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Deformability characterization of fabrics using large and small - - PowerPoint PPT Presentation

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KATHOLIEKE UNIVERSITEIT LEUVEN Deformability characterization of fabrics using large and small scale full field optical strain measurements A. Willems 1 , S. V. Lomov 2 , Zhu Yingbo 2 , I. Verpoest 2 and D. Vandepitte 1 1 Dept. of Mechanical

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KATHOLIEKE UNIVERSITEIT LEUVEN

Deformability characterization of fabrics using large and small scale full field optical strain measurements

  • A. Willems1, S. V. Lomov2, Zhu Yingbo2, I. Verpoest2 and D. Vandepitte1
  • 1Dept. of Mechanical Engineering, K.U.Leuven, Belgium
  • 2Dept. of Metallurgy and Materials Engineering, K.U.Leuven, Belgium

29 August – 1 September 2006

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Outline

Introduction

  • Digital image correlation
  • Large & small scale DIC: goal
  • Materials

Experiments

  • Picture frame tests
  • Biaxial tensile tests

Conclusion

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Digital image correlation

Principle

  • Define subsets (f.i. 15*15 pix) obtaining texture / color

information of material

  • Correlate subsets between deformed images
  • Match affine deformation to every subset

Application

  • 3D (2 cameras)
  • 2D (1 camera perpendicular)

Equipment

  • 600*800 pix CCD
  • 16mm &60 mm lens
  • Strain resolution ~ 0.02%

Introduction DIC Different scales Materials Experiments Picture frame Biaxial tension Conclusion

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Large scale

frame fabric grips fabric

fabric deformation = rig deformation fabric deformation = homogeneous?

Introduction DIC Different scales Materials Experiments Picture frame Biaxial tension Conclusion

SHEAR BIAXIAL TENSION

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Small scale (picture frame)

T T

rotation

lateral compression

shear

deformation modes in RUC ?

Introduction DIC Different scales Materials Experiments Picture frame Biaxial tension Conclusion

  • P. Boisse et al / Comp.Sc. T. , 2005

Validation of fabric meso material model

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Materials

weft warp

Introduction DIC Different scales Materials Experiments Picture frame Biaxial tension Conclusion

WARP: crimp 9.7% WEFT: crimp 0.1%

B2

?

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A

  • 1

3 2

250 180

4 5

a

Picture frame pure shear

Introduction Experiments Picture frame Biaxial tension Conclusion

10 20 30 40 50 60 10 20 crosshead displ. x [mm] shear angle [degree]

  • 2

x

  • x

x e x e 83 . 2 64 . 3 72 . 4

2 2 3 4

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Typical shear diagrams

0.1 0.2 0.3 0.4 0.5 0.6 0.7 20 40

Shear angle, ° Shear force, N/mm

1st 2nd 3rd

Introduction Experiments Picture frame Biaxial tension Conclusion

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Large scale DIC : Uniformity

1° 5° 8° 12°

10 20 30 40 50 60 10 20 30 40 50

frame, ° fabric, °

max mean min

Introduction Experiments Picture frame Biaxial tension Conclusion

DIC kinematics

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Correct data processing

ey/2

  • ex/2
  • 1

2arctan 2 1

x y

  • ,

y x x y

u u x y

  • A

C D

  • ^

2

AC BD

  • Introduction

Experiments Picture frame Biaxial tension Conclusion

B

pure shear general deformation

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  • x/2

y/2 C

  • B

= /2 – 2. atan( ) 1+y 1+x = /2 – AC^BD

A D

Correct data processing

pure shear general deformation

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Glass woven

Large scale DIC frame fabric?

?

Carbon NCF 0° / 90°

?

frame - fabric

Average fabric

  • Before wrinkling*

< 2o /< 8%

  • Beyond wrinkling*

fabric unreliable

max – min < 5o max – min < 3o Scatter of fabric

* *

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Glass/PP woven twill

Large scale DIC frame fabric?

frame - fabric

Average fabric

  • Before wrinkling*

~ 5o @ fabric= 35o /< 14%

  • Beyond wrinkling*

fabric unreliable

max – min ~ 10o @ fabric= 20o

  • Stdev. of fabric < 2o

Scatter of fabric

  • tight weave
  • high linear density
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A B

Meso-scale: intra-yarn shear

Introduction Experiments Picture frame Biaxial tension Conclusion

A B

Intra-yarn shear: ~1/2 fabric shear Inter-yarn shear: ~ fabric shear

Dry fabric Impregnated fabric

Yarn rotation Intra-yarn shear

Harrison P., Composites Part A, 2004

mechanism Glass/PP woven: RR2

1

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B

Meso-scale: intra-yarn shear

Introduction Experiments Picture frame Biaxial tension Conclusion

Glass/PP woven Inter-yarn shear Intra-yarn shear

RR3 RR1

Intra-yarn shear becomes quite important for plain fabric RR3, but is less important for RR1 and RR2

WHY?

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Meso-scale: Lateral compression

B 1 2

1-cos()

Introduction Experiments Picture frame Biaxial tension Conclusion

0.05 0.1 0.15 0.2 5 10 15 20 25 30

frame shear, deg yarn transversal strain RR1 RR2 RR3 1-cos

Glass/PP weave: RR2

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Conclusions: Picture frame

Macro-scale DIC:

  • Local shear angle should be calculated using facet coordinates
  • Homogeneous deformation before onset of wrinkling:

standard deviation < 2%

  • For tight fabrics fabric – frame may become important (RR1:

14%), so that DIC is necessary for reliable registration

  • Beyond wrinkling no reliable shear measurement is possible

Meso-scale DIC:

  • Indicative measurement of intra-yarn shear & lateral

compressive strain

  • Importance of intra-yarn shear very different for other structure,

linear density and tightness – the tighter the fabric, the more important intra-yarn shear

Introduction Experiments Picture frame Biaxial tension Conclusion

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Biaxial test

Introduction Experiments Picture frame Biaxial tension Conclusion

x:y

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Biaxial machine: set-up

Introduction Experiments Picture frame Biaxial tension Conclusion

Initial state @ pretension of 30 N (~1N/warp yarn) Constant velocity ratio

?

const u u k

RIG WEFT WARP RIG WEFT WARP RIG

  • ??
  • FABRIC

WEFT WARP

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Strain fields: Homogeneity

Introduction Experiments Picture frame Biaxial tension Conclusion

In-plane dilatation

  • Quite homogeneous in the central woven area
  • Side-effects at the borders

Subset window: 2.3*2.3 mm RUC: 10*21 mm ~ 4*8 subsets Field for data-averaging

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Strain fields

Introduction Experiments Picture frame Biaxial tension Conclusion

Shear strain 12

  • Overall shear angle ~ zero
  • Local shear angle represents

fabric structure

Subset window: 2.3*2.3 mm RUC: 10*21 mm ~ 4*8 subsets

1 2

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Biaxial curves: yarns removed

Introduction Experiments Picture frame Biaxial tension Conclusion

In warp direction: significant deviation between enforced deformation over the rig and local deformation in the fabric Reason: compliance of the arm parts

  • --- DIC measurement

C AP

k k

  • kAP

kC

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Biaxial curves: yarns removed

Introduction Experiments Picture frame Biaxial tension Conclusion

In warp direction: significant deviation between enforced deformation over the rig and local deformation in the fabric strain ratio kfabric is not constant DIC mandatory for reliable strain assessment

FABRIC FABRIC WEFT WARP RIG WEFT WARP RIG

k const k

  • --- DIC measurement
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General conclusions

Picture frame test

  • In general frame shear represents well the fabric shear. Optical

measurements may be used to control this for “difficult” fabrics

  • Deformation mechanisms confirmed by optical measurements
  • Considerable intra-yarn shear in a tight fabric
  • Onset of transversal compression

Biaxial tensile test

  • DIC necessary for reliable deformation assessment
  • Applied strain ratio in the fabric is not constant

Digital image correlation (DIC)

  • Contact less and adaptable to scale of interest
  • 3D msm cumbersome for wavy surfaces
  • Enough speckle pattern quality and stability

Introduction Experiments Picture frame Biaxial tension Conclusion