Rosenberg, M.; Deppe, P.; Janssen, H.U.; Brabers, V.A.M.; Li, F.S.; Dey, S.

Two sound joints of Al–Cu bimetallic sheet with 6.5 mm in thickness were obtained in Cu (upper)–Al (lower) and Al (upper)–Cu (lower) welding configurations via the electron beam welding and their distinct coupling models were developed to well understand their flow behavior of the molten pool and microstructure evolution mechanisms during the electron beam welding. For the electron beam welding of the Cu–Al bimetallic sheet, liquid Al and Cu flowed into each other and fully combined in the fusion zone and the interface zone under high-temperature environment, forming large amount of intermetallic compounds. For the electron beam welding of the Al–Cu bimetallic sheet, liquid Al was floating on the Cu substrate, while liquid Cu was flowing at the bottom of the molten pool and mutually combined with liquid Al at the interface, forming a relatively small amount of intermetallic compounds. Moreover, a part of liquid Al flowed back to the seam root under the influence of the Marangoni effect. Therefore, the fusion zone and the interface zone with various phase compositions were formed in these two Al–Cu bimetallic joints and the mechanical properties of the corresponding joints were determined. Furthermore, the average tensile strengths of Cu–Al and Al–Cu bimetallic joints were 59 MPa and 67 MPa, respectively. The fracture locations of these two joints were both at the edge of the fusion zone along the Al2Cu intermetallic compound interlayer. Moreover, the fracture characteristics of these joints were mainly cleavage fracture.

No abstract

The dual-chamber solid and liquid mixture (SALiM) isolator exhibits multiple stiffness and damping properties with various parameters. As a passive isolation device, the dual-chamber SALiM isolator can also obtain a variable stiffness property by substituting the valve with an active throttle device. Before that, the dynamic properties of the isolator need to be further investigated. Sine sweep tests under different valve openings were implemented to analyze the frequency response characteristics of the system. Two hydro pressure sensors were added into the two chambers to record the pressure signals, with which the equivalent stiffness, equivalent damping, fluid damping, and equivalent mass of the liquid column were identified. Based on the test results, numerical and theoretical analysis, the dynamic properties of the isolator including the influence of the fluid damping and inertia mass on the equivalent stiffness, the relation between the isolator's equivalent damping and the fluid damping, the fluid capacity of the linking tube, and the equivalent mass of the liquid column were analyzed in depth. Conclusions about stiffness and damping obtained from the test results correspond well with those from the theoretical analysis, but the identification results of the equivalent mass, which show that the negative correlation of equivalent mass of the liquid column with its response amplitude seems controversial. An assumption is proposed to explain the abnormal characteristics of the liquid column. However, the exact model of the inertia track needs further exploration and verification.