Approach the powder contact force, voidage, tensile stress, wall frictional stress and state diagram of powder bed by simple pressure drop monitoring

Abstract

The evaluation of the mechanical properties and the state of a powder bed are essential for industrial powder operations. We assume that the bed incipient yield is approximately the bed incipient fluidization, and the particle contact force, the bed voidage, the bed tensile stress and the bed-wall frictional stress can be determined by simple pressure drop monitoring when gradually increasing the superficial gas velocity from zero. A two-dimensional powder bed voidage-tensile stress state diagram at zero shear stress under anisotropic consolidation is initially prepared. For the sample powder bed, we show that the isotropic tensile stress estimated by the powder yield locus extrapolation, 340 Pa−770 Pa, from a shear tester is different from the anisotropic tensile stress evaluated, 120 Pa–180 Pa, by the pressure drop overshoot approximation.