Compressive mechanical properties and energy absorption characteristics of SLM fabricated Ti6Al4V triply periodic minimal surface cellular structures

Significance 

Additive manufacturing (AM) technologies are suitable for producing components with complex geometric features and cellular structures with excellent properties. In particular, the load-bearing capacity of AM components fabricated via selective laser melting (SLM) has drawn significant research attention. The design of cellular structures has been extensively studied to achieve stable deformation response and high mechanical strength of AM components. It is worth noting that fabricated AM components with desirable properties require a thorough understanding of the nature of the unit cells (stretching- or bending-dominated) and the effects of the size and cell geometry of the cellular structure.

The comprehensive behavior of cellular structures fabricated via SLM is an interesting topic. Dual-phase Ti6Al4V alloy is the most widely used metal in SLM technology-related studies owing to its high-temperature stability, corrosion resistance and good biocompatibility. A series of equations have been proposed to define the relationship between cell configuration and mechanical properties of cellular structures. Since most applications involving cellular structures require high comprehensive strength, triply periodic minimal surface (TPMS) structures have been studied.

While energy absorption and mechanical preparties of cellular structures have been extensively studied, the correlations between relative density, energy absorption and cell configuration, as well as their effects on the performance of Ti6Al4V alloy sheet-based cellular structures, is poorly understood. To fill these gap, Dr. Qidong Sun, Professor Jie Sun and Professor Kai Guo from Shandong University in collaboration with Dr. Leishuo Wang from Zhengzhou University investigated the energy absorption and comprehensive mechanical properties of different TPMS Ti6Al4V sheet-based cellular structures fabricated via SLM. The work is currently published in the journal, Mechanics of Materials.

In their approach, three TPMS Ti6Al4V structures were studied: PMS-Diamond, TPMS-Gyroid and TPMS-primitive. The authors modified the Ashby and Gibson models of the cellular structures by re-fitting the compressive test data. The relationship between the compressive properties and relative densities of these structures as well as their imperfections, were established. Finally, a series of compression tests and numerical simulations were conducted to evaluate the deformation behavior and the effects of different cell configurations. The deformation behaviors were recorded using a camera.

The authors showed that all three structures could be successfully fabricated using the SLM technology, although their actual relative density was higher than their nominal relative density. The layer-by-layer fabrication feature of SLM also induced a staircase effect. An increase in the actual relative density increased the energy absorption capacity of the structures. For different cellular structures, the compressive mechanical properties were mainly governed by the cell geometry and relative density. The TPMS-Diamond structure exhibited the highest compressive performance, whereas TPMS-Primitive displayed the least.

TPMS-Diamond and TPMS-Gyroid structures displayed low-stress fluctuations due to stable deformation mechanisms and smooth cell geometries. In contrast, the TPMS-Primitive structure experienced a buckling of the cell wall, leading to significant stress fluctuation. The excellent absorption capacity of the Ti6Al4V alloy TPMS structures, especially the TPMS-Diamond structure, was attributed to the optimized process parameters as well as smooth interconnected curved surfaces.

In summary, the authors conducted a series of numerical simulations and compressive tests to explore the energy absorption and compressive behaviors of three different Ti6Al4V TPMS structures. The numerical simulation results agreed with the experimental results. TPMS-Dimond and TPMS-Gyroid exhibited excellent plateau stress and stable deformation behavior. In a statement to Advances in Engineering, Professor Kai Guo noted that the study would guide the design of high-performance structures suitable for different applications, especially those requiring high energy absorption capabilities.

Reference

Sun, Q., Sun, J., Guo, K., & Wang, L. (2022). Compressive mechanical properties and energy absorption characteristics of SLM fabricated Ti6Al4V triply periodic minimal surface cellular structuresMechanics of Materials, 166, 104241.

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