【作者】 彭超；

【导师】 黄尚宇； 刘维；

【作者基本信息】 武汉理工大学 ， 材料科学与工程， 2021， 硕士

【摘要】 粉末成形作为粉末冶金工艺中制备高性能材料的一个重要工艺环节,它具有材料利用率高以及能够成形复杂形状零件等优点。在粉末的成形过程中,粉末压坯的致密度是影响最终零件产品性能的重要因素,因此需要对粉末在压制成形过程中的变形行为及致密化机理展开研究。在粉末压制成形的变形行为研究中,通常采用数值模拟手段进行分析,而在采用数值有限元分析粉末压制的变形行为以及致密化机理过程中,材料的本构模型是其中的基础与核心。由于粉末材料和岩土的相似性,基于土塑性力学建立的Drucker-Prager Cap本构模型在粉末压制过程中得到了广泛应用。而在通过传统的实验和半解析法确定Drucker-Prager Cap本构模型参数时,需要进行大量的粉末压制实验来进行确定,且由于需要通过应变片采集应变数据进一步导致其在粉末热压成形过程中的应用受到一定限制。因此简化确定模型参数所需要进行的实验流程,对Drucker-Prager Cap本构模型在更多粉末材料以及粉末热压过程中的应用具有积极意义。本文首先针对粉末压制过程中Drucker-Prager Cap本构模型,结合实验采用半解析法得到其参数,并验证分析了该模型的准确性。随之基于该模型建立了一套参数逆向识别流程,以此来简化确定模型参数所需要进行的实验操作,同时用模压实验验证了逆向识别流程的准确性并将其进一步应用到粉末热压成形过程中的Drucker-Prager Cap本构模型研究。具体内容和结果如下:针对Ti-6Al-4V合金粉末压制成形,进行单轴压缩、径向压缩以及模压实验,结合半解析法构建了密度相关型Drucker-Prager Cap本构模型。对粉末模压过程的模型参数灵敏度展开研究,分析了各模型参数的变化对最终位移载荷曲线的影响。同时结合模压实验,采用优化算法建立了一套模型参数的逆向识别流程,该流程仅需要采集粉末模压过程中的位移载荷数据即可通过反分析手段获取和确定模型参数,并结合模压实验中的压制力和相对密度的分布对该逆向识别流程予以了验证。针对B₄C粉末热压成形,结合建立的参数逆向识别流程以及1500℃、1600℃、1700℃、1800℃和1900℃下的粉末高温成形实验,确定了它们在各温度下的高温Drucker-Prager Cap本构模型参数。分析了温度对该模型硬化屈服应力参数的影响,随着温度的提高,粉末材料硬化屈服应力减小,且在1600℃有明显降低,并对获取的高温参数结合数值模拟进行了分析。更多还原

【Abstract】 Powder forming is an important process link in the preparation of high-performance materials in the powder metallurgy process.It has the advantages of high material utilization and the ability to form parts with complex shapes.In the powder forming process,the compactness of the powder compact is an important factor that affects the performance of the final part.Therefore,it is necessary to conduct research on the deformation behavior and densification mechanism of the powder during the compression forming process.In the study of the deformation behavior of powder compaction,numerical simulation methods are usually used for analysis.In the process of using numerical finite element analysis to analyze the deformation behavior and densification mechanism of powder compaction,the constitutive model of the material is the basis and core.Due to the similarity between powder materials and rock soil,the Drucker-Prager Cap constitutive model based on soil plastic mechanics has been widely used in the powder compaction process.When determining the parameters of the Drucker-Prager Cap constitutive model through traditional experiments and semi-analytical methods,a large number of powder compaction experiments are needed to determine them,and the need to collect strain data through strain gauges further leads to the powder hot pressing process.The application in is subject to certain restrictions.Therefore,simplifying the experimental process required to determine the model parameters has positive significance for the application of the Drucker-Prager Cap constitutive model in more powder materials and powder hot pressing processes.In this paper,firstly,based on the Drucker-Prager Cap constitutive model in the powder compaction process,the semi-analytical method is used to obtain its parameters in combination with experiments,and the accuracy of the model is verified and analyzed.Subsequently,a set of parameter inverse identification process was established based on the model to simplify the experimental operation required to determine the model parameters.At the same time,the accuracy of the inverse identification process was verified by the molding experiment and further applied to the study of the Drucker-Prager Cap constitutive model in the powder hot pressing process.The specific content and results are as follows:For Ti-6Al-4V alloy powder compaction,uniaxial compression,radial compression and compression experiments were carried out,and a density-dependent Drucker-Prager Cap constitutive model was constructed in combination with the semi-analytical method.The sensitivity of the model parameters of the powder molding process was studied,and the influence of the changes of the model parameters on the final displacement load curve was analyzed.At the same time,combined with the molding experiment,an optimization algorithm was used to establish a set of model parameter inverse identification process.This process only needs to collect the displacement load data in the powder molding process to obtain and determine the model parameters through inverse analysis.The suppression force and relative density and their distribution verify the inverse identification process.For B₄C powder hot press forming,combined with the established parameter inverse identification process and powder high temperature forming experiments at1500℃,1600℃,1700℃,1800℃and 1900℃,the high temperature Drucker-Prager Cap values at each temperature are determined.Construct model parameters.The influence of temperature on the hardening yield stress parameters of the model is analyzed.With the increase of temperature,the hardening yield stress of the powder material decreases,and it decreases significantly at 1600℃.The high temperature parameters obtained are analyzed in combination with numerical simulation.更多还原