Shear mode fracture toughness of rock with different core-based specimen geometries

Het, Kıvanç
Shear mode fracture toughness tests on core specimens of gabbro rock were conducted. Tests were conducted under three-point bending and Brazilian type indirect compression load. In order to investigate the reasons for having different fracture toughness values with the different testing methods and geometries, modeling with ABAQUS software was conducted. Stress distributions around the mode II notches were analyzed. In order to assess which specimen geometry results in similar stress distributions as in the stress state of a plate under pure mode II, stress distributions along some paths were compared. Effect of the thickness of the notches on the stress intensity factor was analyzed. In experiments, core specimens had 100 mm diameter and 60 mm thickness, were used. Mode II fracture toughness results were KIIc(CSTBD)=2.35MPa√m and KIIc(CSTBD)=1.76 MPa√m for the Brazilian type CSTBD specimens with notches of 32 mm and 72 mm in length, respectively. Mode II fracture toughness decreased as the notch length increased. This was attributed to the effect of boundary influence on the fracture toughness. Mode I and mode II fracture toughness values for the three-point bend SCB geometry were lower with KIc(SCB)=1.77 MPa√m and KIIc(SCB)=0.92 MPa√m. Another three-point bend circular plate type SNDB geometry method produced closer results to the CSTBD method with KIc(SNDB)=2.10 MPa√m and KIIc(SNDB)=1.18 MPa√m. Reasons for lower fracture toughness with three-point bending loading were explained in terms of having larger yield zones ahead of the notch and cracks, and the boundary influence issue.


Crack propagation in a commercial steel
Bilir , Oğuz Gürkan (Springer Science and Business Media LLC, 1988-5)
In this work, the fatigue crack propagation behaviour of commercial steel sheet specimens containing a circular hole, under uniaxial loading conditions at room temperature was investigated. The experimental data have been analysed in terms of variability of material constants. The results were presented in the form of power relationship between the crack growth rate and the stress intensity factor range.
Effect of stress ratio on the rate of growth of fatigue cracks in 1100 Al-alloy
Bilir, Ömer.G.; Harun, Metin (Elsevier BV, 1990-1)
Axial load fatigue crack propagation tests were conducted on notched sheet specimens made of 1100 aluminum alloy. These tests were made at stress ratios (ratio of the minimum stress to the maximum stress) ranging from −0.5 to 0.5 in order to study the effects of stress ratio on fatigue crack growth. Experimental fatigue crack propagation data were analysed using Paris-Erdoǧan stress intensity analysis. The data from the tests at different stress ratios showed that two regions, namely, region I and region I...
Shear mode rock fracture toughness determination with a circular plate type specimen under three-point bending
Şener Karakaş, Sinem; Tutluoğlu, Levent; Department of Mining Engineering (2011)
Fracture toughness is an important rock property for rock fracturing and fragmentation applications. Theory and practice of opening mode (mode I) and shearing mode (mode II) fracture toughness tests are still in a developing stage for the cylindrical rock cores. A new circular plate type test specimen is used for mode II fracture toughness testing on rock cores. This involves a straight edge notched circular plate type core disc geometry under three-point bending load; new method and its associated specimen...
Stress intensity factor and compliance solutions for a single edge notched specimen with clamped ends
Blatt, Drew; John, Reji; Çöker, Demirkan (Elsevier BV, 1994-01-01)
A single edge notched geometry [SE(T)] with clamped ends is well suited for fracture toughness and fatigue crack growth testing of composites. Closed form expressions for the stress intensity factor and the compliance for an SE(T) with clamped ends were developed using finite element analysis. Using these expressions, automated crack growth tests were conducted on a monolithic Ti-1100 and a [90]8 SCS-6/Ti-24Al-l 1Nb composite. The crack growth behavior, characterized in terms of the crack growth rate versus...
SARIOGLU, F; ABACHI, P; DORUK, M (Springer Science and Business Media LLC, 1993-03-15)
Crack growth tests at 150-degrees-C under constant load conditions were performed on compact tension specimens of 7050-T73651 aluminium alloy. The d.c. potential drop method was employed to monitor crack lengths throughout the tests. Fracture mechanics parameters such as the stress intensity factor (K) and energy-rate line integral (C*) were used to establish correlation with the crack propagation rates. As a result of experiments it was found that crack growth rates (da/dt) versus K, over discrete ranges o...
Citation Formats
K. Het, “Shear mode fracture toughness of rock with different core-based specimen geometries,” Ph.D. - Doctoral Program, Middle East Technical University, 2014.