APPLICATION OF FATIGUE CRACK OPEN EFFECT FOR AIRCRAFT STRUCTURAL HEALTH MONITORING

Transcription

1 VIth International Workshop NDT in Progress October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic APPLICATION OF FATIGUE CRACK OPEN EFFECT FOR AIRCRAFT V.Pavelko, I.Pavelko, E. Ozolinsh, S. Kuznetsov 11/25/2011 VIth International Workshop NDT in Progress, 1 October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic

2 Contents Introduction Experimental study:the fatigue crack open/close effect to ultrasound wave Experimental study: Effect of load level to intensity of a transmitted ultrasound signal Analytical estimation of crack-opening effect Investigation of corrosion influence to crack-opening effect Conclusions 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and Congress center 2 Floret, Prague, Czech Republic

3 Introduction 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic 3

4 Introduction Intention: To create experimental SHM system (ESHM) for the tail beam and estimation of its reliability and technical and economical efficiency. The beam has the form of the truncated cone with a length of 5485 mm, i.e. the length of the beam. The base diameters are 1000 and 550 mm respectively. 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 4 Congress center Floret, Prague, Czech Republic

5 Introduction Figure 1. Common view of the MI8 helicopter tail beam before mounting for full-scale fatigue testing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic 5

6 Imitator of the beam of tail propeller 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, , Hotel and Congress center Floret, Prague, Czech Republic

7 Device of dynamic loading 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, , Hotel and Congress center Floret, Prague, Czech Republic

8 Stress-strain measurement at static and dynamic loading 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 8 and Congress center Floret, Prague, Czech Republic

9 FATIGUE CRACK OPEN EFFECT TO LAMB WAVE IN THIN AL SHEET Basic regularities of the fatigue failure of thin-walled structure 1) Points of stress concentration: the free curvilinear surface of a structural element a) b) First kind of the fatigue crack: a) on the free curvilinear surface of a frame, b) the free hole in a thin wall of a frame 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic 9

10 FATIGUE CRACK OPEN EFFECT TO LAMB WAVE IN THIN AL SHEET Basic regularities of the fatigue failure of thin-walled structure 2) Points of stress concentration: the free curvilinear surface of a structural element The fatigue cracks in a skin are initialized by the stress concentration 1) near the most loaded fastening point in rivet-joint 2) on small hole in skin 1 The fatigue crack in a skin is initialized by stress concentration near last fastening point 1 in pointwelded connection with tip of a stringer 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and Congress center Floret, Prague, Czech Republic 1) near last fastening point 1 in point-welded connection with tip of a stringer 2) near the most loaded fastening point in rivet-joint of two parts of a stringer 10

11 FATIGUE CRACK OPEN V.Pavelko EFFECT, I.Pavelko TO E. Ozolinsh, LAMB S. Kuznetsov WAVE IN THIN AL SHEET Experimental study: Test setup Scheme of sample and sensors installation T 1 (t 1 ) T 2 (t 2 ) VIth International Workshop NDT in Progress, October 10 12, 2011, 11/25/ Hotel and Congress center Floret, Prague, Czech Republic

12 Experimental study: Measurement equipment and loading regime Two sensors PIC x10x50mm (T1 and T2). Coupling: Epoxy Paste HYSOL EA NA QT SYSTEM Measurement equipment: 1. Actuating Equipment: Lamb wave electronics LWDS45 (Cedrat Technology) Frequency 250 khz and 300 khz 2. Sensing and impedance measurement Oscilloscope 4CH (25 MHz version) USB Impedance measurement C60 (Cypher Instruments Ltd) Loading Cyclic load: Maximal.. 12kN Minimal 4kN Cyclic stress: Maximal MPa Minimal 50 MPa Frequency 10 Hz 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 12 and Congress center Floret, Prague, Czech Republic

13 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 13 Congress center Floret, Prague, Czech Republic

14 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 14 Congress center Floret, Prague, Czech Republic

15 Experimental study: Results of fatigue test 1) Before the fatigue crack occur intensity of a transmitted signal remains constant with the cycles number raising 2) After the fatigue crack occur intensity of a transmitted signal decreases with the crack length raising 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, 15 Hotel and Congress center Floret, Prague, Czech Republic

16 Experimental study: Results of fatigue test 1) The effect of a fatigue crack to intensity of a transmitted signal is eider nonloaded or loaded state of a sample 2) The effect of a fatigue crack to intensity of a transmitted signal in loaded state is more significant than in non-loaded state of a sample 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, 16 Hotel and Congress center Floret, Prague, Czech Republic

17 Effect of load level to intensity of a transmitted signal The crack length is equal 27 mm Static loading in the range kn 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, 17 Hotel and Congress center Floret, Prague, Czech Republic

18 Effect of load level to intensity of the transmitted signal and echo 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 18 Congress center Floret, Prague, Czech Republic

19 Analytical estimation of crack-opening effect Dugdale model of a crack with the zone of plastic strain, v x x v E x 1 l ln 2 x l 1 l x l 1 l x l l x l x 1 0 x 1 l ln 2 x l 1 l x l l x where 0 is yield stress, E is the elasticity modulus x x l 0 l l l 0 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, 19 Hotel and Congress center Floret, Prague, Czech Republic

20 Analytical study result:the fatigue crack closing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 20 Congress center Floret, Prague, Czech Republic

21 Analytical study result:the fatigue crack closing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 21 Congress center Floret, Prague, Czech Republic

22 Analytical study result:the fatigue crack closing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 22 Congress center Floret, Prague, Czech Republic

23 Analytical study result:the fatigue crack closing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 23 and Congress center Floret, Prague, Czech Republic

24 Analytical study result:the fatigue crack closing 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 24 and Congress center Floret, Prague, Czech Republic

25 Investigation of corrosion influence to crack-opening effect T 1 T 2 3% solution of the salt (NaCl) is used as the active agent for Al alloy 2024-T3 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 25 and Congress center Floret, Prague, Czech Republic

26 Investigation of corrosion influence to crack-opening effect T 1 T 2 T 1 T 2 1) Echo-signal in the loaded state (2.5 kn) has a tendency to decrease 2) The same tendency is observed for the echo-signal in the unloaded state 3) After unloading and next loading to 2.5 kn the echo-signal practically does no depend from corrosive action 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 26 Congress center Floret, Prague, Czech Republic

27 Investigation of corrosion influence to crack-opening effect T 1 T 2 T 1 T 2 1) Transmitted signal in the loaded state (2.5 kn) has a weak tendency to increase 2) More intensive increasing of transmitted signal is observed for the echo-signal in the unloaded state 3) After unloading and next loading to 2.5 kn the transmitted signal practically does no depend from corrosive action 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel and 27 Congress center Floret, Prague, Czech Republic

28 Conclusions There is stable crack-opening effect (COE) to ultrasonic signal in Al alloy sheet There is relatively small stress (about 45 MPa) corresponded to full crack-opening effect COE can be explained by the fracture mechanics COE remains also at environmental action COE allows to develop the technology of a fatigue crack detection without using prior baseline data 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, , Hotel and Congress center Floret, Prague, Czech Republic

29 Thanks you for your attention! 11/25/2011 VIth International Workshop NDT in Progress, October 10 12, 2011, Hotel 29 and Congress center Floret, Prague, Czech Republic