Reference

NBS

Pubii - cations

A11104 742751

NBS1R 79-1742

Recent Improvements to the

ASTM-type Ultrasonic

Reference Block System

Daniel J. Chwirut

Center for Mechanical Engineering

and Process Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C. 20234

February 1979

Final Report

Issued April 1 979

Prepared for

^*QC

100

,U56

79-1742

Air Force Materials Laboratory

Army Materials and Mechanics Research Center, and

National Aeronautics and Space Administration

Imi of Standards MAY *2 J9?9

NBSIR 79-1742

RECENT IMPROVEMENTS TO THE

ASTM-TYPE ULTRASONIC

REFERENCE BLOCK SYSTEM

Daniel J. Chwirut

Center for Mechanical Engineering

and Process Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D.C. 20234

February 1 979

Final Report

Issued April 1 979

Prepared for Air Force Materials Laboratory

Army Materials and Mechanics Research Center, and

National Aeronautics and Space Administration

U S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary lor Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

2 s

Recent Improvements to the ASTM-type Ultrasonic Reference

Block System

by

Daniel J. Chwirut

ABSTRACT

Recent activities aimed toward improving the ASTM-type ultrasonic reference

block system are described. On the aluminum block system (ASTM E127 and NBS

TN 924), efforts were focused on better definition of the measurement equipment

(transducer and instrument) , the implementation of a Measurement Assurance

Program and Loaner Block Service, and modeling of the distance-amplitude

relationship. It is shown that a large increase in the precision of reference

block readings is easily achievable by implementing simple changes and controls

in the measurement procedure. On steel and titanium blocks (e.g. ASTM E-428)

efforts were directed toward quantifying the extent of reproducibility possible

among blocks fabricated by both conventional drilling and by diffusion bonding.

Reasonable reproducibility is achievable by both, with the diffusion-bonding

process offering both advantages and disadvantages.

Key words: calibration; diffusion bonding; Measurement Assurance Program;

reference blocks; standards; ultrasonics; variability.
- , . * • -V)
1.0 Introduction

The ASTM-type ultrasonic reference blocks [1,2] are cylinders of metal with

flat-bottomed holes drilled into one end of the cylinder. The flat bottom is a

reference reflector for the standardization of ultrasonic systems, either for

verifying system operating characteristics, for reference gain setting for a

particular inspection procedure, or for accept/reject decisions for materials or

structures. Typically these blocks are grouped into sets, either with different

lengths and the same size hole (distance-amplitude set), or with different hole

sizes and the same length (area-amplitude set). Even after numerous revisions in

the standards documents, unacceptable differences in nominally identical blocks

still exist, and inconsistencies or inadequacies in the equipment and procedure

specifications make reproducing data very difficult. Two previous reports [3,4]

have described initial NBS activities directed toward quantifying, understanding,

and minimizing the variability of measurements taken with the ASTM-type reference

block system. These studies identified metallurgical variables as an important

consideration in the manufacture of repeatable reference blocks, identified and

quantified some system parameters that must be controlled if repeatable measurements

are to be obtained, reported results on pilot experiments for new manufacture

concepts, and formed the technical rationale for the establishment of a calibration

and loaner service for aluminum blocks [5],

This report describes further work in this area intended to extend these

concepts to steel and titanium blocks and to better define the system variables and

their effects on measurements. The goal of this activity, ultimately, is a

measurement protocol by which repeatable measurements can be made on different

systems by different operators. An ideal result would also include the mechanism to

transfer measurements between materials with different acoustic properties. This

would allow a single set of physical standards to be used for the inspection of a

variety of materials.
2.0

Technical Progress

2 . 1 Improvements to the Aluminum Reference Block System

Most of the early effort was expended on aluminum reference blocks, since

the system for these blocks probably has a better technical foundation in terms

of supportive data. It was thought that improvements made in the aluminum system

could be applied directly to steel and titanium, or negatively speaking, if you

can’t make repeatable measurements in aluminum, you definitely can’t in steel or

titanium.

2.1.1 Transducer Characterization - The weak link in most ultrasonic measurement

systems is the transducer. Transducers are not reproducible, are unstable, are

damaged easily, and wear out. Unfortunately, their characteristics significantly

affect quantitative results obtained in a test. The ASTM working section on

aluminum reference blocks, E7.06.02, is actively pursuing an improved

specification for transducers used to check reference blocks.

Posakony [6] has been studying the effects of transducer design and

excitation waveform on the output of quartz transducers. At NBS, we completed a

study* intended to quantify the extent of the difference in reference block

response when measured with different but very similar transducers, and to

identify what characteristics of the transducers contributed to these differences

[7], A critical parameter, seldom specified explicitly or exactly, was the shape

of the far-field on-axis pressure amplitude. Among six nominally identical,

*partially supported by this project

2
5-MHz, 0.375- in (9.52-mm) quartz transducers, readings from the same reference

blocks, taken in accordance with the procedures and equipment specified in

ASTI! E-127-75*, differed by more than 25 percent (table 1 and fig. 1), while

axial pressure amplitude varied by as much or more (table 2). Further, the two

were highly correlated (fig. 2). Other commonly-measured characteristics were

fairly uniform among the six transducers (table 3) . This suggested that

far-field axial pressure amplitude is an important parameter that must be

controlled, or corrected for, if reproducible results are to be obtained with

different transducers.

To test this hypothesis, a new experiment was run, whereby, for each

transducer, the system gain was reset at the equivalent water distance for each

reference block being read. This operationally forces the axial profiles of the

transducers to be the same on a point-by-point basis. For this experiment, the

differences among readings of the same reference block, taken using the six

transducers, were less than about 5 percent (table A). These experiments are

described in more detail in [7],

Subsequent to the publication of [7], these experiments were repeated with

two 5-MHz, 0.375-in (9.52-mm) ceramic transducers. These were significantly more

broadband than the six quartz units, and some other characteristics also varied

(table 3). The second experiment, forcing the axial profiles to be the same as

for the quartz, transducers, failed to bring the reference block readings in line

with the results obtained with the quartz transducers (table A). This suggests

*the equipment used in the experiments reported herein is described in more

detail in Appendix A.

3
that axial profile is a necessary though not sufficient transducer parameter, and

possibly points to bandwidth as a parameter requiring additional study.

The goal of these studies is a comprehensive performance specification for

transducers that will allow repeatable measurements to be made, at different

times and places, on either reference blocks or real parts. At present, quartz

transducers are specified in ASTM E 127 and our calibration service because they

were thought to be more stable and uniform. The data shown in figure 1 show that

the present specification is not sufficient. We are having fabricated two

ceramic transducers with the same characteristics as our two lab standard quartz

transducers (LS-3 and LS-4 in table 3), including the same axial pressure

amplitude. If, as anticipated, these new transducers yield the same reference

block readings as the two quartz transducers, we may indeed have a viable

performance specification for transducers used for checking reference blocks.

Since most ultrasonic inspection systems in use today incorporate ceramic

transducers and solid-state broadband pulser-receivers (which lack sufficient

power output to drive quartz transducers), this transfer to ceramic transducers

should be

2.1.2 Other System Effects - An earlier report [4] documented some experiments

performed to determine the effects of certain system operating adjustments on

reference block response. These adjustments included cable type and length,

pulse length, and fine gain control (called "cal" pot in [4]). The conclusion

drawn from these experiments was that reference block response relative to a ball

standard is much more sensitive to changes in system parameters than is reference

f

significant improvement to the system.

4
block response relative to a reference block standard. This conclusion was a

contributing factor in our decision to use a reference block as the primary

standard in our calibration service, rather than a steel ball as in ASTM E 127.

This minimizes the effect of small or unaccounted for changes in the system.

In defining a system for taking reference block measurements, it is fairly

easy to standardize on cable and fine gain. However, variable pulse length is a

desirable feature in order to achieve good front-surface resolution in short

metal-travel blocks and good sensitivity in long blocks.

In order to more accurately specify the procedures for our calibration and

loaner services [5,8], a new series of experiments to determine the effects of

changing the pulse length was performed. The gain was adjusted so that a certain

response was obtained from a steel ball, then a 5-0050 reference block was read

per the ASTM E 127 procedure, at pulse length settings of minimum, approximately

one-half, and maximum. The procedure was repeated with three transducers. The

results are shown in figure 3. The reference block readings, relative to the

ball standard, differed by as much as 13 percent for different pulse length

settings, with significantly more difference noted from one-half to maximum than

from minimum to one-half. Since changing the length of the output pulse changes

the frequency spectrum of the transducer output, these data reinforce the concept

that output bandwidth is an important parameter as noted in section 2.1.1.

Qualitatively, for constant pulse length, the reference blocks read higher with a

more broadband transducer (see table 4). Figure 3 shows that reference block

readings are increased, generally, by broadbanding the pulser (decreasing pulse

length) for a given transducer. In actuality, the bandwidth of radiated field

reflects the characteristics of the electrical pulse and the transducer, and the

system response must be controlled if reproducible results are to be obtained.

5
2.1.3 Measurement Assurance Program and Loaner Blocks - The key elements of a

Measurement Assurance Program are a well defined measurement algorithm that will

allow reproducible measurements to be made in different laboratories, a mechanism

for transferring standards or baselines between laboratories, and a data

feedback/analysis scheme to assess measurement quality. To test the

appropriateness of our calibration procedure for the MAP algorithm, we measured

the ultrasonic responses of a distance amplitude set of blocks with five sets of

equipment, i.e. two CRT's and four pulser/receivers in various combinations.

Since we had already identified transducer variability as a major source of

irreproducibility in reference block readings, we used transducer LS-4 for all

readings in this series of tests in order to assess only instrument variability

effects. The pulse lengths of all systems were adjusted to achieve the

electrical output characteristics of our calibration system [5] as closely as

possible. The results of these tests are shown in table 5. The standard

deviation of the readings taken with the different equipments was generally less

than 1 percent of upper linear limit*. For a standards system in which 40

percent difference among "standards" is not uncommon, this 1 percent is extremely

good reproducibility.

To provide the transfer mechanism, sets of loaner blocks were fabricated. A

special batch of aluminum alloy 7075-T651 extruded rod was purchased for the

*Ultrasonic flaw detector amplitude readings are relative amplitude readings

taken from a cathode ray tube (CRT) display. In practice, the receiver-amplifierdisplay circuits are usually nonlinear above a certain vertical deflection. This

deflection is determined and defined as the "upper linear limit." Vertical

amplitude values can then be expressed in "percent of upper linear limit."

6
fabrication of these blocks. This material was examined metallurgically for

uniformity of texture and grain size among the different bars and was found to be

suitable for this work [9].

Eighteen reference blocks were fabricated in the NBS machine shop from this

material. Of these eighteen, twelve were extremely close to the average of all

data taken to date on the NBS system, and were anodized, plugged, engraved j and

calibrated as NBS Loaner Blocks. The data for one set of these, designated NBS

Loaner Set 1, compared to the average values and the empirical master curve

(described later in sec. 2.1.4) are shown in figure 4.

Loaner Set 1 was used to test the effectiveness of the transfer mechanism

and further quantify system effects, by a complete interlaboratory

intercomparison on three distance- amplitude sets of reference blocks. These sets

were shipped to NBS and calibrated, by us, on our system, directly against the

master standard. They were also checked against ASTM E 127-75 (steel ball

standard). They were then returned to the owner, along with Loaner Set 1 and our

transducer LS-3.

The owner then re checked his blocks on his instrument, with our transducer,

following the NBS calibration procedure [5], with the system gain set such that

the 5-0050 block in the loaner set read its calibrated value of 80.5 percent of

upper linear limit. Thus the loaner block functions as a secondary, or transfer,

standard in the calibration pyramid in much the same way that working-standard

masses or gage blocks are used in a standards lab. The data taken using

transducer LS-3 are shown in table 6. The average difference between the NBS

reading and the owner’s reading for all thirty-six blocks is only 1.3 percent of

the upper linear limit. The data taken using the ASTM E 127-75 procedure are

7
shown in table 7. Here the average difference in readings is 5.8 percent of the

upper linear limit. This intercomparison is an important demonstration that

reasonably precise measurements can be transferred to the field if the problems

of transducer variability can be eliminated. It also points to a weakness in the

ASTM system, in which the use of ball standards introduces a sensitivity to

subtle differences in system parameters that results in larger differences in

reference block readings.

2.1.4 Distance-Amplitude Modeling - Originally a calibration report for a set of

blocks was accompanied only by the average of all data taken to date for

comparison purposes [5], This was because no suitably accurate theoretical or

empirical model for the ultrasonic response of distance- amplitude sets of

reference blocks existed. Such a model would serve at least three useful

functions: 1) it would serve as a basis for comparison for reference block

calibrations, 2) it could serve as the transform algorithm between materials and

possibly lead to the use of single-material reference blocks, and 3) it could be

used to assess the accuracy of or improve the use of the automatic

distance- amplitude-compensation (DAC) systems which are used with many ultrasonic

flaw detectors.

We have accumulated a data base of the ultrasonic response from over 200

aluminum reference blocks read with one system. The least-squares best fits to

this data base were calculated for seven models, some suggested by theory, some

by the electronics used in DAC systems, some by the data [8]. The nonlinear

least squares fitting routines recently developed in DATAPLOT [10] made this a

8
relatively simple computational task. The data base and selected fits are shown

in figure 5.

The best fit, among the models tested, was provided by the generalized

exponential over quadratic, y

= exp (-ax) / (a+bx) 2

. This is theoretically founded,

in that the exponential accounts for material attenuation, and the inverse

quadratic is the predicted relation for reflection from a disc in the far field

(the DGS diagram [11]). For the aluminum reference block data, the a coefficient

was computed to be essentially zero, as one might expect because of the

relatively low attenuation in aluminum at 5 MHz. The a and b coefficients should

be related to transducer characteristics, transducer-to-top surface water

distance, ratio of sound speeds in aluminum and water, reflection and

transmission coefficients, etc. In its present form, this model is useful for

comparison purposes in reference blocks and may be useful in sorting out some of

the problems in DAC systems. Further work will include attempts to relate the

coefficients to physical quantities, system parameters, and material properties.

This could lead to transform algorithms for different materials, including the

use of single-material reference blocks.

2.1.5 Intercomparison with AQD Labs - In the United Kingdom, the Aeronautical

Quality-Assurance Directorate (AQD) Laboratories maintains a master set of

aluminum reference blocks and provides a service for calibrating user blocks

against the master set [12]. We obtained from AQD Labs a set of their "Working

Standards" and calibrated them on our system. The correction factors for these

9
working standards, as assigned by AQD by comparison to their master set, ranged

from -3.2 to +2.6 dB at 5 MHz. However, even when corrected by these amounts,

the blocks read systematically about 2 dB low when compared to our master curve

and data base (fig. 6). No reason for this large, systematic difference is

immediately obvious.

2.2 Development of Standards for Other Materials

2.2.1 Quartz - If the appropriate transfer algorithms can be developed, a single

material could then be used to standardize for a test of any material.

Microstructural uniformity, low attenuation, and optical transparency make quartz

or crown glass possible candidates for these standards. We have fabricated

flat-bottomed-hole blocks in quartz by conventional methods in one piece, by

wringing together two pieces, one with a through-hole, and by thermally fusing

together two pieces. The wringing technique appears to be the more promising

technique, as corner- radius and crazing cracks are difficult to eliminate in

machining quartz and the exact thermo-mechanical cycle for fusion is difficult to

achieve. One disadvantage of all three techniques is the relatively high

fabrication cost compared to metal blocks. An interesting spin-off advantage of

transparent blocks is that they provide a medium for visualizing the sound-beam

interaction with the flat-bottomed hole by techniques such as photoelasticity

[13].

10
2.2.2 Steel and Titanium - Our plan is to establish calibration services and

loaner services for steel and titanium reference blocks similar to those

established for aluminum. As a first step, special order uniform lots of bar

stock were procured. The steel was 4340 alloy, aircraft quality, vacuum

remelted, purchased from a reference block manufacturer, having already passed

his quality control checks. The titanium was 6 A1-4V alloy, special purity and

uniformity, purchased from a titanium producer. Approximately 25 feet of steel

and 50 feet of titanium were purchased.

A primary objective of this study was to determine the relative merits of

the diffusion bonding [14, 15, 16] process versus conventional drilling for

making flat-bottomed-hole reference blocks in titanium and steel. The advantages

of diffusion bonding include: 1) the elimination of the need to drill relatively

deep (at least 0.5 in, 1.2 cm) flat-bottomed holes with tight tolerances on

diameter, flatness, corner radius, and parallelism of the bottom to the entry

surface; 2) when fabricated in the three-piece geometry as shown in figure 7,

each block is really two blocks. The metal distances can be selected and paired

so that all blocks are the same length, thus obviating the need for special

holders or continual adjustment to maintain constant water path in immersion

testing. 3) reference reflectors with other geometries, such as spheres,

hemispheres, ellipsoids, etc. can be easily fabricated. The disadvantages are

mainly cost of fabrication and metallurgy. The bond must be formed in an inert

atmosphere or a vacuum, and a high- temperature furnace in which axial pressure

can be applied is required. When the induction heating coil technique is used, a

very non-uniform heat treatment is applied to the sample. Post-fabrication

11
thermal aging is required. Since the blocks are made individually, each could

experience a slightly different thermal cycle, thus introducing microstructural

variations affecting sound-beam propagation.

We were able to borrow, at different times, two area-amplitude sets of

diffusion-bonded steel blocks. The first set was evaluated only for a 3- in

(76-mm) metal distance. The second set was evaluated for both a 3- in (76-mm) and

a 0.75- in (19-mm) metal distance. Unfortunately, these two sets were evaluated

at different times, and the same ultrasonic equipment was not available to us at

both times. Therefore no direct absolute comparison between the two sets, on an

amplitude basis, could be drawn. However, other conclusions about the

applicability of diffusion bonding could be drawn.

The data for the three "sets" Ttwo at 3- in (76-mm) and one at 0.75-in

(19-mm) metal distance] are shown in table 8 for evaluation at 5 and 10 MHz. The

data for the two 3-in (76-mm) sets are shown in figure 8. The linearity of these

sets is, in general, quite good. Down to the two smallest blocks, where the 1 or

2-unit reading error is greater than 1 dB, the blocks were all within about

+ 1 dB of the least-squares straight line. The residual standard deviations,

measuring the "average" dispersion of the data from the fitted curve, were

7.7 percent and 12.5 percent for the two 3-in (76-mm) sets, both within about

1 dB. Current state-of-the-art (e.g. ASTM E 127 or E 428) is about + 2 dB,

although better results can be achieved with judicious material prescreening or

selection among replicates to match blocks into a good set. No prescreening or

matching was done with the diffusion-bonded blocks. Additionally, the relative

12
responses of a given hole, in the second set, are generally close when inspected

from both ends (see table 8), with the notable exception being the No. 6 hole.

This would indicate good control over the fabrication process, with little

distortion of the hole during bonding. The owner of these blocks intends

eventually to section them for optical inspection. We hope this will show the

cause for the variation in the No. 6 block.

To evaluate more precisely the reproducibility among replicate blocks we had

some blocks fabricated by the two techniques. For conventional drilling, we

contracted to a reference block manufacturer to supply, from the material

described previously, five replicates each of 5-0050 and 5-0300 reference blocks

of steel and titanium (total 20 blocks). The intent of the study was not

revealed to the fabricator beforehand, and no material prescreening or over

production and selection was permitted. The results of the evaluation of these

blocks, at 5 MHz, are shown in table 9. All blocks were within about + 10% of

the average, and all but 2 were within + 5%. This reinforces the concept, stated

earlier for aluminum [4], that blocks reproducible within + 5% can be produced by

competent, experienced machinists, from a single lot of uniform, metallurgically

clean material.

We also fabricated, in the NBS Instrument Shops, two diffusion-bonded

blocks, from each material, with the geometry shown in figure 7. Since the metal

distance, to the hole, is the same on both ends, this gave us four replicates for

each material. The details of the diffusion bonding process, and the techniques

used to evaluate the quality of the bonds, are given in Appendix B.

13
One immediately noticable difference in the diffusion-bonded blocks,

compared to the conventional blocks, is the increased noise level in the

heat-affected zone in titanium. This was not so obvious in steel. Figure 9

shows A-scan presentations of the signals from diffusion-bonded and conventional

blocks of titanium showing an increase, by a factor of about 2, in noise in the

heat-affected zone. This was not removed by a thermal aging cycle of 900 °F

(482 °C) for 8 hours and air cool. This obvious metallurgical variation could

well be responsible for the variation in ultrasonic response of these blocks.

Also, the two steel blocks were slightly skewed (about 1.8 degrees) after

fabrication (fig. 10). However, this did not appear to seriously affect the

usefulness of the blocks for our purposes.

The ultrasonic response values, at 5 MHz, of the diffusion bonded blocks are

shown in table 10 (A) . All readings were taken with the transducer angulated to

maximize the top-surface reflection. It is interesting that the average

responses of the blocks are quite close to the average responses of the

corresponding blocks made by conventional drilling (table 9). However, the

variation among the four readings is somewhat higher for steel and significantly

higher for titanium. Only titanium specimen 1 (A and B) has been thermally aged

subsequent to the bonding process. It should be noted that these were first

efforts, and with experience and refinements in the fabrication procedures the

quality of the end product should improve. As a pilot quantitative assessment of

the inherent variability of blocks made by diffusion bonding, these statistics

could be considered upper bounds.

14
To determine whether the variation in diffusion-bonded block readings was

possibly caused by non-parallelism of the front surface and the bonded surface,

i.e. the flat-bottom hole, the transducer was angulated a few degrees in two

planes and repositioned laterally to obtain maximum flat-bottom hole response.

This is the technique prescribed in [1] for determining the parallelism of hole

bottom-to- top surface, with a 10 percent increase in flat-bottom hole response,

relative to the response with the beam normal to the top surface, being

acceptable. The changes in the response values for the steel blocks were not

significant (table 10 B) , possibly indicating that the non-axial deformation

resulting in the skewness occurred mainly in the 0.25-in (6.4-mm) wafer, thus

leaving the top surface and FBH-surface essentially parallel. Although no

alignment problem was suspected in the titanium blocks, the maximized

flat-bottom-hole responses were significantly higher than the normal response

values. However, similar experiments on conventional blocks of aluminum, steel,

and titanium showed this to be typical of titanium, not typical of steel and

aluminum. Conversations with a reference block manufacturer [17] revealed that,

in his experience, this is not atypical of titanium and some steels, and is not

necessarily related to parallelism of the top surface and flat-bottom hole. It

could be that the attenuation is so nonuniform that changing the ultrasonic path

only slightly by reangulating and repositioning the transducer decreases the

attenuation enough to offset the decrease in response due to misalignment.

Future plans include sectioning the diffusion-bonded blocks to evaluate the

quality of bond, geometry of the hole, attenuation characteristics of the parent

15
material, etc. For diffusion bonding to become a viable alternative for

reference block manufacture, the question of how to evaluate nondestructively the

parallelism of the top surface and FBH surface must be answered. Procedures for

carefully controlling the fabrication parameters (temperature, pressure, time,

alignment) must be developed. Appropriate thermal treatment cycles must be

documented. Others working in this area may have already solved a few of these,

but these fabrication and evaluation procedures must be documented and reevaluated before they can reach the standards stage.

3.0 Discussion and Conclusions

3.1 Aluminum Blocks

3.1.1 Transducer Characterization - The specification in E 127-75 is not

sufficient to allow reproducible results to be obtained with different

transducers. The bandwidth must be specified, and the far field axial profile

must be specified numerically, not just by "similar to," out to 20-25 inches

(51-64 cm) of water. We hope the data with our new ceramic transducers, when

available, will show that transducer material is not important, as long as it

meets the performance specifications.

3.1.2 System Effects - Variable pulse length can introduce errors as large as

+ 0.5 dE. A definite pulse shape (center frequency and bandwidth) must be

specified. If the equipment is properly tuned to specification, results

reproducible within about 1 percent of upper linear limit are achievable, with a

16
given transducer, on different instruments. Steel ball targets, as standards,

introduce a sensitivity to subtle changes in equipment characteristics. Flat

disc reflectors, either in metals or water, yield more consistent results.

3.1.3 MAP - Aluminum loaner blocks are available as transfer standards for

in-house calibrations. For a given transducer, results are reproducible within

1.3 percent of upper linear limit if the NBS TN 924 procedures are followed.

This precision is more than four times better than that obtainable with E 127-75.

3.1.4 Distance-Amplitude Model - The best model, among seven tested, was the

GXD ( — otx) generalized exponential over quadratic y

= —^

. This is, theoretically, the

( a+bx) 2 response of a disc reflector in the far field, corrected for attenuation. This

model and our large data base will serve as a basis for comparison for future

calibrations

3.1.5 AQD Intercomparison - The measurement system used in the United Kingdom is

quite different from ours, using specially designed, rather than commercial,

equipment. This appears to yield no improvement in the reproducibility of

results. The AQD standards are systematically about 2 dB low in response when

compared to typical blocks in this country.

3.2 Other Materials

3.2.1 Quartz - Good reference blocks can be made from optical quartz by wringing

together two pieces, one with no hole, one with a through-hole. The material and

17
machining is expensive compared to metal blocks. Drilling flat-bottomed holes is

not easy in quartz due to crazing. This type of block is useful for visualizing

by photoelasticity, the sound beam interactions with flat-bottomed holes.

3,2.2 Steel and Titanium - Excellent results have been obtained in fabricating

area-amplitude sets of steel blocks by diffusion bonding. With no material

prescreening or block matching, the sets are linear within + 1 dB.

From uniform lots of steel and titanium, replicate blocks fabricated by

conventional drilling are generally reproducible within about + 5 percent when

made by an experienced machinist.

Diffusion-bonded blocks have been made with a variability of about + 10

percent for steel and_+20 percent for titanium. Metallurgical differences caused

by uneven thermal treatment and means for the nondestructive determination of

hole condition appear to be problems in titanium blocks. There does not appear

to be a lower variability of response in diffusion-bonded blocks as compared to

conventional blocks, but the other advantages may make this process a practical

alternative. Also, improvements in manufacturing processes may further improve

the quality of blocks made by this technique.

4.0 Recommendations and Future Directions

Many of the tasks described in this report are continuing. Based on the

results reported here and in previous reports, the following areas appear to be

potentially fruitful:

18
1. The new ceramic transducers built to specification to match the quartz

transducers now used will be evaluated. The specification will be revised

as necessary so that reproducible transducers can be fabricated.

2. Detailed procedures and equipment for calibration and loaner services for

steel and titanium reference blocks will be documented.

3. Further data gathering and modeling will be performed to correlate the

modeling parameters to transducer characteristics and material properties.

This could lead to material- independent reference blocks.

4. Further refinements in the diffusion bonding process will be attempted.

5.0 Acknowledgements

This activity was partially funded by the Air Force Materials Laboratory,

Army Materials and Mechanics Research Center, and NASA Lewis Research Center.

The technical representatives for these organizations were Lee R. Gulley, Jr.,

George A. Darcy, and Robert L. Davies, respectively. The work was administered

through the Air Force Materials Laboratory with Lee R. Gulley, Jr. as project

monitor.

It is a priviledge to acknowledge the assistance, advice, and constructive

criticisms of the following NBS staff:

19
Gary D. Boswell - general laboratory assistance, data reduction, and artwork.

Donald G. Eitzen - technical consultation.

Robert G. Elmer - distance- amplitude modeling.

James J. Filliben - statistics and curve fitting.

Deborah A. Neal - laboratory assistance and manuscript preparation.

Ralph Orwick and Randy Fink - fabrication of diffusion-bonded reference blocks.

Additionally, much valuable advice, suggestions, data, and equipment loans

were offered by people outside NBS. These include the aluminum producers

(especially Alcoa and Reynolds), Armco Inc. (Don L. Conn and Brian Frock), and

Search Unit Systems, Inc. (Jerry T. McElroy)

20
6.0 References

[1] Anon., Standard Recommended Practice for Fabricating and Checking Aluminum

Alloy Ultrasonic Standard Reference Blocks, ASTM Designation E 127-75,

1977 Annual Book of ASTM Standards , Part 11 (Am. Soc. Test. Mat.,

Philadelphia, 1977) p. 251.

[2] Anon., Standard Recommended Practice for Fabrication and Control of Steel

Reference Blocks Used in Ultrasonic Inspection, ASTM Designation E 428-71,

Ibid, P. 517.

[3] Eitzen, D. G., et el., Improved Ultrasonic Standard Reference Blocks,

Progress Report No. 1, Report No. NBSIR 75-685, National Bureau of

Standards, Washington, D.C. April 1975.

[4] Sushinsky, G. F. , et al. , Improved Ultrasonic Standard Reference Blocks,

Report No. AFML-TR-77-40 , for Air Force Materials Laboratory, by National

Bureau of Standards, Washington, D.C., April 1977.

[5] Chwirut, D. J. , et al. , Procedures for the Calibration of ASTM E 127- Type

Ultrasonic Reference Blocks, Report No. NBS TN 924, National Bureau of

Standards, Washington, D.C., September 1976.

[6] Posakony, G. J., Ultrasonic Search Unit Performance Differences, presented

at First International Symposium on Ultrasonic Materials Characterization,

Gaithersburg, Md. , June 1978.

21
[7] Chwirut, D. J. and Boswell, G. D. , The Evaluation of Search Units Used for

Ultrasonic Reference Block Calibrations, Report No. NBSIR 78-1454, National

Bureau of Standards, Washington, D.C., February 1978.

[8] Chwirut, D. J. and Eitzen, D. G., Improving the Reliability of Ultrasonic

Measurements: Recent NBS Progress, presented at 1978 Spring Conference of

American Society for Nondestructive Testing (ASNT) , New Orleans, LA, April

1978.

[9] Bechtoldt, C. J. , Examination of Aluminum Reference Block Specimen, NBS

internal letter report, May 1977.

[10] Filliben, J.J., DATAPLOT - An Interactive System for Graphics, Fortran

Function Evaluation and Linear/Non-Linear Fitting, in Procedings of the

Statistical Computing Section of the American Statistical Association, 1978.

[11] Krautkramer, J. and H. , Ultrasonic Testing of Materials , Translation of the

Second Revised German Edition (Springer-Verlag, New York 1969) p. 77.

[12] Millman, T., An Improved Facility for the Calibration of Aluminum Alloy

Ultrasonic Reference Blocks, Report No. AQD/NDT 1369, AQD Labs, Harefield,

Uxbridge, Middlesex, U.K.

[13] Sachse, W. , et al. Visualization of Transducer - Produced Sound Fields in

Solids, 1978 Ultrasonics Symposium Proceedings, IEEE Cat. // 78 CH 1344-ISU.

22
[14] Paton, N.E., Ultrasonic Samples Using Diffusion Bonding Techniques in

Proceedings of the ARPA/AFML Review of Quantitative NDE, Report No.

AFML-TR-75-212 , for Air Force Materials Laboratory by Rockwell International

Science Center, Thousand Oaks, CA, January 1976.

[15] Conn, D. L., New and Improved ASTM Type Ultrasonic Standard Reference

Blocks, presented at First International Symposium on Ultrasonic Materials

Characterization, Gaithersburg, Md. , June 1978.

[16] Kettering, D.D. , Ultrasonic Nondestructive Testing (NDT) Calibration

Standards, Report No. ADR 14-04-75.2, Grumman Aerospace Corporation,

Bethpage, New York, July 1975.

[17] Steffens, Clyde, Trienco, Inc., private communication, January 1979.

[18] Chwirut, D. J. , Technical Note in preparation.

23
Table 1 - Ultrasonic Reference Block Readings

Taken with Eight Nominally Identical Search Units

Spread /Average

LS-1 LS-2 LS-3 LS-4 LS-5 LS-6 Percent a j

1/8-in ball 80 80 80 80 80 80 80 80

(3.2-mm ball)

3-0050 93.0 82.2 97.7

(a) 92.3 91.2(a) 94.8 (a) + 6.3

-10.5 65 66

3-0100 49.7 50.0 58.5 54.5 51.7 61.3

+12.9

- 8.4 37 36.5

3-0225 20.3 20.2 24.5 23.2 21.7 25.5

+13.0

-10.5 14 ] 4

5/16-in ball 80 80 80 80 80 80 80 80

(7.9-mm ball)

5-0050 78.7 74.7 90.8 85.5 78.8 84.5

(a)

+10.5

- 9.1 63 64.5

5-0100 47.5 48.8 61.3 56.8 50.5 56.8

+14.3

-11.4 37 39.5

5-0225 18.2 18.2 24.8 22.3 19.8 22.7

+18.1

-13.3 14 13.5

11/16-in ball 80 80 80 80 80 80 80 80

(17.5-mm ball)

8-0050 78.8 77.7 91.0 86.5 80.8 86.0 + 9.0

- 6.9 75.5 72

8-0100 50.3 50.8 63.5 59.0 53.0 59.7

+13.3

-10.3 47 44.5

8-0225 20.5 20.2 26.8 24.7 21.2 24.8

+16.3

-12.3 19 18

LS-1 through LS-6 are quartz; Alpha and Gamma are ceramic

All values are in percent of upper linear limit

All values are averages of three independent readings

(a) Not 100% resolved from front surface echo

24
Table 2 - Relative Axial Pressure Amplitude

Values for Selected Water Distances

Water Spread/Average

Distance LS-1 LS-2 L'S-3 LS-4 LS-5 LS-6 Percent a Y

in cm

3.5 8.9 100 100 100 100 100 100 100 100

5.62 14.3 59.8 59.5 71.7 66.3 60.3 66.7

+11.9

- 7.1 57 43

7.75 19.7 32.8 32.5 41.3 37.7 33.5 38.0

+14 .

- 9.6 29 21

13.1 33.3 8.8 9.0 12.2 10.5 8.7 10.7

+22.2

-12.8 6.5 4

LS-1 through LS-6 are quartz; Alpha and Gamma are ceramics.

All values are in percent of upper linear limit

All values are average of three independent readings.

25
o

oI—

o

u

cOp

O'

u

COp

O'

M

COP

O'

LO

CMooi—

O

CTN u

coP

O'

o

o u

COp

O' 0)00u

co qj

4-1 4-1 co

i—i i—

«h a

co XI 4-1 M

COp

O'

i eo

• M

CN 4-4

CO C C

*H 00

I -H CM CO

cO X4J X

•H

x>

u

c

QJp

cr* 0)M

a

x:

- p M 4J

CD CD > M

(0 * O M

(1) 0) M CO

4J 4J A M P c O X X) QJ CL cO (0 *H •H CO 4J X3 0J 5 £ a) CO X X p X X r-H 2 QJ CO cr C P a C O QJ

cO co 00 >% rH P u M

X> X) C O CO H « P-i 4J

PQ PQ a . CO X) X S o

ST

/**N /*«N vO vD CO Z CO XJ U

1 1 o ^ CJ

26

at

maximum

power

output,

continuous

wave

excitation
Table 4-

Reference

Block

Readings

with

Sensitivity

Set

At

Equivalent

Water

Distance

for

Each

Block o

>~

O

O o o rH O' CO

m

cr>

LO

m

m

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vO o> NT 03 co co

0)COd

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m

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CO PL, + 1 + 1 + 1 4-4 0) d d o 04 ex •H 'a

to E d d 04 d CX

<0 04 o T4d

<43 CN CO r^ CU •H 1 • • • d

CO o m

O NOO

d 4-1 04 hJ vO cr> <r CO r^ •H 04 d E d B •H 44 B i—

4-4

cfl O 1-1 4-4 in cn m 00 d O 1 • • • o 04 CO O N3 o NT o r- C d 04 •J vO O' r- co d •H 00

rH

d

dd

x

d 0) CX G) >

rH CX

d

d- CO in < cx 1 • • d 04 CO O vO o 00 o 00 • 

d X vO O' Nf r-» CO r^ N <4-1 d

4-1 o d

w

CO 4-4 04 d d d

cr 0) 1—

co

m coO

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CO

O vO o <£> o n- s-t 0) rJ vT> O' NT co r^* d CX 4<:0

vO

d 0 1 •H i—

CO 40

1-4 04 CN 00 m d 0! 1 • • 44 d O

COO in

O vO o 00

d

X vO O' NT CO r-»

d co 0) o 04 d d d 04 CO 44 i—

4-1 bO

4-4

d 04

d > d • 1-1 rH vO CO m 1 1 T3 | • • • 1 rH rH d

CO

O

O NT o v£> CO rH i—

04 4 vO O' NT f'- CO .-4 <d < d ,—

d d B d B •H £ H a •H O

CN 0

CN CO

m r-. rH

m

NO • r-^ • • • • • O' CO co m rH rH rH CO

4-1 4-4 4J 4-1

HH

d

d co

d CO

d 1—

rH rii

T 1 rH 44 rH 1—

iH rH

O rH rH

a iH rH CJ

d

dO cO

d 0 CO 0

43 40 rH rQ 40 rH rO 1—

43 40 43

d 6 C

B c £

*H E O

B

O •H £ LO 1 1 m | O | 1 CN

\£> CTi 0 vD O' 1—

vD o> CN rH 0 rH • O rH • O

r>» 1 r^- 1 —

r^ 1 m V-/ m m 44 m m v-/ m

27
Table 5 - Ultrasonic Response of Elock Set 122 Measured

with Five Different Instrument Combinations

CRT 1 1 1 2 1 P/R A C B B D Standard

Block Response Response Response Response Response Average Deviation

5-0050 80.0 80.0 80.0 80.0 80.0 80.0 —

-0062 79.0 80.0 79.8 78.4 77.8 79.0 0.8

-0075 63.8 65.2 64.2 63.6 63.0 64.0 0.7

-0088 57.2 59.5 58.2 56.8 57.0 57.7 1.0

-0100 53.2 55.0 54,5 54.4 53.0 54.0 0.8

-0125 42.5 43.8 43.8 42.0 42.5 42.9 0.7

-0175 26.8 27.0 27.2 26.4 26.5 26.8 0.3

-0225 20.4 21.0 21.2 21.2 20.5 20.9 0.3

-0175 71.6 74.5 74.5 — 72.0 73.2 1.4

-0225 56.0 59.5 58.0 — 57.0 57.6 1.3

-0275 43.9 46,8 46.0 — 44.8 45.4 1.1

-0325 33.4 36.0 35.5 — 34.2 34.8 1.0

-0375 28.1 30.0 29.8 — 28.5 29.

0.8

-0425 22.9 24.8 24.5 — 23.8 24.0 0.7

-0475 19.0 20.0 20.0 — 19.5 19.6 0.4

-0525 16.3 16.5 17.2 — 16.8 16.7 0.3

-0575 15.9 16.5 16.8 — 16.0 16.3 0.4

All Response Values are in Percent of Upper Linear Limit

All Data taken with Transducer I.S-4

28
Table 6 - Summary of Intercomparison Data on Set DA 55 Taken

with Transducer LS-3 and NBS TN 924 Procedure

Metal Distance Lab 1

3/64 Hole

Lab 2 Diff. Lab 1

5/64 Hole

Lab 2 Diff. Lab 1

8/64 Hole

Lab 2 Diff.

-0050 70.8 67.6 3.2 80.7 80.0 0.7 66.7 66.7 0.0

-0075 54.7 54.2 0.5 61.3 63.1 1.8 59.2 60.0 0.8

-0100 48.0 48.0 0.0 47.5 ON 00

<r 1.4 40.8 42.2 1.4

-0150 39.8 40.9 1.1 29.0 31.1 2.1 30.7 32.0 1.3

-0200 29.8 31.1 1.3 24.0 24.4 0.4 25.7 26.7 1.0

-0250 23.7 23.1 0.6 17.7 17.8 0.1 16.3 16.9 0.6

-0200 79.0 82.2 3.2 65.5 66.7 1.2 69.3 73.3 4.0

-0250 63.5 66.7 3.2 49.8 49.8 0.0 45.2 44.4 0.8

-0300 47.2 53.3 6.1 43.3 44.4 1.1 35.6 35.6 0.0

-0400 30.8 33.3 2.5 23.3 23.1 0.2 23.0 23.1 0.1

-0500 16.2 18.7 2.5 21.0 21.3 0.3 . 19.2 20.0 0.8

-0600 13.7 15.6 1.9 17.8 17.8 0.0 17.7 17.8 0.1

Average Diff.: 2.2 M Average Diff.: 0.8 Average Dif f .

0.9

Standard Dev. : 1.6 Standard Dev.

0.7 Standard Dev.

1.04

Grand Average Diff.: 1.3

Total Standard Dev.: 1.3

A

1 1 response values are in percent of upper linear Unit

29
Table 7 - Summary of Intercomparison Data on Set DA 55 Taken

with Transducer LS-3 and ASTM E 127-75 Procedure

Metal Distance Lab 1

3/64 Hole

Lab 2 Diff. Lab 1

5/64 Hole

Lab 2 Diff

8/64 Hole

Lab 1 Lab 2 Diff

-0050 72.0 00 5.8 90.0 94.7 4.7 80.0 88.0 8.0

-0075 56.0 63.1 7.1 68.4 75.6 7.2 70.8 79.1 8.3

-0100 49.0 54.2 5.2 53.0 60.0 7.0 48.8 55.6 6.8

-0150 40.5 44.9 4.4 32.3 35.6 3.3 36.7 42.2 5.5

-0200 30.4 34.7 4.3 26.8 30.2 3.4 30.7 35.6 4.9

-0250 24.2 27.1 2.9 19.7 22.2 2.5 19.5 22.2 2.7

-0200 78.0 88.9 10.9 70.7 80.0 9.3 80.2 93.3 13.1

-0250 62.7 71.1 8.4 53.8 62.2 8.4 52.3 60.0 7.7

-0300 46.6 54.2 5.6 46.7 53.3 6.6 41.2 45.3 4.1

-0400 30.4 35.6 5.2 25.1 28.9 3.8 26.6 32.0 5.4

-0500 15.7 22.2 6.5 22.7 27.6 4.9 22.2 26.7 4.5

-0600 13.8 16.0 2.2 19.0 22.2 3.2 20.5 25.8 5.3

Average Diff.: 5.7 Average Dif f .

5.4 Average Diff. : 6 .

Standard Dev.

2.3 Standard Dev.: 2.2 Standard Dev.: 2.6

Grand Average Diff.: 5.8

Total Standard Dev.: 2.4

All response values are in percent of upper linear limit.

30
Table 8 - Evaluation of Three Area-Amplitude Sets of

Diffusion-Bonded Steel Reference Blocks

Set No. 1

Ultrasonic Response

Block 5 MHz 10 MHz

8-0300 67 97.5

7-0300 49 78

6-0300 33 57

5-0300 26 46

4-0300 17 29

3-0300 8 13.5

2-0300 3.5 6

1-0300 1

Set Nos. 2 (a and b)

1

Ultrasonic Response Ultrasonic Response

Block 5 MHz 10 MHz Block 5 MHz 10 MHz

8-0075 67 100 8-0300 67 100

7-0075 57.5 89 7-0300 57.5 90

6-0076 35.5 52 6-0300 41 63.5

5-0075 28 44 5-0300 29 49

4-0075 19 34 4-0300 20.5 31.5

3-0075 10 16 3-0300 9.5 15

2-0075 2.5 6 2-0300 2.5 4

1-0075 0.5 1 1-0300 !_ 0.5

All response values are in percent of upper linear limit.

31
Table 9 - Ultrasonic Response of Nominally Identical Steel and Titanium

Reference Blocks Fabricated by Conventional Drilling

(a) Steel Blocks

Ultrasonic Ultrasonic

Block Response Block Response

5-0050-1 87.2 5-0300-1 64.7

5-0050-2 86 5-0330-2 63

5-0050-3 85.3 5-0300-3 65.3

5-0050-4 92.5 5-0300-4 66.3

5-0050-5 90.8 5-0300-5 64.8

Average 88.4 Average 64.8

-3.5% -2.8%

Spread/Average +4 . 6% Spread/Average +2 . 3%

Rel. St. Dev. 3.2% Rel. St. Dev. 1.7%

(b) Titanium Blocks

Ultrasonic Ultrasonic

Block Response Block Response

5-0050-1 89.8 5-0300-1 76.3

5-0050-2 94.8 5-0300-2 75.3

5-0050-3 95 5-0300-3 66.8

5-0050-4 95.7 5-0300-4 80

5-0050-5 94.2 5-0300-5 73.8

Average 93.9 Average 74.4

-4.4% -10.3%

Spread/Average +1 . 9% Spread /Average +7.5%

Rel. Std. Dev. 2.2% Rel. Std. Dev. o.8%

All individual block response values .are average of three readings

All response values ,are in percent of upper linear limit.

32
Table 10 - Ultrasonic Response of Nominally Identical Steel and

Titanium Reference Blocks Fabricated by Diffusion Bonding

A. Transducer Beam Normal to Top Surface

Steel Titanium

Ultrasonic Ultrasonic

Block - Response Block Response

5-0300-10A 66.7 5-0300-lA 59.3

5-0300-10B 58.5 5-0300-1B 91.5

5-0300-11A 69.3 5-0300-2A 83.0

5-0300-11B 68.5 5-0300-2B 70.0

Average 65.8 76.0

-11.1% -22.0%

Spread/Average + 5.3% +20.4%

Rel. Std. Dev. 6.5% 16.2%

0

B. Transducer Angulated and Positioned for Maximum FBH Response

Steel Titanium

Ultrasonic Ultrasonic

Block Response Block Response

5-0300-10A 67.5 5-0300-lA 75

5-0300-10B 63.5 5-0300-1B 93

5-0300-11A 71 5-0300-2A 100

5-0300-11B 71.2 5-0300-2B 90

Average 68.3 89.5

- 7.0% -16.2%

Spr ead/Average + 4.2% +11 . 7%

Rel. Std. Dev. 4.6% 10.2%

All response values are in percent of upper linear limit.

33
’

.
a

UJ

eo

g~za

x

yj H- o N-l 3 a

cr> z z UJ

<£ ^ * £X <X </) hUJ u>o 03zo

»“«y> oz<x <£

UJ QC a: ociUJ

00 ^ N c OH 3 OCX Z 3«003

O'

O

UJ UJ o 03 3 z. <r UJO

(J) Q£ J—t z UH <E U.Z

ex UJ UJ

h- oco

H-

zK-t >3 >3H- <X nr3h

a wE

UJ 00 o

00

g~

«zt—

3 OCX Z <X wh

Z> </> o

UJ 1 o3 «-4 O

V) UJ z or

<r 3

a:

O

i- K-

u.

nun d*3Nn d3ddn

x '3SwodS3a oxwosyann

34
ULTRASONIC

RESPONSE

OF

REFERENCE

BLOCK,

%

UPPER

LINEAR

LIMIT

100

TRANSDUCER • LS-i

LS-2

©LS-3

ALS-4

OLS-5

LS-6

-0050 REFERENCE BLOCKS

O

UATER DISTANCE * 5.62 IN

(14.3 CPI)

60

O

%

-0100 REFERENCE BLOCKS

40

UATER DISTANCE - 7.75 IN

(19.7 CM)

20

-0225 REFERENCE BLOCKS

UATER DISTANCE

l 1 0 20

- 13.1 IN

(33.3 CM)

I L

40 60

_L

80

ULTRASONIC RESPONSE OF 0.500-IN (12.7-MM) BALL AT EQUIUALENT

UATER DISTANCE, X UPPER LINEAR LIMIT

FIGURE 2 - CORRELATION OF REFERENCE BLOCK READINGS UITH TRANSDUCER

AXIAL PRESSURE AMPLITUDE. 35
107. %

H

G

0

O •

0*

i

Z/H®

OU)

CL

t-<L

<Lce* Ni—i z Qh

OC I <IU) Q-h 2 X

<Ch

CD

V

O

o3

tt

®

ID®

®fi LD©

-3

Dl

XH

C5X

bJ3

CD3

Ui

CD3

3

Qroo

CL

LsJ O

3

CS

CO2

CL

X

< X

I-o

2

UJ

ru

CL

UJ

o

3Q

CD2

<X

QC

0

0

X

I

o

2

UJ

UJ

CD3

X

o

2

CL

UiO

3O

CD2

<ZCL

fr-

'36 nun atGNn d3ddn %

' 3SN0dS3d oiNOSdann

FIGURE

3

-

EFFECTS

OF

PULSE

LENGTH

ADJUSTP1ENT

ON

ULTRASONIC

RESPONSE

OF

A

REFERENCE

BLOCK.
37

EMPIRICAL

MASTER

CURVE

.
CO

LDn

ru

CO

LUXo

LUo

jC- <ri

co»—

o

<xtLU




COoo—I

CDLUo2

LU

DC£ co

LU -J

gc lu _ QO DZiO

—I<

u_O

Q_X

COzQ

COXO

oc<>

DCO

LL. CO

LU

DCLUQD<I

DJhtt.<I(;jOZwO OtCUCOCLOZCOLU

CO

LU

CDCO

LUDC<D

O'

COIco

LU <

CJ LU Z -J S pE co t Q £ I in

LU

DCDO

38
HETAL

DISTANCE

CENTIMETERS

(/) *oo-J

CDa

Od<Qz<

I—COoz

OdO£QO< ui>

OdOLU

(/)

Odoo

OdLU 2

LU 3§ a: ^ ! s pSo2 q

H- LU O Od LU <

Od CL

Od S o o 0 o 1 vuLU

od

Z)g

LU

39
PRESSURE

OHM

zxro

o

40

FIGURE

7

-

FABRICATION

OF

DIFFUSION-BONDED

REFERENCE

BLOCKS.
nun aiddrs % '3SN0dS3a oiuosyann

CXJ o

5-UJin

nun dd3Nii a3ddn * '3SN0dS3a oiNosyann

o

r

t-UJ

in

41

FIGURE

8

-

ULTRASONIC

RESPONSE

DATA

FOR

TUO

AREA-ANPLITUDE

SETS

OF

DIFFUSION-BONDED

REFERENCE

BLOCKS.
(A)

FIGURE 9 - A-SCAN PRESENTATION OF RESPONSE OF TUO 6AL-4V

TITANIUM REFERENCE BLOCKS. (A) DIFFUSION-BONDED

5-0300 BLOCK. <B) CONVENTIONAL 5-0325 BLOCK.

NOTE HIGHER NOISE LEVEL IN HEAT-AFFECTED ZONE IN

DIFFUSION-BONDED BLOCK. 42
(a)

(b)

Figure 10 - Diffusion-bonded reference blocks prior to final machining, (a)

4340 steel, and (b) 6Al-4v titanium. Note skewness in steel blocks.

43
Appendix A

Description of Ultrasonic Instrumentation

The ultrasonic pulser/receiver/display system used for the majority of

the tests described in this report was manufactured by Automation Industries

Sperry Products Division*. The mainframe is a model UM 771B, with 10 N dB

pulser/receiver , D Timer, and H Transigate plug-in modules. The pulser produces

a tuned output electrical pulse at the required frequency. The received signals

are amplified as RF pulses, rectified and filtered, and delivered to the display

as video signals. This system is described in more detail in [5].

For some of the transducer characterization tests (table 3) a broadband

pulser/receiver system was used in conjunction with a broadband oscilloscope

and RF spectrum analyzer. This pulser/receiver was manufactured by Xenotec, Ltd.,

model XP/R-2. This system is described in more detail in [3],

Commercial equipment and instruments are identified by brand name and model

in order to fully specify the experimental procedure. In no way does such

identification imply recommendation or endorsement by the National Bureau of

Standards, nor does it imply that the equipment identified is necessarily the

best available for the purpose.

44

Appendix B

diffusion Bonding Procedure for Reference Blocks.

The procedure used for the fabrication of diffusion-bonded reference blocks

was essentially the same as that used by Don Conn at Armco, Inc. Research

Center, (Reference 15 of the text) although not described in detail in that

paper. A three-piece block is used so that each block takes the place of two

reference standards, depending on which end is interrogated by the transducer.

Usually, the metal distances to the hole would be different on each end, but for

our purpose, i.e. to check for differences in nominally identical blocks, the two

ends were the same, thus giving two measurements from each block.

The sequence of fabrication is shown schematically in figure 7 of the text.

The three pieces were machined to size, the through-hole drilled in the wafer,

and the four interfaces to be bonded rough ground (approximately 10 y in

(0.25 ym) ) . The three pieces were then circumferentially welded together in an

argon atmosphere, thus sealing the to-be-bonded region and obviating the need to

perform the actual bonding process in a vacuum or inert atmosphere.

The diffusion bonding itself was done in air, with the heat supplied by

induction heating coils and the pressure by a small manual hydraulic press. The

bonding parameters for steel were 2000°F (1092 °C) and 2000 lbf/in 2 (1.38 MPa) for

30 minutes (ref. Conn, private communication), and for titanium 1700 °F (926 °C)

and 500 lbf/in 2 (0.35 MPa) for 30 minutes (Reference 14 of text). After bonding,

the blocks can be machined to final diameter.

45
To test the procedure at NBS, a blank (no hole) two-piece block was

fabricated from 4340 steel. A modified ultrasonic C-scan [18], showing a

perspective view of signal amplitude versus X and Y position, is shown in figure

B-l. The signal is gated from the interface region only. Significant

reflections can be seen around the circumference, but none in the important

central region. The signal is null over the central 1.5 in (3.8 cm) of the block

at a gain of 20 dB greater than that which gives full-scale first back

reflection. Possibly the circumferential weld is resisting the applied pressure

and preventing a good bond from forming near the edge. A photomicrograph of the

central region is shown in figure B-2. This shows it to be an excellent

diffusion bond. Modified C-scan perspective plots for both conventional and

diffusion-bonded steel and titanium blocks are shown in figures B-3 and B-4.

46
47

Figure

B-l

-

Modified

C-scan

interface

region

of

blank

(no-hole)

diffusion-bonded

steel

block
200 X

500 X

Figure B2 - Photomicrographs of diffusion bondline in blank (no hole)

4340 steel block.

48
Figure

(a

(b)

-3 Modified C-scan recordings of flat-bottom hole plane

diffusion bonded and (b) conventional 4340 steel blocks

49
(b)

Figure B-4 Modified C-Scan

(a) diffusion bonded and

recordings of flat-bottom hole plane in

(b) conventional 6A1-4V titanium blocks

u50
NBS-114A REV. 9-7 8

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBSIR-79-1742

Nov 3. Recipient's Accession No.

4. TITLE AND SUBTITLE 5. Publication Date Recent Improvements to the ASTM-type Ultrasonic

Reference Block System 6. Performing Organization Code

7. AUTHOR) S) Daniel J. Chwirut

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

Unit No.

11. Contract/Grant No.

DO F33615-76-F-6751

12. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City. State, ZIP)

Air Force Materials Laboratory, WPAFB, Ohio 45433

Army Materials & Mechs. Research Center, Watertown, MA 0217

NASA, Lewis Research Center, Cleveland, OH 44135

13. Type of Report & Period Covered

Final

ng Agency Code

15. SUPPLEMENTARY NOTES

For issuance now as NBSIR; Sponsor will publish later as AFML-TR

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT iA 200-wcrd or lees factual summary of moat significant information. If document includes a significant bibliography or

literature survey, mention it here.) Recer.t Activities aimed toward improving the ASTM-type ultrasonic reference block

system are described. On the aluminum block system (ASTM E 127 and NBS TN 924),

efforts were focused on better definition of the measurement equipment (transducer

and instrument), the implementation of a Measurement Assurance Program and Loaner

Block Service, and modeling of the distance-amplitude relationship. It is shown that

a large increase in the precision of reference block readings is easily achievable

by implementing simple changes and controls in the measurement procedure. On steel

and titanium blocks (e.g. ASTM E-428) , efforts were directed toward quantifying

the extent of reproducibility possible among blocks fabricated by both conventional

drilling and by diffusion bonding. Reasonable reproducibility is achieved by both,

with the diffusion-bonding process offering both advantages and disadvantages.

17 . FY WORDS (six to twelve entries , alphabetical order; capitalize only the first letter of the first key word unless a proper name;

a ?pare ted by semicolons)

Calibration; Diffusion bonding; Measurement Assurance Program; Reference blocks:

Standards; Ultrasonics; Variability.

18. AVAILABILITY f%~[ Unlimited

For Official Distribution. Do Not Release to NTIS

Order From Sup. of Doc., U.S. Government Printing Office, Washington. DC

20402, SD Stock No. SN003-003

X 0 der From National Technical Information Service (NTIS), Springfield, VA. 22161

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF

PRINTED PAGES

53

22. Price

$5.25

USCOMM-DC


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