Process-induced geometric defect sensitivity of Ti–6Al–4V lattice structures with different mesoscopic topologies fabricated by electron beam melting

Abstract

Ti–6Al–4V lattice structures with different cell configurations are fabricated by electron beam melting (EBM) method. Two different cell topologies (octet truss and regular rhombic dodecahedron lattice) corresponding to stretching-dominated and bending-dominated respectively are taken into consideration. The mechanical properties of these specimens are examined by quasi-static compression experiments which are conducted by electronic universal machine, while the deformation evolutions of all the specimens are captured by a digital camera. The results indicate that the specimens with rhombic dodecahedron cells exhibit higher specific strength than the octet truss structures. This unusual phenomenon is proved to be caused by the geometric imperfections in the printed stretching-dominated structures. Then the X-ray computed tomography is adopted to capture the process-induced defects in the EBM-printed specimens, and virtual tests are performed by the X-ray tomography based 3D reconstruction model. The computational study explains that the collapse strength of the rhombic dodecahedron (RD) lattice is mainly affected by the surface roughness of the struts, while the weak connection at the joints of the struts leads to the significant reduction in the strength of the octet truss specimens. Meanwhile, the dynamic performance of the printed specimens is predicted by ideal shock wave model and validated by numerical simulation. The results indicate that the defects lead to the significant discrepancy between the theoretical prediction and numerical simulation of octet truss structure, but the failure mode transition of RD lattice structure can be well predicted by the analytical model.