rtE. UN iTY OF MICHIGAN LRA.-:.When Government drawings:, specifications, or other data are used for any purpose other than in connection with: a. 4definitely related Government procurement operation, the United State.s Goernment thereby incurs no responsibility nor any obligation whatsoever; and -the, -fact; -thatthe. Government may have formulated, furnished, or in any way supp:ied the said drawings, specifications, or other data, is not to be redd by impligationr otherwise as in any manner licensing the holder:or any other person or corporation, or conveying any rights or permission to man-ufactwure,- use,- or sell any patented invention that may in any way be: related:"thereto.:'-:';:?.. -. 0. 7... -:.d /..:......'....:.. This: document is subJect to s.pecial. exportt controls and each transmittal to foreign governents. or fore ign.:ationals.my be made only with prior approval of the Metals'and Ceramics'Division A (MAM) Air Force Materials Laboratory, Wright-Patterson Air Force' Base, Ohio:45433....::::: -......... Distribution of this report. is:.limited because the report contains technology identifiable with items on,-the strategic embargo lists excluded from export under the U. S. Export. Control Act,.. as implkemented:by ARF 310-2 and AFSC. 80-20.. - * t.: 0...... -r Qualified requesters may obtaincopies o this report from the Defense Documentation Center (DDC), Cameron Station, Alexandria, Virginia 22314. ARPA Order No.. 124. Program Code No. 8D10. Name of Contractor: The Regents of.The University of Michigan Effective' Date of- Contract:. July 1968 Contract Expiration Date:..: 30.'.1971.... 197. Amount'of Contract: $2125,313.00 ) - - -..... ('.-...: Contract No. FF33615-68-C-1703.-: -Principal Investigator:. JR. Frederick:-: -..... Phone: ( )-764-3387 Short Title of Work: " Use of Acousticem.issioninon ndestrutive Testing

THE UNIVERSITY OF MICHIGAN COLLEGE OF ENGINEERING Department of Mechanical Engineering Semiannual Report USE OF ACOUSTIC EMISSION IN' NONDESTRUCTIVE TESTING September 1, 1969 - February 28, 1970 J R. Frederick ORA Project 01971 under contract with: UNITED STATES AIR FORCE AIR FORCE SYSTEMS COM1:ALND. AERONAUTICAL SYSTEMS DIVISION CONTRACT NO. F33615-68-C-1703 WRIGHT PATTERSON AIR FORCE BASE, OHIO ARPA Order No. 1244 Program Code No. 8D10 administered through: OFFICE OF RESEARCH ADMINISTRATION ANN ARBOR June 1970

FOREWORD This is the third semiannual report on a study of the use of acoustic emission in nondestructive testing. This research is supported by the Advanced Research Project Agency of the Department of Defense and is monitored by the Air Force Materials Laboratory, MANN, under Contract No. F33615-68-C-1703, initiated under ARPA Order 1244, Program Code 8D10. Mr. R. R. Rowand (MANN) is project engineer. This report covers the period from September 1, 1969 to February 28, 1970. The program is being carried out in the Rheology and Fracture Laboratories of the Mechanical Engineering Department of The University of Michigan. The work is under the direction of Associate Professor J. R. Frederick. Professor David K. Felbeck, Mr. Robert Bill, Mr. Charles Thomas, and Mr. William Bracht have participated in the program.'iii

ABSTRACT Acoustic emission: y be defined as the noise given off spontaneously by solid materials as a result of a sudden relaxation of stresses within the- material. Stress relaxation -can occur as a result of the nucleation or propagation of cracks, or as a consequence of various elastic or plastic deformation processes., The principal elastic or plastic deformation mechanisms that are sources o-f acoustic emission in solids are (1) the slip of existing dislocations in a metal, (2) the activation of dislocation sources,.(3) twinning and (4) grain boundary slip. This report describes the results of an investigation into the effects of one microstructure parameter, namely grain size, on acoustic emission. It also describes a method by which acoustic emission phenomena may possibly be used to determine the amount of residual stress in metals. iv

TABLE OF CONTENTS page 1 0 INTRODUCTION................. - 1 2.0 EXPERIMENTAL PROCEDURES....................................... 2 3.0 MICROSTRUCTURE INVESTIGATION OF ALUMINUM e.................... 5 3.1 MICROSTRUCTURE INVESTIGATION OF ALUMINUM.............. 5 4.0 RESIDUAL STRESS DETERMINATION.-.............**...........*..... 10 4.1 EXPERIMENTATL PROCEDURES......... 14 4.2 RESULTS OF RESIDUAL STRESS TESTS.......... 16 4.3 DISCUSSION OF THE RESULTS OF THE RESIDUAL STRESS TESTS....16 5.0 CONCLUSIONS.*......................................... 22 6.0 FUTURE EFFORT............. 23 REFERENCES.... *..*.. * 0. 24 DISTRIBUTION LIST 25...........................

LIST OF FI'IGURES 1. A float and lever system is used to apply a load to the test specimens. This minimizes the extraneous noise. 2. Block diagram of the electronic components used in the investigation. 3. True-stress, true-strain curves for 99.99% aluminum used in the investigation. 4. The cumulative acoustic emission from 99.99% aluminum depends on grain size. The data shown are for a frequency band of 80 to 200 kHz. 5. The acoustic emission from coarse grained 99.99% aluminum is greater at low frequencies than at higher frequencies. 6. Repeated loading of a test specimen to stress levels below the yield stress results in the type of cumulative emission versus load curve shown in the Figure. 7. Simplified model for a specimen containing uniform compressive and tensile stresses. Region A is in tension. Region B is in compression. 8. Stress levels applied to the specimen shown in Fig. 7 in order to obtain the acoustic emission response shown in Fig. 9. 9. Schematic diagram of the acoustic emission from the model shown in Fig. 7. Region A emits in the manner shown for the tensile loading. Region B emits in the manner shown for the compressive loading. 10. The combined emission for the model in Fig. 7 is a combination of the two curves shown in Fig. 9. 11. If a sufficiently large tensile stress is applied to the specimen shown in Fig. 9 so that the region under compression is put into tension a cumulative emission curve having two points of inflection should result. 12. Cumulative acoustic emission from 6061-T6 aluminum during loading and unloading. The maximum stress applied to the specimen is less than half of the yield stress. 13. Cumulative acoustic emission from a 6061-T6 aluminum specimen that had been bent to about 1/20 and then restraightended. The arrow indicates a region of the load curve in which there is a change in slope, as might be expected from the model in Fig. 11. The applied stress is less than half the yield stress. 14. Acoustic emission from an annealed 1018 steel flat tensile specimen which has no residual stresses. vi

15. Acoustic emission from an annealed 1018 steel flat tensile specimen containing a shrunk-fit insert having a compressive stress of about 16,000 psi. 16. Acoustic emission from an annealed 1018 steel flat tensile specimen containing a rolled-in insert having a compressive stress of about 6000 psi.

1.0 INTRODUCTION One of several possible sources of acoustic emission from metals is dislocation motion. The model being used in the present program to explain the emission process is one proposed by Agarwal, et. al.,(l) namely, that the acoustic emission results from the slip produced by the motion of dislocations which originate from dislocation sources that have been activated by an applied stress. It is assumed in the model that a source continues to operate until it is shut off by the back-stress of piled-up dislocations. One of the tasks that has been pursued has been to investigate the effect of microstructure on acoustic emission. As a result of this effort it has been found that the amount of acoustic emission produced in 99.99% pure aluminum depends on the grain size of the material in an anomalous way, namely, that a peak value of the emission occurs in this material at a grain size of about 350 microns. Above this grain size the emission decreases and approaches a constant value. Below this peak value, the emission also decreases and approaches zero for grain sizes less than 10 microns at the noise threshold level of 4.0 microvolts used in the tests, the results of which are being reported here. Another task that is being pursued is the use of acoustic emission to measure residual stresses in metal. The determination of the intensity of residual stresses remaining in a manufactured part after some form of processing has been performed on it is generally carried out by removing successive layers of material and measuring the change in stress in the material adjacent to the removed section. This process makes the part

unusuable. Hence it would be useful to have some method for determining the intensity of residual stresses in a part nondestructively. Other work in progress involves the acoustic emission from specimens while they are undergoing fatigue or creep, and the development of thermal stressing techniques for inducing emission. The temperatures being used in the latter tests are low enough-so that no significant structural changes are produced in the material being tested. The results of these tests will be reported in subsequent progress reports as definitive results are obtained. 2.0 EXPERIMENTAL PROCEDURES Because of the low level of the acoustic emission phenomena being studied and the range of frequencies (6 to 300 kHz) being used, a low noise-level loading system previously described has been used(2). Schematic diagrams of the mechanical components and the instrumentation are shown in Figs. 1 and 2. The load is applied to the specimen by the float and lever system shown in Fig. 1. This is located inside an "audiometric" room to reduce the amount of ambient noise picked up by the detection system. The walls of the- room have a transmission loss of 60 dB in the octave band of frequencies of 4800 to 9600 Hz. The room is also electrostatically shielded. The low noise-level preamplifier is located in the audiometric room adjacent to the test specimen so that the input lead from the PZT-5 transducer can be as short as possible. The specimen is supported by nylon grips to provide further isolation from extraneous noise.

* indicates that acoustic isolation or mismatch material is used. SYNCIRONUS RUBBER PIUJ 4t II CSPECIMEN 1 B k L IPS I I I I 1 SXECIMEN'II 1 li~s11/ \'TL ~a. 11 T 1 1 RATE AND BA:I AST CONTROL - TANK #2 VALVE #1 r (PcT A PAT':E FfmTENi_ a. l s. This minimize the extr s FIEXIBLE ADJUSTABLE RUBBER - TANK STAND SEPARATE Fig. 1. A float and lever system is used to apply a load to: the test specimens. This minimizes the extraneous noise.

F TANSDUCER PREAMPLIFIER BAND LOU;D PAR PASS, r AMPLIFIER I I ~~~~~~~~~~~SPEAKER TYPE CR4A FILTER I 1 ~TEST OSCILLOSCOPE S P EC~~~I:~ E N -~TE KTRON I X I ~~TRIGGER 55 I. I L~~~LVEL: I CCALIBR'ATOR ELECTRONIC.. L-To I COUNTER I AG HEWLETT- ANALOG CONVERTER 1A~IIrHPCKARD -EWLETT- PACKARD'AUDIOMETRIC 5233 _ 580A I-!ROOM~ I IMODEL 402-A I I VTVM EICO I MODEL 250 I: X-Y. -Y2 RECORDER LOAD IHEWLETT- PACKARDI. I ELL MODEL 136A Fig. 2. Block diagram of the electronic components used in the investigation.

5 3.0 MICROSTRUCTURE INVESTIGATION OF ALUMINUM The microstructure parameter in 99.99% aluminum that was investigated was grain size. Variations in grain size were obtained by the recrystallization and subsequent grain growth in plastically deformed material. True-stress, true-strain curves for three different specimens, each of which had a different average grain sizes, are shown in Fig. 3. As is to be expected the smaller the grain size the higher strength. The cumulative acoustic emission that is obtained for a given applied stress depends on the grain size of the aluminum as shown in Fig. 4. For small or large grain sizes the emission is low, but at an intermediate size there is a maximum total acoustic emission. The bandwidth for the data in Fig. 4 is 80 to 200 kHz. The -same shape of curve is also observed in a frequency band of 6 to 20 kHz. Another effect that is observed concerns the frequency content of the emission. As the grain size increases the amount of emission at low frequencies increases in comparison with the emission at higher frequencies. Fig. 5 shows this effect for three different grain sizes. These data were obtained by analyzing a tape recording of the emission from three different specimens, each of which had a different average grain size. An Ampex FR 100 tape recorder was used to record the acoustic emission. The emission in the various frequency bands was measured by the use of a Krohn-Hite model 310 AB band-pass filter. 3.1 DISCUSSION OF THE RESULTS ON THE EFFECT OF MICROSTRUCTURE ON ACOUSTIC EMISSION The increase and subsequent decrease in the amount of acoustic emission with increasing grain size can be explained on the basis of the model proposed

4000 X 2o00 5002 3000 LlJ c: 2000 IJj Cr% 10' ~000 0 I O..0 TRUE STRIN, g5 or FIg. 3 * Tr, 1ste8 tr5 1sr i cu tes fo 9. 9 aiurje.e i thA.e=, used in the investigtio0

F ~~~~~0 12000 COO to 0~~~~~~ (I) H- 10000 0 z" 0~~~~~ U~~~~~~~~~~ os 8000 o 46000 F:C' cTa4000 0o 00a0 200 400 600 800 1000 1200 1400 1600 1800 AVERAGE GRAIN DIAMETER, MICRONS Fig. Ii. The cumulative acoustic emission from 99.99%6 aluiu depends on grain size. The data shown are for a frequency band of 80 to 200 klz.

E 4000/ groin size 01 /500, graoin size 7000 * 400,4 grain size' 6000 H... C/) 3000.J o 2000 10oo00 10-20kHz 20-30kHz 30-40kHz 40-60kHz 60-70kHz FREQUENCY BANDS Fig. 5. The acoustic emission from coarse grained 99.99% aluminum is greater at low frequencies than at higher frequencies,

9 by Agarwal (1). This postulates that acoustic emission is the result of the activation of sources of dislocations by an applied stress. The sources give off avalanches of dislocations until they are shut off because of the back-stress caused by the pile-up of dislocations against obstacles such as a grain boundaries. The generation of an avalanche of dislocations in a short interval of time satisfies the requirement that acoustic emission is only detected if a sufficient amount of slip occurs in a time interval that is short enough so that acoustic signals can be detected by a piezoelectric transducer. An average grain size of 10 microns in the 99.99% aluminum is sufficient to allow enough dislocations to be generated and glide away from the source so that a detectable strain pulse, or acoustic emission pulse, is produced. As the grain size is increased the dislocation glide distance increases and a larger strain pulse is produced. However, as the grain size increases the grain boundary area decreases. This means that there are fewer grain boundary sources of dislocations. Hence a reduction in the emission is to be expected. This happens at a grain size of about 350 microns for the data shown i.n Fig. 4, and for the threshold level of counting used in theses tests*. The increase in the amount of acoustic emission that is observed at low frequencies for the large grain sizes can be explained as follows. A large grain size means that the dislocation glide distances are greater than for smaller grain sizes. The dislocations are in motion for a longer time interval and thus more dislocations can be emitted before the source is shut off. From this it can be concluded that the average duration of *These results will be reported in more detail in the doctoral dissertation of Mr. Robert Bill at the University of Michigan in the latter part of 1970.

10 the slip events is longer and that the corresponding "effective frequencies" of the acoustic emission (i.e., the reciprocal of the duration of the slip events) are correspondingly lower. As the grain size decreases the source will operate for a shorter time and the "effective frequency" of the acoustic emission increases. 4.0 RESIDUAL STRESS DETERMINATION The basis on which it is proposed to investigate residual stress in metals by acoustic emission techniques is as follows. Most metals produce acoustic emission when strained. The amount of emission is related to the stress level, and to the volume of material stressed. For many engineering materials, including steel and aluminum, the emission is found to have the following characteristics: (1) On repeated loading to a stress below the yield stress of a test specimen the rate of emission is essentially constant and low. The total emission produced on loading to a particular stress level is proportional to the applied stress, as shown in curve "o-a" in Fig. 6. (2) During the unloading part of the cycle the acoustic emission is negligible for a small decrease in the stress level, then it increases in an exponential manner as shown in curve "a-b" in Fig. 6. A simplified model that is proposed for a specimen that contains a region of uniform tensile stress and a region of uniform compressive stress, both of the same magnitude, is shown in Fig. 7. Fig. 8 shows the stress levels reached as a result of applying a tensile load "F". Fig. 9 shows the separate cumulative emission from sections A and B of the model in Fig. 7. Fig. 10 is a combined cumulative emission curve.

b z o \ 9) Cn W W > _ \ D 01 a~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LOAD - Fig. 6. Repeated loading of a test specimen to stress levels below the yield stress results in the type of cumulative emission versus load curve shown in the figure.. ~Fl — -8...: -4 Fig. 7. Simplified model for a specimen containing uniform compressive and tensile stresses. Region A is in tension. Region B is in compression. Sy Stress a:a, a' b7l Strain b,b"/ _'Sy Fig. 8. Stress levels applied to the specimen shown in Fig. 7 in order to obtain the acoustic emission response shown in Fig. 9. -il

C,) b" ro b COM PRESSION TENSION LOAD - Fig. 9. Schematic diagram of the acoustic emission from the model shown in Fig, T..Region A emits in t. rmtemoe hw RgnAem in the manner shown for the tensile loading Region B emits in the compressive loading.

aII b"I 0 cn b' L b LOAD.. Fig. 10. The combined emission for the model in Fig. 7 is a combination of the, two curves shown in Fig. 9.

14 If a large enough stress is applied to the specimen so that the section that was originally in compression is now subjected to a tensile stress, the cumulative emission curve would appear as shown schematically in Fig. 11. HIence, in a general case it is necessary to apply a tensile or compressive stress larger than the residual stress and then to observe the shape of the load and the unload cumulative acoustic emission curves. If a curve such as is shown in Fig.ll is obtained, the change in the slope of the load and unload curves will occur at the peak value of the residual stress. 4.1 EXPERIMENTAL PROCEDURES Tests have been performed on 1018 steel specimens and on 6061-T6 aluminum. The steel specimens were annealed at 950 F for three hours and the aluminum was tested in the T-6 condition. The 6061-T6 aluminum specimens were 0.5 in. in diameter 4.0 in. long and had flat surfaces 1.,5 in. long and 0.1 in. deep milled on both sides. One of these was tested in the "as-received" condition. ReSidual stresses were introduced in the other specimen by bending it to an angle of about 1/2 degree and then straightening it. Three flat specimens of annealed 1018 steel were prepared having a gage section 5/8 in. wide, 1/4 in. thick and 4 in. long. Rectangular slots an inch long and 1/4 in. wide were cut in the center of two of the specimens. A 1018 steel insert 0.0015 in. longer than the slot was shrunk fit into the slot of one specimen. The slot in the other specimen was filled with an insert that was 0.002 in. thicker than the specimen. The specimen was then rolled until the insert was the same thickness as the specimen. The

a" bal 1L. a,b LOAD'' Fig. 11. If a sufficiently large tensile stress is applied to the specimen shown in Fig. 9 so that the region under compression is put into tension,- a cumulative emission curave having two points of inflection should result. 15

16 compressive stress produced in the rtins this way was reduced subsequently by plastically straining the main body of the specimen in a standard tensile machine. The stresses in the inserts were then measured by the use Of strain gages placed on the inserts and applying sufficienttensile load so that no further change in the length Of the insert occurred. These tests indicated that the compressive stresses were approximately. 16, i 000 psi in thfit peimen and 6,000 psi in the rolled-in specimen, 4.2 RESULTS The results of the acoustic emission tests on an annealed (stressfree) and the residual stress specimen are shown in Figs. 12-16. The curves shown are reproducible to within + 3% on any particular specimen.:A pre-load: of 50 pounds was maintained on the- specimens when making a test, hence the applied load is shown in the Figures as ranging from 50 to 400 pounds. The maximum load of 400 pounds in all tests is less than half the yield stress of the materials. 4,3 DISCUSSION OF RESULTS OF THE RESIDUAL STRESS TESTS The effect of residual compressive stresses on the acoustic emission from the 6061-T6 aluminum specimen that has been bent about 1/20 and restraightened is evident by comparing Figs. 12 and 13. The emission obtained on loading the specimen is greater than when no residual compressive stresses are present and there is an increasing rate of emission on loading up to the stress at which the compressive stress is overcome by the applied tensile stress. This point is indicated by the arrow on

12 A/umhIum 606/- T6 K3) 10 z C,) 6 w 21 FD 100 200 300 400 600 LOAD, POUNDS Fig. 12. Cumulative acoustic emission from 6061-6 aluminum during loading and unloading. The maximum stress applied to the specimen is less than half of the yield stress,

12k Alumrnum 606/ - T6 Bent and then straightened I0 o 8 0 W W > 4.4, 100 200 300 400 LOAD, POUNDS Fig. 13. 13. Cumulative acoustic emission from a 6061-T6 aluminum specimen that had been bent to about 1/2~ and then restraightened. The arrow indicates a region of the load curve in which there is a change in slope. as might be expected from the model in Fig. 11. The applied stress is less than half the yield stress.

I O /0/8 Anneoied Steel o1 1 W No Insert Cn Z8 C) 06 UV) In HW 100 200 300 400 LOAD, POUNDS Fig. 14. Acoustic emission from an annealed 1018 steel flat tensile specimen which has no residual stresses.

n 10 1/0/8 Annealed Stee/l with /nsert X z 8 O."..,.....,. 6 W o >W;' 4 > 2 _J ~ I -: 100 200 300 400 LOAD, POUN:DS Fi. l~ Fig. 15. Acoustic emission from an annealed 1018 steel flat tensile specimen containing a shrunk-fit insert having a compressive stress of about 16)000 psi.

lo'o | /O/8Ann/aled Steel with Insert z $'') o_ 6 w4 o I H> 2 100 -200 300 400 LOAD, POUNDS Fig. 16. Acoustic emission froman annealed 1018 steel flat tensile specimen containing a rolled-in insert having a compressive stress of about 6000 psi.

22. the graph at a load of about 250 pounds. Beyond this load the rate of increase of emission is constant. According to the:Model described in Fig. 11 there should be a point of inflection on the unload part of the curve. This is not evident, however, perhaps because of the low value of the unload stress that is associated with that part of the specimen having residual compressive stress. Fig.. 14 shows the emission from a 1018 flat steel specimen having no residual stresses. The constant rate of emission obtained on the application of a load can be noted. In Fig. 15 and 16, however, the emission rate increased during the application of a load. In both specimens it is evident that the applied stress was not sufficient to overcome the residual compressive stress and there is no inflection point on the load curve. 5. 0 CONCLUSIONS The following conclusions can be drawn from the results that have been presented in this report. (1) -.The effect of grain size on acoustic emission can be explained by a model based on the activation of dislocation sources and the subsequent shutting off of these sources by the back-stress of dislocation pile-ups. (2) In those materials in which the unload emission phenomenon is observed it is possible to obtain the unload emission effect by superimposing a tensile stress on a residual compressive stress. (3) The change in rate of acoustic emission when a residual stress is exceeded by an applied stress of opposite sign may have some promise as a means of determining the magnitude of the residual stress.

23 6.0 FUTURE EFFORT No more direct effort will be expended on the effects of microstructure on acoustic emission. It is felt that the work reported here substantiates the model for acoustic emission based on the activation of dislocation sources as proposed by Agarwal, et. al.(l) The model will continue to be applied to the interpretation of the results of acoustic emission tests on the materials tested in future work on the program. Work is continuing on the determination of residual stress. Efforts will be made to correlate the magnitude of stress as determined by acoustic emission with the results of destructive measurements of stress. An investigation of creep and fatigue phenomena is continuing, along with low noise level loading techniques.

24 REFERENCES 1. Agarwal, A.B.L.-;,..Frederick, J.R. and Felbeck, D.K., "Detection of Plastic Microstrain in Aluminum by Acoustic Emission", Metallurgical Transactions, Vol. -, p. 1070, April 1970 2. Sankar, NG., "Unload Emission Behavior of Materials and Its Relation to the Bauschinger Effect", Ph.D. Thesis, University of Michigan, Ann Arbor, Michigan, 1969.

REPORT DISTRIBUTION LIST 1. Mr. John F.. -Moore 10. Lt. Col. Louis Klinker, U.S. Army North American Rockwell Corp. Office Chief of Research & Development Los Angeles Division Materials Sciece & Technology Branch International Airport Highland Building Los Angeles, California 90009 3045 Columbia Pike Arlington, Virginia 22204 2. -Dr. J. R. Frederick University of Michigan 11. Mr.: Edward Criscuolo Dept. of Mechanical Engineering Naval Ordinance Laboratory 2046 East- Engineering Radiation Physics Division (code 223) Ann Arbor, Michigan 48105 White Oak Silver Spring, Maryland 20910 3. Mr. Allen T. Green Aerojet-General Corp. 12. Mr. Stephen D. Hart. Materials Integrity Group Naval Research Laboratory Dept. 0729, Bldg. 2931 - Mechanics Division Sacramento, California 95813 Washington, D.C. 20390 4. Professor R. H. Chambers 13. Dr. A. S. Tetelman, Head Dept. of Physics Materials Division Engineering Experiment Station College of Engineering University of Arizona Univ. of California Tucson, Arizona 85721 Los Angeles, Calif. 90024 5. Professor Stuart A. Hoenig 14. Dr. L. W. Orr Dept. of Electrical Engineering Dept. of Electrical Engineering Engineering Experiment Station Univ. of Michigan Univ. of Arizona Ann Arbor, Michigan 48105 Tucson, Arizona 85721 15. Professor Emmett N. Leith 6. Mr. Eugene Roffman Dept. of Electrical Engineering Frankford Arsenal Univ. of Michigan Fire Control Laboratories Ann Arbor, Michigan 48105 Philadelphia, Pa. 19137 16. Mr. F. S. Williams 7. Mr. Solomon Goldspiel Aero Materials Dept. U.S. Naval Applied Science Laboratory Naval Air Development Center Flushing and Washington Avenues Warminster, Pa. 18974 Brooklyn, N. Y. 11251 17. Mr. J. L. Kreuzer 8. Mr. Otto Gericke Optical Group Test and Evaluation Methods Perkin-Elmer Army Material Command Norwalk, Connecticut 06850 Army Materials & Mechanics Research Center Watertown, Massachusetts 02172 18. Professor R. C. McMasters Nondestructive Testing Research Lab 9. Mr. D. D. Skinner Dept. of Welding Engineering Fellow Engineer The Ohio State University Westinghouse Electric Corp. Columbus, Ohio 43210 Research Laboratories Pittsburgh, Pa. 15235 25

19. Dr. Volker Weiss 28. 3 copies to: Assoc. Chairman Director of Advanced Research Dept:. -of Chemical Engineering Projects Agency & Metallurgy — W- Washington, D.C. 20301 Syracuse University Syracuse,,New York 13210 29. The Institute for Defense Analysis 400 Army-Navy Drive 20. Professor Lawrence- Mann, Jr. Arlington, Virginia 22202 Dept. of Mechanical, Aerospace, & Industrial Engineering 30. The Nondestructive Testing Louisiana State Univ. Information Service Baton Rouge, Louisiana 70803 Watertown Arsenal Watertown, Mass. 02172 21. Howard A. Johnson The Boeing Company 31. Pravin G. Bhuta, Manager Space Division; Aerospace Group Applied Mechanics Laboratory Kent Facility Systems Group of TRW Inc. P.O. Box-3868 One Space Park Seattle-, Washington 98124 Redondo Beach, Calif. 90278 22. C. Gerald Gardner 32. T. Theodore Anderson Southwest Research Institute Argonne National Laboratory 8500 Culebra Road Reactor Engineering Division San Antonio, Texas 78206 D308 9700 S. Cass Avenue 23. Mr. Carlton H. Hastings Argonne, Ill. 60439 Chief, NDT Evaluation AVCO Corp., Space Systems Div. 33. Phil Hutton & D. C. Worlton Lowell Industrial Park Battelle-NorthwestLowell, Mass. 01851 P.O. Box 999 Richland, Washington 99352 24. Mr. David Driscoll - U.S. Army Materials & Mechanics 34. Robert Moss Research- Center Boeing Scientific Research Lab. Watertown, Mass. 02172 1-8000 MS 01-14 25. Dr. R. L. Gause Box 3981 Materials Division Seattle, Washington 98124 Marshall Space Flight Center Huntsville, Alabama 35800 35. Charles Musser The Boeing Company 26. 3 copies to: Saturn Booster Branch AFML/MAMN Org. 5-1752 Attn: Lt. James W. Bohlen MS LE-62 APAFB, Ohio 45433 Box 29100 New Orleans, La. 70129 27. 20 copies to: - Defense Documentation Center DDC 36. Harvey L. Balderston Cameron Station The Boeing Company Alexandria, Virginia 22314 Space Division, Kent Facility P.O. Box 3868 Seattle, Washington 98124 Attn: Orgn. 2-5022 Mail Stop 84-38 26

37. Thomas F. Drouillard 46. Lawrence Radiation Laboratory Dow Chemical Co. Attn: Technical Information Dept L-3 Rocky Flats Division P.O. Box 808 P.O. Box 888 Livermore, Calif. 94550 Golden, Colorado 80401 47. James Bryant 38. R. E. Ringsmuth Office Chief of Res. & Development Jet Propulsion Laboratory Attn: CROPES California Institute of 3045 Columbia Pike Technology Arlington, Va. 22204 4800 Oak Grove Drive Pasadena, Calif. 91103 48. H. E. Pearce McDonnell Douglas Corporation 39. Dwight Parry 1100 17th Street, N.W. Phillips Petroleum Washington, D.C. 20036 P.O. Box 2067 Idaho Falls, Idaho 83401 49. Jay M. Stevens Naval Air Systems Command 40. Brad Schofield Code AIR-52055 Teledyne Materials Research Washington, D.C. 20360 303 Bear Hill Road Waltham, Mass. 02154 50. Mr. Steve Ezangelities Dept. 263, Mail Station 8 41. Hal Dunegan McDonnell Douglas, Western Division University of California 3000 Ocean Park Lawrence Radiation Laboratory Santa Monica, Calif. 90406 P.O. Box 808 Livermore, Calif. 94550 51. Dr. Harold Berger Group Leader, Nondestructive Testing 42. C. D. Bailey Metallurgy Division Lockheed-Georgia Co. Argonne National Laboratory Materials Development Laboratory 9700 South Cass Avenue Dept. 72-14 Argonne, Ill. 60439 Marietta, Georgia 30060 52. Dr. Karl Graff 43. R. F. Saxe The Ohio State University North Carolina State Univ. Engineering Mechanics Department Nuclear Engineering Dept. 212 Boyd Laboratory P.O. Box 5636 155 W. Woodruff Avenue Raleigh, N. C. 27607 Columbus, Ohio 43212 44. John G. Sessler 53. Mr. J. C. Spanner Materials Science NDT Consultant, FFTF Project Syracuse University Research Corp. Battelle Memorial Institute Merrill Lane Pacific Northwest Laboratories Syracuse, N.Y. 13210 P.O. Box 999 Richland, Washington 99352 45. L. J. Chockie General Electric Company 54. Dr. George Martin 175 Curtner Avenue Branch Chief San Jose, Calif. 95125 Advanced Fabrication Development Dept. A253, Mail Station 5 McDonnell Douglas Astronautics Santa Monica, California 90506 27

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