Fracture prediction in plastic deformation processes

Various fracture criteria, based on different assumptions and different mechanical models, have been proposed in the past to predict ductile fracture. The objective of this study is to assess their effectiveness and accuracy in a wide range of process parameters. A series of tests on 2024-T351 aluminum alloy, including upsetting tests and tensile tests is carried out. It is found that none of the existing fracture criteria give consistent results. Two totally different fracture mechanisms are clearly observed from microfractographs of upsetting and tensile specimens. This observation confirms that it is impossible to capture all features of ductile crack formation in different stress states with a single criterion. It is shown that different functions are necessary to predict crack formation for different ranges of stress triaxiality. Weighting functions in a wide range of stress states can be obtained by determining the fracture locus in the space of equivalent strain to fracture and stress triaxiality.

A Comparative Study on Various Ductile Crack Formation Criteria

New ductile fracture criterion for prediction of fracture forming limit diagrams of sheet metals

Micromechanically-motivated phenomenological Hosford–Coulomb model for predicting ductile fracture initiation at low stress triaxialities

On the cut-off value of negative triaxiality for fracture

Ductile Fracture in Axisymmetric Extrusion and Drawing—Part 2: Workability in Extrusion and Drawing

An approximate method for a three-dimensional analysis of rolling

Abstract : This investigation applies theories on flow and fracture in metalworking processes to prediction of workability of materials in axisymmetric bar extrusion and drawing, with special reference to central bursting. Part 1 deals with the determination of deformation mechanics in extrusion and drawing. The matrix method is used as the method of analysis and is shown to be an efficient numerical method which provides useful information on the detailed deformation characteristics for various process variables. In part 2 the validity of a theory on ductile fracture was examined by experimental data found in the literature. Then, combining the formulation of fracture criteria with the deformation mechanics found in Part 1, the workability of materials in extrusion and drawing was determined. Workability in extrusion was examined for aluminum alloy 2024-T351, using data found in the literature, and experiments of workability in drawing were attempted for SAE 1144 colddrawn steel to test the prediction. The results of validation were inconclusive. Conclusive validation of the present workability theory in extrusion and drawing awaits more extensive and systematic experimental investigations, as well as theoretical calculations. (Author)

S. I. Oh

Papers

Ductile Fracture in Axisymmetric Extrusion and Drawing—Part 2: Workability in Extrusion and Drawing

An approximate method for a three-dimensional analysis of rolling

Ductile Fracture in Axisymmetric Extrusion and Drawing—Part 1: Deformation Mechanics of Extrusion and Drawing

Workability of Aluminum Alloy 7075-T6 in Upsetting and Rolling