Pulse-echo Inspection Research Articles

Effects of Porosity on CFRP Repair Performance with Aerospace Applications

On-site repairs of carbon fiber reinforced polymer composites, wet layup repairs with heat blanket method play a critical and practical role for the composite defects that occur in production and assembly. The porosity level should be controlled for the repair parts with heat blanket method since the pressure value, which enables ply consolidation, reduce the risk of delamination in the composite layers, is less or zero with the wet layup repaired parts with heat blanket compared to repair parts with autoclave pressure.
 In this experimental study, an investigation was conducted regarding the tensile strength change of prepreg structures using wet lay-up repair techniques with heat blanket based on the porosity, with a specific focus on stepped-repaired carbon fiber reinforced polymer laminates.
 This work aims to understand the strength and the associated failure mechanisms of on-site repaired woven carbon fiber reinforced polymer laminates through experiments. The Automatic Ultrasonic Pulse Echo Inspection Method was utilized to see whether porosity level of each repaired samples is within allowable design limits for this purpose. Prepreg structure's repairs using wet lay-up produced according to standardized aerospace procedures were tested under uniaxial tension per ASTM 3039D. The relationship between attenuation difference (ΔdB) and tensile fracture values has been explored, with a focus on investigating the associated failure mechanisms. Initially, a 60% strength recovery was observed for repairs with an 8-decibel difference. However, as the decibel difference increased, the strength recovery gradually decreased, ultimately reaching 45.2%.

Design for Inspectability: A Framework to Increase Inspectability of Additive Manufacturing Parts for Pulse-Echo Ultrasonic Inspection Methods

Abstract Additive manufacturing (AM) is used to produce load-bearing, safety-critical components in industries like aerospace, automotive, and medical devices. Designers can create AM components with complex internal features, organic topologies, and lattice structures to reduce part mass or part count. However, such complex features can make designs difficult or impossible to inspect using mature nondestructive testing (NDT) methods. Professional organizations suggest designers keep quality assurance and quality control (QA/QC) in mind early in the design process. The Design for Inspectability (DfI) framework is suggested as a way of meeting the need for early-stage QA/QC considerations. This work presents a case study, where a group of designers considered one type of NDT, known as Pulse-Echo Ultrasonic (PEU) testing. Using heuristics derived from relevant literature, designers were able to create designs with increased inspectability. This improved inspectability came at the cost of other design objectives, however, such as strength and mass. This implies that certain design objectives may be inversely related to increased inspectability, raising significant concerns for the field. This work marks the first step toward mapping out the trade-offs between inspection and performance objectives.

Comparative study of ultrasonic techniques for reconstructing the multilayer structure of composites

The multilayer structure of fiber-reinforced polymers may be extracted by ultrasonic pulse-echo inspection. Depending on the employed ultrasonic frequency and subsequent processing methodology, different depth resolution and dynamic depth range can be achieved. This study compares the performance of different ultrasonic pulse-echo approaches for extracting the ply-by-ply structure of multilayered composites. The following methodologies are studied: Method 1: 50 MHz, 15 MHz, and 5 MHz ultrasound with low-pass filtering using analysis of the instantaneous amplitude, Method 2: 15 MHz ultrasound with Wiener deconvolution (and autoregressive spectral extrapolation) using analysis of the instantaneous amplitude, and Method 3: 5 MHz ultrasound with low-pass or log-Gabor filtering using analysis of the instantaneous phase. In the simulation study, the performance of the various techniques is investigated on synthetic data representative for a 24-ply carbon fiber reinforced polymer. The robustness of the techniques is evaluated for different signal-to-noise ratios. The various techniques are further investigated on experimental data of a 24-ply cross-ply carbon fiber reinforced polymer. The ply-by-ply structure is extracted and presented in the form of both B-scan and C-scan images. The thickness of each ply is estimated for quantitative analysis. The obtained results indicate that the 5 MHz ultrasound coupled to analytic-signal analysis with log-Gabor filter shows the best performance for reconstructing the multilayer structure of the studied composites.

Robotic laser sensing and laser mirror excitation for pulse-echo scanning inspection of fixed composite structures with non-planar geometries

This paper proposes a system for a laser ultrasonic inspection of fixed non-planar composite structures. A pulse-echo configuration is used by which both the sensing and excitation lasers hit the same point on the structure, utilizing bulk waves for a through-the-thickness defect evaluation. A high signal-to-noise ratio is ensured by mounting a laser Doppler vibrometer (LDV), used as the sensing laser, on a 6 degree-of-freedom robot arm, thus allowing the correct distance and angle of the laser incident on the inspected structure to be maintained throughout the scan. The excitation laser is steered separately through a laser mirror scanner (LMS) to keep the robot payload sufficiently low, allowing the use of a lightweight portable robot arm. This robot arm can be mounted on a moveable platform suitable for in-situ inspections. An RGB-D camera is used for imaging the structure in front of the system, and a scan area with the required size can be delimited on the image produced by the camera. A scan path for the robot arm and laser mirror scanner is automatically generated by keeping the shape and distance of the structure within the delimited scan area. A graphical user interface allows the control of all individual blocks and contains the necessary algorithms for image capture of a specimen, geometry calculations, scan-path generation, signal acquisition, signal processing, and display of the results. This is a multithreaded software, ensuring a fast calculation of the structural geometry and scan path prior to the inspection and real-time updating of the results during the inspection. Composite specimens consisting of radial and conic sections with subsurface defects were inspected using the system. The test results show that the system is extremely reliable in detecting defects, particularly in the non-planar parts of the specimen.

Estimating the True Sensitivity of Acceptance Ultrasonic Inspection of Rails

The acoustic path has been analyzed when carrying out the acceptance pulse echo inspection of the rail head. The influence of the parameters of the employed piezoelectric transducers on the sensitivity distribution for the sounding circuit used in the existing installations has been assessed, and the true sensitivity of detecting “nonmetallic inclusion” type flaws has been evaluated.

Guest Editorial: Non‐Destructive Testing

Guest Editorial: Non‐Destructive Testing

Robotic scanning technology for laser pulse‐echo inspection

The full-field pulse-echo ultrasonic propagation imaging (PE UPI) system using a two-axis linear stage has been successfully used to perform a non-destructive evaluation of flat specimens. This study used a six-axis robot arm to develop a robotic scanning algorithm that can be applied to the laser pulse-echo inspection of non-flat objects. The robotic PE UPI system was constructed and verified for both flat and curved specimens. The internal structures and defects of a honeycomb sandwich plate and a glass-fibre-reinforced polymer specimen were visualised by the robotic PE UPI system. The quality of the evaluation of the flat specimen was equivalent to that of a two-axis linear system, and the result of the curved specimen showed improvement compared to that of the linear system. The ability of the robotic scanning technique to evaluate the structural health performance of arbitrarily shaped surfaces was validated.

ОСОБЕННОСТИ УЛЬТРАЗВУКОВОГО КОНТРОЛЯ МОНОЛИТНЫХ ОБРАЗЦОВ ИЗ УГЛЕПЛАСТИКА В ПРОЦЕССЕ ПРОВЕДЕНИЯ ИСПЫТАНИЙ НА МАЛОЦИКЛОВУЮ УСТАЛОСТЬ

The results of CFRP samples ultrasonic inspection during low-cyclic fatigue testing are given in this article. It is established that for ultrasonic pulse-echo inspection during cycling mechanical testing and after the special correction of flaw detector’s gain and inspection’s sensitivity concerning back-wall echo decreasing in compare with testing specimen is necessary.

Using the arduino platform in development of an infrared pulse-echo inspection method

Using the arduino platform in development of an infrared pulse-echo inspection method

Improvement of pulse-echo harmonic generation from a traction-free boundary through phase shift of a dual element transducer

The practical implementation of nonlinear ultrasonic technique has been limited to the through-transmission setup for measuring the second harmonic component induced by the nonlinearity or microstructural changes of test material. A more practical technique such as the pulse-echo testing has been ruled out because a traction-free reflecting boundary destructively alters the nonlinear generation process. A focusing acoustic beam or rigid boundary condition was often employed for biomedical imaging and fluid nonlinearity in the pulse-echo inspection. In this article, we further explore a more general and efficient method to improve the generation of the second harmonic component in the pulse-echo mode with traction-free surface. A dual element planar transdcer with optimal phase shift of the input signal in one element relative to another is proposed for this purpose. The validity of the phase shift concept is confirmed by comparing the enhanced generation of second harmonic amplitudes and the resulting nonlinear parameters with the rigid-boundary case equivalent to the conventional through-transmission setup.

Ply-orientation measurements in composites using structure-tensor analysis of volumetric ultrasonic data

Ply wrinkling in carbon fibre reinforced polymer (CFRP) laminates is often geometrically complex and difficult to quantify using non-destructive techniques. In this paper, an ultrasonic technique for mapping ply wrinkling is presented. The instantaneous-phase three-dimensional dataset obtained from a pulse-echo ultrasonic inspection is processed using the structure-tensor image processing technique to quantify the orientations of the internal plies of a CFRP laminate. It is shown that consideration must be given to the wrapped nature of the phase dataset during processing to obtain accurate orientation maps. Three dimensional ply orientation and ply-location maps obtained from a test coupon are compared with true ply angles and locations by overlaying the ultrasonically-derived results on X-ray CT image slices, showing that accurate orientation maps can be obtained using the proposed technique.

Development of airframe design elements control technique under operational conditions

The paper proposes to use a method of infrared pulse-echo inspection to control airframe designelements, made of polymeric composite materials under operators` conditions. The following is described:skeleton operation diagram of the given method, device structure and results of the preliminary researchesconfirming operation capacity of the method offered

Multi-defect tomographic imaging with a variable shape factor for the RAPID algorithm

Guided wave inspection technique is a well-known large-area inspection method for industrial applications. However, guided wave inspection signals are hard to analyze due to mode complexity. Guided wave tomography is one of the solutions for wave signal interpretation. Guided wave tomography methods are an alternative for online nondestructive inspection and structural health monitoring. In this paper, RAPID (Reconstruction Algorithm for the Probabilistic Inspection of Damage) is applied to visualize guided wave defect signals in plate-like structures. Guided wave signal visualization is complicated by multi-defect complexity. To overcome the lack of sufficient guidelines for the shape factor β, a variable shape factor was applied. A guided wave pulse-echo inspection method is performed to find multiple defects. The results of this experiment show good agreement with real defects and images.

In-line ultrasonic monitoring for sediments stuck on inner wall of a polyvinyl chloride pipe.

This research verified the applicability and effectiveness of the ultrasonic monitoring of sediments stuck on the inner wall of polyvinyl chloride (PVC) pipes. For identifying the transmittance of acoustic energy and the speed of sound in the PVC material, the pulse-echo ultrasonic testing was conducted for PVC sheets of different thicknesses. To simulate the solidified sediment, the hot melt adhesive (HMA) was covered on the inner wall of the PVC pipe in different heights. From the experiment, the speeds of sound in the PVC and the HMA materials were obtained as about 2258 and 2000 m/s, respectively. The thickness of the materials was calculated through the signal processing such as taking the absolute value and low pass filtering, the echo detection, and the measurement of the time of flight. The errors between actual and measured thicknesses of PVC sheets were below 5%. In the case of the substance stuck on the inner wall, the errors were below 2.5%. Since the pulse-echo ultrasonic inspection is available on the outer surface and its measurement accuracy was over 95%, it can be an efficient and effective in-service structural health monitoring for the sediment on the wall of PVC pipes.

Finite Element Simulations to Predict Probability of Detection (PoD) Curves for Ultrasonic Inspection of Nuclear Components

Abstract Nondestructive evaluation (NDE) methods for the qualification of structures in the nuclear industry are required to perform to very high standards of reliability, and hence, establishing the performance capabilities of inspection techniques is of utmost importance. The Probability of Detection (PoD) curve method has emerged as an important tool for the assessment of the performance of NDE techniques, in general. However, the conventional experimental means of generating PoD curves is very expensive, requiring large experimental data sets covering different defects as well as a range of test conditions, plant shut-down and also operator time. Several methods of achieving faster estimates for PoD curves using physics-based modelling have emerged to address this problem. However, most theoretical models remain limited to a small number of materials or defect types: thus numerical modelling techniques are very attractive, especially given the ever increasing computational power available to scientists today. This paper reports the feasibility of using Finite Element (FE) simulations to augment sparse measurements made using experiments, and predict PoD curves for ultrasonic inspection of stainless steel plates and welds. PoD curves are obtained for the case of conventional (bulk P and SV wave) ultrasonic pulse-echo inspection of surface-breaking longitudinal notches in Stainless Steel plates. The main parameters affecting the uncertainty in practical ultrasonic inspection are identified and combinations are achieved, assuming each of them varies according to a normal distribution. FE simulations are performed for each combination of parameters, viz. frequencies, wedge angles, notch dimensions, and the amplitudes of scattered UT signals so predicted are used to generate the PoD curves. The results are compared against trial experimental measurements. Approach towards generating the POD curves for ultrasonic inspection of thick austenitic stainless steel welds will be discussed.

Ultrasonic arrays for quantitative nondestructive testing an engineering approach

The Ultrasonic Pulse-Echo inspection method is extremely capable of detecting cracks that limit the structural integrity of loaded technical components and systems. However, the applied principles of ultrasonic material testing do not in general allow the characterization of flaws and the required measurement of crack dimensions. Appropriate wave field data sampling at the scanned surface with the subsequent field reconstruction improves both the resolution and the contrast sensitivity of inspection results. We use arrays with elements adapted for the inspection task with an optimized arrangement and element apertures of point source character. First results have been received applying linear arrays that are promising for the quantitative assessment of flaws by high-resolved high contrast imaging of inspection results in real-time.

Characterization of Welded Components Flaws Using an Ultrasonic Expert System Based on Static Patterns

Ultrasonic testing of welds is a nondestructive evaluation method in which high-frequency sound waves are introduced into materials for the detection of imperfections or flaws in the material. These sound waves travel through the material and are reflected at interfaces such as surface boundaries, grain boundaries, cracks, and pores. The reflected acoustic energy is converted to electrical signals that are recorded and analyzed to determine the presence and location of flaws or discontinuities. The objective of this study is to present an expert system according to static patterns in pulse-echo inspection. It determines numbers, locations and types of weld defects based on DIN EN 1713. This paper gives a brief outline of how the expert system algorithm operates to identify a number of defect scenarios. Since the proposed algorithm is verified by experiments, it allows the user to automatically address and interpret any defects.

Estimation the mean correlation length of metals by using mode-converted diffuse ultrasonic backscatter model

Diffuse ultrasonic backscatter measurements can explain the phenomenon of the scattering at interfaces in heterogeneous materials. The theoretical models of diffuse ultrasonic backscatter for longitudinal (L-L) and shear (T-T) wave scattering within polycrystalline materials have recently been developed. A mean correlation length of metals is successfully calculated from the L-L model at normal incidence in a pulse-echo inspection. Above the first critical angle, mode-conversion scattering occurs when the longitudinal waves are converted to shear waves (L-T) at material grain boundaries. With a similar formalism, a mode-conversion scattering (L-T) model is presented to describe this process. The model is then to fit the experimental response for a pitch-catch transducer configuration and the correlation length is extracted by modifying the beam function. The mean correlation length from the L-T model is in agreement with both the L-L model and the results obtained from optical micrographs. This presentation outlines the theoretical framework and the method to extract the mean correlation length. Mode-converted backscatter removes the influence of the front-wall reflection and may lead to improvements in microstructural characterization and material property evaluation. [Research supported by FRA.]

Ultrasonic Non-destructive Evaluation of Titanium Diffusion Bonds

Diffusion bonds offer several advantages over alternative welding methods, including the ability to produce near-net shapes and achieve almost parent metal strength. However, voids remnant from the joining process can be tens of microns in their lateral dimension, making them difficult to detect with conventional pulse-echo immersion inspection at any significant metal depth. In titanium the inspection is particularly challenging; the anisotropic microstructure is highly scattering and the diffusion bond itself forms an interface between regions of preferred crystallographic orientation (macrozones), which can act as a weak spatially coherent reflector. A simple interfacial spring model predicts that, for partial bonds (sub-wavelength voids distributed on the bond line) and at certain frequencies, the phase of the signal can be used to separate the component of the signal due to the change in texture at the interface and the component due to the flaw. Here it is shown that the phase of the signal from an interface is also affected by the anisotropic microtexture of Ti–6Al–4V. Good separation between well-bonded and partially bonded samples was achieved using a symmetric inspection, where the magnitude and phase of the reflection coefficient were calculated for normal incidence from opposite sides of the diffusion bond.

Sparsity enhancement for blind deconvolution of ultrasonic signals in nondestructive testing application

The received signal in ultrasonic pulse-echo inspection can be modeled as a convolution between an impulse response and the reflection sequence, which is the impulse characteristic of the inspected object. Deconvolution aims at approximately inverting this process to improve the time resolution so that the overlap between echoes from closely spaced reflectors becomes small. This paper presents a modified minimum entropy blind deconvolution algorithm for deconvolving ultrasonic signals. Enhancement of the resolution is achieved by using the presented method. In addition, the presented approach will, in many cases, lead to a faster computation. A nonlinear function is the key point to the efficiency of the modified blind deconvolution algorithm, which is used to increase the sparsity of the iteration output and to decrease the influence of the added noise by replacing each iteration output by output of the nonlinear function. Simulations showed the efficiency of the modification as compared with minimum entropy deconvolution when deconvolving synthetic ultrasonic signals. Experimental results using real ultrasonic data evaluated further that the exact solution consistently yields good performance. The thickness of a thin steel sample can be calculated by the modified blind deconvolution filter with a reasonable accuracy.