Superior Energy Absorption Capability Research Articles

Crashworthiness and optimization of novel concave thin-walled tubes

In this work, a new type of energy-absorbing thin-walled tubes with concave angles is proposed by a unique structural design method to improve the crashworthiness performance of the traditional hexagonal thin-walled tube (TH). These concave tube structures (CTSs) are named CTS1, CTS2, and CTS3 respectively, while CTS1 is developed by a common design method. The crushing behaviors of the CTS3 are investigated by quasi-static compression experiments and numerical simulations. The crashworthiness and energy dissipation mechanism of all the tubes are investigated, and the results demonstrate that the CTS3 exhibits superior energy absorption capability than the other proposed tubes and TH with the same mass. Then, the mean crush resistance of the CTSs is predicted by theoretical analysis, and the influences of slenderness rate, boundary condition, and loading rate on the crushing responses of CTS3 are performed by numerical analysis. Besides, the comparative analysis of performances of the CTS3 and the typical concave tubes (TCTs) is carried out, and the results indicate that the CTS3 has the best energy absorption capacity among these tubes. In addition, the optimal structure parameters of CTS3 are explored to enhance the capacity of energy absorption further.

Study on the Quasistatic Compression Performance of Arch Microstrut Lattice Structure by Selective Laser Melting

ARCH lattice structure is composed of arch microstrut units arranged in order, which has excellent energy absorption performance, good designability, and good predictability of failure mode. ARCH lattice structure is expected to be applied to a variety of energy absorption and anti‐impact components or devices. Herein, the quasistatic compression experiment is conducted on the ARCH lattice structure samples. The mechanical properties and energy absorption capability of ARCH lattice structures with different unit sizes and different relative densities are experimentally researched. The results show that, compared with other lattice structures, ARCH lattice structures have superior energy absorption capability. The relative density has a great influence on the mechanical properties and energy absorption capability of ARCH lattice structures. The Gibson−Ashby equation is established to estimate the mechanical properties and energy absorption capability of the lattice structures with different relative densities.

Mechanical Properties and Energy Absorption Characteristics of Additively Manufactured Lightweight Novel Re-Entrant Plate-Based Lattice Structures.

In this work, three novel re-entrant plate lattice structures (LSs) have been designed by transforming conventional truss-based lattices into hybrid-plate based lattices, namely, flat-plate modified auxetic (FPMA), vintile (FPV), and tesseract (FPT). Additive manufacturing based on stereolithography (SLA) technology was utilized to fabricate the tensile, compressive, and LS specimens with different relative densities (ρ). The base material’s mechanical properties obtained through mechanical testing were used in a finite element-based numerical homogenization analysis to study the elastic anisotropy of the LSs. Both the FPV and FPMA showed anisotropic behavior; however, the FPT showed cubic symmetry. The universal anisotropic index was found highest for FPV and lowest for FPMA, and it followed the power-law dependence of ρ. The quasi-static compressive response of the LSs was investigated. The Gibson–Ashby power law (≈ρn) analysis revealed that the FPMA’s Young’s modulus was the highest with a mixed bending–stretching behavior (≈ρ1.30), the FPV showed a bending-dominated behavior (≈ρ3.59), and the FPT showed a stretching-dominated behavior (≈ρ1.15). Excellent mechanical properties along with superior energy absorption capabilities were observed, with the FPT showing a specific energy absorption of 4.5 J/g, surpassing most reported lattices while having a far lower density.

Compressive and Energy Absorption Properties of Pyramidal Lattice Structures by Various Preparation Methods.

Metallic three-dimensional lattice structures exhibit many favorable mechanical properties including high specific strength, high mechanical efficiency and superior energy absorption capability, being prospective in a variety of engineering fields such as light aerospace and transportation structures as well as impact protection apparatus. In order to further compare the mechanical properties and better understand the energy absorption characteristics of metal lattice structures, enhanced pyramidal lattice structures of three strut materials was prepared by 3D printing combined with investment casting and direct metal additive manufacturing. The compressive behavior and energy absorption property are theoretically analyzed by finite element simulation and verified by experiments. It is shown that the manufacturing method of 3D printing combined with investment casting eliminates stress fluctuations in plateau stages. The relatively ideal structure is given by examination of stress–strain behavior of lattice structures with varied parameters. Moreover, the theoretical equation of compressive strength is established that can predicts equivalent modulus and absorbed energy of lattice structures.

Energy Absorption Performance of Bio-inspired Honeycombs: Numerical and Theoretical Analysis

Energy absorption performance has been a long-pursued research topic in designing desired materials and structures subject to external dynamic loading. Inspired by natural bio-structures, herein, we develop both numerical and theoretical models to analyze the energy absorption behaviors of Weaire, Floret, and Kagome-shaped thin-walled structures. We demonstrate that these bio-inspired structures possess superior energy absorption capabilities compared to the traditional thin-walled structures, with the specific energy absorption about 44% higher than the traditional honeycomb. The developed mechanical model captures the fundamental characteristics of the bio-inspired honeycomb, and the mean crushing force in all three structures is accurately predicted. Results indicate that although the basic energy absorption and deformation mode remain the same, varied geometry design and the corresponding material distribution can further boost the energy absorption of the structure, providing a much broader design space for the next-generation impact energy absorption structures and systems.

Crashworthiness analysis and optimization of standard and windowed multi-cell hexagonal tubes

Recently, multi-cell structures have received increased attention for crashworthiness applications due to their superior energy absorption capability. However, such structures were featured with high peak collapsing force (PCL) forming a serious safety concern, and this limited their application for vehicle structures. Accordingly, this paper proposes windowed shaped cuttings as a mechanism to reduce the high PCL of the multi-cell hexagonal tubes and systemically investigates the axial crushing of different windowed multi-cell tubes and also seeks for their optimal crashworthiness design. Three different multi-cell configurations were constructed using wall-to-wall (WTW) and corner-to-corner (CTC) connection webs. Validated finite element models were generated using explicit finite element code, LS-DYNA, and were used to run crush simulations on the studied structures. The crashworthiness responses of the multi-cell standard tubes (STs), i.e., without windows, and multi-cell windowed tubes (WTs) were determined and compared. The WTW connection type was found to be more effective for STs and less favorable for WTs. Design of experiments (DoE), response surface methodology (RSM), and multiple objective particle swarm optimization (MOPSO) tools were employed to find the optimal designs of the different STs and WTs. Furthermore, parametric analysis was conducted to uncover the effects of key geometrical parameters on the main crashworthiness responses of all studied structures. The windowed cuttings were found to be able to slightly reduce the PCL of the multi-cell tubes, but this reduction was associated with a major negative implication on their energy absorption capability. This work provides useful insights on designing effective multi-cell structures suitable for vehicle crashworthiness applications.

Experimental investigation of the quasi-static and dynamic axial crushing behavior of carbon/glass epoxy hybrid composite tubes

The energy absorption characteristics of fiber-reinforced composite tubes subjected to axial quasi-static and dynamic crushing were investigated in this research. The influences of fiber volume proportion, ply angle, and loading rate on the specific energy absorption (SEA) were discussed. The SEA of satin weave/carbon unidirectional tape hybrid tubes was more pronounced compared with that of glass weave/carbon unidirectional tape tubes in quasi-static and dynamic tests. The SEA of both tubes was rate insensitive in dynamic tests (7.2 m/s, 10.2 m/s), but the rate effect was remarkable under quasi-static loading (10 mm/min, 600 mm/min). For glass weave of 759/5224 tubes, and carbon unidirectional tapes of G827/5224 tubes with different ply angles and loading rates, the 759/5224 tube shows superior energy absorption capability, and the loading rate effect was observed in quasi-static loading. Finally, the highest mean-load and SEA were obtained when the 759 glass fiber ply angle was equal to 30°, while the lowest energy absorption was observed when the orientation of the 759 fiber plies was ±45°.

Ultra-low density architectured metamaterial with superior mechanical properties and energy absorption capability

The material with negative Poisson's ratio (NPR) is a typical metamaterial, which is considered to have great prospects in energy absorption, but the low modulus and low strength of the materials are the biggest obstacles to its engineering applications. In this paper, the basic mechanical properties and energy absorption performance of an auxetic material with ultra-low density, named as a novel cross-chiral structure (NCCS), are systematically studied under quasi-static and dynamic compression. The results reveal that this auxetic material shows strong anisotropy and enhanced mechanical properties in the principal directions. Compared to the previously reported auxetic materials, it exhibits higher modulus and strength as well as superior energy absorption capability with the relative density less than 0.1, which is validated by both numerical simulations and experiments. In addition, the results indicate that the presented model can be optimized to achieve excellent mechanical properties and outstanding energy absorption capability with ultra-low densities, by tailoring strut's tilt angle and relative density. This architectured metamaterial is expected to find a bright future in the applications of energy absorption such as sandwich cores of armor.

Uncovering a high-performance bio-mimetic cellular structure from trabecular bone

The complex cellular structure of trabecular bone possesses lightweight and superior energy absorption capabilities. By mimicking this novel high-performance structure, engineered cellular structures can be advanced into a new generation of protective systems. The goal of this research is to develop an analytical framework for predicting the critical buckling load, Young’s modulus and energy absorption of a 3D printed bone-like cellular structure. This is achieved by conducting extensive analytical simulations of the bone-inspired unit cell in parallel to traverse every possible combination of its key design parameters. The analytical framework is validated using experimental data and used to evolve the most optimal cellular structure, with the maximum energy absorption as the key performance criterion. The design charts developed in this work can be used to guide the development of a futuristic engineered cellular structure with superior performance and protective capabilities against extreme loads.

Performance of a 3D printed cellular structure inspired by bone

Biological thin-walled cellular structures have intricate arrangements that facilitate lightweight and high energy absorption. A prime example is trabecular bone, which possesses a unique thin-walled cellular structure of connected rods or plates, to minimise weight whilst meeting the loading demands from the body. For example, the femur has a closed cell structure of plates to transmit heavy loads to the ground, whereas a carpal bone has an open cell structure of connected rods. Although existing lightweight thin-walled cellular structures with controlled arrangements have been investigated extensively, such as those with re-entrant geometries, asymmetric instability due to local buckling can hinder their energy absorption capacity. Mimicking the features of trabecular bone can offer the designer a greater degree of control over the buckling and collapse mechanisms of thin-walled cellular structures. This can lead to the development of high-performance protective systems with superior energy absorption capabilities. This study employs 3D printing and finite element analysis techniques to mimic and investigate several key features of the plate-like thin-walled cellular structure of trabecular bone. The performance of the developed bioinspired structure is benchmarked against traditional hexagonal and re-entrant designs. The controlled and progressive buckling and collapse mechanisms observed in the bioinspired structure result in superior energy absorption over its re-entrant and hexagonal counterparts. • Developing a framework for automatically generating a finite element model and 3D printed sample of a bone-like structure. • Benchmarking the performance of the bioinspired structure against existing cellular structures, including hexagonal and re-entrant. • Identifying several parameters that can guide the design of biomimetic thin-walled cellular structures in the future.

Enhanced voltage gradient and energy absorption capability in ZnO varistor ceramics by using nano-sized ZnO powders

In the present study, both enhanced voltage gradient of 803 V/mm and superior energy absorption capability of 400 J/cm3 were achieved in ZnO varistors prepared by nano-sized raw powders. Further analysis indicated that such improvement could be ascribed to the refined micromorphology. As shown by SEM pictures, the average grain size was dramatically decreased by the nano-sized powders, which contributed to the enhanced voltage gradient. Meanwhile, the homogeneous grain size distribution resulted in the improved energy absorption capability. The improved varistors in the present study showed high potential for ultra-high voltage applications. In addition, we proposed an effective approach to quantitatively evaluate the grain size distribution, which is the key parameter for the electrical properties of the varistors. It provided a guideline for further modifications on wide range of electronic ceramics.

A numerical study on the in-plane dynamic crushing of self-similar hierarchical honeycombs

Rather than restating the quasi-static mechanical characteristics of hierarchical honeycombs, this paper aims to explore the coupling effect between self-similar hierarchical characteristics and dynamic mechanical properties. Systematic simulations of hierarchical honeycombs subject to in-plane impact loading indicate that the introduction of a self-similar hierarchy does indeed enrich the types of local deformation bands. Appropriately increasing the hierarchical structural parameter of the honeycomb has the same effect as increasing the impact velocity, which leads to the formation of a localized “I”-shaped deformation band, and hence improves the energy absorption capability. However, deformation patterns can also be categorized into quasi-static, transition, and dynamic modes. The critical velocities at which deformation patterns transit can be obtained from the classification map. By using this method, it is possible to analyze the stress-strain curves of hierarchical honeycombs at the impact end and the plateau stresses in association with the deformation profiles. The following analysis of relative plateau stress further demonstrates that self-similar hierarchical characteristics are favorable for improving the overall performance of honeycombs. When the impact velocity is uncertain, the hierarchical honeycomb has superior energy absorption capability when the hierarchical structural parameter ranges from 0.3 to 0.4. Through the observation and analysis of the results from many cases, it is proven that the hierarchical structural parameter and the impact velocity affect the densification strain simultaneously. The empirical equations of dynamic densification strains for hierarchical honeycombs under different deformation patterns are derived by using least-square fitting.

Heterogeneously tempered martensitic high strength steel by selective laser melting and its micro-lattice: Processing, microstructure, superior performance and mechanisms

Herein, we report the selective laser melting of AISI 4130 high strength steel and its micro-lattice with superior energy absorption capabilities based on a dual material processing and structural design approach. Bulk 4130 was printed to high part qualities with an excellent combination of tensile properties of 1243 ± 25 MPa yield strength, 1449 ± 19 MPa ultimate tensile strength and 15.5 ± 1.5% fracture elongation. Such performance derives from its unique microstructure consisting of an alternating enhanced tempered and well-retained martensitic network. Experiments and simulation reveal the unique microstructure to result from a single-step fusion and quenching process followed by an in-situ rapid dynamic tempering that is associated with the laser scanning patterns. Based on these mechanical properties, orthogonally isotropic micro-lattices were designed and structurally optimized through finite element modelling. Superior per unit weight and volume energy absorption are measured; ranging from 13 to 35 J/g and 12–76 J/cm3 for relative densities of 10–30% respectively along with high energy absorption efficiencies of ~80%. These excellent properties in turn derive from the synergistic design and material properties. This work demonstrates the potential combination of additive manufacturing and design to create microstructure-geometric specific lattice materials for high performance energy absorption applications.

Energy absorption of a bio-inspired honeycomb sandwich panel

In this study, a novel bio-inspired honeycomb sandwich panel (BHSP) based on the microstructure of a woodpecker’s beak is proposed. Unlike a conventional honeycomb, the walls of the bio-inspired honeycomb (BH), which is used as the core of a sandwich panel, are made wavy. Finite element simulation shows that under dynamic crushing the proposed BHSPs exhibit superior energy absorption capability compared with the conventional honeycomb sandwich panel (CHSP). In particular, the specific energy absorption (SEA) of the BHSP increases by 125% and 63.7%, respectively, compared with that of the honeycomb sandwich panel with the same thickness core or the same volume core. In addition, a parametric study of the BHSPs is carried out to investigate the influences of the wave amplitude, wave number and core thickness on the energy absorption performance of the BHSPs. It is found that the BH core with a larger wave number and amplitude shows higher SEA. Furthermore, an increase in core thickness can improve the SEA. These results provide guidelines in the design of a lightweight sandwich panel for high-energy absorption capability.

Compressive properties of hollow lattice truss reinforced honeycombs (Honeytubes) by additive manufacturing: Patterning and tube alignment effects

Honeytubes, a novel type of honeycomb formed by reinforcement with lattice trusses, were reported to exhibit enhanced buckling resistance. However, an in-depth analysis for the compressive performance and energy absorption capacity was lacking. In this paper, the effects of microstructure and tube alignment on compressive properties were studied. Four types of honeytubes were designed based on different topologies, geometries and tube patterns, and fabricated by selective laser sintering (SLS). Out-of-plane compression tests and finite element simulation were performed for the analysis. Results indicated that incorporation of lattice in honeycombs resulted in greater local strain in tubes and tube-rib connections. However, honeytubes exhibited superior energy absorption capability, even surpassing that of some metallic lattices. Balancing the configuration of tubes in honeytubes could ensure enhanced mechanical performance. This work demonstrates that materials designed by capitalizing on micro-topologies can regulate mechanical properties and provide insights for guiding the development of new materials.

Axial crush behaviour of the aluminium alloy in-situ foam filled tubes with very low wall thickness

This paper presents the results of an experimental work carried out to fabricate and characterise the in-situ foam filled tubes (FFTs) made of aluminium alloys prepared by powder metallurgy method, using aluminium alloy tubes with extremely thin walls (∼0.6 mm). The fabrication procedure demonstrates that thin-walled tubes with extremely thin walls can support temperatures near to its melting temperature (∼700 °C) required to form a closed-cell aluminium alloy foam, consequently in-situ filling the tube. The mechanical performance of fabricated structures was evaluated using uniaxial compressive tests and infrared thermography. Results demonstrate that the benefits of the manufacturing process and its product, the FFTs (composite structures). Additionally, they reveal that this is a cost-effective solution to prepare efficient energy absorbing lightweight structures, allowing to adjust the weight and levels of the energy absorption, simultaneously. The results demonstrate that the promising in-situ FFTs with thinner outer tubes axially deform in an efficient mixed mode, showing superior energy absorption capability compared to the empty thin-walled tubes.

An origami-inspired structure with graded stiffness

Origami-inspired structures and mechanical metamaterials are often made up of individual tessellating repeat units, the folding and relative geometry of which determine the overall mechanical properties. If these units are identical, then the mechanical behaviour of the structure is uniform throughout, meaning that it is not able to adapt to changeable loading conditions. Here we create and study an origami structure, based on the Miura-ori folding pattern, which has a varying geometry over its volume and graded stiffness. Using kinematic analysis, we show how geometric parameters of the folding pattern can be varied to create both rigid foldable and self locking stages. We demonstrate both experimentally and numerically that the structure can achieve periodically graded stiffness when subjected to quasi-static out-of-plane compression, and the mechanical responses can be tuned by changing the underlying geometric design. We obtain a structure with superior energy absorption capability to uniform tessellating repeat units, and anticipate that this strategy could be extended to other structures and metamaterials to impart them with non-uniform and graded mechanical properties.

Static and dynamic crushing responses of CFRP sandwich panels filled with different reinforced materials

This study aims to investigate the crashworthiness of carbon fiber reinforced plastic (CFRP) sandwich panels filled with different reinforced materials under quasi-static compression and low velocity impact loading. Four lightweight filler materials (namely EPP foam, aluminum honeycomb, rubber foam balls and plastic hollow balls) were chosen and a series of static and dynamic tests were carried out to explore the damage mechanism, load bearing capacity, energy absorption and cushioning properties of these different sandwich panels. The complete core crushing contributed to the loading resistance and energy absorption under the static compression leaving the top and bottom CFRP facesheet intact. Three distinct load-displacement categories, classified as no rebound (unfilled), incomplete rebound (filled with aluminum honeycomb and plastic balls) and complete rebound (filled with EPP and rubber balls) were observed in the impact tests; the localized facesheet rupture and core crushing were dedicated to significant energy absorption during impact. The specimens filled with aluminum honeycomb and plastic hollow balls exhibited superior energy absorption capabilities (2.8 and 4.8J/g, respectively) in the static compression testes, while the specimens filled with aluminum honeycomb and EPP foam exhibited superior capability of energy absorption (0.8 and 0.9J/g, respectively) in the impact tests.

Energy absorption mechanisms of hierarchical woven lattice composites

Hierarchical cellular materials are predicted to have superior energy absorption capability. To enhance the energy absorption of the woven lattice sandwich panels, hierarchical square lattice panels were designed and manufactured. With sandwich walls, the hierarchical square lattice panels are light but render ideal complete stress–strain curves with high compression strengths, stable displacement plateau at a relative high stress level and large densification strain in experiments. A plastic model has been suggested to predict the limits of the deformation plateau after the peak stress. It is shown that hierarchical lattice structures obviously enhance the energy absorption capability of the light-weight woven textile material.

Mechanical properties of textile-inserted PP/PP knitted composites using injection–compression molding

Abstract This paper concentrates on the experimental investigation of the self-reinforced all-polypropylene composites. There exists an optimum processing condition to produce high quality specimens by injection–compression molding. Tensile and 3-point bending properties of the virgin PP materials were nearly unaffected by the introduction of reinforcing knit layer(s) due to very low fibre content of the knitted fabrics used. 3-point bending properties were also unaffected by the surface of indentation-flexure. The applied impact energy was maintained at 5 J for the homo-PP and 27 J for the block-PP materials, respectively, to cause penetration during drop-weight impact tests. It is interestingly noteworthy that the self-reinforced homo-PP composites exhibited superior energy absorption capability when compared with the virgin matrix materials. The corresponding plate bending performances of the self-reinforced homo-PP composites also revealed consistent improvement as compared to their virgin counterparts. On the other hand, although virgin block-PP material exhibited better impact performances than its composite reinforced by the homo-PP knitted fabric, a notably small increase in the reinforcement fibre content revealed considerable improvement in the impact properties comparable to those of the virgin block-PP matrix materials. These self-reinforced homo-PP/block-PP materials have clearly indicated that they have the potential to out-perform the block-PP materials via modification and/or manipulation of the reinforcement knit structural/geometrical parameters and the content of reinforcement fibres. Both static and dynamic impact properties are likely to be affected by the local area properties of the tested face under indentation, and thereby contributing to the improved performances of the composite specimens with the knit face under the impact.