Energy Absorption Mechanisms Research Articles

Temperature Dependent Dynamic Response of Open-Cell Polyurethane Foams

BackgroundPolyurethane foams have many uses ranging from comfort fitting seats and shoes to protective inserts in helmets and sports equipment. Current military helmet designs employ foam pads of varying densities and bulk material properties to help absorb energy from impacts ranging from quasi-static to ballistic level strain-rates.ObjectiveThis study aims to analyze the thermomechanical uniaxial compression behavior of a high density liner foam pad and a low density liner foam pad used in the Advanced Combat Helmet. These experiments were conducted under strain-rates of 102\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$10^2$$\\end{document} s-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} and under temperature conditions ranging from -20 to 40 °C. This temperature range was chosen to simulate desert and arctic conditions, with a strain-rate regime chosen to represent loads that would occur often throughout the life of the helmet, such as drops, bumps from riding in a vehicle, or heavy collisions from falling.MethodMultiple experimental apparatuses were used in this study, including a Shimadzu TCE-N300 thermostatic chamber (used to create the varying temperature environments) and a custom-built drop-test system (used to induce intermediate strain-rates). Every experiment was paired with two accelerometers and a high speed camera used for Digital Image Correlation (DIC) to analyze sample deformation and resultant acceleration. The foam’s mechanical response and energy absorption properties were investigated from the measured stress-strain curves. Additionally, each foam composition was analyzed with X-ray computed micro-tomography (XCT) to investigate microstructure properties pre and post-mortem.ResultsResults show that temperature decreased the energy absorption of the low density composition by 48% ± 5% as temperature changed from -20 °C to 40 °C, while energy absorption increased by 53% ± 16% for the high density composition over the same temperature.ConclusionA comparison between the loading response and the material’s density characteristics revealed that the foam’s mechanical properties are heavily dependent on strain-rate applications, as well as environmental factors including temperature. Several important characteristics surrounding each foam composition’s deformation mechanics and damage tolerance as a result of temperature are discussed.

Compressive Characteristics and Energy Absorption Capacity of Automobile Energy-Absorbing Box with Filled Porous TPMS Structures

In order to meet the higher requirements of energy-absorbing structures in the lightweight automobile design, the mechanical design and impact energy absorption of porous TPMS structures are studied. Eight kinds of porous TPMS structure elements, Gyroid, Diamond, I-WP, Neovius, Primitive, Fischer-Koch S, F-RD, and PMY, are designed based on Matlab, and the porous structure samples composed of eight elements are printed and molded using SLM. The deformation mechanism, mechanical response, and energy absorption characteristics of different porous TPMS structures are investigated. Gyroid and Primitive elements are selected to fill the internal structure of the energy-absorbing automobile boxes. Traditional thin-walled energy-absorbing boxes served as a control group and were subjected to low-speed impact testing. The results show that the peak load of the energy-absorbing box filled with TPMS porous structures is almost equal to the average load under a 4.4 m/s impact, and the SEA of the energy-absorbing box filled with TPMS porous structures is higher than the traditional thin-walled energy-absorbing box. The problems of excessive peak load and inconsistent load fluctuation of traditional thin-walled energy-absorbing structures are effectively solved by porous TPMS structures with the assurance that the lightweight and energy-absorbing requirements are still met.

Origami-based bidirectional self-locking system for energy absorption

When a periodic cellular structure is subjected to high-intensity loading, lateral splashing can occur, significantly decreasing macro mechanical properties. Periodic structures with self-locking properties can overcome this inherent flaw and achieve excellent performance characteristics, including high energy absorption efficiency. In this regard, thin-walled periodic self-locking dissipative structures have been extensively studied recently. Most existing bend-dominated self-locking dissipative systems are two-dimensional and can only achieve self-locking under specific loading conditions. This paper describes a three-dimensional origami-based bidirectional self-locking system that can achieve self-locking under normal and shear loading. Furthermore, a plastic hinge model revealed the energy absorption mechanism of the origami-based cells, whose specific energy absorption (SEA) is higher than that of other existing bend-dominated self-locking cells. The bidirectional self-locking of the origami-based system was demonstrated through compression, bending and impact tests. This origami-based system has high energy absorption efficiency, and the novel bidirectional self-locking mechanism can significantly broaden the design space for periodic dissipative metamaterials.

Development of porous hydroxyapatite/PVA/gelatin/alginate hybrid flexible scaffolds with improved mechanical properties for bone tissue engineering

Porous scaffolds based on gelatin and hydroxyapatite particles (HAp) are promising for applications in bone tissue engineering and regenerative medicine. However, they are not ideal for stress and shock protection due to low compressive strength, brittleness, and poor toughness. Herein, we developed porous hybrid scaffolds by combining multiple components into a single bone scaffold, including hydroxyapatite nanoparticles (HAp NPs), alginate, polyvinyl alcohol (PVA), and gelatin with different gelatin/PVA composition ratios. HAp NPs were synthesized in situ in PVA solution and scaffolds were fabricated using a freeze-drying method. The results showed good physicochemical properties of the scaffolds: formation of pure HAp NPs phase, high porosity, large pore sizes, large swelling capacity depending on varying gelatin/PVA ratios, as well as a long-term degradation rate up to 28 days. The porous scaffolds exhibited compressive strength close to the cancellous bone with stress-strain behavior exhibiting three-stage flexible behavior indicating improved fracture resistance with an energy absorbing capability up to 1.9 MJ/m3. The scaffolds have a yield strength of 70–403 kPa, a compressive strength at 65 % strain of 0.96–1.80 MPa, a nonporous elastic modulus of 10.44–12.40 GPa, and a densification strain of approximately 0.92 %. This work develops three-dimensional (3D) porous hybrid bone scaffolds with mechanical strength within the minimum compressive strength of cancellous bone and mechanical energy absorption capacity favor for cancellous bone repair, bone tissue engineering, and regenerative medicine applications.

Mechanical properties and energy absorption capabilities of plate-based AlSi10Mg metamaterials produced by laser powder bed fusion

Plate-based lattice structures are an emerging category of mechanical metamaterials with exceptional mechanical performance. In this work, plate-based SCFCC metamaterials of AlSi10Mg with various relative densities are fabricated by laser powder bed fusion (LPBF). Circular holes are strategically designed and placed at the center of each non-load-bearing face for residual powder removal. Quasi-static compression experiments and numerical simulations are performed to investigate their mechanical performance and deformation mechanisms. Results indicate that the elastic modulus of SCFCC metamaterials decreases by 3.5% with the presence of 0.9 mm diameter holes, while increasing the hole size shows negligible impact on the elastic modulus. The novel plate-based SCFCC structure exhibits superior mechanical properties and enhanced energy absorption capacity concerning conventional high-stiffness truss-based and shell-based counterparts. The improvement, at the relative density of 0.2, can be observed in terms of elastic modulus (around 50%), peak compressive strength (around 300%), energy absorption capacity (around 400% or 200%). When increasing the relative density from 0.2 to 0.5, plate-based SCFCC metamaterial still maintains superior mechanical performance while the gaps between SCFCC and its counterparts narrow down gradually owing to the loss of structural features. Moreover, mechanical characteristics and coefficients of three Gibson and Ashby analytical equations are determined. This work proposes a novel type of plate-based structure with both exceptional mechanical performance and good additive manufacturability, which opens a new avenue for the design of lightweight mechanical metamaterials.

Study on the Deformation Mode and Energy Absorption Characteristics of Protective Honeycomb Sandwich Structures Based on the Combined Design of Lotus Root Nodes and Leaf Stem Veins

Sandwich structures are often used as protective structures on ships. To further improve the energy-absorbing characteristics of traditional honeycomb sandwich structures, an energy-absorbing mechanism is proposed based on the gradient folding deformation of lotus root nodes and a leafy stem vein homogenizing load mechanism. A honeycomb sandwich structure is then designed that combines lotus root nodes and leafy stem veins. Four types of peak-nest structures, traditional cellular structure (TCS), lotus root honeycomb structure (LRHS), leaf vein honeycomb structure (LVHS), and lotus root vein combined honeycomb structure (LRVHS), were prepared using 3D printing technology. The deformation modes and energy absorption characteristics of the four honeycomb structures under quasistatic action were investigated using a combination of experimental and simulation methods. It was found that the coupling design improved the energy absorption in the structural platform region of the LRHS by 51.4% compared to that of the TCS due to its mechanical mechanism of helical twisting and deformation. The leaf vein design was found to enhance the peak stress of the structure, resulting in a 4.84% increase in the peak stress of the LVHS compared to that of the TCS. The effects of the number, thickness, and position of the leaf vein plates on the honeycomb structure were further explored. The greatest structural SEA effect of 1.28 J/g was observed when the number of leaf vein plates was four. The highest SEA of 1.36 J/g was achieved with a leaf vein plate thickness of 0.6 mm, representing a 7.3% improvement compared to that of the 0.2 mm thickness. These findings may provide valuable insights into the design of lightweight honeycomb sandwich structures with high specific energy absorption.

Experimental Investigation of Quasi-Static and Dynamic Impact Resistance in Thin Wood Veneer Laminates

The incorporation of sustainability into the design of transport vehicles has become increasingly important in recent years. A low carbon footprint makes wood-based structures attractive to replace other lightweight materials such as aluminum or fiber-reinforced plastics. This paper investigates and compares the static and dynamic impact behavior of thin Beech wood veneer laminates in standardized mechanical tests. The results obtained from Quasi-Static Indentation (QSI) and dynamic Low-Velocity Impact (LVI) tests reveal similarities and differences with regard to load vs. displacement behavior, damage mechanisms, permanent deformation, and energy absorption. While yield strength and damage modes are comparable in both test cases, it is found that the bending stiffness is strain-rate sensitive. Plastic deformation in compression is identified as the governing mechanism for energy absorption. These results can guide the design of sustainable wood-based structures for future transport applications where a thorough understanding of impact and crashworthiness is important.

Ballistic resistance analysis of hard ceramic combined with aluminum foam sandwich constructions

A ballistic resistance of hard ceramic combined with aluminum foam sandwich (CAFS) constructions was investigated in this paper. This combination plate is constructed by a front faceplate (FFP), ceramic plates, an aluminum foam (Al-foam) panel, and a rear faceplate (RFP). The material used for the FFP and RFP was heat-treated mild steel with the thicknesses are 5 mm and 3.5 mm, respectively. The ceramic materials to be evaluated are B4C, SiC, and Al2O3. Al-foams were fabricated by varying the stabilizer weight ratio of MgO and Al2O3. The Al-foams have a porosity of 79.93%–82.57%, a pore diameter of 2.51–2.82 mm, the relative density of 0.17–0.24, and plateau stress of 3.88–6.63 MPa. Ballistic tests were carried out only for aluminum foam sandwich (AFS) construction without ceramics to evaluate the manufacturing effect and to obtain a baseline ballistic plate to be improved. Ballistic tests are conducted by using 5.56 × 45 mm bullet with 50 m shooting range and bullet speed of 929–958 m/s. To validate the damage mode and energy absorption capability of the AFS, a numerical model is constructed. The numerical studies were conducted to investigate the damage mode and energy absorption capabilities of each part. The simulation has a good agreement with the experiment result on the damage mode. This model then to be used to study the effect of the additional hard ceramic layer. An interaction between hard ceramic and AFS is also investigated to get a new insight of the energy absorption mechanism during bullet penetration. A new finding shows that ceramic presses the Al-foam to solidify so that it can increase the energy absorbed by the Al-foam. The ceramic is impacted by a bullet pushing the Al-foam so that it undergoes solidification which leads to increasing absorbed energy.

Influence of Magnetic Field Configuration in Helicon-Negative Ion Source on Increase of the Efficiency of NNBI Heating System

The influence of the magnetic field configuration on the performance of a helicon-based negative ion source is investigated with simulation experiments. Using COMSOL Multiphysics software, a three-dimensional simulation model for a negative ion source, based on a helicon plasma source, is presented in two magnetic field configurations: uniform and nonuniform configurations. The helicon plasma source employed a Nagoya-type antenna to apply radio-frequency (RF) power at a frequency of 13.56 MHz. The injected gas is hydrogen with a flow of 10 standard cubic centimeters per minute. Using a three-dimensional model, helicon wave propagation in the presence of a magnetic filter and the energy absorption mechanism in the helicon system are investigated. In this context, in the presence of the two magnetic field configurations, the influence of the important parameters’ working pressure and RF power on the optimization of negative ion production under volume mode is studied. Six electromagnetic coils at the same current are used for producing the magnetic field in both cases of uniform and nonuniform configurations. The variation of the electron density and electron temperature, in both regions of driver and expansion, are calculated and represented with respect to the different power and the gas pressure. The simulation results of the negative ion density in the expansion region for the uniform and nonuniform magnetic field configurations are compared. The results indicate that at the same applied current of coils, the negative ion density in the presence of the nonuniform magnetic field is about 1.75 times higher than the negative ion density of the uniform case. Moreover, the results show that the negative ion density is decreased by decreasing the magnetic field of the driver region in the nonuniform cases.

Parametric design and performance evaluation of gyroid triply periodic minimal surface preparation by LCD photopolymerization

In this paper, the Gyroid triply periodic minimal surface is prepared by liquid crystal display photopolymerization technology, and 10 models of the periodic parameter T in [1/5, 2] are designed. Using the method of finite element method and experimental verification, when T = 1/3, there are fewer stress concentration areas on the Gyroid surface, the number of grids is moderate, the compression crush rate is the smallest, and the porosity error is reasonable. Through the microscopic morphology, it is found that the surface, after printing, forms gear shape and resin residue so that the actual volume is larger than the theoretical volume, and the porosity is minor. Keeping periodic parameter T = 1/3 and porosity of 50%, four kinds of Gyroid surface structures were designed by changing the parameter surface offset, wall thickness, offset thickness, and gradient arrangement. The effects of different loading directions on its mechanical properties, deformation behavior, and energy absorption were discussed through compression experiments. The results show that the vertical load is applied to form a fault zone from the upper left angle to the lower right angle of 45°, and the parallel load is applied to create a fault zone from the upper right angle to the lower left grade of 45°. When the load is used in the vertical direction, the energy absorption and energy efficiency of the surface offset Gyroid surface are the largest. When the load is applied in the parallel order, the energy absorption curves of the four structures change similarly, and the deformation amplitude of the wall thickness Gyroid surface during the compression process is relatively stable. The energy efficiency of gradient arrangement Gyroid surface increases fastest in the compaction stage.

Effect of geometric structure and fiber orientation on crashworthiness of honeycomb‐inspired composite thin‐walled tubes

AbstractThis study investigates the crashworthiness of biomimetic composite thin‐walled tubes under quasi‐static axial crushing, focusing on the effects of geometric structure and fiber orientation. The thin‐walled tubes, inspired by honeycomb structures, were manufactured using carbon fiber composites through multi‐cavity preform mold method. Quasi‐static crushing tests and CT scanning observation were conducted to characterize the mechanical response, crashworthiness mechanisms and energy absorption capacity of the thin‐walled tubes. Results demonstrated excellent energy absorption capacities across all configurations, with the C‐0/45 configuration achieving the highest specific energy absorption at 115.03 kJ/kg. The optimal crushing energy absorption process for thin‐walled tubes involves achieving high peak loads and maintaining high load levels. Sustaining high loads requires progressive and stable damage without the formation of extensive intermediate cracks between different plies (indicative of strong interlaminar shear strength). The structural integrity of the uncrushed sections must remain intact without significant damage during the crushing process. Fiber orientation parallel to the loading direction enhances peak load levels and interlaminar shear strength between plies, but may compromise circumferential stiffness and structural stability. The influence of geometric configuration is primarily manifested in the progressive and stable crushing phase, where the tube requires sufficient space to accumulate its own debris without causing damage to the uncrushed thin‐walled structure.Highlights Structures and fiber orientation boost crashworthiness in biomimetic composite tubes. Biomimetic structures were produced using a multi‐cavity preform mold method. CT scans were conducted to characterize the energy absorption mechanisms. Composite tubes demonstrated excellent energy absorption capacity of 115 kJ/kg.

A ribbed strategy disrupts conventional metamaterial deformation mechanisms for superior energy absorption

ABSTRACT Enhancing energy absorption in mechanical metamaterials has been a focal point in structural design. Traditional methods often include introducing heterogeneity across unit cells. Herein, we propose a straightforward ribbed strategy to achieve exceptional energy absorption. We demonstrate our concept through modified body-centered cubic (BCC) and face-centered cubic (FCC) ribbed truss-lattice metamaterials (BCCR and FCCR). Using stainless-steel 316L samples, compression tests indicate a 111% and 91% increase in specific energy absorption (SEA) for BCCR and FCCR, respectively, along with an enhancement in compression strength by 61.8% and 40.7%. Deformation mechanisms are comprehensively elucidated through both finite element analysis and theoretical calculations. The mitigation of stress concentration at nodes, redistribution of load transfer pathways within struts, and introduction of multiple plastic hinges collectively contribute to increased energy absorption and higher compression strength. Using rein-based polymer samples, the ribbed truss-lattice metamaterials also exhibit exceptional damage tolerance, experiencing only a 15% loss in maximum strength after cyclic compression at 20% strain, while maintaining a 73% higher SEA compared to their non-ribbed counterpart. This strategy extends beyond the discussed structures, presenting itself as a generic approach to enhance plateau strength and SEA.

Investigating the Impact Behavior of Carbon Fiber/Polymethacrylimide (PMI) Foam Sandwich Composites for Personal Protective Equipment.

To improve the shock resistance of personal protective equipment and reduce casualties due to shock wave accidents, this study prepared four types of carbon fiber/polymethacrylimide (PMI) foam sandwich panels with different face/back layer thicknesses and core layer densities and subjected them to quasi-static compression, low-speed impact, high-speed impact, and non-destructive tests. The mechanical properties and energy absorption capacities of the impact-resistant panels, featuring ceramic/ultra-high molecular-weight polyethylene (UHMWPE) and carbon fiber/PMI foam structures, were evaluated and compared, and the feasibility of using the latter as a raw material for personal impact-resistant equipment was also evaluated. For the PMI sandwich panel with a constant total thickness, increasing the core layer density and face/back layer thickness enhanced the energy absorption capacity, and increased the peak stress of the face layer. Under a constant strain, the energy absorption value of all specimens increased with increasing impact speed. When a 10 kg hammer impacted the specimen surface at a speed of 1.5 m/s, the foam sandwich panels retained better integrity than the ceramic/UHMWPE panel. The results showed that the carbon fiber/PMI foam sandwich panels were suitable for applications that require the flexible movement of the wearer under shock waves, and provide an experimental basis for designing impact-resistant equipment with low weight, high strength, and high energy absorption capacities.

Evaluation of the mechanical properties and energy absorption in a novel hybrid cellular structure

The present study proposes a novel hybrid cellular structure consisting of unit cells with different geometrical designs to tailor Young's modulus and improve the energy absorption capability. An analytical model was developed to predict the mechanical properties of the baseline cellular structure. Using the particle swarm optimization (PSO) algorithm, the geometry of two unit cells is designed with the maximum (Type-2) and minimum (Type-1) stiffnesses compared to the baseline structure. These two unit cells were utilized to design the properties of the novel hybrid cellular structure for an optimized energy absorption capability. For evaluating Specific Energy Absorption (SEA) in the hybrid structure, the samples were 3D printed and subjected to compression testing. Finite Element Modeling (FEM) was also conducted for further study by assuming the elasto-plasto-damage properties. The results indicate that the novel hybrid structure shows a 90% improvement in SEA by reducing the weight by 70% compared to the Type-1 cellular structure. The EA of various polymers, including PLA, PA12, PP, PETG, ABS, TPU, and FLEX, were examined by utilizing the FEM as a virtual test method. Based on the results, SEA capacity in cellular structures can be increased by optimizing the topology and selecting the appropriate material containing high elastic modulus and failure strain.

Auxetic Structure‐Assisted Triboelectric Nanogenerators for Efficient Energy Collection and Wearable Sensing

AbstractTriboelectric nanogenerators (TENGs) are recognized for energy conversion efficiency and applications including electronics and energy storage devices. This study introduces a groundbreaking development in TENG by incorporating negative Poisson's ratio metamaterials to fabricate auxetic‐assisted triboelectric nanogenerators (Auxetic‐TENG), subversively overcoming the low power density of traditional materials. Subtly, an integrated layer‐by‐layer‐assembly and core–shell accumulation strategy is employed to create a synclastic polytetrafluoroethylene negative friction shell‐skeleton, into which positive Poisson's ratio nature collagen aggregate (CA) foam is inwardly embedded as the positive friction core‐material. Surprisingly, the on‐demand introduction of metamaterials in synergy with CA significantly increases the contact area and mechanical energy absorption of the Auxetic‐TENG under pressure. This enhancement in the conversion efficiency of mechanical to electricity capitalizes on the contraction origins of negative Poisson's ratio metamaterials, integrated with the expansion characteristics of the positive Poisson's ratio materials within the structure, facilitating the synergistic compression of the positive and negative friction stratum. Consequently, Auxetic‐TENG achieves an open‐circuit voltage of 85 V, an overturning four times compared to conventional contact–separation TENG, and a power density of 4.2 W m−2. Application experiments demonstrate the superior performance of auxetic‐TENG under various compression ratios and stress conditions, highlighting its potential for real‐time monitoring in healthcare applications.

False banana fiber reinforced geopolymer composite – A novel sustainable material

A new geopolymer composite material was produced using low-calcium fly ash and false banana plant fiber. The effect of fiber content and length on the mechanical and microstructural properties of the resulting composite material was investigated. Results showed that the addition of alkali-treated false banana fiber significantly improved the compressive and splitting tensile strength of the composites. In particular, incorporating a 10 mm length fiber at a 1.4 % volume fraction increased compressive and splitting tensile strength by 31 % and 33 %, respectively, when compared to the pure geopolymer paste specimens. Furthermore, unlike the neat geopolymer paste specimens, all composites failed gracefully. In addition to this, FTIR absorption peaks and SEM micrographs demonstrated that alkali treatment effectively changes fiber morphology and chemical characteristics. Additionally, fiber pull-out, fiber bridging, and fiber fracture were identified as energy-absorbing mechanisms responsible for increasing the mechanical properties of the composites. In general, the results showed that using natural false banana fiber as reinforcement enhances the mechanical properties of geopolymer composites, making them a more environmentally friendly alternative to synthetic fibers in composite production.

Development of hybrid green composites by dual natural fibers (jute/bamboo) reinforcement and investigation of their mechanical behavior

AbstractThis study aims to investigate the mechanical properties of natural fiber hybrid composites, specifically those based on jute and bamboo fibers. Jute fibers made in the form of highly scattered mesh and fine‐meshed bamboo mat were selected as reinforcing materials. The highly scattered meshed jute fabric composite showed poor mechanical properties owing to resin agglomeration, leading to the brittle fracture of the composite before elongation. In contrast, the randomly oriented fine‐meshed bamboo fabric performed better in terms of both mechanical properties and strain energy absorption under the same loading conditions. Hybridization with fine bamboo mesh fibers can be a solution to improve the mechanical properties of jute fabric composites. The tensile, flexural, and in‐plane shear properties of the composites are investigated in our study. We found that hybridizing a fine‐meshed bamboo mat with jute fabric resulted in an improved mechanical performance of the composite. Composite panels have been manufactured using vacuum assisted resin transfer molding (VARTM). Experimental and numerical methods have been used to investigate the flexural behavior. Of the stacking sequences considered, the (J/B4/J) stacking showed the highest flexural strength (141.1 Mpa) and the (B2/J2/B2) 2/2 stacking sequence showed the minimum flexural strength. The alternating stacking sequence (B/J/B/J/B/J) exhibited intermediate properties. The randomly oriented bamboo fabric near the neutral axis enhanced the properties of the hybridized composite. This was verified numerically using the ANSYS ACP software.Highlights Mechanical behavior of Hybrid composite of two natural fibers was investigated. Vacuum assisted resin transfer molding was used to manufacture composite panels. Tensile, in plane shear, 3 point flexural tests and SEM micro analysis were done. FEA was used to validate and compare the experimental and numerical results. Resin agglomeration was improved by fibers with better resin impregnation property.

A wind semi-sub platform with hinged floats for omnidirectional swell wave energy conversion

AbstractThe capacity of wind turbines on offshore wind platforms is presently much greater than that for wave energy conversion. However, wind availability with speed greater than 5 m/s, just above cut in, is typically 30–40% requiring storage to provide uniformity of supply, but this may be improved by adding swell wave energy conversion with typical availability of 90%. A hybrid platform is considered with three effectively rigid cylindrical floats connected by beams at right angles to support a wind turbine with its base on the central float, and two wave energy floats, opposite the wind floats, with beams at 90° and hinges with dampers for mechanical energy absorption on the central float. With swell periods over 10 s, pitch resonance may be achieved with the fore and aft floats about half a wavelength apart with anti-phase forcing causing a moment on hinges above water level. The NREL 5 MW wind turbine is incorporated and average swell wave power absorption in a typical significant wave height of 2 m is over 200 kW. The analysis is by time domain linear diffraction–radiation modelling validated for other multi-float configurations. Significant wave energy conversion is omnidirectional over a wide range of heading angles. An added benefit is that in larger waves associated with strong winds, when the wave energy conversion would be disengaged, the wave float rotation on free hinges reduces the hub accelerations below that for rigid floats, enabling a longer time for wind power generation.

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.

Experimental, analytical, and numerical studies of the energy absorption capacity of bi-material lattice structures based on quadrilateral bipyramid unit cell

The present study investigates the mechanical performance and energy absorption capacity of bi-material 3D lattice structures via experimental, analytical, and numerical approaches. The analytical model has been developed to obtain the effective parameters in energy absorption, such as equivalent elastic modulus and yield stress. Analytical relations based on hyperbolic shear deformation beam theory were extended to calculate the mechanical properties of an extracted unit cell from the lattice structure subjected to applied loads and appropriate boundary conditions. Then, experimental and nonlinear numerical studies have been conducted to analyze the energy absorption properties of the bi-material lattice structure. Quasi-static compression tests were conducted to analyze this lattice structure's mechanical properties and energy absorption capacity. As the numerical study, the elastic-plastic damage behavior was implemented in finite element analyses to examine the nonlinear response of considered structures. The obtained results reveal that the numerical models exhibit an acceptable prediction. According to the results, not only does the use of hybrid structures provide more energy absorption and improve mechanical properties, but also, in comparison to the usual lattice structures fabricated with a single material, the rational combination of two materials makes the bi-material three-dimensional lattice structure to inherit the optimum energy absorption and stiffness.