Experimental Vibration-based Damage

Detection in Aluminum Plates and Blocks

Using the Acoustic Emission Signals

NDTiC 2015

Edmonton, AB

M. Mirsadeghi, M. Sanati, R. Hugo, S. Park

Department of Mechanical & Manufacturing EngineeringSchulich School of Engineering at the University of Calgary

ND

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anada 2015 Conference, June 15-17, 2015, E

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Outline

• Introduction

• Objective

• Theoretical Background

• Experimental Setup

• Results

• Discussion

• Summary

2

Introduction:

NDE Motivation

3

Incidents� Crack propagation in pipelines

� Fatigue and fracture in aircraft structures and engine blades

� Explosions in boilers and nuclear

facilities

� Crack initiation in bridges

Applications� Pipelines and Corrosion monitoring

� Aerospace structures� Civil infrastructures: Ship hulls,

bridges and buildings

� Composite Damage Detection

AcellentTechnologies Inc

Demands� Safe and stable operation of

structures � Enhancing Maintenance Strategies

� Utilizing cost effective NDT

Introduction

4

Challenges:

• Limitation in applying high frequency excitation

• Mostly suitable for rotating

machinery

• Noise and signal spikes

• Defect classification uncertainty

Vibration-based Damage Detection

Advantages:

• Independent to the structural complexity

• Calculation weight

• Global method (compared to

radiography and conventional ultrasonic methods)

• Can be applied in working

conditions

NDT Methods X-ray

Ultrasonic

Eddy Current

Magnetic Particle Testing

Introduction:

Literature Review

5

Vibration-based Damage Detection by GA

(Hao et al 2002)Effect of Delamination Axial Position on Natural Frequencies

(Zou et al 2000)

Development of Vibration-based Structural damage Detection (Composite Airfoil Model

and Given Damage Status)(Yan et al 2007)

Introduction:

Literature Review

6

Steel pipeline on air-bed and placement of accelerometer

(He and Zhu 2011)

Cantilever steel beam damage detection

(Golubovic 2014)

Application of CWT in Vibration-based Damage Detection

(Rucka et al. 2006)

Locating Damage Using CWT in Beams(Qiu et al. 2014)

Objectives

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Vibration based damage detection using AE sensors, and investigating the effect of sensor position

A. Implementation of the experimental procedure and computing FRFs

� Instrumentation and data acquisition

� Processing the signal and plotting FRFs

� Repeating experiments

B. Modal parameters extraction and analysis

� Analyzing variation of the modal parameters

� Mode sensitivity discussion

Experimental Setup

8

Target Structure Properties

Material Aluminum 6061

Dimensions

Plate 152x76x6.3 mm

Block 1 (B1) 152x50.8x25.4 mm

Block 2 (B2) 152x50.8x38.1mm

Boundary ConditionsFree (Using Foam 15cm

thickness)

a. Plate (152x76x6.3 mm) b. Block 1 (152x50.8x25.4) c. Block 2 (152x50.8x38.1 mm)

Test Steps

1 Healthy Structure

2 Damage 1 through hole 8mm diameter

3 Damage 2 through hole 12.5mm diameter

Experimental Setup

Sensors

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Acoustic Emission Sensors (MISTRAS Nano 30)Purpose of AE sensors is to detect the motion of stress waves that cause a local dynamic material displacement and convert this displacement to an electrical signal.

Dynamic Specifications

Peak Sensitivity, Ref V/(m/s) 62 dB

Operating Frequency Range 125-750 KHz

Resonant Frequency, RefV/(m/s) 140 KHz

Weight 2 grams

Note: the measured physical quantity of the AE sensors is

proportional to velocity, contrary to displacement or acceleration

Results

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The figures have been prepared based on following considerations:

1. The plate provide eight natural frequency, however we have focused on the first two natural frequencies to get more reliable results due to higher amplitudes in actuation signal power spectrum.

2. The block specimens typically have two natural frequencies.

3. The figures have been windowed to provide information about changes in dynamic behaviour of the structures in more sensitive modes.

4. The legends are Healthy, Damage 1 and Damage 2 which denote the

reference signal, damage case 1 (through hole 8mm diameter) and damage case 2 (through hole 12.5 mm) respectively.

Results

Specimen: Plate

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Healthy Damage 1 Damage 2

fn (Hz)Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ

Plate

Sensor 1Mode 1 3778 2.85E-01 -4.33E+08 3777 2.46E-01 -3.92E+08 3771 1.88E-01 -2.29E+08

Mode 2 5754 5.29E-01 -4.01E+09 5726 4.17E-01 -4.71E+09 5644 5.00E-01 1.40E+09

Sensor 2Mode 1 3786 2.29E-02 -2.25E+09 3782 1.60E-01 -3.57E+08 3773 1.39E-01 -3.60E+08

Mode 2 5760 5.97E-01 6.65E+08 5699 4.78E-01 7.52E+08 5658 1.86E-01 8.42E+08

Natural frequency sensitivity for plate specimen

ResultsPlate – Sensor in Position 1 – Mode 2

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Results

Specimen: Block 1

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Healthy Damage 1 Damage 2

fn (Hz)Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ

Block 1

Sensor 1Mode 1 8554 4.67E-02 1.83E+09 8557 3.86E-02 6.15E+09 8533 3.83E-02 8.33E+09

Mode 2 NA NA NA NA NA NA NA NA NA

Sensor 2Mode 1 7810 7.49E-01 9.65E+09 7666 1.09E+00 7.25E+09 7467 7.20E-01 2.55E+10

Mode 2 8592 1.71E-01 -2.68E+10 8599 3.51E-01 1.13E+10 8568 1.78E-01 2.29E+10

Natural frequency sensitivity for block 1 specimen

ResultsBlock 1 – Sensor in Position 2 – Mode 1

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Results

Specimen: Block 2

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Healthy Damage 1 Damage 2

fn (Hz)Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ fn (Hz)

Damping

Ratio (%)κ

Block 2

Sensor 1Mode 1 8674 4.17E-02 4.63E+09 8687 4.47E-02 4.33E+09 8680 3.77E-02 2.76E+10

Mode 2 NA NA NA NA NA NA 8723 4.72E-02 4.67E+10

Sensor 2Mode 1 8702 1.86E-01 -2.55E+10 8710 1.04E-01 1.60E+10 8748 3.55E-01 8.70E+09

Mode 2 9125 2.46E-01 -7.84E+10 8972 1.67E-01 2.70E+10 8748 3.55E-01 8.70E+09

Natural frequency sensitivity for block 2 specimen

ResultsBlock 2– Sensor in Position 2- Mode 1 and 2

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Discussion

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• The material discontinuity in the structure could make specific changes to dynamic behavior of the specimen

• The second mode of the plate structure is more sensitive to the damage.

• Sensor positioning is significant to provide enough information about the structure.

• Different trend for natural frequencies variation in experiments for block 2.

• The effect of specimen geometry

• As the acoustic emission sensors have been used we can not provide exact units for the FRFs, however the measured quantity is proportional to the velocity.

Discussion

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Assumptions

• The experiments were performed in free-free boundary condition using the 15cm thickness foam.

• The hammer exactly excites the same point in experiments for different damage levels.

• The effect of adhesive material used for mounting sensors is negligible

Limitations

• Analysis in the low frequency range of AE sensors

• Excitation signal frequency limitation (Max 12500 Hz)

• Challenge in computing stiffness

• Unable to compare mode shapes unless many sensors are used

• Insensitive modes to specific damages

Summary

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• Vibration-based damage detection is a global method and independent of complexities of test objects.

• Experimental vibration-based damage detection using the acoustic emission

sensors was performed.

• It was shown that specific modes of vibration for the different specimens

provides more sensitivity to the damage and is preferred to be used for damage detection.

• Sensor location effect in detection of different modes of structure was studied.

Future Work• Parametric FE study using a verified numerical model• Extending studies to high frequency excitation signal

• Investigation of various kinds of defects (corrosion, fatigue crack, etc.)• Development of methods for reducing noise levels.

Thank You

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