IDENTIFICATION OF THE SIZE AND LOCATION OF A CRACK, USING STATICAL DEFORMATIONS OF A

MARINE ROTOR SHAFT WITH A PROPELLER AT THE OVERHANGING END

Ridwan Hossain Graduate Student

Memorial University of Newfoundland

E-mail: rbh546@mun.ca

1

Ridwan B. HOSSAIN, Rangaswamy SESHADRI & Arisi S.J. SWAMIDAS

Contents • Crack in Marine Propeller Shaft

• Current crack detection methods

• Proposal made in this paper

• Description of the Analysis

• Advantages (What’s New?)

• Limitations & Further Extension

2

Marine Propeller

3

Propeller

Intermediate

Support

Fixed

Support

Courtesy: www.lytewatermarine.com

Cracks in marine propeller shaft

• Mainly caused due to the

alternating stress.

• Can be caused anywhere

along the shaft

• Catastrophic failure can

occur if not detected.

Crack Detection Method

Crack Detection Method

Dynamic Method

Static Method

Artificial Intelligence

Frequency Analysis,

Mode Shapes

Frequency Response Function

Displacement, Strain

measurement

Neural Network, Genetic

Algorithm

Static Analysis

• Easy to execute.

• Provides specific set of useful data.

• Requires less theoretical underpinning

• Requires less probes and sensors than dynamic

analysis

Current Statical Methods

• Static Response due to the reduction of flexural

stiffness (Buda and Caddemi, 2007 )

• Fredholm Integral in terms of bending moment (Di Paola and Bilello, 2004 )

• Induced Damage principle (Caddemi and Morassi, 2007 )

• Using static deflection profile as input signal of

wavelet analysis (Umesha et al, 2009)

Proposal of this paper

• Using a strain-displacement combination to identify damage.

• Strain & Displacements have been identified by FEM for a number of damaged models

• Based on the responses a general crack detection method has been proposed

Propeller

Fig: Propeller used in

the analysis

Fig: Preparing the CAD model from point

cloud

CAD Model

Shaft length= 1300mm, Dia = 15mm

Int. Support location = 1000mm from fixed end

Disp. Sensor location = 300mm, 600mm, 900mm & 1300mm

Strain Gauge location = 300mm, 450mm, 600mm, 750mm, 900mm, 1100mm &

1180mm

Crack Location: 200mm, 400mm, 600mm, 800mm, 950mm, 1100mm, 1185mm

Crack Depth Ratio: 0.05 to 0.6

Meshed Model

Element Type = Quadratic Tetrahedral elements (C3D10)

Shape Function = Quadratic

Family = 3D Stress

No. Of Elements = 31000 (approx.)

Defining Crack

• Crack was defined as ‘seam’ crack.

• Allows separation after load applied

• Physical properties changes based on depth & Location

Results

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

2

4

6

8

10

12

14

16

18

Crack Depth Ratio, a/h

Perc

enta

ge o

f D

iffe

rence

Figure: Percentage change in displacement against crack depth ratio for displacement

sensor located at 1300mm from the fixed end

Displacement

change is about

18% for 0.6 crack

depth ratio, which

is much higher

than frequency

change (6%)

[Tlaisi et al (2012)]

Results (contd.) (a), (b), (c)

represents

displacement

sensors

located in

300mm,

600mm and

900mm from

fixed end

respectively.

Results (Contd.)

Figure 7: Percentage of Difference in strain vs. the crack depth ratio for

strain gauges located at (a) 300mm; (b) 450mm

Results (Contd.)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

50

100

150

200

250

300

350

400

Crack Depth ratio, a/h

Perc

enta

ge o

f D

iffe

rence

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-8

-6

-4

-2

0

2

4x 10

-5

Pri

ncip

le S

train

, E

11

Normalized Beam length

Figure: Percentage of Difference in Strain

against crack depth ratio for strain gauge

located at 1100mm

Figure: Variation of principle strain along the

length of the beam for uncracked condition

Crack Detection Method

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

2

4

6

8

10

12

14

16

18

Crack depth Ratio, a/h

Perc

enta

ge o

f change in d

eflection

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

5

10

15

20

25

30

35

40

Crack Depth ratio, a/h

Perc

enta

ge o

f C

hange in S

train

Figure: Curve fitted data for

displacement measured at 1300mm

Figure: Curve fitted data for strain

measured at 300mm

Crack Detection Method (contd.)

Figure: Fitted Displacement Data Figure: Fitted Strain Data

Crack Detection Method (contd.)

Figure: Input values for displacement Figure: Output values for displacement

Crack Detection Method (contd.)

Figure: Input values for strain Figure: Output values for strain

Crack Detection Method (contd.)

Figure: Intersection of both outputs give the crack location and depth

200 300 400 500 600 700 800 900 1000 1100 1200

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Crack Location, L

Cra

ck D

epth

Ratio,

a/h

Displacement

Strain

Advantages

• Strain provides much higher response (37.5%) than displacement (17.5%)

• Micro level strain measurement is possible

• Combination of strain-displacement measurement can detect crack along the whole beam

• Only two sensors are needed to detect the crack location and size

Limitation & Further Extensions

• Measurement of displacement still poses the problem

• Detailed modelling might affect the result (bearing, contact behaviour)

• Torsional effect was not included and it might have some effect on the results

• Multiple cracks have not been included.

Thank You!!

Questions?