Plastically-driven variation of elastic stiffness in green bodies during powder compaction: Part I Experiments and elastoplastic coupling

TL;DR

This paper presents experimental methods to measure how elastic stiffness in ceramic green bodies increases during powder compaction, highlighting elastoplastic coupling effects crucial for modeling ceramic forming processes.

Contribution

It introduces a protocol for ultrasonic measurement of elastic constants during powder densification and proposes laws describing their variation based on elastoplastic coupling.

Findings

Elastic stiffness increases with forming pressure.

Ultrasonic transmission effectively quantifies elastic constants.

Densification laws are developed based on experimental data.

Abstract

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.