What is Acoustic Emission?

Transcription

1 Acoustic Emission Group Project Coordinator E. Proverbio, University of Messina (IT) Contributions Jean P. Balayssac - LMDC, INSA-UPS TOULOUSE (FR) Laurent Gaillet - LCPC NANTES (FR) Leszek Golaski - Kielce University of Technology (PL) Nora Vilchinska and Energolaboratory Riga (LV)

2 What is Acoustic Emission? Acoustic Emission (AE) is the class of phenomena whereby an elastic wave, in the range of ultrasound usually between 20 KHz and 1 MHz, is generated by the rapid release of energy from a source within a material. The elastic wave propagates through the solid to the surface, where it can be recorded by one or more sensors. The sensor is a transducer that converts the mechanical wave into an electrical signal.

3 The advantages of AE technique as a NDT method are: Volume inspection Localization of deteriorated zones Real time data evaluation but It is possible to detect only damages that are developing (active defects)

4 AE parameters Tinkey B.V., Fowler T.J., and Klinger R.E., (2002) Nondestructive testing of prestressed bridge girders with distributed damage research report n FHWA/TX-03/1857-2

5 AE signal (reinforced concrete) High energy Steel wire breaking Stress corrosion cracking High frequency Low energy High energy Steel corrosion Concrete cracking Medium frequency Source Low energy Low frequency Changes in non linear acoustic behavior of concrete Steel/concrete interface damaging Structure damaging under loading

6 AE data analysis Extrapolation from small sample Rate process analysis Moment tensor analysis Source Parametric analysis Type of crack Codification Intensity analysis Calm ratio Global indexes Energy analysis

7 How to manage AE signal Conventional AE parameters analysis Source identification Waveform analysis Model elements testing Full scale elements testing Source location Full scale structure testing Evaluation of structural integrity

8 Application examples

9 Parametric analysis Hydrogen embrittlement test Jean P. Balayssac - LMDC, INSA-UPS TOULOUSE (FR) Mechanical behaviour of full scale prestressed concrete girder Leszek Golaski - Kielce University of Technology (PL) Monitoring of a bridge during service Leszek Golaski - Kielce University of Technology (PL)

10 Hydrogen embrittlement test 1,00E ,00E Phase 2 Phase 3 Phase 4 Phase 5 Phase 6 1,00E ,00E ,00E ,00E ,00E ,00E Time (s) Cumulative counts Absolute energy (J) Phase 1

11 Group 3 Third group Amplitude (db) Average frequency (khz) Energy (J) 10 8 Duration (µs) Fracture Group 2 Second group Crack propagation Group 1 First group Crack initiation

12 Mechanical behaviour of full scale prestressed concrete girder Leszek Golaski - Kielce University of Technology (PL) Supervised Pattern Recognition used. A 26.5-m long and 1-m high prestressed concrete girder was loaded in 4-point bending.

13 Severity code and description Extent code and description Code Description Code 1 As new condition or defect has no significant effect on the A element (visually or functionally) No significant defect 2 Early signs of deterioration, minor defect/damage, no reduction B in functionality of element Slight, not more than 5% of surface area/length/number 3 Moderate defect/damage, some loss of functionality could be C expected Moderate, 5%-20% of surface area/length/number 4 Severe defect/damage, significant loss of functionality and/or D element is close to failure/collapse Wide, 20%-50% of surface area/length/number 5 The element is non-functional/failed Extensive, more than 50% of surface area/length/number E Description

14 Monitoring of a bridge during service Severely deteriorated three spans bridge Loaded with heavy traffic lorries

15 Severity code and description Extent code and description Code Description Code Description 1 As new condition or defect has no significant effect on the element (visually or functionally) A No significant defect 2 Early signs of deterioration, minor defect/damage, no reduction in functionality of element B Slight, not more than 5% of surface area/length/number 3 Moderate defect/damage, some loss of functionality could be expected C Moderate, 5%-20% of surface area/length/number 4 Severe defect/damage, significant loss of functionality and/or element is close to failure/collapse D Wide, 20%-50% of surface area/length/number 5 The element is non-functional/failed E Extensive, more than 50% of surface area/length/number

16 Bridge monitoring and failure behaviour of a severely corroded post tensioned girder Laurent Gaillet - LCPC NANTES (FR)

17 Merleback bridge

18 Monitoring system

19 Acoustic Emission monitoring during service 100 Evènements acoustiques détectés pendant la survellance de la poutre 5 rive côté sud surveillance Amplitude (g) ar s03 av r03 m ai -0 3 ju in -0 3 ju i l03 m -0 3 ja nv oc t02 no v se pt av r02 m ai -0 2 ju in -0 2 ju il 02 0

20 AE monitoring during bending test

21 Data analysis b value 4,5 4 b-value = 0,613 3,5 log (number of events) 80 to 90 t 80 to 85 t 70 to 75 t loading 40 to 45 t Linéaire (70 to 75 t) Linéaire (80 to 85 t) Linéaire (80 to 90 t) 3 b-value = 0,6048 2,5 b-value = 0, ,5 b-value = 0, , Amplitude range (db)

22 Energy analysis AE monitoring during proof loading of old posttensioned pre cast segmental viaducts E. Proverbio, University of Messina (IT)

23 The viaduct Type: segmental cast-in-place post-tensioned prestressed concrete box girder Age: 50 years Location: near seaside

24 Proof loading

25 Load steps I 30 tons IV 80 tons II 50 tons III 60 tons V 110 tons

26 AE monitoring Sensors: Broadband type (23-80 khz bandwidth, 140 pf capacitance) Threshold: 15 db Gain: 34 db

27 Main results 1 (load step 2)

28 Main results 2 (load step 2)

29 Main results 3 Relaxation ratio analysis all loads

30 Nonlinear analysis Continuous wave AE monitoring of a dam subjected to foundation slow motion Nora Vilchinska and Energolaboratory Riga (LV)

31 Advantages Nonlinear behavior is observed early on in a degradation process, long before linear parameters start to show damage dependent effects. Any increase in the values of nonlinear parameters is univocally related to an increase in microstructural features in the material considered.

32 Cros section of the dam along flow direction by axis of a hydrogenerator. 70 m Water owerflow gates 100 m Hydrogenerator MPG

33 Response spectra in MP V8 development from 15Apr-03 till27 27-Apr-05

34 V18 till and after floods 2004 Analyze in details two silences /High pressure drop down as results of strong oscillations. Q-factor is changed

35 Conclusions for practice 1 AE techniques can be easily applied as health monitoring techniques in prestressed concrete since distributed damage causes consistent changes in the acoustic emission response. The use of global index as well as Historic Index, Calm Ratio and Felicity Ratio allow a good quantification of the distributed damage in such structures. Acoustic emission has several advantages over other NDTs. The main advantage is that it is global. One test can evaluate an entire structure quickly and effectively by placing sensors over the entire structure and stressing it sufficiently. Another advantage is that acoustic emission lends itself well to in-place monitoring. If background noise can be eliminated it may be possible to leave sensors on a bridge, continuously monitor normal traffic, and determine the increase in distributed damage.

36 Conclusions for practice 2 Acoustic emission also has some drawbacks. One of the most significant drawbacks is that its application is specific, i.e. the interpretation of data require a specific reference database (e.g. reinforced concrete structure, steel structures, prestressed concrete structures, massive concrete structure, and so on). Another drawback is the high attenuation of acoustic emission in concrete. Although low-frequency sensors minimize this effect, it is still significant. At least, a high qualified personnel is required for in situ application and interpretation.