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Eingeladener Vortrag
- nein (12)
This paper focuses on the aspect on how damage evolution processes in composite materials and structures including matrix fracture, delamination, fibre-matrix debonding, and fibre fracture can be detected by taking advantage of the material’s inherit mechanical properties. These properties can be described on the basis of non-linear mechanical phenomena measurable as an inert frequency response signal. The approach is proposed as a means for residual life structural assessment specifically in the context of VHCF.
Due to the market needs on steel for high demanding applications non-destructive methods for the determination of steel cleanliness using ultrasound have to be adapted to increase sensitivity respectively.
The basic idea is that the new standard proposal should follow the basic line outs from SEP 1927 and ASTM E588. Additional to these relatives the standard should be open to different types of specimen and inspection frequencies to cover a wide range from bars, rings and plates as well as different inspection sensitivities. For an enhance in resolution the standard draft focuses on immersion focal beam probes which should be selected according to the geometry of the specimen. The selection should be proved with the aid of simulation tools. The frequency shall be at least 10 MHz. For specimen thicknesses of less than 6 mm a frequency of at least 25 MHz shall be used.
Calibration procedures had to be improved significantly compared to the old standards to allow proper sizing of indications. Therefore calibration procedures shall take signal processing into account. For detailed evaluation of the amplitude dependency and for calibration a reference block with a sufficient number of reflectors has to be used. The recorded echo height shall be directly transferred into an equivalent disc shaped reflector EDSR by a distance amplitude curve.
The novelty in this standard draft will be that based on 3D measurements and 3D evaluation the amplitude criterion of an indication becomes just one among some other criteria. This standard takes the signal amplitude, signal amplitude distribution and signal travel time for classification into account.
The standard draft will be open to the definition of the volume to be investigated to be set by the user. This will make evaluation more comparable to other methods because the inspected area has to be user defined.
We recommend CEN/TC 138 to decide on a work item for this proposal to become an EU and an ISO standard using Vienna agreement.
The research leading to these results has received funding from the European Union's Research Fund for Coal and Steel (RFCS) research programme under grant agreement n° RFSR-CT-2013-00014.
Matrix phased array probes become more and more prominent to be used in industrial applications. The main drawbacks, using probes incorporating a very large number of transducer elements, are the needs for an appropriate cabling and an ultrasonic device offering many parallel channels.
Matrix arrays designed for extended functionality feature at least 64 or more elements. Typical arrangements are square matrices, e.g. 10 by 10 or 11 by 11 or rectangular matrices, e.g. 8 by 16 or 10 by 12 to fit a 128-channel phased array system. In some phased array systems, the number of simultaneous active elements is limited to a certain number, e.g. 32 or 64. Those setups do not allow to run the probe with all elements active which may cause a significant change in the directivity pattern of the resulting sound beam.
When only a subset of elements is possible to use during a single acquisition, different strategies may be applied to collect enough data for rebuilding the missing information from the echo signal. Omission of certain elements may be one approach, overlay of subsequent shots with different active areas may be another one.
This paper presents the influence of decreased number of active elements on the sound field and their distribution on the array. An example for 16 active elements out of 121 is given in Figure 1. The sound field divergence and its shape basically remain the same, while the sensitivity is reduced and the amplitudes of the speckle-like side lobes increase significantly.
Solutions using subsets with different element activity patterns on matrix arrays and their advantages and disadvantages concerning the sound field are evaluated using semi-analytic simulation tools. Sound field criteria regarding the consequences for NDT test results and the system setup are discussed.
Increased speed, heavier loads, altered material and modern drive system concepts result in an increasing number of flaws in railways. Caused by the rapid change in damage mechanism by modern rolling stock the appearance of the flaws also alters. Hence, interpretation of non-destructive rail testing results may become difficult. Caused by the changed interplay between detection method and flaw the recorded signals will result in an unknown type for the rail flaws type classification.
Methods for automatic rail inspection according to defect detection and classification have been developed continuously. Signal processing is a key technology to master the challenge of classification and maintain resolution and detection quality independently of operation speed.
The basic ideas of signal processing based on the Glassy-Rail-Diagram for classification purposes will be presented. Examples for the detection of damages caused by rolling contact fatigue are given. Synergetic effects of combined evaluation of diverse inspection methods are shown.
Components made of fibre-reinforced plastic are a prominently used material in modern safety-relevant structures. Periodic in-service non-destructive inspection of these structures is necesary. The EMRP-funded project VITCEA aims on the evaluation of the performance of various non-destructive testing methods on the inspection of fibre-reinforced plastics.
The physical layout of fibre layers leads to complex structures of fibre-reinforced plastic parts. Furthermore different material properties of the fibre and the resin cause anisotropic behaviour of the material.This poses a challenge for ultrasonic NDT by causing a complex acoustical response.
The acoustical behaviour of fibre-reinforced plate materials has been simulated. Specimens with artificial flaws for the evaluation of the detection thresholds have been designed and manufactured.
Mechanized ultrasonic testing methods using phased-array sensors, air-coupled transducers, immersion tank testing and contact technique have been evaluated on the specimen.
In this talk results of different ultrasonic testing methods will be compared and discussed.
A novel approach for rating fatigue-initiating inclusions in highly demanding steel (INCAFAT)
(2018)
INCAFAT project aimed to improve existing fatigue damage models by establishing the most suitable combination of measurement techniques to characterise harmful inclusion populations in highly demanding steels. The different inclusion assessments carried out confirm that, chemical composition, secondary metallurgy and manufacturing route affect content, nature, size and shape of inclusions. According to the FEM model, inclusions produce an alteration of the stress field in their surrounding region, which can promote a fatigue failure. Experimental work on fatigue testing has demonstrated that depending on the stressed direction fatigue failures in highly demanding steels could be produced by different types of inclusions. Fractography analyses confirmed that meso-inclusions harmful in fatigue cannot be rated by standard methods, nor 10 MHz ultrasonic testing (macro) or micro-cleanness assessments. The necessity of rating these meso-inclusions has led to critical evaluation of Extreme Value Analysis according to ASTM E2283-08 and the development of high frequency immersion ultrasonic testing. EVA methodology based on inclusion width can be applied reliably when principal stress is parallel to the rolling direction. On the contrary, if inclusions are testing in the elongated directions its fails. On the other hand, the guidelines and recommendations for high frequency ultrasonic testing have been compiled in a new European standard draft. This method based on focal beam probes and high-resolution devices is able to provide information on meso-inclusion distribution.
Human factors (HFs) are a frequently mentioned topic when talking about the reliability of non-destructive testing (NDT). However, probability of detection (POD), the commonly used measure of NDT reliability, only looks at the technical capability of an NDT system to detect a defect.
After several decades of research on the influence of HFs on NDT reliability, there is still no commonly accepted approach to rendering HFs visible in reliability assessment. This paper provides an overview of possible quantitative and qualitative methods for integrating HFs into the reliability assessment. It is concluded that reliability assessment is best carried out using both quantifiable and non-quantifiable approaches to HFs.
Automated Wall Thickness Evaluation for Turbine Blades Using Robot-Guided Ultrasonic Array Imaging
(2024)
Nondestructive testing has become an essential part of the maintenance of modern gas turbine blades and vanes since it provides an increase in both safety against critical failure and efficiency of operation. Targeted repairs of the blade’s airfoil require localized wall thickness information. This information, however, is hard to obtain by nondestructive testing due to the complex shapes of surfaces, cavities, and material characteristics. To address this problem, we introduce an automated nondestructive testing system that scans the part using an immersed ultrasonic array probe guided by a robot arm. For imaging, we adopt a two-step, surface-adaptive Total Focusing Method (TFM) approach.
For each test position, the TFM allows us to identify the outer surface, followed by calculating an adaptive image of the interior of the part, where the inner surface’s position and shape are obtained. To handle the large volumes of data, the surface features are automatically extracted from the TFM images using specialized image processing algorithms. Subsequently, the collection of 2D extracted surface data is merged and smoothed in 3D space to form the outer and inner surfaces, facilitating wall thickness evaluation. With this approach, representative zones on two gas turbine vanes were tested, and the reconstructed wall thickness values were evaluated via comparison with reference data from an optical scan. For the test zones on two turbine vanes, average errors ranging from 0.05 mm to 0.1 mm were identified, with a standard deviation of 0.06–0.16 mm.