Energy Absorption Mechanisms Research Articles

Curved Architected Triboelectric Metamaterials: Auxeticity‐Enabled Enhanced Figure‐of‐Merit

AbstractTriboelectric generators are integrated into curved architected materials to realize triboelectric metamaterials that simultaneously harvest electricity from wasted mechanical energy and perform mechanical energy absorption. Novel triboelectric mechanical metamaterials (TMMs) of distance‐changing, angle‐changing, and mixed modes are designed, fabricated, and tested under a cyclic compressive load. The open‐circuit voltage and short‐circuit current of lightweight TMMs are found to be as high as 40 V and 10 nA. The introduced TMMs can effectively harvest energy under loadings from two distinctive directions. A theoretical model for predicting the energy harvesting properties of TMMs is developed, and the role of auxeticity on the energy harvesting figure‐of‐merit (FOMes) is elicited. The introduced TMMs exhibit enhanced FOMes enabled by a decrease in their negative Poisson's ratio and an increase in their resilience. The FOMes of curved architected TMMs surpasses by more than 16 times the FOMes of triboelectric materials with conventional architectures (i.e., triangular, quadrilateral, and hexagonal cell topologies). An intelligent skateboard with integrated TMMs is fabricated as a proof of concept to demonstrate motion sensing, shock‐absorbing, and energy harvesting functionalities of multimodal triboelectric metamaterials. The introduced design strategy for triboelectric metamaterials unlocks their applications in self‐powered and self‐monitoring sports equipment, smart soft robots, and large‐scale energy harvesters.

Finite element analysis of the mechanical properties of sheet- and skeleton-gyroid Ti6Al4V structures produced by laser powder bed fusion

Additive manufacturing, and laser powder bed fusion (L-PBF) in particular, can produce complex geometric components with high resolution, and is very suitable for manufacturing lightweight triple periodic minimal surface (TPMS) structures to achieve lightweight. With regard to the two forms of the same structure, most of the previous studies focused on sheet-TPMS, but lacked the understanding of the difference between skeleton-TPMS and sheet-TPMS structures. In order to explore the characteristics of these two structures and provide theoretical support for the development of lightweight structure design, this paper compares the manufacturing performance and defect distribution of skeleton-gyroid (GSK) and sheet-gyroid structures (GSH). It employs high-precision finite element analysis (FEA) prediction and experimental verification to compare comprehensively the mechanical properties, failure behavior and energy absorption characteristics of the two structures. The results show that, compared to GSK, the larger specific surface area of GSH leads to more unmelted powder and draping adhesion, without affecting its higher stiffness and strength. Moreover, the more stable failure mode of GSH leads to more gentle stress platform stage and superior energy absorption performance. The results predicted by simulation are highly consistent with the experimental results. This improved understanding allows better prediction of the mechanical properties of the specimens using the Gibson–Ashby theory, which can reduce the experimental cost and time, and improve the resource consumption of TPMS structural performance research. This study can open new possibilities for the design and application of TPMS structures.

Effect of heat treatment on mechanical properties, failure modes and energy absorption characteristics of lattice skeleton and sheet structures fabricated by SLM

Triply periodical minimal surface (TPMS) structures have attracted much attention in the biomaterials, aerospace, and automotive industries because they are lightweight, have high strength, and can absorb energy and shocks. In this study, uniform skeletal (USK), uniform sheet (USH), grade skeletal (GSK), and grade sheet (GSH) diamond lattice structures with the same 20% volume fraction were fabricated by selective laser melting (SLM) using AlSi10Mg metal powder. Their mechanical properties, deformation behavior, and energy absorption performance were systematically investigated by compression tests and finite element analysis (FEA). The skeleton structures had a higher elastic modulus, yield strength, and more severe stress fluctuation than the sheet structures. In addition, comparing the 45° shear deformation for as-built uniform structures accompanied by a mixture of ductile and brittle fracture modes, both gradient structures fractured by a sub-layer pattern from the layer with a lower volume fraction. Furthermore, the numerical simulation results illustrated that the stress of the skeleton structures was mainly concentrated at the skeleton joint, while the sheet structures were distributed evenly on the thin wall, without being concentrated in the interconnection region. For skeleton structures, heat treatment controlled the failure degree by improving the microstructure of the material, while for GSH structures at 300 °C, the fracture mode changed from the previous layer-by-layer fracture to a 45° shear failure. The accumulated energy absorption of gradient structures was more than that of the uniform structure, especially the GSH structures and the energy absorption efficiency of the skeleton structures was higher.

Bamboo-inspired hierarchical microlattice structures (BHMSs) for high strength and energy absorption

Mechanical metamaterials as a category of lightweight materials have exhibited superior specific mechanical properties and energy absorption. However, lack of reasonable structural design always results in weakening or failure to achieve the optimal mechanical performance of metamaterials. Here, we firstly adopted bio-inspired and structural optimization methods to guideline the design of microlattice structures. Inspired by the strong and ductile ‘Moso’ bamboo, three bamboo-inspired hierarchical microlattice structures (BHMSs) were initially designed, and the bamboo’s features, viz., hollow, gradient distribution, and cellular, were imitated by designed BHMSs. Optimization design with the objective of maximum ratio of strain energy and reaction force was carried out to furthermore improve the mechanical properties of BHMSs. Afterwards, the optimal BHMSs were printed via Stereolithography. The compressive responses of BHMSs were elaborated by experiments and simulation. Results show that these designed biomimetic structures can be easily tailored via tuning the geometric sizes of unit cell, achieving high compressive specific modulus and strength 48.16 kPa m3 kg−1 and 1389.23 Pa m3 kg−1 and the energy-absorbing efficient 85.43% in the octet bamboo-inspired hierarchical microlattice structures (OCT BHMSs). The design strategies and findings shed light on the realization of advanced metamaterials with tailored mechanical properties. How to design ordered cellular structures for lightweight structures with high mechanical strength and energy absorption efficiency remains a crucial challenge in automation, aerospace and lightweight construction fields. Inspired by the lightweight and high load-bearing capacity of nature bamboos and metamaterials in the previous researches (Song et al., Materials & Design, 2019, 173: 107773; Song et al., International Journal of Fatigue, 2017, 100: 126), here a comprehensive approach of bionics and optimization was proposed to design hierarchical microlattice structures with lightweight, good mechanical properties and high energy absorption efficiency. The bamboo’s characteristics, including hollow, gradient enhancement, and cellular, were completely copied to reasonably produce hierarchical microlattice configurations, while the optimal sizes were obtained though the optimization design.

Effect of the direction of the gradient on the mechanical properties and energy absorption of additive manufactured Ti-6Al-4 V functionally graded lattice structures

Functionally graded (FG) lattice structures are gaining increased attention in engineering applications due to their excellent mechanical properties and high energy absorption. This study aims to investigate the effect of the direction of the gradient on mechanical properties and energy absorption of FG sheet-based (FGS) lattice structures. The design approach of FGS lattice structures with different directions of volume fraction gradient was established. The FGS samples with the gradient from perpendicular to parallel to loading directions (θ = 0º−90º) were fabricated by laser powder bed fusion technology with Ti-6Al-4 V powder. The mechanical properties, deformation behaviors, and energy absorption of the FGS samples were systematically investigated. Results show that the deformation behavior of FGS samples changed from local shear to layer-by-layer fracture with the increase of θ, gradually improving the load-bearing capability during the compression process. The fluctuation of the strain-stress curve for FGS lattice structures can be reduced by decreasing the θ. Tunable mechanical properties and energy absorption were achieved by changing the θ. The FGS sample with θ = 0º had the highest elastic-plastic properties, while the FGS sample with θ = 90º absorbed the largest amount of energy before densification. The failure of the FGS lattice structure was influenced by the combination of brittle fracture with smooth plane morphological features and ductile fracture with dimples. Moreover, the deformation behaviors and strain-stress curves of FGS samples were successfully predicted using the finite element method with Johnson-Cook plastic and damage models. Finally, energy absorption plots were provided to select of FGS lattice structures for specific energy-absorbing requirements. This work provides an efficient method to control the mechanical properties and energy absorption of FGS lattice structures for engineering applications.

Micro-CT in the mechanical properties and energy absorption of closed-cell aluminium foam

In situ loading experiments of closed-cell aluminium foam with densities of 0.217 g/cm3, 0.347 g/cm3, 0.414 g/cm3 and 0.588 g/cm3 prepared from industrial pure aluminium 1060 and titanium hydroxide TiH2 foaming agent were carried out by micro-CT. The pore structure parameters such as porosity, pore size distribution and sphericity of aluminium foams with different densities were analyzed, and the effects of pore structure parameters on mechanical properties and energy absorption were investigated to reveal the differences in mechanical characterization of aluminium foams with different densities. The results show that: the collapse of aluminium foam pores in the in-situ loading experiments starts from the high porosity region; aluminium foam with high density has low porosity, small pores and good sphericity; the stress-strain curve of aluminium foam with high density is located above and the elastic modulus is large; the energy absorption capacity is related to the density of aluminium foam, and the energy absorption capacity is large with high density, but the energy absorption efficiency is mainly related to whether the structure is uniform or not.

Damage mechanisms of composite laminates under impact loading including the effect of pre-load

The focus of the present research is on the damage modelling of composite laminates subjected to Low Velocity Impact (LVI). This research also shows how this model can be employed to assess the effect of pre-load. The composite damage model, integrating a VUMAT subroutine and a cohesive zone model, is first validated against the results obtained from conventional impacts on laminates without pre-load. The validated model is then employed to predict the impact response of pre-loaded composite laminates. It was found that the pre-load influences the load response, damage behaviour and energy absorption mechanisms of composite laminates. This is with pre-tension increases the maximum load during the impact event, whereas pre-compression has the opposite effect. Matrix cracking and delamination are found to be reduced slightly due to pre-tension, whilst matrix cracking and delamination are considerably increased by pre-compression. The developed model can provide guidance to the design and maintenance of composite components subjected to pre-load and impact.

Excellent Mechanical Properties and Energy Absorption of Hexagonal‐Body‐Centered Lattice Structure Fabricated by Selective Laser Melting

Inspired by the crystal lattice characteristics of hexagonal‐close‐packed and body‐centered‐cubic metals, a novel hexagonal‐body‐centered (HBC) lattice structure is constructed for energy absorption. HBC lattice structures with three different c/a ratios are prepared by selective laser melting (SLM) using 316 L stainless steel powder. The geometric features and energy absorption performance of the fabricated HBC lattice structures with different c/a ratios are studied by scanning electron microscopy and quasistatic compression tests, respectively. The results show that the HBC lattice structure prepared by SLM not only exhibits good formability, but also demonstrates excellent mechanical properties and energy absorption capacity. The c/a ratio significantly affects the mechanical properties and energy absorption performance of HBC lattice structures. The Young's modulus, yield strength, and energy absorption increase as the c/a ratio decreases. Compared with other lattice structures, the HBC lattice structure exhibits better energy absorption at the same relative density, thus indicating the usefulness of the HBC lattice structure as a lightweight energy‐absorbing structure.

3D printed bending-stretching coupled non-self-similar hierarchical cellular topology under in-plane loading

Ultralight hierarchical metamaterial is a type of promising structure in aerospace and transportation applications owing to the high stiffness/strength to density ratio. Though some hierarchical topologies with distinct in-plane configurations have been reported, the topology with superior mechanical behaviors under plastic deformation is urgent to be tailored. The present study develops a novel bending-stretching coupled Non-Self-Similar Hierarchical Topology (NSSHT) via additive fabricating methodology, and gives an insight into the mechanical responses and energy absorption capacities. It is identified that the softening post initial peak stress is triggered by the bending of the oblique membrane in the first order unit cell when edge length ratio (γ) is low, while by the initial rotation of second order unit cell when γ is high. Compared to the quasi-static measurements, the dynamic specific initial peak stress of NSSHT with uniform wall thickness (η= 1) was enhanced up to 131.9%. The deformation modes at distinct stress stages are different under quasi-static and dynamic loads. For specific energy absorption capacity, the NSSHT with non-uniform wall thickness behaves better, and the majority is dissipated at stress enhancement stage. The developed novel hierarchical structures enable to provide a wider spectrum of choices for tailoring high-performance lightweight components.

Theoretical investigation on energy absorption of single-layer graphene under ballistic impact

The superb mechanical properties make graphene an ideal candidate material for impact protection. Combining molecular dynamics simulations and theoretical analyses, the deformation and failure modes, energy absorption of single-layer graphene under ballistic impact are investigated. According to numerical and theoretical results, the expression for residual velocity of projectile after impact is given. The dependence of deformation and failure modes, energy absorption mechanisms, specific penetration energy (SPE) on impact velocity is analyzed. The results show that during low-velocity impact, there are conical deformation region (CDR), star-like crack and monoatomic carbon chain in graphene. Energy absorption mechanisms of graphene are mainly local deformation and fracture. With increasing impact velocity, the size of CDR decreases. The star-like crack gradually transforms into circular hole. When impact velocity is high enough, carbon atoms within projectile projection area in graphene will be ejected in the form of debris. The kinetic energy (KE) loss of projectile is converted into KE of debris carbon atoms and fracture energy of carbon bonds. Besides, it is also found that SPE (dominant factors are deformation of conical region and KE increments) exhibits a decreasing–increasing trend with increasing impact velocity. When impact velocity is the same, SPE decreases with increasing projectile diameter.

Global sensitivity analysis of complex moduli of carbon fiber reinforced polymer

AbstractGlobal sensitivity analysis of complex moduli of carbon fiber reinforced polymer (CFRP) is performed by using variance‐based sensitivity analysis. Twelve material properties of matrix and fiber are selected as input arguments, including fiber volume fraction, three matrix properties, and eight carbon fiber properties. Ten thousand samples are generated with Sobol sequence. Based on the correspondence principle, six complex moduli of unidirectional CFRP, and two complex moduli of quasi‐isotropic laminate, orthogonal laminate, and symmetric laminate with different fiber angles are predicted using the generalized method of cells and classical laminate theory. The sensitivity indexes of all input arguments are calculated. The results show that the loss factors of CFRP are mainly affected by the matrix loss factor and fiber axial loss factor, and slightly affected by the fiber transverse loss factor.Highlights Sensitivity analysis reveals key factors influencing CFRP complex moduli. Impact of fiber and matrix properties on CFRP damping revealed. Insights for high‐damping and high‐stiffness CFRP development. Enhanced understanding of energy absorption mechanisms. Uncovering the dominant role of matrix and fiber axial properties in damping.

Suture Interface Inspired Self-Recovery Architected Structures for Reusable Energy Absorption.

Designing materials and structures with high energy absorption and self-recoverability remains a challenge for reusable energy absorption, particularly in aerospace engineering applications (i.e., planetary landers). While the prevalent design methods of reusable energy absorbers mainly use the mechanical instability of tilted and curved beams, the limited energy absorption capabilities and low strength of tilted or curved beams limit performance improvement. In nature, Phlorodes diabolicus has evolved extreme impact resistance, in which the suture interface structure plays a key role. Herein, we propose a convex interface slide design strategy for reusability and energy absorption through friction interface, geometry, and bending elasticity, inspired by the elytra of Phlorodes diabolicus. Convex interfaces slide to achieve a more than 270% higher energy absorption capacity per unit volume than the curved beams. The convex interface slide design can be easily integrated with other structures to achieve multiple functions, such as various shapes and self-recoverability. Furthermore, we developed a theoretical model to predict the mechanical behavior and energy absorption performance. Our strategy opens up a new design space for creating reusable energy-absorbing structures.

Full-scale analysis of smart fluid-filled barrier technology: Numerical and experimental study of fixture configurations

Roadside barriers are often deployed to prevent vehicles from colliding with roadside obstacles or hazards and from leaving the road surface. These barriers primarily take the form of guardrails or crash cushions and are designed to absorb energy through severe plastic deformation. Due to the severity of these types of collisions, the energy-absorbing mechanisms can fail resulting in the barrier becoming a hazard. To address this issue, a (US Patented) multi-chambered, smart fluid-filled barrier technology (SFFBT) was proposed as a potential replacement for such roadside barriers. This new patented technology utilizes fluid transport between the internal chambers and viscous dissipation as an additional energy-absorbing mechanism to help reduce the effects the severe deformation imparts on the colliding vehicle and its occupants. Numerical models were developed in ABAQUS dynamic explicit environment, and full-scale experimental testing was conducted at the Midwest Roadside Safety Facility of the University of Nebraska—Lincoln. Three barrier configurations were considered for this study with two different fluid levels resulting in six unique test samples. The three test configurations were (a) free-standing, (b) abutted against a rigid backstop, and (c) anchored. Fluid levels chosen were 25% and 33% filled volume. The results show that the proposed designs and fluid addition provided an increase in energy absorption while decreasing overall deformation stroke by up to 5%. Additionally, kinetic energy reduction increased by 15% with a nearly 140% increase in fluid energy dissipation. The best-performing configurations were the rigid backstop cases, followed by anchored and free-standing configurations. The effects of varying anchoring schemes provide additional performance evaluations for maximizing the energy-absorbing performance of the SFFBT system for use as an impact attenuator.

Static and dynamic mechanical behavior of self-supporting lattice with symmetric gradients

Self-supporting lattice structures (s-LS) have shown great potential in various applications such as energy absorption. However, conventional s-LS designs solely rely on uniform structural configurations, limiting their mechanical properties. In this study, we present gradient lattice structures (GLS) by incorporating a size-graded design strategy. Both bending- and stretching-dominated GLS are fabricated using the Selective Laser Melting (SLM) technique. A comprehensive investigation of their mechanical properties, failure modes, and energy absorption is conducted under both quasi static and dynamic impact loading. It is observed that the stretching-dominated GLS exhibits significantly higher load-carrying capacity and energy absorption efficiency compared to the bending-dominated GLS. The gradient design enabled GLS to manifest different internal stress distribution, deformation processes, and failure modes in response to loadings. Furthermore, GLS also displays significant strain-rate dependent mechanical behavior, leading to improved energy absorption efficiency while maintaining a high material utilization rate. Our gradient-based design strategy may pave the way for more applications in energy absorption using lattice structures.

Auxetic response of additive manufactured cubic chiral lattices at large plastic strains

Auxetic lattices exhibit a negative Poisson’s ratio and excellent energy absorption capability. Here, we investigate the compressive performance of auxetic cubic chiral structures. By utilising finite element analysis (FEA) verified by interrupted mechanical testing and x-ray computed tomography, the auxeticity and failure mechanisms at the large strain deformation have been evaluated. The FEA results show that the initial elastic–plastic response agrees with the prediction of the classic scaling laws of bending-dominated lattices. At increasing plastic deformation, the energy absorption and auxeticity are dependent on relative density, i.e., the slenderness ratio, of the constitutive struts. In the plastic regime, the auxeticity decreases with relative density. Ductile fracture precedes densification in relative densities above 1.2%, thus dictating a new scaling law for the variation of the maximum energy absorbed with density. The numerical model predicts the scaling of mechanical properties, fracture strains, and energy absorption of the constitutive unit cell and finite-sized specimens in the relative density ranging from 0.3% to6.5%. However, to accurately model the failure mechanism, geometrical imperfections should be included. The scaling laws derived from this work may aid the design of next generation auxetic lattices with tailored mechanical properties.

Mechanical Properties and Energy Absorption of Soft–Hard Dual Phase Lattice Structures Manufactured via Selective Laser Melting

Mechanical Properties and Energy Absorption of Soft–Hard Dual Phase Lattice Structures Manufactured via Selective Laser Melting

Enhanced mechanical energy absorption via localized viscoplasticity of nano-cellular polymer coating under supersonic impact loading

Enhanced mechanical energy absorption via localized viscoplasticity of nano-cellular polymer coating under supersonic impact loading

Experimental and numerical studies on mechanical properties of TPMS structures

Due to their exceptional lightweight and mechanical properties, triply periodic minimal surface (TPMS) based lattice structures have been widely studied. In this paper, the energy absorption performance of eight TPMS structures under large deformation was thoroughly studied, and five meshing strategies were evaluated comprehensively for the first time. The research objectives include three parts. First, the mechanical properties of eight TPMS structures, namely Primitive (P), Gyroid (G), Diamond (D), I-Wrapped Package (I-WP), Fischer-Kock (F-K), Neovius (N), I2-Y⁎⁎ and F-Rhombic Dodecahedra (F-RD) lattices, were investigated by utilizing experimental and numerical methods. These TPMS structures were fabricated using 316 L stainless steel powder by selective laser melting (SLM) and compared experimentally under compression in terms of the stress-strain curve, deformation and energy absorption. The results showed that F-RD and D lattice structures exhibit the best energy absorption capacity at relative densities less and greater than 30%, respectively. Second, to evaluate different meshing strategies for these complex structures, five finite elements (FE) models based on the shell, solid, and voxel elements were compared in terms of modeling ease, computational efficiency, data management, and simulation accuracy. It was demonstrated that the quadrilateral shell model shows satisfactory results for lattice structures with low relative densities or thin walls. In contrast, the voxel model shows the best results for structures with higher relative densities or thicker walls. Last, the voxel model was applied to the F-RD and D lattice structures. The numerical results showed that the stress distribution was more uniform in the F-RD, and the internal self-contact occurred later in the D lattice structure, further confirming the experimental observation and revealing the energy absorption mechanisms of TPMS structures.

Composite sepiolite/chitosan layer-by-layer coated flexible polyurethane foams with superior mechanical properties and energy absorption

Flexible polyurethane foam composites with enhanced stiffness and energy dissipation have been prepared via a facile layer-by-layer assembly approach. The composite foams consisted of naturally abundant nanoclay/chitosan multilayers (up to six) deposited onto the foam struts via dip-coating. The nanoclay/chitosan polyurethane foams were characterised using infrared spectroscopy, scanning electron microscopy, elemental mapping and μ-CT scanning. Quasi-static mechanical compression of the foams with 6 bilayers showed a 202% increase in the stiffness and a 33% enhancement in the damping loss factor compared to the uncoated pristine foam. Vibration transmissibility tests showed that the dynamic modulus of the 6-bilayer coated foams was 3 times that of the pristine foam. Remarkably, impact tests registered a 50% decrease in the transmitted impact force of these sepiolite/chitosan layer-by-layer coated open cell polyurethane foams, demonstrating their improved energy dissipation capability compared to other nanocoated foams in open literature.

3D printed hierarchical interpenetrating phase composites with multi-scale mechanical energy absorption mechanisms

Lightweight, strong, and energy-absorbing materials are highly sought after in practical engineering applications. To this end, interpenetrating phase composites (IPC) stand as a novel class of composite materials to better leverage the properties of their constituents. Their structural design, however, has been limited to only specific structural features at a certain length scale in the existing studies. Inspired by the hierarchical composite materials in nature, this work proposes a novel concept of hierarchical interpenetrating phase composites (HIPC) by polymer infiltration into 3D printed hierarchical porous ceramic lattices. The hierarchical porous alumina lattices have up to three levels of porosity, including 3D printed macropores (≈300 μm), emulsion-templated micropores (≈10 μm), and sub-micropores (<1 μm) from partial sintering. Upon epoxy infiltration, three-level HIPC is constructed with hierarchically incorporated epoxy domains and alumina-epoxy interfaces, which leads to its unique multi-scale mechanical energy absorption mechanisms. Featuring a particularly porous and lightweight ceramic lattice, three-level HIPC exhibits an excellent combination of high specific compressive strength (64.6 kN m/kg), specific flexural strength (39.2 kN m/kg), and SEA (18.4 kJ/kg). In addition, even with a low ceramic content, three-level HIPC can effectively enhance the thermal conductivity via its hierarchically continuous ceramic microstructure. Therefore, our three-level HIPC has demonstrated impressive mechanical and thermal enhancement with its exquisite hierarchical architecture. The hierarchical structural engineering approach also represents a paradigm shift from constructing single-scale IPCs to multi-scale HIPCs and can be extended to other material combinations for high-performance structural and functional materials.