Session: 06-09-04: Computational Modeling in Biomedical Applications - IV

Paper Number: 108885

108885 - Finite Element Simulation of Compressing an Additively Manufactured Mesostructure 

Numerical modeling is a useful approach for answering research questions that are either difficult or inefficient to answer experimentally. Before a numerical model can be used to answer a question, this model must be carefully developed and validated against experimental data. Mesostructures manufactured using fused deposition modeling (FDM) have been tested experimentally and subsequently modeled numerically in the literature. This approach has not yet been applied to structures made using stereolithography (SLA). Therefore, the goal of this study was to develop a validated numerical model of an SLA manufactured mesostructure to predict compression behavior.

 

A three-dimensional (3D) model was created for an 80 x 80 x 20 mm compression block. The structure of the block was made of a novel, open-source mesostructure designed by Andreas Bastian. Ansys was used to simulate compression testing of this structure. The lower plate of the structure was fixed while a vertical displacement was prescribed on the upper plate. This loading compressed the mesostructure over multiple static steps in a single simulation. The base material was varied to represent three different SLA polymers from Formlabs (i.e. three different models of the same geometrical structure): flexible (E = 3.1 MPa, ultimate strength = 3.35 MPa); durable (E = 450 MPa, ultimate strength 18.6 MPa); and clear (E = 1600 MPa, ultimate strength = 38 MPa). For each base material, a mesh convergence study was performed to ensure the force-displacement results of the simulation were independent of the mesh size. Using the results of the converging mesh, the force-displacement curve of the simulation was compared to experimental data using cross-correlation. To better understand how the force-displacement curves vary with the material model, a sensitivity analysis was performed for each base material.

 

For each base material, a mesh size of 0.5 mm was needed for the maximum compression force to be independent of the mesh size. The cross-correlation results showed the agreement between the shape of the simulated force-displacement curve and experimental results was highest for the durable material with r = 0.88, next for the clear material with r = 0.77, and lowest for the flexible material with r = 0.43. The simulation and experimental curves started to diverge in agreement at around 10 mm of compressive displacement. The maximum compressive force was correlated with elastic modulus with a Spearman’s r = 1 and p < 0.005 for all base materials. Maximum force was not related to the ultimate tensile strength of the base material.

 

The shape of the force-displacement curves and compression force values agreed well but only for the stiffer materials of clear and durable and only up until 10 mm. This may be where the structure shifts from elastic to plastic behavior and some lattice structures fracture. The simulations are limited in that they do not simulate fracture. The sensitivity data showed force was correlated with the elastic modulus of the material. This could be another source of discrepancy between the simulation and experimental data. A 24% variation in material properties was based on a previous study of impact properties; perhaps elastic modulus is more variable. Future work could focus on bringing this variability down for the experimental data. This simulation tool can be used in the future to predict and optimize the behavior of this lattice structure while operating elastically. This could potentially be used in foam applications, e.g. football helmets.

Presenting Author: Anne Schmitz UW Stout

Presenting Author Biography: Anne Schmitz is an Assistant Professor at the University of Wisconsin-Stout. She teaches courses that serve the Mechanical Engineering, Manufacturing Engineering, and Engineering Technology programs. Her main areas of expertise are computational biomechanics, machine component design, and additive manufacturing.

Authors:

Anne Schmitz UW Stout