Crack Depth Determination Research Articles

Asset Assessment of Concrete Structure

Infrastructures which were constructed in the last century are approaching or have exceeded their design life. It is essential to maintain, repair and rehabilitate existing structures to ensure safety and develop a sensible rehabilitation plan. This paper suggests an inspection program for the condition evaluation of existing structures, particularly for structures that are approaching or exceeding their design/campaign lives. Cracking on concrete bridges is often induced by static and cyclic temperature loading. Throughout the service life of the structure, cracks will initiate, propagate, coalesce and form a greater damaged zone. Depending on the location and severity of the crack network; corrosion of reinforcement, debonding between concrete and reinforcement, and spalling of concrete may occur. The implementation of regular inspection or monitoring of structural condition is an essential component of asset management. Early detection of damaged zones can ease scheduling and reduce the cost of repair, which in turn also allows extension of structural lifespan without compromising safety. Similarly, for industrial properties, asset management and rehabilitation programs are paramount as they can significantly reduce capital expenditures in asset maintenance, if implemented prior to or at the early onset of structural degradation. This paper illustrates the use of NDT techniques for the condition assessment of a prestressed concrete bridge, as well as concrete storage silos. Both of which were either approaching or have exceeded their design campaign life and were needing a proper rehabilitation plan. The assessment included crack movement monitoring, crack depth determination, concrete strength estimation, and the detection of debonding between rebar and concrete.

Detection and Characterization of Fatigue Cracks in Butt Welds of Offshore Structures Using the Eddy Current Method

Abstract A reliable assessment of the actual condition of wind turbines is essential for their continuous operation, or if an extension of their service life is considered. To be able to make valid statements about the condition of the welded structure, an inspection concept for the reliable detection of fatigue cracks and damage on welds of the offshore tower and foundation structures is essential. In the present study, five different eddy current differential sensors were evaluated on cyclically fatigued DY butt welds under tensile load with a focus on the signal-to-noise ratio (SNR). Based on previous evaluations, two sensors were selected for semi-automatic weld testing. It is shown that due to the weld crossing necessary for the detection of fatigue cracks, air coils arranged parallel to the test surface have the highest SNR. This must be contrasted with the potential for crack depth determination. In this context, coils with different arrangements with respect to the test surface were analyzed. It is shown that groove depths can be differentiated based on the imaginary part of the measurement signal for groove depths of up to 8 mm, and actual fatigue cracks in welds with a crack depth of 0.5 mm were detected.

Depth quantification of rolling contact fatigue crack using skewness of eddy current pulsed thermography in stationary and scanning modes

Eddy current pulsed thermography (ECPT) has been used in the characterization of Rolling Contact Fatigue (RCF) cracks in rail by taking advantage of electromagnetic thermal execution. However, quantitative estimation of depths of RCF defects remains challenging due to volume eddy current heating and lateral thermal diffusion under the stationary and scanning inspections. This work proposes math-physic modelling of skewness to quantitatively characterize crack depth in a rail sample. In particular, a physical model linked instrument describing the accumulation of Joule heating via eddy current accompanied by heat diffusion and mathematical skewness has been established. A comparison between the accuracy of crack depth determination in stationary and scanning modes was carried out in terms of the thermal response and skewness. Moreover, the effects of crack types on depth quantification have been analyzed. The comparative experimental results indicated that the skewness under stationary conditions is more robust against the noise, and this has verified the efficiency for quantifying RCF cracks in stationary and scanning modes.

Delamination in Wood, Wood Products and Wood-Based Composites

<i>Delamination in Wood, Wood Products and Wood-Based Composites</i>

Characterization of surface crack depth and repair evaluation using Rayleigh waves

The issues of surface crack depth determination and the evaluation of repair effectiveness are not trivial for concrete engineers. In the present paper, surface waves are applied on concrete blocks with artificial slots to correlate wave parameters with crack depth. To simulate crack repair with an injected material, epoxy is applied to the slots in the laboratory and quantification of the filling percentage is attempted. Simultaneously, a frequency domain boundary element method is employed for the numerical simulation of transient pulses interacting with surface breaking cracks. Experimental results compare well with the numerical ones, showing that the repair effectiveness, which so far can be evaluated only by destructive techniques , is possible by simple surface wave measurements.

Depth Measurement of Surface-Breaking Cracks Using Point-Source/Point-Receiver Acoustic Transducer

ABSTRACTA newly developed point-source/point-receiver (PS/PR) acoustic transducer is used for measuring the depth of surface-breaking cracks. The transducer consists of two miniature conical PZT elements which form a transmitter/receiver pair for generating and detecting surface waves. A tone-burst measurement system operates the PS/PR transducer at a fixed frequency. When a surface-breaking crack is present in between the transmitter and receiver, the change in time-of-flight of surface wave propagation caused by the crack is measured and used to estimate the crack depth. To verify the feasibility of this method, machined slots on a carbon steel sample are tested by the PS/PR transducer for crack depth determination. Good experimental results are obtained. Future applications and improvements on the PS/PR transducer system are addressed.

Application of Surface Wave Transmission Measurements for Crack Depth Determination in Concrete

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Crack depth determination. A modern technique of an established method (In German: English abstract) : Deutsch, V.; Ettel, P.; Platte, M.; Cost, H. Materialprufung, Vol. 38, No. 7–8, pp. 306–310 (Jul.–Aug. 1996)

Crack depth determination. A modern technique of an established method (In German: English abstract) : Deutsch, V.; Ettel, P.; Platte, M.; Cost, H. Materialprufung, Vol. 38, No. 7–8, pp. 306–310 (Jul.–Aug. 1996)

Crack-depth determination by a neutral network with a synthetic training data set. : Takadoya, M.; Notake, M.; Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L; Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19–24 Jul. 1992. Vol. 12A, pp. 803–810. Edited by D.O. Thompson and D.E. Chimenti, Plenum Press (1993). ISBN 0-306-44483-6

Crack-depth determination by a neutral network with a synthetic training data set. : Takadoya, M.; Notake, M.; Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L; Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 19–24 Jul. 1992. Vol. 12A, pp. 803–810. Edited by D.O. Thompson and D.E. Chimenti, Plenum Press (1993). ISBN 0-306-44483-6

Neural network for crack-depth determination from ultrasonic backscattering data : Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L.; Notake, M.; Takadoya, M. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United Stares), 28 Jul. – 2 Aug. 1991. Vol. 11A, pp. 701 708. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

Neural network for crack-depth determination from ultrasonic backscattering data : Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L.; Notake, M.; Takadoya, M. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United Stares), 28 Jul. – 2 Aug. 1991. Vol. 11A, pp. 701 708. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

Neural network for crack-depth determination from ultrasonic backscattering data: 51392 Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L.; Notake, M.; Takadoya, M. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul.–2 Aug. 1991. Vol. 11A, pp. 701 708. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

Neural network for crack-depth determination from ultrasonic backscattering data: 51392 Kitahara, M.; Achenbach, J.D.; Guo, Q.C.; Peterson, M.L.; Notake, M.; Takadoya, M. Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul.–2 Aug. 1991. Vol. 11A, pp. 701 708. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992)

Nondestructive inspection of nozzle inner corner at boiling water reactor pressure vessels with ultrasound-flaw detection and crack depth determination

Abstract The demonstration of inservice inspection methods with ultrasound for the nozzle inner corner at boiling water reactor pressure vessels has shown that a detectability of cracks with a depth in the range of 5–10 mm is possible if optimal inspection parameters are chosen. The investigations concerning the choice of the optimal parameters have delivered the following results: 1. (1) Probe parameters: The angle of refraction should be in the range of 70° and a probe frequency of 1 MHz should be used. The tilting angle can be chose between 18 and 22°. 2. (2) Sensitivity: The calibration of the sensitivity can be carried out with the help of a 7 mm side-drilled hole in a distance corresponding to the maximum sound path for the inspection. 3. (3) Scanning range of the probe: The probe shall be moved in a range of about 100 mm in order to cover the whole gap between minimal and maximal radial distance for an elliptical scanning. 4. (4) The evaluation of indications can be done based on C -scan presentations. In doubtful cases the time-of-flight curves will deliver some useful information. The first hint on the defect size is delivered by the extension of the indication in a C -scan presentation. A dynamic extension can be evaluated and correlated to the real defect size if sufficient knowledge about the specific relationship is available. For critical findings a correct flaw sizing cannot be avoided. In those circumstances it seems to be necessary to apply techniques like the acoustic holography or others.

Measurement of the depth of surface cracks using the Direct Current Potential Drop Method

AbstractThe direct current potential drop method is used to determine the depth of surface cracks in laboratory crack growth experiments. In the present paper calibration tests are described which were done on tensile loaded flat plates containing centrally located surface cracks. The cracks were propagated by fatigue loads and the load shedding technique was used to obtain beach marks on the fracture surface which were needed to calibrate the potential drop readings. Since the resolution of the direct current potential drop method is very low in the case of surface cracks the experimental parameters were optimized such that the accuracy of the crack depth determination can be about ± 1 per cent of the specimen thickness.

Fatigue growth of surface cracks in bending

A simple procedure for calculating the fatigue crack propagation lifetimes of surface-initiated part-through cracks in bending is discussed and agreement is obtained with previously reported experimental data. It is shown that a realistic fatigue analysis of these cracks must include an explicit determination of crack depth as a function of surface length and that, in general, the depth-to-length ratio varies with crack length, crack nucleus geometry and with the stress intensity factor exponent in the Paris growth rate relationship. Numerical results are presented for some typical situations.

The potential of scattered or diffracted ultrasound in the determination of crack depth

This article reports an investigation which was a part of a wider study of defect sizing techniques. The authors have examined the method of crack depth determination using scattered ultrasound developed by Böttcher et al with special reference to contract probe studies with normal grade structural steels. They conclude that the use of amplitude of the scattered signal as a measure of crack depth, as proposed, suffers from a number of serious drawbacks in these contexts. However, the alternative of using the change of time delay between the transmitted and the first received signal has been investigated here and appears to provide a very attractive alternative.