ASTM E3397-23

Standard Practice for Resonance Testing Using the Impulse Excitation Method

SIGNIFICANCE AND USE
4.1 IEM Applications and Capabilities—IEM has been successfully applied to a wide range of NDT applications in the manufacture, maintenance, and repair of metallic and non-metallic parts. Examples of anomalies detected are discussed in 1.1 and 6.2. IEM has been proven to provide fast, cost-effective, and accurate NDT solutions in nearly all manufacturing, maintenance, or repair modalities. Examples of the successful application focuses include, but are not limited to: sintered powder metals, castings, forgings, stampings, ceramics, glass, wood, weldments, heat treatment, composites, additive manufacturing, machined products, and brazed products.  
4.2 General Approach and Equipment Requirements for IEM:  
4.2.1 IEM systems are comprised of hardware and software capable of inducing vibrations, recording the component response to the induced vibrations, and executing analysis of the data collected.  
4.2.2 Hardware Requirements—Examples of a tabletop impact excitation system and a production-grade drop excitation system are shown in Fig. 1 and Fig. 2, respectively. IEM systems include: an excitation device (for example, modal hammer / impact device / dropping system) providing an impulse excitation to the object, a vibration detector (for example., microphone), a signal amplifier, an Analog-to-Digital Converter (ADC), an embedded logic, and a data User Interface (UI). Tested parts can typically be on any surface type, but they can also be supported (for example, foam support, held with an elastic) in consideration of possible damping influences. The following schematics show the basic parts for an impact excitation approach (Fig. 3) and a drop excitation approach (Fig. 4).
FIG. 1 IEM Tabletop Testing System Using a Non-Instrumented Impactor
FIG. 2 Production-Grade Drop Excitation System
FIG. 3 Schematic of Impact Excitation Approach
FIG. 4 Schematic of Drop Excitation Approach  
4.3 Constraints and Limitations:  
4.3.1 IEM needs a change in structural i...
SCOPE
1.1 This practice covers a general procedure for using the Impulse Excitation Method (IEM) to facilitate natural frequency measurement and detection of defects and material variations in metallic and non-metallic parts. This test method is also known as Impulse Excitation Technique (IET), Acoustic Resonance Testing (ART), ping testing, tap testing, and other names. IEM is listed as a Resonance Ultrasound Spectroscopy (RUS) method. The method applies an impulse load to excite and then record resonance frequencies of a part. These recorded resonance frequencies are compared to a reference population or within subgroups/families of examples of the same part, or modeled frequencies, or both.  
1.2 Absolute frequency shifting, resonance damping, and resonance pattern differences can be used to distinguish acceptable parts from parts with material differences and defects. These defects and material differences include, cracks, voids, porosity, material elastic property differences, and residual stress. IEM can be applied to parts made with manufacturing processes including, but not limited to, powdered metal sintering, casting, forging, machining, composite layup, and additive manufacturing (AM).  
1.3 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. This practice does not provide inspection acceptance criteria for parts. However, it does discuss the processes for establishing acceptance criteria specific to impulse testing. These criteria include frequency acceptability windows for absolute frequency shifting, scoring criteria for statistical analysis methods (Z-score), Gage Repeatability & Reproducibility (R&R) for diagnostic resonance modes, and inspection criteria adjustment (compensation) for manufacturing process and environmental variations.  
...

General Information

• Status: Published
• Publication Date: 30-Jun-2023
• ICS: 17.140.01 - Acoustic measurements and noise abatement in general
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.06 - Ultrasonic Method

Relations

• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM E1316-19b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2019
• Refers: ASTM E1316-19 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Mar-2019
• Refers: ASTM E2001-18 - Standard Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts
• Effective Date: 01-Nov-2018
• Refers: ASTM E1316-18 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jan-2018
• Refers: ASTM E1316-17a - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2017
• Refers: ASTM E1316-17 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2017
• Refers: ASTM E1316-16a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Aug-2016
• Refers: ASTM E1316-16 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2016
• Refers: ASTM E1316-15a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2015
• Refers: ASTM E1316-15 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Sep-2015
• Refers: ASTM E1316-14e1 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014
• Refers: ASTM E1316-14 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jun-2014
• Refers: ASTM E1316-13d - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2013
• Refers: ASTM E2001-13 - Standard Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts
• Effective Date: 01-Dec-2013

Overview

ASTM E3397-23 outlines the standard practice for Resonance Testing Using the Impulse Excitation Method (IEM), also referred to as the Impulse Excitation Technique (IET), Acoustic Resonance Testing (ART), ping testing, or tap testing. Developed by ASTM International, this standard provides a comprehensive procedure for natural frequency measurement and detection of defects or material variations in metallic and non-metallic parts using nondestructive testing (NDT). The method employs a mechanical impulse to excite resonant frequencies, capturing the vibrational response to assess part quality, structure, and integrity. IEM serves as a cost-effective, fast, and accurate NDT technique for manufacturing, maintenance, and repair applications across a diverse range of industries.

Key Topics

• Impulse Excitation Method (IEM): Describes the process of applying an impulse load to excite natural frequencies in a component and recording the resulting resonant response for analysis.
• Defect Detection: IEM is capable of identifying anomalies like cracks, voids, porosity, residual stress, and material property differences by analyzing changes in resonance patterns, frequency shifting, and damping.
• System Components: IEM systems include excitation devices (e.g., modal hammers, impact or drop devices), vibration detectors (microphones, accelerometers), signal amplifiers, analog-to-digital converters, embedded logic, and user interfaces.
• Data Analysis: Part acceptance is determined by comparing recorded resonance spectra to reference datasets or modeled frequencies and can incorporate statistical tools like Z-score analysis, frequency windows, and gage repeatability and reproducibility (R&R) assessments.
• Compensation and Limitations: The standard addresses compensation methods to account for process variations (such as mass or temperature fluctuations) and highlights constraints, such as sensitivity variations based on part size, material, and the physics of resonant energy distribution.
• Personnel Qualification: Emphasizes that operators should be qualified in accordance with nationally or internationally recognized NDT personnel standards.

Applications

IEM provides valuable nondestructive evaluation in a broad spectrum of scenarios, including:

• Manufacturing Quality Control: Detection of defects and process inconsistencies during the production of sintered metals, castings, forgings, stampings, ceramics, composites, additive manufacturing (AM) products, glass, wood, weldments, and brazed parts.
• Maintenance and Repair: Assessment of structural integrity and identification of hidden flaws in in-service or refurbished components.
• Process Optimization: Use of resonance data to monitor and improve process consistency, detect subtle material property changes, and prevent acceptance of defective or substandard parts.
• Statistical Quality Assurance: Development of robust acceptance criteria through collection and analysis of reference data, including repeatability studies and compensation for known process variations.
• Whole-Body Testing: IEM enables efficient volumetric inspection, providing coverage of the entire part rather than localized regions.

Related Standards

Several other international standards complement or relate to ASTM E3397-23:

• ASTM E1316: Terminology for Nondestructive Examinations
• ASTM E2001: Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts
• EN 1330-2: Non-destructive Testing - Terminology - Part 2: Terms Common to the Non-Destructive Testing Methods
• ISO 12680-1:2007: Methods of Test for Refractory Products - Part 1: Determination of Dynamic Young’s Modulus (MOE) by Impulse Excitation of Vibration
• ISO 22605:2020: Refractories - Determination of Dynamic Young’s Modulus (MOE) at Elevated Temperatures by Impulse Excitation of Vibration

ASTM E3397-23 plays an essential role in advancing nondestructive testing practices, enabling reliable quality control and defect detection for both metallic and non-metallic parts across industries. For manufacturers and inspectors seeking robust, repeatable, and standardized resonance inspection, this method offers proven benefits in accuracy, efficiency, and cost-effectiveness.

Standards Content (Sample)

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.
Designation: E3397 − 23
Standard Practice for
Resonance Testing Using the Impulse Excitation Method
This standard is issued under the fixed designation E3397; 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 1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers a general procedure for using the
responsibility of the user of this standard to establish appro-
Impulse Excitation Method (IEM) to facilitate natural fre-
priate safety, health, and environmental practices and deter-
quency measurement and detection of defects and material
mine the applicability of regulatory limitations prior to use.
variations in metallic and non-metallic parts. This test method
1.6 This international standard was developed in accor-
is also known as Impulse Excitation Technique (IET), Acoustic
dance with internationally recognized principles on standard-
Resonance Testing (ART), ping testing, tap testing, and other
ization established in the Decision on Principles for the
names. IEM is listed as a Resonance Ultrasound Spectroscopy
Development of International Standards, Guides and Recom-
(RUS) method. The method applies an impulse load to excite
mendations issued by the World Trade Organization Technical
and then record resonance frequencies of a part. These re-
Barriers to Trade (TBT) Committee.
corded resonance frequencies are compared to a reference
population or within subgroups/families of examples of the
2. Referenced Documents
same part, or modeled frequencies, or both.
2.1 ASTM Standards:
1.2 Absolute frequency shifting, resonance damping, and
E1316 Terminology for Nondestructive Examinations
resonance pattern differences can be used to distinguish ac-
E2001 Guide for Resonant Ultrasound Spectroscopy for
ceptable parts from parts with material differences and defects.
Defect Detection in Both Metallic and Non-metallic Parts
These defects and material differences include, cracks, voids,
porosity, material elastic property differences, and residual 2.2 ISO and Other International Standards:
EN 1330-2 Non-destructive testing — Terminology — Part
stress. IEM can be applied to parts made with manufacturing
processes including, but not limited to, powdered metal 2: Terms common to the non-destructive testing methods
ISO 12680-1:2007 Methods of test for refractory products
sintering, casting, forging, machining, composite layup, and
additive manufacturing (AM). — Part 1: Determination of dynamic Young’s modulus
(MOE) by impulse excitation of vibration
1.3 This practice is intended for use with instruments
ISO 22605:2020 Refractories — Determination of dynamic
capable of exciting, measuring, recording, and analyzing mul-
Young’s modulus (MOE) at elevated temperatures by
tiple whole body, mechanical vibration resonance frequencies
impulse excitation of vibration
in acoustic or ultrasonic frequency ranges, or both. This
practice does not provide inspection acceptance criteria for
3. Terminology
parts. However, it does discuss the processes for establishing
acceptance criteria specific to impulse testing. These criteria 3.1 Definitions:
include frequency acceptability windows for absolute fre- 3.1.1 The definitions of terms relating to conventional
quency shifting, scoring criteria for statistical analysis methods ultrasonic examination can be found in Terminology E1316.
(Z-score), Gage Repeatability & Reproducibility (R&R) for 3.2 Definitions of Terms Specific to This Standard:
3.2.1 bandwidth, n—the range of frequencies excited and
diagnostic resonance modes, and inspection criteria adjustment
(compensation) for manufacturing process and environmental recorded in the inspection.
variations.
1.4 This practice uses inch pound units as primary units. SI
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
units are included in parentheses for reference only and are
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
mathematical conversions of the primary units.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- Available from European Committee for Standardization (CEN), Avenue
structive Testing and is the direct responsibility of Subcommittee E07.06 on Marnix 17, B-1000, Brussels, Belgium, http://www.cen.eu.
Ultrasonic Method. Available from International Organization for Standardization (ISO), ISO
Current edition approved July 1, 2023. Published August 2023. DOI: 10.1520/ Central Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
E3397-23. Switzerland, https://www.iso.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3397 − 23
3.2.2 broadband, n—the bandwidth, excitation parameters, 3.2.13 resonant ultrasound spectroscopy (RUS), n—a non-
and data collection parameters developed specifically for a destructive examination method, which employs resonant ul-
particular part type. trasound methodology for the detection and assessment of
variations and mechanical properties of a test object. In this
3.2.3 classification, n—the labeling of a training set of parts
procedure, whereby a rigid part is caused to resonate, the
as acceptable or unacceptable or the labeling of different sets of
resonances are compared to a previously defined resonance
parts according to their manufactured, maintenance, or repair
pattern. Based on this comparison the part is judged to be either
process parameters.
acceptable or unacceptable.
3.2.4 compensation, n—the adjustment of inspection criteria
3.2.14 sort, n—a software program or data analysis method
to accommodate variation in part characteristics caused by
capable of classifying a part as uniquely different from other
manufacturing processes or environmental conditions. Com-
parts. A productionized sort could identify parts as acceptable
pensation requires the correlation of characteristics to reso-
or unacceptable.
nance responses. Examples of variations that can require
3.2.15 training set, n—a group of like parts including
compensation include part mass (caused by manufacturing
examples of known acceptable and known unacceptable com-
process variation) and part temperature during the test caused
ponents representative of the range of acceptable variability
by either process or environmental conditions, or both. Various
and unacceptable variability.
statistical tools can identify combinations of resonance patterns
that are influenced by process variations, and they can accom-
3.2.16 work instruction, n—a document with stepwise in-
modate for these differences.
structions developed for each examination program detailing
the order and application of operations for IEM examination of
3.2.5 false negative, n—part failing the sort but deemed by
a part.
other method of post-test/analysis to have acceptable or con-
forming specifications. 3.2.17 Z-score, n—a statistical analysis that describes the
position of a part’s distance from the calculated mean, when
3.2.6 false positive, n—part passing the sort but exhibiting a
measured in standard deviation units.
flaw (either inside the teaching set of flaws or possibly outside
the teaching set range of flaws) or nonconforming to specifi-
4. Significance and Use
cation.
4.1 IEM Applications and Capabilities—IEM has been suc-
3.2.7 family, n—part with supposed same geometry, size,
cessfully applied to a wide range of NDT applications in the
mass, material.
manufacture, maintenance, and repair of metallic and non-
3.2.8 Fast Fourier Transform (FFT), n—an algorithm that
metallic parts. Examples of anomalies detected are discussed in
calculates the discrete Fourier transform (DTF) of some
1.1 and 6.2. IEM has been proven to provide fast, cost-
sequence. The discrete Fourier transform is a tool to convert
effective, and accurate NDT solutions in nearly all
specific types of sequences of functions into other types of
manufacturing, maintenance, or repair modalities. Examples of
representations. Another way to explain discrete Fourier trans-
the successful application focuses include, but are not limited
form is that it transforms the structure of the cycle of a
to: sintered powder metals, castings, forgings, stampings,
waveform into sine parts.
ceramics, glass, wood, weldments, heat treatment, composites,
3.2.9 impulse excitation method, n—a resonance inspection
additive manufacturing, machined products, and brazed prod-
method that involves striking an object with a mechanical ucts.
impact causing multiple resonances to be simultaneously
4.2 General Approach and Equipment Requirements for
excited.
IEM:
3.2.10 lot, n—a quantity of parts consecutively made under
4.2.1 IEM systems are comprised of hardware and software
the same manufacturing conditions using qualitatively homog- capable of inducing vibrations, recording the component re-
enous materials, usually identified on the parts with a unique
sponse to the induced vibrations, and executing analysis of the
number/letter or combination thereof. This number may be
data collected.
referred to as a lot code, batch code, or date code depending on
4.2.2 Hardware Requirements—Examples of a tabletop im-
the manufacturer’s preference.
pact excitation system and a production-grade drop excitation
system are shown in Fig. 1 and Fig. 2, respectively. IEM
3.2.11 resonance spectra, n—the recorded collection of
systems include: an excitation device (for example, modal
resonance frequency data, representing the vibrational modes,
hammer / impact device / dropping system) providing an
including frequency peak locations and the characteristics of
impulse excitation to the object, a vibration detector (for
the peaks, for a particular part.
example., microphone), a signal amplifier, an Analog-to-
3.2.12 resonant inspection (RI), n—any induced resonant
Digital Converter (ADC), an embedded logic, and a data User
nondestructive examination method that excites mechanical
Interface (UI). Tested parts can typically be on any surface
resonances of a part for the purpose of identifying a part’s
type, but they can also be supported (for example, foam
conformity to an established acceptable pattern.
support, held with an elastic) in consideration of possible
damping influences. The following schematics show the basic
parts for an impact excitation approach (Fig. 3) and a drop
https://www.techopedia.com/definition/7167/fast-fourier-transform-fft. excitation approach (Fig. 4).
E3397 − 23
FIG. 1 IEM Tabletop Testing System Using a Non-Instrumented Impactor
4.3 Constraints and Limitations: materials, or both, may have resonance spectra that fall
4.3.1 IEM needs a change in structural integrity to properly partially or entirely outside of the frequency range of some
sort different parts. This means that parts with only cosmetic IEM systems. The physics of energy distribution from the
issues, such as a visual surface anomaly would still need be impulse and attenuation from interfering harmonic modes can
inspected with a focused visual inspection. also cause a reduction in signal-to-noise ratio at the higher end
4.3.2 The location of a flaw or specific flaw type character- of IEM frequency ranges.
ization is challenging. As IEM measures the whole-body 4.3.7 Materials that resonate poorly or dampen vibrations
response of a part, location and categorization of defects are typically not good candidates for IEM examination.
usually requires additional data (such as additional nondestruc-
5. General Practice
tive and destructive evaluation) and analysis.
4.3.3 Large raw material or process variation, or both, may 5.1 Impulse Excitation Method (IEM) is the oldest form of
limit the sensitivity of IEM without some method for compen-
resonance testing. It has been applied as nondestructive exami-
sating for those variations. nation tool for over a century to detect structural anomalies that
4.3.4 Groups of parts with a wide range of physical tem-
significantly alter part performance. Many modern improve-
peratures are not good subjects for IEM without some method ments in hardware and software have significantly increased
for compensating for those variations. Temperature affects the the method’s repeatability and sensitivity. The range of fre-
natural frequencies, so stabilization of temperature is desired quencies IEM systems can excite and record has expanded into
for parts testing. Data can be taken over a large range of the ultrasonic range, with some systems reaching close to
temperatures, as long as the parts are stable during the testing. 150 kHz. These improvements have also allowed IEM the
4.3.5 IEM is a volumetric inspection method. Sensitivity to capability of segregating parts based on fine process control
defects will be driven by the size of the defect relative to the variations. IEM has demonstrated detection of very small
size and mass of the part. For example, a small hairline crack defects and material property changes. The details of this form
of a certain length that may be detectable in a 0.5 lb part may of resonance testing are outlined in Guide E2001.
not be detectable in a 100 lb part. 5.1.1 IEM is a correlation technology using an impulse to
4.3.6 The expected useful frequency range of the part to be excite and record all of a part’s resonance frequencies. These
tested must be considered when selecting and configuring an frequencies are determined by the part’s mass, geometry, and
IEM examination. Many IEM systems are limited to detecting material properties. The resonance spectrum is then either
frequencies up to 50 kHz, but more modern systems have analyzed compared to a training set of resonance spectra for
demonstrated detection of frequencies up to 150 kHz on some known acceptable parts and unacceptable parts, statistically
parts. Parts with small dimensions or parts made from certain evaluated, or compared to modeled data. For statistical testing,
E3397 − 23
FIG. 2 Production-Grade Drop Excitation System
many methods of analysis can be used on the obtained database that is representative of the total variation range of
resonance data set. Simple individual frequency relationships,
established known acceptable and unacceptable parts is used.
complex covariance matrix relationships, and Z-score analysis
Finally, for modeled data testing, predicted resonance data is
are commonly used. For comparable training set testing, a
E3397 − 23
FIG. 3 Schematic of Impact Excitation Approach
FIG. 4 Schematic of Drop Excitation Approach
provided from a valid design model and the raw IEM reso- make a decision on the test result, and display the data. Fig. 6
nance data is compared and evaluated. shows an example of manual operation of an IEM system. Fig.
7 shows an automated IEM system feeding parts to the
5.2 Fig. 5 shows a collection of typical resonance spectra for
impactor via a conveyor.
multiple parts with resonance peaks indicated.
5.2.1 IEM Equipment typically has four main components,
5.3 Fig. 8 shows a heavy duty automatic system with an
an impactor, a measuring device, a data acquisition device/
integrated scale for part mass measurement.
analyzer, and software. The impactor and measuring device
5.4 Common test surfaces for part placement during testing
come in several different varieties. The impactor options are
(should be low-friction, anti-static). Be sure that surface chosen
typically a manual or automated “hammer” instrumented with
is appropriate to the environment (laboratory or production).
an embedded force sensor, a non-instrumented hammer, or a
5.4.1 Acetyl (or other hard plastic) test surface (should be
fixed impact surface with a load cell (for small parts). A
connected to direct earth ground);
microphone, piezoelectric transducer, accelerometer, and laser
5.4.2 Conveyor (polyurethane, plastic, other non-metallic
vibrometer are the typical measurement device options. Selec-
surfaces);
tion of the impactor and measurement device will be applica-
5.4.3 Wood;
tion driven. The data acquisition device and software work
5.4.4 Hard or soft foam;
together to collect the data from the measuring device and
impactor (if using an instrumented impactor), process the data, 5.4.5 Metallic impact surface (drop test).
FIG. 5 Typical Resonance Spectrum (0 Hz to 94 kHz)
E3397 − 23
FIG. 6 Manual Operation of IEM System for AM Part Inspection
FIG. 7 Production-Grade Automatic IEM System
5.5 The part to be tested should be positioned on the test 5.6 While IEM is a whole-body testing method, meaning
surface in a way that it is free to move after impact and has that the entire structure is excited and tested in a single
limited surface contact to minimize damping. Constricting the impulse, it is important to determine the optimal impact
movement of the part during IEM testing will typically result location on the part in order to elicit a repeatable response from
in decreased amplitude of the resonant frequencies and possi- the part across the range of frequency measurements. To find
bly affect the frequency response of the part. the optimal impact location, impact one part in multiple
E3397 − 23
FIG. 8 Heavy-Duty IEM Automatic System with Integrated Scale to Measure Part Mass
locations and compare the results. The ideal scenario of a part production testing, the impact location should be documented
being tested would be that the frequency and amplitude in the work instructions for the
...