The aerospace industry has a natural demand for lattice structures that combine lightweight design features, high stiffness, and strong energy absorption capabilities. As engineering applications continue to expand, selective laser melting (SLM), which is one of the most promising additive manufacturing (AM) methods for TC4 alloy lattice structures, has become a key technology. Compression loads are the main cause of lattice structure failure, and improvements in the compression performance of lattice structures have attracted widespread attention from scholars. However, the impact of structural parameters on the compression performance of lattice structures is not yet clear, and reports on how the strut angle affects the compression performance of lattice structures are few. To improve the ability of lattice structures to resist out-of-plane loads is of great engineering significance in studying the influence of the strut angle on the compression performance of lattice structures, for further lattice structure optimization.

Lattice structures with strut angles of 60°, 90°, and 120° were fabricated using SLM. Quasistatic compression experiments were conducted on the samples at room temperature, and finite element analysis was performed to describe the deformation behavior and failure modes of each sample during compression. The fracture modes of lattice structures with different strut angles were characterized through fracture surface analysis.

In Fig. 3, the overall performance of the lattice structure is optimal for a strut angle of 60°. The compressive strength reaches 391 MPa, which is 36% and 25% higher than those of the 90° and 120° samples, respectively. The energy absorption capacity is 17.8 MJ/m³, which is 9.5 MJ/m³ and 6.9 MJ/m³ higher than those of the 90° and 120° samples, respectively. The energy absorption efficiency is 64.3%, which is only 0.1 percentage point lower than that of the 120° sample. On the other hand, adjusting the strut angle can change the stress state of the α/α′ martensite phase inside the lattice struts (Fig. 8). The shear stress decreases continuously within the range of (π/3, π/2) and increases continuously within the range of (π/2, 2π/3). The minimum value of shear stress is 0 when θ is π/2, that is, when the strut angle is 90°. A larger shear stress promotes dislocation slip and enhances the resistance of the lattice structure to plastic deformation, thereby explaining the phenomenon that the equivalent plastic strain of the lattice structure decreases first and then increases with a gradual increase of the strut angle. Combining the bending moment calculation formulas, the bending moments of the 60°, 90°, and 120°samples were found to be 1732 N·mm, 2365 N·mm, and 5366 N·mm, respectively. This means that as the strut angle increases, the finite relative rotation angle between two infinitely adjacent cross-sections decreases when the cross-section of the lattice strut reaches the plastic flow stage. The larger bending moments of the 90° and 120° samples cause all the lattice struts in the lattice structure to be close to the compressive strength limit of the TC4 alloy. At this point, any strut fracture immediately leads to the rapid failure of the structure along the maximum shear stress band. However, in the 60° sample, because of the smaller bending moment experienced by the struts, the middle and lower layers of the lattice are not close to the compressive strength limit when the upper lattice is about to fail. After the upper lattice struts fracture, the equivalent stress concentration in the middle and lower layers of the lattice is partially relieved, and the upper lattice continues to undergo plastic deformation, ultimately resulting in failure caused by a layered collapse. This indicates that with a larger strut angle in the BCC lattice structure, the more pronounced is the shear failure exhibited by the lattice structure. The fracture surfaces of all samples were composed of rough planes accumulated by a large number of dimples and smooth areas of quasi-cleavage planes, indicating the mixed ductile and brittle fracture mechanism of the lattice structure (Fig. 13).

The results of the quasi-static compression tests and finite element analysis showed that the energy absorption capacity, energy absorption efficiency, and compression performance of the lattice structure first exhibits a decreasing and then an increasing trend with an increase in the strut angle. The comprehensive performance was optimal, for a strut angle of 60°, reaching 17.8 MJ/m³ (energy absorption capacity), 64.3% (energy absorption efficiency), 391 MPa (compressive strength), and 6.7% (equivalent plastic strain). A positive correlation exists between the strut angle and the plastic bending moment of the lattice struts. The bending moments of the 60°, 90°, and 120° samples were 1732 N·mm, 2365 N·mm, and 5366 N·mm, respectively. The lattice strut in the 60° sample experienced a smaller bending moment, resulting in a failure mode of layered collapse. In contrast, the 90° and 120° samples exhibited shear failure modes. An increase in the bending moment makes the lattice structure more prone to shear failure. The fracture mechanism of the lattice struts in all the samples was a mix of ductile and brittle fracture mode.