is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. The use of HSLA steels for the manufacture of automotive components is interesting from an engineering point of view. This family of steels, while possessing high strength, also has good formability and can be used in forming manufacturing processes. In some forming processes such as blanking, shear strain localization occurs, which causes damage and results in the final fracture of the material. This paper presents an experimental study based on in situ tests to understand and identify the physical mechanisms of ductile damage under two stress states: tension and shear. Different macroscopic tests were performed to calibrate a damage model based on a micromechanical approach. This damage model is based on the Gurson-Tvergaard-Needleman theory and presents recent improvements proposed by Nahshon and Hutchinson and by Nielsen and Tvergaard so as to better predict fracture under a wide range of stress states, especially with low levels of stress triaxiality. These extensions have made the identification of the material parameter more complicated. In this work an identification strategy has been proposed using tests on specimens with different shapes. The identified parameter values are validated and the fracture model show good predictive capability over a wide stress state range.

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. b s t r a c tSequential sheet metal forming processes can result in the accumulation of work hardening and damage effects in the workpiece material. The mechanical strength of the final component depends on the ''evolution'' of these two characteristics in the different production steps. The punching process, which is usually in the beginning of the production chain, has an important impact on the stress, strain and damage states in the punched zones. It is essential that the influence of these mechanical fields be taken into account in the simulation of the forming sequence. In order to evaluate the evolution of each phenomenon, and in particular damage accumulation in the forming process, it is essential to characterize the punching process. The objective of this work is to understand and identify the physical damage mechanisms that occur during the punching operation and to establish relevant numerical models to predict the fracture location. The effect of the punch-die clearance on mechanical fields distribution is also discussed in this work.

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is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tA new extension of the Gurson damage model has been proposed recently to predict ductile fracture under shear dominated loads. The aim of this work is to verify the ability of this approach to simulate, in an accurate way, the damage evolution in shearing processes. An implicit stress integration algorithm is then developed to implement the new model in a finite element code. The numerical procedure is checked through simulations of shear and uniaxial tension tests on a single elements. The extended Gurson damage model is tested and applied to the punching process to compare its predictive ability with the original approach. The obtained numerical results are in good agreement with experimental results of the punching process, showing better ductile fracture predictions compared to the original Gurson model.

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Abstract. The optimization of automotive security components requires good knowledge of the material state after fabrication, particularly with respect to damage that may have been done to the material by the manufacturing process. To achieve this, numerical simulation of the fabrication process is often undertaken. However, classical continuum damage models, like the Gurson [3] model, are not appropriate for the simulation of the blanking by punching operation because the material damage is primarily the result of shear stresses. This work is focused on the use and validation of a modified Gurson type damage model capable of modeling this process, which has recently been proposed by Nahshan [7]. After a brief description of the modification, the implementation and the validation of the modified Gurson model is detailed. A comparison between the original Gurson model and the modified model is presented in order to highlight the importance of the modification for a pure shear stress state and to show that the two models are equivalent for a purely hydrostatic stress state. It is also shown that the results from the modified model are dependent on the finite element mesh size.