薄壁钛管加热绕弯不均匀变形机理及成形性能

It is one of key basic scientific issues to reveal the unequal deformation mechanism and clarify the formability of thin-walled titanium alloy tube at elevated temperatures for exploring the forming potential and achieving precision bending of "bleeding" bent components in advanced aircraft,etc. Taking the large diameter (Outer diameter D/ Wall thickness t> 50) thin-walled TC4 titanium alloy tube as the objective, considering the unique characteristics of tension/compression unequal deformation at the extrados and intrados of bending tube, via the suitable material tests and chracterization methods for thin-walled titanium tube under different temperatures and strain rates, the macroscopic plastic deformation behaviors of titanium tube under various thermo-mechanical loadings should be obtained, the microstructure (such as grain and texture) evolution rules under different thermo-mechanical loadings should be investigated, by combining with the visco-plasticity self-consistent (VPSC) crystal plasticity theory,the physical mechanisms on slipping-twinning coordinated unequal deformation under various tension-compression and thermal loadings should be clarified, thus the rate-dependent macroscopic phenomenological constitutive model should be developed to capture the yield asymmetry and anisotropy behaviors of the duplex titanium alloy tube, then the thermo-mechanical coupling finite element (FE) models for titanium tube numerical control (NC) bending at elevated temperatures should be established including heat transferring between tube and tools,thermo-mechanical coupling warm bending as well as elastic recovering after unloading and cooling, thus, combining with the experiments, the unequal deformation rules and mechanisms of large diameter titanium alloy tube bending at elevated temperature should be revealed, the occurring mechanisms of the instabilities such as wrinkling, wall thinning and cross-section deformation, and springback phenomenon,should be clarified, should be clarified, finally, the bending formability of titanium tube at elevated temperatures should be determined. The obtained methods and results should be of important theoretical significance and practical value in developing the advanced theory and technology for precision forming of high performance and lightweight tubular bent components which is difficult to be formed.

揭示薄壁钛管加热弯曲不均匀变形机理及其成形性能，是发掘难变形钛管成形潜力，实现"血管"类弯曲构件精确制造迫切需解决的关键科学问题。本项目以大直径薄壁钛管TC4为对象，考虑弯管内外侧拉/压不均匀变形特点，拟通过适用于薄壁钛管不同温度、应变速率下材料性能测试，获得钛管在不同热力加载下的宏观塑性变形行为，揭示钛管在相应加载下的微观织构及演变规律；结合粘塑性自适应晶体塑性（VPSC）理论，阐明钛管在不同加载下的滑移-孪生协调不均匀变形物理机制；发展能反映钛管拉/压不对称及各向异性行为的率相关唯象本构模型，建立包含传热、加热弯曲和卸载冷却回弹的钛管热力耦合有限元模型；结合试验，探明大直径薄壁钛管加热弯曲不均匀变形规律和机理；获得起皱、减薄、截面变形等缺陷及回弹现象在局部热力加载下的产生机制，由此确定难变形薄壁钛管加热绕弯成形性能。这对于发展高性能轻量化管件精确成形先进技术具有重要理论意义和实用价值。

先进飞行器等高端装备对高功效、低能耗和长寿命的需求，亟待实现用于燃油、环控等系统的薄壁钛合金弯管这一血管类关键构件的高性能轻量化精确成形。针对薄壁钛管难变形和难成形的问题，提出在原有数控弯曲多模具约束加载基础上匹配热场以协调管材拉压不均匀变形，从而探索出发掘难变形钛管成形潜力、提高其弯曲性能的路径。而揭示薄壁钛管热弯不均匀变形规律及机理并确定其成形性能，是实现“血管”类弯曲构件精确制造迫切需解决的关键科学问题。为此，本项目以大直径薄壁CP3和TC4钛管(外径/壁厚大于50)为对象，考虑弯管内外侧拉/压不均匀变形特点，基于大直径薄壁钛管高温拉伸试样设计和钛管变形粘塑性自洽晶体塑性（VPSC-CP）虚拟实验平台，阐明了大直径薄壁钛管在不同拉压热力加载下的各向异性变形规律和摩擦性能及其机理，建立了考虑温度效应的钛管拉压不对称和各向异性塑性行为的本构模型，将损伤模型和几何微缺陷引入显式有限元算法，建立了薄壁钛管加热-热弯过程热力耦合有限元数值仿真模型，结合试验，探明了大直径薄壁钛管加热弯曲不均匀变形规律和机理，揭示了钛管加热绕弯不均匀变形与多种塑性变形缺陷的关联关系，提出了协调内外侧拉压不均匀变形提高薄壁钛管弯曲性能的差温加热弯曲新原理和方法，这对于发展高性能轻量化管件精确成形先进技术具有重要理论意义和实用价值。上述成果已成功应用于成飞等公司难变形弯管构件精确成形制造难题的解决，显著提升了大口径薄壁CP3和TC4钛管的弯曲成形极限。研究成果在IJP、JMPT和IJMS等重要期刊发表学术论文21篇，SCI收录19篇，IJP发表论文获TOP25最热门论文；获授权国家发明专利4项；撰写中英文书章2章；研究成果作为重要支撑，2014年获陕西省科学技术一等奖，2016年获国家技术发明二等奖1项。