ANALYSIS OF DAMAGE IN TEXTILE COMPOSITES Dmitry S. Ivanov Promotors: Prof. Stepan V. Lomov Jury: Prof. Thomas Pardoen Prof. Ignaas Verpoest Prof. Ignaas Verpoest Prof. Dirk Roose Prof. Dirk Roose Prof. Dirk Vandepitte Prof. Martine Wevers Prof. Masaru Zako Chairman: Prof. Herman Neuckermans Katholieke Universiteit Leuven Department of Metallurgy and Materials Engineering Composite Materials Group 1 11.03.2009 D.S.Ivanov, Pre-defence
Outline Introduction � Textile composites – Multi-scale modelling – Problem statement – Experimental work � Methodology and materials – Mechanical response of the damaged composites – Damage evolution – Multi-scale modelling Multi-scale modelling � � Stress distribution in textile laminates – Novel out-of plane boundary conditions – Symmetry boundary conditions – Damage modelling � Prediction of damage initiation – Main-stream element discount method – New damage modelling approach – Validation of the modelling – Conclusions � 2
Composite materials: applications Sport: Composite wood metal www.itftennis.com % composit es in civil aircraf t 60 50 B787 A350 40 Aerospace: 30 A380 20 A320 A340 A320 10 10 B747 0 1970 1980 1990 2000 2010 Marine: Automotive: Civil: Toyota 1/X …, …, ETC. 3
Diversity of textile structures Patterns 3D woven Woven Braided Knitted Non crimp Laminated Sheared Stitched 4 Diversity = Architectures* Patterns*Lay-ups*Geometry*Textile deformations*…
Design concept: Meso-scale Patterns 3D woven Woven UD fibre bundle Braided Knitted Non crimp Laminated Sheared Stitched Meso scale → → Properties of UD and Matrix + Internal geometry + → → 5 Boundary conditions
Damage development Hierarchy Fibres Yarns Fabrics Parts Patterns Patterns Failure initiation Failure initiation Stress concentration ε ≈ epoxy 4 % failure Fibres ε ≈ UD Triaxial braided NCF 3D woven 0 . 6 % crack onset Stability of crack system Yarn crimp ε ≈ textile composite 0 . 3 % crack onset 6
Problem statement Conclusion of World-Wide Failure Exercise for UD laminated composite: " The overall conclusion to be drawn is that a designer wishing to estimate the stress levels at which initial failure might occur in a multi-directional ! laminate, can only hope to get to within a ± ± 50% , at best , based on ± ± current theories. " Best criteria have been selected according to the principle: "theories achieved predictions to within ± 50% of the experimental values for 80% of the test features " Textile vs. UD laminated composites: Diversity of architectures ↑ ↑ ↑ ↑ Geometrical complexity ↑ ↑ ↑ ↑ Mechanical stress factors (e.g. crimp, yarn interaction) ↑ ↑ ↑ ↑ 3D stress state ↑ ↑ ↑ ↑ Failure mechanisms variability ↑ ↑ ↑ ↑ 7
Part performance Modelling loop Study of macro deformation Reinforcement parameters Local reinforcement geometry x ε ( x ) Macro strain at the Local stiffness point x y Mechanical meso Physical evolution model of RVE of the structure ε ( y ) Meso boundary Meso stress-strain 8 conditions distribution
Outline � Introduction Textile composites – Multi-scale modelling – Problem statement – � Experimental work Ch II Methodology and materials – Mechanical response of the damaged composites – Damage evolution Damage evolution – – � Multi-scale modelling Stress distribution in textile laminates – Novel out-of plane boundary conditions – Symmetry boundary conditions – � Damage modelling Prediction of damage initiation – Main-stream element discount method – New damage modelling approach – Validation of the modelling – � Conclusions 9
Tests of carbon-epoxy composites Materials Biaxial non-crimp fabric Triaxial braided Quasi-UD woven The same manufacturing parameters and epoxy T700, 8-16 plies, T400 fibres, Vf = 20-40% Vf = 20-40% 10 plies, Vf = 45 % 10 plies, Vf = 45 % HTS 5631 Tenax fibres, HTS 5631 Tenax fibres, 4 layers, Vf = 44 % Methodology Tensile test Acoustic emission Strain mapping diagram energy of failure events macro deformation degradation damage initiation meso strain Damage stages Load up to the predefined load levels Damage evolution X-Ray Cross-sectioning SEM crack length Crack position/orientation Micro debonding 10 crack density Delaminations
Manufactured and tested NCF, tensile by Thanh Troung Chi ± 20, 30 ° µ -damage + plasticity, fibre failure ± 45 ° µ -d + plasticity + fibre reorientation + m-cracking, separation of delaminated plies ± 60, 70 ° m-cracking, delaminated plies 11
Manufactured and tested NCF, tensile by Thanh Troung Chi ± 20, 30 ° τ µ -damage + plasticity, 12 ± � 20 σ fibre failure 22 ± � 30 − 3 . 1 ± 45 ° − 7 . 1 ± � 45 µ -d + plasticity + fibre reorientation + m-cracking, 2 . 1 separation of delaminated plies 0 . 6 ± 60, 70 ° m-cracking, 0 . 3 delaminated plies 12
Braided, tensile MD Slight degradation BD Similar to NCF 0, ± 45 ° ± 60 ° 90, 0, ± 45 ° 90, ± 45 ° CD Low strain to failure despite the presence of the ± 45 ° yarns Energy of AE events correlates with the degradation 13
Damage patterns Crack density growth + crack length increase SEM Total crack length correlates with AE energy and stiffness degradation Delaminations at the advanced stage of deformation X-ray images: CD Few cracks per yarn Braiding yarns Inlay yarns Inclined cracks The similar orientation Cross-section of the composite of the cracks in yarns of Loading Inter-yarn meso cracking, not much 14 one direction of µ -damage
Outline � Introduction Textile composites – Multi-scale modelling – Problem statement – � Experimental work Methodology and materials – Mechanical response of the damaged composites – Damage evolution Damage evolution – – � Multi-scale modelling Stress distribution in textile laminates – Ch III Novel out-of plane boundary conditions – Symmetry boundary conditions – � Damage modelling Prediction of damage initiation – Main-stream element discount method – New damage modelling approach – Validation of the modelling – � Conclusions 15
Meso-FE: Road map Geometric modeller Geometry corrector Meshing N+2 N+1 N Assign material properties properties Boundary conditions FE solver, postprocessor Homogenisation Damage analysis 16
Surface role Experimental evidence of the surface effects Braided composite, MD: intra- yarn cracks in outer plies only Quasi-UD woven composite, delaminations in outer plies only Extensive delaminations in surface plies ⇒ ⇒ ⇒ ⇒ Failure scenario governed by the number of plies Reference problem 17
Comparison of stress 18
Stress density function Transverse stress in 90 ° ° ° ° yarns: volume fraction of elements with a particular stress value Stress distribution depends on the number of plies in a textile laminate 19
Deflection profiles ~ = − ε u u x 2 2 22 2 ~ µ u , m 2 The less plies are in the laminate the higher The deflection for all the plies in the deflection the laminate is nearly the same The deflections of N-ply laminates are proportional to each other 20
New BC’s Outer and inner unit cells Energy of effective medium ( ) = σ ε + − σ ε E 2 N 2 11 11 11 11 E outer outer inner inner Energy of heterogeneous medium ( ) = σ ε + − σ ε E 2 N 2 H ij ij ij ij outer inner Deviation from the balance ( ) ∆ λ = − E E E H E Minimisation of the deviation Optimum scaling coefficients Number of the plies, N 2 3 4 5 6 Reference solutions 1.725 1.383 1.273 1.210 1.160 21 Numerical procedure 1.709 1.375 1.253 1.190 1.153
Analysis of the results 22
3D test problem: twill woven FE models are generated by MeshTex software, Osaka University, based on WiseTex geometry Displacement profiles: the same as 2D ⇒ ⇒ ⇒ new BC’s can be used ⇒ 23
Comparison of results � 90 yarns 3.2 ÷ 16.5 3.6 ÷ 16.4 3.4 ÷ 16.1 � 0 yarns 29.3 ÷ 132.8 29.3 ÷ 134.4 49.7 ÷ 131.7 Bottom outer ply of 6 ply Periodic solution Surface solution, 6-ply laminate λ = 1 . 12 Reference solution 24
Laminates with a ply shift “Step” “Stairs” Can one unit cell be representative in the case of laminates with an arbitrary ply shift? Which BC to apply? 25
Stress in laminate with an different ply shifts “Periodic stacking” “Step” “Stairs” -2.3 ÷ ÷ 149.6 -4.0 ÷ ÷ 160.1 ÷ ÷ ÷ ÷ -2.5 ÷ ÷ ÷ ÷ 126.9 Stress in along the loading directions is dramatically influenced by the stacking sequence 26
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