Effects of Metal Absorber Thermal Conductivity on Clear Plastic Laser Transmission Welding

In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.

Dynamic Analysis for Structures Isolated with Dampers

In this paper, mathematical models and dynamic analyses for both SDOF and MDOF structures isolated with dampers are established and performed, and a comprehensive computation method is provided. The shock absorbing effect is illustrated through an example of a two DOF damper-isolated system excited by sinusoidal waves and actual ground acceleration input recorded in earthquakes. It is shown that most of the responses of the structure with dampers reduce greatly near the resonant zone, but acceleration is enlarged in the lower or higher frequency zone; among various parameters, the influence of frictional coefficient n is the most significant, that of damping ratio of the dampers , is the second, and that of stiffness coefficient of the dampers k, is the slightest.

Fabrication and efficient electromagnetic waves attenuation of three-dimensional porous reduced graphene oxide/boron nitride/silicon carbide hierarchical structures

In this work,hierarchical hybrid composites consisting of porous three-dimensional reduced graphene oxide(3D-rGO)skeleton and lamellar boron nitride(BN)/silicon carbide(SiC)coatings are prepared by chemical vapor infiltration(CVI)process.The graphene framework prepared by 3D printing and frozen self-assembly exhibits a lightweight structure and a perforated conductive network,which extends the transmission path of incident microwaves.The introduced ceramic coatings can effectively tune the impedance matching degree and supply a lossy phase,and the hierarchical structure of the composites enhances the multiple scattering of the incident microwaves.As expected,the 3D-rGO/BN/SiC composites possess an excellent absorbing performance with a minimum reflection loss value of–37.8 dB,and the widest effective absorbing bandwidth(RL<–10 dB)of 5.90 GHz is obtained.The controllable fabrication of composites can provide a guideline for rational design and fabrication of high-performance electromagnetic waves absorbing materials in practical applications.