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The University of Southampton
Engineering

Structural Imaging and Analysis

Our structural imaging and analysis research focuses on the application of high resolution imaging to assess the performance and characterise the behaviour of materials and structure subject to load.

Over many years a unique capability has been developed in the application of infra-red imaging for stress and damage analysis. This has included a technique known as thermoelastic stress analysis (TSA), where sophisticated image processing routines have enabled date to be obtained at very high resolution to investigate, e.g. behaviour at interfaces in composite materials and in the vicintity of crack tips. Traditional TSA uses a test machine to provide a strain change to elicit the thermoelastic response; a new approached developed at Southampton has enable TSA data to be gathered from transient and resonant excitations making strain based NDE in the field a real possibility. More recently the team have started to develop white light imaging approaches using mainly digital image correlation to extract strain and displacement behaviour. Identification techniques such as the virtual fields method (www.camfit.fr) have been used to extract materials constitutive behaviour directly from strain images. The expertise in infra-red imaging has enabled the group to develop a means of capturing strain and temperature evolutions from high rate events. Access to 3D data from X-ray computed tomography is enabling the development of methodologies for volume-based DIC allowing displacements and strains to be evaluated not only at the surface but the interior of a component.

Thermal Imaging
Thermal Imaging
Infra –red imaging
Infra –red imaging

Infra –red imaging and thermography

  • The system is a Cedip Silver 480 M (now the FLIR SC5000)
  • Array:

– Indium Antimonide (InSb) detector
– 320 x 256 elements
– 30 μm pitch
– ½” chip (12.3 mm diagonal)
– 3-5 μm wavelength band

  • Standard operational range:

– 278 to 583 K
– maximum frame rate: 383 Hz (at full frame)
– sensitivity 4.12 mK / DL (at 298 to 299 K)
– electronic noise ~17 mK

Extensive experience and the ability for perform standard infrared thermography (IRT), thermoelastic stress analysis (TSA), and pulsed or pulse phase thermography (PT/PPT).

Applications include:

  • Thermal imaging of processes (IRT)
  • Identification of damage initiation in structures (IRT)
  • Evaluation of stresses in actual components (TSA)
  • Identification and monitoring of fatigue crack propagation (TSA)
  • Monitoring of damage evolution and damage accumulation within components (TSA)
  • Finite element model validation (TSA)
  • Non-destructive evaluation of composite or metallic samples, or of bonded joints for the identification of defects (PT/PPT)
Strain Maps
Strain Maps

White light imaging for evaluation of displacement and strains

The white light imaging facilities include a large range of high resolution cameras and lenses. The LaVision DaVis 8.0 or MatchID (www.matchid.org) digital image correlation software is typically used to process the image data into displacements and strains. There are also facilities for using other white light techniques, such as the grid method. There is a capability to perform 2 x 3D DIC by synchronising 4 cameras. We have also developed a system to synchronise white light cameras with infra-red systems to obtain simultaneous measures of strain and temperature evolutions.


Cameras:
LaVision 16Mpx camera, 4 x Manta G504B, 2 x E-lite LaVision, SONY XCD-SX910, Motion Pro X3 Plus (high speed)

Lenses:
3 x Sigma 105 mm, 4 x AF NIKKOR 50mm, 1 x AF NIKKOR 28-105mm, 1 x SILL TZM0198 (telecentric lens), 1 x SIGMA 70 - 300 mm (macro lens), Canon MP-E 65mm f/2.8 1-5x (macro lens)

Example applications:

  • Measurement of deformation or strain maps on the surface of a specimen or structure
  • Strain maps of through thickness strains on bonded joints
  • Deformation of face sheets of sandwich structure during failure
  • Strain measurement of composite, metal and foams specimens subjected to high rate loading

Ultrasound System (C-Scan)

This ultrasonic technique can be used as a non-destructive means for detecting damage and defects within a material. The suite includes a range of transducers for use with different materials, thicknesses and probing depths.

Equipment/Software:

Ultrasonic Sciences Ltd (USL) custom built system including:

  • USL C scan and data acquisition software
  • 500MHz analogue - digital converter
  • Range of Transducers including: 2.25, 5, 10, 15, 30 and 50 MHz some focussed and unfocussed.

 

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