TY - JOUR
T1 - On image gradients in digital image correlation
AU - Neggers, J.
AU - Blaysat, B.
AU - Hoefnagels, J.P.M.
AU - Geers, M.G.D.
PY - 2016/1/27
Y1 - 2016/1/27
N2 - In digital image correlation (DIC), the unknown displacement field is typically identified by minimizing the linearized form of the brightness conservation equation, while the minimization scheme also involves a linearization, yielding a two-step linearization with four implicit assumptions. These assumptions become apparent by minimizing the non-linear brightness conservation equation in a consistent mathematical setting, yielding a one-step linearization allowing a thorough study of the DIC tangent operator. Through this analysis, eight different image gradient operators are defined, and the impact of these alternative image gradients on the accuracy, efficiency, and initial guess robustness is discussed on the basis of a number of academic examples and representative test cases. The main conclusion is that for most cases, the image gradient most common in literature is recommended, except for cases with: (1) large rotations; (2) initial guess instabilities; and (3) costly iterations due to other reasons (e.g., integrated DIC), where a large deformation corrected mixed gradient is recommended instead.
AB - In digital image correlation (DIC), the unknown displacement field is typically identified by minimizing the linearized form of the brightness conservation equation, while the minimization scheme also involves a linearization, yielding a two-step linearization with four implicit assumptions. These assumptions become apparent by minimizing the non-linear brightness conservation equation in a consistent mathematical setting, yielding a one-step linearization allowing a thorough study of the DIC tangent operator. Through this analysis, eight different image gradient operators are defined, and the impact of these alternative image gradients on the accuracy, efficiency, and initial guess robustness is discussed on the basis of a number of academic examples and representative test cases. The main conclusion is that for most cases, the image gradient most common in literature is recommended, except for cases with: (1) large rotations; (2) initial guess instabilities; and (3) costly iterations due to other reasons (e.g., integrated DIC), where a large deformation corrected mixed gradient is recommended instead.
KW - Brightness conservation
KW - Digital image correlation
KW - Displacement fields
KW - Strain measurement
UR - http://www.scopus.com/inward/record.url?scp=84957022528&partnerID=8YFLogxK
U2 - 10.1002/nme.4971
DO - 10.1002/nme.4971
M3 - Article
AN - SCOPUS:84957022528
SN - 0029-5981
VL - 105
SP - 243
EP - 260
JO - International Journal for Numerical Methods in Engineering
JF - International Journal for Numerical Methods in Engineering
IS - 4
ER -