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Numerical Investigation on fracture initiation Properties of Interface Crack in Dissimilar Steel Welded Joints

Chinese Journal of Mechanical Engineering 2020年第3期33卷 142-149页

作者： Longfei Zhao Chendong Shao Yasuhito Takashima Fumiyoshi Minami Fenggui Lu Shanghai Key Laboratory of Materials Laser Processing and Modification School of Materials Science and EngineeringShanghai Jiao Tong UniversityShanghaiChina Joining and Welding Research Institute Osaka UniversityOsakaJapan

fracture toughness property is of significant importance when evaluating structural *** current research of fracture toughness mainly focused on crack in homogeneous material and experimental *** the crack is located in a welded joint with high-gradient microstructure and mechanical property distribution,it becomes difficult to evaluate the fracture toughness behavior since the stress distribution may be affected by various *** recent years,numerical method has become an ideal approach to reveal the essence and mechanism of fracture toughness *** study focuses on the crack initiation behavior and driving force at different interfaces in dissimilar steel welded *** stress and strain fields around the crack tip lying at the interfaces of ductile-ductile,ductile-brittle and brittle-brittle materials are analyzed by the numerical *** the interface of ductile-ductile materials,the strain concentration on the softer material side is responsible for ductile fracture *** the ductile-brittle interface,the shielding effect of the ductile material plays an important role in decreasing the fracture driving force on the brittle material *** the case of brittle-brittle interface,a careful matching is required,because the strength mismatch decreases the fracture driving force in one side,whereas the driving force in another side is *** results are deemed to offer support for the safety assessment of welded structures.

关键词： Dissimilar steel welded joint fracture initiation Interface Strength mismatch Numerical simulation

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An experimental study of fracture initiation mechanisms during hydraulic fracturing

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Petroleum Science 2011年第1期8卷 87-92页

作者： Yan Tie Li Wei Bi Xueliang Key Laboratory of Enhanced Oil ＆ Gas Recovery Ministry of EducationNortheast Petroleum UniversityDaqing Heilongjiang163318China

The mechanism of fracture initiation is the basic issue for hydraulic fracture technology. Because of the huge differences in fracture initiation mechanisms for different reservoirs,some successful fracturing techniques applied to porosity reservoirs are ineffectual for fractured *** tests using a process simulation device were performed to confirm the characteristics of fracture initiation and propagation in different *** influences of crustal stress field,confining pressure,and natural fractures on the fracture initiation and propagation are *** results demonstrate that stress concentration around the hole would significantly increase the fracture pressure of the *** the same time,natural fractures in the borehole wall would eliminate the stress concentration,which leads to a decrease in the fracture initiation pressure.

关键词： Hydraulic fracturing porosity reservoir fractured reservoir fracture initiation fracture propagation simulation experiment

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Hydraulic fracture initiation theory for a horizontal well in a coal seam

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Petroleum Science 2013年第2期10卷 219-225页

作者： Hou Bing Chen Mian Wang Zheng Yuan Jianbo Liu Ming State Key Laboratory of Petroleum Resource and Prospecting China University of Petroleum Security Department Tuha Oil Company

A series of experiments were pertbrmed to determine rock mechanical parameters related to hydraulic fracturing of coal. The effect of confining pressure and pore pressure on the strength of coal was stt, died. Experimental results show that the coal seam in the study areas has a relatively low elastic modulus, high Poisson＇s ratio, high fragility and is easily broken and compressed. The coal seam is considered as a transversely isotropic medium, since the physical properties in the direction of bedding plane and orthogonal to the bedding plane vary markedly. Based on the generalized plane strain model, stress distribution for an arbitrarily orientated wellbore in the coal seam was determined. In a horizontal well, hydraulic fracturing was lbund to initiate in the coal seam mass due to tensile failure, or from cleats due to shear or tensile failure. For those coal seams with abundant natural cleats, hydraulic fracture initiation can be induced by any of these mechanisms. In this study, hydraulic fracture initiation criteria tbr a horizontal well in a coal seam were established.

关键词： Hydraulic fracturing coal seam transversely isotropic fracture initiation cleat naturalfracture

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An analysis of the uniformity of multi-fracture initiation based on downhole video imaging technology: A case study of Mahu tight conglomerate in Junggar Basin, NW China

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Petroleum Exploration and Development 2022年第2期49卷 448-457页

作者： ZANG Chuanzhen JIANG Hanqiao SHI Shanzhi LI Jianmin ZOU Yushi ZHANG Shicheng TIAN Gang YANG Peng State Key Laboratory of Petroleum Resources and Prospecting China University of PetroleumBeijing 102249China Engineering Technology Research Institute PetroChina Xinjiang Oilfield CompanyKaramay 834000China

To solve the problem that the production of Mahu conglomerate reservoir is not up to expectation after the multi-cluster plus temporary plugging fracturing technology is applied in horizontal wells, stages 2–6 in the test well MaHW6285 are selected to carry out erosion tests with different pumping parameters. The downhole video imaging technology is used to monitor the degree of perforations erosion, and then the fracture initiation and proppant distribution of each cluster are analyzed. The results showed that proppant entered 76.7% of the perforations. The proppant was mainly distributed in a few perforation clusters, and the amount of proppant entered in most of the clusters was limited. The proppant distribution in Stage 4 was relatively uniform, and the fracture initiation of each cluster in the stage is more uniform. The proppant distribution in stages 2, 3, 5, and 6 was significantly uneven, and the uniform degree of fracture initiation in each cluster is low. More than 70% of the proppant dose in the stage entered clusters near the heel end, so the addition of diverters did not promote the uniform initiation of hydraulic fractures. There was a positive correlation between the amount of proppant added and the degree of perforations erosion, and the degree of perforations erosion ranged from 15% to 352%, with an average value of 74.5%, which was far higher than the statistical results of shale reservoir tests in North America. The use of 180° phase perforation(horizontal direction) can reduce the “Phase Bias” of perforations erosion, promote uniform perforations erosion and fluid inflow. The research results provide the basis for optimizing the pumping procedure, reducing the perforation erosion and improving the success rate of diversion.

关键词： tight conglomerate temporary plugging fracturing perforation erosion fracture initiation downhole video imaging technology Junggar Basin Mahu sag

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Multiple damage zones around hydraulic fractures generated by high-frequency pulsating hydraulic fracturing

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Petroleum Science 2024年第4期21卷 2688-2702页

作者： Yan Peng Sheng-Jie Wei Guang-Qing Zhang Da-Wei Zhou Chuang-Chao Xu School of Petroleum Engineering China University of Petroleum PetroChina Changqing Oilfield Company

Pulsating hydraulic fracturing(PHF) is a promising fracturing method and can generate a dynamic periodic pressure. The periodic pressure can induce fatigue failure of rocks and decrease initiation pressure of fracture. If the frequency of periodic pressure exceeds 10 Hz, the distribution of pressure along the main fracture will be heterogeneous, which is much different from the one induced by the common fracturing method. In this study, the impact of this special spatial feature of pressure on hydraulic fracture is mainly investigated. A coupled numerical simulation model is first proposed and verified through experimental and theoretical solutions. The mechanism of secondary fracture initiation around the main fracture is then discovered. In addition, sensitivity studies are conducted to find out the application potential of this new method. The results show that(1) this coupled numerical simulation model is accurate. Through comparison with experimental and theoretical data, the average error of this coupled model is less than 1.01%.(2) Even if a reservoir has no natural fracture, this heterogeneous distribution pressure can also cause many secondary fractures around the main fracture.(3) The mechanism of secondary fracture initiation is that this heterogeneous distribution pressure causes tensile stress at many locations along the main fracture.(4) Through adjusting the stimulation parameters, the stimulation efficiency can be improved. The average and amplitude of pressure can increase possibility of secondary fracture initiation. The frequency of this periodic pressure can increase number of secondary fractures. Even 6 secondary fractures along a 100 m-length main fracture can be generated.(5) The influence magnitudes of stimulation parameters are larger than ones of geomechanical properties, therefore, this new fracturing method has a wide application potential.

关键词： Tight reservoir Reservoir stimulation Numerical simulation Secondary fracture fracture initiation

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A STUDY OF fracture OF UNIDIRECTIONAL CF/SiC SINGLE EDGE-NOTCHED BEAM UNDER THREE-POINT BENDING- MACRO/MICRO-NUMERICAL MONTE CARLO SIMULATION

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Acta Mechanica Solida Sinica 2001年第1期14卷 81-88页

作者： Wang Yang Cheng Tianle Xia Yuanming Jiang Dazhi Department of Mechanics & Mechanical Engineering University of Science and Technology of China He fei 230027 Department of Mechanics & Mechanical Engineering University of Science and Technology of China He fei 230027 Department of Mechanics & Mechanical Engineering University of Science and Technology of China He fei 230027 School of Aerospace & Materials Engineering National University of Defense Technology Changsha 410073 China

In this paper, the fracture process of a unidirectional CF/SiCsingle edge-notched beam (SENB) under three-point bending (TPB) isstudied by means of macro/micro-statistical Monte Car- lo *** simulated P-Δcurves are in agreement with the experimentalresults before the peaks of curves, and the simulated microevolutionpatterns are in agreement with the patterns of the crack surfaces,which have verified this method. It is preliminarily demonstratedthat the second turning point in the compliance changing rate curvecorresponds to the fracture initiation for experi- ments on SENBunder TPB of unidirectional CF/SiC composites.

关键词： CF/SiC fracture Monte Carlo simulation fracture initiation

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Mechanical characterization of sisal reinforced cement mortar

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Theoretical & Applied Mechanics Letters 2014年第6期4卷 26-30页

作者： R.Fujiyama F.Darwish M.V.Pereira Department of Mechanical Engineering Para Federal University Department of Civil Engineering Fluminense Federal University Department of Materials Engineering Catholic University of Rio de Janeiro

This work aims at evaluating the mechanical behavior of sisal fiber reinforced cement mortar. The composite material was produced from a mixture of sand, cement, and water. Sisal fibers were added to the mixture in different lengths. Mechanical characterization of both the composite and the plain mortar was carried out using three point bend, compression, and impact tests. Specimens containing notches of different root radii were loaded in three point bending in an effort to determine the effect of the fibers on the fracture toughness of the material. The results obtained indicate that, while fiber reinforcement leads to a decrease in compressive strength, J-integral calculations at maximum load for the different notch root radii have indicated, particularly for the case of long fibers, a significant superiority of the reinforced material in comparison with the plain cement mortar, in consistence with the impact test data.

关键词： composite material impact energy fracture initiation J-integral

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