Static and Fatigue Performance of Additively Manufactured CoCrMo Alloy Simple-Cubic Lattice Structures for Orthopedic Implant Applications

Additively manufactured lattice structures are widely explored for orthopedic implants because they enable stiffness reduction, bone ingrowth, and improved load transfer; however, their long-term mechanical stability under cyclic physiological loading remains insufficiently understood. In this study, the monotonic and fatigue responses of laser powder bed fusion (LPBF)-fabricated CoCrMo simple-cubic lattice structures with 65% (C1) and 45% (C2) porosity were systematically investigated. The architectures were designed to ensure effective load distribution, high surface area, and adequate pore interconnectivity. Monotonic compression and stress-controlled compression–compression fatigue tests were performed at 30%, 60%, and 90% of yield strength.Cyclic deformation behavior was characterized using ratcheting strain evolution, ratcheting strain-rate decay, and plastic strain energy dissipation per cycle. Both structures exhibited an initial transient ratcheting regime followed by stabilization, with a 1.0–10.3% reduction in plastic strain energy dissipation, indicating cyclic hardening and the establishment of elastic or plastic shakedown depending on fatigue loading conditions. The finite element fatigue analysis based on a stress–life approach revealed a proportional relationship between equivalent von Mises stress and equivalent alternating stress, with a nearly constant ratio of ~0.45. Numerical results indicated elastic shakedown at 30% and plastic shakedown at 60% and 90% of yield strength, associated with localized plastic deformation at strut junctions.Post-fatigue compression testing confirmed degradation in stiffness and peak strength, along with an increase in yield strength, indicating fatigue-induced cyclic hardening. These results demonstrate that cyclic stability is governed by shakedown-controlled deformation and relative density effects, providing guidance for fatigue-resistant porous implant design.