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研究金属粉末注射成形坯体在烧结过程中由于不均匀性导致的应力演化过程。基于连续介质模型和热弹粘塑性本构关系,建立描述孔体材料烧结致密化过程的模型。通过热膨胀试验得到模型中的材料参数,通过CT断层成像技术得到坯体的真实断面密度分布,并以此作为烧结模型的粉体含量初始分布。在有限元软件Abaqus中调用用户材料子程序(UMAT)子程序实现上述模型的数值计算。计算结果表明:烧结过程中低密度区域的烧结收缩速率大于高密度区域的收缩速率,从而导致产生内应力;高密度区域存在压应力,低密度区域存在拉应力;局部区域的致密化状态不仅与初始粉体含量相关,而且与烧结过程中的应力演化有关系。
The stress evolution process of metal powder injection molding green body due to inhomogeneity during sintering was studied. Based on the continuum model and thermo-visco-visco-plastic constitutive relation, a model describing the process of sintering densification of porous materials is established. The material parameters in the model were obtained by thermal expansion test. The true cross-section density distribution of the blank was obtained by CT tomography and used as the initial distribution of the powder content in the sintering model. In the finite element software Abaqus call user material subroutine (UMAT) subroutine to achieve the above numerical calculation of the model. The results show that the sintering shrinkage rate in the low density region during sintering is higher than that in the high density region, resulting in internal stress; compressive stress exists in the high density region and tensile stress exists in the low density region; the densified state in the local region is not only related to Initial powder content, but also with the stress evolution in the sintering process.