Bonding a sensing film to a blade surface: what actually fails
Most measurement errors on a blade do not come from the sensor — they come from the bond. Here are the three failure modes we see and how each shows up in the data.
PDRELTEST Engineering · 6 min read · 2026-10-21
A pressure film measures the load transmitted through its contact surface. If the bond between film and blade is not continuous, the film reports the load path through the adhesive, not through the structure. The sensor is usually blamed; the bond is usually responsible.
1. Trapped air under the film
Air pockets show up as isolated low-reading cells inside a high-pressure region, stable across load cycles. They do not move when you change the load — that is the giveaway. On a curved surface they cluster along the direction of curvature.
2. Adhesive creep under sustained load
Under a long hold, an adhesive that creeps lets the film relax. The data drifts downward over hours while the actual load is constant. A repeatability check at the start and end of a hold tells you whether the drift is the sensor or the bond.
3. Edge lift
The sealing zone is 1.5 mm per side (3 mm at combined seams). If the film is trimmed or the edge is pressed into a radius, the edge lifts and the outermost cells read low. On a tiled build this appears as a systematic drop at every seam — easy to mistake for a real structural feature.
What to do about it
Before any campaign, run a flat-plate check: load the bonded panel on a press at two levels and confirm the field is continuous. Ten minutes of that catches all three failure modes, and it is far cheaper than discovering them in the analysis.