【作者】 刘志卫；

【导师】 李明哲；

【作者基本信息】 吉林大学 ， 材料加工工程， 2014， 博士

【摘要】 超高压技术在现代科学研究和工业生产中发挥着不可替代的重要作用。而模具作为超高压设备的核心部件，不但要能承受足够高的压力，还要能提供足够大的腔体容积。因为大容积的腔体不但能够提供足够的样品空间，还能形成稳定且梯度较小的压力场和温度场。可见模具大型化是现代超高压技术发展的必然要求，但目前模具大型化所面临的主要问题就是大件硬质合金制造加工困难。多层交错剖分式超高压模具是一种新型的组合模具。它主要有剖分块和支撑环构成，无需使用大件硬质合金。不但提高了腔体内的压力，而且还扩大了腔体的容积，适于模具大型化制造。本文通过有限元软件对多层交错剖分式超高压模具进行研究。对比分析了多层交错剖分式模具和年轮式模具的应力分布特征，并进一步对多层交错剖分式模具结构进行了优化。探讨了模具各部件的破裂机理，预测了模具的承压能力，并进行了相关的实验验证。通过电-热-结构耦合计算，分析了温度对多层交错剖分式模具应力及其腔体容积的影响。为多层交错剖分式模具的设计、加工和制造提供理论依据。本文研究的主要内容和结论如下：1.多层交错剖分式超高压模具原理和特点。多层交错剖分式模具依据未裂先分的思想对缸体和预紧环进行剖分，从结构上解决了超高压模具大型化所面临的问题。根据倍压原理使作用在压缸内壁处较大的压力分散作用于外层支撑环内壁。通过摩擦阻力的作用进一步减小剖分块对支撑环的接触压力。并采用解析法对多层交错剖分式模具进行了力学分析，推导出内部压力向支撑环传递的力学模型，为模具初步设计提供了依据。2.多层交错剖分式超高压模具应力分析及结构优化。对多层交错剖分式超高压模具有限元模型建立过程中所涉及的边界条件进行了介绍，并建立了基于ANSYS/Workbench的有限元模型。采用静态隐式算法对多层交错剖分式模具的应力特点进行了分析，探讨了其各部件的失效准则，并与年轮式模具进行了对比。另外还对多层交错剖分式模具结构做了进一步改进。结果表明：多层剖分式模具压缸的周向应力要远小于年轮式模具的周向应力，尽管其外层支撑环存在应力集中现象，但总体上仍处于优势；剖分块数从内到外不断减小，能够同时降低支撑环和压缸应力；通过增加剖分层数和摩擦系数，能够进一步减小支撑环应力；通过修改支撑环内壁轮廓形状可以避免出现应力集中现象，进而使支撑环受力更均匀；在压缸剖分块内壁与锥面的结合处采用圆角过渡能够消除该区域的应力峰值，并且压缸内壁为平面或者凸面时，能够显著降低其应力值。3.预紧力对多层交错剖分式超高压模具容积变化的影响。基于多层交错剖分式模具特有的结构，探讨了其预紧力的施加方法，不但可以通过层间或层内过盈来实现预紧力的施加，而且还可以采用钢丝或钢带缠绕剖分块组合体来实现预紧力的施加。并以层间过盈为例，分析了预紧力的施加对多错层交错剖分式模具腔体容积的影响。结果表明：通过施加预紧力的方法，可以大幅度减小腔体在内壁压力作用下的容积增大量，并且采用双层支撑环的效果更佳。另外，经过对具有不同尺寸腔体的模具进行研究发现：压缸径向位移随腔体半径的增加而增加，但在预紧力作用下，其增加幅度较小，并且值也小。例如，在5400MPa压力作用下，腔体半径为50mm多层交错剖分式模具施加合适的预紧力后，其内壁的径向位移仅为0.15mm。4.多层交错剖分式超高压模具承压能力计算。通过响应面法对多层交错剖分式模具的承压能力进行了计算，分析了模具尺寸、剖分层数以及预紧力对承压能力的影响，并与年轮式模具进行了对比。研究表明：当多层交错剖分式模具尺寸或层数不足时，其承压能力由其支撑环的强度决定，当多层交错剖分式模具尺寸或层数足够时，其承压能力由其压缸的强度决定；施加预紧力后，压缸等效应力随着其内壁作用力的增大呈现先减小再增大的趋势，但最终与未施加预紧力时的等效应力趋于一致，支撑环一直处于较高应力状态，不会因压缸内壁压力的加载而出现明显变化；预紧力的施加基本上不会影响多层交错剖分式模具的最终承压能力；经过有限元计算，多层交错剖分式模具内壁的承压能力约是年轮式模具的1.5倍，能够轻易地达到8GPa；相应的物理实验也表明多层交错剖分式模具的承压能力要远高于年轮式模具。5.温度和压力对多层交错剖分式超高压模具性能的影响。通过对多层交错剖分式模具进行多物理场耦合计算，分析了温度和压力载荷对多层交错剖分式模具性能的影响。结果表明：腔体温度为1500℃时，缸体温度约为213℃；温度载荷对压缸应力基本没有影响，压缸的应力值与压缸内壁的压力载荷呈非线性增加关系；温度载荷和压力载荷对腔体容积的变化都有影响，并且都呈现非线性增加关系；当模具没有施加预紧力时，温度载荷对支撑环应力基本无影响，支撑环应力与压力载荷呈非线性增加关系；当模具施加预紧力时，支撑环应力与温度载荷呈非线性减小关系，与压力载荷基本无关；施加预紧力的多层交错剖分式模具，其腔体容积变化率较小，更适于高质量金刚石的合成。更多还原

【Abstract】 Ultrahigh pressure technology plays an irreplaceable role in the fields of modernscientific research and industrial production. As the core component of ultrahighequipment, mold not only to withstand enough high pressure, also need to provide enoughcavity volume. Because of the large volume of the cavity is not only able to provideenough sample space, also can form stable and small gradient of pressure field andtemperature field. This shows large-scale mold is the inevitable requirement of moderndevelopment of ultrahigh pressure technology. But the main problem with large-scalemold is the difficulty of manufacturing large size carbide.Multilayer stagger-split type ultrahigh pressure die is a novel assemble mold. It ismainly composed of divided bodies and supported ring. And it doesn’t need to use largesize tungsten carbide, but provides the access to producing large-scale die. Whatsmore,it not only can expanded the cavity, but also improve the cavity pressure. In this thesis,the performance of multilayer stagger-split die was investigated by finite elementsoftware. The comparison and analysis on stress distribution characteristics of multilayerstagger-split die and belt type die were presented. And then brought forward an improvedstructure for multilayer stagger-split die. This article explored the rupture mechanism ofthe mold parts, and predicted the pressure capacity of multilayer stagger-split die, andthe related experiment was carried out to verify the simulation results. The influences oftemperature on stress and cavity volume of multilayer stagger-split die were analyzed byelectrical-thermal-structure coupling calculation. The results can provide theoreticalbasis for the design and processing of multilayer stagger-split type ultrahigh pressure die.The main contents and conclusions of this contribution are as follows:1. Principle and characters of multilayer stagger-split dieMultilayer stagger-split die has been constructed based on the principle of “dividing dies before cracking”, this solved the problem with manufacturing large-scaleultrahigh pressure mold from the structure. According to the principle of pressuremultiplier, the larger force loaded on inner face of cylinder can be translated on the innerwall of outer supported ring as small force. The contact force between divided block andsupport ring was further reduced through the effect of frictional resistance. Andmechanical analysis of multilayer stagger-split die was performed by the analytic method.The translation mechanical model of the internal pressure to give to support ring isdeduced. It provides a basis for the preliminary design of stagger-split die.2. The stress analysis and structure optimization of multilayers stagger-splittype ultrahigh pressure dieThe boundary conditions for numerical simulation of multilayer stagger-splitultrahigh pressure die are introduced, and the finite element model was established basedon ANSYS/Workbench. The stress distribution disciplinarian were analyzed by adoptingstatic implicit algorithm, and the results were compared with that of belt type die. Alsothe structure of multilayer stagger-split die was further improved. The results shows thatthe cylinder circumferential stress of multilayer stagger-split die pressure is far less thanthat of belt type die. In spite of there is stress concentration phenomenon in the outersupported ring of multilayer stagger-split die, but as a whole, the die is still in theadvantage. The stress of support ring and cylinder can be reduced at the same timethrough the arrangement that the number of divided blocks gradually dwindled down frominside to outside, and the support ring stress can be further reduced by increasing thenumber of divided layers and the coefficient of friction. The stress concentrationphenomenon of supported ring can be avoided by modifying its inner wall contour shape,and then the supported ring stress is more evenly. The junction between inner wall andthe cone of cylinder adopted transition fillet can eliminate the peak stress in the region.The stress value of cylinder can be significantly reduced if the inner wall of the cylinderpressure is design as flat or convex.3. The influence of preload to cavity volume of multilayer stagger-split die.Based on the unique structure of multilayer stagger-split die, the method of preloadapplication was discussed. The preload application can be realized not only by theinterference of inter-layers or between layers, but also by using steel wire or strip to intertwine the divided body assembly. And the influence of preload exerted on the cavityvolume of multilayer stagger-split die was analyzed by the example of inter-layerinterference. The results showed that: the increase amount of cavity volume under innerwall pressure could be greatly reduced by applying a preload force, especially by usingdouble layers support ring. Furthermore, by using different sizes of the mold cavities, itwas found that the normal displacement of inner wall of cylinder increases with theincrease of cavity radius, but both the variation and the increase amplitude becomesmaller when the preload is applied to the cylinder. For example, under the pressure of5400MPa, when the multilayer stagger-split die whose cavity radius is50mm is appliedsuitable preload, the normal displacement of inner wall of cylinder is only0.15mm.4. The pressure capacity calculations of multilayer stagger-split type ultrahighpressure die.The pressure capacity of multilayer stagger-split die was calculated by responsesurface methodology. And the influences of die size, divided layers and preload on thepressure capacity were analyzed, and compared with that of the belt type die. The resultsindicated that when the size or layers of multilayer stagger-split die were insufficient, thepressure capacity was determined by the strength of its support ring, and when the sizeor layers were sufficient, the pressure capacity was determined by the strength of carbide.After applying preload, as the increase of inner wall force, the equivalent stress ofcompression cylinder showed the trend of decrease at first and then increase, but wasconsistent with the equivalent stress without applied preload in the end. The support ringhas been in a high state of stress, will not significant change with the change of theloading on the inner wall of cylinder. And the applying of preload will not affect thepressure capacity of multilayer stagger-split die. According to the finite elementcomputation, the pressure capacity of multilayer stagger-split die is5times higher thanbelt type die, it can reach to8GPa. And corresponding physical experiment also indicatesthat the pressure capacity of multilayer stagger-split die is much higher than belt type die.5. The influences of temperature and pressure on performance of multilayerstagger-split die.The influences of temperature and pressure on the performance of multilayerstagger-split die were analyzed by the calculation of multi-physics coupling. The resultsshow that the cylinder temperature is about213℃, when the chamber temperature is up to1500℃. Temperature loading has no effect on the stress of cylinder, the stress ofcylinder increases nonlinearly with the increase of pressure loading on the inner wall ofcylinder. Both temperature loading and pressure loading affect the variation of cavityvolume, and the variation increased nonlinearly as the temperature and pressure increased.When the die is not applied preload, temperature loading almost showed no effect onstress of supported ring, but the stress of supported ring is increased nonlinearly as thepressure increased. When the die is applied preload, the supported ring stress reduces bynon-linear relationship with temperature load, but no matter with pressure load. Themultilayer stagger-split die which applied to preload is more suitable for synthesis ofhigh quality diamond.更多还原