Plastics, rubber and composites
Composite manufacturing (FRP, GRP, CFRP): what goes wrong and where to inspect
Glass and carbon fibre reinforced plastics form boat hulls, wind blades, tanks, vehicle panels and aerospace structures.
01How the process works
Fibres are placed in a mould as mats, fabrics or prepreg and impregnated with resin by hand lay-up, vacuum infusion, resin transfer moulding or filament winding, then cured at room temperature, in ovens or autoclaves.
Laminate quality depends on fibre content, void content, ply orientation and cure. Delaminations and dry spots are internal and need tap testing or ultrasonic inspection; witness panels prove mechanical properties.
- Mould preparation. Release agent, gel coat.
- Lay-up. Plies placed to the lay-up schedule.
- Impregnation. Resin infused or injected.
- Cure. Room temperature, oven or autoclave cure.
- Trim and inspect. Trimming, NDT, witness panel tests.
02What typically goes wrong
| Defect | Typical cause | How it is found |
|---|---|---|
| Voids and dry spots | Infusion, vacuum leaks | Ultrasonic, visual |
| Delamination | Contamination, impact, cure | Tap test, ultrasonic |
| Wrong ply orientation | Lay-up error | Lay-up records, burn-off test |
| Undercure | Mix ratio, temperature | Barcol hardness, DSC |
| Gel coat defects | Application | Visual |
| Fibre wrinkles | Lay-up handling | Visual, section |
03Where an inspector should look
Before production
- Lay-up schedule and materials
- Resin and fibre certificates
- Witness panel plan
During production
- Ply count and orientation
- Vacuum and temperature records
After production
- NDT (tap, ultrasonic)
- Barcol hardness
- Witness panel mechanical tests
04Standards and references
ISO 1172 (glass content), ISO 14125 (flexural properties), EN 13121 (GRP tanks), class society rules for marine composites.
Standards are named for orientation. The applicable edition and acceptance criteria are those in your contract and specification.