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- Concrete (6)
- Stress (4)
- Beton (2)
- GPR (2)
- Impact echo (2)
- Load (2)
- Microcracking (2)
- Nondestructive evaluation (2)
- Sonic wave velocity (2)
- Ultrasonic (2)
Tunnel lining evaluation is performed in the Hanging Lake Tunnel near Glenwood Springs, Colorado, using variations of four nondestructive evaluation (NDE) methods: air- and ground-coupled ground penetrating radar (GPR), ultrasonic echo (US echo), ultrasonic tomography (UST), and impact echo (IE). Potential regions of interest are identified using high-speed air-coupled GPR and visual inspection. A robotic frame with pneumatically-operated vacuum plates was used to automate the ground-coupled GPR, US echo, and IE tests, while the UST technique was used manually. This study shows that a particular combination of NDE techniques is a powerful tool for assessing the condition of tunnel linings and can detect potential anomalies such as delamination, depth of surface cracks, reinforcement depth and layout, and lining thickness. By mapping the phase shift of the ultrasonic pulses at detected interface, the potential bonding of layer interfaces and reinforcement is assessed.
An in-depth investigation of tunnel linings is performed at Eisenhower Tunnel, 60 miles west of Denver, Colorado, using a combination of four nondestructive testing methods: air- and ground-coupled ground penetrating radar (GPR), ultrasonic echo (US echo), ultrasonic tomography (UST), and impact echo (IE). A robotic frame with pneumatically operated vacuum plates is used to automate GPR, US echo, and IE. UST was performed manually. These techniques are used to identify and locate the reinforcement mesh and structural steel ribs. Local changes in ultrasonic phase are calculated by phase analysis processing techniques and apparent relationships between positive and negative phase shifts and steel and air interfaces are observed. According to previous laboratory research, these relationships indicate the bonded state between the concrete and the embedded steel, but without ground truth verification this can only be suggested. It is shown that this combination of methods can be used synergistically to provide tunnel owners with the layout and possible condition of tunnel lining reinforcement and structural components.
Diffuse ultrasonic measurements are used to monitor progressive stress-induced damage in a number of concrete specimens. Each specimen was subjected to uniaxial compression, applied in small steps over one or several load cycles. At each step, the loading was held constant and a series of ultrasonic measurements parallel and perpendicular to the loading were obtained. The measurements were taken during both the loading and unloading phases. The time scale of the signals was chosen such that the diffuse ultrasonic regime could be recorded. Using Coda Wave Interferometry (CWI), the corresponding changes in the velocity of diffuse ultrasonic waves were monitored. The evolution of the slope of the CWI velocity-stress curve with the increased level of damage in concrete is demonstrated.
A single NDT technique is often not adequate to provide assessments about the integrity of test objects with
the required coverage or accuracy. In such situations, it is often resorted to multi-modal testing, where complementary
and overlapping information from different NDT techniques are combined for a more comprehensive evaluation. Multimodal
material and defect characterization is an interesting task which involves several diverse fields of research,
including signal and image processing, statistics and data mining. The fusion of different modalities may improve
quantitative nondestructive evaluation by effectively exploiting the augmented set of multi-sensor information about the
material. It is the redundant information in particular, whose quantification is expected to lead to increased reliability and
robustness of the inspection results. There are different systematic approaches to data fusion, each with its specific
advantages and drawbacks. In our contribution, these will be discussed in the context of nondestructive materials testing.
A practical study adopting a high-level scheme for the fusion of Eddy Current, GMR and Thermography measurements
on a reference metallic specimen with built-in grooves will be presented. Results show that fusion is able to outperform
the best single sensor regarding detection specificity, while retaining the same level of sensitivity.
Applying contemporary data fusion techniques, the multi-modal nondestructive testing (NDT) data sets can be combined to obtain more reliable results. The reliability can be quantified in terms of the probability of detection of sought material defects. A concise review of the published studies on NDT data fusion is provided here and the key concepts and anticipated challenges are discussed. The detailed steps involved in the NDT fusion process are explained with reference to a case study. The presented data set includes the results of three different NDT techniques on a test specimen with built-in defects. Several pixel-level fusion algorithms were applied and their performances are quantitatively compared.
Ultrasonic examination of anisotropic inhomogeneous austenitic welds is challenging, because of the columnar grain structure of the weld leads to beam skewing and splitting. Modeling tools play an important role in understanding the ultrasound field propagation and optimization of experimental parameters during the ultrasonic testing of austenitic welds as well as the interpretation of the test results. In this contribution, an efficient theoretical model based on the ray tracing concepts is developed to calculate the ultrasonic fields in inhomogeneous austenitic welds quantitatively. The developed model determines the ultrasound fields by taking into account the directivity of the ray source, the inhomogenity of the weld as well as ray transmission coefficients. Directivity of the ray source in columnar grained austenitic materials (including layback orientation) is obtained in three dimensions based on Lamb's reciprocity theorem. Ray energy reflection and transmission coefficients at an interface between two general columnar grained austenitic materials are calculated in three dimensions. The ray tracing model predictions on inhomogeneous austenitic weld material are compared against those from CIVA, a commercial non-destructive modeling and simulation tool. The ultrasonic modeling tools in CIVA are based on semi-analytical solutions. For beam propagation simulation, a so-called 'pencil method' is used, which involves modeling the probe as a set of individual source points, each radiating 'a bundle' of diverging rays into the medium and integrating those elementary contributions. Inhomogenity in the weld region is approximated by mapping the grain orientations on weld macrograph. Simulation results for ultrasonic field profiles for an austenitic weld are shown to be in good agreement with the corresponding experimental results.
Surface wave velocities over the sonic frequency range (<20 KHz) were measured on concrete specimens undergoing various cycles of loading and unloading. Acoustic Emission test (AE) was conducted simultaneously to monitor the microcracking activities. The sonic surface wave velocity was found to be highly stress-dependent. The observed changes in surface wavespeed are repeatable and follow a particular trend. By measuring the wave velocities in both loading and unloading phases, the effects of stress and stress-induced damages could be distinguished. The observed trend could be explained by a combination of acoustoelasticity and microcracking theories.