Crack Propagation Monitoring for Aircraft Structure

Crack Propagation Monitoring for Aircraft Structure

Chaithanya B V1

Dept of Electronics & Communication Engineering GSSS Institute of Engineering Technology for Women Mysuru-570016, India

Siva Subba Rao Patange2 Ph.D. Student, VTU Belagavi & Principal Scientist

Structural Technology Division CSIR-National Aerospace Laboratories

Bengaluru- 560017, India

Sushma S J3

Dept of Electronics & Communication Engineering GSSS Institute of Engineering Technology for Women Mysuru-570016, India

Abstract- Crack propagation monitoring is a structural health monitor which is used to detect the structural health in aircrafts. Generally damage is defined as the change occurs in materials of systems, including changes to the boundary conditions, physical property, dynamic property and system connectivity, which adversely affect the systems performance. PZT sensors are used to identify and even localize damage within the structure. Based on vibration method crack monitoring is done.

Key word: Piezoelectric sensor, Stress, Non Destructive Testing,

1. INTRODUCTION

   As the damage/crack grows, it affects the systems operation which cant be acceptable by the user. Fatigue is the damage commonly occurs in metallic materials. Due to the repeated variation of loads, material changes the stiffness and causes a failure. If a material is in repeated loading the localized and progressive damage will occurs [1].

   circuit. PZT is made up of material which has capability to sense the strain on structure and get the output in the form of voltage and frequency [3].

2. SPECIMEN DESIGN

   Generally Aluminum metal is used in aircraft structure so aluminum plate is used as specimen. Testing is done on three specimens. One is healthy, one is with hole and another one is with hole and crack [4]. Four PZT sensors are mounted on each specimen at different 0 degree and 45 degree. Two are fully mounted and two are half mounted. Each specimen is of 40x20x2.5 cm.

   There are different well developed offline methods like Non Destructive Testing (NDT) are used for inspecting, testing, or evaluating materials. Visual testing, Ultrasonic Testing, Lamb wave testing, Particle testing, Radiographic testing, Magnetic and penetrate testing are some NDT. These offline methods are less efficiency compare to the real time methods [2]. The requirement for damage detection is vibration characteristics methods that can be applied to structures because it investigates and examine changes on the structure. The modal parameters such as mode shapes, modal damping and frequencies are the physical properties of the material those are damping, stiffness and mass. Variation in physical properties, such as reduction in hardness resulting from the initiation of cracks, will detect the changes in the modal properties. Hence changes in modal properties from these quantities are used to detect the crack/damage [3].

   The structural crack commonly occurs in aircraft structure due to the repeated variations in stresses or load. The presence of crack changes the dynamic characteristics of the material and leads to catastrophic failure. In order to this catastrophic failure crack length propagation monitoring is done at the initial stages. In the present work, to identify these cracks propagation, PZT sensors are placed on the structure to be monitored. PZT has selected because of its characteristics such as light weight and easy to bound on the structures. It dont have any internal

   Fig1: Healthy specimen

   100 100

   300

   A B C D

   Fig2: Specimen with hole

   100 100

   300

   5

   A B C D

   Fig3: Specimen with crack

3. METHODOLOGY

   Fig 5: Connection set up of experiment

4. RESULT AND DISCUSSION

   1. Healthy Specimen

      Digital oscilloscope

      Specimen-Al beam with PZT sensor

      2.0

      Electro Dynamic shaker

      1.5

      Voltage V

      1.0

      Conditioner amplifier

      Force transducer

      0.5

      0.0

      S1 S2 S3 S4

      0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

      Frequency Hz

      Signal generator

      Driver amplifier

      Fig 4: Block diagram of the experiment

      Signal generator will generate the sine wave and given as input to vibration generator or driver amplifier. Then output of vibration generator is sent to force transducer [5]. Force transducer send signal to apply force through electric dynamic shaker on specimen used. Force transducer signal is sent to conditioner amplifier to amplify the signal and reduce noise and sent to oscilloscope so that force produced and acceleration can be found [6]. PZT sensor senses the vibration and sent to oscilloscope, which display wave form voltage and frequency can be seen.

      Fig6: output voltage for healthy specimen for 5N Table 1: Sensors output at different modes

      	S1 (V)	S2(V)	S3(V)	S4(V)
      MODE1(32Hz)	1.08	1.82	0.8	0.5
      MODE2(188Hz)	1.2	1.5	0.5	0.1
      MODE3(324Hz)	0.465	0.698	0.33	0.235
      MODE4(445Hz)	0.35	0.61	0.1041	0.00234

      1.6

      1.5 S1

      S2

      1.4

      S3

      1.3

      S4

      1.2

      1.1

      Voltage V

      1.0

      0.9

      0.8

      0.7

      0.6

      0.5

      0.4

      0.3

      0.2

      0.1

      0.0

      0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

      Frequency Hz

      Fig 7: Output voltage for healthy specimen for 10N Table 2: Sensors output at different modes

      	S1	S2	S3	S4
      MODE1 (32Hz)	0.9	1.4	0.6	0.37
      MODE2 (188Hz)	0.7	1.2	0.4	0.1
      MODE3(234Hz)	0.496	0.525	0.217	0.141
      MODE4(445Hz)	0.393	0.603	0.2176	0.1411

   2. Specimen with hole.

      3.0

      2.8 S1

      2.6 S2

      2.4 S3

      2.2 S4

      2.0

      Voltage v

      1.8

      1.6

      1.4

      1.2

      Table 5: Sensors output at different modes

      	S1	S2	S3	S4
      MODE1(31.5Hz)	7.7	9.9	1.56	1
      MODE2(184.8Hz)	3	5	2	1
      MODE3(242Hz)	2	3	1	0.5
      MODE4(420)	1	1.9	0.5	0.1

      1.0

      0.8

      0.6

      0.4

      0.2

      0.0

      0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

      Freqency Hz

      14

      S1

      13

      S2

      12

      S3

      11 S4

      10

      Voltage V

      9

      Fig 8: output voltage for specimen with hole for 5N 8

      7

      Table 3: Sensors output at different modes 5

      4

      	S1	S2	S3	S4
      MODE1(31Hz)	2.1	2.62	1.89	1.17
      MODE2(171Hz)	1.4	1.8	0.695	0.315
      MODE3(242Hz)	0.7	1	0.495	0.215
      MODE4(420Hz)	0.956	1.2	0.552	0.3545

      3

      2

      1

      0

      0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

      Frequency Hz

      6 S1

      5

      S2 S3 S4

      Fig 11: Output voltage for specimen with hole for 10N Table 6: Sensors output at different modes

      Voltage V

      	S1	S2	S3	S4
      MODE1(31.5Hz)	11.35	13.35	4.85	2
      MODE2(184.5Hz)	5.12	7.123	3	2.43
      MODE3(242Hz)	2.1	3.5	1.2	0.5
      MODE4(420Hz)	1.5	2.01	0.9	0.5

      4

      3

      2

      1

      0

      0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

      Freqency Hz

      Fig 9: Output voltage for specimen with hole for 10N Table 4: Sensors output at different modes

      	S1	S2	S3	S4
      MODE1 (31Hz)	4.4	6	2.5	1.5
      MODE2(171Hz)	2	5	1	0.5
      MODE3(242Hz)	1.3	2.13	0.68	0.386
      MODE4(420Hz)	0.753	1	0.6	0.445

   3. Specimen with crack.

   11

   10 S1

   S2

   9 S3

   8 S4

   Voltage V

   7

   6

   5

   4

   3

   2

   1

   0

   0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480 510

   Frequency Hz

   Fig 10: Output voltage for specimen with hole for 5N

   To analyze the practical experimental results the graphs are drawn. Sensor output voltage for different frequencies are shown in below plots for given 5N and 10N in figure6, 8, 10 and figure7,9,11 respectively for different specimens [8] [9]. These plots shows the different voltages obtained from each sensor since four sensors are attached in different angle (00 and 450) and also two sensors are fully bounded and other two are half mounted. In the plots sensor 1 is represented by black line, sensor 2 is represented by red line, sensor3 is represented by blue line and sensor4 is represented by pink line. By comparing voltage value of sensors at modes of frequencies with respect to healthy specimen crack monitoring is done [10].

5. CONCLUSION

In this paper we discussed about monitoring crack propagation on different specimen. As crack propagation increases output voltage of sensor increases. Hence, the crack/damage propagation which is found on the aluminum structure by comparing the healthy structure output voltage and frequency with cracked/damaged structure output voltage and frequency.

ACKNOWLEDGEMENT

The authors would like to thank the Director, Mr. Jitendra J Jadhav CSIR-National Aerospace Laboratories

for his persistence to carry out the work and Dr. Satish Chandra, Head Structural Technologies Division (STTD) for providing all the facilities for completing this work and Dr. S. Raja Group Head of STTD for supporting and inspiring to complete the work.

REFERENCES

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