SM10: Characterising Micro- and Nano- Scale Interfaces in Advanced Composites. Polymers: Multiscale Properties. 8 November 2007

Transcription

1 SM10: Characterising Micro- and Nano- Scale Interfaces in Advanced Composites Polymers: Multiscale Properties 8 November 2007

2 Deliverables D1: Critique of test methods and predictive analysis for characterising interfacial properties in filled systems NPL Report - completed D2: Develop and evaluate new measurement techniques identified in D1 for characterising interfacial properties. Case studies (micro- to nano-scale) on the application of interfacial characterisation methods to filled systems Scientific paper (March 2007) D3: Evaluation of predictive model(s) for characterising interfacial and interphase properties in filled systems Scientific paper (March 2007) 2

3 Case Study 1: GRP Pultruded Rods Fibre products: E-glass and ECR glass Resin: Vinylester Surface treatments: Organosilane Properties: Flexure strength/stiffness Glass transition temperature Environmental durability/permeation Alkaline solution/elevated temperature Combinatorial analysis Suppliers: Fibreforce Composites Ltd Saint-Gobain Vetrotex 3

4 Glass/vinylester Pultruded Rods Fibre Volume Fraction (V f ) Well bonded: 56.2 ± 0.7 Poorly bonded: 55.8 ± 0.8 Glass Transition Temperature (T g ) Well bonded: C Poorly bonded: C Poor Blisters or residue sizing droplets on surface of the fibre Good 4

5 GRP Pultruded Rods Flexure Properties Material Dried at 50 C Well Bonded Poorly Bonded 1 Month Well Bonded Poorly Bonded 3 Months Well Bonded Poorly Bonded Moisture Content (%) ± ± ± ± 0.22 Flexural Modulus (GPa) 33.8 ± ± ± ± ± ± 1.9 Flexural Strength (MPa) 853 ± ± ± ± ± ± 31 Flexural stiffness and strength reduced due to poor fibre/matrix interfacial strength Poorly bonded systems tend to absorb higher levels of moisture 5

6 Nano-scale Characterisation - Recap Force Modulation AFM used to detect surface elasticity Differences between strong and weak interfacial bonding visualised Region of 50 to 300 nm found with different phase & force response 3D and 2D Phase image of third phase detected at the interface of a glass fibre reinforced vinylester pultruded rod with poor bonding

7 Nano-scale Characterisation Key issues of AFM measurements Accuracy Interpretation of data Sensitivity Lack of consensus Comparative characterisation techniques SEM TEM

8 Tip Validation and Image Artifacts 1 μm typical scan of porous aluminium taken using the Autoprobe M5 Estimation of tip geometry based on porous aluminium scan Peak in amplitude Wedge Topographic image of flake (left) in polypropylene matrix (right) with wedge between the two material phases Force modulation amplitude map showing peak in amplitude in the location of the wedge cavity 8

9 Sensitivity of Measurements Reference samples to identify and calibrate The limit of measurements for a particular tip or cantilever Sensitivity of a particular measurement technique Relationship between AFM measurements and indentation results 50 micron scan of the interface of the prototype calibration sample: Fused Silica (right) and PMMA (left) The region of low topography is saturated and is possible due to a void 9

10 Glass/Vinylester Pultruded Rods - Poorly Bonded Magnification (x 10,000) Residue on a glass fibre after fracture Magnification (x 20,000) Film on a glass fibre after fracture 10

11 Poorly Bonded Glass Fibre Conclusions SEM images confirm differences suggested by AFM measurements Further work with AFM required to design suitable a characterisation technique Magnification (x 5,000) Film like layer between matrix and fibre for the poorly bonded glass reinforced vinylester matrix 11

12 Force Displacement (FD) A method of using the AFM to indent the surface at the nanoscale to measure elasticity and adhesion 3 0 approach 1 tip snaps to surface 2 indentation 3 tip retracts 4 tip sticks on surface 5 tip snaps back 6 retract Force Distance Approach Retract Schematic diagram of a typical FD curve 12

13 Force Displacement 2 different AFM used, Differences shown between glass and surface only using relatively stiff cantilevers with diamond tips Indentation measurements taken across a glass fibre reinforced vinylester interface Rate 0.5 Force (N/m) Indent number AQYH Topographic Image of interface indentation measurements taken across interface 13

14 Force Displacement Mapping of surface elasticity is possible using Force Displacement Work required (primarily using reference samples) to establish Accuracy Sensitivity Relationship between measured stiffness to the elastic modulus In order to Provide traceable methods that are transferable between different AFM s and independent of operator Mapping of elastic modulus 14

15 Transmission Electron Microscopy (TEM) TEM analysis requires specimens of less than 100nm for analysis TEM of solids - samples can be prepared by cutting them with an ultra-microtome Focused Ion Beam (FIB) allows preparation of composite material TEM specimens without destroying the interface FIB image of milled section across a glass fibre reinforced vinylester interface 15

16 Focused Ion Beam (FIB) A focused beam of gallium ions used to splutter the atoms at the surface 50nm thick section milled Sample rotated and section milled out from surface Ultra-thin section collected by small robotic arm Gallium liquid metal ion source Gallium liquid metal ion source 50 nm 16

17 Focused Ion Beam Also possible to deposit thin layer of tungsten on surface to prevent differential milling rates Milled section with tungsten strap Milled section without tungsten strap FIB image of milled cross section of glass fibre reinforced vinylester 17

18 Focused Ion Beam FIB image of a glass fibre (left) reinforced vinylester (right) interface FIB image of a glass fibre (left) reinforced vinylester (right) interface 18

19 Summary AFM has been demonstrated to be a suitable method for qualitative imaging of surface elasticity and quantitative measurements SEM is a suitable qualitative comparison for AFM measurements Methodology is being investigated for preparing TEM specimens and subsequent analysis of composite interfaces# Calibration of measurements and relation to elastic modulus, as well as issues of repeatability and sensitivity of measurements will influence the effectiveness of any industrial AFM method Primary research activities Reference samples for AFM measurements Relating AFM measurements to surface modulus TEM preparation and analysis 19

20 Modelling - Transverse Isotropic Concentric Cylinders 20

21 Multi-Model Elastic Property Predictions E-glass/Vinylester Case E 11 (GPa) E 22 (GPa) ν 12 ν 12 G 12 (GPa) α 11 α 22 (10-6 / C) (10-6 / C) Case 1 Undamaged Case 2 Interphase layer properties degraded by 50% Case 3 Interphase layer properties degraded by 75% Case 4 Interphase layer properties degraded by 100% 21

22 E-glass/Vinylester (AXIS Predictions) Axial displacement on crack plane Axial stress on crack plane Displacment (microns) Stress (GPa) Axial Displacement Axial Stress Radial distance (microns) -5 Radial distance (microns) Interfacial shear stress Interfacial radial stress Stress (GPa) 5 4 Stress (GPa) Shear Stress Radial Stress z (microns) z (microns) 22

23 E-glass/Vinylester - Interphase Degraded by 50% (AXIS) Axial stress on crack plane Axial displacement on crack plane Displacment (microns) Axial Displacement Stress (GPa) Axial Stress Radial distance (microns) -2 Radial distance (microns) Interfacial shear stress Interfacial radial stress Stress (GPa) Shear Stress Stress (GPa) Radial Stress z (microns) z (microns) 23

24 E-glass/Vinylester - Interphase Degraded by 100% (AXIS) Axial displacement on crack plane Axial stress on crack plane Displacment (microns) Axial Displacement Stress (GPa) Axial Stress Radial distance (microns) -2 Interfacial Radial distance radial stress (microns) Shear Stress = 0 Stress (GPa) Radial Stress z (microns) 24

25 Case Study 2: Glass Flakes Flake products: REFG302, REFG101 and REF600 or REF160N Resin: Polypropylene Surface treatments: None, aminosilane and titanate Mechanical properties: Hardness Impact (fracture toughness) Flexure strength/stiffness Thermal conductivity/thermal expansion Permeation Supplier: NGF Europe 25

26 Glass-Flake/Polypropylene Physical Properties Material Density (kg/m 3 ) Volume Fraction (%) Shore Hardness D Polypropylene 905 ± 1 N/A 21.9 ± 0.1 Untreated Flake 1,126 ± ± ± 0.1 Titanate 0.09% 0.42% Aminosilane 0.05% 0.28% 1,115 ± 1 1,121 ± 2 1,129 ± 1 1,117 ± ± ± ± ± ± ± ± ± 0.1 Fibre volume fraction and density almost identical for the five composite materials Surface hardness independent of surface treatment and presence of glass flakes 26

27 Glass-Flake/Polypropylene - Flexure Strength (MPa) Material Longitudinal Transverse Polypropylene ± ± 0.13 Untreated Flake ± ± 0.45 Titanate 0.09% 0.42% Aminosilane 0.05% 0.28% ± ± ± ± ± ± ± ± 0.57 Flexural strength increases with increasing filler/matrix interfacial strength Poorly bonded systems tend to exhibit lower flexure strength 27

28 Glass-Flake/PP (Titanate 0.09%) Plan View 0.2mm 28

29 Glass-Flake/PP (Untreated) Side View 0.2mm 0.2mm 29

30 Glass-Flake/Polypropylene (SEM Images) Untreated 30

31 Glass-Flake/Polypropylene (SEM Images) Aminosilane (0.05%) 31

32 Glass-Flake/Polypropylene (SEM Images) Aminosilane (0.28%) 32

33 Planar-Random Short-Fibre Christensen and Waals Micromechanic Predictions E c = E 11f 3 V f + ( 1 + V ) f E 11m ν c = ν 12f 3 V f + ( 1 + V ) f ν 12m ; V f < 0. 2 G c = 2 Ec ( 1 + ν ) c 33

34 Glass-Flake/Polypropylene Elastic Properties * Calculated Material Tension Test Plate Twist Test Predicted Elastic Modulus (GPa) Polypropylene Glass Flake/PP (untreated) Glass Flake/PP (0.05% aminosilane) Poisson s Ratio Polypropylene Glass Flake/PP (untreated) Glass Flake/PP (0.05% aminosilane) Shear Modulus (GPa) Polypropylene Glass Flake/PP (untreated) Glass Flake/PP (0.05% aminosilane) 1.89 ± ± ± ± ± ± * 1.59* 1.86*

35 Glass Flake/Polypropylene Flake Dimensions 95% Certainty in average min thickness 95% Certainty in average max length Average Min Thickness (μm) Average Max Length (μm) Untreated flakes % Aminosilane % Aminosilane % Titanate % Titanate

36 Glass-Flake/Polypropylene Modulus ( %) - Temperature Polypropylene Polypropylene + Glass Flake Polypropylene + Glass Flake + Aminosilane Tensile Modulus, MPa Temperature, C 36

37 Glass-Flake/Polypropylene - CTE F3281 Polypropylene ABEC 6000 F3282 Polypropylene-glass flake ABED Fractional length change, ppm Fractional length change, ppm First cycle, cooling First cycle, heating Second cycle, cooling Second cycle, heating Third cycle, cooling Third cycle heating Final cool Temperature, C 5000 F3283 Polypropylene/glass-flake 0.05% aminosilane ABEE First cycle, cooling First cycle, heating Second cycle, cooling Second cycle, heating Third cycle, cooling Third cycle heating Final cool Fractional length change, ppm Fractional length change, ppm First cycle, cooling First cycle, heating Second cycle, cooling Second cycle, heating Third cycle, cooling Third cycle heating fourth cycle, cooling Fourth cycle, heating Final cool Temperature, C 6000 F3285 Polypropylene/glass flake 0.09% titanate ABEG First cycle, cooling First cycle, heating Second cycle, cooling Second cycle, heating Third cycle, cooling Third cycle heating Final cool Temperature, C Temperature, C 37

38 Glass-Flake/Polypropylene Strain Relaxation Dilatometry CTE Measurements Material Strain Relaxation (%) Polypropylene 0.31 Untreated 0.35 Titanate 0.09% 0.42% Aminosilane 0.05% 0.28%

39 Residual Stress Measurement Techniques Feasibility study in SM09 to examine: Curvature measurements Hole drilling Raman spectroscopy Embedded fibres (Fibre Bragg Grating) Laminate analysis modelling to predict residual stresses Dilatometry (strain relaxation) 39

40 Curvature Measurements z x σ x (z) y σ y (z) 0 /90 CFRP laminate M x M x Residual stress can be determined from the curvature that results during the cooling of unsymmetric composite laminate (e.g. 0 /90 ) 40

41 41 Residual Stress [0 /90 ] Laminate + c 2 2 c c 2 L sin 2h h ρ ρ ρ ( ) ( ) = d E 1 b E 1 d b 6 d E b E 2 d b k E h E h E E c r ρ σ h ρ c 2L

42 Curvature Measurements Layer Removal 42

43 Residual Stress Hole Drilling A hole is drilled into the composite and the residual stress calculated from the strains that develop around the hole 43

44 Residual Stress DIC Images of Drilled Hole Glass Flake/Polypropylene - Untreated 44

45 Radial Displacement around Drilled Holes Glass Flake/Polypropylene radial displacement (µm) ABED Untreated ABED Thermal Cycle ABEE Untreated ABEG Untreated -0.7 Distance from hole centre (µm) ABED - Untreated ABEE Aminosilane (0.05%) ABEG Titanate (0.09%) 45

46 Residual Stress DIC Results radial displacement (µm) Distance from hole centre (µm) ABED Untreated ABED Thermal Cycle ABEE Untreated Polypropylene2 46

47 Glass-Flake/Polypropylene Thermal Properties Material T g T melt Crystallinity (J/g) ( C) ( C) Polypropylene Untreated Flake Titanate 0.09% 0.42% Aminosilane 0.05% 0.28% T g and T melt independent of surface treatment and presence of fibres Crystallinity reduced with introduction of glass flakes Crystallinity decreases slightly with increasing filler/matrix interfacial strength 47

48 Raman Spectroscopy Section of Stokes Raman spectrum of a-quartz Counts (arbitrary) Laser Laser nm Raman shift (cm -1 ) ν = ν 0 - (ν 0 ν ph) Beamsplitter Dilor XY Raman Spectrometer Detector Microscope objective Change with stress of 130 cm -1 feature Sample Counts (arbitrary) Raman shift (cm -1 ) Schematic of scattering from α-quartz (SiO 2 ) (Dilor XY Raman spectrometer) 48

49 Raman Spectroscopy Glass Flake/Polypropylene Dilor XY Raman spectrometer Raman Intensity, (Arbitrary units) Raman shift (cm -1 ) 49

50 Raman Spectroscopy Unidirectional CFRP Renishaw Raman Spectrometer Raman intensity (arbitary units) Raman wavenumber (cm-1) 50

51 DMA Results Glass Flake/Polypropylene 51

52 Case Study 3: Nanocomposite PNCs: Clay and silica nanoparticle reinforced PMMA composites Weight additional levels (wt %) Mechanical properties: Fracture toughness (impact resistance) Tensile properties Creep rupture (environmental effects) Solvent craze resistance Permeation Supplier: Lucite International UK Ltd 52

53 Thank you for listening Any Questions? Case Studies? 53