Abstract
Bi-layered metallic bending tubes are widely used in extreme environments. The spring-back prediction theory for precise forming of such tube configuration is lacking. The layered coupling causes complex section internal force and new boundary conditions. This work proposed a theoretical prediction model of bimetallic tubes’ spring-back under computer numerically controlled (CNC) bending. This model calculated the spring-back angle by importing two new parameters—the composite elastic modulus (Ec) and the composite strain neutral layer (Dε). To investigate Dε, the neutral layer shifting extraction method was proposed to get the shifting value from finite element simulations. Simulations and full-scale bending experiments were carried out to verify the reliability of this prediction model. The theoretical results are closer to the experimental results than the finite element (FE) results and the theoretical results neglecting neutral layer shifting. The change of spring-back angle with the interlaminar friction coefficient was investigated. The results indicated that the normal mechanical bonding bimetallic tube with an interlaminar friction coefficient below 0.3 can reduce spring-back.
Highlights
Bi-layered metallic tubes and their elbow components play an important role in changing the flow direction and improving the flexibility of wiring in pipeline systems [1,2,3]
By making full use of the optimum of different materials, bimetallic tubes can reduce the use of precious metals, lighten the weight of pipes, and reduce production and transportation costs
This paper focused on bimetallic tubes composited by mechanical gap between two layer of straight tube blanks
Summary
Bi-layered metallic tubes and their elbow components play an important role in changing the flow direction and improving the flexibility of wiring in pipeline systems [1,2,3]. The elbow components are formed by cold processing of straight metallic tube blanks. The bending forming quality is directly related to the assembly accuracy, operation safety, and flow stability. Three indexes are used to reflect the forming quality—wall thickness thinning [12,13,14], wrinkling [15,16,17,18], and spring-back. Studies of bimetallic tube bending forming almost focus on analysis of wall thickness variation and wrinkling caused by complex bulking instability under the interaction of two or more layers. Guo et al [19] proposed a model about the wall thickness distribution of Cu-Al bi-layered tube.
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