CHARACTERIZATION OF FIBRE MATRIX INTERFACIAL ADHESION IN FIBRE REINFORCED COMPOSITES BY PUSH IN TEST

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Timothy Skinner
6 years ago
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University of Madrid 8040 - Madrid, Spain

1 CHARACTERIZATION OF FIBRE MATRIX INTERFACIAL ADHESION IN FIBRE REINFORCED COMPOSITES BY PUSH IN TEST M. Rodríguez, J. Molina, C. González, J. LLorca IMDEA Materials Institute & Polytechnic University of Madrid Madrid, Spain COMPTEST 011, Ecole Polytechnique Fédérale de Lausanne, Switzerland.

2 SUMMARY 1. MOTIVATION - Multiscale modeling of composites: role of nanomechanics. PUSH-IN TEST - Background - Application to glass-fiber polymer-matrix composites - Experimental validation: push-out test 3. NUMERICAL SIMULATION of PUSH-IN TEST - Numerical model - Parametric study - Results for carbon-fiber polymer-matrix composites 4. APPLICATIONS: PREDICTION OF LAMINA PROPERTIES - In-plane shear deformation - Transverse tension under hot-wet conditions 5. CONCLUSIONS

mechanics subcomponent component Experimental nanomechanics plays a key role to measure in situ the

3 Virtual Testing of Composites MULTISCALE SIMULATION STRATEGY bottom - up approach Multiscale matrix & fiber Computational micromechanics lamina Computational mesomechanics laminate Computational mechanics subcomponent component Experimental nanomechanics plays a key role to measure in situ the properties of matrix, fibers and interface. This is the first step in the multiscale simulation ladder. structure

4 Push-in test MEASUREMENT OF INTERFACE STRENGTH P Interface strength can be measured through push-in tests in a nanoindentor. w v u Matrix Push-in tests were originally developed for CMC and MMC Fiber

5 Push-in test PUSH-IN TESTS for PMC High accuracy in positioning to push-in very small fibers (5 µm). Continuous load recording (debonding occurs progressively in most PMC). Accurate load-displacement recording to determine the onset of decohesion. Local fiber arrangement plays a significant role on the debonding load fiber radius (!m) Load, P (mn) Fiber displacement, u (nm) 1400

6 EFFECT of LOCAL FIBER ARRANGEMENT Push-in test The shear interface strength can be obtained from the shear-lag model. The load-fiber displacement (P-u) curve is linear before interface decohesion and the slope depends on the packing factor, Re/r. Gm P = (nπref )u n = Ef ln(re /r) npc n The shear interface strength S is given by S = τc = = σf,c πr 50 Criterion to determine Pc fiber radius (!m) Pc P/nr P/nr (mn/µm) % 50 % Fiber displacement, u (nm) 1400 Fiber displacement

7 Push-in test INTERFACE STRENGTH Spush in = 83 ± 3 MPa c "f,c (MPa)! (MPa) packing factor, R / r e Matrix properties (shear strength and cohesion angle) can also be obtained by nanoindentation of matrix pockets on transverse sections of the composite.

8 EXPERIMENTAL VALIDATION: PUSH-OUT TESTS Push-out test The shear interface strength can also be obtained through push-out tests. P r 5 µm δ

9 EXPERIMENTAL VALIDATION: PUSH-OUT TESTS fiber push-out elastic fiber push-in Push-out test Advantages Easier interpretation. S= Pmax πrt Limitations Time consuming sample preparation. Uncertainty to measure thickness plate bending fiber unloading Spush in = 83 ± 3 MPa Spush out = 80 ± 9 MPa EXTENSION of PUSH-IN TESTS The shear-lag model does not take into account the anisotropy of C fibers (and only includes approximately the effect of the surrounding fibers). Higher accuracy can be obtained by means of a 3D simulation of the push-in test.

10 NUMERICAL MODEL OF PUSH-IN TEST 60º symmetric 3D wedge: r = 5 μm, L/r = 100 Hexagonal packing arrangement for first nearest neighbors. Transversally isotropic homogenized material for second nearest neighbors. Numerical Model

11 Numerical Model CONSTITUTIVE EQUATIONS Matrix: linear thermoelastic, isotropic solid Em νm αm Fibers: linear thermo-elastic, transversally isotropic solid (isotropy plane 3) Ef,11 Ef, νf,1 Gf,1 νf,3 αf,11 Matrix properties were obtained from mechanical tests on matrix coupons. Fiber properties were obtained from composite and fiber mechanical properties using Chamis equations. CTE were obtained from literature. Matrix and fibers were discretized with quadratic tetrahedra (C3D10M). Fiber-matrix interface was discretized with cohesive surfaces. αf,

Numerical Model INTERFACE FRACTURE Damage initiation < tn > < ts > < tt > + + =1 S S S t0 δ δ0 Damage evolution Gn Gs Gt + + =1 GIc GIIc GIIc max δf δ f δ max δ 0 D = max f δ δ δ0 δf = Gn, Gt, Gs

12 Numerical Model INTERFACE FRACTURE Damage initiation < tn > < ts > < tt > + + =1 S S S t0 δ δ0 Damage evolution Gn Gs Gt + + =1 GIc GIIc GIIc max δf δ f δ max δ 0 D = max f δ δ δ0 δf = Gn, Gt, Gs are the energies spent in Mode I, II and III. GC t0 GC = GIc + GIIc + GIIc Once the fiber-matrix interface is completely broken, interaction between both surfaces takes place by Coulomb friction (µ)

T = 160ºC radial residual stresses (normal to the fiber-matrix interface) (MPa) Tensile

13 THERMAL RESIDUAL STRESSES Numerical Model The development of thermal residual stresses upon cooling from curing temperature was simulated. T = 160ºC radial residual stresses (normal to the fiber-matrix interface) (MPa) Tensile radial residual stresses (up to 60 MPa) near to the free surface. Compressive radial residual stresses (up to 70 MPa) in the bulk.

14 Numerical Model PARAMETRIC STUDY Objective: assess the effect of µ and Gc (= GIc + GIIc ) on test results. GIc = GIIc S = 80 MPa µ = 0, Gc = 60 J/m µ = 1, Gc = 15 J/m µ = 0, Gc = 15 J/m

15 DEVELOPMENT OF DECOHESION fiber-matrix interface damage D vertical displacement (nm) Numerical Model

16 Numerical Model MEASUREMENT OF INTERFACE STRENGTH Pc Pc µ = 1, Gc µ = 1, Gc µ = 0, Gc µ = 0, Gc = 60 = 15 = 60 = 15 J/m J/m J/m J/m Fiber-matrix friction coefficient can be obtained from push-out tests.

17 Applications IN-PLANE SHEAR V-notched rail shear (ASTM 7078), MTM57 epoxy/ M40J (59%), [0/90]4s Matrix and fiber properties from nanoindentation Fiber properties from manufacturerʼs data sheet τ1 τ1 τ1 τ1 + τ1 =

18 IN-PLANE SHEAR shear parallel to the fibers pm Deformation is localized in matrix bands. Applications shear perpendicular to the fibers pm Deformation is not localized in matrix bands. Fiber rotation.

19 IN-PLANE SHEAR shear parallel to the fibers fiber shear stresses are similar to the matrix shear yield strength. Applications shear perpendicular to the fibers Hardening induced by fiber rotation.

20 IN-PLANE SHEAR Experimental validation Applications Parametrical study effect of interface strength

21 TRANSVERSE TENSILE STRENGTH UNDER HOT-WET Applications Strength under transverse tension is controlled by matrix and interface strength Matrix & interface strength under hot-wet conditions are measured by nanoindentation

22 CONCLUSIONS Conclusions Nanomechanics has very large potential to measure in situ fiber, matrix and interface properties in composites. This is the first step to build up a truly multiscale modeling strategy in composites. The strength of the fiber/matrix interface can be accurately measured using push-in tests. In situ fiber and interface properties, together with computational micromechanics toools, can accurate predict lamina properties. Further developments are on the way to characterize normal interface strength and fracture energies. Acknowledgements Ministerio de Educación y Ciencia, National Program on Materials (MAT ) Comunidad de Madrid, Program ESTRUMAT-CM EU projects MAAXIMUS and DEFCOM

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