Investigation on Feature Guided WavesInvestigation on Feature Guided Waves David Fan, Mike Lowe...

Investigation on Feature Guided Waves

David Fan, Mike Lowe

Non-Destructive Testing Group

David Fan, Mike Lowe

Department of Mechanical Engineering

Imperial College London

SW7 2AZ

United Kingdom

1/18Feature Guided Wave NDT Laboratory

Motivation

• Large area inspection by guided wave

2/18Feature Guided Wave NDT Laboratory

Discovery of feature guiding

• Inspection of plate with weld

Weld guided waveWeld guided wave

J S t (BAE t ) 2006

3/18Feature Guided Wave NDT Laboratory

J.Sargent (BAE systems), 2006

Finite element modelling

Semi-Analytical Finite Element (SAFE) method:

3x2x 12 mm

1x

Ab bi iAb bi i S l PlSt l Pl t W ld

2 mm

6 mm

Absorbing regionAbsorbing region Steel PlateSteel Plate Weld

400 mm800 mm 800 mm

4/18Feature Guided Wave NDT Laboratory

SAFE results – compression mode

6000Phase velocity 150 kHz

m/s Weld guided mode

6mm plate S0

10 l t S0

loci

ty in

m

SH0 in a steel plate

Weld guided mode10mm plate S0200 kHz

Phas

e ve

l

Leaky Non-300 kHLeaky

leaky 300 kHz

50 150 250 350 4500

Frequency in kHz

5/18Feature Guided Wave NDT Laboratory

Discovery of a new mode – shear mode

3500Phase velocity

100 kHz3500

m/s

100 kHz

ocity

in m

SH0 in a steel plate 150 kHz

Phas

e ve

lo

Weld guided mode

P

250 kHz

50 100 150 200 2503000

Frequency in kHzFan & Lowe

Proc. R. Soc. A, 2009

6/18Feature Guided Wave NDT Laboratory

,

Why the waves are trapped?

3x2x

1x

Weld Pl t

1

Weld Plate

SAFE method Analytical method

7/18Feature Guided Wave NDT Laboratory

Why the waves are trapped?

L dPh l it

• Condition 1: Similar mode shape Weld cap Plate

S0 dL mode6000

Phase velocity

Longitudinal mode

S0 mode

F mode 1in m

/s

SH0 mode

velo

city

i

Flexural mode 1

Torsional modeSH0 mode

Phas

e

Flexural mode 2F mode 2 A0 mode

250500

F i kH

8/18Feature Guided Wave NDT Laboratory

25050 Frequency in kHz

Why the waves are trapped?

• Condition 2: Lower velocity in the weld

plate(faster) weld

(slower)

9/18Feature Guided Wave NDT Laboratory

Why the waves are trapped?

• Condition 2: Lower velocity in the weldT d d

6000Phase velocity

S0 L mode

Trapped modes:

S0 mode

n m

/s

Longitudinal mode

velo

city

in

F mode 1

Torsional mode SH0

F mode 1 SH0 mode

Phas

e v F mode 1

F mode 2

A0

0 Exciting mode for inspection

10/18Feature Guided Wave NDT Laboratory

25050 Frequency in kHzc t g ode o spect o

Typical results from FE (crack parallel to the weld)( p )

Absorbing regionMonitor 1

Monitor 2

11/18Feature Guided Wave NDT Laboratory

Defect scattering study

Laser interferometer

Monitor

Shear transducer

12/18Feature Guided Wave NDT Laboratory

Typical results from Experiment

30mm slot parallel to the weld

0.14

30mm slot parallel to the weld

0.1

0.12

oeffi

cien

t

0.06

0.08

ectio

n C

o40 50 60 70 80 90 100 110 120 130 1400.02

0.04Ref

l40 50 60 70 80 90 100 110 120 130

Frequency (kHz)

13/18Feature Guided Wave NDT Laboratory

Discussion - crack parallel to the weld

Different length of the crack:

ent

30 mm24 mm16 mm

0.12

0.14SH0 wave interaction with axial crack on a plate

n C

oeffi

cie

0.08

0.1

Ref

lect

io

0 04

0.06

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02

0.04

Length of crack to wavelength ratio

14/18Feature Guided Wave NDT Laboratory

Discussion - crack parallel to the weld

FE results Experimental results

0.12

0.14

cien

t 0.12

0.1430 mm24 mm16 mm

0.08

0.1

ion

Coe

ffic

0.08

0.1

0.04

0.06

Ref

lect

i

0.04

0.06

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02

0.04

L h f k l h i

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.30.02

0.04

L h f k l h iLength of crack to wavelength ratio Length of crack to wavelength ratio

Possible reason: difference between the milled slot (experiment) and the FE crack

15/18Feature Guided Wave NDT Laboratory

milled slot (experiment) and the FE crack

Discussion - crack normal to the weld

E i l l

0.24

0.26

t 0 35

0.4FE results Experimental results

0 18

0.2

0.2240 mm

Coe

ffici

ent

30 mm0.3

0.35

40 mm

0.14

0.16

0.18

20 mm

Ref

lect

ion

C

0 2

0.25

20 mm

70 80 90 100 110 120 130 1400.1

0.12

R

70 80 90 100 110 120 130 140

0.2 20 mm

Frequency (kHz) Frequency (kHz)

Possible reason: un-uniform of the weld geometry

16/18Feature Guided Wave NDT Laboratory

the weld geometry

Discussion: Flat-bottom hole

Different depth of the hole:

0.2

0 12

0.14100%

FE results Experimental results

0.16

coef

ficie

nt

0.1

0.12

84 %

0 08

0.12

Ref

lect

ion

c

0.06

0.08

49 %

65 %

0.04

0.08R

0.02

0.04

17 %

33 %

0.3 0.40.2

Length of diameter to wavelength ratio0.2 0.25 0.3 0.35 0.4

0

Length of diameter to wavelength ratio

17/18Feature Guided Wave NDT Laboratory

Summary

The feature guided wave has been studied by the SAFE h d B h h i d d hSAFE method. Both the compression mode and the shear mode have been investigated and compared.

The reason for the trapping effect has been di d d i ddiscussed and summarized.

Experiments have been taken to validate the existence of the trapping mode and its sensitivity to certain defects

18/18Feature Guided Wave NDT Laboratory