Specific Energy Absorption Values Research Articles

An experimental investigation into crashworthiness of filament wound intra-yarn hybrid glass/jute epoxy composites tubes under quasi-static axial and lateral compression

The increasing demand for sustainable materials in the automotive industry has driven the research towards exploration of natural fiber composites for crash structures. This study investigates the quasi-static axial and lateral crushing behavior of hybrid glass/jute fiber epoxy tubes. Intra-yarn hybrid mixing ratios of jute and glass fibers were tested to evaluate the feasibility of using natural fibers as eco-friendly alternatives to traditional synthetic composites. A total of five different configurations were fabricated using filament winding process. The experimental results were analyzed for collapsing behavior, failure modes, and energy absorption characteristics. The hybrid epoxy tubes revealed fiber-matrix fracturing, local buckling, and delamination as three primary failure modes under crushing tests. The hybrid configuration with 25 % jute fiber and 75 % glass fiber demonstrated optimal crashworthiness performance, achieving the highest specific energy absorption (SEA) values of 15.85 J/g under axial loading and 2.96 J/g under lateral loading. The configurations with higher jute content of 50 % and 75 %, showed decreasing SEA and crush force efficiency (CFE) values, with brittle fracturing and delamination as dominant failure modes, indicating a trade-off between weight and energy absorption efficiency. The neat glass fiber configuration maintained nearly consistent CFE values of 0.55 and 0.56, between axial and lateral loadings respectively, demonstrating isotropic behavior in energy absorption. Conversely, the neat jute fiber configuration improved SEA to 12.14 J/g under axial loading but exhibited significant limitations under lateral loading, with SEA decreasing to 0.69 J/g. Visual examination of crushed samples highlighted local buckling in GF configurations and brittle fracturing in hybrid and neat jute fiber configurations. The scanning electron microscope (SEM) analysis provided detailed insights into the microstructural characteristics and failure mechanisms, highlighting the inter-laminar debonding between the jute and glass fibers in hybrid configuration. By evaluating the combined effects of hybridization and loading conditions, the present study contributes to developing eco-friendly and efficient materials for automotive safety, aligning with industry sustainability goals.

A multifunctional heterogeneous structure inspired by shell brick-mud structure: Balancing noise reduction and mechanical performance

Electric armoured vehicles, which are crucial for strategic operations, must possess superior mechanical properties and noise reduction to maintain normal functionality. However, achieving high energy absorption and noise reduction performance simultaneously is challenging with a single uniform material or structure. This study introduces heterogeneous structures with metal lattice skeletons filled with polymer materials. The skeleton, known as the bionic mantis shrimp structure (BMS), is filled with polyurethane and epoxy. Impedance tube experiments revealed that the sound absorption coefficients of Heterostructure-polyurethane foam (HS-PU) and Heterostructure-epoxy (HS-EP) are significantly higher than BMS. HS-PU achieved an average sound insulation of 33.6 dB, marking a 739 % improvement over BMS. Compression tests show that polymer filling can inhibit the destructive collapse of BMS and enhance its mechanical performance. HS-EP exhibits specific strength and specific energy absorption values of 57 MPa/(g·cm−3) and 30.75 J/g, respectively, representing an increase of 67.6 % and 315 % compared to BMS. Additionally, as the volume fraction of BMS increased in the heterogeneous structure, the elastic modulus and compressive strength increase while the specific energy absorption decreased. This research suggest that the design of metal/polymer heterogeneous structures offers a promising approach for developing high-strength and noise-reducing protective structures.

Experimental investigation on energy absorption capability of 3D-printed lattice structures: Effect of strut orientation

This experimental study aimed to investigate the effect of strut orientation in various lattice structures that were created using 3D printers on the energy absorption capabilities of the structures. The experiment involved producing three different lattice structures, namely a cube lattice with vertical and horizontal struts, an octet structure with horizontal and 45˚ angled struts, and a body-centered-cubic (BCC) lattice structure with horizontal, vertical, and 45˚ angled struts using the FDM method. Nylon filament mixed with chopped carbon fiber was utilized as filament, and each lattice structure was designed to contain three units in the x and y directions and one and three units in the z-direction. The study conducted axial crushing tests on single-layer and three-layer lattices to determine the energy absorption capabilities of the various lattice structures. The octet lattice demonstrated the highest energy absorption in both single-layer and three-layer samples, making it the most efficient sample. In single-layer lattice samples, the cube and octet structures absorbed 77% and 94% more energy than the BCC structure, which absorbed only 12.8 J. However, the cube structure demonstrated the lowest energy absorption in three-layer samples. This was attributed to the buckling behavior seen in the strut of the lattice structure under axial load. The octet structure had the highest specific energy absorption value in both layers, making it the most energy-efficient sample.

Energy Absorption and Failure Modes of Different Composite Open-Section Crush Elements under Axial Crushing Loading.

In order to study the energy absorption characteristics of the open-section thin-walled composite structures with different cross-sections, axial compression tests were carried out at loading speeds of 0.01 m/s, 0.1 m/s, and 1 m/s. Finite element models were built to predict the crushing response and energy absorption behaviors of these open-section structures. The effects of the cross-section's shape, cross-section aspect ratio, trigger mechanism, and loading speed on the energy absorption characteristics of the composite structures were analyzed. The results show that the average crushing loads of the hat-shaped and Ω-shaped open-section structures are 14.1% and 14.6% higher than those of C-shaped open-section structures, and the specific energy absorption (SEA) values are 14.3% and 14.8% higher than that of C-shaped open-section structures, respectively. For the C-shaped open-section structures, a 45° chamfer trigger is more effective in reducing the initial peak load, while a 15° steeple trigger is more appropriate for the hat-shaped open-section structures. The average crushing loads and SEA of C-shaped, hat-shaped, and Ω-shaped open-section structures are reduced when the loading speed is increased from 0.01 m/s to 1 m/s. The increase in loading speed leads to the splashing of debris and thus reduces the loading area and material utilization of open-section structures, leading to a decrease in energy absorption efficiency.

Design and additive manufacturing of bionic hybrid structure inspired by cuttlebone to achieve superior mechanical properties and shape memory function

Lightweight porous materials with high load-bearing, damage tolerance and energy absorption (EA) as well as intelligence of shape recovery after material deformation are beneficial and critical for many applications, e.g. aerospace, automobiles, electronics, etc. Cuttlebone produced in the cuttlefish has evolved vertical walls with the optimal corrugation gradient, enabling stress homogenization, significant load bearing, and damage tolerance to protect the organism from high external pressures in the deep sea. This work illustrated that the complex hybrid wave shape in cuttlebone walls, becoming more tortuous from bottom to top, creates a lightweight, load-bearing structure with progressive failure. By mimicking the cuttlebone, a novel bionic hybrid structure (BHS) was proposed, and as a comparison, a regular corrugated structure and a straight wall structure were designed. Three types of designed structures have been successfully manufactured by laser powder bed fusion (LPBF) with NiTi powder. The LPBF-processed BHS exhibited a total porosity of 0.042% and a good dimensional accuracy with a peak deviation of 17.4 μm. Microstructural analysis indicated that the LPBF-processed BHS had a strong (001) crystallographic orientation and an average size of 9.85 μm. Mechanical analysis revealed the LPBF-processed BHS could withstand over 25 000 times its weight without significant deformation and had the highest specific EA value (5.32 J·g−1) due to the absence of stress concentration and progressive wall failure during compression. Cyclic compression testing showed that LPBF-processed BHS possessed superior viscoelastic and elasticity energy dissipation capacity. Importantly, the uniform reversible phase transition from martensite to austenite in the walls enables the structure to largely recover its pre-deformation shape when heated (over 99% recovery rate). These design strategies can serve as valuable references for the development of intelligent components that possess high mechanical efficiency and shape memory capabilities.

Crashworthiness behavior of multi-cell structures reinforced with small tubes under axial and inclined loading

In this paper, a novel design for the cross-sectional shapes of square, hexagonal, octagonal, and decagonal structures has been proposed for the development of energy-absorbing devices. The deformation behavior of these structures, which contain multiple small tubes, was analyzed under axial and inclined loads (0°, 10°, 20°, and 30°) using a validated finite element model in LS-DYNA, supported by experimental and analytical data. Various crushing metrics such as specific energy absorption (SEA), peak crushing force (PCF), mean crushing force (MCF), crush force efficiency (CFE), and undulation of load-carrying capacity (ULC) were evaluated for the structures. The results indicated an optimal size for the small tubes that maximizes energy absorption capability. Through the TOPSIS method considering 12 criteria, the multi-cell octagonal structure O5, which includes the highest number of small tubes, was identified as the most effective energy absorber. It demonstrated significantly higher Specific Energy Absorption (SEA) values compared to simpler structures S1, H1, O1, and D1, with improvements of 89%, 65%, 53%, and 46%, respectively. Therefore, it could be utilized in automotive structures for crashworthiness applications.

Energy absorption characteristics of modular assembly structures under quasi-static compression load

Inspired by the assembly of building blocks, an innovative modular assembly structure (MAS) is proposed. With its modular design and versatility, MAS can be tailored to diverse working environments and task requirements. A prototype MAS is generated through three-dimensional (3D) printing, and subsequent compression tests consistently display energy absorption performance akin to a finite element model, affirming the validity of the simulations. Multiple MASs are obtained through the assembly of oblique cross cells, and the effect of compression direction on the energy absorption capacity of MASs is discussed. It is found that transverse compression outperforms longitudinal compression in energy absorption, and MAS with four cells and transverse loading demonstrates the highest specific energy absorption (SEA) value. Furthermore, quadrilateral, pentagonal, and hexagonal cells are proposed to obtain more MASs, and the compression performance of these MASs is evaluated by varying the frame structure thickness d and supporting structure thickness j of cells. Results highlight the superior energy absorption efficiency of the pentagonal element structure. Notably, parameter d has a more pronounced impact on energy absorption compared with parameter j. When j is 2.0 mm and d increases from 1.0 mm to 2.0 mm, the SEA values of quadrilateral, pentagonal, and hexagonal MASs increase by 113.70, 139.45, and 86.25 J/kg. In summary, MASs exhibit impressive energy absorption capabilities, promising versatile applications in energy absorption and anti-collision mechanisms across various scenarios.

Dynamic mechanical properties of selective laser-melted AlSi10Mg lattice structures: experimental and numerical analysis with emphasis on Johnson-Cook model parameters

Additively manufactured lattice structures are extensively utilized because of their unique characteristics, including lightweight design, high energy absorption capabilities, and exceptional specific strength. This study focuses on accurately simulating the dynamic mechanical behavior of AlSi10Mg lattice structures produced using selective laser melting (SLM). A series of experimental studies has been conducted to establish the parameters of the J–C hardening and damage model for additively manufactured AlSi10Mg alloys. The lattice structures, featuring face-centered cubic (FCC) and diamond topologies with a 25% designed relative density, underwent scanning electron microscopy (SEM) for geometrical precision assessment. Dynamic compressive behavior was investigated via split Hopkinson pressure bar (SHPB) tests. Numerical simulations in Ls-Dyna, utilizing the identified J–C parameters, were employed to replicate SHPB tests. Findings indicate that the specific strength and the specific energy absorption values of FCC lattice samples have higher than those of diamond samples at strain rates of 750 and 1100 s−1. While the overall strains and deformation modes were well predicted by numerical analyzes, a deeper insight into local stress concentrations under dynamic loads was achieved. Consequently, the obtained J–C model parameters offer valuable insight into characterizing the dynamic behavior of AlSi10Mg lattice structures produced by SLM.

On the crashworthiness analysis of bio-inspired DNA tubes

This study presents a thorough numerical evaluation of the crashworthiness properties of a new bio-inspired DNA tubes (BIDNATs) with circular, elliptical, and rectangular cross-sections. Deformation and crashworthiness behaviors are evaluated using axial quasi-static crushing simulations by ABAQUS/Explicit (Abaqus 6.14, https://www.3ds.com/products-services/simulia/products/abaqus/). The study compares the performance of conventional tubes with rectangular and elliptical cross-sections to DNA-inspired tubes. Increasing the rotation angle leads to more helices and a pronounced helix angle, resulting in lower initial peak force (IPF). However, lower cross-section aspect ratios generally have higher IPF and specific energy absorption (SEA) values. BIDNATs with rectangular cross-sections and a 540° rotation angle have the lowest SEA and IPF values across all aspect ratios. Notably, for the 110/100 aspect ratio, the SEA of E110/100 is 71% higher than the conventional tube. Overall, BIDNATs with elliptical cross-sections and a 360° rotation angle exhibit higher SEA values and lower IPF values, particularly for a width (W) of 100 mm. Conventional circular and elliptical tubes generally have SEA values exceeding 6 J/g, with only E110/100 surpassing this among DNA-inspired tubes. The NE110/100 tube has the highest SEA, surpassing E110/100 by 54%, while its IPF is 10% greater than DNA-inspired E110/100. It's worth noting that conventional circular and elliptical tubes have higher IPF values compared to their DNA-inspired counterparts. These findings offer valuable insights for engineers and researchers in the design of crash tubes to improve overall vehicle safety for both occupants and pedestrians.

Comparison of in-plane compression of additively manufactured Ti6Al4V 2D auxetic structures: Lattice design, manufacturing speed, and failure mode

The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required.

Quasi-static crush response of lightweight sandwich composite tubes fabricated via newly designed internal thermal expansion technique

Different from conventional unidirectional outward-inward forming methods, this study employs a multidirectional internal expansion shaping approach to fabricate lightweight sandwich composite tubes. Integrating carbon fiber reinforced polymer (CFRP), thermal expansion foam and polymethacrylimide (PMI) foam, the sandwich composite tubes demonstrate adaptability in terms of material properties as validated through several experimental trials. The one-step molding process eliminates the requirements for subsequent structural assembly and bonding, while ensuring adhesion between diverse material components. The sandwich composite tubes exhibit superior impact resistance, showcasing a stable progressive crushing failure. The energy absorption mechanism shifts from single CFRP damage to a multi-material composite energy absorption mode. The specific energy absorption (SEA) value of designed sandwich composite tube is up to 102 J/g. The sandwich composite tubes fabricated in this study hold promising applications in advanced vehicle/aerospace lightweighting and crashworthiness safety.

Investigation on quasi-static axial crushing of Al/PVC foam-filled Al6063-T5 tubes

Abstract This study experimentally investigated the energy-absorbing capability of foam-filled 6063-T5 aluminum tubes. Thus, different sample combinations were created with two different foams, PVC (80 kg m−3) and aluminum (200, 350 kg m−3), which were used as filling materials. The first group of samples consisted of uniform foam-filled aluminum tubes. In contrast, tubes were filled with radially graded foams in the second group, which included a ring PVC foam and a cylindrical aluminum foam in the center. Empty tube absorbed 329 J, while it reached the values of 384, 488, and 606 J by using PVC and low- and high-density aluminum foams, respectively. The specific energy absorption value of the empty tube was obtained as 23.2 J g−1. In comparison, it was 19.3 J g−1 in the high-density aluminum foam-filled sample, although it absorbed the highest energy value. This shows that high-density aluminum foam was inefficient in terms of the crashworthiness of the structure. Finally, the best sample regarding the specific energy absorption and crush force efficiency was obtained in the sample where the PVC foam ring and high-density aluminum tube were used together. This sample had 7 % higher specific energy absorption and 34 % higher crush force efficiency than the empty tube.

Numerical investigation on energy absorption characteristics of impact-resistant lightweight structure of bio-mimetic micro aerial vehicle

With the increasing development of micro aerial vehicle, the impact resistance of the structure has gradually become a research hotspot. The beetle's exoskeleton not only provides important protection for its body and flexible wings but also ensures its good flight performance. Therefore, the beetle's exoskeleton has become an important research content in the field of bio-mimetic micro aerial vehicles. In this study, taking the internal structure of the beetle's exoskeleton as the research object, a kind of bio-mimetic lightweight thin-walled impact-resistant structure that can be used in the micro aerial vehicle is proposed. The energy absorption characteristics of the bio-mimetic structure under axial impact loading are calculated and analyzed by the numerical simulation method, and the important parameters such as impact angle, protective layer thickness, and wall thickness are optimized and discussed. The main results include that the filling method of the hollow column has a certain correlation with the energy absorption characteristics of the structure under different impact angles, and among the different cross-sectional shapes, the hollow column with a circular cross-sectional configuration has the best energy absorption ability. In addition, as the internal space of the structure increase exponentially, the decrease of specific energy absorption value of the bio-mimetic structure is relatively small. Finally, the wall thickness with good energy absorption characteristics is about 1.5 mm, while the preferred span length of the structure is between 90 and 120 mm.

The Mechanical Properties of Functionally Graded Lattice Structures Derived Using Computer-Aided Design for Additive Manufacturing

This study aims to investigate the mechanical properties of Functionally Graded Lattice Structures (FGLSs) and to determine their industrial application possibilities through additive manufacturing. For this purpose, lattice structures with uniform and horizontal, vertical and radially graded configurations are designed using auxetic unit cells were fabricated with RGD720 photopolymer resin using Material Jetting. FGLSs are compared with uniform structures in regards with deformation behavior, structural strength and energy absorption. The results showed that the most significant deviation in the strut diameters of the uniform lattice structures was seen in the rotation lattice structure at 8.2%. The lowest deviation was seen in the chiral structure, which deviated by 5.4%. The lowest deviations (between 3.4% and 9%) in FGLSs were obtained in chiral structures. The highest relative density value (0.3049 g/cm3) among all configurations was observed in the vertically graded chiral structure. The lowest relative density value (0.1865 g/cm3) was obtained in uniform re-entrant structures. According to the compression test results, the highest compressive stress (2.61513 MPa) and elastic modulus (84.63192 MPa) were formed in the rotation structure. The maximum energy absorption capacity value (19.381 KJ) and the maximum specific energy absorption value (3649.905 KJ/kg) were obtained in the uniform chiral structure.

Design, FDM printing, FE and theoretical analysis of auxetic structures consisting of arc-shaped and Dumbell-shaped struts under quasi-static loading

This paper presents the design, 3D printing, and testing of this novel type of auxetic structure formed with arc-shaped unit-cells (UCs). The mechanical behavior of two different re-entrant Dumbell (RED) and Multiple-Arc structures are evaluated. The metamaterials are fabricated using 3D printing via Fused Deposition Modeling (FDM) techniques. Quasi-static compressive loading tests are performed on these metamaterials, and the results are verified using Finite Element (FE) simulation and theoretical analysis. The results of the study reveal that the RED configuration, which includes Dumbell-shaped struts that exhibit negative Poisson’s ratio (NPR) themselves, outperforms the Multiple-Arc, the traditional re-entrant circular (REC), and conventional re-entrant auxetic structures in terms of specific stiffness (Es) specific energy absorption (SEA) and NPR values. In addition, the effects of the geometry parameters, including strut thickness to height ratio, length to height ratio, and angle of Dumbell strut on the SEA and NPR values of the RED structure, are investigated. The findings indicated that the SEA values improved as the thickness-to-height ratio and Dumbell strut angle increased, and the length-to-height ratio decreased. Additionally, the NPR value showed enhancement with increased thickness-to-height ratio and Dumbell strut angle. However, the thickness-to-height ratio did not significantly influence the NPR value.

Lateral compression behavior of expanded polypropylene foam–filled carbon and glass fiber composite tubes

Abstract The crashworthiness and deformation behavior of circular composite tubes that were internally supported with expanded polypropylene (EPP) foams were investigated under lateral compression tests. Carbon woven (CFRP) and glass woven fiber/epoxy (GFRP) composites and EPP foam with densities of 30, 60, and 75 kg·m−3 were used. According to results, empty CFRP and GFRP tubes absorbed almost the same amount of energy; however, the GFRP tube had a higher specific energy absorption value due to its lower weight compared to the CFRP tube. EPP foam filling has a more significant effect on the crashworthiness of CFRP tubes compared to GFRP tubes. The best results in CFRP tubes, in terms of specific energy absorption, were obtained as 2.67 J g−1 at 75 kg·m−3 EPP foam-filled sample; however, 60 kg·m−3 EPP foam–filled sample exhibited the best configuration in terms of force efficiency. For the GFRP tubes, the best configuration was obtained at 60 kg·m−3 EPP foam–filled sample for all of the crashworthiness parameters. It is seen that the crushable length of composite tubes was shortened with the increase of EPP foam density. Lastly, the deformation behaviors of composite tubes showed that the CFRP tubes were more brittle than the GFRP tubes.

Fused-Deposition Modeling 3D Printing of Short-Cut Carbon-Fiber-Reinforced PA6 Composites for Strengthening, Toughening, and Light Weighting.

Additive manufacturing of carbon-fiber-reinforced polymer (CFRP) has been widely used in many fields. However, issues such as inconsistent fiber orientation distribution and void formation during the layer stacking process have hindered the further optimization of the composite material's performance. This study aimed to address these challenges by conducting a comprehensive investigation into the influence of carbon fiber content and printing parameters on the micro-morphology, thermal properties, and mechanical properties of PA6-CF composites. Additionally, a heat treatment process was proposed to enhance the interlayer bonding and tensile properties of the printed composites in the printing direction. The experimental results demonstrate that the PA6-CF25 composite achieved the highest tensile strength of 163 MPa under optimal heat treatment conditions: 120 °C for 7.5 h. This corresponds to a significant tensile strength enhancement of 406% compared to the unreinforced composites, which represents the highest reported improvement in the current field of CFRP-fused deposition 3D printing. Additionally, we have innovatively developed a single-layer monofilament CF-OD model to quantitatively analyze the influence of fiber orientation distribution on the properties of the composite material. Under specific heat treatment conditions, the sample exhibits an average orientation angle μ of 0.43 and an orientation angle variance of 8.02. The peak frequency of fiber orientation closely aligns with 0°, which corresponds to the printing direction. Finally, the study explored the lightweight applications of the composite material, showcasing the impressive specific energy absorption (SEA) value of 17,800 J/kg when implementing 3D-printed PA6-CF composites as fillers in automobile crash boxes.

Energy absorption characteristics of starfruit-inspired biomimetic lattice structure under non-axial compression loading

Lattice structures inspired by biological models often exhibit excellent energy absorption characteristics and gain increasing attention. Inspired by the shape of starfruit, this work proposes a starfruit-inspired biomimetic lattice structure (SBLS) with variable cross-sectional size. The compression performance and energy absorption efficiency of the SBLS are investigated by non-axial compression experiment and simulation. In addition, the potential application scenario of SBLS is presented. SBLS shows excellent energy absorption effect and compression performance. The structural variables of SBLS are changed to study their effects on the energy absorption characteristics. The SBLS with variable cross-section performs better than that with constant cross-section size. Compared with L1-11.2, the energy absorption (EA) and specific energy absorption (SEA) values of L1-5.36 increase by 85.16 % and 119.90 %. Compared with SBLS, the SEA values of L1-5.36, S-0.8, N-5 and T-1.6 increase by 36.31 %, 28.56 %, 35.47 % and 19.98 %. These SBLS models show novel deformation modes. The cells take on the shape of a man with his hands raised upward, and the SBLSs look like people holding hands overlapping. The deformation mode of L2-6.745 likes multiple Yuanbao arranged together. In summary, SBLS exhibits excellent energy absorption characteristics and has broad application prospects.

Spherical porous structures for axial compression

Porous structures have attracted much attention because of the advantages of lightweight and strong energy absorption efficiency. This work proposes a spherical porous structure (SPS) and a square porous structure (SQPS), and the SPS sample is manufactured by selective laser sintering (SLS) technique with the material nylon 11. Their axial compression results of experiment and simulation show that the compressive strength of hollow cylinders is greater than that of porous spheres, and porous spheres are always crushed during compression. SPS exhibits the rapid collapse characteristics of porous spheres layer by layer, and it shows four sharp valley forces and significant negative stiffness characteristic. In addition, the specific energy absorption (SEA) value of SPS is higher than that of SQPS 30.84%. The compression capacity of porous spheres is stronger than that of porous cubes. This study furtherly discuss the mechanical behavior of SPS with different structural parameters. The negative stiffness characteristic, energy absorption efficiency and deformation mode of SPS depends on the strength combination of porous spheres and hollow cylinders, and smaller overall cell size, more cell layers, and thicker cells contribute to improving the anti-compression properties of SPS. The SEA values of SPS- T1.6 and SPS- F7 are 12.52% and 12.16% higher than that of SPS. In summary, SPS shows novel mechanical properties, providing a reference for the design of new energy absorbers.

A nature-inspired gradable elliptic-cell lattice structure based on cypress wood texture; theoretical and experimental analysis for mechanical properties

The accessibility and commercialization of additive manufacturing allow scientists to design affordable, light weighted cellular-graded structures with customized mechanical properties. This study introduced a new functionally graded lattice structure inspired by the porous wood texture of cypress. This structure can simultaneously alter the relative density and unit cell shapes by gradual cell size grading and its porosity in each repetition which can provide graded properties along the particular axis and in each structural point. Different mechanical properties and geometrical features are easily achievable by altering the unit cell’s shape and dimensions. Elastic modulus, Poisson’s ratio, and specific energy absorption values depend on ellipses radii in cell scales, layers of lattices, and structures. Porosity and surface-to-volume ratio are calculated with high accuracy for different structures, which can be optimized for biomaterial and bioimplant substitution. Numerical simulation is carried out as two perpendicular uniaxial compressions for extracting the structural properties. In addition, an experimental test on the polymeric specimen, made by the DLP technique, validates the results, which shows good agreement with numerical ones. Designs of experiments were set up to determine the parameters’ main and interaction effects on the mechanical properties. RSM function is evaluated for two radii as factors in three levels in both unit cells and layers. Linear tessellation of a layer and parallel array of two perpendicular sets results in a highly porous, ultra-light, weighted structure.