Search

为了给大跨径钢桁梁悬索桥抗疲劳设计提供依据，针对杨泗港长江大桥钢桁梁采用的整体焊接节点，开展了多轴疲劳荷载作用下整体焊接节点的有限元疲劳分析和试验研究。首先通过建立全桥有限元模型，基于英国BS 5400规范和Miner准则，获得了在标准疲劳车作用下全桥最不利整体节点及其各杆件200万次等效疲劳轴力幅；其次建立最不利整体节点空间精细化模型，通过对各轴向杆件施加200万次等效疲劳轴力幅，进行了多轴荷载下整体节点的疲劳性能分析；最后基于相似理论，设计了1：6的整体焊接节点缩尺模型，进行多轴荷载下的疲劳试验研究。结果表明：位于距主塔297 m距离的F34节点为疲劳最不利下弦杆整体节点；F34节点最大Von-Mises应力在78.8~130.6 MPa，小于设计规范的疲劳强度；200万次的模型疲劳加载试验过程中，未发现任何疲劳裂纹产生，各测点的应力值与理论值误差小于7.8%；杨泗港长江大桥钢桁梁整体焊接节点疲劳性能满足设计要求，研究成果对大跨径双层悬索桥抗疲劳设计具有直接的指导作用。To provide a reference for anti-fatigue design of long-span steel truss suspension bridge, aimed at integral welded joint adopted in Yangsigang Yangtze River Bridge, finite element analysis and test of integral welded joint under the multi-axial fatigue load were carried out. Firstly, in terms of BS 5400 specification and Miner criterion, the finite element model of whole bridge was established to obtain the most unfavorable integral joint under the standard fatigue vehicle, as well as the equivalent axial force amplitude of each member at integral joint when the cycle times reached two million. Secondly, a space refined model of the most unfavorable integral welded joint was built, and applying the equivalent axial force amplitude to each member, the fatigue performance of integral welded joint under the multi-axial fatigue load was analyzed. Finally, a fatigue test was carried out on a 1:6 scale model of integral welded joint on the basis of the similarity theory. The results show that the F34 node located at the distance of 297 m from the main tower is the most unfavorable integral joint at lower chord, and the maximum Von-Mises stress of the F34 node is between 78.8 MPa and 130.6 MPa, less than the fatigue strength stipulated in design specification. No cracks are detected in the test model after the two million cycles fatigue loading, and the max error between the measured and theoretical values is less than 7.8%. It can be seen that the fatigue performance of integral welded joint at steel truss girder of Yangsigang Bridge is reliable in anti-fatigue design, and the research results have a direct guidance to anti-fatigue design of long-span double-deck suspension bridge. Published version

To improve the wire bonding and homogeneous injecting currents,this paper proposes a Vertical Cavity Surface-emitting Laser(VCSEL) array with a non-closed structure.In this structure,a non-closed groove is etched to form a mesa for simplifying the processing and reducing the damage of devices.The 850 nm VCSEL arrays(including 2×2,3×3 and 4×4 array devices) with the non-closed type top emission structures are tested and analyzed.Results show that the continuous output powers are up to 80,140 and 480 mW at room temperature,threshold currents are 0.15,0.25 and 0.4 A,and the far-field divergence angles in parallel and vertical directions are 9° and 9.6°,13.5°and 14.4°,15° and 14.4°,respectively.In the context of a pulse width of 50 μs and a pulse repetition rate of 100 Hz,the maximum output powers are 90,318 and 1 279 mW and the threshold currents are 0.2,0.5 and 0.7 A,respectively.The power curves of chips are tested before and after packaged.The result shows that the heat saturation current of the chip after packaged is much higher than that of the chip before packaged,which suggests that good packaging can improve the cooling efficiency and reduce the effect of internal heating on the device performance.

For increasing the output powers without improving drive currents to high power Vertical Cavity Surface Emitting Lasers(VCSELs),a VCSEL in series structure was presented.First,the VCSEL chips were soldered on a AlN ceramic heat sink,then the chips were connected by a wire bonding in series.The output powers of four-chip devices in series,two-chip devices in series and a single device were measured under microsecond and nanosecond pulses,which are 775,416,217 mW and 18.9,9.8,5 W,respectively.Test results show that the output powers of the first two kinds of devices in series are about 4 times and twice that of the single device.Moreover,the Full Width at Half Maximum(FWHM) of multiple-chip devices in series is slightly wider than that of the single device,which can be improved by choosing good uniformity cascade chips.In conclusion,the VCSEL in series structure can increase the output power without improving the drive current.

High-brightness tapered laser diode at 850 nm was fabricated based on the AlGaInAs/A1GaAs chip with graded-index waveguide separate confinement hetero-structure.The tapered laser has better performance than the broad laser under the same condition.The lateral divergence angles of the tapered laser and the broad laser were 4° and 6° at the output power of 1 W,while the beam propagation factor M2 were 2.8 and 9.2,respectively.The slope efficiency of the tapered laser had a high value of 0.58 W/A and the conversion efficiency reached 30% in the output power 1.40 W under the injection current of 3 A.The facts indicated the tape-red laser would be an ideal choice for high brightness high power laser diodes.