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Publications & Standards

Read Vibrant’s publications, white papers and ASTM Standards to keep you up-to-date on the latest with PCRT.

Standard Guide for Nondestructive Examination of Metal Additively Manufactured Aerospace Parts After Build

This guide discusses the use of established and emerging nondestructive testing (NDT) procedures used to inspect metal parts made by additive manufacturing (AM). The guide focuses on parts that might be used in aerospace applications, produced by a variety of AM methods. The guide discusses NDE of parts after they have been fabricated with covered methods including computed tomography, eddy current testing , optical metrology, penetrant testing, process compensated resonance testing, radiographic testing, infrared thermography, and ultrasonic testing.

Standard Practice for Part-to-Itself Examination Using Process Compensated Resonance Testing Via Swept Sine Input for Metallic and Non-Metallic Parts

This practice covers a general procedure for using the Process Compensated Resonance Testing (PCRT) via swept sine input method to perform Part-to-Itself (PTI) examination on populations of newly manufactured and in-service parts. PTI examination serves users who may need to evaluate the effects of a single processing step or in-service load in isolation from other sources of variation. For example, a manufacturer may want to perform process monitoring and control on a heat treatment or hardening process. A maintainer may want to evaluate the effect of service cycles in an engine. A PCRT PTI examination measures the resonance frequency spectrum of a part at two points in time and calculates the change in resonance frequencies to evaluate the effect of the intervening process. Control limits can be set on the frequency change to field a PTI PASS/FAIL inspection capability. Manufacturing processes and in-service loads that can be evaluated with a PCRT PTI inspection include, but [...]

AM White Paper

This paper describes ways to apply Vibrant Process Compensated Resonance Testing (PCRT) to parts produced by Additive Manufacturing Technologies.

Validation of Model-Trained Process Compensated Resonance Testing Inspection for Creep Deformation – A Model – Assisted Probability of Detection Study

A model-assisted probability of detection (MAPOD) validation of Process Compensated Resonance Testing (PCRT) inspection for creep deformation is presented. The PCRT inspection was trained entirely with resonance data from PCRT forward models that predicted the effect of creep deformation on resonance frequencies. The MAPOD validation was conducted with a combination of physical validation specimens and modeled specimens. The modeled specimens included simulations of the effects of uncertainty inherent in the measurement of physical samples. The results validated PCRT forward modeling accuracy for creep deformation, and accurate PCRT classification of acceptable and unacceptable levels of creep.

Characterizing Polymer O-Rings Nondestructively using Resonant Ultrasound Spectroscopy

Polymer O-rings are an essential part of many designs, including mission and safety critical systems. Currently, there are no accurate destructive tests for measuring the polymer properties of O-rings (e.g. durometer), let alone nondestructive methods. As such, it is difficult to identify substandard, nonconforming, improperly processed or counterfeit O-rings. This work combines resonant ultrasound spectroscopy (RUS) with machine learning and predictive analytics to sort O-rings based on material and durometer (multinomial classification) and to accurately estimate the mass and durometer with an ultrasonic examination that takes less than 10 seconds. Results from a population including eight materials and six durometers are presented and discussed.

Nondestructive Evaluation of Additive Manufactured Parts Using Process Compensated Resonance Testing

Additive manufacturing (AM) introduces a host of new challenges for nondestructive evaluation. The effects of material state defects and variations on performance and NDE are still being understood. Legacy NDE methods are often confounded by complex geometries and as-built surface roughness common in AM components. Methods that can cope with these factors, like X-ray Computed Tomography, may be challenging to apply beyond small populations because of cost and time constraints. Process Compensated Resonance Testing (PCRT) is a volumetric inspection method that excites the resonance frequencies of a component with a swept sine input and analyzes the resonance response with advanced machine learning and statistical scoring tools. This work describes studies demonstrating PCRT methods for NDE, qualification, monitoring and control of AM processes. PCRT detection of structural defects introduced by build process deviations will be demonstrated. Follow-up characterization with [...]

Fan Blade White Paper

This paper describes ways to apply Vibrant Process Compensated Resonance Testing (PCRT) to Fan Blades to improve Quality and to Reduce Risk.

SX White Paper

This paper describes ways to apply Vibrant Process Compensated Resonance Testing (PCRT) to single crystal parts to verify grain orientation.

Validation of Process Compensated Resonance Testing (PCRT) Sorting Modules Trained with Modeled Data

Process Compensated Resonance Testing (PCRT) combines the collection of broadband resonance data with advanced pattern recognition to produce a fast, accurate, and automated non-destructive inspection for aerospace, automotive, and power generation components. To create a PCRT targeted defect inspection (Sorting Module) the resonance spectra of statistically significant populations of characterized acceptable and unacceptable parts are needed to train PCRT algorithms to recognize the frequency patterns that indicate defects in the midst of normal, acceptable material and geometry variations. In cases where a sufficient number of parts are not available, spectra from physical part populations can be supplemented with ‘virtual’ spectra generated with PCRT forward models. Previous work investigated the creation of model-trained sorting modules for the detection of creep deformation and crystal orientation for coupon and turbine blade geometries made from single crystal Ni-based [...]

Process Compensated Resonance Testing (PCRT) Inversion for Material Characterization and Digital Twin Calibration

The Digital Twin paradigm is based on the idea that a component’s serviceable life and performance can be better predicted and monitored by creating a faithful virtual counterpart of a real component, which in turn leads to improvements in end-product safety and cost. Such a model requires accurate inputs for the initial material state of the part as well as in-service loads and damage states throughout its service life. The resonance frequencies of a part correlate to a part’s material state and damage state. Similarly, changes in resonance frequencies correlate to changes in the part’s material state resulting from in-service loads and damage. Process Compensated Resonance Testing (PCRT) leverages these physical relationships to perform nondestructive evaluation (NDE) and material characterization using the measured resonance frequencies of a component. Prior work has established techniques for modeling the effects of material property variation, crystal orientation, and damage [...]

Detection of Microtexture Regions in Titanium Turbine Engine Disks using Process Compensated Resonance Testing: A Modeling Study

Titanium alloys used by the aerospace industry, like Ti-64 or Ti-6242, with Microtexture Regions (MTR’s) have been shown to exhibit significantly reduced dwell fatigue lifetimes. Over the last several decades, these titanium alloys have been used for critical components such as turbine engine disks, which are then susceptible to failure well below their expected service life. Current Nondestructive Inspection (NDE) methods are time consuming and can miss MTR’s. Process Compensated Resonance Testing (PCRT) is a fast and accurate full-body NDE method that has been proposed for the detection of MTR’s in titanium turbine engine disks. PCRT excites a part’s resonance frequencies and correlates the resonance spectrum to the part’s material and/or damage state. Turbine engine disks with MTR’s will have different resonance spectra than fully isotropic disks. Both the MTR’s geometric parameters (i.e. size, location, and orientation) and the microstructural parameters (i.e. degree of [...]

Standard Guide for Resonant Ultrasound Spectroscopy for Defect Detection in Both Metallic and Non-metallic Parts

This guide describes a procedure for detecting defects in metallic and non-metallic parts using the resonant ultrasound spectroscopy method. The procedure is intended for use with instruments capable of exciting and recording whole body resonant states within parts which exhibit acoustical or ultrasonic ringing. It is used to distinguish acceptable parts from those containing defects, such as cracks, voids, chips, density defects, tempering changes, and dimensional variations that are closely correlated with the parts’ mechanical system dynamic response.

Uncertainty Quantification of Resonant Ultrasound Spectroscopy for Material Property and Single Crystal Orientation Estimation on a Complex Part

A case study is presented evaluating uncertainty in Resonance Ultrasound Spectroscopy (RUS) inversion for a single crystal (SX) Ni-based superalloy Mar-M247 cylindrical dog-bone specimens. A number of surrogate models were developed with FEM model solutions, using different sampling schemes (regular grid, Monte Carlo sampling, Latin Hyper-cube sampling) and model approaches, N-dimensional cubic spline interpolation and Kriging. Repeated studies were used to quantify the well-posedness of the inversion problem, and the uncertainty was assessed in material property and crystallographic orientation estimates given typical geometric dimension variability in aerospace components. Surrogate model quality was found to be an important factor in inversion results when the model more closely represents the test data. One important discovery was when the model matches well with test data, a Kriging surrogate model using un-sorted Latin Hypercube sampled data performed as well as the best [...]

Part-to-Itself Model Inversion in Process Compensated Resonance Testing

Process Compensated Resonance Testing (PCRT) is a non-destructive evaluation (NDE) method involving the collection and analysis of a part’s resonance spectrum to characterize its material or damage state. Prior work used the finite element method (FEM) to develop forward modeling and model inversion techniques. In many cases, the inversion problem can become confounded by multiple parameters having similar effects on a part’s resonance frequencies. To reduce the influence of confounding parameters and isolate the change in a part (e.g. creep), a part-to-itself (PTI) approach can be taken. A PTI approach involves inverting only the change in resonance frequencies from the before and after states of a part. This approach reduces the possible inversion parameters to only those which change in response to in-service loads and damage mechanisms. To evaluate the effectiveness of using a PTI inversion approach, creep strain and material properties were estimated in virtual and real [...]

Process Compensated Resonance Testing Modeling for Damage Evolution and Uncertainty Quantification

Process Compensated Resonance Testing (PCRT) is a nondestructive evaluation (NDE) method based on the fundamentals of Resonant Ultrasound Spectroscopy (RUS). PCRT is used for material characterization, defect detection, process control and life monitoring of critical gas turbine engine and aircraft components. Forward modeling and model inversion for PCRT have the potential to greatly increase the method’s material characterization capability while reducing its dependence on compiling a large population of physical resonance measurements. This paper presents progress on forward modeling studies for damage mechanisms and defects in common to structural materials for gas turbine engines. Finite element method (FEM) models of single crystal (SX) Ni-based superalloy Mar-M247 dog bones and Ti-6Al-4V cylindrical bars were created, and FEM modal analyses calculated the resonance frequencies for the samples in their baseline condition. Then the frequency effects of superalloy creep [...]

Process Compensated Resonance Testing Models for Quantification of Creep Damage in Single Crystal Nickel-Based Superalloys

Process compensated resonant testing (PCRT) is a full body nondestructive evaluation (NDE) method that measures the resonance frequencies of a part and correlates them to the part’s material state, structural integrity, or damage state. This paper describes the quantification of creep damage in a virtual part population via the correlation of PCRT parameters to creep strain using inversion methods and vibrational pattern recognition (VIPR) analysis. Modeled populations were created using the finite element method (FEM) for single crystal (SX) nickel-based superalloy dogbone and turbine engine airfoil geometries. The modeled populations include nominal variation in crystallographic orientation, geometric dimensions, and material properties. Modeled populations also include parts with variable levels of creep strain, allowing for NDE sensitivity studies. FEM model inversion tools quantified creep strain and distinguished it from other variations in the part populations. Resonant [...]

Detection and Quantification of Creep Strain Using Process Compensated Resonance Testing (PCRT) Sorting Modules Trained with Modeled Resonance Spectra

Process Compensated Resonant Testing (PCRT) is a full-body nondestructive testing (NDT) method that measures the resonance frequencies of a part and correlates them to the part’s material and/or damage state. PCRT testing is used in the automotive, aerospace, and power generation industries via automated PASS/FAIL inspections to distinguish parts with nominal process variation from those with the defect(s) of interest. Traditional PCRT tests are created through the statistical analysis of populations of “good” and “bad” parts. However, gathering a statistically significant number of parts can be costly and time-consuming, and the availability of defective parts may be limited. This work uses virtual databases of good and bad parts to create two targeted PCRT inspections for single crystal (SX) nickel-based superalloy turbine blades. Using finite element (FE) models, populations were modeled to include variations in geometric dimensions, material properties, crystallographic [...]

NDT Technology Readiness A P&WC Cast Study

Presentation by Pratt & Whitney Canada to A4A NDT Forum describing a P&WC Case Study for application of PCRT. "P&WC was able to rapidly implement a PCRT inspection process that met the expectation of the various aviation regulatory bodies thus allowing the fleet to continue flying"

Standard Practice for Outlier Screening Using Process Compensated Resonance Testing via Swept Sine Input for Metallic and Non-Metallic Parts

This practice describes a general procedure for using the process compensated resonance testing (PCRT) via swept sine input method to perform outlier screening on populations of newly manufactured and in-service parts. PCRT excites the resonance frequencies of metallic and non-metallic test components using a swept sine wave input over a set frequency range. Some applications experience isolated component failures with unknown causes or causes that propagate from defects that are beyond the sensitivity of the current required inspections, or both. PCRT frequency analysis compares the resonance pattern of a component to the pattern of a known acceptable population of the same component, and fails components that are outliers from the reference population. Resonance outlier components may have material states or defects, or both, that will cause performance deficiencies. These material states and defects include, but are not limited to, cracks, voids, porosity, shrink, inclusions, [...]

Resonance Ultrasound Spectroscopy Forward Modeling and Inverse Characterization of Nickel-based Superalloys

The objective of this paper is to investigate Resonance Ultrasound Spectroscopy (RUS) measurement models to more precisely connect changes in the resonance frequencies of nickel-based super-alloy material to the macro/microscopic state. RUS models using analytical solutions and the finite element method (FEM) were developed to address varying elastic properties, grain structures and creep. Experimental studies were performed investigating the effect of exposure to high temperatures and stress for varying part shape and three grain structure classes: single crystals, directionally-solidified and polycrystalline structures. Inversion using both traditional analytical models was enhanced in order to simultaneously estimate varying material properties and changes in part geometry due to creep. Inversion using surrogate models from FEM simulations was also developed, addressing varying crystal orientation and complex geometries. Results are presented comparing the forward model trends [...]

Uncertainty Quantification in Modeling and Measuring Components with Resonant Ultrasound Spectroscopy

This report presents the motivation, background, methods and results of a Phase II Small Business Innovation Research (SBIR) project that continued the development and application of an uncertainty quantification (UQ) process for models and measurements made with Process Compensated Resonance Testing (PCRT). Resonant Ultrasound Spectroscopy (RUS) is a nondestructive evaluation (NDE) method which can be used for material characterization, defect detection, process control and life monitoring for critical components in gas turbine engines, aircraft and other systems. Accurate forward and inverse modeling for RUS requires a proper accounting of the propagation of uncertainty due to the model and measurement sources. A process for quantifying the propagation of uncertainty to RUS frequency results for models and measurements was developed. Epistemic and aleatory sources of uncertainty were identified for forward model parameters, forward model material property and geometry inputs, [...]

Standard Practice for Process Compensated Resonance Testing Via Swept Sine Input for Metallic and Non-Metallic Parts

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 differences can be used to distinguish acceptable parts with normal process variation from parts with 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.

Delta TechOps Customer Cast Study

PCRT helped Delta reduce failures and unscheduled engine removals while reducing costs and salvaging thousands of previously rejected blades.

Process Compensated Resonance Testing – Whole Body and Surface NDT for Ceramic Balls

Ceramic material advancements have produced many new components to meet the needs of the growing technology requirements. Traditional NDT methods (UT, ET, RT, and PT) often provide incomplete results when used to inspect these components, leading to multiple costly and time consuming inspections. Process Compensated Resonant Testing (PCRT) has been demonstrated as an excellent alternative for inspecting ceramic parts that cannot be inspected with traditional NDT. PCRT goes beyond traditional resonance testing by applying pattern recognition algorithms and process control statistics to precise resonant data. PCRT is a trained method that learns which resonance variation is acceptable, and which is unacceptable, while also monitoring in-control processes. PCRT is used for studying structural integrity and functional performance in a variety of ceramic parts including ceramic balls, seal rings, and armor plates. PCRT is a whole body inspection that detects internal defects such as [...]

A More Comprehensive NDE: PCRT for Ceramic Components

Ceramic material advancements have produced many new components to meet the needs of the growing technology requirements. Traditional NDT methods (UT, ET, RT, and PT) often provide incomplete results when used to inspect these components, leading to multiple costly and time consuming inspections. Process Compensated Resonant Testing (PCRT) has been demonstrated as an excellent alternative for inspecting ceramic parts that cannot be inspected with traditional NDT. PCRT goes beyond traditional resonance testing by applying pattern recognition algorithms and process control statistics to precise resonant data. PCRT is a trained method that learns which resonance variation is acceptable, and which is unacceptable, while also monitoring in-control processes. PCRT is used for studying structural integrity and functional performance in a variety of ceramic parts including ceramic balls, seal rings, and armor plates. PCRT is a whole body inspection that detects internal defects such as [...]

Nondestructive Evaluation of Hybrid Bearing Ceramic Rollers Using Process Compensated Resonant Testing (PCRT)

We have used Process Compensated Resonant Testing (PCRT) for studying structural integrity and functional performance of ceramic balls used in various auxiliary power units (APUs), propulsion engines, and defense and space missiles. The results show that PCRT is successful in sorting acceptable parts from parts with defects such as micro-structural changes, C-cracks, and scuffs. However, PCRT suffers from limitations, generally not determining the type, size or location of the anomaly. The pursuit of improvements to PCRT is an on-going process.

Modern NDT for Aging Aircraft

This technical paper covers the background of the PCRT technology and capabilities as it relates to specific applications for aerospace components. Highlighted are specific details for the application and validation of PCRT for in service testing of JT8D 1st stage high pressure turbine (HPT) blades to improve engine reliability. Experimental information pertaining to high temperature exposure and fatigue are also included. Additional information, related to defect detection in the CF6-80A 1st stage HPT blade and ceramic rolling elements used in hybrid bearings, is included as well.

Process Compensated Resonance Testing JT8D-219 1st Stage Bladea

The JT8D 1st stage turbine blade has had in-service challenges for some time. This has primarily been attributed to multiple failure mechanisms, which often intertwine to produce unscheduled engine removals, in-flight shut downs, and failures. The main contributors are intergranular attack, overtemps, thin walls, core shifts and cracking. Since most inspection techniques only detect cracking, or measure dimensions (thin wall), a significant number of “bad” blades were still escaping the inspection process. Delta engineering desired a better inspection technique to determine the serviceability of each of these conditions. PCRT provided a quick, easy method for determining the structural acceptability of the blade allowing Delta to reject only blades with defects, avoiding the costly wholesale blade replacement with new parts. This resulted in significant savings by not throwing away “good” parts, and will likely increase reliability of the JT8D engine by removing the “bad” blades.

Patents

  • U.S. Patent 10481104, 10718723 for Utilizing RI of in-service parts
  • U.S. Patent 9157788, 10067094 for Part evaluation system/method using both resonances and surface vibration data
  • U.S. Patent 8903675 for Acoustic system and method for NDT of a part through frequency sweeps
  • U.S. Patent 9228981 for Resonance Inspection-based surface defect system/method
  • U.S. Patent 9335300 for SAW mode-based surface defect method
  • U.S. Patent 9927403 for Resonance inspection sorting module array
  • U.S. Patent 10295510 for Part evaluation based upon system natural frequency
  • U.S. Patent 9074927 for Methods for non-destructively evaluating a joined component
  • U.S. Patent 9228980 for Non-destructive evaluation methods for aerospace components
  • U.S. Patent 10746704 for PCRT for process control

ASTM Standards

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