Determining the properties of printed parts
In order to predict the performance of a 3D printed part, Smart Slice constructs and solves a high-fidelity finite element model of the as-printed part. Some of the most important inputs to these models are the mechanical properties of the different regions (wall, top/bottom layer, and infill regions) in the model. The process of determining these properties is the focus of what follows.
First, dogbone shaped test specimens are printed per the manufacturers print profile and then experimental tensile tests are conducted. The data from these tests are used to calculate the linear-elastic properties of the bulk material and a measure of the bond strength between printed layers. This data gets stored in the Smart Slice material database.
With the bulk properties of the materials known, the next step is to compute the properties of the as-printed wall, top/bottom layer, and infill regions. The properties of these regions depend on 2 things: the material and the print settings (e.g. layer height, line width, infill pattern, and infill density) used to slice the part. For example, an infill printed from ABS will have different properties than an infill printed from PLA and an ABS grid infill printed at 20% density will have different properties than an ABS grid infill printed at 55%.
Smart Slice uses finite element-based micromechanics models of repeating unit cells to evaluate the properties of the as-printed regions. Repeating unit cells (aka representative volume elements) can be used when a structure has a repeating pattern. Instead of modelling the entire structure, a model of the smallest repeating unit can be used to compute the properties of the full structure. This method is very common in materials science because it is accurate and economical. As an example, consider the triangular infill pattern. The pattern is graphically represented by the grey structure shown below. The smallest repeating unit in this pattern is a simple triangle and it is represented by the red region. If appropriate boundary conditions are applied to the repeating unit cell, then the properties of the unit cell will match the properties of the full structure and a solution can be achieved in a fraction of the time. This concept also applies to the wall and top/bottom layer regions.
In summary, Smart Slice computes the mechanical properties of the wall, top/bottom layer, and infill regions by constructing and solving micromechanics models based on the print settings and selected material. This information is used by the Smart Slice FEA solver when it computes the displacement and safety factor of the as-printed part.