Vacuum Integrity and Leak Localization in Polymer Composite Manufacturing

Abstract

Vacuum infusion is widely used to manufacture large composite structures where the vacuum integrity of the vacuum bag assembly governs the quality of the resulting laminate. Before resin is infused, manufacturers verify integrity with a vacuum-drop test which confirms whether a leak is present but gives no information about where it is located. When the vacuum-drop test fails, the leak is found by a manual search that is slow, depends on skilled operators and scales poorly to large parts. Published localization methods address this only partially: they infer leak position from flow measured at the vacuum boundary while the pump is operating, rather than from pressure measurements across the part. This thesis investigates whether a distributed array of pressure transducers installed beneath the vacuum film can localize a leak during the vacuum-drop test. Twenty pressure transducers recorded gauge pressure at 1Hz across a 1.86m × 1.20m fabric stack through fourteen experiments, spanning ten pinhole positions and two needle diameters with each leak introduced during pump-off vacuum-drop conditions. In all fourteen experiments the PT(s) recording the largest dP/dt gradient was the one nearest the pinhole. The leak region is identified from the spatial pattern of dP/dt across the array. This pattern proved robust to baseline vacuum drift and per-sensor calibration offsets. Although the peak magnitude varied between nominally identical punctures, the identified location did not. The work demonstrates, at laboratory scale, a route to localizing vacuum film leaks during a vacuum-drop test already performed in industry, using low-cost PTs and standard data acquisition hardware.