单一轴向压力对AZ31镁合金降解行为影响的研究

发布时间：2018-02-26 14:52

  本文关键词： 可降解镁合金 力学环境 数值模拟 体外降解实验　出处：《天津理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：目前临床上常用的骨折内固定修复材料多为不锈钢、钛合金等惰性材料,这些材料强度虽高但在愈合过程中由于弹性模量远大于人骨,故存在应力遮挡效应;另外这些材料在骨愈合后存在不吸收、难降解、需二次手术的缺点,而采用镁合金材料修复骨折可以有效降低骨折愈合过程中应力遮挡效应和避免患者二次手术痛苦。以往的研究表明力学环境对镁合金的降解有一定的影响且多为定性研究,本研究通过对有限元分析软件ABAQUS中vusdfld用户定义场变量子程序的编写,实现在力学环境下对镁合金材料降解过程的模拟预测,以便与体外降解实验进行比较分析从而达到定量分析的目的。研究筛选了总体性能较好的镁合金AZ31,对单一轴向压力下的镁合金降解过程进行了有限元仿真模拟,根据实验要求设计制备镁合金试件、镁合金接骨板、接骨钉及其体外降解的实验装置,进行与仿真对应的验证实验,探究镁合金材料在不同力学环境下的降解规律。主要研究内容如下:(1)阐述可降解镁合金的国内外研究现状,提出课题研究的意义和重要性,确定课题的研究思路。(2)阐述连续损伤理论,编写ABAQUS\EXPLICIT 6.13.1软件中VUSDFLD用户定义场变量子程序,实现降解过程中产生的氢气体积、质损及有效应力的定量式输出。建立有限元分析模型,包括:三种镁合金试件模型及镁合金接骨板固定羊胫骨中段断骨的模型,在ABAQUS\EXPICITE软件中进行数值模拟。(3)对数值模拟结果进行了研究与分析。结果表明:各组镁合金试件模型降解过程氢气体积与质损均具同一性变化规律,轴向压缩载荷大小对模型表面形貌特征、有效应力分布、失效方式以及失效时间起着调控作用,且骨折固定模型中镁合金的降解平缓。(4)设计镁合金试件体外降解实验,研究在单一轴向压力下镁合金试件(常规圆孔)降解行为特点。结果表明镁合金的降解行为,包括氢气体积、质损及pH、最大压缩位移、最大压力及压缩时间均与载荷值有关,一定的轴向载荷会加快镁合金的降解;各组实验轴向载荷越大,pH波动相对较小;在轴向压缩实验过程中,轴向载荷对试件的最大抗压性能有着调控的作用。(5)对仿真结果与实验结果进行对比分析。结果表明:由于常温(25℃)下模拟体液中空气的溶解度大于体温(37℃),导致实验中收集的氢气体积往往略大于仿真结果,但是均可说明在降解过程中一定的轴向载荷将加快镁合金的降解速度;从质损的仿真结果与实验结果可以得出无机降解产物可以强化合金表面,而轴向载荷的大小可以通过调节降解产物的附着与脱落来控制镁合金的降解行为。
[Abstract]:At present, the commonly used internal fixation materials are stainless steel, titanium alloy and other inert materials. Although the strength of these materials is high, the modulus of elasticity is much larger than the human bone during the healing process, so there is stress shielding effect. In addition, these materials have the disadvantages of no absorption, no degradation and the need for secondary surgery after bone healing. Using magnesium alloy to repair the fracture can effectively reduce the stress shielding effect during fracture healing and avoid the pain of secondary operation. Previous studies have shown that the mechanical environment has a certain impact on the degradation of magnesium alloy and most of them are qualitative research. In this study, the subprogram of vusdfld user-defined field variables in finite element analysis software ABAQUS was written to predict the degradation process of magnesium alloy under mechanical environment. In order to compare and analyze the degradation experiment in vitro and achieve the purpose of quantitative analysis, the magnesium alloy AZ31 with good overall performance was selected, and the degradation process of magnesium alloy under single axial pressure was simulated by finite element method. According to the requirements of the experiment, the magnesium alloy specimen, the magnesium alloy plate, the bone nail and the degrade device in vitro were designed and prepared, and the corresponding verification experiments were carried out. The main contents of this paper are as follows: (1) expound the domestic and international research status of degradable magnesium alloy, and put forward the significance and importance of the subject research. This paper describes the theory of continuous damage, compiles the VUSDFLD user-defined subprogram of field variables in ABAQUS\ EXPLICIT 6.13.1 software, and realizes the quantitative output of hydrogen volume, mass loss and effective stress in the process of degradation. The finite element analysis model is established. There are three kinds of magnesium alloy specimen models and the model of fixing the middle tibia of sheep with magnesium alloy plate. The numerical simulation results are studied and analyzed in ABAQUS\ EXPICITE software. The results show that the hydrogen volume and mass loss in the degradation process of each magnesium alloy model have the same change rule. Axial compression load plays an important role in controlling the surface morphology, effective stress distribution, failure mode and failure time of the model, and the degradation of magnesium alloy in fracture fixation model is gentle. 4) the in vitro degradation experiment of magnesium alloy specimen is designed. The degradation behavior of magnesium alloy specimens (conventional round holes) under single axial pressure is studied. The results show that the degradation behavior of magnesium alloys, including hydrogen volume, mass loss, pH, maximum compression displacement, maximum pressure and compression time, are all related to the loading values. A certain axial load will accelerate the degradation of magnesium alloys, the larger the axial load in each group, the smaller the pH fluctuation; in the process of axial compression test, The axial load has a regulating effect on the maximum compressive performance of the specimen. (5) the simulation results are compared with the experimental results. The results show that the solubility of air in the simulated body fluid is higher than that in the body temperature of 37 鈩，

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