Specific Energy Absorption Capability Research Articles

Experimental and numerical investigation of multi-layered honeycomb sandwich composites for impact mechanics applications

This project aims to investigate the design of a multi-layered sandwich composite and its performance under impact loading conditions. An experimental and numerical assessment was performed to conclude the effect of increasing the layers of sandwich panels. Three specimens of four different sandwich panel configurations were manufactured to be tested. The skin of the sandwich panels comprises a twill carbon-reinforced epoxy resin, whereas the core consists of a 2D Nomex honeycomb core. The panels are then subjected to transverse impact loading to investigate their impact behaviour. These experimental results are then used to verify numerical models constructed in LS-Dyna. The models of the honeycomb-reinforced sandwich panels are investigated using MAT-054 and MAT-142 material cards in LS-Dyna to find the most economical computational approach. Finally, the energy absorption characteristics calculated during the experimental and numerical work are used to conclude the multi-layered sandwich composite's performance and provide design recommendations. The findings suggest that by increasing the core and shell numbers through the thickness of the panel, the specific energy absorption capability will increase.

Modified re-entrant auxetic metamaterials with energy absorption enhancement

The re-entrant auxetic topology was one of the first unit-cells proposed to build cellular auxetic structures. This unit cell (UC) is still widely used in energy-absorbing systems, but there is considerable scope for enhancing its design. This paper describes a series of experimental tests and finite element (FE) models used to evaluate the energy absorption capabilities of novel auxetic structures based on replacing straight struts of the re-entrant unit cell with curved-shaped ones. Three structures have been first designed and manufactured using fused deposition modeling (FDM) 3D printing techniques. The samples have then been subjected to quasi-static compressive testing. The results have been compared with those of a traditional re-entrant structure having similar relative densities and showed that the modified metamaterial topologies demonstrate significantly improved energy absorption and specific energy absorption (SEA) capabilities. In addition, all the proposed new topologies exhibit negative Poisson’s ratio (NPR). After selecting the structure with the highest SEA, a geometrical parametric analysis has been performed to investigate the design space to enhance overall SEA and NPR values. The proposed work provides an overview of the state-of-the-art in re-entrant auxetic structures and introduces a new class of modified re-entrant metamaterials with remarkable energy absorption capability.

Bending performance and failure mechanism of 3D-printed hybrid geometry honeycombs with various poisson’s ratios

By utilizing 3D printing technology, experimental three-point bending (TPB) tests, and finite element analysis, six honeycomb structures with a variety of overall Poisson’s ratios (PR) are studied and compared in terms of bending properties and failure mechanisms. Four novel honeycombs that are designed by hybridizing hexagonal and re-entrant units outperform benchmark conventional honeycombs in terms of load-carrying capacity. Architected hybrid geometry honeycombs with zero PR show excellent specific energy absorption capability in comparison to benchmark honeycombs, absorbing approximately 136.9% and 475.1% more energy under TPB. 3D-printed honeycombs consisting of hexagonal units face layer separation damage mode under bending, while honeycombs with re-entrant cells in their lattice fail with joint shear due to the angle of their struts towards loadings. Designing honeycombs with a hybrid geometry lattice can enhance the load-carrying capacity, specific energy absorption, flexibility, and flexural modulus of the structure under bending. Due to their superior performance, the proposed architected hybrid geometry honeycombs with various Poisson’s ratios own promising applications in automotive, protective, and construction industries.

Improving the compressive response of bio-polymeric additively manufactured cellular structures via foam-filling: An experimental and numerical investigation

Additive Manufacturing is effective at addressing advanced innovative design requirements for functional applications. Lattice structures and lightweight composites are the result of engineering designs for enhanced mechanical and structural properties. Inspired by nature, this work investigates the static and cyclic compressive response of 3D-printed Triply-Periodic-Minimal-Surface cellular structures made of Poly-(Butylene-Adipate-co-Terephthalate) (PBAT) biopolymer functionalized with Poly-Urethane foam. The plateau stress of the hybrid structure is 30% higher and the specific energy absorption capability 18% higher than the empty structure due to interaction between the two phases. A finite-element model is developed as a supporting tool to analyze, predict, and optimize structural behavior, as well as improve understanding of the deformation mechanisms. In addition, PBAT proves to be the ideal candidate for greener manufacturing, combining good mechanical properties with biodegradability, paving the way for a range of new applications.

Design and development of fused deposition modeling (FDM) 3D-Printed Orthotic Insole by using gyroid structure

The orthotic insole is a device that is placed between the bottom of the foot and the sole of the shoe. It bears the body weight and directly influences the biomechanics of the foot and the body. These insoles are used to minimize the stress by reducing plantar pressure between support points hence minimizing the pressure. Such customized insoles have usually been produced by either handmade or subtractive methods. Fused deposition modeling (FDM) has opened innovative ways for the manufacture of orthotic insoles. In recent studies, no specific computer-aided design (CAD) tools are available to design and manufacture the insole, which is the primary focus. This work aims to evaluate established CAD techniques for designing and fabricating insoles utilizing different manufacturing processes. The evaluation is based on a prior analysis of the possibilities for functionalizing insole materials and structures. In this study, multiple software tools are utilized for designing custom insoles, considering pressure points and a three-dimensional (3D) foot scan of an individual. The research highlights how the implementation of software enables a significant level of customization by integrating pressure mapping data into the insole design process. A novel CAD approach for designing an orthotic insole has been provided in this work. Soft poly-lactic acid (PLA) is used to fabricate an insole using FDM technology. The gyroid and solid samples were evaluated following ASTM standards. When compared to the solid construction, the gyroid structure has a high specific energy absorption capability, which is used to create the orthotic insole. The results of the experiment suggest that the selection of the structure for customized insole design is significantly affected by the infill density parameter.

Origami-inspired sandwich structures under low-to-high velocity impacts: A numerical simulation approach

In this study, the ballistic impact performance of sandwich structures with Miura-origami pattern inspired core (MPIC) panels subjected to low-to-high velocity impacts is studied. Sandwich panels with MPIC structure were modeled and finite element analysis was performed using commercially available software LS-DYNA to evaluate their specific energy absorption (SEA) and load-bearing capabilities. A cylindrical indenter (diameter = 10 mm and height = 15 mm) with material property of mild Steel (ρ = 7800 kg/m3) was impacted at three different velocities, i.e., 10 m/s (0.46 J), 50 m/s (11.49 J), 100 m/s (45.95 J) under predefined impact conditions. The obtained results were compared with that of a monolithic solid plate under identical loading conditions and geometrical dimensions. The proposed MPIC design was 93% lighter in weight than the monolithic solid plate. On comparison of stress contours, the monolithic solid plate exhibited regions of high-stress concentration at the impact zone. However, for the MPIC sandwich panel, the stress contour was found to be uniform. For an impact velocity of 100 m/s, the SEA of the MPIC sandwich panel was found to be 1142.6 J/kg, while for the monolithic solid plate, it was obtained as 57.17 J/kg. Eventhough complete penetration of the MPIC sandwich panel occurred for an impact velocity of 100 m/s, the SEA of the MPIC sandwich panels were found to be significantly higher than that of the monolithic solid plate. Since MPIC sandwich panels exhibit enhanced energy dissipation characteristics, they can be an alternative to the conventional monolithic solid plate as light-weight high performance designs for specific applications.

Comparative Investigations on Fracture Toughness and Damping Response of Fabric Reinforced Epoxy Composites

Studies were conducted to observe the effect of fracture toughness and damping response on fabric reinforced epoxy polymer composites. The samples of glass fabric, kevlar fabric and carbon fabric having 15wt%, 25wt%, 35wt%, 45wt% and 55wt % fabric content were prepared and tested following ASTM standards. Fracture toughness, peak load and increase in energy absorption are determined for the fabric-epoxy composites. Effect of temperature on storage modulus, loss modulus and tan delta values for various percentages of fabric epoxy composites are noticed and corresponding damping response behaviour is determined. The results revealed that reduction in strength at higher percentage of fabric content is due to improper bonding between fabric and epoxy resin. Higher peak load values and increased values of energy absorption are observed at lower percentage of fabric content. Kevlar fabric proves to be beneficial for specific energy absorption capability. Strength retention capability at higher temperature is far better for carbon fabric epoxy combinations. Composites with lower fabric content retain much higher temperature and peak load. Also the experimental findings are in close proximity with that of theoretical results.

Design and 3D Printing of Graded Bionic Metamaterial Inspired by Pomelo Peel for High Energy Absorption

Light-weight, high-strength metamaterials with excellent specific energy absorption (SEA) capabilities are significant for aerospace and automobile. The SEA of metamaterials largely depends on the material and structural design. Herein, inspired by the superior impact resistance of pomelo peel for protecting the pulp and the elevated SEA ability of a functionally graded structure, a graded bionic polyhedron metamaterial (GBPM) was designed and realized by 3D printing using a soft material (photosensitive resin) and a hard material (Ti-6Al-4V). Guided by compression tests and numerical simulations, the elevated SEA ability was independent of the materials. The fluctuation region appeared in hard-material-fabricated bionic polyhedron metamaterial (BPMs) and was absent in soft-material-fabricated BPMs in the stress–strain curves, resulting in the growth rate of the SEA value of the soft-material-fabricated GBPM being enhanced by 5.9 times compared with that of the hard-material-fabricated GBPM. The SEA values of soft- and hard-material-fabricated GBPM were 1.89 and 44.16 J/g, which exceed those of most soft- and hard-material-fabricated metamaterials reported in previous studies. These findings can guide the design of metamaterials with high energy absorption to resist external impacts.

On the Mechanical Behaviour of Biomimetic Cornstalk-Inspired Lightweight Structures.

This paper presents an investigation on the stiffness and energy absorption capabilities of three proposed biomimetic structures based on the internal architecture of a cornstalk. 3D printing was used to manufacture specimens using a tough and impact-resistant thermoplastic material, acrylonitrile butadiene styrene (ABS). The structural stiffness, maximum stress, densification strain, and energy absorption were extracted from the compression tests performed at a strain rate of 10-3 s-1. A numerical model was developed to analyse the behaviour of the biomimetic structures under compression loading. Further, a damage examination was conducted through optical microscopy and profilometry. The results showed that the cornstalk-inspired biomimetic structure exhibited a superior specific energy absorption (SEA) capability that was three times higher than that of the other core designs as reported in the literature.

Experimental investigation on the perforation behaviour of sandwich panels with hybrid composite face sheets and cellular aluminium core using quasi-static and instrumented inverse impact methods

With the rising demand for lightweight and high-performance shielding systems, sandwich panels made of thin rigid face sheets and cellular material cores have recently received much attention. The present study aims to investigate the perforation behaviour of lightweight sandwich panels made of fibre reinforced composite face sheets and aluminium foam core under quasi-static and dynamic testing conditions. A particular focus is made on the fibre hybridization effect on the overall panel behaviour. Impact perforation tests were conducted using an inverse perforation technique. Instead of conventional free-flying projectile impact tests, studied samples are fixed in a hollow projectile. Then, this assembly is accelerated toward an instrumented steel perforator replacing the incident bar of a split Hopkinson pressure bar. Consequently, this modified split Hopkinson pressure bar system can be used as both a perforator and a measuring device. Therefore, the piercing force-displacement curves, the energy absorption capability as well as the penetration and damage mechanisms of the tested panels was analysed and compared to quasi-static perforating tests. To better assess the testing results, quasi-static tensile and bending tests were carried out on the face sheets materials. Moreover, quasi-static and dynamic compression tests were performed on the aluminium foam core using conventional test methods and direct split Hopkinson pressure bar. Unlike the aluminium alloy face sheets, the experimental findings revealed that the sandwich panels with composite face sheets demonstrated higher rate sensitivity, better perforation resistance and specific energy absorption capability. Results have also shown that the hybridization of carbon and glass fabrics combined their best tension and bending properties as well as their higher dynamic strength, which has increased the sandwich panel's perforation resistance.

A Brief Review on Advanced Sandwich Structures with Customized Design Core and Composite Face Sheet.

Sandwich structures are a class of multifunctional high-performance structural composites that have the advantages of being lightweight, of a high strength-to-weight ratio, and of high specific energy absorption capabilities. The creative design of the core along with the apposite material selection for the fabrication of the face sheet and core are the two prerequisites with encouraging areas for further expedition towards the fabrication of advanced composite sandwich structures. The current review work focused on different types of core designs, such as truss, foam, corrugated, honeycomb, derivative, hybrid, hollow, hierarchical, gradient, folded, and smart core along with different composite materials accessible for face sheet fabrication, including fiber-reinforced composite, metal matrix composite, and polymer matrix composite are considered. The joining method plays a major role for the performance evolution of sandwich structures, which were also investigated. Further discussions are aligned to address major challenges in the fabrication of sandwich structures and further enlighten the future direction of the advanced composite sandwich structure. Finally, the work is summarized with a brief conclusion. This review article provides wider guidelines for researchers in designing and manufacturing next-generation lightweight multilayer core sandwich structures.

State of the art review on mechanical properties of sandwich composite structures

AbstractSandwich composite structures are widely used in various industries namely, aerospace, automotive, packaging, biomedical, civil and electronics due to their high specific strength and energy absorption capabilities. Mechanical properties of sandwich structure depend on material properties of face sheet and core, and strength of face sheet‐core interface. Most commonly used composite materials are carbon fiber reinforced plastics, glass fiber reinforced plastics, ceramic matrix composites, and metal matrix composites. Several researchers have used nano‐fillers namely, nano‐clay, carbon nanotube, and nano‐silica for improvement of mechanical properties of composite structures. In this paper, an extensive literature review has been discussed regarding influence of various material and geometrical parameters on mechanical properties of sandwich composite structure. Initially, influence of various fiber reinforcement and nano‐fillers on mechanical properties are discussed. Then, deformation behavior and mechanical properties of honeycomb core is elaborated. Further, influence of temperature variation on composite structure is discussed. Moreover, crucial insights on reviewed literature are presented and future advancements in the field of sandwich composite structure are discussed.

Energy absorption in carbon fiber honeycomb structures manufactured using a liquid thermoplastic resin

In this study, carbon fiber/thermoplastic (Elium®) honeycombs were manufactured using the resin infusion process in a customized metallic mold. Honeycomb cores, based on different carbon fiber layers, were manufactured to achieve four different fiber weight fraction composites. Two different types of specimens, based on a single honeycomb cell and five honeycomb cells, were prepared and subjected to compression loading. The results of these tests were compared with data from similar honeycomb structures based on carbon fiber–reinforced epoxy composite. It has been shown that the compressive strength and the specific energy absorption capacity of the honeycombs increase rapidly with increasing fiber weight fraction. The specific energy absorption capability of the novel thermoplastic honeycomb structures has been shown to be as high as 50 kJ/kg which compares favorably with other energy-absorbing core materials. The thermoplastic honeycomb specimens exhibited a similar specific energy absorption capability and an improved compressive strength compared to their epoxy counterparts. Furthermore, the CF/thermoplastic honeycombs exhibited enhanced structural stability and displayed a more uniform and progressive core failure mode than the longitudinal splitting observed in the CF/epoxy honeycombs. The honeycomb core that exhibited the best performance was then used to manufacture thermoplastic sandwich specimens based on CF/thermoplastic face sheets. Three point bend tests were conducted to determine the flexural strength of the sandwich samples and to identify the failure modes. Optical micrographs revealed that the flexural damage was primarily due to the core crushing and adhesive failure between the core and the composite skins.

Novel arc-shaped ligaments to enhance energy absorption capabilities of re-entrant anti-trichiral structures

In this study, novel re-entrant anti-trichiral (REAT) structures with arc-shaped ligaments are proposed to enhance both the elastic modulus and energy absorption capabilities through both experimental and numerical approaches. By first replacing straight ligaments with curved ligaments, unique deformation patterns are introduced through the rotation of cylinders, contact interaction between cylinder and ligaments, as well as petal-like cell interactions. Quasi-static compression reveals the effect of curvature along ligaments and their directions on the Young's modulus, Poisson's ratio, plateau stress and specific energy absorption capabilities. The primary finding is an improvement of up to eight times in normalised Young's modulus and up to four times in specific energy absorption (SEA) with the introduction of combined curved ligaments (Dc + Uc) design. In addition, parametric studies on geometrical parameters of ligament curvature and cylinder diameter shows significant influence over mechanical properties and deformation patterns. The present study sheds light on the development of novel REAT honeycombs that can be achieved through simple ligament modifications and combinational designs.

Effect of loading rates on the in-plane compressive properties of additively manufactured ABS and PLA-based hexagonal honeycomb structures

Honeycomb structures find numerous applications in automotive, aerospace, sports, and other similar engineering fields. Such incorporation is made possible by the excellent crushing resistance and specific energy absorption capabilities. However, manufacturing such structures through conventional processes is highly laborious and expensive. Such a drawback can be largely mitigated by the adoption of additive manufacturing (AM) processes. Consequently, in this study, hexagonal honeycomb structures are subjected to experimental tests to determine their compressive strength under different loading rates. In addition to this, attempts have also been made to evaluate the effect of different materials and the unit cell dimensions on the compressive properties. The test specimens of different wall thicknesses are manufactured by fused deposition modelling (FDM) using PLA and ABS as the base materials. The samples are then subjected to compressive tests using a standard UTM to quantify the effect of the cell geometrical parameters and the loading rate on the overall compressive nature of the structures. The results show that the compression properties are primarily affected by the loading rate, material properties and the cell-wall thickness of the structures. The initial compressive yield stress and plateau stress generally increase up to a given value of loading rate, after which the strength decline. The cell-wall thickness of the structure influences the threshold loading rate. Therefore, this study provides a preliminary understanding of the compressive properties of AM hexagonal honeycomb structures to analyse the prospects for application in real-world engineering applications. It is proposed that such structures find profound applications in structural components of aerospace equipment, automotive parts, sports gear, and other similar areas of interest where high strength and energy absorption are of predominant importance.

Axial and lateral crushing performance of plate-lattice filled square sandwich tubes

In this work, a kind of novel sandwich square tube, filling plate-lattice into square tube, was proposed and preparation by 3D printing. The axial and lateral crushing performances of plate-lattice filled sandwich square tube (PLSST) were investigated by a combined experimental–numerical method. The experimental results were in good agreement with the numerical prediction. The results showed that load bearing and specific energy absorption capability (SEA) of sandwich square tube could be significantly increased by filling plate-lattice under axial and lateral crushing. Reinforcement mechanism is that plate-lattice filler in PLFSST can effectively improve the stability of progressive collapse and alter the compressive deformation mode of PLFSST, resulting in elevating crushing performance and energy absorption capability of PLFSST.

Experimental investigation on deformation behavior and energy absorption capability of nested steel tubes under lateral loading

The energy absorption behavior of nested tubes under lateral loading conditions was investigated in this study. Nested tubes are considered as an alternative to energy absorption structures used in many industries including automotive, military, and aerospace. Steel tubes with the same wall thickness and different diameters were used in the experiments. First, experiments of single tubes were carried out, and the deformation behavior of tubes under lateral load was examined in detail. Afterward, experiments were carried out on nested tube samples in which a minimum of 2 and a maximum of 6 tubes were used together in different numbers and sequences. It was seen from the experiments that the best-nested tube configuration in terms of energy absorption capacity was the sample that contains 6 tubes with 1767 J. While this sample absorbed 5% higher energy than the sample with 5 tubes, the specific energy absorption value was calculated to be 10% lower. Additionally, the sample with 6 tubes has a value of 43% in terms of energy efficiency which is 7% lower compared to that of the sample with 5 tubes. It was determined that the sample with 5 tubes yielded the most efficient design when specific energy absorption capability, work effectiveness, and energy efficiency parameters were considered.

Strong and Tough Bioinspired Additive-Manufactured Dual-Phase Mechanical Metamaterial Composites

Nature's materials are generally hybrid composites with superior mechanical properties achieved through delicate architectural designs. Inspired by the precipitation hardening mechanisms observed in biological materials as well as engineering alloys, we develop here dual-phase mechanical metamaterial composites by employing architected lattice materials as the constituent matrix and reinforcement phases. The composite metamaterials made from austenitic stainless steel are simply fabricated using selected laser melting based additive manufacturing. Using quasi-static compression tests and simulation studies, we find that strength and toughness can be simultaneously enhanced with the addition of reinforcement phase grains. Effects of reinforcement phase patterning and connectivity are examined. By fully utilizing the energy dissipation from phase-boundary slip, an optimized dual-phase metamaterial is designed with the maximum slip area, where every truss unit in the matrix phase is completely surrounded by reinforcement phase lattices; this material exhibits a specific energy absorption capability that is ~2.5 times that of the constituent matrix phase lattices. The design rationale for dissipative dual-phase metamaterials is analyzed and summarized with a focus on phase pattering. The present digital multi-phase mechanical metamaterials can emulate almost any of nature's architectures and toughening mechanisms, offering a novel pathway to manipulate mechanical properties through arbitrary phase-material selection and patterning. We believe that this could markedly expand the design space for the development of future materials.

Effects of Aluminum Foam Filling on Compressive Strength and Energy Absorption of Metallic Y-Shape Cored Sandwich Panel

The design of lightweight sandwich structures with high specific strength and energy absorption capability is valuable for weight sensitive applications. A novel all-metallic foam-filled Y-shape cored sandwich panel was designed and fabricated by using aluminum foam as filling material to prevent core member buckling. Experimental and numerical investigation of out-of-plane compressive loading was carried out on aluminum foam-filled Y-shape sandwich panels to study their compressive properties as well as on empty panels for comparison. The results show that due to aluminum foam filling, the specific structural stiffness, strength, and energy absorption of the Y-shape cored sandwich panel increased noticeably. For the foam-filled panel, aluminum foam can supply sufficient lateral support to the corrugated core and vertical leg of the Y-shaped core and causes a much more complicated deformation mode, which cannot occur in the empty panel. The complicated deformation mode leads to an obvious coupling effect, with the stress–strain curve of the foam-filled panel much higher than those of the empty panel and aluminum foam, which were tested separately. Metallic foam filling is an effective method to increase the specific strength and energy absorption of sandwich structures with lattice cores, making it competitive in load carrying and energy absorption applications.

Characterization of additively manufactured triply periodic minimal surface structures under compressive loading

Triply periodic minimal surface (TPMS) structures can produce tailored complex structures for various applications and serve as substitutes for polymeric foams. In this study, six different types of TPMS structures (Neovious, gyroid, Schwarz P, Lidinoid, split P, and diamond) were examined under quasi-static compression in terms of their energy absorption capabilities, mechanical properties, and weights, which were compared with those of expanded polystyrene foam and the original printing material Z-Ultra. It was found that the Neovious, diamond, and Lidinoid structures were most suitable for substituting expanded polystyrene foam, especially in safety helmets requiring high specific energy absorption capabilities.