DIC Course: Lectures

Lecture 1: Basics of light and imaging (duration:1h30) - Details

Objectives

  •  Review and understanding of basic principles of light
  • Review and understanding of basic principles of imaging system ( pinhole camera, lenses, …)

Contents

  • Basics of light: physical nature (what is light and how to describe it, basic wave equation, amplitude, phase), light spectrum, coherence …
  • Interaction between light and surface: refraction, specular and diffusive reflection.
  • Empty magnification
  • Pixels and aliasing
  • Lighting techniques
  • Interferences, diffraction, fringes, …
  • Imaging:
    •    Principle of lenses
    •    Imaging distance, magnification, focal distance
    •    Field of View, Depth of field, aperture (F-number), exposure time
    •    Spherical and chromatic aberration
    •    Distortion
    •    Zoom lenses, macro lenses, telecentric lenses
  • Technology of CCD and CMOS sensors: construction, fill factor, aliasing, integration time
  • Other sensors (ISIS, ICCD…)
  • Camera technology: digitization, difference between general public and industrial cameras, connection (fire wire, utp …) and drivers, frame grabber, synchronization with other devices. Shuttering.
  • Specificities of  (ultra)high speed cameras: frame rate vs. resolution
  • Image formats (8 bit up to 16 bit, tiff format, including compression)
  • Camera selection

Competencies

  • Knowledge of essential elements of geometrical optics
  • Ability to select appropriate lens for a specific application
  • Ability to select an appropriate camera device for a specific application
Lecture 2: 2D Digital Image Correlation (duration:1h30) - Details

Objectives

  • Outline the basic principles of subset-based digital image correlation to perform displacement measurements.

Contents

  • Basic principles of DIC:  Image matching. Why is a speckle pattern needed ( correspondence problem)? What is subset size and step size (what are their limitations)?   
  • Correlation criterion: Cross correlation vs. Sum of Squared Differences, offset and scaling in lighting.
  • Interpolation: DIC measures displacements with subpixel accuracy. How to look in between sampled points.
  • Shape functions: Deformation of the subset for optimal matching according to the deformation process. What order to use? 
  • Optimization routines: How does a basic correlation run works (coarse and refinement) and how to interpret number of iterations.
  • How do we derive strains
  • Initial guess and incremental correlation for large deformations
  • Local versus Global approach

Competencies

  • The trainee is familiar with the basic parametric settings (subset size, step size, correlation criterion, interpolation, shape function …) in a DIC formalism to measure displacements and knows which ones to use in various circumstances.
Lecture 3: 2D uncertainty quantification (duration:2h) - Details

Objectives

  • Digging deeper into 2D DIC and experimental setup issues

Contents

  • UQ terminology for DIC
  • Speckles and lighting: how to obtain the ideal DIC images
  • What is aliasing and how to avoid it?
  • A DIC Game show
    • Impact of non-perpendicular camera alignment
  • Impact of out-of-plane motion
  • Impact of camera motion
  • How does air turbulence influences my images?
  • Impact of lens distortions
  • Concepts of metrology
  • Displacements and strains: resolution vs. signal reconstruction
  • A DIC convergence study
  • An attempt to quantify spatial resolution
  • Practical setup guidelines in a 2D DIC setup

 

Competencies

  • The trainee is provided with a roadmap how to setup a 2D DIC experiment and has a good knowledge on possible error sources and how to avoid them
Lecture 4: Stereo DIC and Stereo UQ (duration:1h30) - Details

Objectives

  • Get the trainee familiar with the basic concepts underlying a stereovision measurement

Contents

  • Bases of stereo vision: from 2D to stereovision measurements – Pro’s and Con’s.
  • The pinhole camera model and camera parameters
  • Calibration procedure
  • Geometry of stereovision: Image reconstruction, epipolar constraint and triangulation
  • UQ in stereovision
  • Camera mounting
  • Practical guidelines for stereovision measurements: lighting, optimal angling for out-of-plane measurements

Competencies

  • The trainee has basic skills to start and analyze successfully a multiple camera DIC setup.

Lecture 5: Material Identification (duration:1h30) - Details

Objectives

  • Get the trainee familiar with the basic concepts of the virtual fields method
  • Understand how full-field measurements impact the uncertainty on identified properties

Contents

  • Why combine full-field techniques with material identification
  • How does an inverse method work
  • Introduction of the principle of virtual work
  • How to select virtual fields
  • Case study: orthotropic foam
  • The identification simulator: quantifying systematic and random errors

Competencies

  • The trainee has basic knowledge on the application of the virtual fields method.
  • Feeling on how test geometry, DIC settings and hardware equipment might influence the identification process
Lecture 6: Model Validation (duration:1h30) - Details

Objectives

  • Get the trainee familiar with synthetic image deformation and how this helps to validate numerical models

Contents

  • Pitfalls in model validation by DIC
  • The alignment problem
  • The location issue
  • Which regularization parameters to select in order to validate my model?
  • Principles of synthetic image generation
  • Model validation: a stereo perspective

Competencies

  • The trainee has basic knowledge on possible pitfalls in model validation and how to interpret the model-measurement different regularization works.