Constitutive behaviour of metal powder during hot forming. Part I: Experimental investigation with lead powder as a simulation material

Lend powder has been chosen as a simulation material for investigating the constitutive behaviour of metal powders during hot pressing. Uniaxial compr ession tests and die pressing tests with radial stress measurement have bee n performed at various temperatures in a wide range of strain rate. At low strain rate a classical viscoplastic behaviour, as already observed with in dustrial powders, has been obtained. At high strain rate, new phenomena due to the saturation of the viscosity of the material have been displayed. Ex perimental data show that the behaviour of the porous material is mainly re lated to the rheology of the constituent material of powder particles. Clas sical and more original rheological functions, that have been identified fr om these data, can be used, in a first approach, for any industrial powder with similar morphological and rheological features. All these results are used in the second part of this paper (Part II: Unified viscoplastic modell ing) to discuss the capability of classical constitutive equations to descr ibe such behaviour. (C) Elsevier, Paris.