| Popis: |
The evolution of porosity during hot rolling of powder-based porous aluminum plates is analyzed by using a pressure dependent constitutive model and a finite element based rolling process model. The constitutive model, which is capable of describing both matrix and densification hardening, consists of two state variables: matrix strength and volume fraction of porosity. The matrix strength is represented by an internal state variable constitutive relationship whose parameters were evaluated by a uniaxial stress compression test at various strain rates and elevated temperatures. The rolling process model uses a Eulerian, velocity-based, finite element formulation. A quasi-three-dimensional nature arises because normal strain rates are independent of through-thickness position. Only one element is taken through a half-thickness rolling plate. Variations are permitted across the width of the plate. High purity aluminum powders were used to fabricate porous thin plates for rolling experiments. Plates with uniform initial porosity underwent various reductions on a bench scale rolling mill at 400°C. Experimental results were compared with numerical solutions generated from the rolling model and the agreement was very good. Experimental results consistently showed that a variation of porosity exists from the center to the edge of plate during the void healing process. The pressure also varies along the width which contributes to the porosity variation. However, the internal state variable which represents the hardness of the matrix does not vary much across the width. |
