No abstract

Compared with a single piezoelectric poly(vinylidene fluoride) (PVDF) sheet, a bimorph can enhance driving performance. The main aim of this work is to study a soft piezoelectric bimorph as an actuator used in a soft sail. PVDF samples were prepared using a hightemperature solvent evaporation method and were then drawn and poled. The crystalline phase, mechanical properties, piezoelectric property and energy-harvesting performance were analyzed. A PVDF piezoelectric bimorph was designed. The capacity of deformation of the parallel bimorph with a pulsed electric field was studied. The deformation of the sample increased almost linearly, and the deformation performance was obvious with the increase in voltage. To evaluate its driving performance in the engineering model, a sail made of Kapton was produced, and the PVDF bimorph was used as an actuator to drive the sail. The deformation was observed by a Video-Simultaneous Triangulation and Resection System. Furthermore, the finite element method was used to further understand the actuation effect of the Kapton sail matrix and PVDF bimorph actuator according to three different laying methods.

C/SiC composites and Nb were vacuum brazed with the Ti 39?4 Ni 39?4 Nb 21?2 alloy being the active filler metal. The mechanical properties of the filler material, the microstructure and the strength of brazing joints were investigated. The results showed that the filler TiNiNb alloy has a tensile strength of 860 MPa, an elongation of 51% and an elastic modulus of 78 GPa. Both Ti and Nb elements in the filler reacted with C/SiC during the brazing process, and a well bonded C/SiC-Nb joint was obtained. The ductile filler metal released the thermal stress in the joint. When the brazing was performed at 1220uC for 20 min, the shear strength of brazed joints reached 149, 120 and 73 MPa at 20, 600 and 800uC respectively.