交流电磁场检测技术(alternating current field measurement, ACFM)以其检测效率高、对表面裂纹响应灵敏、非接触等特性被广泛应用于钢轨表面滚动接触疲劳(rolling contact fatigue, RCF)裂纹的检测。利用COMSOL Multiphysics软件建立...交流电磁场检测技术(alternating current field measurement, ACFM)以其检测效率高、对表面裂纹响应灵敏、非接触等特性被广泛应用于钢轨表面滚动接触疲劳(rolling contact fatigue, RCF)裂纹的检测。利用COMSOL Multiphysics软件建立三维交流电磁场仿真模型,采用有限元的方法研究不同垂直角度的非均匀裂纹簇对ACFM信号的影响,研究表明,相较于均匀裂纹簇,不同垂直角度的非均匀裂纹簇的Bx特征曲线的波谷位置出现偏移,在此基础上研究了非均匀裂纹簇1~5 mm口袋深度、6~20 mm表面长度、5~15 mm裂纹间距对Bx信号的影响。展开更多
The heterogeneity of unconventional reservoir rock tremendously affects its hydrofracturing behavior. A visual representation and accurate characterization of the three-dimensional (3D) growth and distribution of hy...The heterogeneity of unconventional reservoir rock tremendously affects its hydrofracturing behavior. A visual representation and accurate characterization of the three-dimensional (3D) growth and distribution of hydrofracturing cracks within heterogeneous rocks is of particular use to the design and implementation of hydrofracturing stimulation of unconventional reservoirs. However, because of the difficulties involved in visually representing and quantitatively characterizing a 3D hydrofracturing crack-network, this issue remains a challenge. In this paper, a novel method is proposed for physically visualizing and quantitatively characterizing the 3D hydrofracturing crack-network distributed through a heterogeneous structure based on a natural glutenite sample. This method incorporates X-ray microfocus computed tomography (μCT), 3D printing models and hydrofracturing triaxial tests to represent visually the heterogeneous structure, and the 3D crack growth and distribution within a transparent rock model during hydrofracturing. The coupled effects of material heterogeneity and confining geostress on the 3D crack initiation and propagation were analyzed. The results indicate that the breakdown pressure of a heterogeneous rock model is significantly affected by material heterogeneity and confining geostress. The measured breakdown pressures of heterogeneous models are apparently different from those predicted by traditional theories. This study helps to elucidate the quantitative visualization and characterization of the mechanism and influencing factors that determine the hydrofracturing crack initiation and propagation in heterogeneous reservoir rocks.展开更多
Ceramic capillary membrane has received much attention due to its relatively high pack density and favorable mechanical strength.However,it is difficult to prepare capillary membrane on its thin support by a dip-coati...Ceramic capillary membrane has received much attention due to its relatively high pack density and favorable mechanical strength.However,it is difficult to prepare capillary membrane on its thin support by a dip-coating method.In this study,alumina microfiltration membranes were prepared on the inner surface of alumina capillary support(outer diameter 4 mm,inner diameter 2.5 mm)by a dip-coating method.Scanning electron microscopy(SEM)observation,gas bubble pressure(GBP)method and membrane permeation test were carried out to evaluate membrane performance.Two major effects in preparation of crack-free membrane,capillary filtration and film-coating,upon the thin support were studied.The as-prepared crack-free membrane presents a narrow pore size distribution,a mean pore size of about 0.6μm and a high pure water flux of 86000 L·m -2 ·h -1 ·MPa.It is proved that the membrane thickness should be sufficiently large to overcome the defects of support surface,but it is only one of the prerequisites for the formation of crack-free membrane.Furthermore,it is demonstrated that the capillary filtration effect is greatly restricted for thin capillary support with the dip-coating method and the film-coating effect plays a crucial role in the formation of crack-free membrane.展开更多
Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufactu...Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufacturing highlights the capability in manufacturing FGMs with a high geometrical complexity and manufacture flexibility.In this work,the 316L/CuSn10/18Ni300/CoCr four-type materials FGMs were fabricated using SLM.The microstructure and properties of the FGMs were investigated to reveal the effects of SLM processing parameters on the defects.A large number of microcracks were found at the 316L/CuSn10 interface,which initiated from the fusion boundary of 316L region and extended along the building direction.The elastic modulus and nano-hardness in the 18Ni300/CoCr fusion zone decreased significantly,less than those in the 18Ni300 region or the CoCr region.The iron and copper elements were well diffused in the 316L/CuSn10 fusion zone,while elements in the CuSn10/18Ni300 and the 18Ni300/CoCr fusion zones showed significantly gradient transitions.Compared with other regions,the width of the CuSn10/18Ni300 interface and the CuSn10 region expand significantly.The mechanisms of materials fusion and crack generation at the 316L/CuSn10 interface were discussed.In addition,FGM structures without macro-crack were built by only altering the deposition subsequence of 316L and CuSn10,which provides a guide for the additive manufacturing of FGM structures.展开更多
Experimental analysis of the cracking in the ceramics subsequent to water quenching have been conducted to clarify the uncertainties of cracking in the ceramics when subjected to thermal shock.The results here indicat...Experimental analysis of the cracking in the ceramics subsequent to water quenching have been conducted to clarify the uncertainties of cracking in the ceramics when subjected to thermal shock.The results here indicate that at the critical point of quench temperature,the crack density and the depth reached the minimum and the maximum limits,respectively.On increase of the quench temperature,the crack density increased rapidly before reaching its saturation point,while the crack depth initially decreased rapidly and then increased gradually before reaching its saturation point.展开更多
基金We gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grants 51374213 and 51674251), National Natural Science Fund for Distinguished Young Scholars of China (Grant 51125017), Science Fund for Creative Research Groups of the National Natural Science Foundation of China (Grant 51421003), Fund for Innovative Research and Development Group Program of Jiangsu Province (Grant 2014-27), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (Grant PAPD 2014).
文摘The heterogeneity of unconventional reservoir rock tremendously affects its hydrofracturing behavior. A visual representation and accurate characterization of the three-dimensional (3D) growth and distribution of hydrofracturing cracks within heterogeneous rocks is of particular use to the design and implementation of hydrofracturing stimulation of unconventional reservoirs. However, because of the difficulties involved in visually representing and quantitatively characterizing a 3D hydrofracturing crack-network, this issue remains a challenge. In this paper, a novel method is proposed for physically visualizing and quantitatively characterizing the 3D hydrofracturing crack-network distributed through a heterogeneous structure based on a natural glutenite sample. This method incorporates X-ray microfocus computed tomography (μCT), 3D printing models and hydrofracturing triaxial tests to represent visually the heterogeneous structure, and the 3D crack growth and distribution within a transparent rock model during hydrofracturing. The coupled effects of material heterogeneity and confining geostress on the 3D crack initiation and propagation were analyzed. The results indicate that the breakdown pressure of a heterogeneous rock model is significantly affected by material heterogeneity and confining geostress. The measured breakdown pressures of heterogeneous models are apparently different from those predicted by traditional theories. This study helps to elucidate the quantitative visualization and characterization of the mechanism and influencing factors that determine the hydrofracturing crack initiation and propagation in heterogeneous reservoir rocks.
基金Supported by the National High Technology Research and Development Program of China (2007AA030303), the National Basic Research Program of China (2009CB623400) and the National Natural Science Foundation of China (20776067).
文摘Ceramic capillary membrane has received much attention due to its relatively high pack density and favorable mechanical strength.However,it is difficult to prepare capillary membrane on its thin support by a dip-coating method.In this study,alumina microfiltration membranes were prepared on the inner surface of alumina capillary support(outer diameter 4 mm,inner diameter 2.5 mm)by a dip-coating method.Scanning electron microscopy(SEM)observation,gas bubble pressure(GBP)method and membrane permeation test were carried out to evaluate membrane performance.Two major effects in preparation of crack-free membrane,capillary filtration and film-coating,upon the thin support were studied.The as-prepared crack-free membrane presents a narrow pore size distribution,a mean pore size of about 0.6μm and a high pure water flux of 86000 L·m -2 ·h -1 ·MPa.It is proved that the membrane thickness should be sufficiently large to overcome the defects of support surface,but it is only one of the prerequisites for the formation of crack-free membrane.Furthermore,it is demonstrated that the capillary filtration effect is greatly restricted for thin capillary support with the dip-coating method and the film-coating effect plays a crucial role in the formation of crack-free membrane.
基金Project(2020B090922002)supported by Guangdong Provincial Key Field Research and Development Program,ChinaProjects(51875215,52005189)supported by the National Natural Science Foundation of ChinaProject(2019B1515120094)supported by Guangdong Provincial Basic and Applied Basic Research Fund,China。
文摘Functionally graded material(FGM)can tailor properties of components such as wear resistance,corrosion resistance,and functionality to enhance the overall performance.The selective laser melting(SLM)additive manufacturing highlights the capability in manufacturing FGMs with a high geometrical complexity and manufacture flexibility.In this work,the 316L/CuSn10/18Ni300/CoCr four-type materials FGMs were fabricated using SLM.The microstructure and properties of the FGMs were investigated to reveal the effects of SLM processing parameters on the defects.A large number of microcracks were found at the 316L/CuSn10 interface,which initiated from the fusion boundary of 316L region and extended along the building direction.The elastic modulus and nano-hardness in the 18Ni300/CoCr fusion zone decreased significantly,less than those in the 18Ni300 region or the CoCr region.The iron and copper elements were well diffused in the 316L/CuSn10 fusion zone,while elements in the CuSn10/18Ni300 and the 18Ni300/CoCr fusion zones showed significantly gradient transitions.Compared with other regions,the width of the CuSn10/18Ni300 interface and the CuSn10 region expand significantly.The mechanisms of materials fusion and crack generation at the 316L/CuSn10 interface were discussed.In addition,FGM structures without macro-crack were built by only altering the deposition subsequence of 316L and CuSn10,which provides a guide for the additive manufacturing of FGM structures.
基金supported by the National Natural Science Foundation of China(Grant Nos.11023001 and 11272313)
文摘Experimental analysis of the cracking in the ceramics subsequent to water quenching have been conducted to clarify the uncertainties of cracking in the ceramics when subjected to thermal shock.The results here indicate that at the critical point of quench temperature,the crack density and the depth reached the minimum and the maximum limits,respectively.On increase of the quench temperature,the crack density increased rapidly before reaching its saturation point,while the crack depth initially decreased rapidly and then increased gradually before reaching its saturation point.