Long duration biaxial cylinder testing of balloon grade polyethylene films with emphasis on automated data acquisition and control
Characterization of a 2-dimensional material constitutive model in the practical biaxial state for engineering utility of balloon envelope structural analysis is achievable with laboratory cylinder tests. Hoop(circumferential), and longitudinal strains are time-wise measured on axially loaded pressurized cylinders. Pre-programmed ramped loading changes as well as precise long term pressure control are achieved through cascaded PID flow control loops that are part of an integrated data acquisition and process control system. Real time data reduction and analysis allow monitoring of unattended tests that have durations of up to a month. Measured and controlled parameters and variables are discussed; data analysis techniques are reviewed.