DIC Course: Lab Sessions

Lab session A - Details

Part I: Camera set-up and imaging (duration:1h30)

Objectives

  • Set-up camera and get familiar with concepts like field of view, depth of field, object distance, resolution , ...
  • Understand relationship between object distance and magnification for fixed focal length. 
  • Understand relationship between lighting, aperture and exposure time.
  • Understand relationship between magnification and aliasing. Impact of image prefiltering.
  • Record images for different configurations. Draw histograms. Evaluate sensor noise.
  • Make report.

Competencies

  •  The trainee is able to  prepare a DIC experiment with care by selecting the appropriate combination of camera, lenses, light,  spatial resolution and gets familiar with aliasing problems.

 

Part II: Speckle pattern generation and specimen preparation (duration:1h)

Objectives

  • acquire some basic skills for pattern generation by spray painting
  • explore the possibilities of bonded paper with printed patterns.
  • practicing with silk printing, air brushing, ...

Competencies

  • The trainee knows how to attach a good speckle pattern

Lab session B - Details

Part I:  Compression test on a circular disc  (Brazilian disk setup) (duration:1h30)

Objectives

  • Perform compression tensile test in elastic range. Record a few images during the loading.
  • Compare to analytical solution

Competencies

  • resolution vs. spatial resolution in practice

Part II: Disk in inflation: stereo image correlation (duration:1h30)

Objectives

  • Operate calibration with target that fits field of view. Check whether the calibration is done well via epipolar constraint and MatchID calibration platform
  • Validate the cross camera matching by reconstructing the initial shape of undeformed specimen. As such, the calibration, speckle pattern and noise can be checked before the real test takes place.
  • circular plate clamped at its edges and submitted to a uniform pressure at the bottom surface. For small deformations there is a closed form solution.  Images captured at larger deformations give then a qualitative view of the deformation process.

Competencies

  •  The trainee knows how to perform a good calibration
  •  The trainee is familiar with setting up a stereovision system and perform the synchronized image registration

DIC Course: Data processing

Data processing 1 Simulated speckle images (duration : 5h00) - Details

Objectives

  • Learn how to use the MatchID 2D software
  • Process simulated images
  • Understand the effect of spatial resolution (without noise) by playing with subset size.
  • Understand the effect of noise on displacements and strain.
  • Understand the effect of smoothing on resolution and spatial resolution ( strain window dimensions)

Competencies

  • The trainee knows how to process images in a DIC system and is familiar with concepts as subset size, step size and strain window size.

Data processing 2 Experimental speckle images ( duration : 4h30) - Details

Objectives

  • Process experimental images: determine subset size, step and strain window size
  • Work out displacement map for two static images of the dogbone specimen, plot obtained strain standard deviation as a function of subset size.
  • Estimate artificial out-of-plane strain fields by processing the translated images, plot obtained strain standard deviation as a function of strain window size.
  • Compare with simulated images results and exact (closed-form) solutions for the disc
  • Extract Young’s modulus, Poisson coefficient and yield stress for dogbone

Competencies

  • Participants know how to process experimental images in a DIC system and are familiar with concepts as subset size, step size and strain window size.
  • Participants are familiar with extracting information from the obtained displacement and strain field data.

Data processing 3 Process  stereo speckle images ( duration : 3 h) - Details

Objectives

  • Demonstrate the MatchID Stereo software for stereo correlation
  • Qualitative assessment: epipolar constraint, 3D displacement and strain fields
  • Coordinate frame selection
  • Eventually comparison to simulated ( FEA) displacement and strain fields

Competencies

  • Participants know how to process images in a stereovision DIC system and are familiar with coordinate frames involved.