scholarly journals Fluid‐Driven Tensile Fracture and Fracture Toughness in Nash Point Shale at Elevated Pressure

2020 ◽  
Vol 125 (2) ◽  
Author(s):  
S. Gehne ◽  
N. D. Forbes Inskip ◽  
Philip M. Benson ◽  
P. G. Meredith ◽  
N. Koor
Keyword(s):  
Fracture Toughness ◽  
Elevated Pressure ◽  
Tensile Fracture ◽  
Nash Point

scholarly journals Fluid-driven tensile fracture and fracture toughness in Nash Point Shale at elevated pressure.

2020 ◽  
Author(s):  
Philip Benson ◽  
Stephan Gehne ◽  
Nathaniel Forbes Inskip ◽  
Philip Meredith ◽  
Nick Koor
Keyword(s):  
Fracture Toughness ◽  
Ambient Pressure ◽  
Fluid Pressure ◽  
Radial Strain ◽  
Injection Pressure ◽  
Confining Pressure ◽  
Fluid Injection ◽  
Tensile Fracture ◽  
Fracture Orientation ◽  
Nash Point

<p>Fluid-driven fracturing is a key process in enhancing production in both the hydrocarbon and geothermal energy extraction industries. However, whilst a large number of studies have now developed laboratory methods to simulate the process in a range of settings, and across a number of different rock types, data relating the fundamental material parameters (such as fracture toughness) to the overall rock mechanics response as a function of parameters such as confining and pore pressure remain limited. Here we report a new analysis to recover fracture toughness across a range of effective pressures from hydraulic fracturing experiments that use a modified thick-walled cylinder sample mounted in a conventional triaxial deformation apparatus. We use samples that are 90mm in length and 40mm diameter, with a central, axially drilled borehole 12.6 mm in diameter. An array of 16 ports in the engineered, nitrile, sample jacket allows us to record radial strain (4 channels), acoustic emission output (11 channels) and borehole fluid pressure (1 channel) continuously throughout each test. The sample material was Nash Point shale (NPS) from the south coast of Wales, UK, with samples cored both normal and parallel to bedding in order to investigate the effect of anisotropy. Earlier, ambient pressure fracture toughness tests using the Semi-Circular Bend sample geometry had indicated significant anisotropy, values of 0.24 – 0.30 MPa.m<sup>1/2 </sup>in the Short-Transverse (ST) orientation, and 0.71 - 0.73 MPa.m<sup>1/2 </sup>in the Divider (DIV) orientation.</p><p>Here, we present results from a suite of 9 experiments, 6 with samples cored parallel to bedding (ST fracture orientation) and 3 with samples cored normal to bedding (DIV fracture orientation). We find that the fluid injection pressure required to fracture our annular shell samples is significantly higher for DIV samples than for ST samples, and increases significantly with increasing confining pressure in both orientations; ranging from 10 to 36 MPa for ST samples and 30 to 58 MPa for DIV samples as confining pressure is increased from 2.2 to 20.5 MPa. We note that the fluid injection pressure undergoes a number of oscillations between fracture nucleation and the fracture reaching the sample boundary. Such oscillations are more common in ST samples than in DIV samples, and in experiments at lower confining pressures. We use the magnitude of each pressure oscillation to estimate the associated increment of fracture extension via the proportion of AE energy generated relative to the total energy accumulated when the fracture reaches the sample boundary. This analysis produces fracture toughness values ranging from 0.36 to 2.76 MPa.m<sup>1/2</sup> (ST orientation) and 2.98 to 4.05 MPa.m<sup>1/2 </sup>(DIV orientation) as confining pressure was increased from 2.2 to 20.5 MPa. We further find that the increase in fracture toughness increases essentially linearly with increasing effective pressure, and this trend appears to be independent of orientation and the material anisotropy.</p>

scholarly journals An experimental method to determine the intralaminar fracture toughness of high-strength carbon-fibre reinforced composite aerostructures

2018 ◽  
Vol 122 (1255) ◽  
pp. 1352-1370 ◽  
Author(s):  
H. Liu ◽  
B.G. Falzon ◽  
G. Catalanotti ◽  
W. Tan
Keyword(s):  
Fracture Toughness ◽  
Tensile Strength ◽  
Crack Tip ◽  
Damage Mechanism ◽  
Calibration Method ◽  
Compact Tension ◽  
Tensile Fracture ◽  
High Tensile Strength ◽  
Physical Test ◽  
Area Method

ABSTRACTCarbon fibres with high tensile strength are being increasingly utilised in the manufacture of advanced composite aerostructures. A Modified Compact Tension (MCT) specimen is often deployed to measure the longitudinal intralaminar fracture toughness but a high tensile strength often leads to premature damage away from the crack tip. We present an approach whereby the MCT specimen is supported by external fixtures to prevent premature damage. In addition, we have developed a novel measurement technique, based on the fibre failure strain and C-scanning, to determine the crack length in the presence of surface sublaminate delamination which masks the crack tip location. A set of cross-ply specimens, with a ((90/0)s)4 layup, were manufactured from an IMS60/epoxy composite system Two different data reduction schemes, compliance calibration and the area method, are used to determine the fibre-dominated initiation and propagation intralaminar fracture toughness values. Propagation values of fracture toughness were measured at 774.9 ± 5.2% kJ/m2 and 768.5 ± 4.1% kJ/m2, when using the compliance calibration method and the area method, respectively. Scanning Electron Microscopy (SEM) is carried out on the fracture surface to obtain insight into the damage mechanism of high-tensile-strength fibre-reinforced unidirectional composites. The measured tensile fracture toughness value is used in a fully validated computational model to simulate the physical test.

Hydrogen Effects on Fracture Toughness of Additively Manufactured Type 304L Stainless Steel

2019 ◽  
Author(s):  
Anthony McWilliams ◽  
Michael Morgan ◽  
Paul Korinko
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Tensile Properties ◽  
Energy Deposition ◽  
Deposition Process ◽  
High Density ◽  
Tensile Fracture ◽  
304L Stainless Steel ◽  
Directed Energy ◽  
304L Steel

Abstract Rectangular blocks of Type 304L stainless steel were additively manufactured (AM) using the directed energy deposition process. These samples were characterized using tensile, fracture toughness, fractography, and metallography and compared to forged Type 304L steel. The AM materials exhibited high density, tensile properties consistent with mechanically deformed stainless steel, and acceptable fracture toughness properties (> 100 Mpam) in the as fabricated and hydrogen charged (approximately 2500 appm) conditions.

scholarly journals Fracture Toughness, Breakthrough Morphology, Microstructural Analysis of the T2 Copper-45 Steel Welded Joints

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 488 ◽  
Author(s):  
Hao Ding ◽  
Qi Huang ◽  
Peng Liu ◽  
Yumei Bao ◽  
Guozhong Chai
Keyword(s):  
Fracture Toughness ◽  
Welded Joints ◽  
Mixed Model ◽  
Experimental Testing ◽  
Microstructural Analysis ◽  
Bending Test ◽  
Dissimilar Welding ◽  
Tensile Fracture ◽  
Three Point Bending ◽  
Welding Materials

The performance and flaws of welded joints are important features that characteristics of the welding material influence. There is significant research activity on the performance and characteristics of welding joint materials. However, the properties of dissimilar welding materials and the cracking problem have not been thoroughly investigated. This investigation focuses on the evaluation and analysis of fracture mechanics, including fracture toughness, microstructural analysis, and crack initiation of T2 copper-45 steel dissimilar welding materials. Standard tensile and three-point bending experiments were performed to calculate the ultimate strength, yield strength, and elastic modulus for fracture toughness. The macro/micro-fracture morphology for tensile fracture and three-point bending fracture were analysed. Based on these investigations, it was concluded that the fracture types were quasi-cleavage and an intergranular brittle fracture mixed model. The deflection of the crack path was discussed and it was determined that the crack was extended along the weld area and tilted towards the T2 copper. Finally, the crack propagation and deflecting direction after the three-point bending test could provide the basis for improvement in the performance of welded joints based on experimental testing parameters and ABAQUS finite element analysis.

An Experimental and Numerical Study of the Effect of Pre-Strain on the Fracture Toughness of Line Pipe Steel

2004 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins ◽  
Andrew Palmer
Keyword(s):  
Fracture Toughness ◽  
Pipe Steel ◽  
Numerical Study ◽  
Experimental Studies ◽  
Ground Movement ◽  
Tensile Fracture ◽  
Material Damage ◽  
Virgin Material ◽  
Line Pipe ◽  
Line Pipe Steel

Oil and gas pipelines may be subject to high plastic strains, either intentionally as a result of the method of installation, or the requirements of the design and operation, or accidentally (due to mechanical damage), before they enter service (transportation, construction/installation, etc.) and during operation. Pre-strain is introduced by denting, cold bending, land slides, subsidence, frost heave, ice gouging, earthquake induced ground movement, reeling, installation in deep water, and wrinkling or buckling. Material subjected to pre-strain will have different material properties to that of the virgin material. Previous experimental studies have indicated that pre-strain has a detrimental effect on the fracture toughness of steel: it reduces the resistance to crack initiation, reduces the resistance to crack growth, and increases the transition temperature. To investigate the effect of pre-strain on the fracture toughness of line pipe steel a programme of tests and numerical analyses has been undertaken. The results of tensile, notched tensile, fracture toughness (J-integral and CTOD) and Charpy V-notch impact tests of virgin (not pre-strained) material, prestrained material and artificially strain aged material are reported. It is shown that the effect of pre-strain can be simulated numerically using a finite element model incorporating the influence of material damage through a Gurson-Tvergaard constitutive model. The properties of the virgin material that influence the effect of pre-strain on toughness are discussed. The role of material damage (void nucleation and growth, etc.) during the introduction of pre-strain is shown to be less significant than the changes to the tensile properties and ductility caused by pre-strain. The effect of tensile pre-strain on fracture toughness can be characterised in terms of the effect of pre-strain on the stress-strain characteristics of the material, the critical fracture strain, and several parameters that relate to the conditions for ductile fracture (or cleavage fracture). A simple, engineering approximation to the effect of pre-strain on fracture toughness for application to pipeline design and fitness-for-purpose assessment is proposed in terms of the true strain at the tensile strength of the virgin material.

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