Lattice Core Research Articles

Mechanical characterization of a 3D printed lattice core sandwich structure

AbstractSandwich structures have garnered interest as versatile structures for applications in advanced engineering structures. To fabricate sandwich structures, plastics have replaced conventional materials; however, most of these plastics remain in the environment beyond their functional lifespan. This study describes the fabrication of sustainable hybrid sandwich structures with 3D printed poly‐lactic acid (PLA) cores and self‐reinforced polyethylene terephthalate (srPET) face sheets. The mechanical responses of the hybrid sandwich structures with three types of lattice cores, S‐90, S‐45, and S‐V, were compared with those of the parent material sandwich structures after performing bending and impact tests. The face sheet in the hybrid sandwich structure transferred the load to the core without failure. The hybrid sandwich structure containing the S‐90 core exhibited a higher fracture strength (52.4 MPa) and tangent modulus of elasticity (2860 MPa) than those of the other structures. S‐V exhibited the highest fracture strains of 3.3% and 5% for parent material and hybrid sandwich structures, respectively. This study highlights the sandwich structures with excellent mechanical properties for structural applications.Highlights Novel sandwich structures with 3D printed PLA cores are fabricated. Three‐point bending and low‐velocity impact tests are performed. Failure occurred in the core, but the Sr‐PET face sheets did not deform. Hybrid sandwich structures significantly improve mechanical performance.

Vibration behavior of sandwich circular cylindrical shells with auxetic lattice core and CNT-reinforced facesheets

Vibration behavior of sandwich circular cylindrical shells with auxetic lattice core and CNT-reinforced facesheets

Multiple damage detection in sandwich composite structures with lattice core using regression-based machine learning techniques

The abstract discusses the importance of Structural Health Monitoring (SHM) in ensuring the reliability and health of structures. It introduces a novel approach for recognizing cracks and delamination in sandwich composite structures using advanced methods for data analysis and machine learning algorithms. The research leverages artificial intelligence and machine learning to accurately identify and locate damage such as delamination and cracks in composite sandwich layers, which can significantly enhance troubleshooting performance, improve detection accuracy, and reduce the time and cost associated with repairs. The article presents a damage detection technique utilizing regression analysis for sandwich composite structures with a lattice core, capable of identifying and locating multiple cracks and delamination, as well as simultaneous defects in the structure. The analysis is conducted based on the sandwich composite structure’s healthy and damaged conditions in Abaqus software, and acceleration responses under random forces obtained through the finite element method were used to train various machine learning models, including regression algorithms like k-Nearest Neighborhood Regression (KNN), Light Gradient Boost Machine (LGBM), and Decision Tree Regression (DTR) to detect the damage location. The results indicate that the regression (LGBM), k-Nearest neighborhood, and decision tree regression (DTR) were the most successful functions, respectively, and the damage classification models accurately identified the damage and its location in the composite structure, achieving an accuracy rate of approximately 98.8%.

Nonlinear vibration analysis of sandwich plates with inverse-designed 3D auxetic core by deep generative model

Building on a deep generative model (DGM), this paper introduces an innovative sandwich plate structure featuring an inverse-designed auxetic 3D lattice core and conducts a detailed investigation of its nonlinear vibration characteristics and effective Poisson's ratios under various parameter settings. By incorporating a conditional estimator and quality loss evaluation functions, the enhanced conditional generative adversarial networks are capable of designing 3D truss auxetic topologies that achieve customized negative Poisson's ratios without reliance on subjective experience. Additionally, lattice specimens are created using 3D metal printing, and the mechanical properties of these DGM-based 3D auxetic structures are validated through vibration experiments and finite element models. These structures exhibit significantly superior natural frequencies compared to those obtained through conventional topology optimization methods reported in existing literature. The study also explores the impact of different functionally graded configurations, temperature variations, boundary conditions, and dimensional parameters on the natural frequency, nonlinear vibration response, and effective Poisson's ratio of the inverse designed auxetic sandwich plates.

Low-velocity impact response and damage mechanism of cosine function cell-based lattice core sandwich panels

This study aims to investigate the impact response and damage mechanism of cosine-function cell-based (CFCB) lattice core sandwich panels. Several low-velocity impact tests were conducted to explore their advantages in impact resistance by comparing them with traditional body-centered cubic (BCC) lattice-core sandwich panels. The impact response and deformation patterns of CFCB lattice core sandwich panels with two different faceplate materials (aluminum alloy and carbon fiber reinforced plastic composite) were experimentally investigated. The CFCB lattice core sandwich panels exhibited higher impact resistance and energy absorption capacity than their BCC lattice core counterparts. Furthermore, sandwich panels with aluminum alloy faceplates provided better impact resistance capacity than those with CFRP faceplates. Subsequently, several numerical models were developed to explore the deformation mechanisms and energy absorption characteristics of CFCB lattice core sandwich panels. In addition, the effects of the core structural parameters on mechanical performance were numerically investigated. Results indicated that increasing the cell rod diameter and/or reducing the cosine period length could decrease the indentation depth and enhance crush force efficiency. Finally, based on the principle of minimum potential energy, a theoretical model was developed to predict the initial peak load of CFCB lattice core sandwich panels with isotropic faceplates. This study aimed to explore the impact response and provide design guidance for CFCB lattice core sandwich panels.

Effects of the manufacturing process on the flexural properties of EBMed lattice structures

AbstractLattice structures are very interesting since they present good mechanical properties coupled with lightness. Today, the maturity reached by additive manufacturing technologies allows the production of such structures. However, the mechanical properties of the constituting material can be affected by the process itself, because of the particular geometry. In fact, in a previous work, the mechanical characteristics of the bulk‐printed material were used for modelling the bending behavior of lattice‐cored specimens made of Ti6Al4V and produced through electron beam melting (EBM) process, but a certain discrepancy with experimental results was found. Therefore, in this work, a procedure was proposed to determine the mechanical properties of the material the lattice specimen is made of, in order to reduce the gap between the numerical and the experimental results. By considering the redetermined yield strength, such mismatch was reduced. Moreover, the metallographic analysis of the material found that the α laths of the α + β microstructure, typical of the studied alloy, were thinner than those of bulk specimens, and the presence of α′ martensite was discovered too. The fracture surface analysis determined a ductile failure mode for the lattice core while a fragile mode for the skins.

Global buckling response of sandwich panels with additively manufactured lattice cores

This paper deals with the analytical and numerical global buckling analysis of rectangular sandwich plates utilized AlSi10 Mg in both facesheets and lattice cores. In this study, six different strut-based lattice core models are designed. Additionally, the buckling resistance of lattice panels is compared with a typical honeycomb panel. Analytical studies were carried out using Kirchoff plate theory (CLPT), first-order shear deformation theory (FSDT) coded on MATLAB and finite element (FE) analyses in Abaqus. In the theoretical approaches, the Navier solution is derived for sandwich plates with simply supported boundary conditions at all edges. In the FE analyses, validated homogenized lattice structures models were used to avoid excessive numbers of elements and to save computational time. The parametric effects of side-to-thickness ratio, and different designed core cells on global buckling responses are investigated. As a result of comparing the analytical results with the FE model, a good agreement is obtained, and it is found that analytical buckling analyses FSDT can be used within certain size limits for the global buckling analysis of lattice core sandwich structures.

Proposing novel body-centered cubic lattice core sandwich panels as satellite structure

In the present paper, a comparative study on the load-bearing as well as shielding performance against hypervelocity impact of space debris of sandwich panels with body-centered cubic lattice core is performed numerically in order to evaluate their eligibility to be utilized as the satellite structure. To this end, four types of body-centered cubic lattice structures, with similar areal densities which are assumed to be made of 5A06 aluminum alloy, including BCC, BCCz (BCC reinforced in Z direction), and also BCCz-I and BCCz-II were considered. Whipple shield structure of same material and areal density was also investigated in order to justify the necessity of lattice structures application, especially in protection field. The present study simulates hypervelocity impact of a spherical projectile with 2 mm diameter, represented the space debris, collides with the structures at the velocity range of 2–6 km/s. Current numerical simulation process accuracy and efficiency were verified through comparing its obtained data based on simulating a problem had been investigated at a valid experimental study to the data proposed by the mentioned research. BCCz-II structure which is newly proposed at this study provided outstanding shielding and load-bearing capabilities in comparison to other structures. Furthermore, the detailed effects of projectile impact location and a middle structure placed plate on the protection performance were investigated and the mentioned items were found to have crucial impact on the structure shielding performance.

A machine learning approach for predicting flexural strength of 3D printed hexagon lattice-cored sandwich structures

The development of sandwich structures using Fused Filament Fabrication (FFF) technology is an effective method for the rapid construction of complex profiles and is widely recognized for various structural applications. In this study, hexagon lattice-cored sandwich structures are developed by placing the lattice core in the center portion of the PLA polymeric specimen. The performance is analyzed with respect to varying levels of 3D-Printing Factors (3D-PFs) such as Nozzle Temperature (NT), Line Width (LW), Printing Speed (PS), and Layer Height (LH). The levels of the respective 3D-PFs are varied as follows: NT (180, 190, 200, and 210 °C), LH (0.15, 0.2, 0.25, and 0.3 mm), PS (15, 20, 25, and 30 mm/s), and LW (0.1, 0.2, 0.3, and 0.4 mm). The sandwich flexural samples are 3D printed using an FFF 3D printer, and their flexural properties are examined using a Universal Testing Machine (UTM). In the present work, various Machine Learning (ML) algorithms, such as Least Angle Regression (LARS), Support Vector Machine (SVM), Decision Tree (DT), and Ridge Regression (Ridge), are employed to predict the Flexural Strength (FS) of the 3D-printed sandwich structures and help in determining the optimized levels of 3D-PFs for achieving higher FS. The findings indicate that the LARS algorithm, particularly when applied within the Bagging Ensemble Learning Technique (ELT), exhibits the highest precision, showcasing a Mean Absolute Error (MAE) of 0.163, Root Mean Square Error (RMSE) of 0.153, and Median Absolute Error (MedAE) of 0.129. With the help of the LARS algorithm under Bagging ELT, the impact of 3D-PFs on the resulting FS is analyzed, which helps in determining the optimized levels of 3D-PFs concerning FS. The sandwich structures fabricated at the optimized levels show improved flexural properties, making them suitable for various structural applications.

Homogenization-based topology optimization for self-supporting additive-manufactured lattice-infilled structure

Lattice-infilled structures possess prominent properties at relatively low mass, which are of great significance in academic investigations and engineering fields such as aerospace science and biomedical applications. However, both the macro geometry and relative density distribution of the infilled microstructure exert considerable influence on performances of lattice-infilled structure and the structural manufacturability needs to be considered. In this work, an optimization design methodology for self-supporting additive-manufactured lattice-infilled structures is proposed, in which the macro geometry and relative density distribution of the microstructure are concurrently optimized. Microstructure is infilled after topology optimization and octree structure is introduced into the boundary layers of the lattice core to support the top shell during fabrication. The effectiveness of the proposed optimization design method for self-supporting additive-manufactured lattice-infilled structures was proved by both three-point-bending test and full-scale finite element simulation. Compared with the uniformly-infilled sample, mass-specific stiffness and strength of the topologyoptimized sample were improved by 41.2% and 112.1%, respectively. The proposed design method for lattice-infilled structures provides potential for designing additive-manufactured high-performance lightweight structures, which will broaden the boundaries of lattice structure in engineering applications.

Forced convection heat transfer in AlSi7Mg lattice structures fabricated by additive manufacturing

The thermal-hydraulic performance of lattice structures with different topologies and relative densities was investigated. AlSi7Mg sandwich panels cored with vertical fin, pyramidal, and tetrahedral lattices were fabricated using additive manufacturing. Four different relative densities (7.5 %, 10 %, 12.5 %, and 15 %) were considered for each lattice core. The experiment was conducted under constant heat flux and steady-state forced convection. Results showed that increasing relative density led to an increase in the average Nusselt number by 3.2–12.5 % in the vertical fin, 23.8–56.4 % in the pyramidal lattice, and 38.8–46.9 % in the tetrahedral lattice. To evaluate the efficiency of different topologies, the average Nusselt number was compared at a fixed pumping power. The pyramidal lattice exhibited the best performance among the test samples, followed by the tetrahedral lattice. The numerical analysis was performed to gain further insights into the heat transfer mechanisms involved. As the relative density increased, an increase in both the maximum fluid velocity and turbulent kinetic energy was observed in all test samples. The numerical results demonstrate that the observed improvement in thermal-hydraulic performance with increasing relative densities in experiments is attributable to the enhanced momentum of the fluid and turbulent mixing.

Optimized Sandwich and Topological Structures for Enhanced Haptic Transparency.

Humans rely on multimodal perception to form representations of the world. This implies that environmental stimuli must remain consistent and predictable throughout their journey to our sensory organs. When it comes to vision, electromagnetic waves are minimally affected when passing through air or glass treated for chromatic aberrations. Similar conclusions can be drawn for hearing and acoustic waves. However, tools that propagate elastic waves to our cutaneous afferents tend to color tactual perception due to parasitic mechanical attributes such as resonances and inertia. These issues are often overlooked, despite their critical importance for haptic devices that aim to faithfully render or record tactile interactions. Here, we investigate how to optimize this mechanical transmission with sandwich structures made from rigid, lightweight carbon fiber sheets arranged around a 3D-printed lattice core. Through a comprehensive parametric evaluation, we demonstrate how this design paradigm provides superior haptic transparency, regardless of the lattice types. Drawing an analogy with topology optimization, our solution approaches a foreseeable technological limit. It offers a practical way to create high-fidelity haptic interfaces, opening new avenues for research on tool-mediated interactions.

Analysis of vibration characteristics of lattice-core sandwich annular spherical shells

This paper investigates the vibrational characteristics of lattice-core sandwich annular spherical shells. An effective analytical model, based on the Smeared Stiffener technique, is employed to integrate the stiffness contributions of the core with those of the shells. Helical stiffeners are modeled as beams capable of bearing axial forces and bending moments. The governing equations are derived from Donnell's classical thin shell theory. The Galerkin method is applied to extract the natural frequencies. To validate the analytical results and conduct a comprehensive parametric study, a 3D finite element model is developed using ABAQUS CAE software. Comparisons demonstrate a satisfactory agreement between the analytical and numerical results. Additionally, the effects of the spherical shell's geometric parameters, lamination angle, stiffener orientation angle, and various lattice core configurations are examined.

Rapid stress prediction of additively manufactured sandwich panels with lattice cores in thermal environments

Lattice-core sandwich panels (LCSPs) with fabricated by additive manufacturing have attracted extensive interest stemming from their exceptional mechanical properties and multi-functionalities. Nevertheless, the direct correlation among stress distributions in sandwiches, external loads, and ambient environments remains unclear. This study develops an analytical predictive model capable of efficiently capturing the mechanical response of LCSPs under various temperatures. The equivalent elastic modulus of lattice cores with different unit-cell aspect ratios is first determined according to finite element (FE) results. Subsequently, the thermo-mechanical field of the homogenized sandwich in various ambient temperatures is analytically predicted based on the higher-order shear deformation theory. Finally, truss stresses within lattice cores are directly calculated using an effective displacement transition method. The prediction exhibits outstanding consistency with FE simulations. Furthermore, the impact of several key variables on the truss stress distribution is demonstrated based on parametric analysis. The results reveal that the vertical truss is the main object of bearing the major uniaxial compressive load within the body-centered cubic (BCCZ) and vertically reinforced face-centered cubic (F2CCZ) lattice cores. The increased transverse layer number/power index and/or the smaller length-to-thickness ratio contribute to a significant reduction in inclined/vertical truss stresses. In contrast, the elevated longitudinal layer number, ambient temperature, and thermal expansion of face sheets result in stress accumulation. Furthermore, the stress distributions in BCCZ LCSPs are commonly higher than those within F2CCZ LCSPs. These results can provide a useful path for the design and fabrication of additively manufactured sandwich panels with desired mechanical properties.

Effect of Degradation of Polylactic Acid (PLA) on Dynamic Mechanical Response of 3D Printed Lattice Structures.

Material-extrusion-based 3D printing with polylactic acid (PLA) has transformed the production of lightweight lattice structures with a high strength-to-weight ratio for various industries. While PLA offers advantages such as eco-friendliness, affordability, and printability, its mechanical properties degrade due to environmental factors. This study investigated the impact resistance of PLA lattice structures subjected to material degradation under room temperature, humidity, and natural light exposure. Four lattice core types (auxetic, negative-to-positive (NTP) gradient in terms of Poisson's ratio, positive-to-negative (PTN) gradient in terms of Poisson's ratio, and honeycomb) were analyzed for variations in mechanical properties due to declines in yield stress and failure strain. Mechanical testing and numerical simulations at various yield stress and failure strain levels evaluated the degradation effect, using undegraded material as a reference. The results showed that structures with a negative Poisson's ratio exhibited superior resistance to local crushing despite material weakening. Reducing the material's brittleness (failure strain) had a greater impact on impact response compared to reducing its yield stress. This study also revealed the potential of gradient cores, which exhibited a balance between strength (maintaining similar peak force to auxetic cores around 800 N) and energy absorption (up to 40% higher than auxetic cores) under moderate degradation (yield strength and failure strain at 60% and 80% of reference values). These findings suggest that gradient structures with varying Poisson's ratios employing auxetic designs are valuable choices for AM parts requiring both strength and resilience in variable environmental conditions.

Evaluating load-bearing and hypervelocity impact shielding capabilities of face-centered cubic lattice core sandwich panels

In the present paper, a comparative study on load-bearing as well as hypervelocity impact shielding performance of sandwich panels with face-centered cubic (FCC) lattice core is numerically performed in order to evaluate their competency in satellite structure applications. To this end, 5A06 aluminum alloy FCC and FCCz beside cube and octahedron lattice structures with similar areal densities were investigated. Whipple shield structure of same material and areal density was also studied in order to be compared to lattice structure in protection field. The present study simulates hypervelocity impact of a spherical projectile with 2 mm diameter, represents the space debris, collides with the structures at the velocity range of 2–6 km/s. Numerical simulation model was validated by performed experimental study. Authors were inspired by cube and FCCz topologies to propose a novel lattice structure could provide outstanding shielding and load-bearing capabilities in comparison to the other structures studied in this research. Furthermore, the detailed effects of projectile impact location on the protection performance were investigated and the mentioned item was found to have considerable influence on the structure shielding performance.

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.

Analytical and numerical analysis of composite sandwich structures with additively manufactured lattice cores

In this study, an analytical and numerical analysis of a hybrid sandwich structure with a lattice core produced by additive manufacturing with composite facesheets is carried out. This paper aims to analytically calculate the mechanical behavior of the hybrid sandwich structure under three-point bending and to verify the results by the finite element method. The analytical method used in this article for the analysis of the composite sandwich structure is the First-Order Shear Deformation Theory (FSDT). The numerical analysis of the hybrid sandwich structure was performed in ANSYS. In the analyses, homogenized models of lattice structures, which had been previously validated, were employed to reduce the number of elements and thereby save time during the solution process. As a result of the study, an extensive investigation into the deformation, shear, and normal stress values of sandwich structures with lattice cores of varying aspect ratios has been carried out. The findings suggest a potential for optimization in lightweight structures, which could lead to innovative advancements in design and manufacturing processes within the aerospace and automotive sectors.

Analytical and numerical analysis on local and global buckling of sandwich panels with strut-based lattice cores

Additive manufacturing (AM) offers new possibilities to fabricate and design lightweight lattice materials. Due to the superior mechanical properties of these lattice structures, they have the potential to replace honeycombs as cores in sandwich panels. In addition to the advantage of the integral fabrication thanks to AM, additively manufactured lattice core sandwich panels may be also used as heat exchangers, enabling a multifunctional use of the core. To ensure a reliable and safe structure, the mechanical response of lattice core sandwich panels under given load conditions must be predictable. In conventional sandwich panels subjected to compressive loads, the sandwich’s global buckling and the face sheets’ local buckling are the dominant failure modes. In constrast, core strut buckling may be the critical failure mode in lattice core sandwich panels. Therefore, an analytical 2D model to predict the local buckling of lattice core struts is considered in this study. Furthermore, the critical load for global buckling is obtained based on the first-order shear deformation theory. Thus, the transition from local buckling to global buckling depending on the length-to-thickness ratio is captured by the presented model. The comparison with finite element modeling of the sandwich model with truss cores has proved the accuracy of the derived model.

Vibration analysis of anisogrid composite lattice sandwich truncated conical shells: Theoretical and experimental approaches

Drawing upon both theoretical and experimental methodologies, this study investigates the vibrational characteristics of lattice sandwich truncated conical shells featuring composite ribs made of carbon and E-glass fibers. Toward this aim, the equations of motion along with the corresponding boundary conditions of such sandwich shells are derived using classical Donnell’s shell theory and the smeared stiffness technique. Subsequently, the governing equations are solved to obtain a closed-form expression for natural frequencies employing the Galerkin method. In addition, ABAQUS simulations are presented to study the vibration behavior of single-skin and three-skin conical shells. To validate the theoretical methods, the specimens of three-layer sandwich conical shells were fabricated from two Kevlar fabric laminates and a composite lattice core with hexagonal cells using a manual filament winding process. The composite ribs consist of carbon and E-glass fibers with a ratio of 3:1. Finally, experimental modal tests were conducted to extract natural frequencies and mode shapes by measuring frequency responses at 40 points over a duration of 60 s using a laser vibrometer. A strong correspondence is observed between the theoretical outcomes (utilizing the Galerkin and FE methods) and the experimental findings (with a maximum discrepancy of approximately 16% for the initial four mode shapes). Findings indicate that the excellent performance of the composite lattice core in vibration behavior, which can increase approximately 19% and 16% the natural frequencies corresponding to the first and second mode shapes, respectively.