Mechanical Properties Of Lattice Structures Research Articles

Mechanical Properties of Lattice Structures with a Central Cube: Experiments and Simulations.

In this study, a new structure is proposed based on the body-centered cubic (BCC) lattice structure by adding a cubic truss in the center of the BCC structure and denoting it TLC (truss-lattice-cube). The different dimensions of the central cube can notably affect the mechanical properties of the lattice structure. With a fixed length (15 mm) of a unit cell, the optimal size for the central cube is determined to be 5 mm. Quasi-static compressive tests are performed on specimens made of polylactic acid (PLA) using additive manufacturing technology. The deformation characteristics of the new structure are analyzed in detail by experiments and numerical simulations. Compared to the BCC structure, the mechanical properties of the TLC structure were significantly improved. The initial flow stress of the TLC increased by 122% at a strain of 0.1; the specific strength enhanced by 293% at a strain of 0.5; and the specific energy absorption improved by 312% at a strain of 0.6. Printing defects in the lattice structure may remarkably damage its mechanical properties. In this work, incorporation of microcracks into the finite element model allows the simulation to capture the influence of printing defects and significantly improve the predictive accuracy of the simulation.

Experimental study on the influence of abrasive flow machining on the surface quality and mechanical properties of BCC lattice structure manufactured by L-PBF

During the L-PBF process for preparing porous biomaterials, the "spheroidization effect" and the "stair-step effect" lead to defects such as pore clogging and rod diameter thickening in the actual components. These defects affect the part's dimensional accuracy, which in turn has the critical influence on the mechanical properties of the workpiece. Thus, suitable post treatment methods are required to improve the surface quality of porous biomaterials. This paper aims to investigate the effects of abrasive flow machining on the surface quality and mechanical properties of body-centered cubic (BCC) lattice-structured specimens molded by L-PBF at different pressures and abrasive concentrations and their mechanisms. Experimental results indicate that the number of powders adhering to the rod diameter of the member is significantly reduced after the abrasive grain flow process treatment. The roughness of the rod diameter surface is reduced from 17.48 μm to 6.82 μm, and the surface finishing is improved by 60.98%. The abrasive flow machining can effectively eliminate the "spheroidization effect" on the mechanical properties of the lattice structure. The maximum compressive strength of specimens subjected to abrasive flow machining have all been increased. Especially, with the abrasive flow machining under the pressure of 4 MPa and the abrasive grain concentration of 60%, the maximum compressive strength of the specimens was even been increased by 8.89%.

Numerical investigation of the mechanical properties of lattice structures inspired from polycrystalline materials

In this work, polycrystalline-like lattice structures that are inspired by the geometry of polycrystalline materials are designed. They are generated by filling periodic lattice structures into a Voronoi diagram. Then, finite element analyses of two periodic and eight polycrystalline-like lattice structures are performed to compare their mechanical properties. The numerical results show that polycrystalline-like lattice structures consisting of anisotropic rectangular X-type periodic unit cells are isotropic at the macroscale. Moreover, they have a higher specific stiffness and specific strength than periodic lattice structures under compression. Then, the energy absorption capability is investigated. Five energy absorption indicators (energy absorption, energy absorption per unit volume, specific energy absorption per unit mass, crush stress efficiency, and plateau stress) reveal that polycrystalline-like lattice structures are better energy absorption structures. Furthermore, the defect sensitivity of missing struts is discussed. The findings of this work offer a new route for designing novel lattice structures.

Rate-dependent behaviour of additively manufactured topology optimised lattice structures

Lattice structures offer a wide range of tuneable qualities that cannot be achieved with bulk materials. While lattice structures offer a range of tuneable qualities, including isotropic properties achievable in bulk materials, the advent of additive manufacturing (AM) advances research in this domain. Although several studies have characterized the quasi-static mechanical properties of lattice structures, there is limited experimental data available on their rate-dependent behaviour. Additionally, most lattice structures are anisotropic, making them unsuitable for applications where loading directions are unknown. In this study, a topology-optimised unit cell with nearly perfect isotropic stiffness is investigated for its isotropic specific energy absorption under high strain rates. The dynamic response of the structure is evaluated using 3 different materials: CPTi, AlSi10Mg, and 316LSS, and both experimental and numerical methods are employed. The influence of topology and relative density on the mechanical properties of the structure are explored, and the specific energy absorption isotropy is determined by loading the lattices in various orientations numerically. This research fills the gap in knowledge regarding the rate-dependent behaviour of lattice structures and offers insight into the potential for isotropic lattice structures in engineering applications.

The coupled effect of aspect ratio and strut micro-deformation mode on the mechanical properties of lattice structures

Lattice structures have been integrated into various industrial applications owing to their unique compressive properties. Mechanical characterisation is usually done by testing a small specimen which is assumed representative of the utilised lattice. A specimen's aspect ratio (height to diameter/width ratio) is known to affect compressive properties in various engineering materials, yet its influence in lattices has not been investigated thoroughly. In this study, titanium lattice specimens designed with different aspect ratios (ranging from 0.5 to 3.0) and four different topologies (displaying bend and stretch-dominated micro-deformation modes) were fabricated using powder bed fusion and tested in quasi-static compression. Their compressive properties and failure modes were evaluated using acquired stress-strain curves and digital image correlation (DIC) analysis. Reducing the aspect ratio in the bend-dominated lattices increased the measured stiffness of the specimens by up to 40%. Conversely, increasing the aspect ratio of the stretch dominated lattices increased the measured stiffness of the specimens by up to 30%. For both topology types, decreasing the aspect ratio increased the measured strength of the specimens, but the effect was less than that observed for stiffness. Different responses were attributed to gradient strain accumulation and different failure patterns (densification versus shear banding) that were observed depending on the combination of aspect ratio and topology. These findings are particularly important for better predicting the mechanical behaviour of lattice-based components that have aspect ratios outside the range of conventional test specimens.

Enhanced Mechanical Properties of Lattice Structures Enabled by Tailoring Oblique Truss Orientation Angle

The significant effect of the strut angle on the mechanical properties of strut‐based lattice structures is systematically explored through experimental and numerical investigations. The highest values of elastic modulus and yield strength, surpassing those observed in cubic lattices with the same relative density, have been experimentally observed at the strut angle of 71.76°. A correlation among elastic modulus, yield strength, and strut angles in lattices, validated by experimental tests, has been identified through developing a theoretical modelling and conducting a detailed finite element analysis. Transition from a bending dominated deformation mechanism to one dominated by compression within the lattice structures has been realized, contingent upon the tailoring of the strut angle. The deformation mechanism of these lattices is significantly influenced by the interplay between ductile bending and brittle failure of the struts. The superior energy absorption and yield strength demonstrated by the optimized lattice design have been underscored through a comparative analysis with other previously reported lattices. These lightweight structures hold promise for applications in the development of mechanical metamaterials with on‐demand mechanical properties.

Novel optimal design-making model of additive manufactured lattice structures based on mechanical physical model

Biostructure-inspired design methods play an important role in improving the mechanical properties of lattice structures with the same volume fraction. However, the current biostructure-inspired design methods mostly stay in the imitation of physical form/structure, and the natural evolution mechanism of biological structure is not clear in the optimization strategy of lattice structure. Combined with the fact that the zero-value average curvature of the minimal surface follows the Principle of Least Action (PLA), a new mechanical design strategy is proposed in this paper. Firstly, the mechanical model of BCC is solved. Furthermore, the physical model descripting the mechanical properties of lattice structures is solved equivalently, which shows that the regulation of mechanical properties of lattice structures can be more intuitively understood as the extreme motion for the pellet under various influencing factors. Moreover, the new design strategy for the mechanical properties of lattice structures is solved based on PLA. Finally, serials of BCC lattice structures are gained through node radius optimization. Then, the curvature characteristics and mechanical properties of optimized BCC structure are explored by means of simulation and experiment. The results show that the proposed design strategy has obvious effect in improving mechanical properties and provides a theoretical basis and technical route for the development of multiphysics applications of lattice structures.

Controlling mechanical properties and energy absorption in AlSi10Mg lattice structures through solution and aging heat treatments

The use of Selective Laser Melting (SLM) has gained popularity due to its ability to produce complex-shaped parts, which includes lightweight lattice structures that are appealing to a variety of industries. AlSi10Mg alloy is a favored choice for SLM due to its excellent specific properties. The utilization of AlSi10Mg in lattice structures further reduces their mass while enhancing specific mechanical properties. However, the inherent brittle deformation behavior of as-built AlSi10Mg restricts the energy absorption potential of lattice structures. This study explores the control of mechanical properties and energy absorption in AlSi10Mg lattice structures and bulk tensile samples through solution and aging heat treatments, examining their impact on microstructural transformations. The results show that solution heat treatment decreases the mechanical properties of lattice structures and bulk tensile samples while improving their ductility and energy absorption. This change is attributed to the transformation of the alloy's fine cellular microstructure into coarser Si-precipitates. Subsequent aging treatments lead to increased mechanical properties in lattice structures solution heat treated at 500 and 550 °C, albeit with a slight reduction in energy absorption. Intriguingly, lattice structures heat treated at 460 °C exhibit unchanged mechanical properties and energy absorption, as confirmed by the t-test. Additionally, the absence of the Al5FeSi intermetallic phase suggests that aging did not occur following solution heat treatment at 460 °C. These findings offer valuable insights into manipulating the mechanical properties and energy absorption of AlSi10Mg lattice structures through controlled heat treatments. Such control can significantly enhance the performance and functionality of lattice structures in practical applications.

Compressive mechanical properties of lattice structures filled with silicone rubber

The lattice structure is a periodically repeating three-dimensional open-cell architecture, and the introduction of polymer materials into its gaps results in a lattice structure filled with silicone rubber that can simultaneously exhibit vibration reduction, energy absorption, and other functional characteristics. In this study, the compressive behavior of both the lattice structure and the lattice structure filled with silicone rubber were investigated through a combination of finite element analysis and experimental investigations. The results show that the finite element analysis results are consistent with the experimental ones, and the method can be used to analyze such structures. Lattice structures filled with silicone rubber have better load-bearing capacity compared to lattice structures, and the integration of silicone rubber increases the compressive strength of the lattice structure, reducing the occurrence of structural localization phenomena.

Effect of cell size and wall thickness on the compression performance of triply periodic minimal surface based AlSi10Mg lattice structures

Triply periodic minimal surface (TPMS) are mathematical surfaces with zero mean curvature and are spatially invariant. Recently, these surfaces are investigated for potential application in the manufacturing of cellular materials or lattice structures for a variety of purposes. However, designing such structures is a difficult task as the dedicated design platforms impose higher costs. Therefore, in this study, lattice structures have been designed using an in-house developed opensource tool for different cell sizes and cell wall thicknesses. The lattice structures have been additively manufactured through laser powder bed fusion (LPBF) and their design compliance and manufacturing defects have been investigated through optical micrography and SEM. The lattice structures have been subjected to quasistatic uniaxial compression test in as-manufactured and heat-treated conditions and the resulting compressive stress-strain curves have been analyzed in detail to draw a relationship between the two varying quantities and the mechanical properties of the lattice structure. The results show that there has been small but visible differences between the as-designed and as-manufactured lattice structures. The mechanical properties of lattice structures deteriorated with increasing cell size at constant wall thickness and improved with increasing cell wall thickness at constant unit cell size. The heat treatment procedures homogenized and increased plastic deformation while decreasing the strength and modulus values. Overall the study outlined a significant effect of cell geometry, size, and cell wall thickness on the mechanical properties of the TPMS lattice structures.

Synergetic control mechanism for enhancing energy-absorption of 3D-printed lattice structures

It is difficult for controlling the failure mechanisms to improve the mechanical properties of lattice structures in a specified way. To this end, inspired by biological tissue/alloy microstructure, a novel synergetic control mechanism with gradient- and Orowan-strengthening is proposed to enhance energy-absorption (EA) of lattice. Gradient, Orowan and Grad-Oro lattices with different Reinforcement Phase (RP) spacing are designed and manufactured by 3D-printing with little defect. By experiments, simulations and theoretical analysis, compressive behaviors and failure modes of designed lattices are studied to explore the effects of synergetic control mechanism on mechanical properties. Results show that a 31.0%∼35.1% higher SEA than Matrix lattice is identified for Grad-Oro lattices which also surpass Orowan or Gradient lattices. Then, the transitional failure mechanisms of lattices are revealed to explain the improvement. It is illustrated that Zigzag shear-path induced by the Gradient-Orowan synergism can dissipate more energy than any single mechanism (bypassing shear-path or progressive collapse). It is finally found that closer RP spacing brings about stronger interactions between RP boundaries to affect failure modes like the grain boundary strengthening. This novel concept and structural design method greatly contribute to controllable mechanical design of lattice.

Improving the Mechanical Properties of a Lattice Structure Composed of Struts with a Tri-Directional Elliptical Cylindrical Section via Selective Laser Melting.

In recent years, lattice structures produced via additive manufacturing have been increasingly investigated for their unique mechanical properties and the flexible and diverse approaches available to design them. The design of a strut with variable cross-sections in a lattice structure is required to improve the mechanical properties. In this study, a lattice structure design method based on a strut cross-section composed of a mixture of three ellipses named a tri-directional elliptical cylindrical section (TEC) is proposed. The lattice structures were fabricated via the selective laser melting of 316L alloy. The finite element analysis results show that the TEC strut possessed the high mechanical properties of lattice structures. Compression experiments confirmed that the novel lattice structure with the TEC strut exhibited increases in the elastic modulus, compressive yield strength, and energy absorption capacity of 24.99%, 21.66%, and 20.50%, respectively, compared with the conventional lattice structure at an equal level of porosity.

Mechanical Characterisation and Simulation of the Tensile Behaviour of Polymeric Additively Manufactured Lattice Structures

BackgroundThe mechanical properties of lattice structures have been primarily investigated using uniaxial compression loads. Particularly for polymers, tensile properties are rarely considered because of the difficulties of defining a suitable specimen design in which the fracture occurs within the gauge length.ObjectiveThis work proposes a novel formulation to obtain a specimen for the tensile test with a gradation of the lattice density at the interface with the bulk portion, which realises a uniform stress distribution. The aim is to combine a localisation of the fracture in the gauge length with a specimen geometry accomplishing the EN ISO 527 standard and analyse the correlation between the mechanical performance and the defects induced by the process on such thin structures.MethodsThe formulation is experimentally and numerically (FEM) tested by designed specimens with different cell topology, cell size, strut diameter, and number of cells in the sample thickness. Also, results from uniaxial compression tests are used to validate the tensile properties. The specimens are manufactured in different orientations in the building volume by laser powder bed fusion with Polyamide 12. The effects of the pores morphology, distribution, and inherent anisotropy are investigated using X-ray computed tomography analysis. This data is also used to tune a numerical model.ResultsThe numerical analysis showed a uniform stress distribution; experimentally, the fracture is localised inside the gauge length in respect of the ISO standard. Remarkably, among the different strut-based architectures, the elongation at break is, in the best case, 50% of the corresponding bulk material, while the tensile strengths are comparable. Vertical printed specimens exhibited a slight decrease in tensile strength, and the elongation at break was lower than 50% compared to the counterparts built along the horizontal orientation. Modifying the numerical model according to process-related dimensional deviations between the actual and the nominal structures significantly improved the numerical results. The remaining deviation highlighted the incorrectness of modelling the lattice material from the bulk properties.ConclusionDensity gradation is a reliable approach for describing the tensile behaviour of polymeric lattice structures. However, the lower amount of porosity and the different shape in the lattice led to a different material mechanical performance with respect to the corresponding bulk counterpart. Therefore, for polymeric lattice structures, the relationship between process-design-material appears crucial for correctly representing the structure behaviour.

Flexural Properties of Lattices Fabricated with Planar and Curved Layered Fused Filament Fabrication.

The use of curved layers in fused filament fabrication could lead to various advantages in surface finishing and mechanical properties. Here, the influence of three different structural and manufacturing parameters (volume fraction, raster arrangement, and the use of curved or planar layers) on the mechanical properties of lattice structures under three-point bending is studied. Two different raster arrangements were considered, i.e., those with rasters at planes parallel to the principal axes of the samples and those diagonally arranged, all at four different volume fractions. All different samples were additively manufactured using planar and curved layers. Samples were further dimensionally inspected to refine the computational models before their analysis via finite element simulations. The linear elastic region of the load-displacement curves was further analyzed numerically via finite element models. Predictions with finite element models resulted in good agreement with errors below 10%. Samples with diagonal rasters were 70% softer than those parallel to the principal axes.

Enhancing Mechanical Properties of 3D Printing Metallic Lattice Structure Inspired by Bambusa Emeiensis.

Metallic additive manufacturing process parameters, such as inclination angle and minimum radius, impose constraints on the printable lattice cell configurations in complex components. As a result, their mechanical properties are usually lower than their design values. Meanwhile, due to unavoidable process constraints (e.g., additional support structure), engineering structures filled with various lattice cells usually fail to be printed or cannot achieve the designed mechanical performances. Optimizing the cell configuration and printing process are effective ways to solve these problems, but this is becoming more and more difficult and costly with the increasing demand for properties. Therefore, it is very important to redesign the existing printable lattice structures to improve their mechanical properties. In this paper, inspired by the macro- and meso-structures of bamboo, a bionic lattice structure was partitioned, and the cell rod had a radius gradient, similar to the macro-scale bamboo joint and meso-scale bamboo tube, respectively. Experimental and simulated results showed that this design can significantly enhance the mechanical properties without adding mass and changing the printable cell configuration. Finally, the compression and shear properties of the Bambusa-lattice structure were analyzed. Compared with the original scheme, the bamboo lattice structure design can improve the strength by 1.51 times (β=1.5). This proposed strategy offers an effective pathway to manipulate the mechanical properties of lattice structures simultaneously, which is useful for practical applications.

Experimental investigation of mechanical properties and energy absorption capabilities of hybrid lattice structures manufactured using fused filament fabrication

Hybrid lattice structures are composed of several dissimilar unit cells arranged in specific patterns. Unlike their one-phase counterparts, hybrid lattices remain relatively unexplored. In this work, novel hybrid lattice structures composed of Pillar Octahedral (PO) and Rhombic Dodecahedron (RD) lattices having variable strut diameters are arranged in different orders to form hybrid vertical piles (HVP), 2D and 3D chessboard order (HCh2D and HCh3D), are proposed, and their mechanical properties, energy absorption characteristics, and deformation modes are investigated under quasistatic compression. The empirical results indicated that the mechanical properties of hybrid lattice structures are the average of those of their parent lattices. HVP lattice structure has a high yield stress of 1.2, 2.22, and 3.54 MPa when strut diameter is 1.5, 1.75, and 2 mm respectively, and stable post-buckling region. It was also observed that hybrid lattice structures are more efficient in absorbing the energy of the deformation. When strut diameter is 1.5 mm, PO lattice structure has an efficiency of 50%, while HVP, HCh2D, and HCh3D lattices have an efficiency of about 70–80%. Finally, Gibson-Ashby models were proposed to predict the mechanical properties of lattice structures as the function of relative density.

Mechanical Properties of AISI 316L Lattice Structures via Laser Powder Bed Fusion as a Function of Unit Cell Features.

The growth of additive manufacturing processes has enabled the production of complex and smart structures. These fabrication techniques have led research efforts to focus on the application of cellular materials, which are known for their thermal and mechanical benefits. Herein, we studied the mechanical behavior of stainless-steel (AISI 316L) lattice structures both experimentally and computationally. The lattice architectures were body-centered cubic, hexagonal vertex centroid, and tetrahedron in two cell sizes and at two different rotation angles. A preliminary computational study assessed the deformation behavior of porous cylindrical samples under compression. After the simulation results, selected samples were manufactured via laser powder bed fusion. The results showed the effects of the pore architecture, unit cell size, and orientation on the reduction in the mechanical properties. The relative densities between 23% and 69% showed a decrease in the bulk material stiffness up to 93%. Furthermore, the different rotation angles resulted in a similar porosity level but different stiffnesses. The simulation analysis and experimental results indicate that the variation in the strut position with respect to the force affected the deformation mechanism. The tetrahedron unit cell showed the smallest variation in the elastic modulus and off-axis displacements due to the cell orientation. This study collected computational and experimental data for tuning the mechanical properties of lattice structures by changing the geometry, size, and orientation of the unit cell.

Additively Manufactured Lattice Materials with a Double Level of Gradation: A Comparison of Their Compressive Properties when Fabricated with Material Extrusion and Vat Photopolymerization Processes.

Natural porous materials adjust their resulting mechanical properties by the optimal use of matter and space. When these are produced synthetically, they are known as mechanical metamaterials. This paper adds degrees of tailoring of mechanical properties by producing double levels of gradation in lattice structures via cross-section variation in struts in uniformly periodic lattice structures (UPLS) and layered lattice structures (LLS). These were then additively manufactured via material extrusion (ME) and vat photopolymerization (VP). Their effective mechanical properties under compressive loads were characterized, and their stiffness contrasted with finite element models (FEM). According to the simulation and experimental results, a better correlation was obtained in the structures manufactured via VP than by ME, denoting that printing defects affect the correlation results. The brittle natural behavior of the resin caused a lack of a plateau region in the stress-strain curves for the UPLS structures, as opposed to those fabricated with ME. The LLS increased energy absorption up to 244% and increased the plateau stress up to 100% compared to the UPLS. The results presented in this paper demonstrate that the mechanical properties of lattice structures with the same base topology could be modified by incorporating variations in the strut diameter and then arranging these differently.

Optimizing the specific mechanical properties of lattice structures fabricated by material extrusion additive manufacturing

Lattice-structured materials are becoming increasingly adopted for impact absorption and load-carrying applications. This study presents the design of experiments approach for examining the mechanical performance of the Schwarz Primitive (SP) lattice structure and the body-centered cubic (BCC) plate lattice in order to optimize their design for material extrusion additive manufacturing. The present study investigates the effect of varying the design parameters (unit cell length, shell thickness, relative density) of these structures on tailoring their specific mechanical properties. This study explores the answers to two major research questions: Does varying the unit cell length of lattice structures affect their specific energy absorption (SEA)? Does varying the relative density of lattice structures affect their specific compressive modulus? The Analysis of Variance indicated that the relative density of the lattice structures is the statistically significant design factor when considering the improvement of SEA. Furthermore, the unit cell length of the lattice structures is the statistically significant design factor when considering the improvement of the specific compressive modulus. It was found that the BCC plate lattices outperformed the SP lattice structures of the same relative density in terms of SEA and specific compressive modulus. The Finite Element Analysis software Abaqus was utilized to regenerate results of the quasi-static compression experiments. Once the numerical model was validated, it was then used to predict the mechanical properties of unprintable and untested body-centered cubic plate lattices.

Compression and Deformation Behaviors of Hierarchical Circular-Cell Lattice Structure with Enhanced Mechanical Properties and Energy Absorption Capacity

The design of lightweight lattice structures with excellent specific mechanical properties has received great attention in recent years. In this paper, inspired by the hierarchical structure of biological materials, a novel hierarchical circular-cell configuration of a lattice structure was proposed. The advantage of the new lattice configuration is that the use of a smooth circular cell is able to alleviate the stress concentration induced by the intersection of straight struts. Additionally, the consideration of structural hierarchy can bring improved mechanical properties of lattice structures. The hierarchical circular lattice structures with 5 × 5 × 5 unit cells were fabricated through a digital light processing (DLP) 3D printer, using the hard-tough resin. The mechanical properties of the lattice structures were investigated by a compression experiment and a numerical simulation. Results show that the interaction effect of structural hierarchy was the potential mechanism for the enhancement of mechanical properties. The designed hierarchical circular-cell lattice structure exhibits improved stress distribution uniformity, enhanced mechanical performance, and energy absorption capacity. The maximum improvement values are ~342.4% for specific stiffness, ~13% for specific strength, ~126.6% for specific energy absorption (SEA), and ~18% for crash load efficiency (CLE). The developed hierarchical circular-cell lattice configuration will enrich the present lattice systems and be useful for future multifunctional applications.