Material extrusion-based polymer additive manufacturing (AM) processes such as fused deposition modeling (FDM) or fused filament fabrication (FFF) are increasingly being used for large scale structural applications. The strength of such parts in the build direction (Z-strength) is lower than the strength along the extruded strand direction and is a limiting factor in design. Furthermore, the Z- strength is sensitive to the process parameters of the print and could change depending on the geometry of the part, or even at different locations within the same part. This presents a challenge for qualification and characterization of the part’s structural performance and highlights the need for predictive models for Z-strength. In this work, a methodology is presented for predicting Z-strength by breaking it down into a combination of interlayer adhesion, bead shape and effective contact area, surface stress concentrations, and notch sensitivity. Through a combination of parametric studies using both experiments and computational modeling, individual dependencies were established for each of the identified components of Z-strength on the process parameters. The predictions were validated with tensile test coupons cut from the walls of AM parts, with over 50 combinations of different process parameters including layer height, extrusion temperature, layer time, and print angle (layer offset). The methodology was also integrated into existing commercial software GENOA 3DP along with finite element software ABAQUS and demonstrated to predict part level structural performance incorporating variable Z-strength.
Learning Objectives:
- Understand the significance of Z-strength in polymer AM, and how it depends on process
- Utilize the presented methodology to develop or improve existing computational tools for incorporating Z-strength prediction in the design process.
