Ti6Al4V Lattice Structures Research Articles

Mechanical Properties and Deformation Behaviors of Node‐Reinforced Ti–6Al–4V Lattice Structures Manufactured by Laser Powder Bed Fusion

Mechanical Properties and Deformation Behaviors of Node‐Reinforced Ti–6Al–4V Lattice Structures Manufactured by Laser Powder Bed Fusion

Effect of geometric defects on the mechanical properties of additive manufactured Ti6Al4V lattice structures

Lattice structures realized by additive manufacturing (AM) have the great potential for a broad range of engineering applications. However, the lattice structures are involved in geometric defects. This paper focuses the effect of geometric defects on the mechanical properties of Ti6Al4V lattice structures manufactured by laser powder bed fusion (L-PBF), three cell topologies, i.e., body centered cubic with vertical struts (BCCZ), face centered cubic with vertical struts (FCCZ), and face and body centered cubic with vertical struts (FBCCZ) were studied. X-ray computed tomography was used to extract the shape and the distribution of process-induced geometric defects of these three kinds of samples. Probability density distributions of geometric defects in each layer were also established to analyze the effect of the printing sequence on geometric defects. Then these distributions of geometric defects were inputted into Abaqus to build the modified statistical models to study the effect of geometric defects on mechanical properties. It is shown that the deviation of the cross-section radius exhibits normal distribution and the deviation of the center axis offset exhibits logarithmic distribution. And the middle layer of the sample has a better manufacturing precision. The modified statistical model can predict the mechanical properties within an error of 5 %. The strut thickness deviation had a more significant effect on the mechanical properties than the strut waviness.

Effect of unit cell rotation on mechanical performance of selective laser melted Gyroid structures for bone tissue engineering

Gyroid lattice structures, inspired by the natural interconnectivity of human bone, show promise in bone tissue engineering (BTE). This study explores the mechanical properties, and failure mechanisms of selective laser melted (SLM) Gyroid Ti6Al4V lattice structures with varying unit cell rotation angles (RA) of 0∘ (G0), 30∘ (G30), and 60∘ (G60) around the x-axis. The study assesses their mechanical and energy absorption properties through quasi-static compression testing and elastoplastic finite element (FE) analysis. Despite similar relative densities for all designed lattices, the RA variation significantly impacts mechanical performance. G30 exhibits superior load-bearing capacity, with higher modulus of elasticity, yield strength, ultimate strength, and plateau stress. It also has the highest energy absorption capacity, while G60 shows the highest surface area (SA) and surface area-to-volume ratio (SA/VR). These findings highlight the potential of Gyroid lattices for bone replacements due to their tunable mechanical and biological responses.

Superior Lightness-Strength and biocompatibility of bio-inspired heterogeneous glass sponge Ti6Al4V lattice structure fabricated via laser powder bed fusion

Ti6Al4V lattice structures (LSs) have great potentials in medical implants due to their excellent biocompatibility and high strength-to-weight ratio. This paper investigates the manufacturability and performance of unique Ti6Al4V heterogeneous glass sponge (GS) LSs fabricated via laser powder bed fusion (LPBF). Compared with the commonly used LSs, including Cross, body-centered cubic (BCC), Diamond and octet-truss (OCT), Ti6Al4V GS LSs exhibit the strongest compressive strength and energy absorption ability of 58 MPa and 23.84 J/cm3, respectively. Finite element (FE) models are established to evaluate the macroscopic deformation, microscopic stress and strain evolution in the solid struts of five different LSs. Local plastic stresses are found to generate near the nodes of Cross, BCC, Diamond and OCT LSs, thus forming plastic hinges, while the GS LSs can evenly transfer local plastic stresses to the grid-like rods of each layer, eventually showing a uniform stress distribution. Moreover, all the LSs are featured with satisfactory biocompatibility concerning cytotoxicity, cell proliferation, and cell attachment. The results indicate that the Ti6Al4V GS LSs can address the conflict between lightness and strength simultaneously, thus achieving excellent energy absorption performance, compressive properties and great biocompatibility, endowing it with tremendous application potential in the field of medical implants.

Mechanical and microstructural characterization of Ti6Al4V lattice structures with and without solid shell manufactured via electron beam powder bed fusion

The topological optimization of components by means of lattice structures allows to reduce their weight avoiding a loss in the mechanical performance. Often the lattice parts are integrated in a more complex geometry, and they present an interface with a solid part.In the present paper, the mechanical and microstructural characterization of Ti6Al4V lattice structures with body-centered cubic unit cell was carried out. Samples with and without an external solid shell were designed and produced with electron beam powder bed fusion in order to investigate the behavior of these complex structures, especially at the interface between the solid and lattice parts. The microstructure and defects were analyzed, and compression tests were performed on the samples with and without solid shell to understand the influence of the solid part and its interaction with the lattice structure. After the fracture and detachment of the shell, the same behavior for both set of samples was observed.Finally, a finite element model was defined to better understand the mechanical behavior of the investigated structures. The nominal sample stiffness was significantly higher than the experimental one. This discrepancy can be attributed to local defects, both in terms of porosities and deviations from ideal geometry.

Graded cellular structures for enhanced performance of additively manufactured orthopaedic implants

AbstractHip implants face a significant challenge due to their limited lifespan, a concern amplified by the rising human life expectancy. Lattice structures have demonstrated the ability to provide precise control over geometry, thereby significantly enhancing implant performance. This paper introduces the development of graded additively manufactured Ti6Al4V lattice structures for orthopaedic implants. The objective focuses on developing a graded lattice unit cell design mirroring human bone properties, emphasising high surface curvature and design versatility to improve mechanical and biomedical properties, specifically osseointegration and stress shielding. The study involves modelling and grading simple cubic (SC) and body-centred cubic (BCC) lattice structures with various geometries and graded conditions and conducting compressive tests to identify the optimal configuration. The results showed that filleting was found to be the mechanical strength. On the other hand, BCC lattice structures demonstrated superior performance compared to SC structures. The optimised structure with a pore size of 400 µm provided an elastic modulus of 15.7 GPa, yield strength of 296 MPa and compressive strength of 530 MPa. This graded lattice design approach provides a promising technique for enhancing hip implant performance, offering potential improvements.

Influence of mean stress and building orientation on the fatigue properties of sub-unital thin-strut miniaturized Ti6Al4V specimens additively manufactured via Laser-Powder Bed Fusion

Fatigue is a complex, localized phenomenon affecting lattice structures at the level of struts and junctions. This study examines the fatigue properties of Laser-Powder Bed Fusion (L-PBF) Ti6Al4V miniaturized strut-like specimens, printed in four distinct building orientations (0°, 15°, 45°, 90°), and subjected to four stress ratios (R = 0.1, R = −1, R = −4, R = 10). Experimental data, summarized in Haigh diagrams, align well with predictions from the SWT and Walker methods. Notably, the dependency on mean stress diminishes as the building angle increases, attributed to progressively lower surface roughness which primarily drive failure at R = 0.1 and R = −1. In contrast, vertical specimens at R = −4 display a pronounced susceptibility to sub-surface defects affecting their fatigue strength, a finding corroborated by CT scan analyses. Additionally, the influence of buckling on fatigue performance is investigated and incorporated into the Haigh diagrams. These findings can contribute to a more informed design of L-PBF Ti6Al4V lattice structures against fatigue.

Effects of cell orientation on compressive behaviour of electron beam powder bed fusion Ti6Al4V lattice structures

Electron beam powder bed fusion (EBPBF) is suitable for making porous (or lattice) structures for medical implant applications. However, it is challenging for a lattice structure with a high porosity level to have sufficient strength, while lattice structures with sufficient strength are required for orthopedic applications. Furthermore, strength anisotropy needs to be understood for the design of femoral stems as load direction (LD) is location dependent. The present study aims to understand the effects of cell orientation on the compressive behavior of simple cubic lattice structures built using EBPBF and Ti6Al4V alloy, with [001]//LD or [111]//LD. It has been found that the apparent yield strength (σy-L) of [001] lattices is 1.8 times higher than that of [111] lattices, by experimental determination and also by numerical simulation. Simulation has shown that, with the [001]//LD condition, σ1 in vertical load supporting struts is low when the structure yields. But locally, σ1 (>1,000 MPa) is positive and high for the [111]/LD condition when yielding of the structure occurs with the load value only 57% of the value that is required for causing yielding in the [001]//LD condition. The predictive yield strength values by simulation of both [001] and [111] lattices have been found to be slightly lower than the experimentally determined values. Explanation for this will be provided by considering the effect of the struct effective diameter with EBPBF strut irregularity on the strength of the lattice structures.

An Innovative Method to Analyse the Geometrical Accuracy of Ti6Al4V Octet-Truss Lattice Structures.

Metal lattice structures manufactured utilising additive techniques are attracting increasing attention thanks to the high structural efficiency they can offer. Although many studies exist on the characterisation of massive parts in Ti6Al4V processed by Electron Beam Melting (EBM), several investigations are necessary to characterise the Ti6Al4V lattice structures made by the EBM process. The objective of this paper is to develop a measurement method to assess the dimensional accuracy of Ti6Al4V octet truss lattice structures manufactured by EBM technology. Beam specimens with a 2 mm diameter and different growth orientations with respect to the build direction were analysed. The geometry differences between the designed and the manufactured beam specimens were highlighted. Two effects were identified: (i) The EBM-manufactured beams are generally thinner than the designed ones, and (ii) the shape of the section was found to be almost circular for the beam specimens oriented at 45° and 90°; on the contrary, the section of the horizontal beam (0°) cannot be considered circular.

Ti6Al4V lattice structures manufactured by electron beam powder bed fusion - Microstructural and mechanical characterization based on advanced in situ techniques

Powder bed fusion (PBF) processes enable the manufacturing of complex components in a time- and cost-efficient manner. Especially lattice structures are currently focused since they show varying mechanical properties, including different deformation and damage behaviors, which can be used to locally tailor the mechanical behavior. However, the present process-structure-property relationships are highly complex and have to be understood in detail in order to enable an implementation of PBF manufactured lattice structures in safety-relevant applications. Within the present work Ti6Al4V lattice structures were manufactured by electron beam powder bed fusion of metals (PBF-EB/M). Based on the classification of bending- and stretch-dominated deformation behavior, two different lattice types, i.e. body-centered cubic like (BCC-) and face-centered cubic like (F2CCZ) structures were selected. Microstructural features were detected to evaluate if potential different microstructures can occur due to different lattice types and to answer the question if microstructural features might contribute to the mechanical behavior shown in this work. Furthermore, X-ray microfocus computed tomography (μCT) analysis were carried out to enable a comparison between the computer-aided designed (CAD) and as-built geometry. For mechanical characterization, quasi-static and cyclic tests were used. In particular, the BCC lattice type showed a more ductile material behavior whereby higher stiffness and strength was determined for the F2CCZ lattice type. Additionally, different in-situ measurement techniques such as direct current potential drop system and digital image correlation could be deployed to describe the damage progress both under quasi-static and cyclic loading.

Influence of bracing on the mechanical properties of Ti6Al4V lattice structures

In this paper, three novel lattice structures were designed based on the body-centered cubic (BCC) unit cell. These lattice structures with different porosities were fabricated by selective laser melting (SLM). We investigated the mechanical properties, deformation-induced failure modes, and energy absorption of these structures under uniaxial compression. We added the bracings in a BCC unit cell, resulting in the shift from the bending-dominated mode to the stretch-dominated mode during deformation. Specifically, the vertical and horizontal bracings dramatically increased the compressive strength of the lattice structures. Importantly, the combination of the two bracings improved the strength by 287 %. Additionally, while boosting energy absorption, the bracings prevented the original structure from the failure-induced efficiency decrease in energy absorption. These findings are expected to provide experimental data and a scientific basis for the design and engineering applications of 3D-printed BCC unit cell structures.

Investigating mechanical and biological properties of additive manufactured Ti6Al4V lattice structures for orthopedic implants

Investigating mechanical and biological properties of additive manufactured Ti6Al4V lattice structures for orthopedic implants

A novel approach to fabricate load-bearing Ti6Al4V-Barium titanate piezoelectric bone scaffolds by coupling electron beam melting and field-assisted sintering

A critical-size bone defect in load-bearing areas is a challenging clinical problem in orthopaedic surgery. Titanium alloy (Ti6Al4V) scaffolds have advantages because of their biomechanical stability but lack electrical activity, which hinders their further use. This work is focused on the fabrication of Ti6Al4V-Barium Titanate (BaTiO3) bulk composite scaffolds to combine the biomechanical stability of Ti6Al4V with electrical activity through BaTiO3. For the first time, a hollow cylindrical Ti6Al4V is additively manufactured by electron beam melting and combined with piezoelectric BaTiO3 powder for joint processing in field-assisted sintering. Scanning electron microscope images on the interface of the Ti6Al4V-BaTiO3 composite scaffold showed that after sintering, the Ti6Al4V lattice structure bounded with BaTiO3 matrix without its major deformation. The Ti6Al4V-BaTiO3 scaffold had average piezoelectric constants of (0.63 ± 0.12) pC/N directly after sintering due to partial dipole alignment of the BaTiO3 tetragonal phase, which increased to (4.92 ± 0.75) pC/N after a successful corona poling. Moreover, the nanoindentation values of Ti6Al4V exhibited an average hardness and Young’s modulus of (5.9 ± 0.9) GPa and (130 ± 14) GPa, and BaTiO3 showed (4.0 ± 0.6) GPa and (106 ± 10) GPa, respectively. It reveals that the Ti6Al4V is the harder and stiffer part in the Ti6Al4V-BaTiO3 composite scaffold. Such a scaffold has the potential to treat critical-size bone defects in load-bearing areas and guide tissue regeneration by physical stimulation.

Investigation on effect of pillar size on the comprehensive properties of Ti6Al4V lattice fabricated by selective laser melting

To investigate the effect of pillar size on the mechanical properties of Ti6Al4V lattice fabricated by selective laser melting (SLM), seven groups of Ti6Al4V lattice structures with different pillar sizes were fabricated by SLM technology. The compression process of the lattice structure of body-centered cubic element was studied by numerical simulation method, and then the numerical simulation results were verified by experiments. The porosity of the lattice structure was characterized by dry weight method, and the compressive and compressive fatigue properties of the lattice structure were tested. The results showed that the actual porosity of all lattice structures with different pillar sizes was less than the designed porosity due to the thermal adsorption of the surrounding powder on the pillar. The numerical simulation was in good agreement with the experimental results, which can be used to predict the displacement changes in the elastic region of the lattice structure. With the increase of the pillar size, the difference between the actual porosity and the designed porosity of the lattice structure increased first and then decreased. The compression resistance of the unit cell topology was better. Meanwhile, the compression and yield strength of the lattice structure were increased. The larger the pillar size of lattice structure, the better the plasticity. It can withstand higher cyclic load and have better fatigue performance.

Mechanical Properties and Failure Modes of Additively Manufactured Ti6Al4V Lattice Structures Under Quasi-Static Compressive Loading

Additive manufacturing (AM) has many advantages over traditional manufacturing technologies as it allows the fabrication of lattice structures with complex designs and inherent features within a single part without any separation. Currently, lattice structures have wide application prospects due to their excellent mechanical performance and design freedom. This paper provides both experimental and numerical investigations for the failure behaviors of selective laser melting (SLM) Ti6Al4V lattice structures under uniaxial compressive loading. Lattice structures with different cell topologies and strut radii were chosen to conduct quasi-static compression simulations to examine their mechanical properties and failure modes. It is found that adding [Formula: see text]-direction struts in the loading direction could significantly improve the load-carrying capacity and the most superior mechanical properties were presented by FCCZ. The slopes of the double logarithmic relationship between the equivalent stiffness and the relative density of lattice structures can be distinguished as close to 1.0 and 3.0, implying bending-dominated or stretch-dominated behavior of lattice structures, respectively. For stretch-dominated lattice structures under uniaxial compression, FCCZ, BCCZ and FBCCZ, the failure modes would experience a transformation from strut buckling to fracture with the increase of strut radii, which is different from FCC and BCC demonstrated as the bending-dominated lattice structures.

Mechanical characteristic comparison of additively manufactured Ti–6Al–4V lattice structures in biocompatible bone tissue growth

This study proposed the development of Ti–6Al–4V lattice structures suitable for the growth of bone cells using laser powder bed fusion (PBF) and heat treatment of vacuum furnace tubes. The designed and fabricated Diamond (DIA), Trifolium (TF), and Trishuriken (TS) lattice structures had high mechanical strength and Young's modulus similar to human cancellous bone. The pore size, porosity, compressive strength, and internal defect of the lattice structures are also discussed herein. According to the experimental observations, after the holding temperature at 950 °C for 1, 2, and 3 h, the grain sizes of TS500 samples were 3.59, 5.05 and 7.87 μm2, respectively. The compressive strength and ductility of these lattice structures changed significantly after the heat treatment. Two kinds of internal defects appeared in PBF production, namely, the powder that did not melt completely during printing and the micro-spherical pores caused by the residual gas. These were found concentrated at the middle location of the cross of the laser scanning path. Furthermore, the defect distribution can be detected through micro computed tomography.

Investigation of the Performance of Ti6Al4V Lattice Structures Designed for Biomedical Implants Using the Finite Element Method

The development of medical implants is an ongoing process pursued by many studies in the biomedical field. The focus is on enhancing the structure of the implants to improve their biomechanical properties, thus reducing the imperfections for the patient and increasing the lifespan of the prosthesis. The purpose of this study was to investigate the effects of different lattice structures under laboratory conditions and in a numerical manner to choose the best unit cell design, able to generate a structure as close to that of human bone as possible. Four types of unit cell were designed using the ANSYS software and investigated through comparison between the results of laboratory compression tests and those of the finite element simulation. Three samples of each unit cell type were 3D printed, using direct metal laser sintering technology, and tested according to the ISO standards. Ti6Al4V was selected as the material for the samples. Stress–strain characteristics were determined, and the effective Young’s modulus was calculated. Detailed comparative analysis was conducted between the laboratory and the numerical results. The average Young’s modulus values were 11 GPa, 9 GPa, and 8 GPa for the Octahedral lattice type, both the 3D lattice infill type and the double-pyramid lattice and face diagonals type, and the double-pyramid lattice with cross type, respectively. The deviation between the lab results and the simulated ones was up to 10%. Our results show how each type of unit cell structure is suitable for each specific type of human bone.

Hybrid Ti6Al4V/Silk Fibroin Composite for Load-Bearing Implants: A Hierarchical Multifunctional Cellular Scaffold.

Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically in terms of osseointegration. Morphological accuracy of sub-unital elements along with the printing resolution are major constraints in the design workspace of a lattice, hindering the possibility of manufacturing structures optimized for proper osteointegration. To overcome these issues, the authors developed a new hybrid multifunctional composite scaffold consisting of an AM Ti6Al4V lattice structure and a silk fibroin/gelatin foam. The composite was realized by combining laser powder bed fusion (L-PBF) of simple cubic lattice structures with foaming techniques. A combined process of foaming and electrodeposition has been also evaluated. The multifunctional scaffolds were characterized to evaluate their pore size, morphology, and distribution as well as their adhesion and behavior at the metal–polymer interface. Pull-out tests in dry and hydrated conditions were employed for the mechanical characterization. Additionally, a cytotoxicity assessment was performed to preliminarily evaluate their potential application in the biomedical field as load-bearing next-generation medical devices.

Mechanical behavior of Ti6Al4V lattice structures; numerical and experimental analysis

This study deals with the mechanical behavior of lattice structures produced by the Laser Powder Bed Fusion process experimentally and numerically for four different topologies of Body-Centered Cubic, Body-Centered Cubic with struts along Z-direction, Face-Centered Cubic and Face-Centered Cubic with struts along Z-direction. To study the effect of cross-section geometry of the struts on the mechanical behavior of the structure, three circular, rectangular and I-shaped cross-sections with the same surface area were manufactured and tested. Their simulations were done using Abaqus software and the simulation results were in great agreement with the test results. Numerical and experimental investigations showed that samples with the I-shaped cross-section of the strut exhibit more stiffness and strength.

Mechanoregulation modelling of stretching versus bending dominated periodic cellular solids

With additive manufacturing advancements, the possibility of creating lattice-based 3D-printed implants can enhance the osseointegration of orthopedic devices. To this date, there is no study that characterizes Ti6Al4V lattice structure microscopic geometrical parameters based on mechano-regulatory theories. This research compared twenty-four different lattice topologies using bone ingrowth stimulations, at ten different relative densities (between 5 % and 50 %) subjected to four different pressures (0.5 MPa, 1 MPa, 1.5 MPa and 2 MPa). A total of 964 results from the numerical mechano-regulation analysis are presented. Sub-groups of Stretching-dominated lattice (SDL) and Bending-dominated lattice (BDL) topologies were compared. The analyzed topologies include AFCC, Auxetic, BCC, Diamond, FBCC, FCC, G7/ Octahedron, Kelvin cell, Vintile, Rhombic Dodecahedron, Cubic, Octet, Cuboctahedron, Rhombicuboctahedron, Iso-truss, Truncated Cube, Truncated Cuboctahedron, and BCCZ, FCCZ, FBCCXYZ and Cubic Center. Higher deformation and fluid flow were observed in BDL topologies leading to better mature bone growth stimulation compared to the SDL topologies. Topologies with lower Young’s Moduli were also leading to better growth stimulation. It is found that the most favourable BDL topologies include, BCC, Diamond, FBCC, G7, Octahedron. On the other hand, the most favourable SDL are Tetrahedron and Tesseract. Material selection design charts are created which will help in the design of novel Ti6Al4V lattice-based implants.