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= Expand/Improve NDE Section in Article on Testing of Advanced Thermoplastic Composite Welds = Compare with current Wikipedia article on Testing_of_advanced_thermoplastic_composite_welds

 DRAFT for Testing of advanced thermoplastic composite welds 

Many of the NDT methods available for testing of thermoplastic composite base materials can be used, in some cases with modifications, for welds in thermoplastic composites as well. Some national and international standards exist   for the inspection of the base materials, albeit not necessarily for the welds in those materials.

The methods include:


 * Visual Inspection is typically the first option for any attempt at NDT, being the least expensive and usually requiring few if any special tools. Defects on the surfaces of thermoplastic composite welds can be detected visually if they are of sufficient size. Weld defects such as misalignment, porosity, lack of fusion and degradation of the matrix and/or fibers may be visually apparent.  Subsurface defects would not necessarily be visible, unless the composite matrix was nearly transparent and the embedded fibers did not obscure them.


 * Radiographic testing can be performed in any number of ways. Typically low energies are required, 20kV or below, for testing of composites in order to see any detail, which restricts the sources to be used to x-ray sources rather than gamma sources like Ir-192 or Cobalt-60, which tend to have higher energy levels.  Data may be recorded either on film or digitally, using specially developed screens for detecting and saving an image than can be manipulated later with the proper software and hardware.  Because radiographic testing relies on differences in material density to provide an image, resolution of fibers like carbon from the thermoplastic matrix is not always very high, since the density of the plastic does not differ much from that of the carbon filaments.  For digital imaging, the lack of contrast may be dealt with after the radiographic images are taken, using digital imaging software.  Lack of fusion in a thermoplastic composite weld, if perpendicular to the direction of the source of radiation, may be visible by radiographic methods, as well as porosity, voids and possibly either differences in or the absence of fibers in the matrix due to the welding process.


 * Ultrasonic testing, given the right frequencies, equipment and test design, may offer the most detailed NDT information for welded thermoplastic composites. Tests can be done with shear wave or transverse waves, though the composite materials often attenuate the signals significantly and care must be taken to account for this.  Contact methods using either manual or automated transducers coupled to the part being inspected or non-contact methods using water immersion or a bubbler (i.e a continuous stream of water through which the ultrasound passes to get to the part being tested) can be effective if designed and calibrated properly.  A-scan data can be used to generate B-scan or C-scan images, which can show the materials being welded at various, discrete depths, if needed, a capability generally not available with radiographic methods.  Ultrasound can detect delaminations, lack of fusion, porosity, voids, inclusions and other defects mostly regardless of their orientation.

Deterring factors include that the method is time consuming and the data are open to some interpretation, requiring skilled technician to perform and interpret the test.




 * Thermography involves testing the part for discontinuities that can be seen by an infrared camera when the part is heated or cooled. It offers a significant improvement on some of the more traditional NDT methods in that it can be used on large areas of, for example, airplane parts or storage tanks.
 * Eddy Current testing has been found to be useful for characterizing the nature of fibers and their orientation in composite materials, though much higher magnetic field frequencies are used to generate the eddy currents used for testing than are typical for metals. Though delaminations in the material were either undetectable or nearly so, more recent research has found that by induction heating the part in addition to exciting an alternating magnetic field, some delaminations could also be detected in CFRP.
 * Laser Shearography involves accurately measuring perturbations in the surfaces of a (usually thin) part under load or strain with the aid of lasers scanning across the surface being evaluated. Voids, pores, delaminations and other defects in composite welds can be detected by this method.
 * Acoustic Emission testing provides qualitative information on the presence and potential growth of defects such as cracks and delaminations in welded composite materials. Typically this method is used to help narrow down the locations(s) of defects in large structures before using a more precise NDT method such as radiography or ultrasonic testing to help localize and characterize the nature of the defect.
 * Laser Shearography involves accurately measuring perturbations in the surfaces of a (usually thin) part under load or strain with the aid of lasers scanning across the surface being evaluated. Voids, pores, delaminations and other defects in composite welds can be detected by this method.
 * Acoustic Emission testing provides qualitative information on the presence and potential growth of defects such as cracks and delaminations in welded composite materials. Typically this method is used to help narrow down the locations(s) of defects in large structures before using a more precise NDT method such as radiography or ultrasonic testing to help localize and characterize the nature of the defect.
 * Acoustic Emission testing provides qualitative information on the presence and potential growth of defects such as cracks and delaminations in welded composite materials. Typically this method is used to help narrow down the locations(s) of defects in large structures before using a more precise NDT method such as radiography or ultrasonic testing to help localize and characterize the nature of the defect.

References:


 * 1) Edwards, G. R. THE NON-DESTRUCTIVE TESTING OF WELDS IN CONTINUOUS FIBRE REINFORCED THERMOPLASTICS, Composites Evaluation, Butterworth-Heinemann, 1987, Pages 3-10.
 * 2) BS EN 13100-1:2017 NON DESTRUCTIVE TESTING OF WELDED JOINTS OF THERMOPLASTICS SEMI-FINISHED PRODUCTS - PART 1: VISUAL EXAMINATION
 * 3) BS EN 13100-2:2004 NON-DESTRUCTIVE TESTING OF WELDED JOINTS IN THERMOPLASTICS SEMI-FINISHED PRODUCTS - PART 2: X-RAY RADIOGRAPHIC TESTING
 * 4) BS EN 13100-3:2004 NON DESTRUCTIVE TESTING OF WELDED JOINTS IN THERMOPLASTICS SEMI-FINISHED PRODUCTS - PART 3: ULTRASONIC TESTING
 * 5) BS EN 13100-4:2012 NON DESTRUCTIVE TESTING OF WELDED JOINTS OF THERMOPLASTICS SEMIFINISHED PRODUCTS - PART 4: HIGH VOLTAGE TESTING
 * 6) Nino, GF, Ahmed, TJ, Bersee, HEN, Beukers, A.,Thermal NDI of resistance welded composite structures.   COMPOSITES PART B-ENGINEERING, Volume 40, April 2009, P 237-248
 * 7) Goeje MPDE,WapenaarKED. Non-destructive inspection of carbon fibre reinforced plastics using eddy current methods. Composites 1992;23 (3):147–57.
 * 8) Detection of delamination in thermoplastic CFRP welded zones using induction heating assisted eddy current testing. Mizukami, K., Mizutani, Y., Todoroki, A., Suzuki, Y. NDT&E International Vol. 74 (2015) pp. 106–111
 * 9) Bossi, R., and Georgeson, G. Nondestructive Testing of Composites. Materials Evaluation, Vol. 76 Issue 8, 1 August 2018, pp. 1049-1060
 * 10) Tushar, C., Ralish, R. Rajesh, M.,  Manikandan, M., Rajapandi, R., Kar, V.R., Jayakrishna, K. Structural Health Monitoring of Biocomposites, Fibre-Reinforced Composites and Hybrid Composites, Chapter 8. Maintenance and monitoring of composites, Woodhead Publishing, 2019, Pages 129-151.