A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radia...A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radiation, and convection. A formula for the calculation of the heat conductivity of a sintering system containing solid phase, liquid phase, and gas phase is given. Due to the continuous movement of the laser beam, a local coordinate system centered on the laser beam is used to simplify the analytical calculation. Assuming that it is approximately a Gaussian laser beam, the heat conduction equation is resolved based on the assumption of the thermal insulating boundary conditions and the fixed thermal physical parameters. The FORTRAN language is employed to compile the program to simulate the temperature field in the direct copper powder sintering process. It shows a good agreement with the preliminary experimental results.[KH3/4D]展开更多
The interaction of a single three-level trapped ion with two laser beams has been studied theoretically. With application of two successive unitary transformations, an analytical solution to this quantum system has be...The interaction of a single three-level trapped ion with two laser beams has been studied theoretically. With application of two successive unitary transformations, an analytical solution to this quantum system has been obtained.展开更多
The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine,and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under...The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine,and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating.Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field,molecular dynamics(MD)simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys.The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation,and the temperature field of the molten pool is normally distributed from the center to the edge.When the center temperature reaches the critical point of ignition,the extended combustion occurs,and the extended combustion path advances along the direction of the air flow.Compared with Ti-6Al alloy,Ti-48Al alloy has higher fire retardancy under laser ablation.This is due to the better heat transfer performance of Ti-48Al,which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field.So it is necessary to increase the partial pressure of oxygen,and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source.In the aspect of extended combustion path,the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow.That is,the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction,resulting in a concentration of heat near the boundary.So the combustion path also tends to expand along this direction.展开更多
文摘A mathematical model is developed for simulating the heat transferring behavior in a direct metal laser sintering process. The model considers the thermal phenomena involved in the process, including conduction, radiation, and convection. A formula for the calculation of the heat conductivity of a sintering system containing solid phase, liquid phase, and gas phase is given. Due to the continuous movement of the laser beam, a local coordinate system centered on the laser beam is used to simplify the analytical calculation. Assuming that it is approximately a Gaussian laser beam, the heat conduction equation is resolved based on the assumption of the thermal insulating boundary conditions and the fixed thermal physical parameters. The FORTRAN language is employed to compile the program to simulate the temperature field in the direct copper powder sintering process. It shows a good agreement with the preliminary experimental results.[KH3/4D]
基金The project supported by the Natural Science Foundation of Education Committee of Anhui Province of China under Grant No. 2004kj186
文摘The interaction of a single three-level trapped ion with two laser beams has been studied theoretically. With application of two successive unitary transformations, an analytical solution to this quantum system has been obtained.
基金China“Ye Qisun”Science Foundation Project of National Natural Science Foundation(U2141222)AECC Innovation Fund(CXPT-2022-034)AECC BIAM Innovation Fund(KJSJ231506)。
文摘The high temperature fire retardancy of titanium alloy is an important factor restricting its application in aero-engine,and the laser ignition method can accurately reflect the fire retardancy of titanium alloy under local heating.Due to the limitations of laser ignition experiments on the microscopic boundary and the transient propagation mechanism of the temperature field,molecular dynamics(MD)simulations and JMatPro calculation were applied to study the temperature field of Ti-6Al and Ti-48Al alloys.The results show that a molten pool is formed on the surface of Ti-Al alloys under continuous laser irradiation,and the temperature field of the molten pool is normally distributed from the center to the edge.When the center temperature reaches the critical point of ignition,the extended combustion occurs,and the extended combustion path advances along the direction of the air flow.Compared with Ti-6Al alloy,Ti-48Al alloy has higher fire retardancy under laser ablation.This is due to the better heat transfer performance of Ti-48Al,which leads to the weakening of the heat concentration effect near the boundary of the spot temperature field.So it is necessary to increase the partial pressure of oxygen,and thus to reduce the ignition point of the alloy in order to achieve the ignition boundary condition of Ti-48Al alloy under the same laser heat source.In the aspect of extended combustion path,the boundary heat collection effect of specimens shown by MD models reveals another mechanism affecting combustion expansion path besides the direction of air flow.That is,the heat generated by the laser spot is interrupted when it is transmitted to the boundary of the specimen along the short side direction,resulting in a concentration of heat near the boundary.So the combustion path also tends to expand along this direction.
