複合包芯材擠製加工之破斷條件研究

Abstract

複合包芯材是指由兩種或兩種以上不同材料所組成之複合材料，此種複合材料因其優異的機械特性，故廣泛的被應用於工業界中。但此種複合材料由於組成材料機械性質的差異，因此在材料進行擠製加工時，往往因不當的加工條件組合，造成擠製後的產品為非健全之擠製材。 本論文主要的研究對象是針對複合包芯材擠製時芯材的破斷做研究，研究中使用極限解析（Limit Analysis）中的上界法（Upper-Bound Method）來做解析。解析過程中，在運動可容許速度場的構築上，我們除了建構一芯材和被覆材正常變形時之三維運動可容許速度場外，我們另外假設當芯材產生局部之頸縮變形時，因芯材變形界面的改變而會有一偏差速度場的存在。結合兩速度場並導入一可變參數控制偏差速度場之大小，我們可以得到此次解析所需之運動可容速度場。藉由簡單形搜尋（Simplex Method）最佳化方法改變可變參數，求出滿足於塑性變形消耗能量最小之運動可容許速度場，並從中判斷此運動可容許速度場中偏差速度場的存在與否，當偏差速度場存在則我們判定芯材會產生破斷，反之則判定芯材為健全；最後我們將利用此一判斷標準，探討在不同加工條件組合下，芯材的破壞界限。

Composite clad rods that are composed of two or more different materials being used extensive in the industry because of their excellent mechanical characteristics. However, owing to the different properties of the constituent materials, it is very often encountered various defects during extrusion process. In this study, the fracture of the core of the composite clad rods is our major object. We present a numerical simulation model based on the upper-bound theorem to analyze the core of composite clad rods in extrusion. Beside a normal three-dimensional admissible velocity fields that dictates the normal deformation of core and sleeve, an extra velocity fields depicts the necking of core is superimposed on this normal velocity fields. Both of the normal and the extra velocity fields are derived under the condition of incompressibility of materials or the constant volume flow. One pseudo-parameter was added on the extra velocity fields, while the total energy consumptions are subjected to minimization. If the result shows that a non-extra velocity fields exist, then we concluded core fracture would happen. Use the proposed criterion, combination of working parameters sound extrusion are established.