Error Estimation in Digital Image Correlation Caused by Rigid Particles

1. Error Estimation in Digital Image Correlation Caused by Rigid Particles By Xiaodan (Danna) Ke

2. Content • Introduction • Simulation Process • Particle Extraction Algorithm • Particle Translation Algorithm • Preliminary Results • Future Work

3. Introduction to Digital Image Correlation (DIC) 1 Speckle patterns DIC is a non-contacting measurement method based on tracking speckle patterns on material surface before and after deformation to determinedisplacement and strain fields. Force Reference state Deformed state

4. Introduction to Digital Image Correlation 2 Speckle patterns • Working Principles: Calculate cross-correlation factor of subsets in both states • Center locations of subsets at deformed state will be correlated with those at reference state • Accuracy:±0.02 pixels Subset F Reference state (u,v) Deformed state

5. Introduction to Digital Image Correlation 3 • DIC assumes no difference bt. background and particles in pattern Background and particles deform the same way • Problem caused by rigid particles Error estimation is needed ! Stretch and translate Only translate Flexible particles Rigid particles Reference state Deformed state Deformed state

6. Simulation Process 1 • Rigid particles are introduced when applying DIC to biological materials • Simulation method is used to evaluate errors induced by rigid particles Mouse carotid vessel 0.5 mm

7. Simulation Process 2 Challenge part! • Extract individual particles from reference image • Translate extracted particles according to pre-assigned displacement • Generate deformed image • Use Vic-2D (a given DIC package) to calculate displacement and strain • Compare result from DIC with pre-assigned displacement

8. Particle Extraction Algorithm 2 • Why to extract individual particles Calculate centroid location and obtain accurate displacement assignment 20 29 41 30 105 34 51 40 Centroid 85 16 50 120 10 38 50 99 u u1 x

9. Particle Extraction Algorithm 3 • Local neighborhood searching algorithm • Intensity threshold (60) • Extract continuous pixels for individual particles Start 24 32 32 33 41 39 36 29 23 30 38 41 58 74 68 52 34 27 34 44 66 100 124 116 75 38 29 39 44 75 130 158 141 89 46 31 38 40 64 96 124 118 70 38 29 31 39 41 55 62 65 45 32 25

10. Particle Extraction Algorithm 3 • Results Original image Extracted particles

11. Particle Translation Algorithm 1 • Calculate centroid in subpixels • Assign displacement to particles • Translate particles • Integration • Deform background pixels • Fill holes based on interpolation • Generate deformed image

12. Particle Translation Algorithm 2 • Results Pure rigid motion 10 pixel in width direction Pure 50% stretch in width direction Original image

13. Particle Extraction Algorithm 3 • Results Flexible particles Rigid particles Pure 50% stretch in width direction

14. Preliminary Results of Error Estimation ? ? ? ?

15. Future Work • Debug codes • Separate clogged particles • Estimate errors for complicated deformation

16. Thank you!