A polyethylene weather balloon collapsed during ascent, well below the target altitude. The engineering team recovered the polymer fragments to investigate the root cause. The initial hypothesis pointed to a micro-imperfection in the blow mold which, as the material expanded due to low atmospheric pressure, would have acted as a stress concentrator and catastrophic crack initiator.
Workflow: scanning, modeling, and FEM simulation 🛠️
The process began with 3D scanning of the fracture edges using GOM Inspect to capture the surface topography. A 50-micrometer cavity was identified in the crack initiation zone. This geometry was imported into Siemens NX to model a segment of the balloon membrane, including the imperfection as an elliptical notch. The mesh was exported to Abaqus, where a membrane analysis with decreasing differential pressure simulating altitude was applied. The results showed that the stress intensity factor exceeded the polymer's fracture toughness exactly at the collapse point recorded by the flight sensors.
Lessons for polymer fatigue simulation 📘
This case confirms that manufacturing micro-imperfections are critical in components subjected to large deformations and differential pressures. The correlation between high-resolution 3D scanning and finite element analysis allows validating linear elastic fracture mechanics models in viscoelastic materials. For future designs, it is recommended to inspect molds with industrial tomography and adjust blow molding parameters to eliminate cavities below 10 micrometers.
Which finite element simulation (FEM) parameters or crack growth laws (such as Paris or NASGRO) are most critical for accurately modeling the propagation of a microcrack in a low-density polyethylene film under differential pressure conditions and dynamic loads during the ascent of a stratospheric balloon?
(PS: Material fatigue is like yours after 10 hours of simulation.)