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Impulse response measurements as dependent on crack depth. Delamination; ; Impulsresponsmaetningars beroende av sprickdjup. Delaminering

Technical Report:

Abstract

The purpose of the project is to investigate the impulse-response method's ability to detect delamination at different depths. This method is of particular interest, since some of it's realizations strongly resembles established methods like 'bomknackning' . Since the personnel that will be responsible for future measurements with new technology, should feel confidence in new methods, it is an advantage if the new methods connect to older, accepted methods. The project consists of three parts and a fourth is planned. The first part of the investigation is made with a vibrator connected to an impedance head which in turn is connected to the surface of the concrete test specimen with internal delaminations at different depths. The vibrator is controlled by a dynamic signal analyze, which also measures the force- and acceleration signals from the impedance head and convert them to impedance. Since the impedance head must be glued to the surface of the concrete this method is only of laboratory interest. This method gives a complete description of the behavior of the concrete for the frequencies investigated. Thus in following investigations the frequencies of interest are known. From the experiment it follows that delamination down to a depth of 80-100 mm  More>>
Authors:
Ulriksen, Peter [1] 
  1. Lund Univ., Lund (Sweden). Div. of Engineering Geology
Publication Date:
Feb 15, 2011
Product Type:
Technical Report
Report Number:
ELFORSK-11-11
Resource Relation:
Other Information: 22 refs., 102 figs., 6 tabs.
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; CRACKS; PULSES; MECHANICAL IMPEDANCE; CONCRETES; MECHANICAL VIBRATIONS; MATERIALS TESTING; SLABS; ACCELEROMETERS
OSTI ID:
1010791
Research Organizations:
Elforsk AB, Stockholm (Sweden)
Country of Origin:
Sweden
Language:
Swedish
Other Identifying Numbers:
TRN: SE1108057
Availability:
Available from: Elforsk AB, SE-10153 Stockholm, Sweden, E-mail: kontakt @elforsk.se or from homepage: www.elforsk.se
Submitting Site:
SWDN
Size:
153 p. pages
Announcement Date:
Apr 11, 2011

Technical Report:

Citation Formats

Ulriksen, Peter. Impulse response measurements as dependent on crack depth. Delamination; ; Impulsresponsmaetningars beroende av sprickdjup. Delaminering. Sweden: N. p., 2011. Web.
Ulriksen, Peter. Impulse response measurements as dependent on crack depth. Delamination; ; Impulsresponsmaetningars beroende av sprickdjup. Delaminering. Sweden.
Ulriksen, Peter. 2011. "Impulse response measurements as dependent on crack depth. Delamination; ; Impulsresponsmaetningars beroende av sprickdjup. Delaminering." Sweden.
@misc{etde_1010791,
title = {Impulse response measurements as dependent on crack depth. Delamination; ; Impulsresponsmaetningars beroende av sprickdjup. Delaminering}
author = {Ulriksen, Peter}
abstractNote = {The purpose of the project is to investigate the impulse-response method's ability to detect delamination at different depths. This method is of particular interest, since some of it's realizations strongly resembles established methods like 'bomknackning' . Since the personnel that will be responsible for future measurements with new technology, should feel confidence in new methods, it is an advantage if the new methods connect to older, accepted methods. The project consists of three parts and a fourth is planned. The first part of the investigation is made with a vibrator connected to an impedance head which in turn is connected to the surface of the concrete test specimen with internal delaminations at different depths. The vibrator is controlled by a dynamic signal analyze, which also measures the force- and acceleration signals from the impedance head and convert them to impedance. Since the impedance head must be glued to the surface of the concrete this method is only of laboratory interest. This method gives a complete description of the behavior of the concrete for the frequencies investigated. Thus in following investigations the frequencies of interest are known. From the experiment it follows that delamination down to a depth of 80-100 mm can be detected through a clear and solitary resonance peak. This resonance frequency is a function of concrete slab thickness and extension, so if the extension can be measured it may be possible to calculate depth. The second part of the investigation is about using an instrumented hammer to hit the different delamination specimens. The hammer is equipped with a force transducer giving an opportunity to measure the force exerted by the strike against the concrete surface. When a hammer is struck against a concrete surface a spectrum of vibrations is created, dependent on the weight of the hammer and the elasticity of the concrete. A light hammer generates higher frequencies than a heavy one. Three different hammer sizes were used. The vibrations of the concrete surface was measured with an accelerometer pushed manually to the surface and also by an adjacent microphone. The results indicate clearly that the small hammer generates a spectrum better suited to the present resonance frequencies and that both the accelerometer- and microphone signals can be used to detect delamination down to a depth of 120 mm. This is somewhat deeper than what was possible with the vibrator and impedance head, which may be attributed to higher energy in the hammer blows. The large hammer was not suited for the present resonance frequencies. The possibility of using a microphone as a vibration sensor opens for a remote application, when the microphone is fixed in the room and only a modally tuned hammer is used for striking the concrete. The third part of the project is using the big hammer to strike two types of hand held impedance heads. One measures force and velocity F/v the other measures force and acceleration F/a. There are three experiments in the third part a-c. a) The first experiment showed that the small hard-metal points used to improve contact with the concrete contributed undesired oscillations in the F/v impedance head. For this reason these points have not been used in further experiments. b) The second experiment showed that the F/v impedance head produce results that better couple to the properties like delamination depth and width than does the F/a impedance head. It also showed that the two parameters measured in the time domain: Fmax/vmax-impedance and concrete spring constant F/d are good indicators of these delamination properties. The experiment demonstrated that it is best to measure the spring constant in the rebound movement of the concrete surface. c) The third experiment demonstrated that it is possible to use the F/v impedance head for measurements in the frequency domain. However the dominating frequency was lower than that obtained with the vibrator and with the small hammers. It could possibly be explained by the low frequency content of the big hammer blows. If these do not contain the resonance frequencies previously obtained some other frequency will dominate the spectrum. A future fourth part is planned to use an accelerometer attached to a pneumatic cylinder. The idea is that the impact generates an oscillation in the concrete and that during the short period the accelerometer is forced against the concrete, it is possible to record the generated spectrum of the oscillation. From the laboratory experiments one can draw the conclusion that the big hammer and the F/v impedance head is best suited for measurements in the time domain, while the smaller hammers are best suited for measurements in the frequency domain. In the frequency domain delamination has been detected down to a depth of 120 mm, while in the time domain delamination has been detected down to 180 mm, the largest investigated delamination depth.}
place = {Sweden}
year = {2011}
month = {Feb}
}