Based on the upper-bound theorem in limit analysis, a theoretical model for core fracture in bimetal rods during extrusion has been developed and a fracture criterion established. The variables affecting core fracture are: reduction in area (r%), die geometry, friction (m), relative size of the core and relative strength of the core. Within the wide range of possible combinations of these process variables, only a small range permits extrusion without fracture. With suitable modifications the present analysis can be extended to develop criteria for sleeve fracture during extrusion and for both core and sleeve fracture during drawing.

Based on the generalized method of images, the elastic field of an in-plane line force acting in a two-phase orthotropic medium is analyzed. Several special cases of technological interest are deduced from the general solution, including the case of a line force applied on the free surface of a half space. Application of the results to the determination of the elastic field of an edge dislocation in a semi-infinite orthotropic medium is illustrated.

The process of core fracture in bimetals during extrusion was reexamined. The new analysis, based on the upper-bound theorem in limit analysis, eliminated the lengthy numerical computations employed in the previous work [1]. The criterion for core fracture was derived and discussed.

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In conjunction with the previous analysis on core fracture [1, 2], a criterion for prevention of sleeve fracture in extrusion of bimetal rods is developed. The sleeve fracture is likewise affected by a set of independent process parameters, namely the reduction in area, die angle, friction, interfacial bonding, relative size, and relative strength of the sleeve. It is shown that the usage of the present criterion for sleeve fracture and the criterion previously described for core fracture can provide an effective path to a successful extrusion operation for bimetal rods and wires.