Fracture toughness determination and micromechanics of rock under Mode I and Mode II loading [Elektronische Ressource] / von Tobias Backers

Tobias Backers

Informations

• Publié par: universitat_potsdam
• Publié le: 01 janvier 2005
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Institut für Geowissenschaften
Sektion 3.2 Deformation und Rheologie des GFZ Potsdam




Fracture Toughness Determination and Micromechanics of Rock Under
Mode I and Mode II Loading














Dissertation
zur Erlangung des akademischen Grades
"doctor rerum naturalium"
(Dr. rer. nat.)
in der Wissenschaftsdisziplin " Geologie "




eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam


von
Tobias Backers



Potsdam, den 12. August 2004 II



























Doctoral Thesis
by
Tobias Backers


Supervised by
Prof. Dr. rer. nat. Georg Dresen and Prof. Ove Stephansson, PhD.


Submitted to
University of Potsdam, Germany


2004 – 08 – 12
III
































A pdf-version of the thesis is available through the author.
Set in 9/10/11/12/14 pt Garamond.
IV
















This thesis is dedicated to Yvonne Backers. Much too young my
mother died.
VVI

ACKNOWLEDGEMENTS/CREDITS
I debt my gratitude to a lot of people who helped me to pass the hassles of this thesis. This
includes people at the GeoForschungsZentrum (GFZ) Potsdam, Germany, at the Royal Institute of
Technology (KTH) in Stockholm, Sweden, and at the Ruhr-Universität Bochum, Germany, but also my
friends and family.
I acknowledge the financial support of this work through GFZ and DFG grant DR 213/9-1 and
DR 213/9-3.
I want to thank my supervisors, Prof. Dr. rer. nat. Georg Dresen and Prof. Dr. Ove Stephansson
for their valuable advice and guidance through my studies. Numerous and intense discussions improved
my understanding of fracture mechanics and rock mechanics both from a microstructural and engineering
point of view. Besides this academic support there was also room for friendly chats.
The collaboration I had with my co-authors on the publications I want to acknowledge. These are
Prof. Dr.-Ing. Michael Alber, MSc (Ruhr-Universität Bochum), Dr. Nader Fardin (KTH Stockholm), Dr.
Erik Rybacki (GFZ Potsdam) and Dr. Sergei Stanchits (GFZ Potsdam). It was a very fruitful work that
led to good results.
I had valuable discussions with Michael Alber on very principle things that led to satisfying
experiments. Further, he let me use his facilities at Bochum University, i.e. a large diameter Hoek-Cell, the
loading frame and the sample preparation laboratories. Nader Fardin did surface roughness
measurements of samples. Sergei Stanchits did recording of Acoustic Emissions and analysis of the data.
Many others helped at the different research institutes whom I cannot all mention here. Also the
reviewers of the manuscripts and guests at GFZ provided good discussions. Nevertheless I want to allude
Stefan Gehrman (GFZ Potsdam), who helped me with sample preparation, Dipl.-Ing. Michael Naumann
(GFZ Potsdam), whose ideas led to the final design of the devices for testing, and Erik Rybacki, who was
always available for a discussion or chat. Thanks also to all my former and recent colleagues at GFZ,
Section 3.2.
I would like to express my sincere appreciation to those who read through the thesis or parts of it
and gave their comments, namely my supervisors, Ann, Anna, Ann-Elen, Erik, Geoff, Stefan and my
father.
I want to thank all those who went for a beer and laughter during the course of the last three years.
For mental support I want to thank my friends, and my sister, Gabi.
For lots of things, which are too many to list here, thanks to Daniela.

Tobias

Potsdam, August 2004
VIIVIII

CONTENT
Acknowledgements VII
Content IX
Summary/Zusammenfassung XIII

1 INTRODUCTION____________________________________________ 1
2 INTRODUCTION TO THEORY OF FRACTURE MECHANICS
AND FRACTURE TOUGHNESS DETERMINATION ______________ 5
2.1 Discontinuities in rock 5
2.2 Mode of fracturing, stress distribution, stress intensity factor and
fracture toughness 6
2.3 The Griffith concept and Energy Release Rate 8
2.4 The process of fracturing and fracture process zone (FPZ) models 9
2.4.1 The process of fracturing 9
2.4.2 Static – dynamic versus stable (– subcritical) – critical – unstable
fracture growth 10
2.4.3 Fracture process zone models 11
2.5 Fracture toughness testing methods, influencing factors and data 13
2.5.1 Mode I fracture toughness testing methods 13
2.5.2 Mode II fracture toughness testing methods 14
2.5.3 Factors influencing fracture toughness 15
Confining pressure 15
Other parameters 16
2.5.4 Typical data on K and K for rocks 16 IC IIC
3 EQUIPMENT AND MATERIALS ______________________________ 17
3.1 Loading equipment 17
3.2 Acoustic Emission equipment
3.3 Tested materials
Äspö Diorite 17
Aue Granite 19
Mizunami 19
Carrara Marble 19
Flechtingen Sandstone 19
Rüdersdorf Limestone 19
IX4 MODE I LOADING – METHODS, RESULTS AND DISCUSSION ___ 21
4.1 Methods 21
4.1.1 Chevron Bend method 21
Sample preparation and testing set-up 21
Testing procedure 22
Evaluation 22
4.1.2 Roughness determination 23
4.1.3 Microstructural analysis 24
4.2 Results 24
4.2.1 K determined by the Chevron Bend method for several rock IC
types 24
4.2.2 The influence of loading rate on different parameters in Mode I
testing of Flechtingen sandstone 24
Mechanical data and Fracture Toughness 24
Fracture Roughness 26
Microstructure 26
Acoustic Emission 26
4.3 Discussion 31
4.3.1 Determined fracture toughnesses
4.3.2 The influence of loading rate on Mode I testing of Flechtingen
sandstone 31
Mechanical data and Fracture Toughness 31
Fracture Roughness and Microstructure 32 Emission 32
5 MODE II LOADING – METHOD, RESULTS AND DISCUSSION____ 35
5.1 Method – Punch-Through Shear (PTS-) test 35
Devices 35
Sample preparation and testing set-up 37
Testing procedure 37
Evaluation (Displacement Extrapolation Technique) 38
FEM analysis of suggested geometry 40
5.2 Results from experimental testing and analysis 40
5.2.1 Results from geometry variation 40
Influence of notch depth 40
Influence of notch curvature and sample diameter 42
Influence of notch width 42
5.2.2 Influence of displacement rate 43
5.2.3 Influence of confining pressure 43
5.2.4 Cyclic loading 44
5.2.5 Fracture evolution 45
5.2.6 Influence of confining pressure on the fracture pattern of Carrara
marble 48
Macro Scale observations 48
Micro Scale observations 49
5.2.7 Results from Acoustic Emission recording 52
5.3 Discussion 52
5.3.1 Geometry variation
Notch depth and Sample height 52
Notch diameter 52 width 53
X