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Development of techniques for measurements of shock wave response and moisture content in granite
KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

For measuring small, fast deformations on a micrometre scale optical methods are common. Various forms of interferometry are available, and holography is another possibility. However, if there are complications such as limited space and hazardous environments special demands arise. In our case a granite block was subject to a detonation from a small explosive charge, sending shock waves through the block. In some cases there was risk of expulsion with flying rock shards, with possible damage to expensive optics. Therefore a robust solution with no expensive, fragile parts near the test surface was needed.

A fast four-channel fibre-optic sensor for measuring dynamic surface displacements was developed. Light from an LED is sent through a plastic optic fibre and reflected from the observed surface back into the fibre. A photodetector is used to measure the intensity of the reflected light, which gives the distance to the surface. Based on simple principles, micrometre and microsecond resolution was achieved. The only parts near the test surface were the fibres, easy to replace.

The sensor was used for measuring the propagation velocity of the shock wave, the surface displacement and its particle velocity. One of the most important factors for the wave transmission in granite is the water content of the rock material. The pores in the granite allow for about 0.1% of the granite’s weight to come from liquid water. This is enough to affect the aforementioned measured quantities, from a few percent in some cases to over 100% in other cases. Therefore an investigation was undertaken aiming to control the water content of the granite blocks. Several series of small blocks were both soaked in water and dried, the water content measured with a high performance balance, to ensure well-controlled blasting experiments.

On a larger scale, the aim with the project of which this thesis is a part was to gain systematic knowledge on the effects of penetrating weapons on granite rock shelters. This thesis shows how the raw data was obtained, presents the data itself and exemplifies its application.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 53 p.
Series
Trita-IIP, ISSN 1650-1888 ; 05:10
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
URN: urn:nbn:se:kth:diva-573ISBN: 91-7178-236-2 (print)OAI: oai:DiVA.org:kth-573DiVA: diva2:14477
Presentation
2005-12-09, M311, Brinellvägen 66, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101222Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2010-12-22Bibliographically approved
List of papers
1. Fast four-channel fibre-optic displacement sensor for measuring impact waves at low cost
Open this publication in new window or tab >>Fast four-channel fibre-optic displacement sensor for measuring impact waves at low cost
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2006 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 17, no 5, 1162-1166 p.Article in journal (Refereed) Published
Abstract [en]

We have developed a fast four-channel fibre-optic sensor for measuring dynamic surface displacements caused by shock waves. Light from an LED emitter is sent through a plastic fibre and reflected from the surface back into the fibre. The intensity of the reflected light gives the distance to the surface unambigously. Based on simple principles and utilizing inexpensive components, micrometre and microsecond resolution is achieved at lower cost and with easier usage than for interferometric methods and with better reliability than an accelerometer. The sensor is comparatively easy to set up. It is battery operated for reduced sensitivity to electromagnetic interference. The design of the fibre probe facilitates access in narrow and hostile environments.

Keyword
Cost, Displacement, Distance, Fibre-optic, Impact waves, Intensity, Plastic fibre
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-8965 (URN)10.1088/0957-0233/17/5/S38 (DOI)000238310400039 ()2-s2.0-33646200100 (Scopus ID)
Note
QC 20100914. Conference: 17th International Conference on Optical Fibre Sensors. Brugge, BELGIUM. MAY 23-27, 2005. Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2017-12-14Bibliographically approved
2. Measurement of Explosively Induced Movement and Spalling of Granite Model Blocks
Open this publication in new window or tab >>Measurement of Explosively Induced Movement and Spalling of Granite Model Blocks
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2007 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 34, no 12, 1936-1952 p.Article in journal (Refereed) Published
Abstract [en]

Charges of high explosives have been buried (countersunk) in granite blocks and detonated. This article describes the measurement and evaluation of the shock wave propagating through the granite blocks. It also demonstrates how the shock wave data can be used to improve computer simulations of granite's behaviour. The overall goal has been to investigate how granite withstands penetrating weapons, that first penetrate the ground and then detonates within the created cavity. Several variables have been investigated. It is shown that water content of the granite can increase the shock wave amplitude with up to a factor 2, and a crack in the granite often attenuates the shock wave amplitude with a factor 4 or more. Also, the granite block thickness needed to prevent internal crack formation has been investigated.

Keyword
granite, spalling, shock wave, crack, water
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-8966 (URN)10.1016/j.ijimpeng.2006.11.006 (DOI)000248761500003 ()2-s2.0-34347212498 (Scopus ID)
Note
QC 20100922. Uppdaterad från Submitted till Published (20100922).Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2017-12-14Bibliographically approved
3. Measurement of water sorption and desorption in granite blocks
Open this publication in new window or tab >>Measurement of water sorption and desorption in granite blocks
2005 (English)Report (Other academic)
Publisher
26 p.
Series
Trita-IIP, ISSN 1650-1888 ; 2005:07
National Category
Production Engineering, Human Work Science and Ergonomics
Identifiers
urn:nbn:se:kth:diva-8967 (URN)
Note
QC 20101222Available from: 2005-12-27 Created: 2005-12-27 Last updated: 2010-12-22Bibliographically approved

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