ULTRASONIC FOR FAA AERO CENTER

39 Pages·2001·3.01 MB·English

ULTRASONIC
FOR FAAA EROC ENTER
RECEIVED
APR 2 5 :?‘:
LIBRARY '
AIRCRAFT
U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
ULTRASONIC NONDESTRUCTIVE
TESTING FOR AIRCRAFT
1975
U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
FLIGHT STANDARDS SERVICE
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 2@M2 - Price $1
TABLE OF CONTENTS
Page
Chapter 1. INTRODUCTION
1. General ___-___--________------------------------------------------------- 1
, 2. Use of Ultrasonics -----_---_--_-___---------- ______ ---- ___________-____ -__ 1
3. Limits on Application of Ultrasonics _---_--_--_---------__________ _________ 1
4. Ultrasonic Inspection for Corrosion Detection - ____________-_-_ -_-- _________ 1
5.-9. Reserved ________________-_-_____________________------------------------- 1
Chapter 2. TRANSDUCERS (SEARCH UNITS, PROBES, CRYSTALS)
10. General ~-_--_-~-~----___------~--~---~-------~~---~~--~----------~~~~---~ 3
11. Transducer Materials ______________--_--_____________________------------- 3
12. Piezoelectric Effect ---~___--_--_-__----------~-~-~-~~-~~--------~~~-~~~~~- 3
13. Transducer Type Search Units __-___-------_--_--_____________________----- 3
14. Transducer Groups ---___----------~~_~------~~~----~--~~~-~-----~~~~~~~~~ 4
15.-20. Reserved ______----______________________________------------------------- 5
Chapter 3. WAVE PROPAGATION
21. Ultrasonic Waves -----_-_---------_-_------------------------------------- 7
7.2. Longitudinal Waves ______ ----_-__-__- _________ -_--_-_-__--------- _________ 7
23. Shear Waves --_------_-----------------~-~~~~----------~~~~~-~~-~~~~~~~~~ 7
24. Surface (Rayleigh) Waves ----_--_-- __________ --_--_--_---------- _________ 8
25. Plate (Lamb) Waves --------------_--_-_-------------- _-__ -_--_- ____-____ 8
26.-30. Reserved ---_---~~--_____----____________________~~~-~~~----~------------- 8
Chapter 4. ULTRASONIC VIBRATIONS
31. Testing Methods ~~~-----__~__~~~-----------------------~~~~~~~~~~~--~-~~~~ 9
32. Reflection of Ultrasonic Waves -------------_--_---______ _____-_-____--_____ 9
33. Refraction and Mode Conversion of Ultrasonic Waves ---------------_________ 10
34. Beam Divergence ----_-__-----_--_-______________________----------------- 10
35.-40. Reserved ~-~--_--------__-------~--~~-~~~~~~~~------~---~~--~----~~------- 10
Chapter 5. ULTRASONIC SYSTEMS
41. General -_-____------_--_------------------------------------------------- 11
42. Pulsed ~-------__~_~-~--__~____________________~~~-~--~~~~~~~~~~~~-~~~~~~~ 11
43. Reasonance ---------------~~-------------~~~~~---------~~~~~~~~~~~~~~~~--~ 12
44.-50. Reserved ------~~~~---_--~_~~____________________------~~~~~~~~~~~~~~~~~-~ 13
Chapter 6. PRESENTATION
51. Observing and Recording Response Patterns _____---_--_--_-----_____________ 15
52. Cathode-Ray Tube (CRT) ----- ---- __-_ -_---------_---- ______-_- - --_-_____ 15
53. Scan Presentation --~-----~~-~------~-____________________---------~~~~~~~~ 16
54. Indications ____------_-__------------------------------------------------- 16
55.-60. Reserved ______-------_-_------------------------------------------------- 19
Chapter 7. RECORDERS
61. Types ---------~---------~____________________-~--------~--~~~----~~~~---~ 21
62. Deflection Modulation, Conventional Pen-Chart Recorders ---~~-~--~--________ 21
63. Intensity Modulation, C-Scan Mehod of Facsimile Recording --------________ 21
64.-70. Reserved --------~-------~~~-____________________----~--~~~~~~~~--~~~~~~~- 21
I
TABLE OF CONTENTS-Continued
Page
Chapter 8. ELECTRONIC GATING
71. Functions ~___~-__-~_-_-__~--_____________________~~~-~~---~~--~---~---~-~ 23
72. Basic Operating Principles of Gates --------------------____________________ 23
73.-75. Reserved --~-----------_--___-~-~---~---~~-~~~-~~~-~~~-~._~-___--__-__~~__ 24
Chapter 9. DELAY LINE
76. Description -_~--~~--_~--_-~--~---~---~~----------------~---~----~------~-- 25
77.~80. Reserved _~~___-___-__--~__~-____________________-~~---~---~~--~~--~---~-- 25
Chapter 10. COUPLANT
.
81. General ~---~---~--_~~~--~---~---~~------~----~---~---~-----~--~--~~--~~-- 27
82. Description ---------~----~------~---~~---~---~----~--~~-~~~--------~~~~~-~ 27
83.-85. Reserved ---~-~-~~~-_~---~~--____________________----------------~~~-~~~-~ 27
Chapter 11. ULTRASONIC REFERENCE BLOCKS
86. Introduction _~--~~-----------_~------~~--~---~~---~--~~--~~----~--~--~~~~~ 29
87. Distance-Amplitude Comparison Blocks -_---_--------_---_-_________________ 29
88. Area-Amplitude Comparison Blocks (Alcoa Blocks) __-___- __________________ 30
89. I.I.W. Welding Blocks -------------------_----------------------- _________ 30
90. ASME Weld Reference Plate --------------------------------------------- 30
91. Special Reference Standards ---_-----------_------------------------------- 30
92.-95. Reserved _~-__~~-~---~~_-~~-~-~---~---~~--~--------~---~~--~~~--~--~---~~- 31
Chapter 12. TESTING METHODS
96. Description ~__---_~--_~~-__~--_____________________~~--~-----~~-~~-----~~- 33
97. Contact Testing --~-~-~---~----~-------~---~---~~--------~---~-~----~-~~~~~ 33
98. Immersion Testing ---------------_-------~~-------~--------~--~~--~~-~~~~~ 33
99. Immersed Scanning Technique -_------------------____________________----- 34
100. Water Column Technique (Bubbler, Squirter) -------_-------__---__________ 36
101. Wheel Search Unit ----------_--------_-----------~--~-~--~~--~----~~-~~~~ 36
102. Ultrasonic Image Converter ~~--~~--_~- -_-- --_---_---__---_----_____________ 36
103.-110. Reserved ~------_---_--------____________________-----~~----------~~~-~~~- 37
Chapter 13. INSPECTION OF INTEGRAL FUEL TANKS FOR CORRISON
111. General _---~_---~----~--~-------~~~~~~~~~-~~~-~-~-~~~~-~~--~~~~-~--~~---~ 39
112. Method ~---_--__---_------_-~--~~-~--~~~--~~--~~--~~---~-~-~~--~---~---~~ 39
113. Equipment __--__-____-__-_____------------------------------------------- 39
114. Indications --------------_---_~----~~~-~~~--~~-~~~-~~~~-~~--~~~~~~~~~~~--~ 39
115.-120. Reserved -_-_-___-___--__________________________------------------------- 39
Chapter 14. INSPECTION OF REPRESENTATIVE AIRCRAFT PARTS
121. General -_~--_~--~-~--~---~----~--~~-------~-----~~-~---~---~~------~---~- 41
122. Main and Nose Landing Gear Wheels --_----_---_-------------------------- 41
123. Main Landing Gear Torsion Link -__---_---_--_-_---_---------------------- 41
124. Main Landing Gear Torsion Link 1,ugs __-___- ____ --_.-_-_--___-___--__--___ 41
125. Main Landing Gear Oleo Outrr Cylinder --------_--------_----------------- 42
126. Main Landing Gear Trunnion Support Strnvtow __---_--_----__-_-_-________ 42
127. Nose I,anding Gear Outer Cylinder ----------__---_---_____________________- 42
128. Inboard and Outboard Nacelle Strut Front Spar Fittings ---_-------_---__--- 43
129. Nose Landing Gear Outer Cylinder _-------__------------------------------ 43
130.-l%. Reserved _~~-_~--~---~---~---____________________--~------------~~~~~--~- 43
II
LIST OF ILLUSTRATIONS
Figure Page
1. Angle Beam Search Unit ________________________________________--------------- 3
2. Generation of Ultrasonic Vibration ________________________________________------ 3
3. Diagram of an Ultrasonic Search Unit ________________________________________-- 4
4. Natural Quartz Crystal (X and Y Cut) _____ - ____________________________________ 4
5. Common Transmitter-Receiver Search Unit __________ -_-- _____ - __________________ 4
6. Combined Transmitter-Receiver Search Unit ____________________________________ 4
7. Separate Transmitter-Receiver Search Unit ______________________________________ 5
8. Mechanical Analogy of Wave Propagation --__----_-_--__-__- _______ - ____________ 7
9. Longitudinal Waves ________________________________________-------------------- 7
10. Shear Waves ________________________________________--------------------------- 7
11. Transmitting A Wave at a Small Angle __________ - _______________________________ 8
12. Surface Waves ____-_____-_____________________________------------------------- 8
13. Surface Wave Technique ________________________________________--------------- 8
14. Plate Waves ________________________________________--------------------------- 8
15. Reflection of Ultrasound ________________________________________--------------- 9
16. Refraction of the Ultrasonic Beam ______ - _______________________________________ 10
17. Generating Shear Waves __-_______--_--____-____________________---------------- 10
18. Generating Surface Waves ___-_____-_-__--_-______________________-------------- 10
19. Beam Divergence of Sound Waves in Steel _______________________________________ 10
20. Diagram of Longitudinal Sound Striking a Surface ___- ___________________________ 10
21. Block Diagram of Basic Pulse-Echo System _-__- _____ - ___________________________ 11
22. Oscilloscope Display in Relationship to Flaw Detection ____________________________ 11
23. Through-Transmission Technique -_- ________________________________________----- 12
24. Conditions of Ultrasonic Resonance in Metal Plate _______________ - _______________ 12
25. Block Diagram of Resonance Thickness Measuring System ________________________ 12
26. RadieFrequency Trace and Video Trace ________________________________________ 15
27. Types of Marker Systems ________________________________________--------------- 16
28. A-Scan Presentation ________________________________________-------------------- 16
29. B-Scan Presentation ______-_________________________________-------------------- 16
30. C-Scan Presentation _-__-____-__-__-________________________-------------------- 16
31. Immersion Crystal Focused on Test Block and Indications to he Expected ___________ 17
32. Immersion Crystal Focused on Block with Defect and Non-parallel Surface ________ 17
33. Immersion Crystal Focused on Shaft too Long for Back Reflecion of Return _________ 17
34. Angle Beam Penetrating a Weld Bead ________________________________________--- 18
35. Angle Beam Penetrating a Weld Bead ________________________________________--- 18
36. Angle Beam Penetrating a Flat Plate ________________________________________---- 18
37. Results of a Rough Front and Back Surface ___--_-- ______________________________ 18
38. Evaluating Braze of Carbide Tip to Steel __- ______ -__- ___________________________ 19
39. Indication Received from Porous Material _____ - ______ -___- ____ - _________________ 19
40. Irregular Part ________________________________________------------------------- 19
41. Various Recording Charts ________________________________________--------------- 21
42. Ultrasonic Recording of Brazed Honeycomb Panel ________________________________ 21
43. Controllable Gated Zone in Test Piece ___- ___________ - _____ - ____________________ 23
44. Threshold Gate Circuit Diagram ________________________________________--------- 23
45. Threshold Gate Wave Form ________________________________________------------- 24
46. Ultrasonic Delay Time ____ - _____ -__- _____ - _____________________________________ 25
47. Couplant (Contact Testing) ________________________________________------------ 27
48. Couplant (Immersion Testing) ________________________________________---------- 27
49. Distance-Amplitude Comparison _-_-- ________________________________________---- 29
50. Step Block ________________________________________---------------------------- 30
51. Area Amplitude Comparison Blocks ________________________________________------ 30
52. I.I.W. Weld Block _________-_______---____________________--------------------- 31
53. ASME Weld Reference Plate ________________________________________----------- 31
III
LIST OF ILLUSTRATIONS-Continued
Figure Page
54. Contact Angle-Beam Test into Hidden Weld Region of a Landing Gear Oleo Strut ---_ 33
55. Ultrasonic Inspection of a Wing Front Spar --------~--~~-~~- --__- - __-____________ 33
56. Ultrasonic Inspection of a Pylon Structural Member --------------~~-~~-__________ 33
57. Principle of Ultrasonic Testing (Contact) ----_--------------- _--------~-~~--~~-- 34
58. Principle of Ultrasonic Testing (Immersion) --------~~-~~- ~~~~~~~~~_~~__~________ 34
59. Bubbler Angle-Beam Testing (Pipe) ----_--_---------------~~--~~~~-~~-~~-~~-~~~ 34
60. Wheel Scanning Method ~-------------------------~~-~~-~~~~~~~~~~~~~~~~~~~~~~~ 34
61. Immersed Angle-Beam Technique (Pipe or Tube) --------------------___________ 34
62. Immersed Angle-Beam Technique (Plate or Sheet) --_--_------------------------ 35
63. Immersed Through-Transmission Technique -----------------_--______ __-_____ -___ 35
64. Removing First Multiple of Interface Indication From Test Area --------~-----_~-~~ 35
65. Focused Search Unit ----_--_--____-__-__--------------------------------------- 35
66. Beam Collimator -------------------~---------------------~--~--~~-~~-~~~~------ 35
67. Bubbler Scanning Method -----------------------------------~-----~~--~~~~~~-- 36
68. Bubbler Angle-Beam Technique (Plate) ---_-__--_------------------------------ 36
69. Wheel Search Unit in a Fixed Position ------------------------- ----- -- _---_-_ -_- 36
70. Wheel Search Unit over the Material ----_-------------------------------------- 36
71. Schematic-Ultrasonic Image Converter System ---------------_----_______________ 37
72. Main and Nose Landing Gear Wheels ------------------------------------------ 41
73. Main Landing Gear Torsion Link ----_--_--_--_--_--_--------------------------- 41
74. Main Landing Gear Torsion Link Lugs -----------------_-- _-__- ----_---_-_--_-_- 41
75. Main Landing Gear Oleo Outer Cyclinder ---------------------------------------- 42
76. Main Landing Gear Trunnion Support Structure ------------------_______________ 42
77. Nose Landing Gear Outer Cylinder -----_-----_--------------------------------- 42
78. Inboard and Outboard Nacelle Strut Front Spar Fitting --------------------------- 43
79. Nose Landing Gear Outer Cylinder -------------------_-------------------------- 43
Chapter 1. INTRODUCTION
1. GENERAL. Ultrasonic inspection of aircraft a. Sensitivity. The ability of the instrument to
plays an important role from both a safety and detect the small amount of energy reflected from a
economic aspect. In order to accomplish the pre- discontinuity.
scribed ultrasonic inspection, only minor aircraft
b. Resolution. The ability of the instrumenta-
open-up for accessibility is usually required. For
tion to detect flaws lying close to the test surface or
example, in the case of the aircraft engine, inspec-
to separate and distinguish the indications from
tions are performed “on the wing” with the engine
several defects occurring close together in the
still installed in the aircraft. For the airframe,
specimen.
ultrasonics required a minimum of disassembly and
removal of interfering equipment. Aircraft inspec- c. Noise discrimination. The capacity of the
tions with ultrasonics can be performed “at the instrumentation for differentiating between the sig-
ramp” or “on the line” under circumstances entirely nals from defects and the unwanted noise of either
different from total disassembly. It is an extremely electrical or acoustics nature.
sensitive method of nondestructing testing. The d. These factors are affected by others, such
limitations are few and when direct coupling (or as frequency and pulse energy. For example, when
contact) with the part being checked can be estab- frequency is increased, the sensitivity increases.
lished, the resolving capabilities are excellent. How- With the increase in sensitivity, smaller inhomo-
ever, interpretation by trained personnel is required. geneties within the material will become detectable.
This will increase the noise level, thus hindering
2. USE OF ULTRASONICS. Ultrasonics employ signal discrimination. With an increase in pulse
electronically produced, high-frequency sound waves
energy, material noise will increase and resolution
that will penetrate metals, liquids, composites, and
will decrease.
other materials at speeds of several thousand feet
per second. This technique can be used to:
4. ULTRASONIC INSPECTION FOR CORROSION
a. Detect laps, seams, laminations, inclusions, DETECTION. Although ultrasonic inspections have
cracks, corrosion, and other defects in installed been employed by the aviation industry for several
parts. years, it was not until recently that ultrasonics have
6. Locate porosity, cupping, and nonmetallic in- been used as a means of corrosion ,detection. Pres-
clusions in bar stock. ently, this method of corrosion detection is still in
c. Locate cracks, blow holes, insufficient penetra- the early stages and certainly not infallible; but it
tion, lack of fusion, and other discontinuities in has been demonstrated that, within limitations,
welds. ultrasonics can provide a fairly reliable indication
of corrosion attack. Highly trained personnel must
d. Evaluate bond quality in brazed joints and
conduct the examination if any useful information
honeycomb composites assemblies.
is to be derived from the indicating devices. This
e. Inspect forgings such as turbine engine is compounded by the fact that the results obtained
shafts, turbine engine discs, and landing gear struc-
vary, depending on the model and make of equip-
tural members.
ment used, and on the techniques used by the in-
3. LIMITS ON APPLICATION OF ULTRASONIC dividual performing the examination.
TESTING. Among the factors which may limit the
application of ultrasonic testing are: 5.-9. RESERVED.
Chapter 2. TRANSDUCERS (SEARCH UNITS, PROBES, CRYSTALS)
10. GENERAL. To understand how inaudible may be of any conducting material such as alu-
sound is used to reveal certain conditions which are minum, silver, gold, or chromium. However, coat-
.
not perceptible in the normal hearing range, it is ings are difficult to deposit on lithium sulphate
first necessary to know how ultrasound is transmitted crystals so thin metallic foils are often cemented to
and received. the crystal.
11. TRANSDUCER MATERIALS. Three transducer 12. PIEZOELECTRIC EFFECT. Ultrasonic testing
materials which can be used in the manufacture may use the piezoelectric effect to generate ultra-
of ultrasonic search units are natural quartz crystals, sonic vibrations. Crystals, when subjected to an
lithium sulfate, and polarized crystalline ceramics. alternating electric charge, expand and contract
a. Quartz. Principal advantages are : electrical under the influence of these charges. Conversely,
and thermal stability, insolubility in most liquids, it was found that these materials when subjected
high mechanical strength, wear resistance, excellent to alternating compression and tension developed
uniformity and resistance to aging. A limitation alternating electric charges on their faces. (See
of quartz is its comparatively low electromechanical Figure 2.) This was named the piezoelectric effect.
conversion efficiency. The heart of an ultrasonic testing system is this
method of converting electrical energy into me-
b. Lithium Sulfate. Principal advantages are :
chanical vibrations, and converting the mechancial
ease of obtaining optimum acoustic damping for
vibrations back into electrical energy.
best resolution, intermediate conversion efficiency,
and negligible mode interaction.
ALTERNATING VOLTAGE APPLIED *
c. Polarized Ceramics. Principal advantages TO AN X-CUT CRYSTAL
are: high conversion efficiency which yields high
search unit sensitivity. Because of lower mechan-
ical strength and relatively high electrical capaci-
tance, their use is generally restricted to frequencies r=- 4.J
below 15 Mega-Hertz (MHz). Another limitation
CRYSTAL EXPANDS CRYSTAL CONTRACTS
is some interaction between various modes of vibra-
FIGURF.2 .-Generation of Ultrasonic Vibration
tion.
In order for a crystal to utilize its piezoelectric Generation of the ultrasonic pulse is usually ac-
characteristics, it is placed in a circuit much like a complished by producing a radio-frequency wave
condenser. That is, both faces are coated with a train of the desired frequency at a precise time and
conducting material with no contact between the converting this into vibrations by means of piezo-
two faces. (See Figure 1.) Coatings for crystals electric transducers. Some ultraconsic instruments
do not use a radio-frequency wave train, but in-
k COAXIAL CABLE CONNECTION stead, use a shock pulse and allow the search unit
to select the frequency of operation.
13. TRANSDUCER TYPE SEARCH UNITS. The
PLATED BACK search unit consists of a shell for mechanical pro-
CRYSTAL tection, a means to conveniently handle or mount
PLATED FACE the unit for use, the transducer element, electrical
connections, and a backing material to dampen
the backward directed energy that is transmitted
FIGURE l.-Angle Beam Search Unit by the crystal. (See Figure 3.)
3
ELECT. 14. TRANSDUCER GROUPS. There are three gen-
CONNECTION eral groups of transmitter-receiver search units:
, SHELL a. Common Transmitter-Receiver IT-RI. These
search units employ a single crystal and have com-
BACKING mon connections to the transmitter and receiver
‘MATERIAL amplifier units. (See Figure 5.)
I
SPECIMES PIEZOELECTRIC
CRYSTAL
FIGURE 3.-Diagram of an Ultrasonic Search Unit
Transducers are available in a wide variety of
\
types which include :
\
I I
a. X-Cut crystals for longitudinal-wave gen- PECIMFN
eration. (See Figure 4.) II \ i
I \
b. Y-Cut crystals for shear-wave generation. I I
(See Figure 4.)
FIGURF. 5.-Common Transmitter-Receiver Search Unit
C. Dual crystals with common holder.
d. Mosaics-three or more crystals. Since the search unit acts as both transmitter
e. High frequency, 50 MHz or more. and receiver, it transmits a pulse of 1 to 4 micro-
f. Alternate crystal materials. seconds duration ; then acts as a receiver for a period
up to several thousand microseconds. This cycle
Sandwich and tandem arrangements.
9.
of transmitting and receiving is repeated at a rate
h. Curved crysals to fit the specimen.
of 50 to 5,000 times per second, or higher if re-
i. Wheel search units.
quired for high-speed automatic scanning.
i. Focused search units.
b. C o m b i n e d Transmitter-Receiver IT-RI.
k. Temperature search units (for measuring
These search units have two transducers mounted
wall thickness at temperature up to
on a single head and insulated acoustically from
l,lOO°F).
each other. One transducer is connected to the
pulser and the other is connected to the receiver.
% AXIS
The combined T-R search unit is used for testing
close to the entry surface and for thickness measure-
ments from .040” to 2.0” when the opposite side is
rough or corroded. The transmitting search unit
-p roje-c ts a beam of vibrations into the material ; the
vibrations travel through the material and are re-
X-CUT ‘X AXIS
/Y AXIS
Y-CL’T
z AXIS
FIGURE 4.-Natural Quartz Crystal (X and Y Cut)
Transducers are available that are smaller than
l/a” diameter and larger than 1” x 4”. However,
for most ultrasonic testing, standard diameters of
l/b”, l/2”, and 1.0” are used. FIGURE 6.-Combined Transmitter-Receiver Search Unit
4
fleeted back to the receiving search unit from any
discontinuities or from the opposite boundary if
Ly parallel to the entrant surface. --(See Figure 6.)
-
c. Separate Transmitter-Receiver U-RI or
Pitch-Catch, Search Units. Two heads are em-
ployed in these units having separate electrical con-
nections to the transmitter and the receiving units.
One head is used as the transmitting unit while the
other head is the receiving unit. (See Figure 7.)
. Materials which are coarse grained tend to scat-
ter the ultrasonic sound beam; these materials can
be effectively inspected using separate T-R search
units that are mounted on individual wedges of a
suitable plastic solid. When separate wedges are FIGURE 7.--Separate Transmitter-Receiver Search Unit
used, the angle of incidence may be varied accord-
ing to the section thickness to be examined. 15.-20. RESERVED.
5