ASTM E2534-20

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2534 − 15 E2534 − 20
Standard Practice for
Targeted Defect Detection Using Process Compensated
Resonance Testing Via Swept Sine Input for Metallic and
Non-Metallic Parts
This standard is issued under the fixed designation E2534; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Scope*
1.1 This practice describes a general procedure for using the process compensated resonance testing (PCRT) via swept sine input
method to detect resonance pattern differences in metallic and non-metallic parts. The resonance for metallic or non-metallic parts
to compare resonance patterns from a sample under test to reference teaching sets of known acceptable and targeted defect samples.
The resonance pattern differences can be used to distinguish acceptable parts with normal process variation from parts with targeted
material states and defects that will cause performance deficiencies. These material states and defects include, but are not limited
to, cracks, voids, porosity, shrink, inclusions, discontinuities, grain and crystalline structure differences, density-related anomalies,
heat treatment variations, material elastic property differences, residual stress, and dimensional variations. This practice is intended
for use with instruments capable of exciting, measuring, recording, and analyzing multiple whole body, mechanical vibration
resonance frequencies in acoustic or ultrasonic frequency ranges, or both.
1.2 Units—This practice uses inch pound units as primary units. SI units are included in parentheses for reference only, and The
values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions
of the primary units.to SI units that are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E1316 Terminology for Nondestructive Examinations
E2001 Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts
E3081 Practice for Outlier Screening Using Process Compensated Resonance Testing via Swept Sine Input for Metallic and
Non-Metallic Parts
E3213 Practice for Part-to-Itself Examination Using Process Compensated Resonance Testing Via Swept Sine Input for Metallic
and Non-Metallic Parts
This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.06 on Ultrasonic Method.
Current edition approved Dec. 1, 2015Dec. 1, 2020. Published December 2015January 2021. Originally approved in 2010. Last previous edition approved in 20102015
as E2534E2534 – 15.-10. DOI: 10.1520 ⁄E2534-15 ⁄E2534-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2534 − 20
3. Terminology
3.1 Definitions:
The definitions of terms relating to conventional ultrasonic examination can be found in Terminology E1316.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 broadband—broadband, n—the range of frequencies, excitation parameters, and data collection parameters developed
specifically for a particular part type.
3.2.2 classification—classification, n—the labeling of a teaching set of parts as acceptable or unacceptable.
3.2.3 false negative, n—part failing the sort but deemed by other method of post-test/analysis to have acceptable or conforming
specifications
3.2.4 false positive, n—part passing the sort but exhibiting a flaw (either inside the teaching set of flaws or possibly outside the
teaching set range of flaws) or nonconforming to specification.
3.2.5 margin part—part, n—a single part representative of a part type that is used to determine measurement repeatability and for
system verification.
3.2.6 Process Compensated ResonantResonance Testing (PCRT)—(PCRT), n—a nondestructive examination method that
enhances swept sine input RUS with pattern recognition capability. PCRT more effectively discriminates between resonance
frequency shifts due to unacceptable conditions from resonance frequency shifts due to normal, acceptable manufacturing process
variations. The process employs the measurement and analysis of acoustic or ultrasound resonance frequency patterns, or both.
PCRT pattern recognition tools identify the combinations of resonance patterns that most effectively differentiate acceptable and
unacceptable components. Statistical scoring of the resonance frequencies is used to compare components to known acceptable and
unacceptable populations, quantify process variation, and characterize component populations. capability and statistical scoring.
3.2.6.1 Discussion—
PCRT more effectively discriminates between resonance frequency shifts due to unacceptable conditions and resonance frequency
shifts due to normal, acceptable manufacturing process variations. The process employs the measurement and analysis of acoustic
or ultrasound resonance frequency patterns, or both. PCRT pattern recognition tools identify the combinations of resonance
patterns that most effectively differentiate acceptable and unacceptable components. Statistical scoring of the resonance
frequencies is used to compare components to known acceptable and unacceptable populations, quantify process variation, and
characterize component populations.
3.2.7 resonance spectra—spectra, n—the recorded collection of resonance frequency data, including frequency peak locations and
the characteristics of the peaks, for a particular part.
3.2.8 Resonant Ultrasound Spectroscopy (RUS)—Basic RUS (1) was originally applied in fundamental research applications in
physics and materials science. Other recognizable names include acoustic resonance spectroscopy, acoustic resonant inspection,
and resonant inspection. Guide E2001 documents RUS extensively. RUS is a nondestructive examination method that employs the
measurement and analysis of acoustic or ultrasonic resonance frequencies, or both, for the identification of acceptable variations
in the physical characteristics of test parts in production environments. In this procedure an isolated, rigid component is excited,
producing oscillation at the natural frequencies of vibration of the component. Diagnostic resonance frequencies are measured and
compared to resonance frequency patterns previously defined as acceptable. Based on this comparison, the part is judged to be
acceptable or, if it does not conform to the established pattern, unacceptable.
3.2.8.1 Discussion—
Other recognizable names include acoustic resonance spectroscopy, acoustic resonant inspection, and resonant inspection. Guide
E2001 documents RUS extensively. RUS is a nondestructive examination method that employs the measurement and analysis of
acoustic or ultrasonic resonance frequencies, or both, for the identification of acceptable variations in the physical characteristics
of test parts in production environments. In this procedure, an isolated, rigid component is excited, producing oscillation at the
natural frequencies of vibration of the component. Diagnostic resonance frequencies are measured and compared to resonance
frequency patterns previously defined as acceptable. Based on this comparison, the part is judged to be acceptable or, if it does
not conform to the established pattern, unacceptable.
The boldface numbers in parentheses refer to athe list of references at the end of this practice.
E2534 − 20
3.2.9 sort—sort, n—a software program capable of classifying a component as acceptable or unacceptable.
3.2.10 teaching set—set, n—a grouppopulation of like components including examples of known acceptable and known
unacceptable components representative of the range of acceptable variability and unacceptable variability.variability; the teaching
set may consist entirely of physical components, or a combination of physical components and modeled components whose
resonance spectra are generated by physics-based simulations.
3.2.11 work instruction—instruction, n—stepwise instructions developed for each examination program detailing the order and
application of operations for PCRT examination of a part.
4. Summary of Practice
4.1 Introduction:
4.1.1 Many variations on resonance testing have been applied as nondestructive examination tools to detect structural anomalies
that significantly alter component performance. The details of this basic form of resonance testing are outlined in Guide E2001.
4.1.2 Process Compensated ResonantResonance Testing (PCRT) is a progressive development of the fundamental principles of
RUS, and can employ various methods for enhancing the discrimination capability of RUS. Throughout the 1990s, application of
RUS for production NDT led to better understanding of the challenges associated with differentiating resonance variations caused
by structural anomalies from resonance variation from normal and acceptable process variations in mass, material properties, and
dimensions (2,3). PCRT first became commonly used in the production examination of metal and ceramic parts in the late 1990s
(4). By the early 2000s, PCRT had essentially developed into the robust NDT capability it is today (5).
4.1.3 PCRT is a comparison technology using a swept sine wave to excite the components through a range of resonance
frequencies determined by the part’s mass, geometry, and material properties. The resonance spectrum is then compared to
resonance spectra for known acceptable components and unacceptable components. The database of known acceptable and
unacceptable components is established through the collection of a teaching set of components that represent the range of
acceptable process variation and the unacceptable conditions of interest. PCRT applications are taught to be sensitive to resonance
variations associated with unacceptable components and also taught to be insensitive to variations associated with acceptable
components. PCRT pattern recognition tools identify the combination of resonance frequencies that most effectively differentiate
the acceptable and unacceptable components. Statistical tools score each component based on its similarity to the known acceptable
and unacceptable populations,populations and establish scoring PASS/FAIL limits for each criteria.criterion. A component with
resonance frequencies sufficiently similar to the acceptable components and different from the unacceptable components will pass
the PCRT inspection. A component that fails either criteria will be rejected. In one examination cycle, PCRT-based techniques can
test for a single anomaly, or for combinations of anomalies, as listed in 1.1. The PCRT measurement yields a whole body
whole-body response, finding structurally-significant structurally significant anomalies anywhere within the part, but it is generally
not capable of determining the type or location of the anomaly. A teaching set of parts must contain both acceptable and
unacceptable samples as determined by someone knowledgeable of the design, validation testing, and minimum functional
requirements of the part. If unacceptable samples are not available, an alternative PCRT approach called PCRT Outlier Screening
may be applied. Practice E3081 describes the Outlier Screening approach.
4.1.4 PCRT can be applied to new parts in the production environment, to parts currently in service, or in a combined program
in which parts are initially classified as free of substantial anomalies in production, and then periodically re-examined with PCRT
in order to monitor for the accumulation of fatigue and damage resulting from use. The process for using frequency changes
between different points in time to perform NDT and process monitoring and control is described in more detail in Practice E3213.
One example of a PCRT application is gas turbine engine blades. Application of PCRT to the blades in the production environment
can detect targeted manufacturing and material defects such as casting shrinkage, cracks, voids, shifted cores, heat treatment
irregularities, and other material variation. Since turbine blades are periodically inspected throughout their useful lives, PCRT can
be applied during these in-service inspections to accept only parts that are free of service induced service-induced defects such as
gamma prime solutioning, rafting, creep, cracks, inter-granular attack, and excessive wear and fatigue.
4.1.5 This practice is intended to provide a practical guide to the application of PCRT-based nondestructive testing (NDT) to
targeted defects in both metallic and non-metallic parts. It highlights the steps necessary to produce robust and accurate test
applications and outlines potential weaknesses, limitations, and factors that could lead to misclassification of a part. Some basic
explanations of resonances, and the effects of anomalies on them, are found in 4.2. Some successful applications and general
description of the equipment necessary to successfully apply PCRT for classification of production parts are outlined in 5.1 and
E2534 − 20
5.2, respectively. Additionally, some constraints and limitations are discussed in 5.3. The general procedure for developing a
part-specific PCRT application is laid out in 6.1.
4.2 Resonances and the Effect of Anomalies:
4.2.1 The swept sine method of vibration analysis operates by driving a part at given frequencies (acoustic through ultrasonic,
depending on the part characteristics) and measuring its mechanical response. Fig. 1 contains a schematic for one embodiment of
a PCRT apparatus. The swept sine wave proceeds in small frequency steps over a previously determined broadband frequency
range of interest. When the excitation frequency is not matched to one of the part’s resonance frequencies, very little energy is
coupled to the part; that is, there is essentially no vibration. At resonance, however, the energy delivered to the part is coupled,
generating much larger vibrations. A part’s resonance frequencies are determined by its geometry, density, and material elastic
constants (mechanically equivalent to mass, stiffness, and damping) of the material. An example of the resonance spectra for a part
is shown in Fig. 2 for reference.
4.2.2 If a structural anomaly, such as a crack, is introduced into a region under strain, it will change the effective stiffness of a
part (decrease stiffness for a crack). That is, the part’s resistance to deformation will change and will shift some of the part’s
resonant frequencies (downward for decreasing stiffness). Voids in a region can reduce mass and increase certain resonant
frequencies. In general, any change to a part that alters the structural integrity, changes a geometric feature or affects the material
properties will alter its natural resonance frequencies. Graphic examples of the effects of various anomalies on resonances are
presented in Guide E2001.
4.2.3 For example, the torsional (twisting) (Fig. 3) resonant modes represent a twisting of a part about its axis. In the simple
example of a long cylinder, these resonances are easily identified because some of their frequencies remain constant for a fixed
length, independent of diameter. A crack will reduce the ability of the part to resist twisting, thereby reducing the effective stiffness,
and thus, the frequency of a torsional mode both shifts to a lower value and then alters the mode shape. Other resonances
representing different resonance mode shapes of the part will not be affected in the same manner. Also, a large structural anomaly
can be detected readily by its effect on the first few resonant frequencies. However, smaller structural anomalies have much more
subtle and localized effects on stiffness, and therefore, often require higher frequencies (high-order resonant modes and harmonics)
to be detected. In general, it must be remembered that most parts will exhibit complex motions when resonating. Analyzing the
relationship between the resonant frequencies provides one way to generate the information necessary to interpret the data resulting
from measuring the frequencies of the various resonant modes. These relationships form one basis for detecting the difference
between normal, expected variations and variations indicating significant structural or geometric differences from one part to
another. A broad body of research is available describing various other nonproprietary approaches to identifying significant features
(flaws, damage, etc) from changes in their vibration characteristics in the presence of environment or process variation.(6)
5. Significance and Use
5.1 PCRT Applications and Capabilities—PCRT has been applied successfully to a wide range of NDT applications in the
manufacture and maintenance of metallic and non-metallic parts. Examples of anomalies detected are discussed in 1.1. PCRT has
FIG. 1 PCRT System SchematicSchematics
E2534 − 20
FIG. 2 Resonance Spectra (50 kHz – 120 kHz)
FIG. 3 Torsional Mode for Cylinder
been shown to provide cost effective and accurate NDT solutions in many industries including automotive, aerospace, and power
generation. Examples of successful applications currently employed in commercial use include, but are not limited to:
(1) Silicon nitride bearing elements
(2) Steel, iron, and aluminum rocker and control arms
(3) Gas Aircraft and industrial gas turbine engine components (blades, vanes, disks)
(4) Cast cylinder heads and cylinder blocks
(5) Sintered powder metal gears and clutch plates
(6) Machined forged steel steering and transmission components (gears, shafts, racks)
(7) Ceramic oxygen sensors
(8) Silicon wafers
(9) Gears Gears, including those with induction hardened or carburized teeth
(10) Ceramic matrix composite (CMC) material samples and components
(11) Components with shot peened surfaces
(12) Machined or rolled-formed, or both, steel rolled-formed fasteners
(13) Additive manufactured componentsComponents made with additive manufacturing
(14) Aircraft landing gear, wheel, and brake components
(15) Components made with metal injection molding
5.2 General Approach and Equipment Requirements for PCRT via Swept Sine Input:
5.2.1 PCRT systems are comprised of comprise hardware and software capable of inducing vibrations, recording the component
response to the induced vibrations, and executing analysis of the data collected. Inputting a swept sine wave into the part has
proven to be an effective means of introducing mechanical vibration,vibration and can be achieved with a high quality signal
generator coupled with an appropriate active transducer in physical contact with the part. Collection of the part’s frequency
response can be achieved by recording the signal generated by an appropriate passive vibration transducer. The software required
to analyze the available data may include a variety of suitable statistical analysis and pattern recognition tools. Measurement
accuracy and repeatability are extremely important to the application of PCRT.
E2534 − 20
5.2.2 Hardware Requirements—A swept sine wave signal generator and response measurement system operating over the desired
frequency range of the test part are required with accuracy better than 0.002 %. The signal generator should be calibrated to
applicable industry standards. Transducers must be operable over same frequency range. Three transducers are typically used; one
Drive transducer and two Receive transducers. Transducers typically operate in a dry environment, providing direct contact
coupling to the part under examination. However, noncontactingnon-contacting response methods can operate suitably when parts
are wet or oil-coated. Other than fixturing and transducer contact, no other contact with the part is allowed as these mechanical
forces dampen certain vibrations. For optimal examination, parts should be placed precisely on the transducers (generally, 60.062
in. (1.6 mm) in each axis provides acceptable results). The examination nest and cabling shall isolate the Drive from Receive
signals and ground returns, so as to not produce (mechanical or electrical) cross talk between channels. Excessive external
vibration or audible noise, or both, will compromise the measurements.
5.3 Constraints and Limitations:
5.3.1 PCRT cannot separate parts based on visually detectable anomalies that do not affect the structural integrity of the part. It
may be necessary to provide additional visual inspection of parts to identify these indications.
5.3.2 Excessive process variation of parts may limit the sensitivity of PCRT. For example, mass/dimensional variations exceeding
5 % may cause PCRT to be unusable.
5.3.3 Specific anomaly identification is highly unlikely. PCRT is a whole body measurement,measurement and differentiating
between a crack and a void in the same location is generally not possible. It may be possible to differentiate some anomalies by
using multiple patterns and training sets. The use of physics-based modeling and simulation to predict the resonance frequency
spectrum of a component may also allow relationships between resonance frequencies and defect locations/characteristics to be
established.
5.3.4 PCRT will only work with stiff objects that provide resonances whose frequency divided by their width at half of the
maximum amplitude (Q) are greater than 400 to 500. Although steel parts may be very stiff and perfectly reasonable to use for
PCRT, steel foil would generally not be.
5.3.5 While PCRT can be applied to painted and coated parts in many cases, the presence of some surface coatings such as
vibration-absorbing materials and heavy oil layers may limit or preclude the application of PCRT.
5.3.6 While PCRT can be applied to parts over a wide range of temperatures, it canshould not be applied to parts that are rapidly
changing temperature. The part temperature should be stabilized before collecting resonance data.
5.3.7 Misclassified parts in the teaching set, along with the presence of unknown anomalies in the teaching set, can significantly
reduce the accuracy and sensitivity of PCRT.
6. Procedure
6.1 Successful PCRT application development and implementation follows a standard flow. The stepwise functions required in the
flow are:
(1) Collection of a teaching set of components
(2) Design and fabrication of a test nest or appropriate fixturing
(3) Understanding the effects of temperature on the resonance spectra
(4) Specification of a resonance broadband data collection parameters
(5) Evaluate system measurement repeatability and reproducibility (similar to Gauge R and R) with respect to mounting
parameters
(6) Collection of data from the teaching set of parts
(7) Analysis of collected dat
...