Composites Design and Manufacture (Plymouth University teaching support materials) Non-Destructive Testing (NDT) of advanced composites.

Lecture PowerPoint

Review papers

Subject Index

PowerPoint presentation (778 KB file)

Summerscales [1-3], Burt and Smith [4], Karbhari [5], Fahr [6], Ibrahim [7] and Wang et al [8] have reviewed the use of non-destructive evaluation/examination (NDE) or NDT for fibre-reinforced composite materials/structures.  The applications of NDE/NDT can be considered to fulfil three functions (Table 1):

Table 1:  The functions of NDT

For samples in the laboratory	For structures during manufacture and service
initial inspection of test samples	confirmation of structural integrity.
monitoring sample tests in progress	monitoring components under service loads, especially when changing over time, or verification of structural integrity for life extension.
analysis of reasons for failure	analysis of reasons for failure.

The various techniques can be arranged under three categories and further sub-divided by operating frequency albeit that some overlap may occur (Figure 1):

Figure 1: The various NDT techniques mapped to frequency

In the list which follows, references are provided for recent books or review articles pertinent to each topic.  Working from high frequency/short wavelength, the various techniques in each of the three categories are:

• radiography
• Yeager et al [9] conducted static synchrotron X-ray phase-contrast imaging (PCI) of simulated explosive materials to determine the feasibility of imaging the material response to high-strain rate events (10²–10⁷ s⁻¹) at a microstructural level using the Advanced Photon Source. High spatial resolution (2 μm) with 5 μs exposures allowed features such as interfaces, cracks, voids, and bubbles to be clearly observed with good indications that sufficient phase information can be obtained at even shoreter exposures (e.g. 0.2–0.5 μs).
• x-ray computed microtomography (X-ray μCT) [10-13]
• Straumit et al [14] have used X-ray micro-computed tomography registration with statistical image segmentation of the textile internal architecture to calculate a correct (within the experimental scatter) homogenised textile reinforcement permeability for a non-crimp fabric using computational fluid dynamics with voxel geometrical models.
• Vilà et al [15] conducted in situ synchrotron X-ray computed tomography (SXCT) to study the mechanisms of microfluid flow and void formation during vacuum-assisted infiltration experiments within a fiber tow.
• Coherent x-rays (normally generated in large accelerators) can also be generated by shining coherent 780 nm infrared through a gas-filled tube where the atoms absorb 'bunches' of photons and produce coherent 29 nm x-ray beams.  Tabletop coherent diffractive microscopy with soft x-ray illumination then becomes possible.
• Ptychography is a technique for reforming images from scattered x-rays in a similar manner to other lensless systems.  Image resolution is determined only by the effective numerical aperture of the detector.  The technique recovers the phase of the wave after travel through the specimen with high accuracy and high contrast, and hence can be used for examination of low absorption samples including transparent biological cells.
• ultraviolet
• ultraviolet lights may be used to highlight cracks during dye penetrant inspection.
• visible light
• liquid penetrants and brittle lacquers
• Santos et al [16] used bacterial cell suspensions to identify micro defects on metal (Al, Cu and steel) surfaces in a procedure similar to the dye penetrant technique. The penetration, liquid removal and revelation stages, used Rhodococcus erythropolis bacteria to validate the approach and understand the phenomena involved. The detectability limit was estimated for the test conditions and identified defects with a depth of 2.9, 4.3 and 6.8 µm for steel, Al and Cu, respectively.
• edge replication and the de-ply technique
• optical fringes
• photoelasticity
• optical caustics
• optical coherence tomography (OCT)
• OCT generates high-resolution, cross-sectional tomographic microstructure images for materials (and biological systems) by measurement and image processing of backscattered or backreflected light.  Imaging can be performed in situ in real time with resolution down to ~1 μm [17].
• Liu et al [18] used (OCCT) to study delamination and its propagation in a glass fiber composite wind turbine blade.  The system produces high-resolution cross-sectional and volumetric microstructure images.  Advanced signal processing of the OCT images could reconstruct 3D crack surface profiles to monitor crack growth in the composites.
• coherent light
• interferometry [19, 20]
• holography
• speckle [21]
• shearography
• embedded optical fibres
• In 1978, Hill and Meltz [22] first demonstrated the formation of permanent gratings in an optical fibre. In 1989, Meltz et al [23] reported their pioneering sensors.
• Fibre Bragg Gratings (FBG) are regular periodic changes in the refractive index of the core of an optical fibre over a short distance.  The grating acts as an in-line optical filter (reflector) at a specific wavelength governed by the grating spacing.  Under strain, the spacing changes in a linear manner which can be monitored as a peak in the reflected signal or a trough in the transmitted signal.
• Chirped Fibre Bragg Gratings (CFBG) may be up to 120 mm in length and have a linear increase in the grating spacing.  The reflection peak/transmission trough becomes a plateau corresponding to the length of the FBG.  Under uniform strain, the whole plateau moves, while perturbation on the plateau can indicate the position of damage.
• near-infrared [24]
• see chemical spectroscopy below.
• thermography [25-29]
• externally applied thermal field (EATF, also known as active thermography)
• transient thermography uses halogen lamps, heater mats or hot-air blowers as the heat source
• pulsed thermography uses high-energy flash systems and is normally used with thin samples
• lock-in thermography excites the test object with a periodic harmonically-modulated energy source
• stress generated thermal field (SGTF), including
• vibrothermography (mechanical or ultrasonic excitation), and
• thermosonics (ultrasonic excitation).
• fiber orientation evaluation method for carbon fibre composites based on measurement of anisotropic in-plane thermal diffusivity distribution [30]
• photothermal tomography [31-33]
• Thermal tomography uses a diffusive process with heat propagated through a solid and damped according to the location and shifted in time.  The sample is heated by a lamp or laser to create a time-dependent temperature change.  A focal plane array IR camera, or similar noncontact infrared detector, detects the thermal radiation from the specimen.  This process physics are comparable to transient heat conduction in classical active thermography.  Modern numerical transient heat diffusion models enable reliable detection and identification of defects for 3D defect representation and the determination of the absolute size and depth of defects.
• thermal flow permeametry (TFP)
• Järveläinen et al [34] presented the TFP method in which hot air is flowed through a structure with local temperature variations monitored by a thermal camera.  The system was very sensitive to local permeability changes in the flow channels due to thickness, density and flow channel tortuosity.
• TeraHertz (THz) spectroscopy [35-43]
• The THz (tera = 10¹²) frequency spectrum ranges between 100 GHz - 10000GHz (i.e. between the far-infrared and microwave bands respectively) with wavelengths in the range 100-1000 μm. The technologies are known by various alternative names including sub-millimetre radiation, T-light, T-lux, T-rays and T-waves.  THz techniques are non-invasive, non-contact (no couplant required), non-ionising and have minimal health risks.  The technology is already attracting significant interest in the context of security applications as it penetrates paper, cardboard, plastics, composites and clothing and has high chemical sensitivity so can be used to detect explosives.
• Many polymers are transparent to THz frequencies, while fillers and reinforcements will change the dielectric characteristics.  The refractive index, birefringence and absorption coefficient of polymer composites all increase with rising additive content.   At each concentration, the refractive index and the absorption coefficient are higher when the glass fibre orientation is parallel, rather than perpendicular, to the polarisation of the incident radiation pulse.  THz systems have sub-millimetre transverse resolution and can detect surface defects, hidden voids, delamination and damage.  Depth resolution is better than spatial resolution.
• THz technology is a relatively new field facilitated by the development of femtosecond (fs) pulsed lasers and the semiconductor Quantum Cascade Laser (QCL).  A "most pressing component technology development remains in the area of THz sources [with significant power output]" [Siegel, 35] which may be addressed by the use of "designer spoof surface plasmon structures" to collimate THz laser beams [44].
• Naito et al measured THz time domain spectroscopy (TDS) transmission functions for ~1 mm thick plain weave [45] and 8-harness satin [46] E-glass composites.  The transmittance was ~60% at 0.2 THz and almost zero at 1.0 THz frequency.  The dielectric properties of the composite were obtained in the range 0.2-1.0 THz (Table 2).  The real part of the complex dielectric constant, ε'(ω) had with minimal frequency dependence.  The imaginary part of the dielectric constant, ε"(ω), increased linearly with increasing frequency.  Series models for the dielectric constant and the dielectric loss tangent of the polyimide composite could be roughly estimated using the E-glass fabric and data.

Table 2: Dielectric constants for glass fibre/polyimide composites and the constituents at THz frequencies [46]

Material	Thickness	ε'(ω)	ε'(0.2 THz)	ε'(1.0 THz)
Plain weave (PW) E-glass fabric (IPC 7628 style)	~334 μm	6.53	~0.23	~1.17
Epoxy matrix (ANSI standard FR-4)	n/a	n/a	n/a	n/a
0°/90° six-ply PW/epoxy composite (Vf #50%)	~1.0 mm	~4.45	~0.13	~0.37
Eight-harness satin (8HS) E-glass fabric (MIL 181 style, ~0.117 mm thick)	~117 μm	6.53	~0.23	~1.17
Skybond 703 IST polyimide matrix	~1.0 mm	3.22	~0.12	~0.16
0°/90° four-ply 8HS/PI composite (Vf ~ 43%)	~1.1 mm	~3.87	~0.12	~0.33

• Jordens et al [40] used a THz (200-10000 GHz) TDS system, driven by laser pulses of around 100 fs duration, in transmission mode.  The spectrum had water absorption lines around 550 and 750 GHz.  They examined injection moulded 220 μm glass fibres in a high-density polyethylene matrix at 420 GHz (corresponding to the best signal-to-noise ratio within the range of their system) and were able to determine filler volume fractions and the orientation and proportion of oriented fibres.
• Stoik et al [41] used 0-3 THz TDS in the reflection configuration to study glassfibre-skin honeycomb-core aircraft components.  Surface defects, including paint removal, puncture holes and burn damage were detected using amplitude and phase imaging techniques.  Hidden voids were detected using the relative amplitude of the first Fabry-Perot reflection.
• Chady et al [47] studied impact damaged glassfibre composite samples with three methods: (a) TeraHertz time domain inspection, (b) active thermography with convective excitation and (c) active thermography with microwave excitation.  Of the three techniques, pulsed THz provided defect depth information, high resolution and spectroscopic information.
• Hsu et al [48] used THz TDS to examine composite wind turbines.  For GFRP, the THz pulse was able to detect a smaller crack behing a large crack (unlike ultrasound).  For CFRP, the penetration depth of the radiation was limited and detection of defects was strongly influenced by the relative alignment of the electric field and the fibre orientation.
• Abina et al [49] have demonstrated the THz time-domain spectroscopy and pulsed imaging method to analyse the distribution of voids, inclusions and beads in the macroscopic structure of foamed polymers.  The method has potential to become an important alternative or supplementary technique SEM and X-ray microtomography for the chemical and structural characterization, and to provide insight into the formation process, for these materials.
• Watts et al [50] have developed a low power THz imaging system which uses an ultra-low power (67 nW) THz source, a metamaterial light modulator and single-pixel camera system to computationally reconstruct images.  Scan rates are claimed to be six-times faster than for traditional raster-scan THz devices.
• Dong et al [51] compared the spatial resolution of THz imaging and ultrasonic C-scans.  THz imaging provided higher resolution of both the area and the depth of delaminations.  they recommended that THz imaging can be an alternative or complementary modality to ultrasonic C-scans.
• Mitrofanov [52] proposed and demonstrated a nanostructured photoconductive THz detector able to sample down to a level of λ/150 at 1 THz to detect highly confined evanescent THz fields coupled through a 2 μm aperture and permit higher spatial resolution and higher sensitivity near-field microscopy and time-domain spectroscopy.
• Ryu et al [53] devised a pulsed terahertz time-domain spectroscopy (THz-TDS) imaging system, using reflection mode with a 25° incidence angle, to detect hidden (overlapped) multi-delamination in a hand-laminated prepreg unidirectional glass-fibre reinforced plastic (GFRP) composite laminates.  The model defects were generated using 100μm PTFE film.  Each delamination was analysed for shape (rectangles, circles or triangles) and thickness plus location in the z-direction using THz wave power and phase.  THz image results were compared with those from a 15 MHz ultrasound scanning acoustic microscope with tomographic acoustic micro imaging (TAMI).  The THz-TDS imaging system successfully detected, with location errors below 5%, and imaged the hidden multi-delamination in the GFRP composite laminate.
• Dai et al [54] used a THz nondestructive method to detect delaminations within a multi-layered sample.  Since the air layer at the separation is too thin to detect, they proposed a wavelet transform method to process the 3D THz data and then reconstruct the image to clearly identify and locate the delaminated area.
• Dong et al [55] have used polarization-sensitive THz imaging to characterise sub-surface damage in the first ply of woven carbon fiber-reinforced composite laminates, including matrix cracking, fiber distortion/fracture, and intra-ply delamination.
• Mieloszyk et al [56] used a THz spectroscopy technique to detect and localise glass fibre optics embedded in a glass fibre reinforced polymer.
• A novel approach can produce and control terahertz waves using nanometric materials to produce light from THz waves in a controlled manner [57-58].  The process allows detection of the microscopic composition and spatial spectroscopy of materials at distance without chemical laboratory testing.
• Calvo de la Rosa et al [59] used teraertz pulsed C-scan imaging to determine the process-induced microstructure of 2x2 twill woven glass fabric reinforced polyamide composites.  Parameters measured included inter-yarn distances and fibre-bundle orientation.
• Zhu et al [60] used Terahertz time-domain spectroscopy (THz-TDS) to detect interply disturbances in dry glass fibre preforms before Liquid Composite Moulding (LCM).  The errors on defect lengths, widths, angles and diameters were in the ranges 8–34%, 19–75%, 0.3%–6.7% and 1–10% respectively.
• Zhai et al [61] employed reflective THz imaging to accurately characterize a GFRP laminate containing a delamination.  While traditional methods that rely on experience for manual feature extraction, the proposed methods provide a three-dimensional characterization of GFRP laminates in a noncontact and nondestructive manner.
• Webinar on NDE with THz EM Radiation by David Citrin (Georgia Institute of Technology ~ USA) for Indian Society for Non-destructive Testing.
• microwaves
• Hernandez-Edo et al [62] have used an open-ended microwave resonator to non-destructively quantify the moisture content in either epoxy resin or polyamide-6 (PA6).  The penetration depths for the standing microwaves were ~24 mm in the epoxy or >7.35 mm in the PA6.  The measurements were conducted for unreinforced polymers, not composites.
• Mukherjee et al [63] used time reversal processing to reflection mode microwave data to detect impact damage and drilled holes in GFRP composite structures.
• eddy current
• Heuer et al [64] have reviewed radio-frequency (FR) eddy current testing for fabrics, preforms and CFRP composites.  They report that textural analyses and fault testing can be performed with an image quality up to 500 μm resolution, and that permittivity changes allow the characterisation of the curing process.
• Hughes et al [65] developed a high-frequency (10, 15 or 20 MHz) eddy-current system using a miniature Howland current source (HCS) which can operate in transmit-receive mode. The sensor has been shown to detect small crack-like features on the surface of a carbon fibre composite sample. The pattern of the woven fibre can be seen on the scan.
• Cheng et al [66] ...
• dielectric [67, 68]
• Ye et al [69] have demonstrated the feasibility of a planar Electrical Capacitance Tomography (ECT) system with an electrode geometry that allows near subsurface 3D imaging.
• electric
• corona discharge
• magnetic
• Bo and Runqiao [70] used a superconducting quantum interference device (SQUID) to measure the internal magnetisation curve of CFRP (weakly paramagnetic with relative permeability of ~1.0005-1.0010) at ambient temperature.   The positive and negative magnetisation curve was non-linear with saturation at ~1 Oe magnetic field and minimal hysteresis.  The sensor could detect magnetic anaomalies due to delamination defects.

• ultraviolet
• Raman [71]
• Raman spectroscopy is a form of vibrational spectroscopy due to inelastic scattering of visible light.  The bond vibration must produce a change in the polarisability of the molecule to be Raman active.  Entities with strong Raman responses tend to have weak IR responses and vice versa.
• Raman Explained  (Renishaw plc)
• 2D materials : growth and characterisation of 2D materials beyond graphene  (Renishaw/Oxford Instruments 53"14' webinar)
• infrared (IR)

Table 3: The wave numbers and wavelengths of the three infrared bands


Band	Energy	Wave number (cm-1) [72]	Wavelength (μm) [72]	Wave number (cm-1) [73]	Wavelength (μm) [73]
Near infrared (NIR)	high	14000-4000	0.8-2.5	12820-4000	0.78-3
Mid infrared (MIR)	medium	4000-400	2.5-25	4000-400	3-30
Far infrared	low	400-10	25-1000	400-33	30-300

• stretching and bending vibrations in adjacent atoms (bond deformations) within a polar molecule result in oscillating dipole moments which absorb electromagnetic radiation in the infrared region of the spectrum.  Each chemical bond has a specific frequency and wavelength which corresponds to the energy difference between the excited and ground states.
• the NIR spectrum has numerous bands due to overtones and to combination modes with considerable overlap. This "multicolinearity" must be removed to sensibly interpret the spectrum. For conventional spectral analysis, signal analysis uses derivative methods, Fourier self deconvolution and curve fitting, isotope exchange, polarisation spectra or theoretical frameworks. Two-dimensional (2D) correlation spectroscopy is increasingly used. The third approach is "chemometrics" using multiple linear regression (MLR), principal component analysis (PCA), principal component regression (PCR), partial least squares (PLS) or self-modelling curve resolution (SMCR) [74].
• Heigl et al [75] have reviewed the application of NIR spectroscopy in the context of physico-chemical and morphological parameters for polymeric materials.
• Kulcke et al [76] have described an on-line system for the classification of polymer parts on a conveyor belt for real-time automated industrial polymer waste sorting.
• FTIR spectral bands for natural fibres.
• electron spin resonance
• nuclear magnetic resonance
• Kotsikos et al [77] have used nuclear magnetic resonance imaging to study seawater uptake in marine fibreglass composites.

• scanning acoustic microscopy
• ultrasonics [78]
• ultrasound can have a variety of modes of propagation in a solid:
• Bulk waves
• longitudinal/compression
• transverse/shear
• Surface waves
• P-waves: head waves (pressure waves)
• S-waves: SH or SV (shear waves: horizontal or vertical)
• Rayleigh  Stoneley  creeping waves
• Plate waves
• Lamb  Love  rod waves
• Edge waves [79]
• the SSVC video uses Schlieren photography to visualise ultrasound pulses travelling in a glass block and really helps with understanding the technology (CSHL CD-ROM  OneDrive)
• ultrasound data can be presented in a number of ways:
• A-scan: voltage/time at one position (see Flash Movie animation by Wavelength-NDT)
• B-scan: size and position vs probe movement (see Flash Movie animation by Wavelength-NDT)
• C-scan: attenuation vs x-y position (see Flash Movie animation by Wavelength-NDT)
• D-scan: attenuation vs x-z position
• F-scan: feature scan
• P-scan: projection/tomography
• S-scan: sector scan (phased array technique)
Figure 2: Two photographs of the progress of the meeting flow front from two injection ports located at the centres of the left and lower edges in Resin Transfer Moulding (left).
The top right corner is outside of the moulded plate.  The corresponding C-scan of the cured plate (right: black is most attenuated, white is least attenuated ultrasound).

• phased arrays [80]: transducers containing an array of elements which are individually wired, individually pulsed and where each can be time-shifted relative to other elements of the array by delays accurate to ~2 nanoseconds.
• Olympus have released an eBook on advances in the field of phased array ultrasonic testing (PAUT).
• Smith et al [81] have recently presented the state-of-the-art in automated analysis and advanced defect detection from ultrasonic scans of composites.
• Drinkwater [82] has published Ultrasonic Array Imaging for Non-Destructive Testing.
• acousto-ultrasonics
• Acousto-Ultrasonics (AU) is the combination of ultrasonic signal injection and acoustic-emission monitoring of the complete sample or component, originated by Alex Vary at NASA Lewis Research Center.  Early equipment was designed to return a "stress wave factor" (SWF).
• A-Ultra is a portable acousto-ultrasonics device used to ensure that military personnel have uncompromised body armour protection sensors to check for damage in just 10 seconds, saving time and money and making such inspections simple in even remote locations [83].
• acoustic emission
• Kaiser effect
• Felicity effect
• CARP (Committee on Acoustic Emission from Reinforced Plastics) procedures, for example:
• ASTM E976-15 Standard guide for determining the reproducibility of acoustic emission sensor response.
• ASTM E1067/E1067M-18 Standard practice for acoustic emission examination of fibreglass reinforced plastic resin (FRP) tanks/vessels.
• ASTM E1118/E1118M-16 Standard practice for acoustic emission examination of reinforced thermosetting resin pipe (RTRP).
• ASTM E2076/E2076M-15 Standard test method for examination of fiberglass reinforced plastic fan blades using acoustic emission.
• ASTM E2191/E2191M-16 Standard test method for examination of gas-filled filament-wound composite pressure vessels using acoustic emission.
• ASTM E2478-11 Standard practice for determining damage-based design criteria for fiberglass reinforced plastics (FRP) materials using acoustic emission.
• ASTM F914/F914M-18 Standard test method for acoustic emission for insulated and non-insulated aerial personnel devices without supplemental load handling attachments.
• ASTM F1430/F1430M-18 Standard test method for acoustic emission testing of insulated and non-insulated aerial personnel devices with supplemental load handling attachments.
• ASTM F1797-18 Standard test method for acoustic emission testing of insulated and non-insulated digger derricks.
• amplitude and frequency analysis
• acoustic emission source location (AESL) [84]
• Li and Dong [85] developed a novel efficient closed-form solution (ECS) for acoustic emission source location (AESL) in three-dimensional complex material structures using time difference of arrival (TDOA) measurements.
• acoustic emission tomography (AET) [86]
• acoustic tomography involves sending multiple acoustic sound waves, generated by a series of transducers at various locations, through an object at many different angles.  The sound waves are collected at receivers (which are normally dual function transmit-receive transducers).  If the number of transducers is N, then N² ray paths result.  With at least four transducers, it is then possible to solve the nonlinear system of equations to derive three orthogonal source coordinates (x, y, z) and the source time (t).  An image can then be computed to represent the physical characteristics of the object (e.g. attenuation or wave speed in transmission tomography or acoustic impedance mismatch in reflection tomography.  Two major classes of tomographic reconstruction techniques exist: (i) Fourier transform based methods, and (ii) iterative procedures.
• The concept of acoustic tomography can be easily adapted to use acoustic emission events as tomographic sources and become Acoustic Emission Tomography.  Acoustic sources may be produced artificially (calibration sources, hammer blows or transducers) or may be stress generated through damage propagation.  AET can "see" both active and non-active (acoustically "passive") regions within the specimen.  AET is a purely algorithic extension of traditional AE systems using exactly the same data.
• fracto-emission
• fracto-emission (FE) is the emission of particles (electrons, ions, neutral species and photons) as well as long wavelength electromagnetic radiation.  FE is complementary to acoustic emission, insofar as it requires failure of some part of the material.  The practical application of these techniques is limited.
• Aman et al [87] monitored failure of a 15 layer bidirectional 0°/90° 6K Tenax HTS carbon fibre/epoxy composites during crushing with a glass ball.  The composites were carrying an electric current supplied by a standard 9V battery. Microwave emissions over a frequency range 8-12 GHz were received by an X-band horn antenna, amplified by 25 dB using an Agilent 83107A with the HF signals converted to video signals by a 8473C coaxial diode.  The duration of the microwave emission impulses was on a nanosecond timescale.  The number of detected impulses was three orders of magnitude smaller than the estimate for the total number of broken fibres, although te system is working close to the limits of detection.
• vibration and damping [88, 89]
• wheel tap
• coin tap.

Summerscales [1] presented a preliminary assessment of the capabilities of the various NDT techniques for the detection of a variety of composites issues in the Table below where green indicates an established technology and orange indicates a technique with limited applicability or potential for development:

Baker et al [90] have similarly summarised the advantages and disadvantages of conventional NDI techniques in Table 1 (only accessible with a journal subscrption) of their paper.

Signal processing and Probability of Detection (POD)

Leavey et al [91] have presented an introductory tutorial on the use of wavelet analysis for signal processing in this context.  Yella et al [92] have recently reviewed the use of artificial intelligence techniques for the automatic interpretation of data from NDT.  Addin et al [93] have reviewed the use of neural networks in the prediction and detection of failures in laminated composite materials, with specific reference to NDT by vibration mode and frequency, use of Lamb waves and electrical conductivity.  Gros [94, 95] has reviewed the use of data fusion for handling multiple data sources in NDT.

Backman [96, 97] has considered how safety methods can be made available to the engineering community without requiring huge statistical databases for use in reliability analysis.  The book considers the probability of safe flight, and is thus perhaps essential reading for those involved in aerospace structural design, although much of the analysis is undertaken at the level of orders of magnitude rather than in fine detail.  Of particular relevance here is the consideration of probability of detection against damage size for various regions [Figure 3] and the ability of each non-destructive testing technique relative to the respective damage sizes.  Wall et al [98] have considered probability of detection (POD) data in industrial applications and suggest that could be benefits from the use of simple POD generator models validated against experimental data with a more structured and standardised approach to the use and correction of POD data (using expert judgement, modelling and signal-based methods).

Figure 3: Probability of Detection (POD) against damage size (after Backman [96]).

The various NDT techniques have an important role to play in both Condition Monitoring (CM) and Structural Health Monitoring (SHM) which are covered in a lecture delivered to both module MECH512 Design for Structural Integrity and MECH 513 Smart Materials and Intelligent Structural Systems.

Resources:

• HIGHLY RECOMMENDED: Seeing is believing: basic ultrasonics, Services Sound and Vision Corporation (Ministry of Defence), 1987.  UPmedia (requires login).
  This recording uses Schlieren photography to visualise ultrasound pulses travelling in a glass block.
• Characterisation of surface and coatings

References:

1. John Summerscales, Non-destructive testing of advanced composites: a review of recent advances, British Journal of Non-Destructive Testing, November 1990, 32(11), 568-577.  MooDLE: This version has additional images.
2. J Summerscales, Non-destructive measurement of the moisture content in fibre reinforced plastics, British Journal of Non-Destructive Testing, February 1994, 36(2), pp 64-72.  MooDLE.
3. J Summerscales, Manufacturing Defects in Fibre Reinforced Plastics Composites, Insight, December 1994, 36(12), pp 936-942.  MooDLE.
4. EA Birt and RA Smith, A review of NDE methods for porosity measurement in fibre-reinforced polymer composites, Insight - Non-Destructive Testing and Condition Monitoring (The Journal of the British Institute of Non-Destructive Testing), November 2004, 46(11), 681-686.  made available to University of Plymouth students with the kind permission of the British Institute of Non-Destructive Testing, the authors and QinetiQ Ltd.  MooDLE.
5. VM Karbhari (editor), Non-destructive evaluation (NDE) of polymer matrix composites, Woodhead Publishing, Cambridge, 2013. ISBN 1987-0-85709-344-8. ISBN 978-0-85709-355-4 (ebook).  PU CSH Library.
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16. TG Santos, RM Miranda and CCCR de Carvalho, A new NDT technique based on bacterial cells to detect micro surface defects, NDT&E International, April 2014, 63, 43-49.
17. JG Fujimoto, C Pitris, SA Boppart and ME Brezinski, Optical Coherence Tomography: an emerging technology for biomedical imaging and optical biopsy, Neoplasia, January-April 2000, 2(1-2), 9–25.
18. Ping Liu, RM Groves and R Benedictus, 3D monitoring of delamination growth in a wind turbine blade composite using Optical Coherence Tomography, NDT&E International, June 2014, 64, 52-58.
19. H Shang and J Gao, Theories and industrial applications of optical interferometric NDT techniques: a review, Insight, May 2009, 51(5), 240-251.
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41. C Stoik, M Bohn and J Blackshire, Nondestructive evaluation of aircraft composites using reflective terahertz time domain spectroscopy, NDT&E International, March 2010, 43(2), 106-115.
42. K Fukunaga and M Picollo, Terahertz time domain imaging for cultural heritage, Insight, March 2014, 56(3), 142-146.
43. J Moody, Moody's memoranda, NDT News, November 2015, (147), 8.
44. N Yu, QJ Wang, MA Kats, JA Fan, SP Khanna, L Li, AG Davies, EH Linfield and F Capasso, Designer spoof surface plasmon structures collimate terahertz laser beams, Nature: Materials, September 2010, 9, 730-735.
45. K Naito, Y Kagawa, S Utsuno, T Naganuma and K Kurihara, Dielectric properties of woven fabric glass fiber reinforced polymer-matrix composites in the THz frequency range, Composites Science and Technology, September 2009, 69(11-12), 2027-2029.
46. K Naito, Y Kagawa, S Utsuno, T Naganuma and K Kurihara, Dielectric properties of eight-harness-stain fabric glass fiber reinforced polyimide matrix composite in the THz frequency range, NDT&E International, July 2009, 42(5), 441-445.
47. T Chady, P Lopato and B Szymanik, TeraHertz and thermal testing of glass-fiber reinforced composites with impact damages, Journal of Sensors, 2012, Article ID 954867.
48. DK Hsu, K-S Lee, J-W Park, Y-D Woo and K-H Im, NDE inspection of terahertz waves in wind turbine composites, International Journal of Precision Engineering and Manufacturing, July 2012, 13(7), 1183-1189.
49. A Abina, U Puc, A Jeglič and A Zidanšek, Structural analysis of insulating polymer foams with terahertz spectroscopy and imaging, Polymer Testing, June 2013, 32(4), 739-747.
50. CM Watts, D Shrekenhamer, J Montoya, G Lipworth, J Hunt, T Sleasman, S Krishna, DR Smith and WJ Padilla, Terahertz compressive imaging with metamaterial spatial light modulators, Nature Photonics, 2014.
51. J Dong, B Kim, A Locquet, P McKeon, N Declercq and DS Citrin, Nondestructive evaluation of forced delamination in glass fiber-reinforced composites by terahertz and ultrasonic waves, Composites Part B: Engineering, 15 September 2015, 79, 667-675.
52. O Mitrofanov, I Brener, TS Luk and JL Reno, Photoconductive terahertz near-field detector with a hybrid nanoantenna array cavity, ACS Photonics, 19 November 2015, 2(12), 1763–1768.
53. C-H Ryu, S-H Park, D-H Kim, K-Y Jhang and H-S Kim, Nondestructive evaluation of hidden multi-delamination in a glass-fiber-reinforced plastic composite using terahertz spectroscopy, Composite Structures, 15 November 2016, 156, 338-347.
54. B Dai, P Wang, T-Y Wang, C-W You, Z-G Yang, K-J Wang and J-S Liu, Improved terahertz nondestructive detection of debonds locating in layered structures based on wavelet transform, Composite Structures, 15 May 2017, 168, 562-568.
55. J Dong, P Pomarè, L Chehami, A Locquet, F Meraghni, NF Declercq and DS Citrin, Visualization of subsurface damage in woven carbon fiber-reinforced composites using polarization-sensitive terahertz imaging, NDT & E International, October 2018, 99, 72-79.
56. M Mieloszyk, K Majewska and WOstachowicz, Application of THz spectroscopy for localisation of fibre optics embedded into glass fibre reinforced composite, Composite Structures, 1 February 2019, 209, 548-560.
57. S Keren-Zur, M Tal, S Fleischer, DM Mittleman and T Ellenbogen, Generation of spatiotemporally tailored terahertz wavepackets by nonlinear metasurfaces, Nature Communications, 2019, 10, article 1778.
58. S Joseph, Manipulating terahertz waves with nanomaterials, Materials World, February 2020, 28(2), 17.
59. J Calvo de la Rosa, P Pomarède, P Antonik, F Meraghni, DS Citrin, D Rontani and A Locquet, Determination of the process-induced microstructure of woven glass fabric reinforced polyamide 6.6/6 composite using terahertz pulsed imaging, NDT & E International, June 2023, 136, 102799.
60. P Zhu, H Zhang, F Robitaille and X Maldague, Terahertz time-domain spectroscopy for the inspection of dry fibre preforms, NDT & E International, July 2024, 145, 103133.
61. M Zhai, A Locquet and DS Citrin, Terahertz nondestructive layer thickness measurement and delamination characterization of GFRP laminates, NDT & E International, September 2024, 146, 103170.
62. E Hernandez-Edo, M Hoffmann, M Amkreutz and B Mayer, Characterization of a non-destructive microwave technique for the detection and quantification of water in thermosets and thermoplastics, NDT & E International, December 2015, 76, 9-16.
63. S Mukherjee, A Tamburrino, M Haq, S Udpa and L Udpaa, Far field microwave NDE of composite structures using time reversal mirror, NDT&E International, January 2018, 93, 7-17.
64. H Heuer, M Schulze, M Pooch, S Gabler, A Nocke, G Bardl, Ch Cherif, M Klein, R Kupke, R Vetter, F Lenz, M Kliem, C Bulow, J Goyvaerts, T Mayer and S Petrenz, Review on quality assurance along the CFRP value chain: non-destructive testing of fabrics, preforms and CFRP by HF radio wave techniques, Composites Part B: Engineering, August 2015, 77, 494-501.
65. F Hughes, R Day, N Tung and S Dixon, High-frequency eddy current measurements using sensor-mounted electronics, Insight - Non-Destructive Testing and Condition Monitoring, November 2016, 58(11), 596-600.
66. Jun Cheng, J Qiu, H Ji, E Wang, T Takagi and T Uchimoto, Application of low frequency ECT [eddy current testing] method in noncontact detection and visualization of CFRP material, Composites Part B: Engineering, 1 February 2017, 110, 141–152.
67. RA Pethrick and D Hayward, Real time dielectric relaxation studies of dynamic polymeric systems, Progress in Polymer Science, 2002, 27(9), 1983-2017.
68. Koji Asami, Characterization of heterogeneous systems by dielectric spectroscopy, Progress in Polymer Science, 2002, 27(8), 1617-1659.
69. Z Ye, R Banasiak and M Soleimani, Planar array 3D electrical capacitance tomography, Insight, December 2013, 55(12), 675-680.
70. H Bo and Y Runqiao, Micro-magnetic NDT for delamianation defects in carbon fibre-reinforced plastic, Insight, February 2015, 57(2), 74-77.
71. Gi Xue, Fourier transform Raman spectroscopy and its application for the analysis of polymeric materials, Progress in Polymer Science, 1997, 22(2), 313-406.
72. M Reichenbächer and J Popp, Vibrational Spectroscopy, Challenges in Molecular Structure Determination, Springer-Verlag, Berlin Heidelberg, 2012, 63-143.
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75. N Heigl, CH Petter, M Rainer, M Najam-ul-Haq, RM Vallant, R Bakry, GK Bonn and CW Huck, Review: Near infrared spectroscopy for polymer research, quality control and reaction monitoring, Journal of Near Infrared Spectroscopy, 2007, 15(5), 269–282.
76. A Kulcke, C Gurschler, G Spöck, R Leitner and M Kraft, On-line classification of synthetic polymers using near infrared spectral imaging, Journal of Near Infrared Spectroscopy, 2003, 11(1), 71–81.
77. G Kotsikos, AG Gibson and J Mawella, Assessment of moisture absorption in marine GRP laminates with aid of nuclear magnetic resonance imaging, Plastics, Rubber and Composites, 2007, 36(9), 413-418.
78. BW Drinkwater and PD Wilcox, Ultrasonic arrays for non-destructive evaluation: a review, NDT & E International, 2006, 39(7), 525-541.
79. JB Lawrie and J Kaplunov, Edge waves and resonance on elastic structures: an overview, Mathematics and Mechanics of Solids, 2012, 17 (1), 4-16.
80. M Moles, N Dubé, S Labbé and E Ginzel, Review of ultrasonic phased arrays for pressure vessel and pipeline weld inspections, Journal of Pressure Vessel Technology, August 2005, 127(3), 351-356.
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82. B Drinkwater, Ultrasonic Array Imaging for Non-Destructive Testing, UK Forum for Engineering Structural Integrity (FESI), Preston, 2021. ISBN 978-09935485-4-3.
83. Anonymous, Innovation Watch: Ultrasonic armour inspection, Ingenia, June 2019, 79, 47.
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89. Y Zou, L Tong and GP Steven, Vibration-based model-dependent damage (delamination) identification and health monitoring for composite structures - a review, Journal of Sound and Vibration, 2000, 230(2), 357-378.
90. A Baker, AJ Gunnion and J Wang, On the certification of bonded repairs to primary composite aircraft components, The Journal of Adhesion, available online 01 April 2014.
91. CM Leavey, MN James, J Summerscales and R Sutton, An introduction to wavelet transforms: a tutorial approach, Insight, May 2003, 45(5), 344-353.  MooDLE: This paper describes recent developments in signal processing.
92. S Yella, MS Dougherty and NK Gupta, Artificial intelligence techniques for the automatic interpretation of data from non-destructive testing, Insight, January 2006, 48(1), 10-20.
93. AO Addin, SM Sapuan, E Mahdi and M Othman, Prediction and detection of failures in laminated composite materials using neural networks - a review, Polymers and Polymer Composites, 2006, 14(4), 433-441.
94. XE Gros, NDT Data Fusion, Butterworth-Heinemann, 1997.  ISBN 0-340-67648-5.  PU CSH Library.
95. XE Gros, Applications of NDT Data Fusion, Kluwer Academic Publishers, Dordrecht (NL), 2001.  ISBN: 0-7923-7412-6.
96. Bjorn Backman, Composite Structures, Design, Safety and Innovation, Elsevier, Amsterdam, 2005.  ISBN 0-08-044545-4.  PU CSH Library
97. Bjorn Backman, Composite Structures: Safety Management, Elsevier Science, May 2008. ISBN-13: 978-0-08-054809-8.
98. M Wall, SF Burch and J Lilley, Review of models and simulators for NDT reliability (POD), Insight, November 2009, 51(11), 612-619.

Further reading (reverse chronological order)

1. A Fahr, Aeronautical Applications of Non-destructive Testing, Destech Publications, lancaster PA, 2014.  ISBN 978-1-60595-120-1.
2. VM Karbhari, Non-destructive evaluation (NDE) of polymer matrix composites: techniques and applications, Woodhead Publishing, Cambrdge, 2013.  PU CSH Library
3. MA Drewry and GA Georgiou, A review of NDT techniques for wind turbines, Insight, March 2007, 49(3), 137-141.
4. BW Drinkwater and PD Wilcox, Ultrasonic arrays for non-destructive evaluation: a review, NDT & E International, 2006, 39(7), 525-541.
5. David J Smith, Reliability, Maintainability and Risk - Practical Methods for Engineers including Reliability Centred Maintenance and Safety-Related Systems - seventh edition, Elsevier, 2005.  ISBN13: 9780-7506-6694-7.  PU CSH Library.
6. RA Pethrick and D Hayward, Real time dielectric relaxation studies of dynamic polymeric systems, Progress in Polymer Science, 2002, 27(9), 1983-2017.
7. Koji Asami, Characterization of heterogeneous systems by dielectric spectroscopy, Progress in Polymer Science, 2002, 27(8), 1617-1659.
8. R Chandra, SP Singh and K Gupta, Damping studies in fiber-reinforced composites: a review, Composite Structures, 1999, 46(1), 41-51.
9. Gi Xue, Fourier transform Raman spectroscopy and its application for the analysis of polymeric materials, Progress in Polymer Science, 1997, 22(2) 313-406.
10. J Summerscales, Non-Destructive Testing of Fibre Reinforced Plastics Composites - volume 2, Elsevier Applied Science Publishers, Barking, 1990.  ISBN 1-85166-468-8. Now distributed by Springer.  PU CSH Library.
11. J Summerscales, Non-Destructive Testing of Fibre Reinforced Plastics Composites - volume 1, Elsevier Applied Science Publishers, Barking UK, September 1987.  ISBN 1-85166-093-3. Now distributed by Springer.  PU CSH Library.

The British Institute of Non-Destructive Testing has published a useful series of introductory texts under the title NDT Fundamentals,
The ultrasonics papers are made available here to University of Plymouth students with the kind permission of the British Institute of Non-Destructive Testing and of the author.

• MooDLE:  B Venkataraman and B Raj, Performance parameters for thermal imaging systems, Insight, August 2003, 45(8), 531-535.
• MooDLE:  JC Drury, Ultrasonics, part 1: basic principles of sound, Insight, November 2004, 46(11), 650-652.
• MooDLE:  JC Drury, Ultrasonics, part 2: properties of sound waves, Insight, December 2004, 46(12), 762-764.
• MooDLE:  JC Drury, Ultrasonics, part 3: refraction and mode conversion, Insight, January 2005, 47(1), 44-46.
• MooDLE:  JC Drury, Ultrasonics, part 4: transducers for generating and detecting sound waves, Insight, February 2005, 47(2), 98-100.
• MooDLE:  JC Drury, Ultrasonics, part 5: probe construction, Insight, March 2005, 47(3), 168-171.
• MooDLE:  JC Drury, Ultrasonics, part 6: pulse-echo flaw detector, Insight, April 2005, 47(4), 236-238.
• MooDLE:  JC Drury, Ultrasonics, part 7: the ultrasonic beam, Insight, May 2005, 47(5), 297-299.
• MooDLE:  JC Drury, Ultrasonics, part 8: calibration and reference standards, Insight, June 2005, 47(6), 364-365.
• MooDLE:  JC Drury, Ultrasonics, part 9: compression wave techniques, Insight, July 2005, 47(7), 425-428.
• MooDLE:  JC Drury, Ultrasonics, part 10: shear wave techniques, Insight, August 2005, 47(8), 495-499.
• MooDLE:  JC Drury, Ultrasonics, part 11: surface and TOFD techniques, Insight, September 2005, 47(9), 569-571.
• MooDLE:  S Cochran, Ultrasonics, part 12: fundamentals of ultrasonic phased arrays, Insight, April 2006, 48(4), 212-217.
• MooDLE:  J Hansen, The Eddy current inspection method, part 1: history and electrical theory, Insight, May 2004, 46(5), 279-281.
• MooDLE:  J Hansen, The Eddy current inspection method, part 2: the impedance plane and probes, Insight, June 2004, 46(6), 364-365.
• MooDLE:  J Hansen, The Eddy current inspection method, part 3: instrumentation and applications, Insight, July 2004, 46(7), 414-416.
• MooDLE:  J Hansen, The Eddy current inspection method, part 4: applications, practical testing and advanced concepts, Insight, August 2004, 46(8), 480-483.

FREE three-part whitepaper series for thermographers:

• M Hovens, How to be successful in building thermography: the do's and don'ts in a crime scene case study, Infrared Training Centre (ITC) User Conference, Stockholm, 24 September 2014, 161-170.
• Sreten Dobrivojevic, Detection Partial Discharges on High Voltage Equipment with Infrared Thermography, Infrared Forum Research and Applications (InfraR&D), 47-56.
• M Scott and D Kruger, Infrared Thermography as a Diagnostic Tool for Subsurface Assessments of Concrete Structures, Infrared Training Centre (ITC) User Conference,Stockholm, 24 September 2014, 155-160.