Journal articles: 'RFPA'

1

Li, Tang, Rutqvist, Hu, Li, Zhang, and Huang. "The Influence of an Interlayer on Dual Hydraulic Fractures Propagation." Energies 13, no. 3 (January 23, 2020): 555. http://dx.doi.org/10.3390/en13030555.

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Multi-cluster hydraulic fracturing of long-range horizontal wells is an approach for enhancing the productivity of low-permeability shale reservoirs. In this study, RFPA-Petrol (rock failure process analysis on petroleum problems) is applied for modeling hydraulic fracture propagation in multilayered formations. RFPA-Petrol based on coupled hydraulic-mechanical-damage (HMD) modeling was first tested by modeling a laboratory scale experiment on a physical (cement) model with a single completion. The modeling demonstrated the capability of RFPA-Petrol for simulating hydraulic fracture propagation. Then, we used RFPA-Petrol to investigate how the difference in material properties between oil-bearing layers and interlayers and the fracturing fluid properties influence the propagation of dual fractures in multilayered laboratory-scale models. In this case, the models with geological discontinuities in the vertical direction are strongly heterogeneous and RFPA-Petrol simulations successfully modeled the fracture configurations.

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Ruslan Hadi, Noor Syakirah, Zubaida Yusoff, Md Golam Sadeque, Shaiful Jahari Hashim, and Muhammad Akmal Chaudhary. "High gain over an octave bandwidth class-F RF power amplifier design using 10W GaN HEM." Bulletin of Electrical Engineering and Informatics 9, no. 5 (October 1, 2020): 1899–906. http://dx.doi.org/10.11591/eei.v9i5.2226.

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The wireless communication industry grows faster each day. In terms of RF power amplifier (RFPA), the requirements on efficiency, linearity, bandwidth, output power and cost are getting more stringent. RFPA is considered as the most important component because of consuming large power in a base station. In this paper, a systematic approach is used to design a high flat gain class-F RFPA over an octave bandwidth. The simulation of a 1.5GHz class-F power amplifier mode demonstrates a high drain efficiency while accomplishing a high flat gain over a wide bandwidth. To identify the optimum impedance for the output matching and input matching network, the load-pull and source-pull are performed. The simulation results show that the RFPA can deliver a drain efficiency of 68.37 % at the output power of 40.79 dBm with power added efficiency of 66.94 %. The designed PA achieved a high gain between 13 dB to 17 dB from 0.5 GHz to 2.0 GHz of a frequency band. The matching circuits are realized on an FR-4 substrate to keep the cost as low as possible. A 10W GaN HEMT CGH40010 transistor from Cree has been used for this RFPA design.

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Ravanat, C., M. Freund, S. Schuhler, P. Grunert, L. Meyer, and J.-P. Cazenave. "Species Specific Immunoassays to Measure Blood Platelet and Coagulation Activation in the Rat." Thrombosis and Haemostasis 76, no. 06 (1996): 1090–95. http://dx.doi.org/10.1055/s-0038-1650711.

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SummaryThe purpose of this study was to develop specific and sensitive immunoassays to detect early indices of hypercoagulability in the rat. Rat platelet factor 4 (rPF4) and rat fibrinopeptide A (rFPA) assays, tools for the detection of activation of platelets and coagulation respectively, were designed using antibodies raised against purified rPF4 and against synthetic rFPA. The relevance of these new assays and of the commercially available ELISA kit for thrombin-antithrombin III (TAT) complexes was demonstrated in a rat model of a prethrombotic state induced by intravenous infusion of varying doses of thromboplastin (90 to 2400 μl/kg/h). In this model, the immunoassays allowed simultaneous detection of low levels of rFPA and rPF4 which were correlated with fibrinogen and platelet consumption and TAT generation and further proved to be of higher sensitivity than the classical methods of platelet count or measurement of fibrinogen levels. Plasma concentrations of rFPA, rPF4 and TAT were dependent on infusion time and thromboplastin dose, while hirudin (1 mg/kg) prevented their appearance. Thus the new specific immunoassays for rPF4 and rFPA and the commercial human TAT assay represent useful tools for pathophysiological studies or the screening of antithrombotic drugs in rats.

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Sadeque, Md Golam, Zubaida Yusoff, and Mardeni Roslee. "A high-efficiency continuous class-F power amplifier design using simplified real frequency technique." Bulletin of Electrical Engineering and Informatics 9, no. 5 (October 1, 2020): 1924–32. http://dx.doi.org/10.11591/eei.v9i5.2227.

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The fourth-generation (4G) wireless communication has been deployed in many countries. However, there are still some problems such as spectrum crisis due to the increase of wireless mobile devices and servicing. Therefore, the fifth-generation (5G) communication system will be employed at some different spectrum other than 4G frequency band. The radio frequency power amplifier (RFPA) is the key component of the 5G system. In this paper, a broadband continuous class-F (CCF) RFPA is designed for the 5G frequency band from 3.3-4.3 GHz. The input and output matching network are designed using the simplified real frequency technique (SRFT). Using a 10W GaN CGH40010F Cree device, the efficiency of the RFPA achieved greater than 70.7% for the whole frequency band with a maximum of 81.5%. The output power and the gain are more than 40 dBm and 10 dB respectively

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Tang, Chun’an, and Shibin Tang. "Applications of rock failure process analysis (RFPA) method." Journal of Rock Mechanics and Geotechnical Engineering 3, no. 4 (December 2011): 352–72. http://dx.doi.org/10.3724/sp.j.1235.2011.00352.

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Tang, Shi Bin, Zheng Zhao Liang, and Ya Fang Zhang. "Study on the Thermal Cracking Processes of Composite Subjected to Thermal Loading." Applied Mechanics and Materials 256-259 (December 2012): 2867–70. http://dx.doi.org/10.4028/www.scientific.net/amm.256-259.2867.

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A numerical method RFPA-T (Thermal Induced Rock Failure Process Analysis) code is used to study the thermal cracking processes of quasi-brittle materials subjected to high or low temperature. The numerical results indicate that thermal stress concentrating along the interface between the matrix and the embedded grains due to their different coefficient of thermal expansion (CTE). The modeling results indicate that θ-crack is generated during temperature increment as the CTE of the embedded grain is smaller than that of the matrix. However, radial-cracks emerged when the temperature decrease. The results obtained from RFPA-T code show a good agreement with experimental evidence of crack patterns caused by thermal expansion mismatch.

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Zhu, Wan Cheng, Jin Chao Duan, Chun An Tang, and Shan Yong Wang. "Digital Image Based Simulation on Failure Process of Heterogeneous Brittle Materials." Key Engineering Materials 324-325 (November 2006): 315–18. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.315.

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Rock and concrete are typical heterogeneous material that the meso-scale heterogeneity may have a significant effect on their macro-scale mechanical responses. In this work, a digital image-based (DIB) technique is employed to characterize and quantify the heterogeneity of concrete, and the obtained data is directly imported into a numerical code named RFPA (Rock Failure Process Analysis) to study the effect of heterogeneity on the failure process of concrete. The upgraded RFPA is capable to simulate the progressive failure of brittle materials such as rock and concrete, representing both the growth of existing fractures and the formation of new fractures, obviating the need to identify crack tips and their interaction explicitly. The simulated results are in reasonable agreement with experimental measurements and phenomenological observations reported in previous studies.

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Tang, Lie Xian, Lian Jun Guo, Da Ning Zhang, and Jian Ming Zheng. "Numerical Simulation and Analysis of Centrifuge Model Tests with Nonhomogeneous Materials in Geotechnical Engineering." Applied Mechanics and Materials 353-356 (August 2013): 495–501. http://dx.doi.org/10.4028/www.scientific.net/amm.353-356.495.

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The primary methods are antetype observation and model tests which to check the actual engineering status in geotechnical engineering field. The antetype observation is the best direct and convictive method, but approach miscellaneous and spend hugely. The general model tests can not fulfil the same stress between model and antetype. Geotechnical centrifuge model test can not only minish the measure of model and fulfil the comparability condition, but also can found all kinds of non-symmetrical models and simulation all kinds of complicated engineering. So the geotechnical centrifuge model test is applied widely in the geotechnical engineering. This paper used the RFPA-Centrifuge and recured to the principle of geotechnical centrifuge model test, evaluated the safety of model only by increase the physical strength. Though the numerical calculating in nonhomogeneous models with different scales showed that stress, displacement and failure mode were accord with conform ratio of centrifuge model tests. Showed the advantage that the results of RFPA can be validated each other with results of physical tests. For some specifical complicated items in geotechnical engineering, make a good test model is not only very hard and have to spend much time, but also need expensive test equipment and much money for test materials. It is very good if we can use a method to conquer these shortages. So it is advisable that using the mechod which geotechnical centrifuge tests combine RFPA-Centrifuge numerical simulation analysis method.

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Tang, Lie Xian, Dong Zhang, Zhen Tong An, and Jun Yan Zhang. "Research of Soundless Crack with Different Number of Drillholes." Applied Mechanics and Materials 580-583 (July 2014): 689–92. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.689.

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The special advantages of Soundless Crack method are safety and environmental protection. Soundless Crack is widely used in stone exploitation, partly crack of brittleness materials such as rock and concrete, and backout of building in city. In these engineering, we must drill many holes for loading Soundless Cracking Agents, but the drilling cost is expensive including human cost and materials cost, at the same time need much time to drill these holes. So we hope to gain the best crack results at the minimum drillhole numbers. This paper used RFPA software to set up some models with different drillhole numbers, gained different failure process of models. Adopted different drilling plan will occur different results. We should drill more holes if we need partly crack smoothly. We can plan the number of drillholes based on our need if we can use RFPA to simulate the failure process before beginning.

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Zhang, Yu Wei, Lie Xian Tang, Da Chuan Bai, and Peng Zhou. "Numerical Simulation of Failure Process on Soil Slope with Different Support Measures." Applied Mechanics and Materials 580-583 (July 2014): 665–68. http://dx.doi.org/10.4028/www.scientific.net/amm.580-583.665.

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In conventional analysis methods of soil slope, we must presume potential sliding surface at first and then gain the safety factors, judge the stability of slope by the safety factors. In fact, if we know a slope is unstability but don’t know where will be slide or failure, we can’t adopt effective measures to support and prevent the sliding accidents appearing. This paper use RFPA-Centrifuge to numerical simulate the failure of soil slope with different support measures without presume any potential sliding surface, success to gain the failure process and the corresponding safety factors. From the calculate results of RFPA-Centrifuge, we can find where is the first failure point and all the slide mass. So if we can use good analysis software to simulate the failure process of slope and adopt corresponding support measures before the engineering beginning, the stability of slope will be better and the accidents will be disappeared or reduced.

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11

Collins, David J., Roberto Quaglia, Jeff R. Powell, and Steve C. Cripps. "The Orthogonal LMBA: A Novel RFPA Architecture With Broadband Reconfigurability." IEEE Microwave and Wireless Components Letters 30, no. 9 (September 2020): 888–91. http://dx.doi.org/10.1109/lmwc.2020.3010817.

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Xu, Nu Wen, Chu Nan Tang, Chun Sha, and Ru Lin Zhang. "Numerical Simulation on Failure Mechanism of Rock Slope Using RFPA." Applied Mechanics and Materials 50-51 (February 2011): 568–72. http://dx.doi.org/10.4028/www.scientific.net/amm.50-51.568.

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This research applied a numerical code, RFPA2D (Realistic Failure Process Analysis) to evaluate the stability and investigate the failure mode of the high rock slope during excavations based on Strength Reduction Method (SRM). The corresponding shapes and positions of the potential slip surfaces are rationally simulated in different stages, and the related safety coefficients are obtained, which agrees well with the allowable minimum safety factors of the slope. The numerical results show that the safety coefficient drops from 1.25 at the natural state to 1.09 after excavation, and then increases to 1.35 after slope reinforcement. Moreover, the potential slip surface of the left bank moves into deep rock mass after taking support measures, which demonstrates the reinforcement is reasonable and efficient. The study shows that cracks and faults will cause crucial influences on the slope stability, and RFPA2D is a good tool to directly display the potential slip surface of the slope, which will offer valuable guidance for bolt support.

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13

Han, Feng Shan, and Li Song. "Numerical Simulation of Compressive Experiment for Rock with a Natural Interlayer." Applied Mechanics and Materials 217-219 (November 2012): 1389–92. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.1389.

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It is difficulty to make physical experiment for compressive experiment of rock with a natural interlayer I Natural interlayer affect greatly on mechanical property of rock. In this paper, Rock Failure Process Analysis Code RFPA is used to simulate influence of natural interlayer to compressive strength of rock by numerical simulation under compression. Through numerical simulation complete stress strain curve and peak load can be obtained for compressive experiment of rock with a natural interlayer. RFPA can be effectively used to investigate anisotropy of compression for rock with natural interlayer under different confining pressure. Numerical simulation show that anisotropy of compressive strength of rock with a natural interlayer varies with inclination of natural interlayer, as the confining pressure increase, the compressive strength, the plasticity and ductility increase for rock with a natural interlayer. That provides new method to analyze and investigate mechanical behavior for multilayer composite material such as rock mass with a natural interlayer，finally Index of Anisotropy for rock with a natural interlayer are put forward

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Lu, Weiyong, Yonglong Wang, and Xin Zhang. "Numerical Simulation on the Basic Rules of Multihole Linear Codirectional Hydraulic Fracturing." Geofluids 2020 (March 3, 2020): 1–14. http://dx.doi.org/10.1155/2020/6497368.

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Directional rupture is one of the most important and common problems in rock breaking engineering. The purpose of directional rock breaking can be effectively realized by using multihole linear codirectional hydraulic fracturing. In this paper, realistic failure process analysis (RFPA) software is used to verify the experimental results of multihole linear codirectional hydraulic fracturing and investigate its basic law. The following results are demonstrated: (1) RFPA software can be very helpful to study the basic law of multihole linear codirectional hydraulic fracturing; (2) the process of multihole linear codirectional hydraulic fracturing can be divided into four stages: water injection boost, fracture initiation, stable fracture propagation, and fracture connection; and (3) multihole linear codirectional hydraulic fractures propagate along the direction of borehole distribution. Multihole codirectional hydraulic fracturing is influenced by the angle between the direction of the hole distribution and maximum principal stress, the difference of the principal stress, and the spacing of the boreholes. The smaller the angle, the difference value of the principal stress, and the hole spacing, the better the multihole codirectional hydraulic fracturing effect.

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Li, L. C., C. A. Tang, C. W. Li, and W. C. Zhu. "Slope stability analysis by SRM-based rock failure process analysis (RFPA)." Geomechanics and Geoengineering 1, no. 1 (March 22, 2006): 51–62. http://dx.doi.org/10.1080/17486020600552223.

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Yuan, L., Tao Xu, and Q. Xu. "Spallation of Concrete under Dynamic Loading: Mesh Size Effect." Applied Mechanics and Materials 50-51 (February 2011): 929–33. http://dx.doi.org/10.4028/www.scientific.net/amm.50-51.929.

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Spallation of concrete under dynamic loading has been the hot issue of concern about civil engineering structures and protective engineering. In the present paper, the principle of propagation of stress wave and the induced spallation process along a one-dimensional bar and the RFPA-Dynamics code which considers the heterogeneity of the concrete materials are briefly introduced. In order to numerically investigate the effect of mesh size of numerical model on the computational results, the failure process of concrete with three mesh sizes under dynamic loads was numerically simulated using RFPA-Dynamics code. Numerical simulations show that the failure patterns of concrete with different mesh sizes under dynamic stress waves are different. It is found that for the numerical models with the same mechanical parameters, the smaller mesh size of the numerical model is, the longer propagation of stress wave delay, the smaller the compressive stress is, thus the greater the tensile stress is, and the number of cracks is increasing, in general, rupture is more serious. The accuracy of mesh is little to improve when the number of the grid increases to a certain value.

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Zhang, Yanbo, Jian Li, and Baozhu Tian. "Numerical Simulation of Rock Burst of Circular Roadway Based on RFPA Software." MATEC Web of Conferences 31 (2015): 13002. http://dx.doi.org/10.1051/matecconf/20153113002.

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Tang, Chun An, Chien Hsin Yang, Tao Xu, and Tian Hong Yang. "Theoretical, Numerical and Experimental Study of Deformation and Failure Process of Rock." Key Engineering Materials 261-263 (April 2004): 1529–34. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.1529.

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In this paper, theoretical constitutive model, numerical tool, viz., RFPA code and servo-type testing machine, viz., RMT-150B rock testing systems were briefly described, respectively. Then, based on theoretical analysis, numerical simulation and experimental tests for rock specimens in uniaxial compression, the relations and differences between theoretical, numerical and experimental results, especially the complete stress-strain curves, were contrastively analyzed and investigated. The reason for these relations and differences among results was also proposed in this paper.

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Liu, Bao Yong, and Di Yang. "Numerical Simulation Study on High Dip Bedded Soft Rock Slope Stability of Surface Mine." Advanced Materials Research 868 (December 2013): 391–94. http://dx.doi.org/10.4028/www.scientific.net/amr.868.391.

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According to the actual progress of a certain Surface Mine and based on strength reduction method, the deformation and fracture processes of the high dip bedded soft rock slope was simulated with RFPA-SRM, the stability of the slope was calculated. By analyzing the numerical simulation results, the characters of the deformation of high dip bedded soft rock slope and the landslide mode were demonstrated, which could provide a scientific basis for reasonable landslide control measures.

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Zuo, Yu Jun, Yong Bin Zhang, Shu Cai Li, Yi Ping Zhang, and Chun Chun Chen. "Numerical Tests of Tunnel Reinforcing Influences on Zonal Disintegration within Rockmass around Deep Tunnel." Advanced Materials Research 261-263 (May 2011): 1282–86. http://dx.doi.org/10.4028/www.scientific.net/amr.261-263.1282.

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Nnumerical tests on three-dimensional failure process of rock samples containing vertical wall semi-arched tunnel with and without reinforcing are carried out with Mechsoft’s RFPA-Parallel system running on Lenovo 1800 Cluster, reproducing zonal disintegration phenomenon within rockmass around deep tunnels, and then the deep tunnel reinforcing influences on zonal disintegration within rockmass around tunnel is analyzed. Numerical results indicate that deep tunnel reinforcing does not change the general nature to form zonal disintegration phenomenon, but it can improve the stability of the tunnel wall.

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Huang, Bo, Tian Hui Ma, Ai Shan Li, Jian Qiu Sun, and Liao Yuan Zhang. "Study on Hydraulic Fracturing Affected by Horizontal Principal Stress." Applied Mechanics and Materials 423-426 (September 2013): 1467–70. http://dx.doi.org/10.4028/www.scientific.net/amm.423-426.1467.

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Adopted with the actual value of statistic geo-stress, using RFPA software to simulate the hydraulic fracturing of underground. The sample is treated as elastomers and simplified into plane problem, submit strength, elastic modulus, poisson ratio to weibull distribution. It could be found in figures that the size, length, extending direction of two crack is not identical. The cracks` forms grow into symmetry horizontal double-wing crack from the final result, besides, crack propagation direction is perpendicular to the direction of the minimum principal stress.

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Zou, Guang Ping, and Pei Xiu Xia. "Numerical Testing for Dynamic Fracture of Three Point Bending Cement Mortar Specimen with Off-Center Edge-Crack." Key Engineering Materials 348-349 (September 2007): 533–36. http://dx.doi.org/10.4028/www.scientific.net/kem.348-349.533.

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In this paper, RFPA－dynamic numerical simulation system was adopted to simulate the entire process of the three–point bending specimen with off–center edge-crack propagation to the specimen macroscopic crack which under the dynamic load function. And showed the whole process of the cement mortar specimen crack propagation which under the dynamic load function, as well as the whole field stress distribution picture, and has carried on analysis the specimen destruction process, has pointed out the influence of the no dimension quantity a/L change to crack expansion path and the destruction form.

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Wang, Yan, and Zheng Zhao Liang. "Numerical Study of the Rock Fragmentation by Three TBM Cutters." Advanced Materials Research 594-597 (November 2012): 3–7. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.3.

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Based on the mesoscopic damage theory and the finite element method, a numerical code RFPA was applied to investigate the rock fragmentation by three TBM cutters loaded one after another in different time interval. The whole process of crack initiation and propagation was successfully simulated by the cutters loaded with different step intervals. The time interval of the disc cutters has significant influence on the fracture patterns and the rock breaking efficiency. The simulated results show that there are three types of breakage mode of the rock subjected to compression by the cutters.

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Nan, Hua, Tao Xu, and Zhi Dong Wei. "Application of RFPA^2D in Sublevel Caving Mining Extra-Thick Coal Seams." Materials Science Forum 575-578 (April 2008): 1246–51. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.1246.

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On the basis of suitable arrangement for the special stress surrounding and parameters selection, Realistic Failure Process Analysis 2-D (RFPA2D) numerical simulation of extra-thick coal seams’ displacement and failure is carried out. It’s proved that the numerical simulation results are consistent with the in-sit measurement results of top coal’s advance supporting stress and deep-hole displacement. So application of RFPA2D in sub-level caving mining extra-thick coal seams is reliable. It’s also proved that application of RFPA2D in sub-level caving mining can do great help to study the nature of top coal’s displacement, fragmentation and failure process of extra-thick coal seams. As the top coal’s displacement and failure situation under certain circumstance can be forecasted by RFPA2D numerical simulation, the most suitable top coal thickness under certain circumstance can be predicted by RFPA2D numerical simulation test, which can do great benefit to extra-thick coal seams’ safe and high efficient mining.

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Wang, Dong, Lan-zhu Cao, Chun-de Piao, Ying-dong Xue, and Meng Wang. "Study on high and steep slope stability of surface mine based on RFPA-SRM." Journal of Coal Science and Engineering (China) 17, no. 2 (May 21, 2011): 119–23. http://dx.doi.org/10.1007/s12404-011-0202-5.

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Fan, Cheng. "Failure Behavior Numerical Test of Empress All-Ceramic Crowns." Advanced Materials Research 699 (May 2013): 476–79. http://dx.doi.org/10.4028/www.scientific.net/amr.699.476.

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All-ceramic crown restorations are more widely used, however the brittleness of ceramics and stress mismatch of porcelain interlaminar often leads to damage of all-ceramic crown, and damage mechanism is not very clear. In this paper, a two dimensional model of Empress all-ceramic crowns is constructed using the RFPA (realistic failure process analysis) system to simulate the fracture process and analysis the fracture mechanism. The most advantage of this system is that the crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application.

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Wang, Da Guo, Ju Ying Yang, Li Chong Li, and Wei Jiang. "Numerical Simulation of Short Cracks in Fiber-Reinforced Ceramics." Key Engineering Materials 324-325 (November 2006): 947–50. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.947.

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In this paper, a numerical code, Realistic Failure Process Analysis code (RFPA), was used to perform a microscopic analysis of a crack in a fiber-reinforced ceramic, when the crack length is the same order of magnitude as the fiber spacing. The numerical results performed in the paper shown the failure process of fiber-reinforced ceramic subjected to tension loading, which indicate that the reinforcing fibers in a ceramic composite have a significant effect in inhibiting crack propagation even during the stages of the development of crack. Moreover, the fiber evidently increased the load-carrying capacity.

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Wang, Shu Hong, Juan Xia Zhang, Chun An Tang, and Shan Yong Wang. "Modeling of the Effect of Excavation Mode on the Extent of the Anisotropic Zone Surrounding Deep Tunnels." Key Engineering Materials 353-358 (September 2007): 3014–17. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.3014.

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A series of numerical model tests were performed to investigate the behaviour of the anisotropic rock surrounding circular excavations under high confining pressures. The aim was to provide information on the formation of fractures and failure around deep level rock tunnels under controlled conditions. Solid cubes containing a circular hole were confined to a vertical pressure with same as the confinement in the horizontal directions. In this modeling, the inhomogeneous rock is generated by using Weibull parameters which are related to the microstructural properties determined by crack size distribution and grain size. The fracture angle is assumed to be 45o. The observed failure zone around the excavation was simulated using both the maximum tensile strain criterion and Mohr-Coulomb criterion respectively (as the damage threshold). And RFPA (Realistic Failure Process Analysis) code was used as the calculating tool in this modelling, three opening modes are simulated and compared. Computational model predictions that include crack propagation and failure modes of rock show a good agreement with those of the observation in site. It is pointed out that the damage evolution of EDZ strongly depends on the inhomogeneous, the excavation mode, anisotropic property, and the various loading conditions. Concerning the existence of a weak plane, the amount of displacement at the side wall of the tunnel was quite large, since the shear deformation occurred in EDZ. The model is implemented in RFPA code and is able to represent the change in fracture patterns between the solid and jointed parts. This provides confidence for the application of the numerical model to the design of rock tunnels at great depth.

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Fan, Cheng, Geng Chen, and Shan Shan Wang. "Numerical Simulation of Failure Process of VITA All-Ceramic Crowns." Advanced Materials Research 602-604 (December 2012): 544–47. http://dx.doi.org/10.4028/www.scientific.net/amr.602-604.544.

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Ceramic materials has approximate color and translucency with natural tooth, which is unmatched by other restorative materials. Because of its beautiful appearance, good physical and chemical properties, all-ceramic crown restorations are more widely used. However, due to the brittleness of ceramics and the stress mismatch between different materials, failure phenomenon is often observed during the service period of all-ceramic crowns. The failure process and mechanism are not clear, in this paper, the force performance of all-ceramic crowns is analyzed using the RFPA (realistic failure process analysis) system. The crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application.

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Fan, Cheng. "Analysis of Fracture Behavior of Metal/Ceramic Functionally Graded Materials under Thermal Stress." Advanced Materials Research 750-752 (August 2013): 2200–2205. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.2200.

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In this presented work, a coupled thermo-mechanical model is employed to analyze the thermo-mechanical behavior of ceramic functionally graded materials (FGMs) and the crack formation and propagation process of ceramic coating was simulated step in step and step by step using the RFPA (Realistic Failure Process Analysis) 2D-Thermo code. The thermal shock fracture behavior is discussed based on the basis of the simulated crack morphology and elucidated the mechanism of crack deformation and crack propagation. The state change from compression to tension whose magnitude is large enough to exceed the tension strength of ceramic causes the vertical crack. The numerical results agreed well with the experimental results in the previous literature.

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Zhang, Zhi Zhen, Feng Gao, Yang Cui, and Xiao Ji Shang. "Study of Crack Initiation and Propagation in Rock under Coupled Static and Dynamic Loads." Applied Mechanics and Materials 99-100 (September 2011): 687–91. http://dx.doi.org/10.4028/www.scientific.net/amm.99-100.687.

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In order to research the crack initiation and propagation behavior in rock mass under coupled static and dynamic loads, the crack initiation angle and expansion angle formulas are set up by use of the fracture mechanics theory, then numerical simulation of crack propagation are conducted using software RFPA. The results show that: the crack always extend toward the dynamic stress direction; the bigger of the crack dip, the smaller of the crack initiation angle and the more difficulty of the crack initiation and propagation, meanwhile the less influence to the damage of rock. What’s more, when the crack dip is small, theoretical value and numerical simulation value of initiation angle will be have good uniformity.

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Li, Tianjiao, Chun'an Tang, Jonny Rutqvist, and Mengsu Hu. "TOUGH-RFPA: Coupled thermal-hydraulic-mechanical Rock Failure Process Analysis with application to deep geothermal wells." International Journal of Rock Mechanics and Mining Sciences 142 (June 2021): 104726. http://dx.doi.org/10.1016/j.ijrmms.2021.104726.

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Liu, Hong Lei, and Tao Qin. "Numerical Study on Seepage Mechanism of Rock Failure." Applied Mechanics and Materials 522-524 (February 2014): 1399–402. http://dx.doi.org/10.4028/www.scientific.net/amm.522-524.1399.

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Based on the heterogeneity of rock, the application of the theory of elastic damage mechanics, the Biot seepage mechanics and the theory of effective stress, considering the rock damage before and after the crack extension and penetration, the numerical calculation model using software RFPA is established in this article. Through the simulation research of rock specimens under the conditions of different osmotic pressure difference of seepage damage law, results show that the permeability coefficient of the rock and the crack, expansion and penetration is directly related to, but also affected by the failure mode of the rock. Permeability changes obviously lags behind the rock damage and crack or fissure extension, permeability of kick also lags behind the peak strength of rock.

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Huang, Zhi Qiang, Xiao Yu Zhou, and Jie Hou. "Numerical Analysis on Roller Compacted Concrete under the Action of Pure Water Pressure." Applied Mechanics and Materials 174-177 (May 2012): 502–7. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.502.

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Based on the RCC（roller compacted concrete） gravity dam, considering the multiphase, heterogeneity and microscopic structure characteristics of RCC, we use the RFPA analysis system to analyze the whole destruction process of the RCC weak level under the action of the pure water pressure in this paper. By simulation, we obtained the distribution of the stress, elastic modulus, water pressure on the whole failure process of RCC weak level and several parameters, such as the up crack load, instability load and critical crack propagation length. By calculation, we got the double K fracture toughness of RCC under the different of water pressure, and the results show that the up crack toughness and instability toughness change regularly with the increasing of water pressure initial value in the mass.

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Mariappan, Selvakumar, Jagadheswaran Rajendran, Harikrishnan Ramiah, Norlaili Mohd Noh, and Asrulnizam Abd Manaf. "The Evolution of Integrated CMOS Power Amplifiers for Next Generation Mobile Wireless Transceivers." Journal of Circuits, Systems and Computers 29, no. 07 (September 24, 2019): 2030007. http://dx.doi.org/10.1142/s021812662030007x.

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Wireless communication standard continues to evolve in order to fulfill the demand for high data rate operation. This leads to the exertion on the design of radio frequency power amplifier (RFPA) which consumes high DC power in order to support linear transmission of high data rate signal. Hence, operating the PA with low DC power consumption without trading-off the linearity is vital in order to achieve the goal of achieving fully integrated system-on-chip (SoC) solution for 4G and 5G transceivers. In this paper, the evolution of CMOS PA toward achieving a fully integrated transceiver solution is discussed through the review of multifarious CMOS PA design. This is categorized into the review of efficiency enhancement designs followed by linearity enhancement designs of the CMOS PA.

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Fan, Cheng. "Fracture Mechanics Analysis of GI All-Ceramic Crowns." Advanced Materials Research 750-752 (August 2013): 529–32. http://dx.doi.org/10.4028/www.scientific.net/amr.750-752.529.

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Dental ceramic materials have approximate color and translucency with natural tooth, which is unmatched by other restorative materials. Because of its beautiful appearance, good physical and chemical properties, all-ceramic crown restorations are more widely used., However, due to the brittleness of ceramics and the stress mismatch between different materials, dropping or fracture phenomenon of porcelain veneer is often occurred in clinical application during the service period of all-ceramic crowns. The porcelain veneer failure mechanism is still not very clear, in this paper, the force performance of all-ceramic crowns is analyzed using the RFPA (realistic failure process analysis) system. The crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application

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Wang, Shu Hong, Deng Pan Qiao, Peng Jia, and Nan Zhang. "Micromechanical Analysis of Excavation Damaged Zone in Anisotropic Rock Mass." Key Engineering Materials 324-325 (November 2006): 81–84. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.81.

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Rock is a heterogeneous and anisotropic compound material, containing many shear surfaces, cracks, weak surfaces and faults. Damage and failure in a rock mass can occur through sliding along persistent discontinuities, or fractures. A new micromechanical approach to modeling the mechanical behavior of excavation damaged or disturbed zone (EDZ) of anisotropic rock is presented based on knowledge of the inhomogeneity of rock. In this numerical model, damage is analyzed as a direct consequence of microcracks growth. A study of the effect of elastic and failure anisotropy plus inhomogeneity on the underground excavations reveals that the modes of failure can be significantly influenced by the rock structure on the small and large scales. Fractures that develop progressively around underground excavations can be simulated using a numerical code called RFPA (Realistic Failure Process Analysis). This code incorporates the microscopic inhomogeneity in Young’s modulus and strength characteristic of rock. In the numerical models of a rock mass, values of Young’s modulus and rock strength are realized according to a Weibull distribution in which the distribution parameters represent the level of inhomogeneity of the medium. Another notable feature of this code is that no a priori assumptions need to be made about where and how fracture and failure will occur – cracking can occur spontaneously and can exhibit a variety of mechanisms when certain local stress conditions are met. These unique features have made RFPA capable of simulating the whole fracturing process of initiation, propagation and coalescence of fractures around excavations under a variety of loading conditions. The results of the simulations show that the code can be used not only to produce fracturing patterns similar to those reported in previous studies, but also to predict fracturing patterns under a variety of loading conditions. The numerical model was able to reproduce the associated complex stress patterns and the microseismic emission distribution for a variety of rock structural conditions.

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Sun, Ya Zhen, Xiao Xing Zhai, and Jie Min Liu. "Analysis of Failure Mode and Propagation for Crack in Uniaxial Compression." Applied Mechanics and Materials 166-169 (May 2012): 2929–32. http://dx.doi.org/10.4028/www.scientific.net/amm.166-169.2929.

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This paper analyzed the failure mode for crack in uniaxial compression according to the stress intensity factor, and obtain that the failure mode for crack in uniaxial compression is compression-shear. The wing crack was deformed, after the crack tip initiate. By analyzing the dimensionless stress intensity factor, we obtain that the failure mode for wing crack in uniaxial compression is tension-shear, and we obtain that the dimensionless stress intensity factor for wing crack decreased with inclined angle increased. The inclined crack propagation in uniaxial compression was numerically studied using rock failure process analysis code (rfpa), and obtain that one inclined crack in uniaxial compression formed mode I offset crack parallel to load direction in the end. The numerical results of failure mode are accordance with stress intensity factor.

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Fan, Cheng. "Fracture Pattern Comparison Research of Different Types of All-Ceramic Crown." Advanced Materials Research 699 (May 2013): 480–83. http://dx.doi.org/10.4028/www.scientific.net/amr.699.480.

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All-ceramic crown restorations are more widely used. The mechanical properties of different type of all-ceramic crown are evident different because of the differences of materials and production process. To study the failure pattern of different all-ceramic crown under load, two dimensional finite element model of three different all-ceramic crown models are constructed using the RFPA (realistic failure process analysis) system in this paper. Due to the difference of stress mismatch between different porcelain layers, it is found that the failure modes of different all-ceramic crown model are significantly different in the study. The advantage of this system is that the crack initiation, propagation and failure process of all-ceramic crown can be clearly observed and the research results provide guidance for clinical application.

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Li, Lian Chong, Chun An Tang, and P. A. Lindqvist. "Fracture Behavior in a Rock Pillar Subjected to Coupled Thermo-Mechanical Loading." Key Engineering Materials 324-325 (November 2006): 443–46. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.443.

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Using RFPA code, analyses have been carried out to investigate the stability of a rock pillar in a experiment for nuclear waste repositories, the numerically obtained stress field, temperature distribution, failure pattern of the pillar rock and associated AE events are all agree well with the in-situ data. Minor fracture initiation may take place in the vicinity of the boreholes after heating. Heating induces minor spalling at central pillar wall for 0.5 m sections below the tunnel floor, but the area of spalling is found to be limited. The core of the pillar remains intact for stress conditions corresponding to 120 days of heating which not only prove that the proposed technique provides a powerfully alternative and effective approach for the study on thermal-mechanical-damage coupling mechanism but also provide meaningful guides for the experiment design and associated applications.

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Zhao, Hong Hui, Hong Wen Jing, and Hai Jian Su. "Study on Strength Properties and Crack Expansion Evolution Laws of Rock Containing Multiple Fissures." Applied Mechanics and Materials 353-356 (August 2013): 608–13. http://dx.doi.org/10.4028/www.scientific.net/amm.353-356.608.

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Through experiments that were carried out to study the rock-like specimens with nine fissures under uniaxial compression by YNS2000 electro-hydraulic servo test system, to reveal the mechanism about strength and mechanism about crack expansion evolution laws of rock containing multiple fissures. Applying numerical simulation (RFPA) for the whole failure process of rock containing multiple fissures with reasonable parameters, the results present the influence mechanism of different confining pressures for strength and crack expansion characteristics. The experimental results show: the peak strength of specimens with nine fissures degrades obviously compared with complete specimens; Specimens containing multiple fissures begin to crack with tension cracks, and break with shear cracks finally. With the increase of confining pressure, the compressive strength of rock containing multiple fissures increases gradually; And crack expansion generally occurs on the middle diagonal fissure-plane under high confining pressure.

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Ma, Tianhui, Long Wang, Fidelis Tawiah Suorineni, and Chunan Tang. "Numerical Analysis on Failure Modes and Mechanisms of Mine Pillars under Shear Loading." Shock and Vibration 2016 (2016): 1–14. http://dx.doi.org/10.1155/2016/6195482.

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Severe damage occurs frequently in mine pillars subjected to shear stresses. The empirical design charts or formulas for mine pillars are not applicable to orebodies under shear. In this paper, the failure process of pillars under shear stresses was investigated by numerical simulations using the rock failure process analysis (RFPA) 2D software. The numerical simulation results indicate that the strength of mine pillars and the corresponding failure mode vary with different width-to-height ratios and dip angles. With increasing dip angle, stress concentration first occurs at the intersection between the pillar and the roof, leading to formation of microcracks. Damage gradually develops from the surface to the core of the pillar. The damage process is tracked with acoustic emission monitoring. The study in this paper can provide an effective means for understanding the failure mechanism, planning, and design of mine pillars.

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Chau, K. T., Wan Cheng Zhu, Chun An Tang, and S. Z. Wu. "Numerical Simulations of Failure of Brittle Solids under Dynamic Impact Using a New Computer Program - DIFAR." Key Engineering Materials 261-263 (April 2004): 239–44. http://dx.doi.org/10.4028/www.scientific.net/kem.261-263.239.

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This paper presents a new computer program called DIFAR (or dynamic incremental failure analysis of rock) that can simulate fracture process of brittle rocks under dynamic impacts. The program is based on a linear elastic finite element method incorporated with a failure criterion for damage checking. Modulus is reduced once the failure criterion is satisfied. In addition, Weibull distribution of the modulus and strength of the elements are used for modeling the mesoscopic heterogeneity. The failure criterion is a Mohr-Coulomb type of condition with a tensile cut-off, in which strength parameters are functions of the strain rate. More importantly, the whole fracture process of rock fragmentation can be simulated, including initiation, propagation, and coalescence of microcracks. The program DIFAR has been used to simulate elastic wave propagation and nonlinear fragmentation, and validity and efficiency of this program is demonstrated. The program can be considered as a dynamic counterpart of the RFPA, a failure analysis program for static loads, developed at Northeastern University, China.

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Zhang, Yong Jun, Nian Jie Ma, Zi Min Zhang, and Tian Rang Jia. "Numerical Simulation of Gas Distribution and Mined Seepage Passage with the Pressure Relief of Short Distance Protective Coal Stratum." Applied Mechanics and Materials 105-107 (September 2011): 1517–20. http://dx.doi.org/10.4028/www.scientific.net/amm.105-107.1517.

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With the full consideration of the heterogeneity, existing joints, and cracks in the rock, the coupled gas-rock model for investigating the failure process of coal-rock is established by introducing the related equations governing the evolution of stress, damage and gas permeability along with the deformation of coal and rock. A numerical approach of realistic failure process analysis (RFPA) to simulate the stratum movement, layer separation, the whole collapse progresses, and gas permeability changing of the protected coal seam is proposed. The numerical simulation results well displayed the whole processes of the cracks growth of gas seepage passage and the change of gas permeability for the closed distance protected coal seam. It can be seen from the distribution of acoustic emission in the space that the stratum failure is transferred from deeper to surface. By the analysis of the stress fields changing, the reasons of the gas permeability improvement of the protected coal seam are presented.

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Feng, Huan Huan, Kui Chen, Jian Jun Zhou, Feng Yuan Li, and Zhu Feng Wang. "Design and Study on a Vertical Comprehensive Experimental Platform for Function between Disc Cutter and Rock." Advanced Materials Research 798-799 (September 2013): 361–64. http://dx.doi.org/10.4028/www.scientific.net/amr.798-799.361.

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For better research on rock breaking mechanism of shield disc cutter, a kind of vertical experimental platform was designed after the characteristic analysis of existing linear cutting rig, using rock box turning to realize the rotary simulated motion of shield disc cutter. Compared with the linear device, this experiment platform overcomes the lack of real simulation of shield disc cutter movement condition. The design of comprehensive experimental platform was described particularly from the three aspects of electronic control system, hydraulic system and an adjusting device for cutter space. On the produced platform, which is the first one in China, the experiments of rolling experiment under three cutters sequential indentation were performed. The experimental data and analysis result were basically consistent with engineering data and simulation result based on RFPA. The correctness of design scheme, advancement and scientificalness of experiment platform were confirmed, with the hoping of providing dependable platform for the research on rock breaking mechanism of shield disc cutter.

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Song, Li, Hou Quan Zhang, Zheng Zhao Liang, Ming Ruo Jiao, Tian Hui Ma, Juan Xia Zhang, and Liexian Tang. "Effect of Element Size on Rock Shear Strength and Failure Pattern by Rock Failure Progress Analysis (RFPA^2D)." Key Engineering Materials 297-300 (November 2005): 2573–78. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2573.

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Six types of numerical specimens containing two notches are set up to numerically investigate the effect of element size on rock shear strength and failure pattern using RFPA2D (rock failure process analysis) code. These specimens are of the same geometrical dimension 180 mm×180 mm and have been discretized into 61×61, 122×122, 183×183, 244×244, 305×305, and 366×366 elements.The width of notches is about 2.95 (180/61) mm and the length is 45mm. The specimens are placed in a direct shear box. A lateral confining pressure with a value of 0.15MPa is invariably loaded in the vertical direction and an increasing horizontal displacement with 0.002mm/step is applied in the horizontal direction. The whole shear failure progress and associated stress field for the specimens are visually represented. Results show that the crack propagation is mostly influenced by the stress field in the vicinity of the notch tip, the required element size would be necessary in order to obtain good results. In general, for a coarse mesh, the stress field close to the notch tip can’t be represented accurately and shear strength obtained by such discretisation is slightly higher than the accurate value. For a fine mesh, the notch tip spreads through a relatively large number of elements and the stress field in vicinity of notch tip is well represented by the finite element approximation, therefore the failure pattern is consistent with real physical fracture mode.

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Hu, Jun, Ling Xu, and Nu Wen Xu. "Numerical Analysis of Faults on Deep-Buried Tunnel Surrounding Rock Damaged Zones." Applied Mechanics and Materials 90-93 (September 2011): 74–78. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.74.

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Fault is one of the most important factors affecting tunnel instability. As a significant and casual construction of Jinping II hydropower station, when the drain tunnel is excavated at depth of 1600 m, rockbursts and water inrush induced by several huge faults and zone of fracture have restricted the development of the whole construction. In this paper, a progressive failure progress numerical analysis code-RFPA (abbreviated from Rock Failure Process Analysis) is applied to investigate the influence of faults on tunnel instability and damaged zones. Numerical simulation is performed to analyze the stress distribution and wreck regions of the tunnel, and the results are consistent with the phenomena obtained from field observation. Moreover, the effects of fault characteristics and positions on the construction mechanical response are studied in details. Some distribution rules of surrounding rock stress of deep-buried tunnel are summarized to provide the reasonable references to TBM excavation and post-support of the drain tunnel, as well as the design and construction of similar engineering in future.

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Gao, Mingzhong, Sheng Zhang, Jie Li, and Haiyun Wang. "The dynamic failure mechanism of coal and gas outbursts and response mechanism of support structure." Thermal Science 23, Suppl. 3 (2019): 867–75. http://dx.doi.org/10.2298/tsci180610122g.

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In view of the common mine disasters such as coal and gas outburst caused by the destruction of gas and coal, the numerical model of RFPA-GAS software was used to establish a numerical model based on a gas outburst accident took place in return roadway of working face 15-17-16041 in Pingdingshan mine. The dynamic failure mechanism of coal and gas outburst under the conditions of different support strengths protection and unsupported conditions was analyzed. Four dynamic processes of coal and gas outburst were discussed, and the dynamic failure mechanism of coal and gas outburst was revealed. The results show that the outstanding effect of the roadway without support treatment is similar to that of the field, and the coal and gas outburst is obviously weakened for supported roadway. Which has effective control of the active support for the protrusion. When the support method is designed, the response mechanism of the coupled support structure should be considered. It provides some theoretical support for the gas outburst control.

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Yu, Xiang, Kang Zhao, Qing Wang, Yajing Yan, Yongjun Zhang, and Junqiang Wang. "Relationship between Movement Laws of the Overlaying Strata and Time Space of the Mined-Out Volume." Geofluids 2020 (March 27, 2020): 1–9. http://dx.doi.org/10.1155/2020/2854187.

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The study and accurate prediction of the movement of overburden rock mass and surface subsidence are crucial for a safe production in metal mines. This study investigates the relationship between the movement laws of overlaying strata and the time space of a mined-out volume using Rock Failure Process Analysis (RFPA) System. Furthermore, the movement, deformation, and failure laws of overlaying strata are examined in different positions when a goaf volume is certain and the failure behavior of the overlaying strata. This study analyzes the similarities and differences of the overlaying strata comparatively. Results show that, regardless of the movement range or subsidence value of the overlying rock mass, a power function relationship is observed between them and working face advancement. Setting the equation shows that the scope of the overlying rock mass is significant when the ratio of a certain position distance roof to the working face distance is small. The results provide a reference for controlling the displacement of the overlying rock mass and treating goaf.

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Zhang, Ying, Lian Feng Gao, Shao Zhong Zhang, Juan Sun, and Peng Zhang. "Behaviour Characteristics of Pressure Bump of Deep Mining in Kailuan Coal Mine and Micro Seismic Monitoring Technology." Advanced Materials Research 201-203 (February 2011): 404–7. http://dx.doi.org/10.4028/www.scientific.net/amr.201-203.404.

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Pressure bump is a serious disaster to threat coal mine production safety. The roof and floor strata in Kailuan coal mine are made of sandstone and mudstone with relatively poor rigidity. Most of mines have been into the deep mining stage over one thousand meters. High-stress becomes the key factor induced pressure bump. In this paper, according to coal mining strata, fault development, mine inflow and other geological factors, based on fracturing parameters of mine rock and wall rock in the pilot mines (Qianjiaying Mine, Tangshan Coal Mine), boundary conditions of the occurrence of pressure bump is tested by numerical simulation using RFPA software. It discusses the mechanism and laws of pressure bump under high stress in the deep mining. Mining face and roadway are taken real-time monitoring, using micro seismic monitoring system (MMS). The location and level of micro seismic events within the coal formation caused by breakdown could achieve precise position. Spatial distribution and characteristics of coal and rock bursting could be identified. The stability of coal and rock could be monitored real-time and analyzed. Pressure bump could be predicted and prevented effectively.

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Journal articles on the topic 'RFPA'

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