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 Engineering, K.U.Leuven, Belgium 2 Dept. of Metallurgy and Materials Engineering, K.U.Leuven, Belgium 29 August – 1 September 2006 downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 1
Outline KATHOLIEKE UNIVERSITEIT LEUVEN Introduction • Digital image correlation • Large & small scale DIC: goal • Materials Experiments • Picture frame tests • Biaxial tensile tests Conclusion downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 2
Digital image correlation KATHOLIEKE UNIVERSITEIT LEUVEN Principle • Define subsets (f.i. 15*15 pix) obtaining texture / color information of material Introduction • Correlate subsets between deformed images DIC • Match affine deformation to every subset Different scales Application Materials Experiments • 3D (2 cameras) Picture frame • 2D (1 camera perpendicular) Biaxial tension Equipment Conclusion • 600*800 pix CCD • 16mm &60 mm lens • Strain resolution ~ 0.02% downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 3
Large scale KATHOLIEKE UNIVERSITEIT LEUVEN SHEAR BIAXIAL TENSION Introduction � fabric DIC � fabric Different scales Materials Experiments Picture frame Biaxial tension � grips Conclusion fabric deformation = rig deformation � frame fabric deformation = homogeneous ? downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 4
Small scale (picture frame) KATHOLIEKE UNIVERSITEIT LEUVEN T Validation of fabric shear meso material model Introduction rotation DIC T Different scales Materials Experiments lateral compression Picture frame P. Boisse et al / Comp.Sc. T. , 2005 Biaxial tension Conclusion deformation modes in RUC ? downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 5
Materials KATHOLIEKE UNIVERSITEIT LEUVEN warp weft Introduction ? B2 DIC WARP: crimp 9.7% Different scales WEFT: crimp 0.1% Materials Experiments Picture frame Biaxial tension Conclusion downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 6
� Picture frame � pure shear KATHOLIEKE UNIVERSITEIT LEUVEN Introduction Experiments 3 Picture frame 1 Biaxial tension 4 Conclusion 5 4 3 2 2 4 . 72 e � x 3 . 64 e � x 2 . 83 x � � � � � 60 180 shear angle � [degree] 50 40 250 30 x 20 2 10 A 0 0 10 20 � � 2 a � � � crosshead displ. x [mm] downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 7
Typical shear diagrams KATHOLIEKE UNIVERSITEIT LEUVEN Introduction Experiments 0.7 Picture frame 1st 0.6 Shear force, N/mm Biaxial tension 2nd 0.5 Conclusion 3rd 0.4 0.3 0.2 0.1 0 0 20 40 Shear angle, ° downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 8
Large scale DIC : Uniformity KATHOLIEKE UNIVERSITEIT LEUVEN Introduction 1° 5° 8° 12° Experiments Picture frame 60 � fabric, ° Biaxial tension max 50 Conclusion DIC mean 40 min 30 20 kinematics 10 � frame, ° 0 0 10 20 30 40 50 downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 9
Correct data processing KATHOLIEKE UNIVERSITEIT LEUVEN pure shear general deformation B C e y /2 Introduction Experiments Picture frame Biaxial tension � A Conclusion -e x /2 D � 1 � � � � x 2arctan � � � � � � � AC BD ^ 2 1 � 2 � y u u � � y x , � � � � x y x y � � downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 10
Correct data processing KATHOLIEKE UNIVERSITEIT LEUVEN pure shear general deformation � y /2 B C A � - � x /2 D � 1+ � x �� = � /2 – � AC^BD �� = � /2 – 2. atan( ) 1+ � y downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 11
Large scale DIC � � frame � � fabric ? KATHOLIEKE UNIVERSITEIT LEUVEN Carbon NCF 0° / 90° Glass woven Average � fabric ? ? o Before wrinkling* ��� < 2 o �� / �� < 8% o Beyond wrinkling* � frame - � fabric � fabric unreliable * * Scatter of � fabric � max – � min < 5 o � max – � min < 3 o downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 12
Large scale DIC � � frame � � fabric ? KATHOLIEKE UNIVERSITEIT LEUVEN Glass/PP woven twill Average � fabric • tight weave o Before wrinkling* • high linear density ��� ~ 5 o @ � fabric = 35 o �� / �� < 14% o Beyond wrinkling* � frame - � fabric � fabric unreliable Scatter of � fabric � max – � min ~ 10 o @ � fabric = 20 o Stdev. of � fabric < 2 o downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 13
Meso-scale: intra-yarn shear KATHOLIEKE UNIVERSITEIT LEUVEN Glass/PP woven: RR2 B B Inter-yarn shear: ~ fabric shear Introduction A Experiments Picture frame A Biaxial tension Intra-yarn shear: Conclusion ~1/2 fabric shear mechanism 1 Yarn rotation Harrison P., Composites Part A, 2004 Intra-yarn shear 0 Impregnated Dry fabric fabric downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 14
Meso-scale: intra-yarn shear KATHOLIEKE UNIVERSITEIT LEUVEN Glass/PP woven B RR1 Inter-yarn shear Introduction Experiments Picture frame Biaxial tension Intra-yarn shear Conclusion Intra-yarn shear becomes RR3 quite important for plain fabric RR3, but is less important for RR1 and RR2 WHY? downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 15
Meso-scale: Lateral compression KATHOLIEKE UNIVERSITEIT LEUVEN Glass/PP weave: RR2 Introduction RR1 0.2 Experiments yarn transversal strain RR2 Picture frame 2 RR3 0.15 1 Biaxial tension 1-cos Conclusion 0.1 B 0.05 0 0 5 10 15 20 25 30 frame shear, deg 1-cos( � ) downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 16
Conclusions: Picture frame KATHOLIEKE UNIVERSITEIT LEUVEN Macro-scale DIC: • Local shear angle should be calculated using facet coordinates Introduction • Homogeneous deformation before onset of wrinkling: Experiments standard deviation < 2% Picture frame • For tight fabrics � fabric – � frame may become important (RR1: Biaxial tension 14%), so that DIC is necessary for reliable registration Conclusion • 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 downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 17
Biaxial test KATHOLIEKE UNIVERSITEIT LEUVEN Introduction Experiments � x : � y Picture frame Biaxial tension Conclusion downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 18
Biaxial machine: set-up KATHOLIEKE UNIVERSITEIT LEUVEN Introduction Experiments Picture frame Biaxial tension Conclusion Initial state @ pretension of 30 N (~1N/warp yarn) Constant velocity ratio ? u � � � � � � � � � � � WARP WARP WARP k const ?? � � � � � � � � � � RIG � � � � � � u � � � � � � � � � � � WEFT WEFT WEFT RIG RIG FABRIC downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 19
Strain fields: Homogeneity KATHOLIEKE UNIVERSITEIT LEUVEN In-plane dilatation • Quite homogeneous in the central woven area • Side-effects at the borders Introduction Experiments Picture frame Biaxial tension Conclusion Subset window: 2.3*2.3 mm Field for data-averaging RUC: 10*21 mm ~ 4*8 subsets downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 20
Strain fields KATHOLIEKE UNIVERSITEIT LEUVEN Shear strain � 12 • Overall shear angle ~ zero • Local shear angle represents 2 fabric structure Introduction Experiments Picture frame Biaxial tension 1 Conclusion Subset window: 2.3*2.3 mm RUC: 10*21 mm ~ 4*8 subsets downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 21
Biaxial curves: yarns removed KATHOLIEKE UNIVERSITEIT LEUVEN ---- DIC measurement Introduction Experiments Picture frame Biaxial tension Conclusion In warp direction: significant deviation between enforced deformation over the rig k AP and local deformation in the fabric k C Reason: compliance of the arm parts k k � AP C downloaded from: http://www.mtm.kuleuven.ac.be/Research/C2/poly/index.htm 22
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