小弯曲半径薄壁管热-力-分块介质耦合作用下差温推弯机理及成形极限

小弯曲半径薄壁管是飞机及其发动机管路关键连接构件，但1D(D为管径)以下小弯曲半径管常温推弯成形困难，弯曲内侧极易失稳起皱。为此，本项目开展小弯曲半径薄壁管热-力-分块介质耦合作用下差温推弯机理及成形极限研究。差温推弯中，模具弯曲内侧通水冷却提高管材强度避免起皱，弯曲外侧加热降低管材抗力利于流动；同时以分块式耐热介质填充管内抵抗起皱；并差异化润滑管弯曲内外侧，降低内侧摩擦力减少起皱，形成热-力-分块介质耦合作用，以实现1D以下小弯曲半径薄壁管推弯。项目首先构建差温推弯数值模型，研究薄壁管热-力-分块介质耦合作用下差温推弯流变行为；其次采用数值模拟与实验，揭示非均匀温度场与复杂应力场下差温推弯起皱机理；进而探索薄壁管各因素耦合作用下差温推弯极限；最后研究差温推弯管件组织性能演变规律及控制方法。从而最终建立小弯曲半径薄壁管差温推弯新方法、新理论，为该技术在航空工业应用奠定坚实的理论基础。

Thin-walled tube with small bending radius is the key connecting part in pipeline of airplane and its engine. But the thin-walled tubes with small bending radius less than 1D(tube diameter) are fabricated difficultly by push-bending process at room temperature. It is found that the wrinkle is extremely easy to occured inside of the bend. Therefore, the forming limit and mechanism of differential temperature push-bending with thermo-mechanical-sectional medium coupling effect for thin-walled tube with small bending radius is investiagted and this method is proposed to push-bend the thin-walled tube with small bending radius less than 1D in this project. In this method, the inner side of the die bending chamber is cooled by water which improves the strength in intrados of the tube to avoid wrinkling, whilst the outer side of the die bending chamber is heated which reduces the resistance in extrados of the tube to improve the materials flow. Meanwhile, the sectional thermostable medium is used to fill into the tube to resist wrinkling and differential lubrication between the intrados and extrados of the tube wall is adopted to reduce the friction inside of the bend in order to eliminate wrinkle. In this project, numerical model of differential temperature push-bending is first constructed to study the rheological behavior of thin-walled tube under the coupled action of thermo-mechanical-sectional medium. Secondly, numerical simulations and experiments are adopted to reveal the mechanism of wrinkling in the differential temperature push-bending process under non-uniform temperature field and complex stress field. Furthermore, the forming limit of differential temperature push-bending of thin-walled tube is explored under the coupling effect of multi-factor. Finally, the evolution law and control method of microstructure and property of the bent tubes are studied. Thereby, a new method and theory of differential temperature push-bending of thin-walled tube with small bending radius are established and lay a solid theoretical foundation for application of this technology in aircraft industry.