  Cold compaction of ceramic powders is driven by plastic strain, during which
the elastic stiffness of the material progressively increases from values
typical of granular matter to those representative of a fully dense solid. This
increase of stiffness strongly affects the mechanical behaviour of the green
body and is crucial in the modelling of forming processes for ceramics. A
protocol for ultrasonic experimental investigation (via P and S waves
transmission) is proposed to quantify the elastic constants (Young modulus and
Poisson's ratio) as functions of the forming pressure. Experimental results
performed in uniaxial strain allow for the introduction of laws that describe
the variation of the elastic constants during densification. These laws are
motivated in terms of elastoplastic coupling through the simulation of an
isostatic pressure compaction process of alumina powder. A micromechanical
explanation of the stiffening of elastic properties during densification is
deferred to Part II of this study.
