ndt

1. A Seminar On
Recent Advances in the NDT of
Composite Materials
By
Bhavya K
2nd Sem.,AME,M.Tech.
NITK,Surathkal

2. Contents
 Introduction
 Visual testing
 Liquid penetrants
 Radiography
 High frequency ultrasonics
 Low frequency ultrasonics
 Fokker bond tester
 Infra-red thermography
 Holography
 Acoustic emission
 Other NDT techniques
 Emerging technologies and challenges
 Conclusion

3. Introduction
 Greater specific strength
 Higher modulus
 Better thermal properties

4. Applications

5. Defects
Ply collation:
Foreign objects
Ply misorientations
Ply wrinkling
Curing:
Porosity & voids
Delaminations
Matrix microcracking
Adhesive bonding:
Adhesive unbonds
Foreign objects
Core defects
Machining & assembly:
Delaminations
Surface nicks
Scratches
In-service:
Delaminations
Moisture/temperature
degradation

6. VT & LPT
 VT : Defects exposed to the surface
Magnifying glasses
High intensity illuminators
Fibroscopes using optical fibres
 LPT : Discontinuities open to the surface
Cracks,porosity & delaminations exposed to the
outer surface of FRP materials-dye penetrant tests
Cheap & easy
Minimum amount of inspection time

8. Radiography
 Internal structure is seen by
exposing the sample to a
source of penetrating radiation
& recording the shadow image
on a radiographic film placed
on the opposite side
 X-rays & Gamma rays
 Relaxation of fibres,foreign
inclusions,delaminations,intern
al cracks,voids etc.
 The thickness of FRP laminates
& the exact no. of plies & their
orientation can also be
determined

9. Real-time X-ray
 Very fast,more accurate location & sizing of
the defects

10. Microfocus X-ray
 Small source,
great
magnification
ranging from
3X to 1000X

11. Computed tomography
 Computer processing of the distribution of
the X-ray transmission coefficient in a
structure using a series of viewing angles
 Resin content in FRP specimens
 Gamma rays Backscatter technique-uses
Compton Backscatter phenomenon
 Beta particles transmitted are counted and
then the attenuation studied
 The difference in absorption co-efficients
between the reinforcement and the resin
for beta particles

12. High Frequency Ultrasonics
 High energy sound
waves
 Piezo-electric
transducers
 Cathode-ray tube
 Pulse-echo & through
transmission methods
 Disbands,voids &
cracks
 Characterisation
studies of composites

13. Low Frequency Ultrasonics
 Ultrasonic frequencies of the order of 25KHz
 Probes are pointed in shape
 No liquid couplant
 Phase & amplitude changes
 Locating & measuring the extent of debonds
Fokker bond tester:
 Bond strength within an accuracy of +5%
 Honeycomb sandwich CFRP products
 Variation in US resonance frequency due to the
effect of loading on the transducer

14. Infra-red Thermography
 Space applications
 Very fast,& non-contact
method
 Large objects which are
inaccessible
 Delamination,debonds,
internal voids

15. Holography
 Recording &
reconstruction of an
optical wavefront
 Duplicates the original
wrt both amplitude &
phase distribution
 Stored in a sensitive
photographic plate
(hologram)
 Sub-surface defects in
the FRP materials

16. Acoustic Emission
 Proof pressure testing of composite
pressure vessels used in space
applications
 Detects dynamic flaws
 Can predict burst pressure to a high level
of accuracy

17. Using EMATs
 Requires no couplant,noncontact
 Measurements can be done with high degree of
reproducibility
 Graphite-epoxy,glass-epoxy,CMC
 Detection of mechanical anisotropy,skin-core
separation of a honeycomb sandwich structure

18. Laser shearography
Disbond indication

19. Industrial applications of shearography
in inspection of aircraft components
Helicopter rotorblade inspection system View inside the vacuum chamber
withrotorblade in testing position
Automatic shearography system for abradable
seals inspection
Portable shearography system for field
inspection of composite materials

20. Columbia accident
 high temperature degradation of carbon-
carbon composites
 pinholes could have led to a weakening of
leading edge wing panels made of carbon-
carbon composite
 the panels could have been susceptible to
damage by foam debris that hit the
shuttle's left wing after liftoff.

21. Other NDT Techniques
 Microwave techniques,eddy current
techniques,liquid crystals,nuclear magnetic
resonance principles,dry & air coupled
ultrasonics,cure monitoring using
dielectrometry & ultrasonics,ultrasonic
tomography,laser ultrasonics etc.

22. Emerging Technologies &
Challenges
 Computer simulation models,neural
networks,data fusion & inversion techniques
 Challenges:defect characterisation
material property evaluation
rapid scanning of large areas
smart structures application
residual stress measurement
weathering & corrosion damage
assessment

23. Conclusion
 Adoption of NDT technique depends on a
no. of parameters like minimum
detectable flaw size & thickness of the
part,type & direction of flaw,instrument
availability & ease of implementing
operation
 Used in conjunction to bring out the most
successful evaluation of a composite
structure

24. References
 By Thomas C. Koshy
 www.laser-ndt.co.uk/ images/laser-
shearography.jpg
 www.umaine.edu