Enhanced Energy Absorption Capacity Research Articles

A multi-step auxetic metamaterial with instability regulation

A stable deformation mode is highly desired for mechanical metamaterials, especially when coupled with a negative Poisson’s ratio. However, such metamaterials often face challenges in terms of scalability toward large deformation or strain. In response, we propose a multi-step hierarchical auxetic metamaterial design paradigm, incorporating a series of incrementally scaled-down structures with same scale factor α into a re-entrant framework. This design enables instability regulation and multi-step deformation capabilities while preserving auxetic behavior, even under significant strain. Such multi-step metamaterials exhibit excellent properties, including tailored multi-phase compression modulus and strength, along with an enhanced energy absorption capacity that is as large as 2.1 times that of the original auxetic metamaterial. Experiments and simulations demonstrate that the deformation mechanism and compression response of the proposed multi-step auxetics are strongly influenced by the reduction factor and the order of the inner structure. A particularly intriguing observation is that the incorporation of embedded microstructures can restore stable deformation, even in the presence of significant initial instability, particularly with a reduction factor of 1/5. At high relative density, its specific energy absorption stands out favorably compared to other configurations, highlighting the success of the recoverable buckling mechanism. This work paves the way for designing multi-step mechanical metamaterials for use in impact resistance and body protection.

Compression response and optimization design of a novel glass-sponge inspired lattice structure with enhanced energy absorption capacity

Lattice structures have shown tremendous prospects in engineering fields, because of the ultralight, strong and toughness properties. In this paper, a novel configuration of lattice structure (GSIBCC) inspired by the hierarchical skeleton system of glass sponges is proposed. The new configuration of the unit cell is based on modifying the inner cross struts of the body-centered cubic (BCC) lattice, by considering the double diagonal reinforcements and hybridization of unit cells. The compression properties and deformation mechanism of the GSIBCC lattice structure are compared with BCC, OCT (Octet) and other glass sponge inspired lattices. A multi-objective optimization method is established, for maximizing the specific energy absorption (SEA) and simultaneously reducing the compression strength. The novel GSIBCC lattice exhibits superior specific energy absorption than BCC, OCT, and other glass sponge inspired lattices. For example, GSIBCC shows maximum 145.06% improvement (ρ¯=0.124) of SEA with respect to BCC, and maximum 117.4% improvement (ρ¯=0.124) of SEA with respect to OCT. The novel lattice exhibits the whole deformation type and obvious second stress reinforcement effect. Besides, the mechanical properties of GSIBCC are further improved using the multi-objective optimization. The reported biomimicry design strategy, deformation and failure mechanism, and multi-objective optimization method will be beneficial for enriching the lattice system and promoting the multifunctional applications of lattice structures in engineering fields.

Enhanced strength and toughness of carbon fiber reinforced aluminum matrix composite prepared via novel indirect extrusion method

The fabrication of large-sized, high-performance CF/Al composites presents significant challenges for the aerospace industry. This study introduces a novel indirect extrusion (IE) method for the high-quality production of CF/Al composites. The study investigates the infiltration mechanism of the alloy liquid during the IE process, highlights the technique's advantages, and systematically analyzes the mechanical properties and failure mechanisms of CF/Al composites. Results show that the aluminum liquid initially fills the interlayers and subsequently penetrates the fiber bundles, effectively shortening the infiltration distance. At a casting temperature of 800°C and an infiltration pressure of 40 MPa, the composite exhibits excellent forming quality and microstructural integrity. Compared to direct extrusion (DE) CF/Al composites, IE-CF/Al composites show significant improvements in compressive strength (16.72 %), flexural strength (16.87 %), fracture toughness (43.18 %), and work of fracture (90.61 %). The interlayer alloy and increased fiber spacing in IE-CF/Al composites enhance energy absorption capacity and reduce the risk of brittle fracture. This process lays a solid foundation for the high-quality production and application of CF/Al composites.

Experimental and numerical study of drop hammer test on honeycomb sandwich panel resistant to rock burst in coal mine roadway

This study addresses the ubiquitous issue of effective support resistant to the rock bursts within coal mine roadways and introduces an innovative solution in the form of a steel honeycomb sandwich panel (HSP). It is designed for installation on traditional metal supports in coal mine roadways, serves as an integral element of an energy-absorption support system tailored to withstand rock burst impacts. The investigation incorporates drop hammer impact tests conducted on eight HSP specimens, varying in cell wall thickness and core height. A comprehensive three-dimensional finite element model, inclusive of mesh considerations, was constructed and subsequently validated. Combining experimental and numerical approaches, the drop hammer impact response and energy absorption characteristics of HSP structures were analyzed. The findings reveal good energy absorption capabilities, with HSPs dissipating over 90 % of impact energy, over 85 % attributed to the core layer. Thinner core cell walls reduce peak impact loads, mitigating structural impact effects. In the experimental parameters delineated in the present study, it is observed that core layers with thicknesses of 1.0 mm and 1.5 mm demonstrate enhanced energy absorption capabilities. Variations in core height minimally affect peak impact forces, with only a 7.41 % distinction between 60 mm and 140 mm core layers. However, it is worth noting that higher core layers can achieve an enhanced energy absorption capacity. Thinner facesheets enhance energy absorption, and alterations in impactor mass have minimal effects under constant impact energy conditions. Additionally, a predictive equation for estimating indentation depth was proposed, closely aligned with finite element results. This equation holds potential for informing future HSP designs, offering valuable insights for diverse engineering applications.

A class of elastic isotropic plate lattice materials with near-isotropic yield stress

Thoughtfully engineered lattice materials offer a canvas for tailoring a diverse range of mechanical attributes. Yet, their pronounced anisotropy and inherently unstable nonlinear mechanical behavior curtail their suitability for energy absorption applications. Here, we propose the adoption of lightweight plate lattice structures for energy absorption and loading support. This involves strategically integrating plates into the rhombic dodecahedron framework, facilitating elastic isotropy and nearly yield isotropy. The proposed plate lattices showcase remarkable properties, including an exceptionally high bulk modulus that reaches the HS bound. Moreover, they boast an enhanced energy absorption capacity, surpassing that of the rhombic dodecahedron truss lattice by up to 2.58 times. The effects of relative density and loading direction on the mechanical properties were thoroughly explored through numerical simulations. Simulation predictions were rigorously validated through experimental verification. The failure modes of plate samples transition from being dependent on the loading direction, leading to collapse, to becoming stable regardless of the loading direction as the relative density increases from 0.1 to 0.2. It is noteworthy that plate lattices demonstrate SEA values comparable to those of shell lattices, even surpassing the stiffest isotropic plate lattice. These characteristics underscore their potential for applications in loading support and energy absorption.

4D printing of cellular silicones with negative stiffness effect for enhanced energy absorption and impact protection

Cellular silicone foams are renowned for their exceptional flexibility, ultra-elasticity, and durability, which have gained significant attention in diverse applications. However, manufacturing porous silicone foams featuring substantial bending curvatures and customized mechanical properties remains a challenge. Herein, this work presents a new strategy for manufacturing curved porous silicone foams with both 4D printed bending curvature and tailored meta-mechanical properties. The foam is achieved by direct ink writing of composite silicone inks embedded with thermal expandable microspheres as foaming agents. The work studied in detail the thermal expansion of microspheres, foaming of composite silicone inks, as well as properties of the expanded foam. Utilizing the strain mismatch under thermal stimuli, the printed bilayer structures achieved shape-shifting. Additionally, silicones composed of stacked bilayer filaments exhibited negative stiffness properties under compression, leading to enhanced energy absorption capacity, which can be fine-tuned through different printing structural designs, demonstrating its potential in fields such as energy dissipation and shock absorption while protecting objects with curved shapes.

Mechanical properties and energy absorption capabilities of plate-based AlSi10Mg metamaterials produced by laser powder bed fusion

Plate-based lattice structures are an emerging category of mechanical metamaterials with exceptional mechanical performance. In this work, plate-based SCFCC metamaterials of AlSi10Mg with various relative densities are fabricated by laser powder bed fusion (LPBF). Circular holes are strategically designed and placed at the center of each non-load-bearing face for residual powder removal. Quasi-static compression experiments and numerical simulations are performed to investigate their mechanical performance and deformation mechanisms. Results indicate that the elastic modulus of SCFCC metamaterials decreases by 3.5% with the presence of 0.9 mm diameter holes, while increasing the hole size shows negligible impact on the elastic modulus. The novel plate-based SCFCC structure exhibits superior mechanical properties and enhanced energy absorption capacity concerning conventional high-stiffness truss-based and shell-based counterparts. The improvement, at the relative density of 0.2, can be observed in terms of elastic modulus (around 50%), peak compressive strength (around 300%), energy absorption capacity (around 400% or 200%). When increasing the relative density from 0.2 to 0.5, plate-based SCFCC metamaterial still maintains superior mechanical performance while the gaps between SCFCC and its counterparts narrow down gradually owing to the loss of structural features. Moreover, mechanical characteristics and coefficients of three Gibson and Ashby analytical equations are determined. This work proposes a novel type of plate-based structure with both exceptional mechanical performance and good additive manufacturability, which opens a new avenue for the design of lightweight mechanical metamaterials.

Exploring the vibration and energy absorption characteristic of auxetic tubular structure: an experimental analysis

This experimental study delves into the vibration response and energy absorption characteristics of three distinct auxetic tubular structures under quasi-static compression: the Reentrant, Double-V, and Anti-Trichiral designs. Notably characterized by their negative Poisson’s ratio, these structures exhibit superior mechanical properties in comparison to conventional tubular structures with a positive Poisson’s ratio. For consistency, all samples were standardized in terms of diameter and height, while variations due to unit cell geometry were parameterized based on the structure’s weight. The samples were fabricated using Fused Deposition Modeling (FDM) with both PLA and PLA-Carbon filaments. Modal testing was conducted to evaluate structural damping, providing insights through time domain plots and frequency response functions. Subsequent compression testing facilitated the assessment of force-displacement relationships, thereby enabling the quantification of energy absorbed, specific energy absorption, and peak crushing force metrics. The analysis revealed that Reentrant unit cells constructed from PLA exhibited a 5% higher damping efficiency compared to Double-V and 4% higher than Anti-Trichiral units. Similarly, Reentrant units in PLA-Carbon demonstrated an 8 and 30% increase in damping relative to Double-V and Anti-Trichiral, respectively. During quasi-static compression, Double-V units in PLA showcased a 66 and 13% superior energy absorption capacity over Reentrant and Anti-Trichiral units, respectively. With PLA-Carbon, Double-V units exhibited a 28 and 116% enhanced energy absorption capacity compared to Reentrant and Anti-Trichiral units, respectively. This comprehensive evaluation offers insightful revelations into the damping and energy absorption capabilities of varying auxetic cell structures when composed of different materials, highlighting their potential in engineering applications.

Deformation and Energy Absorption Performance of Functionally Graded TPMS Structures Fabricated by Selective Laser Melting

Triply periodic minimal surface (TPMS) structures have unique geometries and excellent mechanical properties, which have attracted much attention in many fields. However, the relationship between different filling forms and different directions of functionally graded TPMS structures on energy absorption has not been fully studied. In this study, a functionally graded strategy was proposed to investigate the effect of filling form and direction gradient on the energy absorption of TPMS structures. The design of functionally graded Gyroid and Diamond TPMS cellular structures with multiple forms was characterized, and the structures were fabricated using additive manufacturing technology. The effects of uniformity and different directional gradients on the deformation and energy absorption properties of the structures were studied experimentally and numerically. According to the compression test results, it was found that different filling forms of the TPMS structure behave differently in terms of yield plateau and deformation pattern, and the sheet structures can develop a better deformation pattern to enhance energy absorption capacity. Functionally graded sheet Diamond TPMS cellular structures along the compression direction exhibit a 32% reduction in initial peak force, providing more advantages in structural deformation and energy absorption. More closely, it is possible to further reduce the initial peak force, delay the densification point, and thus increase the energy absorption capacity by designing functionally graded sheet Diamond TPMS based cellular structures. The results of this study provide valuable guidance for the design of high-performance impact-protection components.

Microstructure and failure behavior of ultrasonic-assisted resistance spot welded AA6061/Ti6Al4V joints

The ultrasonic-assisted resistance spot welding (UaRSW) technique was applied to join AA6061 aluminum alloy to Ti6Al4V titanium alloy, the microstructure and mechanical performance of the joints with and without ultrasonic were investigated. Ultrasonic increased the maximum load by 43%, doubled the displacement at fracture and significantly enhanced energy absorption capacity. The solid phase transformation zone formed in Ti6Al4V, and its microstructure was lath martensite. Due to the welding defects and coarse columnar dendrite, conventional spot welded joints fractured by interfacial failure mode with poor performance. Ultrasonic promoted the diffusion of AA6061, removed the welding defects, generated consistent equiaxed grains in weld zone, and the joints fractured in AA6061 base metal by button pull-out mode result from the higher bonding strength.

Superior energy absorption characteristics of additively-manufactured hollow-walled lattices

Designing innovative lightweight architected materials with enhanced mechanical properties and superior energy absorption is a long-term pursuit to protect against impact-induced damage. Compared with dense-walled lattices, innovative engineering designs indicate that hollow-walled lattices exhibit unprecedented combinations of mechanical properties and functionalities with minimal weight. This paper proposed a novel hollow-walled lattice structure with variable cross-sections that can improve energy absorption significantly. A series of hollow-walled lattices were additively manufactured by the selective laser melting technique with the twinning-induced plasticity steel. The quasi-static uniaxial compressive tests were conducted to study the mechanical property and energy absorption capacity. Experimental results indicated that the hollow-walled lattices with a constant cross-section and those with a variable cross-section can improve the specific energy absorption by 29.2 % and 135.6 % compared with the conventional dense-walled lattices. Besides, finite element models of hollow-walled lattices were established by using the FE package LS-DYNA to investigate the effects of various structural parameters on mechanical properties and energy absorption capacity. A comprehensive parametric analysis based on the validated finite element models shows that the maximal ratio of the diameter to thickness in hollow-walled lattices leads to the optimal energy absorption capacity for the lattices with the same relative density. In addition, three typical tailored parameters, including the necking ratio, the necking local coefficient and the ratio of the thickness to diameter of variable struts, were tailored to achieve a better energy absorption capacity of hollow-walled lattice structures. Finally, the novel proposed hollow-walled lattice with a variable cross-section was also applicable in other lattices to enhance energy absorption capacity.

Blast performance of 3D-printed auxetic honeycomb sandwich beams

Little research has been conducted on comparing the blasting characteristics between the regular hexagonal and auxetic honeycomb sandwich beams (RHSBs and AHSBs). To address this gap in knowledge, the study utilised both experimental and numerical analyses. The HSBs consisted of steel top and rear face sheets bonded to a stainless- steel honeycomb core. The parameters considered in this test included the core configuration (regular vs. auxetic hexagonal) and face-core bonding method (adhesive vs. integrated). Results revealed that at scaled distances of 0.8617 m/kg1/3 and 0.7971 m/kg1/3, the AHSB core exhibited a reduction in mid-span displacement of only 3.3 % and 3.7 %, respectively, compared to the RHSB core. However, the compression value of the AHSB core significantly exceeded that of the RHSB core by 171.5 % and 161.5 %, respectively. This finding indicates that auxetic honeycomb cores possess enhanced energy absorption capacity to withstand blast loading. In addition, using unbonded face sheets increases the range of local cell deformation and decreases the global flexural bending by 22.66 % and 24.14 % at scaled distances of 0.8617 m/kg1/3 and 0.7971 m/kg1/3, respectively, compared to the AHSBs with face sheet debonding. To further investigate the damage mechanism of HSBs subjected to blast loading, a well-validated finite element model was employed. Notably, parametric simulations demonstrated that the dynamic behaviour of AHSBs under blast loading is significantly influenced by cell wall thickness, face sheet thickness, and cell angle.

Mechanical characteristics of a novel rotating star-rhombic auxetic structure with multi-plateau stages

Auxetic structures have attracted further attention owing to their outstanding designability and mechanical properties. Designing innovative cellular structures with improved mechanical behavior is critical to achieving structural crashworthiness. In this paper, a novel rotating star-rhombic auxetic structure (RSAS) inspired by the rigid square rotating units is proposed, which has significant negative Poisson’s ratio characteristics and enhanced energy absorption capacity. The mechanical responses of the RSAS are investigated by quasi-static experiments and finite element (FE) simulations, and a multi-stage deformation mode that facilitates the tuning of mechanical properties is found. The theoretical model based on the theory of plastic dissipation is validated, and it can accurately predict the plateau stresses and critical strains of the RSAS in multiple deformation stages. In addition, parametric analysis shows that the second plateau stress is close to the average plateau stress, it decreases with increasing the re-entrant angle α and pre-rotation angle β, and increases with increasing t or decreasing b. Increasing t/b can significantly enhance the plateau stresses, and the thickness gradient strategy further improves energy absorption. These studies can provide insights into the optimum design of auxetic cellular structures and the improvement of energy absorption.

A self-constrained energy-absorbing structure with robust crashworthiness inspired by photonic micropillars pattern in beetle’s elytra

Beetle’s elytra provide elaborate microstructural designs to achieve functional synergies in face of external environments. Natural design strategies can provide effective solutions to the long-standing challenges about how to design an energy absorbing structure with comprehensively improved mechanical properties. Inspired by the pattern of the micropillars distributed in photonic structures of beetle’s elytra, this paper proposes a bio-inspired “photonic micropillar pattern” (PMP) honeycomb with robust crashworthiness, self-constrain, self-adaptability, and enhanced energy absorption capacity as an alternative material to the conventional single hexagonal-celled (SHC) honeycomb. The computational and experimental results both show that all in-plane crashworthiness indicators of the PMP honeycomb have been significantly improved compared with that of the SHC honeycomb. Subsequently, the collapse and energy absorption mechanisms of the PMP honeycomb are revealed by the analytical model established in this study. Based on numerical simulations and precisely theoretical predictions, the effects of the relative density, cell wall angle, impact velocity and thickness distribution on the in-plane crashworthiness performance of the PMP honeycomb are analyzed and discussed. This study creates a possibility for future excavation of advanced energy-absorbing structures with multifunctional synergies.

Design and optimization of the bumper beam with corrugated core structure of fiber metal laminate subjected to low-velocity impact

Fiber metal laminates (FMLs) exhibit good impact resistance performance with hybrid structures based on alternating stacking of metal alloy layers and fiber-reinforced composite plies. Therefore, FMLs become excellent candidates for bumper beams in automobiles with an enhanced energy absorption capacity. Herein, the design and optimization of the bumper beam consisted of FMLs corrugated sandwich structure subjected to low-velocity impact were investigated. Firstly, material characteristic parameters of aluminum alloy and carbon fiber reinforced thermoset polymer (CFRP) were obtained from the quasi-static and dynamic experiments respectively. Then, finite element analysis (FEA) of cap structures of FMLs was established to capture the deformation process of the low-velocity impact. The simulation results were well-validated using material parameters from the dynamic mechanical tests. Afterward, the influence of material type and stacking sequences on performance was numerically investigated under low-velocity impact loading, whereas the performance of aluminum alloy and CFRP were set as controls. A multi-objective optimization method was considered to realize the maximum energy absorption with minimum impact peak force. The non-dominated sorting genetic algorithm II (NSGA-II) was introduced to obtain the global optimum solution. The current work highlights the excellent mechanical performance of the FMLs bumper beam in low-velocity impact.

Enhanced compressive mechanical properties in stochastic bicontinuous porous structures

Inspired by the morphology of dealloyed nanoporous metals, we derive a novel open-celled porous structure with stochastic bicontinuous cell. The polymeric porous specimens are fabricated by additive manufacturing (AM), and the compressive mechanical properties and energy absorption capacity are explored experimentally. Results show that Young’s modulus, yield stress, plateau stress, and energy absorption characteristics are monotonically increasing with the relative density, obeying the Gibson-Ashby power correlation. Due to more defects generated in the specimen with smaller ligament diameter during AM, there is a significant decrease in Young’s modulus and a slight decrease in yield stress with the decrease of ligament diameter, which is opposite to the size effect in nanomaterials. Attributing to the bending and yielding deformation of ligaments, the stochastic bicontinuous porous solids show an enhanced energy absorption capacity. The ligament morphological structure has shown to be an additional factor affecting the mechanical responses of porous solids, and might magnify its sensitivity to structural characteristics. This study provides valuable idea and guidance for designing efficient open-celled porous structures in the promising application of energy absorption.

Introducing a new hybrid surface strut-based lattice structure with enhanced energy absorption capacity

The present study aims to assess a new lattice structure with high energy absorption capacity. Lattice structures with surface-based unit cell have higher energy absorption than those with strut-based unit cell. A new lattice structure is presented by adding the strut to the surface-based unit cell which has a higher energy absorption capacity than the lattice structures with surface-based unit cell. First, the high energy absorption capacity of surface-based lattice structures was evaluated by adding the strut. Such analyzes are conducted by providing a numerical model which considers the elasto-plasto-damage properties of materials under tension and compression. Then, a number of experimental samples were made using additive manufacturing and the compression test was performed. The results of finite element analysis were consistent with those of the experimental results. Based on the results, adding strut increased the energy absorption for surface-based lattice structures by about 106%. Finally, the effect of the ratio of geometric parameters of the unit cell on its mechanical behavior was evaluated.

Numerical study on influence of target thickness on impact response of GFRP composites

Due to rise in threats like ballistic impacts, blast loading and vehicle collision in armored military vehicles, the demand for materials with high strength and enhanced energy absorption capacity has been increased. Applications of Fiber reinforced composites as armor material in military vehicles is being considered as one of the measures to reduce such threats. The focus of this work is to investigate the energy absorption capacity of a GFRP plates subjected to a rigid projectile with blunt-nosed at the intermediate velocity range by using non-linear finite element code LS-DYNA. It has been found that the numerically computed results of ballistic limit velocity and residual velocity, closely resemble the test results reported in the literature. With altering target thickness, it has also been explored how the energy absorption capacity, projectile's residual velocity, ballistic velocity limit and damage mechanism of composite. The numerical results make it evident that the target thicknesses have a significant impact on the target's ballistic resistance and delamination area.

Experimental investigation on low-velocity impact response of spherical core sandwich structure

In the present work, the low-velocity impact characteristics of the spherical core sandwich structures made of glass fibre reinforced plastic (GFRP) are tested at different strike velocities (3, 5, and 7 m/s). Four different types of core orientation, namely, regular, interlock, inverted, and stagger, are designed and fabricated by the hand-layup method. Vinyl ester resin and woven glass fibre fabrics are used as matrices and reinforcements, respectively. The diameter of the spherical core and the pitch distance is chosen as 16 mm and 32 mm, respectively. The impact behaviour of the novel spherical sandwich structures is examined based on the maximum contact force, energy absorption capacity, coefficient of restitution (COR), and damage behaviour. The Regular model shows enhanced energy absorption capacity with a specific absorbed energy of 0.092 J/(kg/m3) at 7 m/s impact velocity. Similarly the Interlock model shows good damage resistance. The typical failure patterns observed in the Interlock model at 3 m/s are matrix cracking (MC) and fibre breakage (FB), whereas, at 5 and 7 m/s impact velocities, the damage core crushing (C) is observed.

Polyurea-coated ceramic-aluminum composite plates subjected to low velocity large fragment impact

Research on high-velocity bullet impact resistance of composite plates has been widely used in bulletproof material field, but limited studies have focused on the response of composite plate under low velocity and large fragment impact. In this paper, the impact response of polyurea-coated ceramic-aluminum composite plate to low velocity and large mass fragment was experimentally and numerically studied. The fragments were launched using a self-designed launcher, which can realize the free flip impact test of low velocity and large mass fragments with flight speed of 100–300 m/s and the mass of 0–100 g. Based on finite element method and smooth particle hydrodynamics, the impact model of low-velocity large fragments on composite plates was established to study fragment deformation and composite plate damage and compared with the experimental results to verify the effectiveness of the model. The multi-angle impact response of the fragment on the composite plate was studied. Results indicated that unlike the high-velocity impact of traditional bullets, low-velocity and large-mass fragments will flip in varying degrees after hitting the target accompanied by the deformation of the fragments, which remarkably influence the impact penetration ability of the fragments. Moreover, with the increase of biting angle, the composite plates show enhanced energy absorption capacity.