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Fibre Composite Reinforcement > 5: Moulding > Flashcards

5: Moulding Flashcards

1
Q

What is the mechanism of moulding of thermosets?

A

-Energy (heat, photons, electrons, ect) applied to hardener to create reactive species
-Combined with base resin (monomers/oligomers)
-Exothermic crosslinking reaction creates thermoset polymer

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2
Q

Describe the Kamal-Sourour curing reaction model for thermoset resins

A

Degree of cure:
-increases with time
-converges to 100% as time tends to infinity

Cure rate:
-increases with degree of cure
-as exothermic reaction rate decreases with increased degree of cure, the rate slows

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3
Q

What does Differential Scanning Calorimetry measure for thermoset resins?

A

Heat flux to or from the resin while temperature is raised

-First drop step in curve indicates glass transition point
-Later peak shows exothermic heat flux (curing reaction)
-With increasing time the glass transition temperature increases, and rate of curing reaction (exothermic energy) decreases

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4
Q

Explain the thermoset resin processing chain (storage, moulding, curing, post-curing, cooling)

A

Storage:
-Glassy uncured resin is stored at low temperature (solid resin)

Moulding:
-Temperature increases above glass transition (resin becomes liquid)

Curing:
-Cross-linking reaction forms single molecule polymer network (gelation), cross-linking continues

Post-Curing:
-Additional heat applied
-Higher degree of cross-linking (increasing mechanical properties)

Cooling:
-Rubbery to hard solid as temperature is below glass transition

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5
Q

How does the glass transition temperature vary between the liquid resin and crosslinked resin for thermoset matrices?

A

-Glass transition of the liquid resin is lower than the crosslinked resin

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6
Q

What are the 3 stages of thermoset resin processing?

A

A-Stage:
-Early chemical reaction (resin + hardener mixed)
-Liquid at rtp
-used as “out of the bucket” composite manufacturing

B-Stage:
-Intermediate reaction (partially cured but not gelled)
-Tacky at rtp, so frozen for storage to halt the reaction until use
-Used in prepreg laminates (activated by heat)

C-Stage:
-Resin is solidified (finished component

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7
Q

Explain the importance of viscosity for thermoset resins

A

-Viscosity is correlated to permeability (depends on shear rate, however negligible at low flow rates)

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8
Q

How does viscosity vary during the processing of thermoset resins?

A

-Decreasing viscosity with increasing temperature
-Increasing viscosity with increasing degree of cure
-Viscosity, degree of cure and temperature all depend on time
-Low viscosity increases wet-out (full impregnation), so set the moulding temperature accordingly
-Can determine an appropriate processing window

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9
Q

How does volumetric shrinkage vary between non-isothermal cure and isothermal cure in thermosets?

A

-Volumetric shrinkage is greater for non-isothermal cure, resulting in higher residual stresses
-Increased volume change leads to increased risk of deformations

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10
Q

How is temperature controlled for non-isothermal and isothermal thermoset reactions?

A

Non-isothermal:
-Temperature is not controlled (Temp increases due to exothermic reaction)

Isothermal:
-Temperature is controlled (To reduce volumetric shrinkage)

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11
Q

How does modulus vary with temperature during crosslinking of a thermoset?

A

-For cured resin; high glass transition temperature is related to high degree of cure
-If temperature is very high then the cross-linked resin will degrade

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12
Q

Why is temperature control during moulding of thermosets important?

A

-Controls viscosity (ability of wet-out)
-Maximise the degree of crosslinking (improving mechanical properties)
-Minimises the residual stresses

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13
Q

How do stress/strain plots vary for processed thermosets tested at different temperatures?

A

-Glass transition here is 90 degrees, reflected by the graph (transition from brittle to more ductile as temperature increases)

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14
Q

What is the structure of amorphous thermoplastics?

A

-Entangled chain molecules

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15
Q

What is the structure of semi-crystalline thermoplastics?

A

-Chain molecules are partially structured in lamellae
-Amorphous phase between lamellae
-Lamellae arranged in larger structures (spherulites)

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16
Q

Explain the thermoplastic matrix processing chain (storage, moulding, cooling)

A

Storage:
-stored at room temperature

Moulding:
-Temperature increases above glass transition, formable then liquid (for amorphous)
-Temperature increases above glass transition and melt temperature (higher energy needed to break crystalline phase) (for semi-crystalline)

Cooling:
-Cool below glass transition, hardens (brittle)

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17
Q

Explain the importance of viscosity for thermoplastic matrices

A

-During moulding, flow depends on viscosity
-No effect of viscosity on degree of cure (as no cross-linking reaction occurs)
-Shear rate dependence is important at high flow velocities (eg. injection moulding)
-Viscosity varies as a function of temperature

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18
Q

How does specific volume vary with temperature for thermoplastics?

A

-Shrinkage during cooling is greater for semi-crystalline polymers than for amorphous polymers
-Effect of pressure: higher the pressure, the curves shift towards smaller specific volume and higher glass transition temperature
-Thermoplastic heating process is generally reversible (unless quenched)

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19
Q

How does volumetric shrinkage affect the material properties?

A

-Higher volumetric shrinkage results in large residual stresses, leading to deformations

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20
Q

How does Quenching (rapid cooling) of semi-crystalline thermoplastics affect the structure?

A

-Reduces the formation of lamellae and therefore remains an amorphous structure after quenching
-Upon reheating, the lamellae can recrystalise

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21
Q

How do mechanical properties of thermoplastics vary with temperature?

A

Amorphous:
-Hard & brittle below glass transition (high modulus)
-At glass transition, material is “rubbery” (reduction in modulus)
-Liquid above glass transition, therefore can only be used below the glass transition temperature

Semi-Crystalline:
-High modulus below glass transition
-Small reduction in modulus at the glass transition temperature (crystalline phase is unaffected)
-Significant drop in modulus at melt temperature as crystalline phase is disrupted

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22
Q

Why is the control of temperature important during the moulding process of thermoplastics?

A

-To control viscosity
-Important to control the cooling rate to manage the degree of crystallinity and glass transition temperature

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23
Q

How does controlling of pressure help during the moulding process of thermoplastics?

A

It helps compensate for shrinkage

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24
Q

Explain the wet-layup open mould process

A

-Apply release agent to mould surface
-Add layer of reinforcement mat/fabric
-Apply resin (“wet-out”) with a brush/roller
-Consolidate with roller to fully distribute the resin and remove air
-Allow to cure
-Demould and trim

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25
Q

What is a gelcoat in the wet-layup open mould process

A

Additional resin layer which defines visible part surface properties

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26
Q

What are the advantages of the wet-layup open mould process

A

-Low investment costs
-Flexible (easy production of most geometries)

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27
Q

What are the disadvantages of the wet-layup open mould process

A

-Time consuming
-Labour intensive
-Low repeatability of accurate parts (due to user errors)
-Poor dimensional control
-Relatively low fibre volume fractions (can be increased if vacuum bagged after impregnation)

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28
Q

What are the applications of the wet-layup open mould process

A

-Marine craft
-Large, lightly loaded structures
-Short production runs/one offs
-DIY/hobby applications
-Repairs

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29
Q

Explain the spray-up open mould process

A

-Mix of thermoset resin (polyester) & fibres (glass), chopped in a hand-held gun, sprayed onto the mould tool
-Left to cure at rtp
-Use of single sided mould (good surface finish on one side)
-100-500 parts per year

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30
Q

What are the advantages of the spray-up open mould process

A

-Uses roving (low cost material form)
-High deposition rates possible
-Not as labour intensive as wet lay-up
-Can be automated
-Suitable for large components

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31
Q

What are the disadvantages of the spray-up open mould process

A

-Operator is exposed to styrene emissions
-Low reproducibility (random fibre orientations)
-Poor dimensional control

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32
Q

What are the characteristics of Autoclave processing?

A

-Heated pressure vessel, isostatic pressure normal to the surface
-Connective heating (temperature control)
-Connections to vacuum pump

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33
Q

What intermediates are typically used in the autoclave process?

A

-Processing of lay-ups from thermoset prepregs
-B-stage thermoset resin & reinforcements already combined

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34
Q

What are the Autoclave process stages?

A

-Prepreg laid on tooling surface
-Lay-up enclosed in vacuum bag
-Tooling with lay-up is moved into an autoclave where it is cured

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35
Q

What does applied pressure & vacuum achieve in the Autoclave process?

A

Lay-up consolidation

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36
Q

What does applied Heating achieve in the Autoclave process?

A

Induce resin cure

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37
Q

What is the ideal tooling material used in the Autoclave process?

A

Same material as the laminate (same thermal expansion to prevent warping)

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38
Q

In practise, what is the tooling material used in the Autoclave process?

A

-Usually metal (high dimensional stability and more durable)

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39
Q

What is the purpose of cut-outs in the tooling used in the Autoclave process?

A

Allows sufficient airflow to control thermal expansion

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40
Q

How is heat capacity of the tool material important in the Autoclave process?

A

Affects the rate of heating to cure temperature

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41
Q

What are the components of the vacuum bag in the Autoclave process?

A

-Vacuum film: seals lay-up from outside air

-Breather: non-woven felt, allows airflow when a vacuum is applied

-Barrier film: prevents resin from permeating into breather

-Bleeder: non-woven felt, absorbs excess resin

-Peel ply: porous fabric (allows excess resin to permeate into the bleeder), prevents sticking between the bleeder and laminate (leaves a textured surface)

-Prepreg lay-up: Resin infused reinforcement fibre

-Mould release: prevents the laminate from bonding to the tool

-Tooling: provides 3D shape for prepreg to conform to

-Sealant tape: seals lay-up from outside air

All components must withstand the curing temperature (high disposable waste process)

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42
Q

Explain the autoclave cycle steps

A

-Increase temperature to reduce resin viscosity (rate determined by thermal mass (heat capacity) of tooling & lay-up)
-Resin flows at reduced viscosity, vacuum removes trapped air
-Ramp up to cure temperature, pressure increases to compress residual voids
-Hold pressure & temperature until curing is complete
-Cool down to demoulding temperature, vent to ambient pressure

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43
Q

What are the advantages of the Autoclave process?

A

-High part quality (good mechanical properties due to low void content)

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44
Q

What are the disadvantages of the Autoclave process?

A

-High cost (high energy, high setup costs and high material costs)
-Labour intensive

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45
Q

What are the process steps for Liquid Composite Moulding (LCM)?

A

-Dry fibre reinforcement placed in tooling
-Compaction pressure is applied
-Dry fibre is impregnated with liquid resin, pressure gradient is applied
-Composite is left to cure, and removed from the tooling

46
Q

What materials are usually used in Liquid Composite Moulding (LCM)?

A

-mats/fabrics
-Preforms from fabrics
-Thermoset resins

47
Q

How does resin flow velocity affect the product in Liquid Composite Moulding (LCM)?

A

-Impregnation amount
-Time required for complete impregnation (wet-out)

48
Q

What material properties are desirable for good resin flow for Liquid Composite Moulding (LCM)?

A

-High permeability of the reinforcement
-Low viscosity of the fluid
-High pressure gradient

49
Q

How does permeability vary with Volume fraction for Liquid Composite Moulding (LCM)?

A

-Increasing Vf reduces permeability
-Can vary with fibre orientations

50
Q

How do you achieve low viscosity of the resin for Liquid Composite Moulding (LCM)?

A

-Preheat the resin prior to injection
-Heat the tool prior to injection

However, this accelerates the curing process, increasing viscosity over time

51
Q

Why are molten thermoplastics unsuitable for Liquid Composite Moulding (LCM)?

A

Viscosity is too high, can be achieved with injection moulding, but is uncommon

52
Q

How can poor mould design affect Liquid Composite Moulding (LCM)?

A

Can result in zero pressure gradients (stalled resin flow (dry spots))

53
Q

Explain the Resin Transfer Moulding (RTM) process variant of Liquid Composite Moulding (LCM)

A

Stiff matched (dual) tooling, Positive pressure and/or vacuum applied (~10bar pressure difference)

-Preparation: produce preform, apply mould release and place dry preform in cavity

-Injection: Mix resin and hardener, inject resin into cavity

-Curing: Heat mould to accelerate curing reaction

-Demoulding: Demould cured part and finish component

54
Q

What are the properties of the Resin Transfer Moulding (RTM) process variant of Liquid Composite Moulding (LCM)?

A

-Cycle time: ~hours
-Production rate: ~30,000ppa
-Good surface quality on both sides
-Fibre volume fraction: ~50%
-Geometrically complex components with high levels of parts integration

55
Q

What occurs if the mould is not stiff enough in the Resin Transfer Moulding (RTM) process variant of Liquid Composite Moulding (LCM)?

A

Preform compaction pressure and resin injection pressure can result in deflection.

Affects: thickness, Vf and permeability

56
Q

What are the properties of the High Pressure Resin Transfer Moulding (HP-RTM) process variant of Liquid Composite Moulding (LCM)?

A

-Cycle time: <10min
-Injection pressure: ~100bar)
-Faster impregnation

57
Q

What are the issues with the High Pressure Resin Transfer Moulding (HP-RTM) process variant of Liquid Composite Moulding (LCM)?

A

-High tool closing force required
-Sealing of mould tool is required
-Fluid pressure can deform or displace the preform
-Expensive

58
Q

Explain the Vacuum Infusion (VI) process variant of Liquid Composite Moulding (LCM)

A

-Stiff tooling on one side, vacuum bag on the other side of the component
-Resin flow is driven by vacuum only from a resin reservoir (resin trap prevents resin flow to the pump)
-Components are cured at room temperature

59
Q

What are the components of the vacuum bag in the Vacuum Infusion (VI) process variant of Liquid Composite Moulding (LCM) process?

A

-Vacuum film: Seals lay-up from outside air

-Flow medium: Allows resin distribution

-Peel ply: Porous fabric allowing resin exchange between flow medium and reinforcement

-Reinforcement: dry reinforcement fabric

-Mould release: Prevents laminate from bonding to tooling

-Tooling: Provides 3D shape for finished part

-Sealant tape: Seals lay-up from outside air

60
Q

What are the advantages of the Vacuum Infusion (VI) process variant of Liquid Composite Moulding (LCM)?

A

-Good surface quality on one side
-Tooling costs are lower than for Resin Transfer Moulding (RTM)
-Suitable for manufacture of large components (eg. ship hulls, wind turbines)

61
Q

What are the disadvantages of the Vacuum Infusion (VI) process variant of Liquid Composite Moulding (LCM)?

A

-Slow process
-Poor dimensional control
-Lots of consumables used
-Long cycle time (slow curing due to long infusion and low pressure gradient)

62
Q

Explain the Filament Winding Process

A

-Continuous dry fibres are wetted in resin (excess removed) and deposited on a rotating mandrel
-Mandrel removed once cured leaving a hollow component
-Any fibre can be used
-Fibres positioned along a pre-determined pattern (CNC controlled by guide linear speed and mandrel rotation speed)

63
Q

What are the available patterns and applications for the Filament Winding Process?

A

Hoop:
-For internal pressures (pipework)
-Open ended

Helical:
-For torque applications (Driveshafts)
-Open ended

Polar:
-For internal pressures (pressure vessels), metal liner required internally preventing gas permeation
-Closed ended

64
Q

What are the fibre path properties for the Filament Winding Process?

A

-Fibre path must be geodesic (shortest possible line due to tension), to prevent tow slipping
-Non-geodesic paths are possible if a tacky material is used
-Possible fibre paths are constrained with double curvature geometries
-Fibre angle must be adjusted for changes to mandrel diameter (avoids fibre bridging)

65
Q

How does fibre tension affect the properties in the Filament Winding Process?

A

-Tension translates to radial compaction pressure
-Affects fibre volume fraction
-Affects void content

66
Q

What are the advantages for the Filament Winding Process?

A

-High Vf (good for structural parts)
-Metallic fasteners can be integrated (ends of component)
-Highly automated
-Highly reproducible
-High deposition rates (~50kg/hr)

67
Q

What are the disadvantages for the Filament Winding Process?

A

-Geometric restrictions
-Poor dimensional accuracy (surface quality) on the outer surface (can be mitigated using heat shrink after manufacture)

68
Q

What are the applications for the Filament Winding Process?

A

-Pipes (hoop pattern)
-Drive shafts (helical pattern)
-Pressure vessels (polar pattern)
-Wind turbine blades
-Railway carriages

69
Q

Explain the Pultrusion moulding Process

A

-Manufacture of continuous profiles (extrusions)
-Fibre bundles wetted (resin bath) & passed through a heated die (for curing)
-Mostly unidirectional rovings/tows (can use mats/fabrics)
-Typically glass fibre & thermoset resin (polyester)
-Reduced friction in the die due to polyester shrinkage (easier demoulding)
-Fully automated process

70
Q

What are the properties in the Pultrusion moulding Process?

A

-Diameter: ~3-150mm
-Speed: ~1-2m/min
-Pulling speed dependent on material & cross-section
-Influenced by: heat-up, curing & cooling
-Wall thickness: ~1-76mm

71
Q

What are the advantages of the Pultrusion moulding Process?

A

-High productivity
-Low labour content
-Precise cross-sectional dimensions
-Good surface finish
-Homogeneous fibre distribution
-High Vf
-Minimal fibre crimp & curvature

72
Q

What are the disadvantages of the Pultrusion moulding Process?

A

-Geometric limitations (extrusion shapes)
-Complex (expensive) die designs
-High capital equipment cost (minimum 500ppa)

73
Q

Explain the Thermoplastic Stamping moulding process (preparation, heating, consolidation, cooling, demoulding)

A

Preparation:
-Apply release agent to mould
-Untreated blank constrained in a spring-frame

Heating:
-Controlled heating (avoids polymer degradation) melts thermoplastic prepreg tapes/sheets (heaters/oven)

Consolidation:
-Transfer blank (2D) to matched tool, temperature below Tm
-Apply pressure to drape/form (3D)

Cooling:
-Solidify thermoplastic material (cooling rate determines residual stress & crystallinity)

Demoulding:
-Eject part and finish component (suitable for shell structures with uniform thickness)

74
Q

Give an overview of Compression Moulding

A

-Discontinuous fibres & thermoset resin are pressed by heated tool, left to cure
-Short cycle time (high volume production; >100,000ppa)
-Hydraulic press with moulded tool (50-150 bar)
-Isothermal process (component is hot-demoulded)

75
Q

Explain the Compression Moulding process

A

-Fibre/matrix pellet (charge) cut and weighed
-Charge is placed in the preheated matched tool (male + female dies)
-Tool rapidly closed and pressure is applied
-Charge flows to fill extremities of the tool
-Matrix material cross-links (due to heat)
-Tool is opened, ejecting the part
-Tool must be cleaned before next cycle

76
Q

What are the tooling conditions for the Compression Moulding process?

A

-Very high quality tool surface finish (for class A composites and fast cycles)

-Hardened & chromed P20 steel for tooling

-Locally hardened sections for critical wear areas (shear edges)

-Uniform mould temperature and fast thermal response (heat transfer is critical)

-Air (flash) gap required (~0.2mm)

77
Q

What induces fibre alignment (driven by shear) during the Compression Moulding process?

A

-Initial shape of the charge (%tool coverage)
-Position of the charge
-Geometry of the tool (divergent=perpendicular to flow, convergent=parallel to flow)
-Tool closing speed

78
Q

How can mechanical properties vary in components manufactured by the Compression Moulding process?

A

-Fibre alignment (longitudinal alignment to applied load is optimal)
-Weld lines (where 2 fronts meet, leads to a stress concentration)

79
Q

What are the advantages of the Compression Moulding process?

A

-Highly automated
-Short cycle time (<10mins)
-High production volume (>100,000ppa)
-Complex geometries (with closed dimensional control)
-Low material wastage (net shape components)
-Class-A surface finish
-Simple mould designs (no gating)

80
Q

What are the disadvantages of the Compression Moulding process?

A

-Highly variable (weld lines, fibre/matrix separation, agglomerations)
-Non-uniform consolidation pressure (determined by die geometry)
-Limited fibre volume fraction (<50%), varies with charge/pellet type
-High tooling costs

81
Q

Explain the Injection Moulding process steps

A
82
Q

How is shear stress calculated during Injection Moulding?

A

Shear stress = Viscosity * Shear rate

83
Q

How is shear stress rate calculated during Injection Moulding?

A

Differential of velocity with respect to displacement

84
Q

Explain the relative velocity and shear rate against through-thickness position for Newtonian and Non-Newtonian behaviour

A
85
Q

What are the advantages of the Injection Moulding process?

A

-Very high production rates (>250,000ppa)
-Highly automated
-Complex geometries
-Good tolerances on small parts
-Minimum material wastage

86
Q

What are the disadvantages of the Injection Moulding process?

A

-High tooling cost
-Only suitable for high production volume
-Varied thickness & cooling rates leads to warping
-Large undercuts cannot be executed
-Melt flow distance limited in plane
-Limited mechanical properties (short/discontinuous fibres)

87
Q

Why is Non-Destructive Testing (NDT) used?

A

-To identify and characterise damage within and on the surface without altering the part
-To be used after visual & dimensional inspection

88
Q

Why does Non-Destructive Testing (NDT) carry substantial costs?

A

-Staff
-Equipment
-Disruptions to production

89
Q

How does cost of inspection and probability of defect detected vary with inspection methods?

A

-Probability of an undetected defect decreases with each inspection process

-Cost of inspection increases with each inspection process

90
Q

What defects are aimed to be detected by Non-Destructive Testing (NDT)?

A

-Delamination
-Cracks
-Voids (porosity)
-Resin richness
-Contaminants (foreign objects) within the laminate
-Ply misalignment (incorrect layup)
-Fabric wrinkles
-Fibre bridging
-Incomplete bond lines in adhesive joints
-Core crush in sandwich panels

91
Q

What are visual inspection methods in Non-Destructive Testing (NDT)?

A

-Look for surface pitting (suggests internal voidage)
-Add surface coatings (contrasts show irregularities)
-Fluorescent matrix material (contrasts under UV light)
-Dye application (permeates and developed to draw to the surface, inspected under UV)

92
Q

What is Dimensional Inspection used for in Non-Destructive Testing (NDT)?

A

-First article inspection (check manufacturing equipment is installed correctly)
-Quality control (ensure components are within tolerance)

93
Q

Why is Dimensional Inspection used in Non-Destructive Testing (NDT)?

A

-Compare dimensions against original CAD model
-Check for changes in dimensions (due to shrinkage)

94
Q

What are the methods of Dimensional Inspection used for in Non-Destructive Testing (NDT)?

A

Contact:
-Coordinate measuring machine (CMM)

Non-Contact:
-Structured white light 3D scanner
-3D laser scanning

95
Q

What determines what method is used for Dimensional Inspection used for in Non-Destructive Testing (NDT)?

A

-Reflectivity of surface (unsuitable for scanning methods)
-Compliance of material/structure (unsuitable for contact methods)
-Colour of object (Black doesn’t work for white light scanning)
-Scale of object (contact unsuitable for small, complex parts)

96
Q

Explain Non-Destructive Testing (NDT) Tap testing method

A

-Tap every point with a coin/hammer
-Acoustic response differs for local material stiffness
-Clear sound (indicates stiffness, structure intact)
-Dull sound (reduced stiffness, delamination or void)

97
Q

What are the advantages of the Non-Destructive Testing (NDT) Tap testing method?

A

-Very simple and cheap method

98
Q

What are the disadvantages of the Non-Destructive Testing (NDT) Tap testing method?

A

-Results rely on inspector perception (however, advanced test rigs exist)

99
Q

Explain Non-Destructive Testing (NDT) Ultrasonic methods

A

-High frequency sound waves (1MHz-50MHz) detects internal flaws
-Coupling medium is required (eg. water allows acoustic transmission to the part)

Either reflection method:
-Material surface or internal defects
-Transducer transmits and receives the signal
-Amplitude and delay of reflection are measured to give an image

Or transmission method:
-Transmitter and receiver on opposite sides of the specimen
-Measure amplitude of the transmitted signal giving an image

100
Q

Explain the A-scan Ultrasonic Non-Destructive Testing (NDT) method

A

-Amplitude of the pulse is recorded against time
-Information at a single point
-Defects cause an additional echo appearing as a signal
-Depth of defect determines echo delay and pulse strength

101
Q

Explain the B-scan Ultrasonic Non-Destructive Testing (NDT) method

A

-A-scans recorded while transducer moves on the specimen surface
-Gives cross-section information on depth of defects

102
Q

Explain the C-scan Ultrasonic Non-Destructive Testing (NDT) method

A

-Most popular (gives attenuation as a function of 2D position)
-No depth information (only defect detection)
-Used in reflection or transmission set-up
-Benchmark required to interpret scan data

103
Q

What are the advantages of the C-scan Ultrasonic Non-Destructive Testing (NDT) method?

A

-Most common NDT inspection technique
-Easily detect voids as air greatly affects sound attenuation
-Fast scanning speeds
-High resolution

104
Q

What are the disadvantages of the C-scan Ultrasonic Non-Destructive Testing (NDT) method?

A

-High equipment costs
-Skilled operator required
-Some composites are hydrophilic, therefore water coupling can cause issues

105
Q

Explain the Radiography-x-Ray Non-Destructive Testing (NDT) method

A

-Non-contact NDT method
-Short wavelength electromagnetic radiation (0.03nm-3nm)
-Transmission degree depends on: Material density, thickness and composition
-Difficult to distinguish between fibre/resins (similar density)
-Voids & cracks are detectable due to air pockets
-Glass fibres (good absorbers) used as tracers
in CFRP parts
-Safety precautions are required

106
Q

Explain the x-Ray Computed Tomography Non-Destructive Testing (NDT) method

A

-X-Ray measurements are taken at different angles (virtual slices)
-Specimen typically rotated in front of x-Ray source
-3D reconstruction to visualise internal features
-Relatively slow process, computing power required
-Laboratory environment required

107
Q

Explain the Thermography Non-Destructive Testing (NDT) method

A

-Analysis of thermal flow from excitation of an object
-Thermal energy propagation within object influences surface temperature over time
-Thermal cameras used to visualise temperature field
-Thermal conductivity affected by material structure
-Detects: fibre architecture irregularities (orientation, Vf, ect.), Delamination and voids

108
Q

What is the Externally Applied Thermal Field (EATF) Thermography Non-Destructive Testing (NDT) method?

A

-Heat source is applied directly to the laminate
-Heat distribution on the opposite surface maps through thickness diffusivity

109
Q

What is the Stress Generated Thermal Field (SGTF) Thermography Non-Destructive Testing (NDT) method?

A

-A small cyclic load is applied to the structure
-Temperature distribution is generated

110
Q

Explain the Structural Health Monitoring Non-Destructive Testing (NDT) method

A

-In-service monitoring of structures
-Used for large stiffness driven components (wind turbine blades, bridges, yacht masts)
-Optical fibre & sensors (can create stress concentrations) are embedded (strain and temperature affects the wavelength of transmitted light)

111
Q

Describe the Kamal-Sourour curing rate model for thermoset resins

A

Curing rate:
-has a maximum at a certain degree of cure
-Increases with increasing temperature

Fibre Composite Reinforcement (10 decks)

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