Pyramidal Lattice Core Research Articles

Legendre–Ritz solutions for vibration characteristics of three-dimensional double-layer lattice truss sandwich plates

In this paper, Legendre–Ritz solutions for vibration characteristics of double-layer lattice truss sandwich plates are proposed based on three-dimensional (3-D) elasticity theory. Double-layer lattice truss sandwich plates consist of three face sheets and two cores. The face sheets are composed of fiber-reinforced composites and the cores are composed of pyramidal lattice trusses made of isotropic materials. The pyramidal lattice core is equated to a homogeneous plate according to equivalence principle. Based on 3-D elasticity theory and pseudo excitation method (PEM), each layer's energy expressions of double-layer lattice truss sandwich plates are constructed. After that, Legendre polynomials are adopted to describe displacement components in length, width and thickness directions. On this basis, the Rayleigh-Ritz method is used to solve energy functions to obtain motion equations of double-layer lattice truss sandwich plates. The accuracy and validity of the present method are corroborated by comparisons with references and finite element method (FEM). Additionally, in order to find out effects of relevant parameters on dynamical characteristics of double-layer lattice truss sandwich plates, parametric studies are carried out by means of some numerical examples.

Static and dynamic response of pyramidal lattice sandwich plate with composite face sheets reinforced by graphene platelets

For the pursuit of lightweight structures with excellent mechanical performance, sandwich structures with lightweight cores and strengthened face sheets have become popular in the advanced engineering fields in recent years. In this paper, the nonlinear static and dynamic responses of the sandwich plate constructed with the aluminum pyramidal lattice core and functionally graded graphene platelets reinforced composite (FG-GPLRC) face layers are analyzed. The partial differential equations of the pyramidal lattice sandwich plate considering the geometric nonlinearity are achieved based on the Reddy’s third order shear deformation theory (TSDT), which are solved by the combination of finite element model, Raphson’s method and Newmark numerical integration method. Four different types of the impact loads including the step loading, triangular loading, half-sine loading and exponential loading with the same peak value and duration time are investigated. The influences of the thickness-to-truss radium ratio and the angle of the truss core, as well as the weight fraction and distribution patterns of graphene platelets (GPLs) over the face sheets under different impact loads and different boundary conditions are analyzed. According to the numerical results, it is concluded that the sandwich plate with higher weight fraction of GPLs, lower thickness-to-truss radium ratio, and higher angle of the truss core can exhibit better performance in both static and dynamic loading conditions. The FG-X distribution of GPLs presents the best dynamic performance as compared to the other GPL distributions. The combination of lightweight truss core with the advanced GPLRC face sheets is instructive for potential applications and further research.

Heat transfer property of C/SiC composite pyramidal lattice core sandwich structures

An explicit analytical model for predicting the heat transfer in C/SiC composite pyramidal lattice core sandwich structures is proposed with considering the radiation emitted from the struts. Temperature gradient in thickness direction of the lattice core sandwich structuresis considered in the proposed model. The predictions are compared with the published experimental data and analytical results. It indicates the effect of the radiation emitted from the struts on the equivalent thermal conductivity becomes more significant at high temperature and cannot be overlooked. The present model is more accurate in estimating the high-temperature equivalent thermal conductivity of pyramidal lattice core sandwich structures than those models without considering the radiation of struts. The effects of geometry, solid emissivity, and temperature on the equivalent thermal conductivity of pyramidal lattice core sandwich structures are well discussed.

Modeling and simulation of static and dynamic behavior in composite sandwich plates with hourglass lattice cores based on reduced-order model

The composite sandwich plate with hourglass lattice cores (CSP-HLC) is a novel cellular structure that can increase the width-to-length ratio and reduce the inter-node spacing. However, its static and dynamic behaviors are difficult to analyze due to the complex microstructures. In this work, a computational homogenization method is proposed for calculating the constitutive parameters. A reduced-order plate model is then derived through dimensional reduction from the three-dimensional orthotropic thermoelasticity framework. The effectiveness and accuracy of the proposed model were verified by comparing with the static-displacement and free-vibration results of 3D direct numerical simulations. The parameter analysis showed that the different material and structural parameters of the hourglass lattice core had different effects on the equivalent stiffnesses and natural frequencies of the CSP-HLC. Compared with the composite sandwich plate with pyramidal lattice cores, the displacement of the CSP-HLC was smaller under the same load and boundary conditions, and the natural frequencies were also smaller, which may have been because the additional equivalent density of the CSP-HLC influenced the frequency more predominantly than the extra equivalent stiffness.

Comparative study on the blast load response of woven and lattice core metallic sandwich panels

Sandwich structures are potential alternatives to monolithic plates for the purpose of absorbing energy and managing the impulse associated with blast loading. The study of sandwich structures subjected to blast loading is a rapidly expanding area of activity. Sandwich structures are extensively used in blast dissipation applications on account of their excellent physical and mechanical properties. These sacrificial cladding structures absorb energy through progressive plastic deformation of the front-facing plate and the core layer; thus minimizing the transfer of the peak force to the non-sacrificial structure. The core absorbs most of the energy and hence has a significant influence on the blast behavior of sandwich structures. The core layer can have several topologies, which in turn have various configurations. The present study numerically evaluated and compared the effectiveness of using Triangular Woven and Pyramidal Lattice core configurations in sandwich panels for resisting blast loads. The parametric study consisted of the effect of change in outer layer thicknesses of sandwich panels and the application of successive blast loads in the performance of the sandwich panels. The study was conducted for seven outer layer thickness combinations modeled in ANSYS Workbench Explicit Dynamics. All the models were subjected to a blast load with the same scaled distance. The comparison of the simulated results was used to determine the more suitable core configuration for dissipating blast loads. Pyramidal lattice panels were found to be 5% and 48% more efficient than a triangular woven panel of comparable relative core density under normal blast load and successive blast load respectively.

Experimental and numerical investigation of adhesively bonded additive manufactured sandwich structures with a pyramidal lattice core

ASBTRACT The application of adhesively bonded joints has increased in a large variety of different industrial sectors over the last decades. In comparison to other joining techniques, adhesively bonded joints can offer easier assembly, weight reduction, lower stress concentration, etc. Additive Manufacturing (AM) as a transformational approach in Industry 4.0 can even improve the structural performance of such joints in terms of more weight reduction, making more homogenous stresses in the adhesive layer of the bonded area. In this work, an adhesively bonded single lap joint (SLJ) with metallic sandwich structures and a pyramidal lattice core as adherend by using AM was designed, produced and tensile tested. The result of this study showed that in addition to the significant savings in the weight of the adhesively bonded joint, the additive manufactured sandwich adherend produces a more homogenous stress distribution compared to conventional adherends with the same material. Furthermore, two different finite element (FE) approaches were used for modelling the fracture behaviour of the additive manufactured joint, namely a solid element formulation and a simplified model using shell-beam formulation. The simplified shell-beam formulation reduces the modelling and calculation efforts massively and shows a good agreement with experimental results.

3D lattice-based structural elements for industrial application

A concept of construction plate based on steel sandwich panel with pyramidal lattice core is proposed. A space between the outer sheets of the sandwich is filled with concrete. The considered plate has large dimensions within standard range in order to provide meaningful data for industrial case and capture geometry nonlinearity in stress analysis. The ultimate compressive load is estimated by the simulation procedure using Abaqus FEA software. The result is that proposed structure shows 1.4 higher ultimate load in comparison with conventional concrete plate reinforced by steel bars, while the metal consumption is identical.

Fabrication and Statics Performance of Pyramidal Lattice Stitched Foam Sandwich Composites

In this study, the pyramidal lattice stitched foam sandwich composite materials were manufactured by integrating top and bottom panels with pyramidal lattice core to overcome the weak interface between the core and the skins of the sandwich structure. The influence of the reinforcing core rods on the mechanical properties including compressive, shear, and three-point bending performances of the foam sandwich composite materials were revealed through theoretical analysis and comparative experiments. The theoretical predictions were consistent with the experimental results. Compressive test, shear test and three-point bending test were performed. The experimental results show that the core rods can significantly improve the compressive performance and energy absorption efficiency of the pyramidal lattice stitched foam sandwich structure. The effect is related to the diameter of the core rod. The core rod with large diameter has better effect. Compared with the foam sandwich structure, the pyramidal lattice reinforcing foam composites have stronger shear and bending resistance. The failure modes and failure mechanisms of the pyramidal lattice stitched foam sandwich structure under the shear load are given. The failure modes and failure mechanisms of the pyramidal lattice stitched foam sandwich structure under the three-point bending load are also given. The study concludes that compared with the foam sandwich structure, the overall mechanical properties of the lattice stitched foam sandwich structure composites are significantly improved.

Predicting the equivalent thermal conductivity of pyramidal lattice core sandwich structures based on Monte Carlo model

An analytical model is presented to predict the equivalent thermal conductivity of the pyramidal lattice core sandwich structure. The equivalent thermal conductivity of the pyramidal lattice core sandwich structure is attributed to both conduction and radiation. The equivalent thermal conductivity caused by heat conduction is evaluated based on Fourier's law. The configuration factor is calculated by the Monte Carlo method considering the effect of radiation in all directions. The predictions are compared with the previous analytical and experimental results. It reveals that the present model is more accurate in estimating the equivalent thermal conductivity for the pyramidal lattice core sandwich structures. The effects of the geometrical parameters, solid emissivity and temperature on the equivalent thermal conductivity of the pyramidal lattice core sandwich structures are well discussed.

Bending behavior of lightweight C/SiC pyramidal lattice core sandwich panels

Due to the excellent mechanical and chemical properties at ultra-high temperature, ceramic matrix composite structures have potential applications for thermal protection systems of hypersonic vehicles. This paper presented a PIP method to fabricate C/SiC pyramidal lattice core sandwich panels (LCSPs). Their bending behaviors with different core angles were experimentally studied firstly. Then the critical failure loads of different failure modes, including facesheet crushing or wrinkling, core member crushing, core shear failure and interlayer delamination, were theoretically established to construct the failure mechanism maps. The influence of geometric parameters, such as the length and the core angle of the core strut, and the thickness of the facesheet, on the failure mode was also analyzed. In addition, further failure process under bending load was investigated by finite element analysis (FEA) method. Elastic-damage constitutive model and cohesive element were applied to modeling the behavior of C/SiC composite and interlayer delamination between the sheet of the core and the facesheet. Theoretical and FEA results agreed well with experimental data. This work is believed to be helpful to understand the bending mechanism C/SiC pyramidal LCSPs.

Design and compressive behavior of a wood-based pyramidal lattice core sandwich structure

Eco-friendly wood-based engineering materials have often received considerable interest worldwide because of their high specific strength/stiffness and biodegradability. To design and enhance an axially compressive member of a wooden structure, a pyramidal lattice core sandwich structure was fabricated with larch sawn timber as the face sheet and birch dowel as the core by using a slotting and adhesive bonding approach. A flatwise compressive experiment was conducted to reveal the compressive behavior and failure modes of the structure. The enhanced designs of the face sheet and the core were based on the failure mechanism and mechanical properties of raw materials. Theoretical analysis and finite element method were applied to predict the structural compressive behavior. Comparison of theoretical, numerical, and experimental results suggested good agreement in the structural compressive response. The results revealed that the reasonable design of the face sheet and the core played an important role in the compressive response and failure modes of the wood-based pyramidal lattice core sandwich structure.

The mechanical compression performance of ultra-fine grained stainless steel pyramidal lattice core

Severe plastic deformation (SPD) techniques are prospective ones having ability for desirable high mechanical properties to be achieved without any chemical change in metals. Equal-channel angular pressing (ECAP), one of SPD techniques, was used to obtain ultra-high mechanical compressive response of stainless steel pyramidal lattice core. For this purpose, the stainless steel 304 L samples were processed by ECAP at 500 °C. Then, it was sliced into struts and built lattice core after bending processes. At the compression tests, the ECAP lattice core has huge mechanical properties, at nearly two times collapse load and energy absorption values.

Mechanical behaviors of C/SiC pyramidal lattice core sandwich panel under in-plane compression

C/SiC composite lattice-core sandwich panels combined with thermal insulation and load-bearing capacities are considered as the most promising candidates for thermal protection system (TPS). In this study, C/SiC pyramidal lattice-core sandwich panel with different inclination angles were fabricated using a compression molding and precursor infiltration and pyrolysis (PIP) method. In-plane compressive experiments are conducted to study the failure behavior of these sandwich panels. The analytical failure modes including elastic buckling, face sheet wrinkling, face sheet crushing and interlayer delamination are established to construct the mechanism maps. The effect of geometrical parameters on failure modes are symmetrically and analytically studied. Due to the limits of the cost, virtual tests are supplemented by finite element method (FEM). Face sheet crushing is experimentally observed for almost all specimens with different inclination angles, which is in good agreement with analytical predictions. Numerical simulation results show that interlayer delamination occurs at the attachment between face sheet and lattice core after elastic buckling and core shear buckling. This paper gives us some fundamental understanding of the mechanical response and failure mechanism of C/SiC composite lattice-core sandwich panels.

Lattice materials with pyramidal hierarchy: Systematic analysis and three dimensional failure mechanism maps

Sandwich core materials that offer superior mechanical properties at minimum weight are essential in designing high-performance sandwich structures. Hierarchical materials are ideal templates for this purpose. In this paper, we investigate the mechanical performance of a pyramidal–pyramidal hierarchical lattice material to highlight its potential as the core material for sandwich structures. Three-dimensional failure mechanism maps for the pyramidal–pyramidal hierarchical lattice material are developed under different loading conditions and the results are compared to finite element simulations. Next, we study the mechanical response and failure modes of a sandwich panel with self-similar pyramidal lattice core construction subjected to in-plane compression and three-point bending. The current study indicates that the pyramidal–pyramidal hierarchical configuration can improve the load bearing capacity and core buckling resistance of the sandwich structures at low density. The study provides insights into the role of structural hierarchy in tuning the mechanical response of the lattice materials and expands the application envelope of lightweight sandwich structures by effectively increasing the structural buckling resistance.

Comparative evaluations of thermofluidic characteristics of sandwich panels with X-lattice and Pyramidal-lattice cores

This study compares the thermo-fluidic characteristics of sandwich panels with the X-lattice and the Pyramidal lattice at a given porosity and surface area density. The numerical model is validated against available experimental data at first. At a given Reynolds number in the range of 3100–5700, numerical results reveal that the X-lattice sandwich panel provides a 47–60% higher average overall Nusselt number. The special topology of the X-lattice induces counter-rotating spiral primary flow and more complex secondary flows, including one which becomes a longitudinal vortex later. The flow in the Pyramidal lattice sandwich panel is composed of a parallel primary flow and a counter-rotating vortex pair entrenched in the zone behind ligaments of the Pyramidal lattice. Compared with the Pyramidal lattice sandwich panel, endwall heat transfer of the X-lattice sandwich panel is enhanced by 75–97% and the ligaments surface heat transfer is enhanced by 85–97% at a given Reynolds number. It is also found that the friction factor of the X-lattice sandwich panel is about 2 times higher for the spiral primary flow and more complex secondary flows induced by the staggered ligaments. Finally, at a given pumping power, the cooling performance of the X-lattice is much better, too. Taking the identical fabrication method and cost into account, apparently the X-lattice is superior in engineering applications.

Introducing composite lattice core sandwich structure as an alternative proposal for engine hood

Pedestrian protection capability is critical for lightweight design of automotive engine hood. Here, a novel and lightweight composite sandwich hood including two fiber reinforced composite panels and a lattice core was proposed and the corresponding pedestrian protection performance was evaluated via Head Injury Criterion (HIC). The novel double-curvature composite sandwich hood with a pyramidal lattice core was designed based on a commercialized product with a weight reduction by 25%, and fabricated using interlocking approach. A homogenized constitutive model was developed for the pyramidal lattice core and utilized in the following headform-to-hood impact simulations with LS-DYNA. The stiffer sandwich hood revealed better pedestrian safety performance compared with the corresponding baseline hood without lattice core where secondary collision happened. Also, effects of geometrical variables, material selection and core types were discussed. The variation of panel thickness played a more important role in the average HIC values compared with that of core geometries. Among various material selections, hoods designed with carbon fiber reinforced composite (CFRC) panels and a flax fiber reinforced composite (FFRC) lattice core achieved the minimum head injury. Additionally, lattice core outperformed traditional honeycomb and foam in sandwich hood design. The present study demonstrates the feasibility of employing lattice materials in lightweight design of hood and other car body coverage.

Vibration analysis of sandwich plates with lattice truss core

ABSTRACTAn effective methodology is developed to investigate the vibration of the sandwich plate with pyramidal lattice core. Equation of motion of lattice sandwich plate is established by Hamilton's principle. Displacement fields are expressed with a simple method, and the natural frequencies of the lattice sandwich plate are conveniently calculated. The correctness of the analytical method is verified by comparing the present results with published literatures. The effects of structural and material parameters on the vibration characteristics of lattice sandwich plate are analyzed. The present method will be useful for vibration analysis and design of lattice sandwich plates.

Investigations on the influences of elastic foundations on the aerothermoelastic flutter and thermal buckling properties of lattice sandwich panels in supersonic airflow

The lattice sandwich panels supported on elastic mediums are often applied in the construction of aerospace structures because of the low specific weight, excellent bending rigidity and outstanding vibration properties. This elastic medium can be any spring materials including damping tapes or heat shields which are attached to one side of the sandwich panel. Therefore, in this paper, aerothermoelastic flutter and thermal buckling characteristics of sandwich panels with the pyramidal lattice core resting on elastic foundations in supersonic airflow are studied. The influences of geometrical parameters and elastic foundation on the panel flutter and thermal buckling of the structures are analyzed in detail. In the structural modeling, the first-order shear deformation theory is applied, and the effective material properties of the lattice core are used. The aerodynamic pressure is evaluated by the supersonic piston theory. Hamilton's principle and the assumed modes method are applied to formulate the equation of motion. The highlight point of this investigation is that an effective thermal buckling suppression method utilizing the elastic foundation is proposed, based on which the thermal buckling of the structure can be completely eliminated with the natural frequencies remaining unchanged when the shearing layer parameter is equal to the thermal load. Through the numerical results, the influences of the elastic foundation, aspect ratio, core-to-facesheet thickness ratio, and inclination angle of the core truss on the aerothermoelastic behaviors of the lattice sandwich panel are analyzed, and the thermal buckling elimination effects are also examined.

High temperature mechanical properties of lightweight C/SiC composite pyramidal lattice core sandwich panel

Lattice core sandwich panels, fabricated from metal or resin matrix composites, can not be used under high temperature. Here, we devise a novel pyramidal lattice core sandwich panel fabricated from ceramic matrix C/SiC composite which can be used up to 1600°C. We evaluate the high temperature mechanical properties through experiments, theoretical analysis, and finite element analysis. Under room temperature, 1200°C and 1600°C, the compressive strengths are as high as 12.70, 5.35 and 2.45MPa, and the modulus are 630, 260 and 120MPa, respectively. The specific bending strengths are up to 260.7, 168.7 and 152.1MPa/(g·cm3). We also exclusively reveal that with increasing temperature, the critical relative density for the failure models shows significant reduction, indicating service temperature increment enables the original fracture failure to transfer to the buckling of the core bars. Moreover, we develop a finite element analysis model which can well calculate the damage evolution, failure mechanism and models observed in experiments. The failure model under compression is the fracture of the core bars while the bending failure is shear failure of the core bars. These results indicate that the C/SiC sandwich panel integrates high temperature resistance, lightweight characteristic and robust mechanical properties.

Design and analysis of integrated thermal protection system based on lightweight C/SiC pyramidal lattice core sandwich panel

Thermal protection system (TPS) plays the key role to successful development of hypersonic vehicles. Here, a novel structurally and thermally integrated thermal protection system (ITPS) based on the lightweight C/SiC pyramidal core lattice sandwich panel is proposed. This ITPS integrates advantages of low areal density and high temperature resistance up to 1600°C. Heat transfer characteristics and compressive responses of the C/SiC sandwich panel are established in advance. The results demonstrate that filling alumina fibers in the pore significantly reduce the effective thermal conductivity from 2.45–4.83W/m°C to no more than 0.7W/m°C. The critical relative density is determinated for the failure models under aerodynamic pressure load. Meanwhile, an analysis procedure of the ITPS is exclusively established under typical aerodynamic heat flux and pressure load. With fulfillment of both temperature and mechanical constraints, minimum areal density is obtained. Compared with current metal corrugated core ITPS, the ITPS proposed here significantly raises the temperature limitation up to 1600°C and reduces the areal density up to 35%, and is very promising for potential application in hypersonic vehicles.