Delamination — Definition & NDT Use
The separation or splitting of layers in composite materials, laminated structures, or coatings. Delaminations reduce load-bearing capacity and structural integrity, particularly in composites and adhesively-bonded structures. Ultrasonic C-scans are excellent for detecting and mapping delaminations due to the strong reflection from the separated layers. Delaminations in critical aerospace composites must be detected early as they can propagate rapidly under cyclic loading.
In service, Delamination starts as a discontinuity that may or may not breach the acceptance criteria of the governing code; the NDT method's job is to detect it, characterise it, and size it so an engineer can decide whether to repair, monitor, or accept. In a composite, the layered structure means impedance changes at every ply boundary; a true delamination registers as a strong reflector at a depth that the C-scan can map across the part to size the affected area for an engineering disposition. The fitness-for-service decision typically pairs the NDT call with material data and stress information; the inspector's job is to give the engineer a clean characterisation rather than to make the keep-or-reject call alone.
The decision tree around Delamination runs: detect, characterise, size, and refer to the acceptance table in the governing code; only the last step decides repair, accept-as-is, or fitness-for-service review. On aerospace components, NAS 410 personnel qualifications and tighter acceptance criteria mean the same indication may be flagged that would be passed on a structural weld.
- Etymology / Origin
- Latin de- + lamina (thin plate); coined for composite and laminate failure modes in the 1960s aerospace literature.
- Formula
- Detected by impedance mismatch at the ply-ply interface; reflection coefficient ≈ 1 at the air-filled gap.
- Units
- Areal extent in mm^2 or % of laminate area.
- Typical Range
- Detectable ≥ 6 mm diameter in 4 mm CFRP at 5 MHz immersion UT; minimum reportable defined per AMS 2154.
- Measured / Produced By
- Through-transmission UT, pulse-echo C-scan, IR thermography, shearography, tap test (gross only).
- Code References
- AMS 2154 (composite UT acceptance); ASTM E2580 (CFRP UT); Boeing BSS 7037 (composite NDT)
- Worked Example
- A 25 × 40 mm delamination in a wing skin spans 2 plies; C-scan shows a contiguous bright region with sharp edges, distinguishing it from porosity (diffuse, low-amplitude).
ASME Section V Article 4
Ultrasonic examination methods for welds and components.
ASTM E114 / E164 / E2375
ASTM straight-beam, contact, and wrought-product UT practices.
ISO 16810 / ISO 16811
General principles and sensitivity setting for industrial UT.
NAS 410
Aerospace personnel qualification and certification standard for NDT.
Confusing delamination with a generic "indication" is a recurring error; the term carries an engineering implication, and the report should distinguish the discontinuity (what was seen) from the disposition (what code says about it).
What does "Delamination" mean in NDT?
The separation or splitting of layers in composite materials, laminated structures, or coatings. Delaminations reduce load-bearing capacity and structural integrity, particularly in composites and adhesively-bonded structures
Is delamination always rejectable?
No. Whether a delamination indication is rejectable depends on the acceptance criteria of the governing code (AWS D1.1, ASME Section VIII, API 1104, etc.), the size and orientation of the indication, and any fitness-for-service evaluation the engineer chooses to apply.
What other NDT concepts should I read alongside Delamination?
The most directly related entries in this glossary are "composite", "lamination", "separation"; reading those together gives you the surrounding vocabulary used in inspection reports and procedures.