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Significance and Use
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 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) Investment cast steel rocker arms
(3) Cast gas turbine blades
(4) Stamped and brazed steel rocker arms
(5) Cast aluminum knuckles and control arms
(6) Cast ductile iron control arms
(7) Cast cylinder heads and cylinder blocks
(8) Sintered powder metal gears and clutch plates
(9) Machined forged steel steering racks
(10) Machined forged steel transmission gears and shafts
(11) Ceramic oxygen sensors
(12) Silicon wafers
(13) Gas turbine components
General Approach and Equipment Requirements for PCRT via Swept Sine Input:
PCRT systems are comprised of hardware and software capable of inducing vibrations, recording part 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, 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.
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, noncontacting 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, ±0.062 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.
Constraints and Limitations:
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.
Excessive process variation of parts may limit the sensitivity of PCRT. For example, mass/dimensional variations exceeding 5 % may cause PCRT to be unusable.
Specific anomaly identification is highly unlikely. PCRT is a whole body 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.
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.
While PCRT can be applied to painted and coated parts in many cases, the presence of some surface coatings such as vibrating absorbing materials and heavy oil layers may limit or preclude the application of PCRT.
While PCRT can be applied to parts over a wide range of temperatures, it can not be applied to parts that are rapidly changing temperature.
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.
1.1 This practice describes a general procedure for using the process compensated resonance testing (PCRT) via swept sine input method to identify metallic and non-metallic parts’ resonant pattern differences that can be used to indentify parts with anomalies causing deficiencies in the expected performance of the part in service. This practice is intended for use with instruments capable of exciting, measuring, recording, and analyzing multiple whole body mechanical vibration resonant frequencies within parts exhibiting acoustical ringing in the audio, or ultrasonic, resonant frequency ranges, or both. PCRT is used in the presence of manufacturing process variance to distinguish acceptable parts from those containing significant anomalies in physical characteristics expected to significantly alter the performance. Such physical characteristics 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 properties differences, residual stress, and dimensional variations.
1.2 This practice uses inch pound units as primary units. SI units are included in parentheses for reference only, and are mathematical conversions of the primary units.
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 and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E1316 Terminology for Nondestructive Examinations
E2001 Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts
ICS Number Code 17.160 (Vibrations, shock and vibration measurement)