxetic cores were embedded into GFRP/epoxy sandwich panels and tested under 100 J LVI using a drop-weight setup. Among the tested configurations, the reentrant core exhibited the highest peak contact force (16.96 kN), while the arrowhead core achieved the highest absorbed energy (87.30 J) and SEA (1.89 J/g), indicating a more progressive deformation. The kiteshaped core provided the longest impact duration and smoothest deceleration profile, suggesting superior energy distribution. Finite element simulations in LS-DYNA correlated well with quasi-static compression experimental results, capturing the deformation mechanisms and validating the structural response. The findings highlight the critical role of unit cell topology and wall thickness in tailoring the impact performance of auxetic core sandwich structures for lightweight and energy-absorbing applications.