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Thermal Acoustic Studies
DOT/FAA/AR-09/54

of Engine Disk Materials
Air Traffic Organization
NextGen & Operations Planning
Office of Research and
Technology Development
Washington, DC 20591

March 2010

Final Report

This document is available to the U.S. public
through the National Technical Information
Service (NTIS), Springfield, Virginia 22161.

U.S. Department of Transportation
Federal Aviation Administration
NOTICE

This document is disseminated under the sponsorship of the U.S.
Department of Transportation in the interest of information exchange. The
United States Government assumes no liability for the contents or use
thereof. The United States Government does not endorse products or
manufacturers. Trade or manufacturer’s names appear herein solely
because they are considered essential to the objective of this report. This
document does not constitute FAA certification policy. Consult your local
FAA aircraft certification office as to its use.

This report is available at the Federal Aviation Administration William J.
Hughes Technical Center’s Full-Text Technical Reports page:
actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF).
Technical Report Documentation Page
1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AR-09/54
4. Title and Subtitle 5. Report Date

THERMAL ACOUSTIC STUDIES OF ENGINE DISK MATERIALS March 2010
6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

John Lively1, Zhong Ouyang1, Steve Holland2, Dave Eisenmann2, Bill Meeker2, Lisa
Brasche2, Jeremy Renshaw2, Chris Uhl2, Ming Li2, Tom Bantel3, Barney Lawless3,
Daniel Ford3, Thadd Patton3, Kevin Smith1, Surendra Singh4, and Waled Hassan5
9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)
4 Honeywell Engines & Systems
1 Pratt & Whitney 111 S. 34th Street
400 Main Street MD Q-8
Phoenix, AZ 85034
East Hartford, CT 06108

2 Iowa State University 5 Rolls-Royce Corporation
2001 South Tibbs Avenue
1915 Scholl Road
Indianapolis, IN 46241
Ames, IA 50011
3 General Electric Aviation 11. Contract or Grant No.

1 Neumann Way

Cincinnati, OH 45215
12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered

U.S. Department of Transportation
Final Report
Federal Aviation Administration
Air Traffic Organization NextGen & Operations Planning
Office of Research and Technology Development
Washington, DC 20591 14. Sponsoring Agency Code
ANE-110
15. Supplementary Notes
The Federal Aviation Administration Airport and Aircraft Safety R&D Division COTR was Cu Nguyen.
16. Abstract

Thermal acoustics, sonic infrared inspection, and vibrothermography are all names given to an emerging technique that shows
great promise for crack detection. The basic principle of the method involves application of an external source operating in the
kilohertz range, which causes crack faces to rub, generating frictional heating. The heating is then detected using an infrared
camera. While there have been some demonstrations of the approach and limited production usage, widespread utilization
requires improved fundamental understanding, additional technique development and optimization, application to real part
geometries, industrial standards, and training resources. As a first step toward widespread use, this program evaluated the
applicability of thermal acoustic inspection methods for engine materials and components, including studies of the process
parameters and their relationship to inspection effectiveness, and assessed the potential of thermal acoustic methods to induce
damage in the component and cause additional crack initiation or growth. The program concluded that, with the appropriate
selection of test parameters and equipment, this method can be safely applied to engine materials. When reasonable decisions
were made regarding the excitation source (amplitude, tip type, or coupling), no evidence of life debit was found and existing
surface-breaking fatigue cracks did not propagate. However, crack growth can occur at higher stress levels and when resonance
conditions occur. In designing an inspection, care should be taken to ensure that the imparted stresses are well below yield for
the materials being tested. Additional efforts to improve the understanding of this method on actual part geometries are needed.
Additional fundamental understanding of the factors that affect defect detection (crack morphology and crack closure); the ability
to model the inspection practice; and the role material selection, surface condition, and surface coatings play in detection are
recommended. Further studies that consider practical approaches to calibration and sensitivity verification, including the
development of industrial standards, would be beneficial. Last, the availability of training materials and other educational
resources are needed.
17. Key Words 18. Distribution Statement

Engine inspection, Vibrothermography, Thermal acoustics, This document is available to the U.S. public through the
Probability of detection, Sonic infrared inspection National Technical Information Service (NTIS), Springfield,
Virginia 22161.
19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price
Unclassified Unclassified 183

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY xv

1. INTRODUCTION 1
1.1 Purpose 1
1.2 Background 2
1.3 Related Activities and Documents 3

2. TECHNICAL APPROACH 5
3. RESULTS 15
3.1 Specimen Fabrication 15

3.1.1 Localized Damage Specimens 15

3.1.2 Low-Cycle Fatigue Specimens 19

3.1.3 High-Cycle Fatigue Specimens 19

3.1.4 Finite Element Modeling Study for Shifting Stress Concentration
From Radius Transition Region to Gage Section 29

3.2 Localized Damage Study 32

3.2.1 Experimental Matrix 32
3.2.2 Characterization 42
3.2.3 Summary of LDS 47

3.3 Crack Initiation and Fatigue Life Debit Study 51

3.3.1 The HCF Test Plan 51
3.3.2 Characterization 54
3.3.3 The HCF Test Data 55
3.3.4 Summary of Impact on HCF Life 57

3.4 Crack Growth Assessment 58

3.4.1 Crack Growth Study Plan 58
3.4.2 Characterization 58
3.4.3 The LCF Crack Data 59
3.4.4 Summary of Crack Growth Study Plan 65
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3.5 Probability of Detection Study 66

3.5.1 Experimental Plan 66

3.5.2 The POD Experiments 68

3.5.3 Probability of Detection Processing 73

3.5.4 The POD Results 79

3.5.5 Probability of Detection Estimation Based on the Thermal
Acoustic Data 80

3.5.6 Summary of POD Study 96

3.6 Observed Crack Propagation in Specimen 05-031 97

3.6.1 History of Specimen 05-031 97
3.6.2 Characterization of Specimen 05-031 107
3.6.3 Conclusions of Specimen 05-031 110
3.6.4 Summary of Specimen 05-031 Results 111

4. CONCLUSIONS 111
5. REFERENCES 113
APPENDICES

A—Low-Cycle Fatigue Specimen Fabrication Procedure

B—Vibrometer Energy Calculations

C—Stall Data From Localized Damage Study

D—Localized Damage Specimens Characterization

E—Basic General Electric Aviation Setup Procedure for Generating Engine
Titanium Consortium Thermal Acoustic Studies Probability of Detection Data

F—Basic General Electric Aviation Setup Procedure for Acquiring Engine
Titanium Consortium Thermal Acoustic Studies Probability of Detection Data

G—Example Experiment Log From the Probability of Detection Experiment

iv
LIST OF FIGURES

Figure Page

1 Examples of Three Different Flaw Sizes and Their Corresponding Brightness Level
Using Thermal Acoustic Inspection 3

2 Probability of Detection Curve for Thermal Acoustic Inspection of Ti6-4 Specimens 4

3 Specimens Used in Localized Damage Studies, Crack Growth and POD Studies,
HCF Test, and Typical Crack Morphology 6

4 Configuration of GE, ISU, and PW Systems, Showing Exciters, Thermal Cameras,
Vibrometers, and Clamping Fixtures 7

5 The LCF Specimen-Clamping Fixture at GE and HCF Specimen-Clamping Fixture
at PW 10

6 Typical Optical and UVA Images for Specimens Used in the Crack Growth and POD
Assessment 14

7 Extraction of Localized Damage Specimens for Inconel and Titanium 16

8 Schematic of Localized Damage Specimens 17

9 Localized Damage Specimens, Milled and Ground Surfaces 17

10 Inspection Surfaces and Depth Zones for Ultrasonic C-Scans of the Titanium Forging 20

11 Inspection Surfaces and Depth Zones for Ultrasonic C-Scans of the Inconel Forging 20

12 A C-Scan of the Front of the Titanium Forging, Showing the Banding of Grain Noise 21

13 A C-Scan of the Back of the Titanium Forging, Showing the Grain Noise Banding 21

14 Titanium Disk Prior to Cut-Up 22

15 Titanium Cut-Out Plan With Specimen 401 at the 0o Mark 22

16 Front Side of Inconel Forging, Showing Torch Marks 23

17 A C-Scan of the Front of the Inconel Forging, Showing Torch Marks and a More
Uniform Grain Noise Distribution 23

18 Back Side of Inconel Forging, Showing Torch Marks 24
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19 A C-Scan of the Back of the Inconel Forging, Showing Torch Marks and More
Uniform Grain Noise Distribution 24

20 Inconel Forging Cut-Out Plan With Specimen 001 to the Left of the Missing Wedge 25

21 Original HCF Specimen Drawing 25

22 An HCF Unshot-Peened Specimen 26

23 An HCF Specimen With Radius Transition Failure 26

24 The ISU Specimen Clamping Jaws With Friction Finish 27

25 HCF Specimen 483 Showing a Break in the Transition Area With Axial Slippage
Marks in the Grip Area and HCF Specimen 498 Showing a Break in the Gage Area
With no Slippage Marks 28

26 Pinned HCF Specimen With Gage to Radius Transition Failure, Specimen 05-041 29

27 Stress of Model in Original Specimen Geometry 30

28 Stress of Model in HCF Specimen With 20-mil Radius Rounded Edge 30

29 Stress of Model in HCF Specimen With a 34-mil Chamfer at the Middle 31

30 Stress of Model With Large Radius Toward the Center 31

31 Flat-, Rounded-, and Spherical-Tip Geometries 32

32 The HAE Energy Curves for PW System, In718, Flat Tip, No Coupling 34

33 The HAE Energy Curves for PW System, In718, Flat Tip, With Coupling 34

34 The HAE Energy Curves for PW System, In718, Rounded Tip, No Coupling 35

35 The HAE Energy Curves for PW System, In718, Rounded Tip, With Coupling 35

36 The HAE Energy Curves for PW System, Ti64, Flat Tip, No Coupling 36

37 The HAE Energy Curves for PW System, Ti64, Flat Tip, With Coupling 36

38 The HAE Energy Curves for PW System, Ti64, Rounded Tip, No Coupling 37

39 The HAE Energy Curves for PW System, Ti64, Rounded Tip, With Coupling 37

vi
40 The HAE Energy Curves for GE System, In718, Flat Tip, No Coupling 38

41 The HAE Energy Curves for GE System, In718, Flat Tip, With Coupling 38

42 The HAE Energy Curves for GE System, In718, Rounded Tip, No Coupling 39

43 The HAE Energy Curves for GE System, In718, Rounded Tip, With Coupling 39

44 Typical Laser Vibrometer Data for Inconel and Titanium Specimens 42

45 Two-Dimensional View of Profilometry for Scan of Ti64-20 White-Light Image of
Ti64-20 at 40x Magnification 43

46 Three-Dimensional View of Profilometry Scan for Ti64-20 Showing no Indentation
due to Excitation 43

47 Two-Dimensional View of Profilometry Scan for Ti64-16, White-Light Image of
Ti64-16 at 40x Magnification 45

48 Three-Dimensional View of Profilometry Scan for Ti64-16 Showing an Indentation
due to Excitation 45

49 Specimen Configuration for Local Damage Specimens Showing Measurement
Location for Hardness Determination 46

50 Localized Damage Specimen With Surface Displacement (Ti64-16B, GE, Flat Tip,
No Coupling) 49

51 Localized Damage Specimen With Surface Displacement (In718-19T, PW, Flat Tip,
No Coupling) 50

52 Localized Damage Specimen With Surface Displacement (In718-14T, PW,
Spherical Tip, no Coupling, Point Left on Tip After Machining) 51

53 Load Frame Used for all HCF Tests 52

54 The HCF Specimen Loaded in Test Grips Prior to Test 52

55 The HCF Specimen Showing Regions of Specimen 53

56 The HCF Specimen With Fracture in Transition Region 53

57 The HCF Specimen With Fracture in Center of Gage Section 53

58 Composite Image of HCF Gage Section Taken at 40x Magnification 54

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59 The HCF Specimen Configuration 54

60 Typical Fracture Location Within the Gage Section After HCF Tests 55

61 In718-53 Fracture Initiated on the Front Side Approximately 5 mm in From the
Lower Corner 55

62 Statistical Analysis Results of Ti HCF Data 57

63 Statistical Analysis Results for Ni HCF Data 57

64 Images at 1000x Magnification of Pre- and Posttests of Specimen 407 58

65 Specimen 407 at 100x Magnification 59

66 Example 10- to 25-kHz Response Spectra for a Ti64 Specimen 05-472, Before and
After Cutting 60

67 Increase in Resonant Frequencies of Three Ti64 Specimens as Length is Decreased 60

68 Spatial Motion Distribution of a Typical In718 Specimen After Cutting 61

69 Measured Motion Profile of In718 Specimen 05-077 at 20 kHz After Cutting 61

70 Histogram of Ultimate Resonant Frequencies of Ti64 Specimens, as Measured
During the POD Study 62

71 Histogram of the Ultimate Resonant Frequencies of In718 Specimens, as Measured
During the POD Study 62

72 The LCF Crack Growth Excitation Setup 64

73 Before and After Excitation Photographs of Ti64 LCF Crack Growth
Specimen 05-442 (0.1057″) 65

74 Before and After Excitation Photographs of Ti64 LCF Crack Growth
Specimen 05-410 (0.0465″) 65

75 Histogram of Crack Lengths in Ti64 POD Specimens 67

76 Histogram of Crack Lengths in In718 POD Specimens 68

77 Schematic Configuration for the POD Experiment 68
viii
78 Example ISU Medium (2.2 v) Amplitude Infrared Image of Crack Heating With
Vibrometry Waveform From Ti64 Specimen 05-447 70

79 Example PW Medium (30%) Amplitude Infrared Image of Crack Heating With
Vibrometry Waveform From Ti64 Specimen 05-447 71

80 Example GE Medium (30%) Amplitude Infrared Image of Crack Heating With
Vibrometry Waveform From Ti64 Specimen 05-447 71

81 Example GE Medium (30%) Amplitude Infrared Image of Crack Heating With
Vibrometry Waveform From Ti64 Specimen 05-447 72

82 Images Used to Verify the Quality of the Surface Fit Used for Estimating Crack
Heating From the ISU Data Shown in Figure 78: (a) the Raw Infrared Data,
(b) Data After the High-Pass Spatial Filter was Applied, and (c) Elliptical
Gaussian Fit to (a) 74

83 Relationship Between Crack Heating and Crack Length as Measured at ISU
for Ti64 75

84 Relationship Between Crack Heating and Crack Length as Measured at PW
for Ti64 76

85 Relationship Between Crack Heating and Crack Length as Measured at GE
for Ti64 76

86 Relationship Between Crack Heating and Crack Length as Measured by all Sites
for Ti64 77

87 Relationship Between Crack Heating and Crack Length as Measured at ISU
for In718 77

88 Relationship Between Crack Heating and Crack Length as Measured at PW
for In718 78

89 Relationship Between Crack Heating and Crack Length as Measured at GE
for In718 78

90 Relationship Between Crack Heating and Crack Length as Measured at all Sites
for In718 79

91 Crack Detectability Surface for Titanium LCF Specimens Based on ISU Data 80

92 Measured Stress Versus the Experimental Amplitude Value for the Tests on
Ti64 Specimens Measured at ISU 85

ix