Enhanced Energy Absorption Capacity Research Articles

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 attentions in diverse applications. However, manufacturing porous silicone foams featuring substantial bending curvatures and customized mechanical properties remain 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.

Mechanical Properties of High Strength SCC Made with Hybrid Steel Fibers from Discarded Bead Wires

The tire manufacturing sector occupies a significant portion of the global economy. The production of vehicle tires requires the utilization of different raw and processed materials. Steel beads are one of these main ingredients, used to reinforce the treads and sidewalls of car tires. In this study, the effect of incorporating steel fibers cut from discarded bead wire (DBW) during the tire manufacturing process on the rheological, mechanical, and flexural toughness of high-strength self-compacting concrete (SCC) was investigated. Four SCC mixes were prepared with four discarded bead wires, at volume fractions of 0%, 0.3%, 0.6%, and 1%. Four lengths of the discarded bead wires were used in the term of hybridization: 10, 20, 30, and 35 mm. These were mixed together, with each length comprising 25% of the total. Investigations of fresh and hardened concrete properties were carried out. The results showed that discarded bead wires affected the rheological properties of the high-strength SCC adversely, causing a considerable reduction in slump flow and passing ability and an increase in T500 and V-funnel time, and enhancing segregation resistance. On the other hand, the mechanical properties, such as compressive strength and splitting tensile strength were improved significantly with the inclusion of the discarded bead wire. Moreover, investigations of flexural toughness based on ASTM requirements were conducted. Overall, the presence of different lengths of the discarded bead wire helped to transfer the load from the cementitious matrix to the short fibers, and then to the long ones, leading to the enhanced energy absorption capacity of high-strength SCC.

Compression behaviors of the bio-inspired hierarchical lattice structure with improved mechanical properties and energy absorption capacity

Nature materials usually possess unique hierarchical structures, like spongy bone, tendon and bamboo, and often exhibit remarkable mechanical properties. In this paper, inspired by the structural hierarchy of biological materials, the novel configuration design of unit cell with inner hierarchy was developed. The new lattice configuration takes advantage of the space filling and volume utilization of original BCC structure. The hierarchical lattices with 5 × 5 × 5 unit cells were manufactured by digital light processing (DLP) printing technique, using a hard-tough resin material. Numerical simulation and quasi-static experiment were performed to investigate the mechanical performance and deformation mechanisms of the lattice structures. The novel lattice configuration exhibits superior mechanical properties and enhanced energy absorption capacity with respect to conventional BCC lattice, e.g. when loading along x-axis, the improvement can be 38.9% for specific stiffness, 36.5% for specific energy absorption (SEA) and 73.1% for the crash load efficiency (CLE). Besides, the enhancement of mechanical performance and energy absorption capacity is more strong when loading along the z-axis. The mechanical interaction effect between structural hierarchy, e.g. master and slave cells, is proved to be the main reason that contributes to the enhancement of mechanical properties of hierarchical lattices. The designed novel configuration of hierarchical lattice will enrich the current lattice systems and promote the development of multifunctional applications in the future.

Cyclic Loading Behaviour of Externally Bonded CFRP Reinforced Concrete Beam-Column Joint

Cyclic loading behaviour of RC beam-column joints strengthened with externally bonded Carbon Fiber Reinforced Plastic (CFRP) was analysed through Abaqus CAE software. Effect of the number of CFRP layers and the strengthening technique on failure modes, hysteretic curves, skeleton curves, ductility, and energy dissipation capacity were studied. The results show that the strengthening of RC beam-column joints by externally bonded CFRP can effectively improve the cyclic loading behaviour. Strengthening the joint by fiber bands enhances ductility and energy absorption capacity. The increase in the number of CFRP layers leads to enhance energy absorption capacity significantly as compared to ductility.

Ni/Al-Hybrid Cellular Foams: An Interface Study by Combination of 3D-Phase Morphology Imaging, Microbeam Fracture Mechanics and In Situ Synchrotron Stress Analysis.

Nickel(Ni)/aluminium(Al) hybrid foams are Al base foams coated with Ni by electrodeposition. Hybrid foams offer an enhanced energy absorption capacity. To ensure a good adhering Ni coating, necessary for a shear resistant interface, the influence of a chemical pre-treatment of the base foam was investigated by a combination of an interface morphology analysis by focused ion beam (FIB) tomography and in situ mechanical testing. The critical energy for interfacial decohesion from these microbending fracture tests in the scanning electron microscope (SEM) were contrasted to and the results validated by depth-resolved measurements of the evolving stresses in the Ni coating during three-point bending tests at the energy-dispersive diffraction (EDDI) beamline at the synchrotron BESSY II. Such a multi-method assessment of the interface decohesion resistance with respect to the interface morphology provides a reliable investigation strategy for further improvement of the interface morphology.

Study of mechanical properties and enhancing auxetic mechanism of composite auxetic structures

AbstractThe auxetic structures attract much attention because of their good properties, such as enhanced energy absorption capacity and buckling resistance. It is an important topic to combine the auxetic structures with other materials or structures to improve their mechanical properties. In this paper, a composite auxetic structure was proposed, in which the embedded structure and re‐entrant structure can deform independently to adjust the mechanical properties. Under uniaxial compression, the effects of changes in the embedded structure and re‐entrant structure on Poisson's ratio, relative Young's modulus, and energy absorption of the composite auxetic structure were studied. By introducing the rate of change of mechanical properties, the effects of the embedded structure and re‐entrant structure on the composite auxetic structure were studied. The results show that changing the embedded structure for Poisson's ratio and relative Young's modulus and changing the re‐entrant structure for energy absorption can maximize the material utilization. And changing the re‐entrant structure can make the mechanical properties of the composite auxetic structure reach a larger adjustable range. This study can provide a new way for the combination of future auxetic structures to meet the needs of different applications in civil engineering.