NUMERICAL APPROACH FOR SIMULATING THE TENSIONING PROCESS OF COMPLEX PRESTRESSED CABLE-NET STRUCTURES

The stability of cable-net structures depends on the prestress of the system. Due to the large displacement and mutual effect of the cables, it is difficult to simulate the tensioning process and control the forming accuracy. The Backward Algorithm (BA) has been used to simulate the tensioning process. The traditional BA involves complicated and tedious matrix operations. In this paper, a new numerical method based on the Vector Form Intrinsic Finite Element (VFIFE) method is proposed for BA application. Moreover, the tensioning sequence of a complex cable-net structure is introduced. Subsequently, a new approach for BA application in the simulation of the tensioning process is presented, which combines the VFIFE approach and the notion of form-finding. Finally, a numerical example is simulated in detail and the results of different tensioning stages are analyzed to verify the feasibility of the proposed approach. This study provides a significant reference for improving the construction control and forming accuracy of complex prestressed cable-net structures.

Simulation and Optimization of Temperature Field of Tank Cover with Super Large Diameter during the Creep Aging Forming Process

The uniformity of temperature field distribution in creep aging process is very important to the forming accuracy of components. In this paper, the temperature field distribution of 2219 aluminum alloy tank cover during aging forming is simulated by using the finite element software FLUENT, and a two-stage heating process is proposed to reduce the temperature field distribution heterogeneity. The results show that the temperature difference of the tank cover is large in the single-stage heating process, and the maximum temperature difference is above 27°C,which seriously affects the forming accuracy of the tank cover. With two-stage heating process, the temperature difference in the first stage has almost no direct impact on the forming accuracy of the top cover. In the second stage, the temperature difference of the tank cover is controlled within 10°C, compared with the single-stage heating, the maximum temperature difference is reduced by more than 17°C. The two-stage heating effectively reduces the heterogeneity of the temperature field of the top cover. The research provides technical support for the precise thermal mechanical coupling of large-scale creep aging forming components.

Oscillating Wire Arc Additive Manufacture of Rocket Motor Bimetallic Conical Shell

This paper studies the temperature field, dynamic strain and forming accuracy of the Oscillate-WAAM conical shell in the forming process and manufactures the WAAM conical shell part. The results show that compared with the offset filling WAAM, the oscillate-WAAM conical shell shows the following characteristics：the temperature difference value between the inner and outer walls of the shell is significantly reduced, the cooling rate doubled decreased, the interlayer temperature is above 300°C, as well as the average temperature gradient, the dynamic strain stability value and deformation are reduced by about 50%. Under the same process parameters, the travel speed of Oscillate-WAAM is low, which increased the heat input large and the interlayer temperature high. Meanwhile, the molten pool of Oscillate-WAAM is in consistent with the width of the shell. The molten pool simultaneous solidifying changes the stress state of printed shell form three-dimensional to two-dimensional. All above are conductive to stress release, and reduce the strain and deformation of components. The bimetallic rocket motor shell composed of HS600 and HS950 is manufactured by oscillate-WAAM. The section roundness of the shell is 0.31mm and the overall forming accuracy is ±0.625mm. The deposited metal in HS600 part of conical shell is composed of pearlite and pro-eutectoid ferrite. While the deposited metal of HS950 is composed of pearlite, acicular ferrite and bainite. The forming accuracy and mechanical properties of conical shell formed by Oscillate-WAAM meet the requirements.

Deformation behavior in multi-point forming using a strip steel pad

The blank is prone to wrinkles and spring-back in multi-point forming, seriously affecting the quality and forming accuracy of the formed part. To improve this state, a sandwich structure constructed from a strip steel pad and blank was presented. The deformation behaviour and forming accuracy using three forming processes, namely, without a cushion, using a polyurethane elastic pad and using a strip steel pad, were analysed by numerical simulation and experimentation. The results showed that the use of the strip steel pad in multi-point forming can effectively increase the deformation resistance of the sheet bending; make the material evenly thinned during forming; suppress defects such as wrinkles, spring-back, dimples and straight edges; and improve the forming accuracy.