Pre-Bonding Surface Check: Inspecting the Adherend

What this stage covers

The scope is the bond-line preparation surface, checked before the adhesive is applied. TOFD scans the prepared surface at this stage, and the result forms part of the record that follows the bond line through assembly and into service. The check is fast, and the risk it removes is the one that is hardest to fix once the shell is closed.

What the inspection includes

• TOFD scan of the bond-line preparation surface before the adhesive goes down
• The joint inspected while it is still open, so a surface problem is a re-prep rather than a re-bond
• The result folded into the same record that follows the bond line through assembly
• Part of the coverage that satisfies IEC 61400-5 Section 11 on a primary bond line

Where the value sits

The stage is about sequence rather than sensitivity. A surface defect found before bonding is a re-prep, and the same defect found after bonding shows up as a bond-line void that requires the joint to be opened. Because the adhesive joint is a primary bond line, the inspection it carries is part of the coverage Section 11 asks for, and logging the surface result to the blade serial means the segment is documented before the bond exists rather than reconstructed afterwards. Cheap now, expensive later, and that asymmetry is the whole argument.

How to plan this stage

Run these checks in order. By Step 5 the scan, the threshold and the record are aligned to the stage.

1. Fix the acceptance threshold. Start from the threshold the zone carries, not from the method you happen to own. IEC 61400-5 Section 11 asks for volumetric detection of indications 6 mm and larger in the laminate plane, and DNV-ST-0126 tightens the leading edge to 3 mm, so the threshold is set before the probe is chosen.
2. Read the geometry off the drawing. Measure the thickness and the curvature the probe has to travel. A spar cap up to 80 mm of unidirectional laminate and a root transition of changing radius are two different scan problems, and the radius decides how the array is coupled.
3. Choose the modality pair. Pick modules by defect geometry, not by habit. PAUT images planar separations that lie parallel to the plies, TOFD catches volumetric clusters whatever their orientation, and running both on a 256-channel system puts the two mechanisms in one pass.
4. Automate the scan path. Put the probe on an encoder-driven carriage and let the path, not the technician, set coverage. A 600 mm spar cap falls to one longitudinal pass at 500 mm/s on a linear array, where a single-element probe needs 20 parallel passes and runs about five times longer.
5. Lock the evidence chain. Write the coverage map, the daily calibration and the indication log to the blade serial while the scan is running. It is the difference between a 3-day type-certification audit and a 3-hour document review, and it is what ISO 9712 qualification is there to sign.

Nothing here is rounded up for effect. Each value is the one on the equipment sheet or in the field report behind it.