It has been reported in literature that extrusion dies most often fail by fatigue fracture. Experimental studies have shown that cracks pre-exist in dies because of various factors including machining, heat treatment and surface hardening. High levels of repeated mechanical and thermal loads result in crack propagation leading to ultimate fracture failure. In an earlier work by the authors, a simplified approach of plate-with-edge-crack was used to develop a fracture mechanics based fatigue life prediction model for tube dies. In the current work, extrusion die is modeled as a pressurized-cylinder-with-internal-crack, a more realistic approach for a hollow (tube) die. Stochastic nature of various fatigue-related die parameters has been used to reflect their variability. Monte Carlo simulation has been performed to forecast fracture failure of extrusion dies under a given set of operating conditions and mechanical properties. Predicted mean-time-to-failure is quite close to actual average extrusion die life data from the industry. Using tube die as a basis, fracture life of other hollow profiles can be estimated through their shape complexity values. Analysis has also been carried out to evaluate how sensitive fracture life of hollow extrusion dies is to material and process parameters. Major findings are that die life is highly sensitive to initial crack size, wall thickness, profile outer diameter and billet length; moderately sensitive to Paris constant and extrusion ratio; and only slightly sensitive to fracture toughness and ram speed. These results can contribute to a deeper understanding of the factors responsible for fracture failure of an extrusion die exposed to thermo-mechanical fatigue environment.
|الصفحات (من إلى)||434-444|
|دورية||Fatigue and Fracture of Engineering Materials and Structures|
|المعرِّفات الرقمية للأشياء|
|حالة النشر||Published - أبريل 1 2015|
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