Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 01 Jun 2010

3D Digital Imaging Correlation: Applications to Tire Testing

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Page Range: 100 – 118
DOI: 10.2346/1.3428948
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Abstract

Three-dimensional digital imaging correlation (DIC) techniques are a viable method for measuring surface displacements and strains on tires. DIC provides the capability to measure the full-field noncontact tire surface deformation and strain state, which supports multiple objectives: validation of tire models based on finite element (FE) predictions, setting targets for improving FE predictions and providing insight into the tire deformation state under static and dynamic conditions. A method for verifying the accuracy of the DIC measurement process is presented whereby a thin, rectangular test sample of rubber material is subjected to a combination of strains and rigid body motions of known amounts. Once the measurement technique is proven accurate with a simple specimen, the focus shifts to the objectives explained above. Tire surface strains will be discussed for purposes of validating model predictions of sidewall and belt edge strains. Several types of specimen geometries will be reviewed and their effect on material properties will be presented. Also, the DIC technique can provide insight into complex physical problems that may otherwise be very difficult to measure. Some examples presented here include tire sidewall standing waves at high speeds and strains near tread lugs of agricultural tires. The DIC measurement method is an accurate, noncontacting full field technique for measuring in-plane surface displacements and strains of the magnitudes encountered in tire analysis. This technique serves many functions and has become a valuable tool for both tire testing and development.

Keywords: digital imaging correlation; DIC; strain; surface strain; displacement; prediction; FEA
Copyright: The Tire Society
FIG. 1
FIG. 1

DIC experimental setup.

FIG. 2
FIG. 2

Bracket to stretch rubber sample a known distance and rotational base to rotate rubber sample a known angle.

FIG. 3
FIG. 3

Bracket measured at tilt angle using digital level.

FIG. 7
FIG. 7

Tire showing coordinate system and terminology used for strains.

FIG. 4
FIG. 4

Rubber sample showing optical compression and shear, which DIC method accounts for.

FIG. 5
FIG. 5

DIC method validation results at different normal strain levels, degrees of tilt and rotation.

FIG. 6
FIG. 6

Representative 2D cross-sectional mesh showing twice as much mesh refinement in the shoulder as in the rest of the cross section.

FIG. 8
FIG. 8

Radial Engineering Strain in tire sidewall vs. radial position (measurement and FEA).

FIG. 9
FIG. 9

Difference in radial engineering surface strain between DIC measurement and FEA.

FIG. 10
FIG. 10

Difference in radial location of peak radial surface strain between DIC measurement and FEA.

FIG. 11
FIG. 11

Test tire with 2 inch wide window removed from shoulder exposing the edges of two steel plies and sketch showing shear strain in rubber material (dashed region) between two plys with steel cords.

FIG. 12
FIG. 12

Engineering Shear Strain between two steel plies vs window position

FIG. 13
FIG. 13

Engineering Shear Strain between two steel plies vs % radial load

FIG. 14
FIG. 14

Concept for biaxial testing.

FIG. 15
FIG. 15

Membrane holding device and 2D contour of growth.

FIG. 16
FIG. 16

Predicted fit to biaxial test data when using the same material model that fits uniaxial and planar tension.

FIG. 17
FIG. 17

FEA fit to biaxial test data when using lower order Neo Hookean and higher order Ogden 4-Term material models.

FIG. 18
FIG. 18

Load frame for Ag tire DIC measurements.

FIG. 19
FIG. 19

Loaded Ag tire showing peak strain in front of tread lug.

FIG. 20
FIG. 20

Loaded Ag tire showing peak strain directly above tread lug.

FIG. 21
FIG. 21

Loaded Ag tire showing peak strain behind tread lug.

FIG. 22
FIG. 22

Tire sidewall with standing wave at high speed.

FIG. 23
FIG. 23

Sample tire with random speckle pattern for high speed DIC measurement.

FIG. 24
FIG. 24

3D tire sidewall deformations at high speed.

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