Long term stability analysis of a guided wave SHM system for platelike structures V. Attarian, F.B. Cegla, P. Cawley Non-Destructive Testing Group Department of Mechanical Engineering Imperial College London SW7 2AZ United Kingdom
Outline • Introduction – Motivation – Background – Project goals • Ruggedized SHM system development • Testing • Results • Conclusions • Questions V. Attarian V. Attarian NDE Group NDE Group 2/19
Introduction Motivation V. Attarian V. Attarian NDE Group NDE Group 3/19
Background Guided wave transducers in sparse arrays Features Sensors (1) Suitability for large area inspection (2) Defect sensitivity (3) Complex feature effects V. Attarian V. Attarian NDE Group NDE Group 4/19
Background Issues for monitoring platelike structures • Feature density high in 2D TIME DOMAIN SIGNALS DEFECT NO DEFECT WITH DEFECT AMPLITUDE Baseline 0 100 200 300 TIME ( µ s) subtraction RESIDUAL DEFECT AMPLITUDE 0 100 200 300 TIME ( µ s) • Environmental variability effects Compensation – E.g. Temperature induced delays strategies V. Attarian V. Attarian NDE Group NDE Group 5/19
Background Temperature compensation strategies • Optimal baseline subtraction RESIDUAL AMPLITUDE T o C Optimal Baseline 0 100 200 300 400 TIME ( µ s) • Baseline signal stretch Defect Defect OPTIMAL BASELINE AMPLITUDE (AFTER STRETCH) WITH DEFECT RELATIVE TO AMPLITUDE OF 1st ARRIVAL RESIDUAL -20 -40 dB -40 dB 0 100 200 300 400 -60 TIME ( µ s) Defect -80 0 100 200 300 400 AMPLITUDE After TIME ( µ s) stretch 100 200 300 400 TIME ( µ s) V. Attarian V. Attarian NDE Group NDE Group 6/19
Background Defect detection in container panel Triangulating with all 1 -30 sensor pairs T o C 2 -35 4 x x 1.5 Y (M) dB -40 1 -45 0.5 Y 0 -50 0 0.5 1 X (M) Clarke et al (IEEE 2009) X Ellipse imaging 2 -20 3 DEFECT -30 1st ARRIVAL Compensated dB baseline subtraction -40 Optimal Baseline -50 -60 0 100 200 300 400 500 TIME ( µ s) V. Attarian V. Attarian NDE Group NDE Group 7/19
Project goals Performance in real life scenario? • Long term testing of structure in exposed weather – Need to ruggedize transducer • Assess feasibility and variability of reliable monitoring – Robustness – Baseline stability • Study on simple plate and complex structure V. Attarian V. Attarian NDE Group NDE Group 8/19
Ruggedized SHM system development Transducer design Phase stability Finite element analysis Pure mode excitation Strain relief +V Epoxy Waterproof Cap Electrical connectivity/ grounding V. Attarian V. Attarian NDE Group NDE Group 9/19
Ruggedized SHM system development D/2 Not to scale v PZT v A0 5 mm v S0 d = 300 mm x10 -6 100 Velocity FRFs (m/s/V) S0 • Want to excite PZT A0 80 60 – Strong S0 40 20 – Off PZT resonance (outside red region) 0 50 100 150 200 20 kHz Energy in S0 to A0(dB) 15 – High S0/A0 ratio (green) 10 8 dB 5 0 -5 -10 50 100 150 200 Excitation Frequency (kHz) V. Attarian V. Attarian NDE Group NDE Group 10/19
Ruggedized SHM system development Minimize cap reverberations • Undesirable coupling of portal frame dynamics in excited S0 Velocity (mm/s) UNENCAPSULATED 0.05 ) In-plane 1ST PROTOTYPE CAP ( 0 h -0.05 0 100 200 300 2 mm Time (µs) • Parametric + material changes allow shift to and damping Velocity (mm/s) UNENCAPSULATED 0.05 FINAL CAP In-plane 0 -0.05 0 100 200 300 Time (µs) V. Attarian V. Attarian NDE Group NDE Group 11/19
Ruggedized SHM system development Final transducer V. Attarian V. Attarian NDE Group NDE Group 12/19
Testing Baseline database collection • Baselines collected after 3 months of outdoor robustness testing Signals acquired at 0.5 o C increments in [-5, 40] o C • TEMPERATURE ( o C) 50 50 50 40 40 40 30 30 30 PLATE 20 20 20 10 10 10 0 0 0 -10 -10 -10 -10 0 10 20 30 40 50 -10 -10 0 0 10 10 20 20 30 30 40 40 50 50 SETPOINT ( o C) Noise floor imaged with 0.5 o C gap to nearest baseline throughout range • 0 -40 0 -40 0.2 0.2 -42 -42 0.4 0.4 Y (M) Y (M) <-40 dB Sufficiently -44 -44 d 0.6 0.6 dB dB low noise for SHM -46 -46 0.8 0.8 1 1 -48 -48 1.2 1.2 -50 -50 0 0.5 1 0 0.5 1 X (M) X (M) V. Attarian V. Attarian NDE Group NDE Group 13/19
Testing Instrumented plate outdoors PC control transducers Multiplexer Waveform thermocouples generator Tx A/D Rx High pass filter • Monitoring since beginning of March for +4 months V. Attarian V. Attarian NDE Group NDE Group 14/19
Results Robustness • Tx-Rx ok for yr through temperature swings (-10 to 30 o C), rain, light snow • Signal amplitudes SENSOR PAIR TRANSMITTER 1 - RECEIVER 2 0 DATA FIT RELATIVE INITIAL (%) -10 ∆ AMPLITUDE -20 -30 -40 0 20 40 60 80 100 DAYS – >80% pairs show △ amplitude • To -37% initial value, on average • Unrelated to temperature – Regressions on noise levels/pair indicate correlation with △ amplitude V. Attarian V. Attarian NDE Group NDE Group 15/19
Results Baseline stability assessments • Imaging suggests issues for monitoring small reflectors +1 week +3 weeks +6 weeks +11 weeks +14 weeks -30 g ; ; 0 0 0 0 0 0.2 0.2 0.2 0.2 0.2 0.4 0.4 0.4 0.4 0.4 0.6 0.6 0.6 0.6 0.6 dB -35 0.8 0.8 0.8 0.8 0.8 1 1 1 1 1 1.2 1.2 1.2 1.2 1.2 -40 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2 Noise level in area -30 -25 0 0.2 -30 0.4 Statistics -35 Y (M) -35 dB 0.6 from within -40 area 0.8 -45 1 1.2 -40 -50 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 X (M) TIME (DAYS) V. Attarian V. Attarian NDE Group NDE Group 16/19
Results Spatial distribution of noise • Statistical metric suggests noise exhibits lack of sensitivity to location in coverage area -30 -25 0 0.2 -30 0.4 WEEK 12 r o -35 M (dB) Y (M) 0.6 -35 r i WEEK 8 dB -40 0.8 WEEK 1-2 -45 1 dB 1.2 -40 -50 0 0.2 0.4 0.6 0.8 1 1.2 0 0.2 0.4 0.6 X (M) R (M) V. Attarian V. Attarian NDE Group NDE Group 17/19
Conclusions • Key findings – Rugged transduction of GW Possibility of frequent data o feasible for >6 months collection and o amplitudes decline over time identified detrending – Noise floor changes quantified ------------------------ o drifts to -25 dB in +4 months observed + analyzed A. Galvagni talk o trends don’t exhibit spatial dependency @ 11:30 AM • Future work – Continued monitoring outdoors/analysis – Fix amplitude decline issue – Quantifying defect detection sensitivity over time – Further prototyping of array on complex structure V. Attarian V. Attarian NDE Group NDE Group 18/19
Thank you. Questions? Transducer @ ½ yr
Recommend
More recommend
