Micromechanical Aspects of Transgranular and Intergranular Failure Competition

2011 ◽  
Vol 465 ◽  
pp. 399-402 ◽  
Author(s):  
Ivo Dlouhy ◽  
Mita Tarafder ◽  
Hynek Hadraba
Keyword(s):  
Fracture Initiation ◽  
Type Specimens ◽  
Fracture Surface Roughness ◽  
Three Point Bending ◽  
Intergranular Embrittlement ◽  
Initiation And Propagation ◽  
Fracture Micromechanism ◽  
High Level ◽  
Impurity Elements ◽  
Determine Fracture Toughness

Quantification of characteristics that govern intergranular fracture initiation and propagation of this fracture micromechanism in competition with cleavage one is main aim of the paper. A NiCr steel of commercial quality and the same steel with an increased content of impurity elements, Sn and Sb, were used. Step cooling ageing was applied in order to induce intergranular embrittlement. Standard and pre-cracked Charpy type specimens were both tested in three-point bending to determine fracture toughness characteristics. In order to characterise the quantitative differences in fracture surfaces roughness a fractal analysis was applied. A boundary level of fractal dimension has been determined to be 1.12: fracture surface roughness with a higher value reflects high level of intergranular embrittlement and thus fracture resistance degradation.

Investigation of the Microstructure Factors Affecting the Brittle Fracture Initiation of Pre-Cracked Charpy-Type Samples of VVER-1000 RPV Steel

2013 ◽  
Vol 592-593 ◽  
pp. 635-638
Author(s):  
Evgenia A. Kuleshova ◽  
Maxim A. Artamonov ◽  
Artem D. Erak
Keyword(s):  
Brittle Fracture ◽  
Base Metal ◽  
Fracture Initiation ◽  
Type Specimens ◽  
Fracture Origin ◽  
Factors Affecting ◽  
Three Point Bending ◽  
Weld Metals ◽  
Rpv Steel ◽  
Higher Temperature

The correlation between fracture toughness parameter KJc and cleavage initiation distance (CID) for the three point bending (3PB) pre-crecked Charpy type specimens of VVER-1000 reactor pressure vessel base and weld metals was observed. Two types of brittle fracture origin sites were found: nonmetallic inclusions and grain or subgrain boundaries. It was shown that KJc values are shifted to the higher temperature area for weld metal with respect to base metal data. In case when the initiation origin is grain or subgrain boundary, the KJc values are higher for base metal at the same CID values. This indicates the higher crack resistance of base metal.

Fracture Initiation and Propagation in a Deep Shale Gas Reservoir Subject to an Alternating-Fluid-Injection Hydraulic-Fracturing Treatment

SPE Journal ◽  
2019 ◽  
Vol 24 (04) ◽  
pp. 1839-1855 ◽  
Author(s):  
Bing Hou ◽  
Zhi Chang ◽  
Weineng Fu ◽  
Yeerfulati Muhadasi ◽  
Mian Chen
Keyword(s):  
Hydraulic Fracturing ◽  
Shale Gas ◽  
Fracture Initiation ◽  
Fluid Injection ◽  
Hydraulic Fractures ◽  
Stress Difference ◽  
Gas Reservoirs ◽  
Complex Fracture ◽  
Initiation And Propagation

Summary Deep shale gas reservoirs are characterized by high in-situ stresses, a high horizontal-stress difference (12 MPa), development of bedding seams and natural fractures, and stronger plasticity than shallow shale. All of these factors hinder the extension of hydraulic fractures and the formation of complex fracture networks. Conventional hydraulic-fracturing techniques (that use a single fluid, such as guar fluid or slickwater) do not account for the initiation and propagation of primary fractures and the formation of secondary fractures induced by the primary fractures. For this reason, we proposed an alternating-fluid-injection hydraulic-fracturing treatment. True triaxial hydraulic-fracturing tests were conducted on shale outcrop specimens excavated from the Shallow Silurian Longmaxi Formation to study the initiation and propagation of hydraulic fractures while the specimens were subjected to an alternating fluid injection with guar fluid and slickwater. The initiation and propagation of fractures in the specimens were monitored using an acoustic-emission (AE) system connected to a visual display. The results revealed that the guar fluid and slickwater each played a different role in hydraulic fracturing. At a high in-situ stress difference, the guar fluid tended to open the transverse fractures, whereas the slickwater tended to activate the bedding planes as a result of the temporary blocking effect of the guar fluid. On the basis of the development of fractures around the initiation point, the initiation patterns were classified into three categories: (1) transverse-fracture initiation, (2) bedding-seam initiation, and (3) natural-fracture initiation. Each of these fracture-initiation patterns had a different propagation mode. The alternating-fluid-injection treatment exploited the advantages of the two fracturing fluids to form a large complex fracture network in deep shale gas reservoirs; therefore, we concluded that this method is an efficient way to enhance the stimulated reservoir volume compared with conventional hydraulic-fracturing technologies.

Fracture Initiation and Propagation in Fatigue Contact Loading of AA6082 Aluminium Alloy

2006 ◽  
Vol 324-325 ◽  
pp. 1091-1094
Author(s):  
Angela Benedetti ◽  
Pier Gabriele Molari ◽  
Piero Morelli
Keyword(s):  
Aluminium Alloy ◽  
Contact Area ◽  
Contact Fatigue ◽  
Fracture Initiation ◽  
Free Edge ◽  
Element Analysis ◽  
Contact Loading ◽  
Linear Finite Element ◽  
Initiation And Propagation ◽  
Microscopy Analysis

This paper presents the results of an experimental investigation on surface contact fatigue of AA6082 aluminium alloy. After testing, microscopy analysis of the specimen contact area shows plastic deformation at the centre and circumferential cracks at the very edge of the print. Major cracks develop at a certain depth under the border of the contact area and propagate beneath the surface, in the direction of both the centre of contact and the lateral free edge of the specimens. No cracks have been observed at the centre of contact, neither on the surface, nor inside the material. Tensile properties of the alloy have been measured and a non linear finite element analysis has been performed in order to calculate the field of deformation and stress in the contact zone. Finally, stress intensities are correlated with the crack initiation points and an interpretation of the propagation paths, in regard to stress distribution, is given.

scholarly journals Development of Integrated Mechanistically-Based Degradation-Mode Models for Performance Assessment of High-Level Waste Containers

1999 ◽  
Vol 556 ◽  
Author(s):  
J. C. Farmer ◽  
R. D. Mccright ◽  
J. C. Estill ◽  
S. R. Gordon
Keyword(s):  
Stainless Steel ◽  
Crevice Corrosion ◽  
Chloride Concentration ◽  
Yucca Mountain ◽  
304 Stainless Steel ◽  
High Level Waste ◽  
Mechanistic Models ◽  
Alloy 22 ◽  
High Level ◽  
Impurity Elements

AbstractAlloy 22 [UNS N06022] is now being considered for construction of high level waste containers to be emplaced at Yucca Mountain and elsewhere. In essence, this alloy is 20.0–22.5% Cr, 12.5–14.5% Mo, 2.0–6.0% Fe, 2.5–3.5% W, with the balance being Ni. Other impurity elements include P, Si, S, Mn, Co and V. Cobalt may be present at a maximum concentration of 2.5%. Detailed mechanistic models have been developed to account for the corrosion of Alloy 22 surfaces in crevices that will inevitably form. Such occluded areas experience substantial decreases in pH, with corresponding elevations in chloride concentration. Experimental work has been undertaken to validate the crevice corrosion model, including parallel studies with 304 stainless steel.

scholarly journals In-situ synchrotron characterisation of fracture initiation and propagation in shales during indentation

Energy ◽  
2021 ◽  
Vol 215 ◽  
pp. 119161
Author(s):  
Lin Ma ◽  
Anne-Laure Fauchille ◽  
Michael R. Chandler ◽  
Patrick Dowey ◽  
Kevin G. Taylor ◽  
...  
Keyword(s):  
Fracture Initiation ◽  
Initiation And Propagation

Dimple Fracture Simulation of Fracture Specimen under Different Constraint Conditions

2004 ◽  
Vol 261-263 ◽  
pp. 675-680
Author(s):  
Masanori Kikuchi ◽  
Jun Sasaki ◽  
Takehito Ishihara
Keyword(s):  
Fracture Surface ◽  
Stress Triaxiality ◽  
Stress Fields ◽  
The Finite Element Method ◽  
Constraint Condition ◽  
Fracture Surface Roughness ◽  
Three Point Bending ◽  
Fracture Simulation ◽  
Dimple Fracture ◽  
Fracture Specimens

Three kinds of fracture specimens are tested under different constraint conditions. One is 3PB(Three Point Bending) specimen, another is CCT(Center Cracked Tension) specimen, and the third one is called CCB(Center Cracked Bending) specimen. By the SEM (Scanning Electron Microscope) observation, it is shown that the roughness of fracture surface is different from each other largely. They are the effect of constraint condition. The dimple fracture process is simulated by the finite element method using Gurson's constitutive equation, and the crack tip stress fields are obtained. The distributions of stress triaxiality components are qualitatively agree with the experimental results. The J-R curves obtained also qualitatively agree with those of experiments, and the fracture surface roughness is well simulated.

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