Determination of initial compression stresses when extruding bimetallic tubes with porous internal layer

The effect of strain hardening in the extrusion of bimetallic tubes of porous internal layer

“…Following a similar procedure as in Refs. [4,5], the materials were also kept the same for both the layers, i.e. a sintered steel with chemical composition: 4% Ni, 1.5% Cu and 0.5% Mo was selected as fabrication material of internal tube with porosity parameters m = 1.1 and n = 1.4, whilst a similar pore-free material was considered for the external layer.…”

“…The data at the die entrance were obtained as in Ref. [5], i.e.σ m10 = −1.1,σ m20 = −0.85, dε i0 /dε eq20 = 1.408 and in case of ε eq20 = 0.01: ε i = 0.014, ε m10 = −0.012, ε r10 = 0.012, ε θ10 = 0, ε θ20 = 0, ε m20 = −0.012, ε r20 = 0.0078 [5]. Two different cases of bimetallic's materials were considered:…”

“…[4,5]. For establishing the regularities of the plastic deformation, the Plasticity Theory of Real Porous Materials (PTRPM) [1,5] is applied.…”

“…[4,5]. For establishing the regularities of the plastic deformation, the Plasticity Theory of Real Porous Materials (PTRPM) [1,5] is applied. According to this methodology, the conceptions of equivalent stress σ eq and equivalent strain increment dε eq are combined along with the mass preservation law and the flow law associated with the plasticity conditions, providing, in this manner, the following basic equations of the flow theory of real porous materials [5]: where σ i is the stress intensity, σ ij the components of stress tensor, σ 0 = δ ij σ ij /3 the mean stress, dε i the intensity of strain increments, dε ij the components of strain increment tensor, dε 0 = δ ij dε ij /3 the mean strain increment and δ ij is the Kronecker's symbol.…”

“…(1)-(4) describe the behaviour of pore-free materials [4,5]. In the following, it is assumed that the equivalent stress σ eq is a function of an integral of equivalent strain increment dε eq , which does not depend on the stress state conditions and the porosity of material, i.e.…”