Burst Pressure Strength Prediction for Topology-Optimized Polymer AM Structures

Topology-optimized structures are becoming more commonplace, revealing the need for generalized strength prediction methods for such structures. Complex geometry and failure mechanisms of additively manufactured (AM) structures makes the application of classical analysis methods difficult or impossible. Additionally, in the burst pressure case for polymeric AM ducting, testing to collect failure data is dangerous.

To overcome these limitations, a FEM-based approach has been developed where the failure criteria as well as the material allowables are embedded within the FEM code. Complex models can then be loaded in any arbitrary manner, with the FEM software evaluating the state variables at all locations in the model continuously during loading. State variables are then automatically utilized by the failure criteria to determine the occurrence of failure. At the occurrence of failure, corresponding elements are deleted from any further structural interaction and the progression of failure is tracked by a series of initiations. This approach involves Explicit Finite Element analysis and the creation of material subroutines that encapsulate the failure criteria as well as basic strength allowables. Using only basic tensile and compressive stress strain curves as input, strength values for a variety of metallic and polymeric AM structures such as fittings, lugs, angle clips, channels among others has been predicted within 10% of the test data in most cases.

The ability to predict the structural burst pressure strength for AM polymers provides a significant advantage enabling virtual design optimizations and trade studies, considerably reducing the size of the test matrix for physical tests. Case studies are presented over a range of topology-optimized structure used in aircraft. The case studies include both positive and negative pressure on polymer AM ducting. Virtual testing capabilities have been correlated with test data and closed-form solutions, expanding these methods to a variety of topology optimized structures.