Investigating plastic instability of DD14 steel sheet in deep drawing process: A material characterisation and FEM analysis of die radius impact

What is it about?

The deep drawing process is one of the most complex forming processes, as several problems related to the plastic instability of the material to be deep drawn are notably necking, rupture and tearing. However, the parameters of the deep drawing process can cause these phenomena as well as the geometry of the deep drawn part. Particularly, a material having the formability for such a deep drawing operation remains the desired solution in this process. In this sense, the aim of this work is to investigate a problem of plastic instability of the material through a characterisation and modelling of the anisotropy of DD14 hot-rolled steel sheet intended for deep drawing prismatic cups, using the Hill48 criterion. In addition, FEM analysis of the die radius influence on the occurrence of lateral and corner ruptures on deep drawn parts is carried out in numerical simulation. For this, an 3D simulation of the stamping operation is elaborated by finite element calculation code Abaqus/CAE Explicite ® . Following an incremental approach and from the numerical results, the areas most subjected to plastic strain and that represent a high thinning are located. Thus, the degree of influence of the die radius on the evolution of plastic strain is determined. Furthermore, finite element analysis helps us to predict the material behavior during plastic deformation as a function of this parameter. As a result, the optimum die radius levels which represent the best distribution of plastic strain and improve product quality, are the highest.

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Why is it important?

The originality of this work emerged through the results of the numerical simulation model which highlights a perfect localisation of plastic instability areas, similar to those recorded on the component’s deep drawn parts. The results of the tests, planned according to the four levels of die radius,have helped us to successfully determine the influence of die radius on plastic strain evolution. On another scale, the finite element method allows us to numerically analyse the phenomenon of plastic instability within the deep drawn part, following a chosen node's path, sufficiently informing us about the probable scenarios of plastic strain evolution according to each chosen level of the die radius.

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