【作者】 王勇；

【导师】 苑世剑； 韩聪；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2014， 博士

【摘要】 航空发动机、液体火箭发动机和高速飞行器燃料输送管路系统需要相对弯曲半径小于0.5的铝合金和钛合金小弯曲半径整体弯管,以节约空间、提高管路的耐压能力和减轻重量。传统弯曲方法,因外拉内压的变形方式的限制,无法制造这种小弯曲半径弯管。针对这一难题,本文提出了管材充液剪切弯曲方法,其变形方式由外拉内压变为剪切变形,因此可以实现小弯曲半径弯管的成形。通过实验研究、数值模拟和组织观察,对5A02铝合金和TA18钛合金管材充液剪切弯曲进行了系统的研究,为其应用提供了理论指导和技术支持。采用单向拉伸测试方法,对实验所用的5A02铝合金和TA18钛合金无缝管进行了力学性能测试,为数值模拟和实验提供力学性能参数。设计了试件的形状和尺寸,介绍了管材充液剪切弯曲的实验装置和主要成形参数,以及应变网格方法和微观组织性能的测试方法。通过物理实验,研究了5A02铝合金管材充液剪切弯曲成形过程,分析了内压和进给比对5A02铝合金管材充液剪切弯曲成形缺陷的影响规律,给出了充液剪切弯曲的成形窗口,成功研制出相对弯曲半径为0.08的5A02铝合金弯管。揭示了壁厚分布和弯曲半径的变化规律,研究了内压和进给比的影响,获得了不同内压和进给比下的合格试件,并进行了耐压测试。利用电子背散射衍射(EBSD)和电子透射(TEM)技术,研究了铝合金充液剪切弯曲管特征位置的微观组织特征,给出了铝合金充液剪切弯曲管特征区域的微观组织形貌和晶粒分布特征,发现了剪切变形对晶粒细化作用明显,晶粒尺寸由11.08μm降低至1.46μm。采用塑性力学和位错理论,阐明了产生晶粒细化的机理:剪应力下,位错发生开动和重排,形成位错墙,位错墙发展为小角晶界进而演变为大角晶界将原始晶粒分割。对特征位置的硬度进行了测试,分析了剪切变形、硬度分布和晶粒细化的内在关系。采用ABAQUS动态显式有限元程序,对5A02铝合金管材充液剪切弯曲成形过程进行了数值模拟,揭示了剪应力和剪应变分布规律,给出了典型部位的应力应变状态。针对钛合金室温成形性能差,提出了TA18钛合金管材分步充液剪切弯曲成形方法。分别进行单步和两步充液剪切弯曲实验,获得了单步成形条件下的剪裂和拉裂两种特征缺陷,采用SEM观察了断口形貌。研究了内压和进给比对单步成形极限横向进给量的影响,获得了单步成形的最优工艺参数。采用EBSD和TEM研究了钛合金管特征区域的微观组织形貌和晶粒分布,揭示了剪切变形导致钛合金弯曲管件剪切变形区小角晶界含量较高,孪晶界含量很低,晶粒细化程度较大的微观机理。采用单向拉伸、硬度测试和自由胀形测试方法,研究了钛合金管件性能的分布特征,揭示了加工硬化和细晶强化导致剪切变形区硬度值和抗拉强度均高于未变形区,而延伸率低于未变形区的内在机理。采用两步成形方法,成功地研制出外圆角11mm,相对弯曲半径达到0.37的TA18钛合金小弯曲半径弯管。更多还原

【Abstract】 Elbow tubes with small relative bending radius(R/D≤0.5) are widely used innarrow space to connect hydraulics and fuel piping, in aero turbine engines andunmanned air crafts.The light materials like aluminum and titanium alloys areutilized to meet the demand of weight reduction. However, the tubes with smallbending radius cannot be successfully manufactured due to the limit ofcompressive-extrusion deformation mechanism by traditional bending methods. Inorder to solve the critical problem, a shear hydro-bending process was proposed. Ittakes the advantage of shear deformation to forming the ultra-small radius bendingtubes. The shear hydro-bending of aluminum and titanium alloy tubes will besystematically investigated with experiments, numerical simulation andmicrostructure observation. It is expected to provide theory foundation andtechnology support for the application of this new process.The mechanical properties of 5A02 aluminum alloy tubes and TA18 titaniumalloy tubes were measured by uniaxial tensile tests, which served as the fundamentalproperty parameters for experimental and FEM simulation. The target specimen wasdesigned, associating with the experimental device. The strain analysis of eachspecimen was made with the ASAME automatic strain measuring system. Thecorresponding microstructure was observed to reveal the deformation mechanism.The shear hydro-bending of 5A02 aluminum alloy tube and strain measurementwere carried out to investigate the influences of internal pressure and feeding ratio onthe deformation defects, thickness distribution and corner radius. The processwindow was obtained. The shear hydro-bending tubes were achieved in differentinternal pressures and feeding ratios, the distribution of effective strain was broughtto light. The bursting pressure was measured by free bulging test.The microstructure in typical deformation area was observed by electronbackscatter diffraction(EBSD) and transmission electron microscopy(TEM). Thecorresponding microstructure morphology and grain distribution were analyzed. Theobvious microstructural refinement could be obtained due to the shear deformation.The mechanism of grain refinement was clarified by plasticity theory and dislocationtheory. Meanwhile, the micro-hardness was measured to reveal the relationshipbetween shear deformation with grain refinement.The shear hydro-bending process was numerically simulated based on dynamicexplicit finite element method in Abaqus 6.10. The distributions of shear stress andshear strain were analyzed. It was proved that the shear stress was only found on theside. The analysis formula of shear strain in shearing area was obtained.Muti-step shear hydro-bending was proposed for the shear hydro-being oftitanium alloy. One-step and two-steps shear hydro-bending of TA18 titanium alloytube were conducted. Two typical defects, shear fracture and tension fracture wereobtained in the one-step shear hydro-bending process. The fracture morphology wasobserved by SEM. The effects of internal pressure and feeding ratio on limittransverse feeding was investigated. The optimal process parameter in one-step shearhydro-bending process was obtained. The microstructure and grain sizes wereinvestigated by EBSD and TEM. The microscopic mechanism in shear deformationarea was revealed, accompanying with low-angle grain boundaries increasing, twinboundaries decreasing and grain refinement degree improving. The performanceproperties of titanium alloy tube components were measured by uniaxial tensile test,micro-hardness test and free bulging test. It was obvious that the higher strength andlower elongation was achieved in the shear deformation area relative to theundeformed area. The mechanisms of work hardening and grain refinementstrengthening appeared in the shear deformation area were revealed. The TA18 titanium alloy tube with out radius of 11 mm, relative bending radius Rb=0.37, wasformed successfully by two steps shear hydro-bending with inter annealing.更多还原