How NDT will underpin the certification of greener aircraft€¦ · How NDT will underpin the...

How NDT will underpin the certification

of greener aircraft

Robert A Smith

Professor of NDT and High Value manufacturing,

University of Bristol.

President – British Institute of NDT

Acknowledgements

• Prof Stephen Hallett

• Dr Luke Nelson

• Dr Martin Mienczakowski

• Dr Rostand Tayong

• Miss Ningbo Xie (PhD student)

• Acknowledgements

• The Green Challenge

• Composite materials

• Non-destructive Testing (NDT) and aircraft design

• Ultrasound

• Microscopic 3D imaging

• NDT-based prediction of strength

• Conclusions - Will Green Aircraft Fly?

Content

The Green Challenge…

Image: Airbus Image: Rolls Royce

Environmental targets:

• Advisory Council for Aeronautical Research in Europe (ACARE) target:

• 50% reduction in CO2 per passenger-km by 2020

• ‘FlightPath 2050’ (EU) targets:

• 75% reduction in CO2 per passenger-km by 2050

• 65% reduction in noise by 2050

The Green Challenge

• Transport-mode CO2 trends projected to 2050

The Green Challenge

Source: Road & Rail – TREMOVE v3.3.1 (EU-27 + 3 countries) Air – TRENDS (EU-15 countries)

• Air CO2 trends projected to 2050, with targets

The Green Challenge

Source: TRENDS (EU-15 countries)

The Green Challenge

AIRBUS Concept Plane Fuel-efficient (green) design

Longer, slimmer wings reduce drag.

Engines at rear and semi-embedded. Reliable, quiet and fuel-efficient.

U-shaped tail shields noise.

Images: Airbus

The Green Challenge

• Environmentally-friendly Aircraft

• Low CO2 emissions

• Low noise

• Low fuel burn

• High speed

• Low hassle

• Low-cost flights

• Perfectly safe

• Let’s look at safety…

Image: Airbus

The amazing safety of air travel

Source: Bureau of Aircraft Accidents Archive


Source: Bureau of Aircraft Accidents Archive Source: ICAO http://www.theguardian.com/world/ng-interactive/2014/aviation-100-years

http://www.theguardian.com/world/ng-interactive/2014/aviation-100-years








Source: Bureau of Aircraft Accidents Archive Source: ICAO

1/8bn










Source: Bureau of Aircraft Accidents Archive Source: ICAO

NDT is not solely responsible for this increase in safety but it is largely the reason why air travel is still affordable and (reasonably) delay-free whilst also being safe.


• Safety is improving consistently due to:

• advanced modelling and simulation techniques

• rigorous testing of specimens, components and full-scale tests such as on wings…


• Safety is paramount

• The absolute level of safety demanded by certifying authorities will not decrease.

• Manufacturing variations / deviations

• do not reduce safety because:

• designs are made stronger to maintain safety levels

• NDT will be key to the achievable level of:

• environmental impact (CO2, noise, fuel burn, etc)

• cost (manufacture, maintenance, fuel, etc)

• reliability / hassle (take-off delays, cancellations)

- whilst achieving certification for safe flight.

• Better NDT opens up the design envelope by:

• increasing confidence, and

• reducing uncertainty in performance.

Why Wouldn’t Green Aircraft Fly?

Composite materials

Increased strength compared with the same weight of metal, allowing weight reduction.

• Carbon-fibre polymer-matrix (plastic) composites.

• Long fibres made of carbon, embedded in…

• Matrix – epoxy (eg Araldite®)

Composite materials

1 mm

• Composites use a stack of crossed fibres 45°/0°/-45°/90°

• Deviations from straight fibres reduce the strength.

Composite materials

0°

45°

90°

-45°

1 mm

6 mm

• Effect of fibre waviness.

Mukhopadhyay, Jones & Hallett (2013)

Composite materials

TENSION

COMPRESSION

6 mm

6 mm

Just prior to damage Fibre failure in axial ply

Delamination & further fibre failure

Full compressive failure



Composite materials

Wrinkle Angle

• How wrinkles are avoided

• Mould-shape optimisation

• Rigorous testing and sectioning of specimens

• Optimum sequence of plies, especially at corners

• Any remaining wrinkles are compensated by:

• adding extra plies (thickness) to maintain safety levels

Composite materials

• Metals are only replaced by composites if:

• Appropriate properties are considerably improved

• Other materials

• Used for a reason

• Lower cost, or

• Harder, or

• Heat tolerant

Composite materials

Material breakdown for an Airbus A350 (Stansbury, 2014)

Image: Airbus

AIRBUS composite usage history

Image: Airbus

• Few options for more composite components.

The future for composites?

Co

mp

osi

tes

Stru

ctu

ral W

eig

ht

[%]

80

70

60

50

40

30

20

10

0

1970 1980 1990 2000 2010 2020 2030 2040 2050

Maximum number of composite components

Non-destructive Testing (NDT)

and the design envelope

The more we can guarantee that performance of composite will be as expected, the happier the certifying authority will be to certify the lighter designs.

• Many of the visionary objectives are in conflict.

• Most of the technical challenges are expensive.

• Low emissions conflict with low noise in engines.

Why Wouldn’t Green Aircraft Fly?

Low CO2

High cost High noise

Low cost High CO2

High noise

• Design goals met by thinner components

• Less weight

• Less drag (friction)

• Less raw material

• Less fuel

• Less CO2

• Less noise

• At what cost?

NDT and the design envelope

Image: Rolls Royce. Composite fan test-bed.

• Manufacturing goals for thinner components

• High quality

• Confirmed quality

• High yield (success)

• High throughput

• Low cost

• NDT can help!


Image: Boeing


• The aim:

• To help meet both design AND manufacturing goals.

• Thinner components, made faster and cheaper.

Ultrasonic NDT

Transmitting Transducer

Receiving Transducer

Loudspeaker Microphone

Ultrasound Transducers

Ultrasound Transducers

Audible sound Transducers

• Defects cause echoes that can be detected.

Ultrasonic NDT

Transducer

Specimen

F B

Time delay

F

B

Defect

Send pulse

B-scan (Brightness Scan)

• Plot the ‘brightness’ of the echo at every point.

• Standard medical image is a B-scan

B-scan Presentation

• Plot the ‘brightness’ of the echo at every point.

B-scan Presentation

Microscopic 3D imaging

Using ultrasound to probe microscopic structure.

• Ultrasonic vibrations of a composite

• Composite plies are stacked like resonant tubes.

• Plies of fibres – like tubes.

• Resin layers – like air gaps.


• Ultrasonic vibrations of a composite

• Measure resonant frequency, calculate ply thickness


• ‘Ply drops’ can be shown to have a significant impact on laminate strength

Ply tracking through ply drops

3D tracking of resin inter-ply layers

• Ply-drop coupons

• X-ray CT: 49 kV, 20 μm voxel size, 4 shots

48

3D tracking of resin layers

• Understanding the ultrasonic interaction

B-scans B-scan slice

3D tracking of resin layers

• Understanding the ultrasonic interaction

Ply surface height…


51

• In-plane fibre orientation

In-plane slice shows

Echoes at one time

Delay.

Variations due to the

Fibre bundles.


52

In-plane slice

• In-plane fibre orientation

In-plane slice shows

Echoes at one time

Delay.

Variations due to the

Fibre bundles.


53

In-plane slice

• 3D map of

• Fibre bunches

• 3D orientation


• 3D map of

• Fibre bunches

• 3D orientation


Dr Luke Nelson, Research Associate

NDT-based prediction of strength

• Predict performance of component.

• Materials model with actual 3D NDT data inputs

• Create a volume-element mesh using ply interface heights

• Populate with fibre directions

z y

x


Miss Ningbo Xie, PhD student


Modelled failure modes

• Delaminations

• Matrix crack (split wood)

• Fibre kink

Simulation and modelling




Composite materials

Wrinkle Angle

Wrinkle Shape Parameters Analysis

62

Ultrasonics and NDT Group

𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 = 𝐴𝑒−𝑥2 𝑊1

2 cos2𝜋𝑥

𝐿

Wrinkle shape along x-direction: Wrinkle shape along y-direction:

X (fibre-direction)

(thickness-direction) Z

(width-direction) y

A: amplitude L: wavelength θ: maximum angle

x

Gaussian envelope: governs wrinkle volume

Cosine phase: defines wrinkle shape


63


The depiction of two amplitude distributions:

𝐴𝑖 = 𝐴𝑒− 𝑖−𝑖𝑚𝑖𝑑2/𝑛2

4-Interface Group reduction:

1.0:0.63:0.39:0.0

1.0

0.63

0.39

0.0

Gaussian reduction:

decrease continuously

0.63

0.39

0.0

decrease continuously


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Knock-down of failure stress:

4-Interface Group reduction:

1.0:0.63:0.39:0.0

Co

mp

ress

ion

Fai

lure

Str

ess

Kn

ock

-do

wn

(M

Pa)

For a wrinkle region with fixed volume, maximum angle is the major parameter for determining compression strength.

Knock-down = tested pristine value (643.5 MPa ) - model value

Gaussian reduction:

𝐴𝑖 = 𝐴𝑒− 𝑖−𝑖𝑚𝑖𝑑2/𝑛2

• The future –

• 3D mapping and modelling of Porosity

• Further gains in weight due to extra confidence

Composite materials

Summary

• Increased confidence at the design stage allows:

• better understanding of the effect of defects

• designs that reduce weight, fuel and CO2

• design for low in-service maintenance

Reducing weight

• Increased confidence at manufacture allows:

• confirmation of conformance to design

• less need for extra thickness/weight to mitigate risk

• process-control feedback to increase manufacturing yield

Reducing weight

• New, green aircraft will fly; but

• how green?

• how expensive?

• Depends on increased confidence in:

• optimised designs.

• conformance to design at manufacture

• The future:

• 3D mapping of internal microscopic properties

• Certification of lighter designs, low CO2 emissions.

Conclusions

How NDT will underpin the certification of greener aircraft€¦ · How NDT will underpin the...

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