Lattice Core Research Articles

Study on bending performance of laminated bamboo sandwich panels with different lattice core layers: Cleaner production of green material

In order to improve the utilization and development of bamboo resources and promote its application in the engineering field, the effects of different lattice cores and processing methods on the bending performance of laminated bamboo sandwich panels were discussed in this study. These structures featured distinct lattice cores, namely triangular lattice, square lattice, and Kagome lattice. The manufacturing process included using laminated bamboo as the raw material and adopting the interlocking method and partition method. Four-point bending tests were carried out on laminated bamboo sandwich panels with different lattice cores, and the bending performance of sandwich panels was discussed. The failure mechanism of sandwich panels under bending load, as well as the variation law of mid-span deflection, bending stiffness and ultimate bearing capacity, are analyzed, and the specific stiffness and specific strength of laminated bamboo sandwich panels with four different core layers were compared. At the same time, a four-point bending test model of laminated bamboo sandwich panels was established by using finite element software ABAQUS, and numerical simulation was carried out. Three kinds of sandwich panels with different lattice core processed by the interlocking method all show shear failure during the bending loading, among which the triangular lattice sandwich panel has the best bearing capacity, while the specific strength of the laminated bamboo sandwich panel with triangular lattice is also the largest. The failure mode of the laminated bamboo sandwich panel with square lattice processed by partition method is that the upper layer yields under compression and the lower layer is damaged in tension. Its bearing capacity and specific strength are better than those of the three sandwich panels processed by interlocking method, which are 21.6 % and 43.6 % higher than those of the triangular lattice interlocking sandwich panel respectively. The error between the simulation results and the experimental results is less than 5 %, which has good consistency and can effectively predict the bending performance of the laminated bamboo sandwich panels. The laminated bamboo square lattice sandwich panel processing by partition method has excellent bending performance among the four kinds of sandwich panels, which can better present the lightweight and high-strength advantages of laminated bamboo. The research results can provide an effective structural form and theoretical basis for the application of bamboo in the engineering field.

Mechanical Analysis of Sandwich Plates with Lattice Metal Composite Cores

This study investigates the modal and static behaviour of sandwich panels with lattice core structures, comparing the real cellular solid structures’ response with an equivalent homogenised model. The mechanical model has been described through the Finite Element Method (FEM), and 3D elements with reduced integration have been employed to guarantee an accurate description of skins and the lattice geometry. Different Body Centred Cubic (BCC) cell configurations have been considered: standard metal BCC cell, metal BCC cell with waved struts, standard metal composite BCC cell. Depending on the configuration, the homogenised materials showed isotropic or orthotropic properties. The composite core has been modelled using two different materials, namely an Aluminium matrix with an AlSiC filler, which is enclosed inside the other hence constituting the BCC cell’s strut. A free-vibration and static analysis parametric study has been conducted varying the strut’s diameter, the strut’s waviness and the thickness ratio of the composite struts. For the static analysis, a multiscale approach has been adopted; a first step considering the whole homogenised sandwich panel and a second step comparing the multiscale results of the homogenised model and those of real structure considering a small portion of the panel. Results reveal insights into the effects of core structure parameters on the mechanical response of sandwich panels, aiding in design optimisation and structural enhancement.

Aeroelastic analysis of a lightweight topology-optimized sandwich panel

Sandwich structures with lattice cores are novel, lightweight composite structures and are widely used in the aerospace industry. Besides, the aeroelastic behavior of sandwich panels in a supersonic flow regime still needs to be thoroughly studied. This work investigates the supersonic flutter of a sandwich panel whose core is topology-optimized. A finite element model of a sandwich panel based on the layerwise theory, coupled with the first-order piston theory, is presented. The sandwich panel core is assessed using a topology optimization approach with flutter loading constraints. The subsequent analytical homogenization scheme is developed to provide the equivalent mechanical properties of the topology-optimized panel. The modeling approach is fully validated, and the results demonstrate that the sandwich panel is capable of enlarging the flutter-free operational flight range when compared with other conventional panel designs. A parametric analysis of the topology-optimized sandwich panel regarding the critical flutter conditions is performed.

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.

Impact behavior of periodic, stochastic, and anisotropic minimal surface-lattice sandwich structures

Recent advancements in 3D printing technologies have made it possible to fabricate intricate lattice architectures with high precision. These lattices can now be utilized to design lightweight sandwich structures that serve multiple functions. To enhance the impact loading performance of these structures, it is crucial to understand how the lattice's topological properties, particularly those with minimal surface attributes like periodic or stochastic Primitive and Gyroid triply periodic minimal surfaces (TPMS) and spinodal-like stochastic cellular materials, associate with the mechanical properties of sandwich structures while keeping the skin thickness fixed. Thus, this paper explores the low-velocity impact behavior of various sheet/shell-based minimal surface-latticed cores of sandwich structures with woven composite skins. The elasto-plastic-damage numerical simulations consider lattice core periodicity, randomness, and anisotropy while keeping the relative density constant. Core lattice randomness and anisotropy are designed using the Gaussian Random Field (GRF) method for spinodal-based stochastic cellular materials and stochastic TPMS. The simulation results showed that the periodic Primitive-lattice core exhibits high out-of-plane shearing strength, enabling the sandwich structure to demonstrate the highest perforation limit. GRF spinodal-based core achieved the highest peak load due to its anisotropic mechanical properties. However, the post-yielding bending of the lattice sheet limited its ability to resist perforation, and absorb and dissipated energy. Interestingly, the stochastic Gyroid TPMS topology, with its inherent densely-distributed microstructure, showed high sensitivity to loading rate, resulting in enhanced energy absorption and dissipation of the sandwich structure. These findings offer valuable insights for optimizing multifunctional sandwich structures with superior impact performance and their design for additive manufacturing.

Developing a lightweight hybrid profile concept with a steel shell and polymeric lattice core for optimal mechanical performance

The building industry needs new design approaches to minimize resource consumption and negative environmental impacts. This study proposes a lightweight hybrid profile that combines a thin steel shell and a polymeric lattice core. The core density and internal structure variation possibilities control the slender steel profile’s load-bearing capacity and optimize the hybrid structure’s weight because of a synergy of the composite section components. The test campaign employs a 3D printing technology for prototyping the lattice core because the manufacturing preciseness (including the internal stiffener structure) is vital for structural optimization and developing adequate numerical models. A straightforward example illustrates the proposed concept. Lateral compression tests on 100 mm long fragments of the slender rectangular hollow section (RHS) 200/100/4 mm (height/width/thickness) profile prove the mechanical efficiency of the proposed hybrid section concept. Reducing the RHS fragment length ensures the experimental identification of the stiffening mechanism in the polymeric insert using a digital image correlation (DIC) technique and simplifies the numerical model. The 3D-printed lattice polymeric core added only 28% to the weight of the hybrid RHS fragment and increased its mechanical resistance twice compared to the reference empty shell fragments. This effect is equivalent to raising the profile thickness from 4 mm to 6 mm, resulting in a 1.5-times increase in weight. Using recycled plastics, adhesive connecting the inserts, and optimizing the internal geometry of the core stiffeners, depending on the loading conditions, may further increase the economic benefits of the proposed hybrid profile concept.

Efficient mechanical modeling of sandwich panels with functionally graded lattice cores under thermal environments

3D-printed sandwich panels with functionally graded (FG) lattice cores have garnered widespread attention owing to their outstanding mechanical performance. However, the straightforward interplay between the service environment, strut structure, and their mechanical behavior has not been systematically explored. In this study, an analytical two-step prediction modeling is developed to efficiently obtain the mechanical response of 3D printed sandwich panels with FG lattice cores. Initially, the effective elastic moduli of FG lattice cores are identified based on finite element (FE) analysis. The stress and deformation of the core-homogenized sandwiches in thermal environments are predicted using the higher-order shear deformation theory. Subsequently, the de-homogenization is employed to calculate strut stresses. The prediction shows excellent agreement with the FE results in the literature. Furthermore, parametric analysis is performed to uncover the impact of crucial variables on the strut stresses within the FG lattice cores. The results show that the strut stress decreases with the increased transverse layer number and power index, while increasing with the higher ambient temperature, length-to-thickness ratio, and thermal expansion of the sandwich panels. The proposed model can serve as an efficient tool for the design and printing of high-performance lattice-core sandwich panels.

Design, thermal-mechanical coupling analysis, and optimization of polymeric matrix composite sandwiches with a lattice core exposed to a high temperature

This study presents the design of a sandwich structure tailored for post-heat transfer applications subjected to out-of-plane compression. A three-dimensional finite element simulation model was developed to analyze the temperature distribution within the sandwich structure and investigate the effects of high-temperature exposure on its mechanical behaviors. The structure was subjected to a temperature of 300 °C for 400 s, and the temperature distribution at the upper connection point between the top face sheet and the struts of the core was determined. Subsequently, upon returning the sandwich to ambient temperature, a comprehensive calculation of its mechanical properties was conducted and then enhanced by applying different optimization techniques. The results demonstrate that filling the core with Saffil alumina fibers in the presence of a 1.5 mm a thermal barrier coating of Superwool 607 helps increase the mechanical properties of the sandwich structure by around 55%.

Static and dynamic atom displacements in nanocrystalline powders from diffraction analysis at finite temperature

We evaluate the accuracy of x-ray diffraction analysis performed by Rietveld refinement in extracting the static and dynamic atomic displacement parameters of spherical gold nanocrystals with sizes of 30 nm and below and within a temperature interval of 10–300 K. A self-consistent computational workflow composed of real- and reciprocal- space analyses is designed for this purpose. We obtain average lattice parameters, static and thermal atomic displacements as well as their temperature and particle size dependence in an ideally monodispersed and realistic nanocrystalline powder generated by molecular dynamics simulations. Then, we compare crystallographic parameters obtained from real- and reciprocal- space analyses to evaluate the accuracy of diffraction analysis. We also extend the comparison to local variations of crystallographic parameters in the nanocrystals and show how Rietveld refinement relates to the average parameters of the core and surface regions separately. We show that 1) average lattice parameters obtained from Rietveld refinement are greater than the mean lattice parameter of small nanocrystals and converge to the core lattice parameter with increasing particle size, 2) Rietveld refinement significantly underestimates static atom displacements of surface atoms in small nanocrystals, 3) dynamic atomic displacements in nanocrystalline gold powders are reliably obtained within 5 % error by Rietveld refinement, provided that thermal diffuse scattering is adequately removed from the diffraction data, 4) the discrepancy between real- and reciprocal-space analysis increases for the smallest gold nanocrystal.

Titanium/FRP hybrid sandwich: in-plane flexural behaviour of short beam specimens

Adopting novel sandwich structures with FRP (Fibre Reinforced Polymer) skins and a metallic lattice core, both of which have high specific strength and stiffness, is one way to achieve better mechanical performance while remaining lightweight. Flexural stress is a load pattern that frequently occurs in the structural frame components of automobiles; nonetheless, while the in-plane load scheme has scarcely been examined, the out-of-plane load one has. As a result, the former configuration received consideration in this work. Moreover, short beam specimens were taken into account. The mechanical response of specimens with three different kinds of composite materials as skin material was analysed. The skins were made of CFRP (Carbon Fiber Reinforced Polymer), with two different weaving styles, and AFRP (Aramid Fiber Reinforced Polymer). All-titanium specimens were studied, too. Similar maximum loads and maximum displacement at break were recorded for both CFRP and AFRP specimens, while the all-titanium one resulted stronger. In terms of the load-displacement curves, the first section featured an initial linear phase, followed by a minor load drop, likely attributed to the breakage of fibres. The CFRP specimens showed a sharp fracture of the skin fibres, while for the AFRP, a fraying was observed.

Thermo-mechanical modeling of lattice-core sandwich panels in powder bed fusion

Residual stresses play detrimental roles in the mechanical performance of lattice-core sandwich panels (LCSPs) via powder bed fusion (PBF), owing to the laser-induced high-temperature gradients. Thus, it is essential to understand the thermo-mechanical behavior of LCSPs during PBF. However, the relation between process settings and the mechanical response of as-printed LCSPs has not been systematically investigated. In this study, an integrated thermo-mechanical modeling is developed to effectively capture the strut stress and deformation of PBF-built LCSPs. The key advance is that the effective thermo-mechanical field within printed LCSPs is first determined based on the homogenization-based differential quadrature method, where the structure-dependent thermophysical and mechanical properties of lattice cores are considered. The effective displacement is used to directly calculate strut stresses through a de-homogenization process. The accuracy of the predicted results is verified by the comparison with the literature. Furthermore, the effect of process parameters, geometrical dimensions, and strut structures on the thermo-mechanical behavior of pyramidal and vertically reinforced pyramid LCSPs is demonstrated. The results show that the strut stress and vertical warpage increase with the higher energy density, length-to-thickness ratio, and vertical strut addition, while decreasing as the inclined angle and environmental temperature enlarge. These findings can offer a guideline for the high-quality printing of LCSPs with desired mechanical performance and dimensional accuracy.

Buckling and post-buckling of anisogrid lattice-core sandwich plates with nanocomposite skins

This research offers an in-depth examination of the buckling and post-buckling responses observed in sandwich plates distinguished by the presence of an anisogrid lattice core and face layers composed of functionally graded carbon nanotube-reinforced composites (FG-CNTRC). To model this structure, a global continuous model for the lattice core is employed, while the displacement field is approximated using the First-Order Shear Deformation Theory (FSDT). Geometrically nonlinear strain relations based on the von-Kármán assumptions are incorporated to accurately capture the structural response. The homogenization of the FG-CNTRC skins is achieved through the modified rule of mixture, enabling estimations of effective material properties. To separate pre-buckling and post-buckling phases, we implement the adjacent-equilibrium criterion. Solving the linear (pertaining to buckling) and nonlinear (related to post-buckling) equations is based on the Generalized Differential Quadrature (GDQ) technique alongside an iterative method grounded in the displacement control strategy. Our analysis explores the influence of core and skin characteristics on the stability of these sandwich plates. By examining critical buckling thresholds, post-buckling equilibrium paths, and the underlying mechanisms driving these responses, we contribute insights into the structural stability and performance of such composite structures. This study not only enhances our understanding of buckling behavior in anisogrid lattice core sandwich plates but also holds promise for diverse engineering applications where structural stability is paramount.

Novel conformal sandwich lattice structures: Design concept, fabrication and mechanical properties

A novel conformal sandwich lattice is proposed by introducing the design concept of bioinspired sandwich structures into the microstructure design of triply periodic minimal surface (TPMS) lattices, and the mechanical properties of the conformal sandwich lattice (P-SC) with P-TPMS lattice skins and simple cubic (SC) plate lattice cores are investigated numerically and experimentally. The P-SC specimen manufactured by the laser powder bed fusion (L-PBF) with glass bead-filled polyamide composite exhibits negligible anisotropy in its mechanical properties, as confirmed by tensile tests conducted on specimens fabricated at various build orientations. The elastic properties of the P-SC can be widely tailored by modifying the structural parameters. Especially, the anisotropic index can be tailored to obtain an elastically-isotropic P-SC sandwich lattice. Additionally, the P-SC exhibits superior elastic properties and energy absorption compared with the conventional lattices. The findings provide insights into the design flexibility of advanced high-performance structural materials for complex engineering applications.

A Non-uniform Equivalent Model for Free Vibration Analysis of Sandwich Composite Panels with Trapezoidal Lattice Core

A Non-uniform Equivalent Model for Free Vibration Analysis of Sandwich Composite Panels with Trapezoidal Lattice Core

Aeroelasticity analysis of anisogrid lattice sandwich cylindrical shells: Extended potential and piston theories

Based on the extended potential and piston aerodynamics theories, buckling and vibration analysis of sandwich cylindrical shells subjected to external airflow in both subsonic and supersonic regimes is presented. Sandwich cylindrical shells are considered to be made of same homogenous face sheets and an anisogrid composite lattice core with hexagonal cells. An equivalent single layer (ESL) theory in the framework of classical Love’s shell theory is used to formulate the global mechanical behavior of such shells. According to the extended potential and piston aerodynamic theories, aerodynamic pressure distributions are determined for steady, inviscid, irrotational compressible, and external airflow. The closed–form solutions of critical upstream pressure and natural frequency are developed for different boundary conditions using the Galerkin method. Finally, case studies are presented to compare between results of extended potential and piston theories and investigate the effects of upstream speed, geometric ratios, boundary conditions, and lattice specifications on various response quantities. Findings indicate that the differences in results of extended potential and piston theories are less than 3% in the supersonic regime with 2.3 ≤ M ∞ ≤ 2.7 for intermediate-length shells with a wide range of R . The piston theory is inadequate for analyzing aeroelasticity behavior of very long thin sandwich cylindrical shells.

'Getting Better'-Is It a Feasible Strategy of Broad Pan-Antiherpesviral Drug Targeting by Using the Nuclear Egress-Directed Mechanism?

The herpesviral nuclear egress represents an essential step of viral replication efficiency in host cells, as it defines the nucleocytoplasmic release of viral capsids. Due to the size limitation of the nuclear pores, viral nuclear capsids are unable to traverse the nuclear envelope without a destabilization of this natural host-specific barrier. To this end, herpesviruses evolved the regulatory nuclear egress complex (NEC), composed of a heterodimer unit of two conserved viral NEC proteins (core NEC) and a large-size extension of this complex including various viral and cellular NEC-associated proteins (multicomponent NEC). Notably, the NEC harbors the pronounced ability to oligomerize (core NEC hexamers and lattices), to multimerize into higher-order complexes, and, ultimately, to closely interact with the migrating nuclear capsids. Moreover, most, if not all, of these NEC proteins comprise regulatory modifications by phosphorylation, so that the responsible kinases, and additional enzymatic activities, are part of the multicomponent NEC. This sophisticated basis of NEC-specific structural and functional interactions offers a variety of different modes of antiviral interference by pharmacological or nonconventional inhibitors. Since the multifaceted combination of NEC activities represents a highly conserved key regulatory stage of herpesviral replication, it may provide a unique opportunity towards a broad, pan-antiherpesviral mechanism of drug targeting. This review presents an update on chances, challenges, and current achievements in the development of NEC-directed antiherpesviral strategies.

The defect sensitivity of brittle truss-based metamaterials

Architected strut-based metamaterials fabricated via three-dimensional printing exhibit a wide range of geometric and material heterogeneity, including variations in strut size, surface roughness, embedded micro-cracks and disconnected struts. The locations and severity of these defects are highly variable; combined with the complexity of the structure itself, it is exceedingly difficult to identify critical defects that limit performance and inform qualification protocols. To address this challenge, we consider the impact of distributions of defects for various strut-based lattice topologies. The role of defects is analyzed using Weibull distributions of strut failure strains. We relate the statistical distributions of strut properties to macroscopic stress-strain performance, using high through-put finite element predictions in thousands of virtual tests. Increasing the prevalence of defects decreases macroscopic strength; however, this has the complementary effect of introducing apparent ductility, i.e. load capacity even after the onset of strut failures. Hence, there is a trade-off between achieving high strength and gradual loss of stiffness that is desirable for thermal loading or lattice cores. Predictions of average strength as a function of Weibull modulus provide knock-down factors relative to the defect-free strength. In turn, these clearly identify quantitative processing targets to mitigate the impact of defects.

Mechanical Performance Comparison of Sandwich Panels with Graded Lattice and Honeycomb Cores.

The design of graded and multifunctional lattice cores is driven by the increasing demand for high-performance components in lightweight engineering. This trend benefits from significant achievements in additive manufacturing, where the lattice core and the face sheets are fabricated simultaneously in a single print job. This work systematically compares the mechanical performance of sandwich panels comprising various graded lattice cores subjected to concentrated loads. In addition to graded lattice cores, uniform lattices and conventional honeycomb cores are analyzed. To obtain an optimized graded lattice core, a fully stressed design method is applied. Stresses and displacements are determined using a linear elastic analytical model that allows grading the core properties in a layerwise manner through the core thickness. The analysis indicates the superior performance of graded lattice cores compared to homogeneous lattice cores. However, conventional honeycombs outperform graded lattice cores in terms of load-to-weight ratio and stiffness-to-weight ratio. This study provides valuable insights for the design of lattice core sandwich panels and the advantages of several design approaches.

Functionally graded multi-morphology lattice structures as an optimized sandwich core via digital light processing additive manufacturing

This investigation aims to present a high-strength sandwich core with functionally graded multi-morphology lattice inner structures through vat photo-polymerization additive manufacturing (AM). The five better strut-based designs based on [1], are considered here. All printed specimens have been fabricated from photopolymer resin to ensure manufacturability in a digital light processing (DLP) 3D printer. Firstly, the resin and structural characteristics have been examined. Simultaneously, the lattice core is divided into three regions based on the von Mises stress distribution and tensile and compression responses in finite element analysis (FEA). Based on the mechanical responses of the beam-based structures, these topologies have been applied in each region in an optimal fixed relative density distribution, considering different steps and types. This proposed technique is numerically investigated and experimentally validated using a three-point bending test. As a result, the optimized core demonstrated a 96% increase in maximum fracture force and a 174% increase in stiffness compared to the homogeneous body. Additionally, it exhibited a different deformation mode than the single morphology under similar conditions. These significant findings indicate that this approach provides a new perspective on a high-strength design involving more than three morphologies, and it is faster than computational topology optimization processes.

Tunable Multifunctional Metamaterial Sandwich Panel with Quasi‐Zero Stiffness Lattice Cores: Load‐Bearing, Energy Absorption, and Vibration Isolation

AbstractThe interest in novel mechanical metamaterials that offer advanced functionalities and mechanical tunability for highly compatible multifunctional performance in state‐of‐the‐art engineering applications is growing. Here, a novel tunable multifunctional mechanical metamaterial, also known as a metamaterial sandwich panel, which can achieve load‐bearing, energy absorption, and low‐frequency vibration isolation properties simultaneously, is reported. The designed metamaterial sandwich panel is composed of a quasi‐zero stiffness (QZS) lattice core and two kirigami‐style surfaces, which endow the metamaterial sandwich panel with multi‐function performance and tunable properties. As a proof‐of‐concept, the mechanical properties and tunable multifunctional performance of the proposed metamaterial sandwich panel are demonstrated both in simulations and experiments. This work provides a new alternative for designing novel mechanical metamaterials with tunable multifunctional performance and may have potential applications in a variety of engineering applications, such as medical transportation, marine systems, and aerospace applications.