SIM-AM 2023

Effect of Residual Stresses on the Mechanical Properties of TPMS Lattice Structures Manufactured Using 316L Stainless Steel

  • Mapari, Hrushikesh (Ansys Germany GmbH)
  • Kruse, Henrik (Chair for Digital Additive Production DAP)
  • Escobar, Enrique (Ansys Germany GmbH)
  • Matei, Alexandre (Ansys France SAS)
  • Schleifenbaum, Johannes Henrich (Chair for Digital Additive Production DAP)

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In recent years, the use of Triply Periodic Minimal Surface (TPMS) lattice structures has gained popularity due to their advantages like high surface to volume ratio and self-supporting structures. Nowadays, these structures are seen in many fields, including aerospace and medical applications. Advances in metal additive manufacturing (AM) technologies enable the production of these complex designs with very high precision. However, the advantages of 3D printing over traditional manufacturing technologies (e.g., forming, casting) can only be used to a limited extent for the manufacturing of lattice structures due to various phenomena (e.g., warpage base on residual stresses and strains or porosity). The determination of a component- and material-specific process window requires a considerable experimental effort, which can be drastically reduced by adoption of adequate simulations tools. During the Laser Powder Bed Fusion (L-PBF) process, transient temperature change is caused by the cyclic nature of the thermal load which causes a difference in strain between new and pre/solidified layers, resulting in the accumulation of residual stresses. Reasons like gas entrapment in the melt pool, presence of hollow powder particles, and irregularities in the melt pool flow can give rise to porosity. The residual stresses and the porosity, both in individual capacity and in combined effect, can cause dimensional inaccuracies and have a severe impact on the loading capacity and performance of the part. In this paper, the effect of residual stresses and porosity defects on the mechanical properties of the primitive and gyroid TPMS lattice is studied using FEA and experimental studies. The AM simulation is performed using a sequentially coupled thermomechanical finite element model to evaluate the thermal histories and residual stress evolution throughout the process. These results are used to measure the properties Young’s modulus, yield strength and the Specific Energy Absorption (SEA). Similarly, porosity defects are included in the modelling of the lattices, and its effect on the properties is studied. The lattices are fabricated using 316 Stainless steel and undergo compression testing. The results of the compression tests are compared with the FEA simulation. This paper provides a methodology to perform FEA simulations to quantify the accumulated residual stresses, included porosity defects and its effects on the mechanical properties of complex TPMS lattices.