Showing papers in "Nondestructive Testing and Evaluation in 1995"
TL;DR: In this paper, a simple test measuring the sorptivity (a measure of the absorption property if concrete) and the air and water permeability of concrete on site is described. And statistically satisfactory results can be obtained from a mean of three tests.
Abstract: This paper descirbes a simple test measuring the sorptivity (a measure of the absorption property if concrete) and the air and water permeability of concrete on site. Using this test, the decay of pressure is monitired for the air permeability test.whereas water penetrating into the concrete at a constant pressure of 0.01 bar and 1.5 bar are recorded for the sorptivity and the water permeability tests respectively. These tests are essentially non-destructive in nature and a skilled operator is not needed. It is possible to carry out a number of tests quickly and efficiently on site without prior planning. It has been found that statistically satisfactory results can be obtained from a mean of three tests. As the flow lines are largely concentrated within 40 mm from the surface, reasonably reliable results can be obtained by drying the surface even if the surface under test is initially wet.
33 citations
TL;DR: In this article, a systematic parametric analysis was undertaken of electromagnetic wave propagation through concrete structures, and it was shown that the use of the simplified expression for wave velocity in relation to concrete structures is seen to be erroneous at lower frequencies - especially at higher conductivities.
Abstract: It has been shown that one of the most important factors affecting a radar survey of a concrete structure is the operational frequency of the antenna. The operational choice of frequency is difficult as there is always a compromise between signal penetration and resolution. Whilst case histories have proved valuable sources of information, they have not yielded the systematic data needed by structural engineers specifying investigative studies. In the work reported herein, a systematic parametric analysis was undertaken of electromagnetic wave propagation through concrete structures. From this, the use of the simplified expression for wave velocity in relation to concrete structures is seen to be erroneous at lower frequencies - especially at higher conductivities. For a given frequency the skin depth )a measure of penetration( drops as conductivity increases. Also, the frequency of the electromagnetic pulse through concrete is shown to be the order of 75% of the centre frequency of the antenna a...
23 citations
TL;DR: In this paper, the effect of biaxial stress on magnetic properties obtained from hysteresis loops is reviewed and both experimental and theoretical work is discussed, with a focus on the effect on the magnetic properties.
Abstract: This paper reviews recent work on the effect of biaxial stress on magnetic properties obtained from hysteresis loops. Both experimental and theoretical work are discussed. Biaxial stress measuremen...
17 citations
TL;DR: Sub-surface impulse radar has recently become an established technique for detecting a wide range of buried features in concrete, with particular attention concentrated upon voids as discussed by the authors, and the ability of a I GHz system to detect air and water filled voids is discussed in detail, and practical guidance is offered to assist the execution and interpretation of such investigations.
Abstract: Sub-surface impulse radar has recently become an established technique for detecting a wide range of buried features in concrete. The background and scope of this technique are outlined in this paper, together with relevant findings of a recent major 5. E. R. C. funded project undertaken at Liverpool University. Location and identification of buried steel reinforcing bars and voids represent two important applications which are considered, with particular attention concentrated upon voids. A wide range of experimental results have been obtained for various configurations of size, shape and depth and are supported by numerical modelling. The ability of a I GHz system to detect air and water filled voids is discussed in detail, and practical guidance is offered to assist the execution and interpretation of such investigations.
9 citations
TL;DR: A number of power laws for ultrasonic attenuation have been proposed in the non-destructive evaluation (NDE) literature empirically or derived analytically, for various regimes of wavelength relati... as mentioned in this paper.
Abstract: A number of power laws for ultrasonic attenuation have been proposed in the non-destructive evaluation (NDE) literature empirically or derived analytically, for various regimes of wavelength relati...
9 citations
TL;DR: In this article, the need for the development of non-destructive methods for evaluating structural brickwork is outlined and different approaches to the application of NDE are reviewed; an approach based on the separate evaluation of the bricks themselves, the mortar and the most important variable in practice, the workmanship, is advocated.
Abstract: The need for the development of non-destructive methods for evaluating structural brickwork is outlined and different approaches to the application of NDE are reviewed. An approach based on the separate evaluation of the bricks themselves, the mortar and the most important variable in practice, the workmanship, is advocated. Anevaluation method usingchanges in ultrasonic pulse transit timeasa measure of variations in quality is developed based on a range of test data. The approach is shown to be capable of detecting potential construction errors, such as the use of under strength mortar or the incomplete filling of the mortar joints.
5 citations
TL;DR: In this article, a non-destructive testing is performed on impacted and artificial inclusion implanted laminates by an automated ultrasonic C-scanning system, where Amplitude and phase of frequency components of the received ultrasonic signal have been used for showing images instead of conventionally used peak amplitude and time of flight.
Abstract: Composite materials provide a serious challenge to the investigators as these materials may develop several types of damages during service such as delamination, voids, porosity, matrix cracking, fibre break etc., either individually or in combinations. Evaluation of exact type of damage quantitatively in composite materials is far more complicated than in the conventional homogenous materials which contain voids and cracks as primary defects. In the present investigation, a non-destructive testing is performed on impacted and artificial inclusion implanted laminates by an automated ultrasonic C-scanning system. Amplitude and phase of frequency components of the received ultrasonic signal have been used for showing images instead of conventionally used peak amplitude and time of flight. Cluster analysis has been employed to group the data units, either individuaJly or in combinations of them in a systematic way. The C-scan images show that the analysis of certain harmonics individually or taken t...
4 citations
TL;DR: In this article, a new nondestructive technique for monitoring the hydration process of cement within concrete and measurement of the compressive strength of concrete is presented, which has so far been primarily used in the fields of chemistry and medicine.
Abstract: A new nondestructive technique for monitoring the hydration process of cement within concrete and measurement of the compressive strength of concrete is presented. The technique called the Nuclear Magnetic Resonance (NMR) has so far been primarily used in the fields of chemistry and medicine. Its application to construction materials has been very limited or nonexistent. In this study, NMR is used to monitor the. hydration of cement paste in concrete with two different water cement ratios. The first objective of this study was to distinguish between the amounts of remaining free water, and water consumed in the hydration process during the 28 days monitoring period. The second objective was to relate the compressive strength of concrete to NMR signals. A number of standard compression tests were performed in parallel with the NMR tests. Correlation of the responses from nondestructive tests with NMR and those of standard compression tests indicated almost a linear relationship.
4 citations
TL;DR: In this paper, a method for local stress strain state definition of thin walled construction elements is developed for determining local bending stresses in the elements by using holographic interferograms of the normal components of the displacement vector.
Abstract: A method has been developed for local stress strain state definition of thin walled construction elements. Holographic interferograms of the normal components of the displacement vector of the studied element surfaces are used to determinate of local bending stresses in the elements. Some experimental results including local bending state definition ahead of the crack in the elements are represented.
1 citations
TL;DR: In this article, a serial link robot manipulator can be used to perform raster scans (as used in ultrasonic c-scanning) with precision as good as is required in the NDT industry and normally achieved by means of conventional x-y cartesian scanners.
Abstract: Published studies of serial link arm usage for the manipulation of sensors in NDT are rare, perhaps because there is a perception that the cumulative errors in spatial location along such arms are too great for satisfactory imaging. These errors, with good programming. are not as serious as they might seem at first sight and the flexibility of serial arms is most attractive. This paper shows that a serial link robot manipulator ann can be used to perform raster scans (as used in ultrasonic c-scanning) with precision in spatial resolution as good as is required in the NDT industry and normally achieved by means of conventional x-y cartesian scanners. It also presents an iterative method to compute the inverse kinematics (ie the programme of sequence of joint angles) needed to constrain a serial link robot manipulator to perform an NDT scanning operation (eg to perform a plan or raster scan whilst maintaining a constant angle between the probe and the surface under inspection). The iterative method...
1 citations
TL;DR: In this article, the oxidation behavior of a cold-rolled motor lamination (CRML) steel was investigated in a simulated exothermic atmosphere and a nitrogen/hydrogen atmosphere.
Abstract: The oxidation behavior of a cold rolled motor lamination (CRML) steel was investigated in a simulated exothermic atmosphere and a nitrogen/hydrogen atmosphere. The weight gain and the surface composition after annealing were studied using Thermo-gravimetric Analysis (TGA) and X-ray photoelectron spectroscopy (XPS). respectively. We found that annealing in the exothermic atmosphere increased the surface oxidation. The nitrogen/hydrogen annealing atmosphere significantly reduced the surface oxidation.