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 B. HOSSAIN, Rangaswamy SESHADRI & Arisi S.J. SWAMIDAS Ridwan Hossain Graduate Student Memorial University of Newfoundland E-mail: rbh546@mun.ca 1
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 Propeller Fixed Support Intermediate Support Courtesy: www.lytewatermarine.com 3
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
Percentage of Difference Results 18 16 14 12 10 8 6 4 Displacement change is about 18% for 0.6 crack depth ratio, which is much higher than frequency change (6%) [Tlaisi et al (2012)] 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Crack Depth Ratio, a/h Figure: Percentage change in displacement against crack depth ratio for displacement sensor located at 1300mm from the fixed end
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
Percentage of Difference Principle Strain, E11 Results (Contd.) 400 4 x 10-5 350 300 250 2 0 200-2 150 100 50-4 -6 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Crack Depth ratio, a/h -8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 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
Percentage of change in deflection Percentage of Change in Strain Crack Detection Method 18 40 16 14 12 10 8 6 4 2 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Crack depth Ratio, a/h Figure: Curve fitted data for displacement measured at 1300mm 35 30 25 20 15 10 5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Crack Depth ratio, a/h 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 Depth Ratio, a/h Crack Detection Method (contd.) 0.5 0.45 0.4 Displacement Strain 0.35 0.3 0.25 0.2 200 300 400 500 600 700 800 900 1000 1100 1200 Crack Location, L Figure: Intersection of both outputs give the crack location and depth
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?