By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure, two series of experiments on sandstone are carried out to research the failure mode of rock during the course...By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure, two series of experiments on sandstone are carried out to research the failure mode of rock during the course of exploitation of resources in deep. One is under the conditions that the con-fining pressure is fixed and the axial pressure is changeable. The other is under the conditions that the confining pressure becomes and the axial pressure is fixed. It is found that samples break up evenly after impacting when axial static pressures are low, there is great disparity in size of fragments when axial static pressures are high, and the main bodies of samples after the tests under the combination of dy-namic and static loads frequently show the type of V or X. The samples are more close-grained at the elastic stage and impacts make many cracks be generated and developed, as makes samples more crackable. At the initial phase of damage stage, the static pressures make some cracks in the samples which are undeveloped and the impacts′ role is similar to that at the elastic stage. At the metaphase or anaphase of damage stage, these cracks in the samples develop adequately and the impacts mainly accelerate samples′ failure. The main bodies of samples show the type of V or X after impacting due to the confining pressures′ restraining samples′ lateral formation at the elastic stage or the initial phase of damage stage, the main bodies of samples have almost formed at the stage loading static pressures and the results after impacting usually are similar to those under the axial pressures tests.展开更多
The aim of the article concerns to the achieved research results regarding the viability of a megawatt-class space power plant based on the Rankine cycle for which the main objectives are to highlight the key issues r...The aim of the article concerns to the achieved research results regarding the viability of a megawatt-class space power plant based on the Rankine cycle for which the main objectives are to highlight the key issues responsible for improving the Rankine cycle efficiency. Two working fluids are studied （water and ammonia） on the basis of its well known characteristics. Cycles operating under top and bottom temperatures approaching the state of the art technology associated to cooling fluid reservoirs are key to improve the efficiency. With such strategy, the achieved thermal efficiency increases more than 20% with respect to conventional power plants. Mentioned benefits associated to the strategy based on the reduction of the required payload capacity, the condenser radiation surface and the power plant mass represent the main advantages of the proposed innovation techniques.展开更多
In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-part...In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-particle model(BPM),which is suitable to simulate the fracture process of RC under explosive load,has been developed in the frame of discrete element method (DEM).In this model,only the elastic deformations of beams between concrete particles were considered.The matrix displacement method(MDM)was employed to describe the relationship between the deformation and forces of the beam.A fracture criterion expressed by stress was suggested to identify the state of the beam.A BPM for steel bar,which can simulate the deformation of steel bar under high loading rate,was also developed based on the Cowper-Symonds theory.A program has been coded using C++language.Experiments of RC slab under explosive load were carried out using the program.Good agreement was achieved between the experimental and simulated results.It is indicated that the proposed theoretical model can well simulate the fracture characteristics of RC slab under explosive load such as blasting pit formation,cracks extension, spallation formation,etc.展开更多
基金Supported by National Natural Science Foundation of China(No.10472134 and No.50490274)
文摘By means of the improved split Hopkionson pressure bar(SHPB) with axial pre-pressure and confined pressure, two series of experiments on sandstone are carried out to research the failure mode of rock during the course of exploitation of resources in deep. One is under the conditions that the con-fining pressure is fixed and the axial pressure is changeable. The other is under the conditions that the confining pressure becomes and the axial pressure is fixed. It is found that samples break up evenly after impacting when axial static pressures are low, there is great disparity in size of fragments when axial static pressures are high, and the main bodies of samples after the tests under the combination of dy-namic and static loads frequently show the type of V or X. The samples are more close-grained at the elastic stage and impacts make many cracks be generated and developed, as makes samples more crackable. At the initial phase of damage stage, the static pressures make some cracks in the samples which are undeveloped and the impacts′ role is similar to that at the elastic stage. At the metaphase or anaphase of damage stage, these cracks in the samples develop adequately and the impacts mainly accelerate samples′ failure. The main bodies of samples show the type of V or X after impacting due to the confining pressures′ restraining samples′ lateral formation at the elastic stage or the initial phase of damage stage, the main bodies of samples have almost formed at the stage loading static pressures and the results after impacting usually are similar to those under the axial pressures tests.
文摘The aim of the article concerns to the achieved research results regarding the viability of a megawatt-class space power plant based on the Rankine cycle for which the main objectives are to highlight the key issues responsible for improving the Rankine cycle efficiency. Two working fluids are studied （water and ammonia） on the basis of its well known characteristics. Cycles operating under top and bottom temperatures approaching the state of the art technology associated to cooling fluid reservoirs are key to improve the efficiency. With such strategy, the achieved thermal efficiency increases more than 20% with respect to conventional power plants. Mentioned benefits associated to the strategy based on the reduction of the required payload capacity, the condenser radiation surface and the power plant mass represent the main advantages of the proposed innovation techniques.
基金supported by the National Natural Science Foundation of China(Grant No.51044003)the National Basic Research Program of China("973"Project)(Grant No.2007CB714104)
文摘In the field of disaster prevention mitigation and protection engineering,it is important to identify the mechanical behaviors of reinforced concrete(RC)under explosive load by simulation.A three dimensional beam-particle model(BPM),which is suitable to simulate the fracture process of RC under explosive load,has been developed in the frame of discrete element method (DEM).In this model,only the elastic deformations of beams between concrete particles were considered.The matrix displacement method(MDM)was employed to describe the relationship between the deformation and forces of the beam.A fracture criterion expressed by stress was suggested to identify the state of the beam.A BPM for steel bar,which can simulate the deformation of steel bar under high loading rate,was also developed based on the Cowper-Symonds theory.A program has been coded using C++language.Experiments of RC slab under explosive load were carried out using the program.Good agreement was achieved between the experimental and simulated results.It is indicated that the proposed theoretical model can well simulate the fracture characteristics of RC slab under explosive load such as blasting pit formation,cracks extension, spallation formation,etc.
