Selected Laser Melting Forming Inlaid Lattice Structure and Mechanical Properties

Failure and energy absorption characteristics of four lattice structures under dynamic loading

Three types of layered‐hybrid lattice structures (LHLSs) with different layer thicknesses composed of body‐centered‐cubic (BCC) and face‐centered‐cubic (FCC) unit cells are designed and manufactured by selective laser melting using Ti–6Al–4V powder. The microstructure and surface morphologies of the three types of the selective laser melting‐formed LHLSs are examined by an optical microscope and scanning electron microscope (SEM), respectively. Quasistatic compression experiments are carried out to investigate the mechanical properties. The results show that the layer thickness has a significant effect on the mechanical properties and deformation behaviors. The elastic modulus, yield strength, and ultimate compressive strength of LHLS increase with the increasing BCC and FCC layer thickness, respectively. Based on the observations of deformation process, a 45° shear band and axial fracture are observed in LHLS‐8, and step‐like deformation bands are observed in both LHLS‐4 and LHLS‐2 samples. Besides, the influence of different loading directions on mechanical properties is also investigated; it is found that the ultimate compressive strength loaded in the transverse direction is independent of the layer thickness in LHLSs.

Invar36 alloy, renowned for its exceptionally low coefficient of thermal expansion and excellent mechanical properties, is widely used in precision instruments, high-accuracy molds, and related fields. Metastructures fabricated via laser powder bed fusion (LPBF) have significantly broadened the application scope of Invar36 alloy, owing to their unique advantages such as lightweight design, high specific strength, and high specific stiffness. However, the structure–property coupling relationship in Invar-based metallic lattice structures remains insufficiently understood, which poses a major obstacle to their further engineering utilization. In this study, 36 lattice structures with varying design parameters were fabricated and experimentally evaluated. The design variables included lattice architecture (body-centered cubic (BCC), diamond (DIA), face-centered cubic (FCC), and octet (OCT)), strut diameter (0.6 mm, 0.8 mm, and 1.0 mm), and inclination angle (35°, 45°, and 55°). The influence of these structural parameters on the mechanical performance was systematically investigated. The results indicate that lattice architecture has a significant impact on mechanical properties, with the OCT structure, characterized by stretch-dominated behavior, exhibiting the best overall performance. Under the conditions of a 35° inclination angle and a strut diameter of 1.0 mm, the elastic modulus, compressive strength, plateau stress, and energy absorption of the OCT structure reaches 2525.92 MPa, 110.65 MPa, 162.26 MPa, and 78.22 mJ/mm3, respectively. Furthermore, increasing the strut diameter substantially improves mechanical performance, while variations in inclination angle primarily influence the dominant deformation mode. These findings demonstrate that the mechanical properties of Invar36 alloy lattice structures fabricated via LPBF can be effectively tuned over a broad range, offering both theoretical insights and practical guidance for customized performance optimization.

The aim of this study are exhibiting visual observation result of 316L cellular structures and comparing mechanical properties among them which had been manufactured by selective laser melting (SLM). Some pre-defined cellular structures including cubic primitive (C), face center cubic (FCC), body center cubic (BCC) and hexagonal close packed (HCP) were designed with 0.5-1mm strut's diameter then applied to tensile test specimen shapes. These designs were generated to three dimensional object using SLM. Visual observations were performed to investigate these resulted objects. Mechanical properties were measured using tensile test to get their strength and modulus young. The result shows some struts size was not completely uniform. The FCC has the highest strength and modulus young with 105.4 MPa and 14110 MPa respectively. The HCP lattice exhibits the widest area of plasticity. The BCC strength and stiffness are almost similar to the HCP with lower plastic deformation area. The cubic has the lowest strength among them. In conclusion, each lattice structure, successfully fabricated by SLM, had specific tensile behavior.

Chapter 2 - Mechanical metamaterials

Fatigue properties of Ti-6Al-4V Gyroid graded lattice structures fabricated by laser powder bed fusion with lateral loading

Invar36 alloy is a low expansion alloy, and the triply periodic minimal surfaces (TPMS) structures have excellent lightweight, high energy absorption capacity and superior thermal and acoustic insulation properties. It is, however, difficult to manufacture by traditional processing methods. Laser powder bed fusion (LPBF) as a metal additive manufacturing technology, is extremely advantageous for forming complex lattice structures. In this study, five different TPMS cell structures, Gyroid (G), Diamond (D), Schwarz-P (P), Lidinoid (L), and Neovius (N) with Invar36 alloy as the material, were prepared using the LPBF process. The deformation behavior, mechanical properties, and energy absorption efficiency of these structures under different load directions were studied, and the effects and mechanisms of structure design, wall thickness, and load direction were further investigated. The results show that except for the P cell structure, which collapsed layer by layer, the other four TPMS cell structures all exhibited uniform plastic collapse. The G and D cell structures had excellent mechanical properties, and the energy absorption efficiency could reach more than 80%. In addition, it was found that the wall thickness could adjust the apparent density, relative platform stress, relative stiffness, energy absorption, energy absorption efficiency, and deformation behavior of the structure. Printed TPMS cell structures have better mechanical properties in the horizontal direction due to intrinsic printing process and structural design.

Effect of heat treatment on mechanical properties, failure modes and energy absorption characteristics of lattice skeleton and sheet structures fabricated by SLM

Previous studies have revealed the influence of various lattice structures on the material density and mechanical properties. However, the majority of the topologies that are considered as study objects directly refer to metal/non-crystal lattice cell configurations. Therefore, this paper proposes a configuration generation approach for generating a lattice structure, which can obtain a lattice configuration that enjoys the advantages of both ultra-low weight and favorable mechanical properties. Based on this approach, a new type of face-centered cubic lattice (all face-centered cubic, AFCC) structure with comprehensively optimal properties in terms of mass and mechanical properties is obtained. The experimental samples are formed with Ti6Al4V by the selective laser melting (SLM) method. Quasi-static uniaxial compression performance experiments and finite element analysis (FEA) are conducted on an AFCC structure and the control group body-centered cubic (BCC) structure. The results demonstrates that our optimized AFCC lattice structure is superior to the BCC structure, with elastic modulus and yield limit increases of 143% and 120%, respectively. For the same degree of deformation, the energy absorbed increases approximately 2.4 times. The AFCC demonstrates significant advantages in terms of its mechanical properties and anti-explosion impact resistance while maintaining favorable ultra-low weight, which validates the hypothesis that the proposed configuration generation approach can provide guidance for the design and further research on ultra-light lattice structures in related fields.

Herein, three types of multihierarchical lattice structures (MHLSs) with different configurations are designed based on the body‐centered‐cubic (BCC) unit cell. The designed lattice structures are fabricated using Ti‐6Al‐4 V powder as feedstock material through selective laser melting (SLM) technology. The microstructure and surface morphology of the SLM‐formed samples are observed by optical microscopy and scanning electron microscopy, respectively. Theoretical calculation and quasistatic compression experiment are carried out to investigate their mechanical properties. The result shows that the size error of slave cell with small strut diameters is greater than that of master cell with larger strut diameters. All MHLSs exhibit superior mechanical properties compared to the BCC lattice structure. Moreover, the specific elastic modulus and specific yield strength of MHLSs with the best mechanical properties are 70.1% and 51.0% higher than that of BCC lattice structure, respectively. Meanwhile, theoretical calculation results of the elastic modulus and yield strength are consistent with the results of quasi‐static compression testing. The fracture morphology analysis indicates that the struts of the MHLSs samples exhibit a mixed brittle–plastic fracture mode, while the nodes exhibit a plastic fracture mode.

Mechanical responses of sheet-based gyroid-type triply periodic minimal surface lattice structures fabricated using selective laser melting

Compressive performance and fracture mechanism of bio-inspired heterogeneous glass sponge lattice structures manufactured by selective laser melting

By adding vertical bracings at the nodes of the body‐centered cubic (BCC) unit cell diagonal pillars, at the midpoints between the nodes and the pillar endpoints, at the quarter points near the endpoints, and at the endpoints, four new types of BCCZ unit cell structures are designed. Employing laser powder bed fusion (L‐PBF), two sets of Ti6Al4V lattice structures with 75 and 85% porosities are produced. The mechanical properties, deformation failure modes, and energy absorption of the BCC and the novel body‐centered cubic (BCCZ) under uniaxial compression are investigated, followed by comparative analysis. The study reveals the position of vertical bracings within the unit cell influences the mechanical behavior of lattice structures. Under the same porosity, the BCCZ‐3 exhibits the best mechanical performance, while the BCC shows the lowest. The energy absorption capacity of the BCCZ‐3 is significantly higher than the other four structures. The energy absorption rates of A‐BCCZ‐3 and B‐BCCZ‐3 are 24.19 times and 15.08 times higher than that of the BCC, respectively, and 13.67 times and 8.27 times higher than BCCZ‐1. These findings indicate that the novel BCCZ structures have significant potential for load‐bearing applications compared to the conventional BCC and BCCZ lattice structures.

Lattice structures are multi-functional materials with various advantages such as high specific stiffness, high energy absorption capacity and good thermal management capability. Recently, the development of manufacturing technologies using metal powders has facilitated fabrication of complex products; consequently, interest in lattice structures has grown. In this work, two kinds of lattice structures, pyramidal and tetrahedral, were designed and fabricated via a selective laser melting (SLM) process using stainless steel 316L powder. Scanning electron microscope (SEM) and optical microscope (OM) results revealed that lattice structures with various unit cell sizes and angles of inclination can be manufactured using SLM without the need for additional support structures. However, many unmelted and partially melted particles were observed on the surface of the lattice structures, which caused dimensional errors related to the struts. This research examined the effects of topology and unit cell design parameters on the macroscopic compressive behavior of lattice structures. Compressive characteristics, including elastic modulus, initial peak stress, strain energy absorption and mean stress, were evaluated through uniaxial compression tests. Lattice structures with the same relative density exhibited excellent elastic modulus, initial peak stress, energy absorption and mean stress results at inclination angles of 45–50°. These characteristics showed a tendency to increase with increasing relative density at the same inclination angle. The experimental results suggested these design parameters are the main factors influencing the mechanical characteristics of lattice structures.

Effect of heat treatment on compression properties of the 316L diamond structure fabricated through selective laser melting