Method and system for direct strain imaging

Patent metadata

Field	Value
Publication number	US-9311566-B2
Application number	US-201313958247-A
Country	US
Kind code	B2
Filing date	Aug 2, 2013
Priority date	Aug 3, 2012
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

A method and system for measuring and determining the full-field spatial distributions of strain tensor field components in a two or three-dimensional space, as a consequence of deformation under generalized loading conditions. One or more digital cameras may be used to acquire successive images of a deforming body with optically distinctive features on its surface. A method for determining the location of characteristic points of the surface features and another one for tracking these points as deformation occurs. Elongations between neighboring points on the vicinity of a location of interest are computed. The elongation between points is calculated even though discontinuities may exist between them. Strain tensor fields are directly calculated as a tensor approximation from these elongations without determining or using the displacement vector distributions.

First claim

What is claimed is:

1. A computer-implemented method for determining strain characteristics in a vicinity of a point of interest w={x w , y w } T in two parametric dimensions embedded in a two or three dimensional space, wherein the point of interest w is part of a deformable domain or body having a plurality of features which may be represented as a node pattern of n nodes, the method comprising:
receiving a first set of captured data of a plurality of features and representing the plurality of features by nodes indexed by i or j in the domain in an un-deformed configuration;
receiving a second set of captured data of the plurality of features represented by nodes i,j in the domain in a deformed configuration;
measuring engineering strains e i,j between a plurality of node combinations in the vicinity of w to produce e w ={e 21 , e 31 , . . . e 42 . . . , e n(n-1) } T ; and
applying an approximation or interpolation to the engineering strains e i,j to approximate strain ε h in the vicinity of w.

2. The method of claim 1 , wherein the approximation defines an overdetermined system of equations.

3. The method of claim 1 , wherein the moving least squares approximation expresses strain ε h in two parametric dimensions embedded in a two or three dimensional space by

ɛ
xx
h

⁡

(
w
)

≡

ɛ
xx
h

⁡

(

w
;
w

)

=

Φ
xx

⁡

(
w
)

⁢

e
w

ɛ
yy
h

⁡

(
w
)

≡

ɛ
yy
h

⁡

(

w
;
w

)

=

Φ
yy

⁡

(
w
)

⁢

e
w

ɛ
xy
h

⁡

(
w
)

≡

ɛ
xy
h

⁡

(

w
;
w

)

=

Φ
xy

⁡

(
w
)

⁢

e
w

}

where Φ α (w)=p T (w)M α (w) are shape functions of strain components for the vicinity of w for α=xx, yy, xy.

4. The method of claim 3 , wherein the first and second sets of captured data each being a digital images, and further comprising identifying real mean strain e i,j between a number of node combinations by

e
ij

=

ɛ

xx
′

_

⁡

(

x
i

,

x
j

)

=

l
ij
′

Assignees

• George Mason Res Foundation Inc
• Us Navy

Inventors

• Iliopoulos Athanasios
• Michopoulos John G

Classifications

• G06T7/285

  using a sequence of stereo image pairs · CPC title

• G06K9/6232 Primary

  Physics · mapped topic

• G01N2203/0647

  Image analysis · CPC title

• G06T2207/30108

  Industrial image inspection · CPC title

• G01N2203/0212

  Theories, calculations · CPC title