粉體/固體複合包芯材擠製之研究

Abstract

本論文之目的在於對粉體╱固體複合包芯材的擠製製程進行分析研究。論文中的研究集中在三個主題，包括粉體的變形特性、直接複合擠製和靜水壓複合擠製。釔鋇銅超導粉末的變形特性是以修正的Drucker-Prager/Cap 降伏準則來描述，而降伏準則裡的材料參數則是由直接剪力試驗和拘束壓縮試驗所求得，並且引用到粉體╱固體複合包芯材的有限元素分析模型中的材料特性中。經由有限元素軟體ABAQUS所模擬出的預測值與實驗有相當的一致性；同時透過系統化的分析，針對每個加工參數對粉體的緻密狀況、芯材半徑的穩定度和最大擠製負載的效應都進行了相當程度的研究和探討。在靜水壓擠製的有限元素模型中，我們導入了流體元素來施加包覆擠製胚料的高壓流體邊界條件。由此模型所得到結果與實驗值也相當地一致。

The purpose of this dissertation is to investigate the extrusion process of powder/solid composite clad rod. The studies focus on three subjects; the deformation characterization of powder, direct composite extrusion, and hydrostatic composite extrusion. The deformation characterization of YBCO superconducting powder was modeled by modified Drucker-Prager/Cap yield criterion in which material parameters were obtained by direct shear tests and constrained compression tests. The material parameters were then included into the material properties for the finite element model of powder/solid composite clad rod. The predicted results from simulations by using finite element software ABAQUS displayed a good agreement with direct extrusion experiments. Through systematic analyses, the effects on consolidation condition, stability of the powdered core radius and the maximum extrusion load of each chosen forming parameter were investigated and discussed respectively. Fluid elements introduced into the finite element model of hydrostatic extrusion process were used to apply the boundary condition of high-pressure fluid surrounding the billet. The results from this finite element model also show a good agreement with hydrostatic experimental data.