This paper analyzes the anomalous power-law dependence of the ultrasound attenuation on frequency by means of a percolation model. It was suggested that the anomaLous ultrasound attenuation is associated with strongly...This paper analyzes the anomalous power-law dependence of the ultrasound attenuation on frequency by means of a percolation model. It was suggested that the anomaLous ultrasound attenuation is associated with strongly localized eigen modes (to be called fracton) in disordered systems. There exits a steplike increase in the density of vibrational states at crossover frequency ω(co).Computer simulation of vibration spectrum in disordered system is also reported. The density of vibrational states is consistent with the results of relevant experiment outlined above.展开更多
A new mechanical model for powder metallurgy compaction is presented. In this model, various amount of voids can be introduced into a continuous solid, therefore porosity can be conveniently controlled. The elastic-pl...A new mechanical model for powder metallurgy compaction is presented. In this model, various amount of voids can be introduced into a continuous solid, therefore porosity can be conveniently controlled. The elastic-plastic finite element method was used to analyze the sintered powder material. The model was used to simulate compressing of a sintered cylinder. MSC.Marc of MSC. Software Corporation was applied here, and the sintered powder model was built in MSC.Mentat. The sintered cylindrical powder metallurgy part is treated as a piece of normal metal with pores in the model. The metal block is considered as cylinder with a radius of 6.0 mm and a total height of 10.0 mm. Young’s module was assumed to be 4 000 MPa. Poisson’s ratio was 0.269. The initial yield stress is 210 MPa. Friction coefficient used for the upper and lower contact surfaces is 0.3. Coulomb principle is adopted. Considering axisymmetricity, just half a section is analyzed. Totally there are 1 240 elements. Experiment was carried out by a computer controlled a universal tensile testing machine. During the experiment, the sample was prepared from highly compressible water atomized iron powder with 0.6wt% polymeric lubricant. Particle size is about 100～150 μm. The comparison was performed using a sintered cylindrical sample. The green compact was sintered at 1 140 ℃ for 2 hours. Initially, H0 is 10.20 mm, Φ0 is 12.01 mm and the initial relative density is 0.789. After pressing, H is 7.30 mm, Φ1 is 13.10 mm, Φ2 is 14.64 mm and relative density is 0.88. The load-displacement curves agree with the experimental results very well. Plastic deformation of metallic material is mostly caused by the slipping of crystal lattice. Although very small, a metal powder particle is composed of metallic crystal. Mechanical properties of a powder particle should be very close to their as solid metal counterpart.展开更多
The porous superalloy materials with hollow spherical pores were fabricated by using metal powder sintering process. The scanning electron microscope （SEM） observation was applied to the test samples and it revealed...The porous superalloy materials with hollow spherical pores were fabricated by using metal powder sintering process. The scanning electron microscope （SEM） observation was applied to the test samples and it revealed that the pores of the porous material exhibited a uniform distribution and the apertures were of same size in principle. The sintering necks appeared between adjacent particles on metal skeleton after sintering. The mechanical properties of the test samples were analyzed and the result showed that this kind of materials possessed excellent energy absorption capability, and the compression resistance decreased with increasing the porosity and aperture.展开更多
文摘This paper analyzes the anomalous power-law dependence of the ultrasound attenuation on frequency by means of a percolation model. It was suggested that the anomaLous ultrasound attenuation is associated with strongly localized eigen modes (to be called fracton) in disordered systems. There exits a steplike increase in the density of vibrational states at crossover frequency ω(co).Computer simulation of vibration spectrum in disordered system is also reported. The density of vibrational states is consistent with the results of relevant experiment outlined above.
文摘A new mechanical model for powder metallurgy compaction is presented. In this model, various amount of voids can be introduced into a continuous solid, therefore porosity can be conveniently controlled. The elastic-plastic finite element method was used to analyze the sintered powder material. The model was used to simulate compressing of a sintered cylinder. MSC.Marc of MSC. Software Corporation was applied here, and the sintered powder model was built in MSC.Mentat. The sintered cylindrical powder metallurgy part is treated as a piece of normal metal with pores in the model. The metal block is considered as cylinder with a radius of 6.0 mm and a total height of 10.0 mm. Young’s module was assumed to be 4 000 MPa. Poisson’s ratio was 0.269. The initial yield stress is 210 MPa. Friction coefficient used for the upper and lower contact surfaces is 0.3. Coulomb principle is adopted. Considering axisymmetricity, just half a section is analyzed. Totally there are 1 240 elements. Experiment was carried out by a computer controlled a universal tensile testing machine. During the experiment, the sample was prepared from highly compressible water atomized iron powder with 0.6wt% polymeric lubricant. Particle size is about 100～150 μm. The comparison was performed using a sintered cylindrical sample. The green compact was sintered at 1 140 ℃ for 2 hours. Initially, H0 is 10.20 mm, Φ0 is 12.01 mm and the initial relative density is 0.789. After pressing, H is 7.30 mm, Φ1 is 13.10 mm, Φ2 is 14.64 mm and relative density is 0.88. The load-displacement curves agree with the experimental results very well. Plastic deformation of metallic material is mostly caused by the slipping of crystal lattice. Although very small, a metal powder particle is composed of metallic crystal. Mechanical properties of a powder particle should be very close to their as solid metal counterpart.
基金Item Sponsored by the Innovation Fund for Outstanding Scholar of Henan Province (0621000700)
文摘The porous superalloy materials with hollow spherical pores were fabricated by using metal powder sintering process. The scanning electron microscope （SEM） observation was applied to the test samples and it revealed that the pores of the porous material exhibited a uniform distribution and the apertures were of same size in principle. The sintering necks appeared between adjacent particles on metal skeleton after sintering. The mechanical properties of the test samples were analyzed and the result showed that this kind of materials possessed excellent energy absorption capability, and the compression resistance decreased with increasing the porosity and aperture.
