Abstract
Concentrated metal-in-polymer suspensions (55 vol.% and 60 vol.%) of aluminum powder dispersed in low molecular weight polyethylene glycol) demonstrate elastoplastic properties under compression and shear. The rheological behavior of concentrated suspensions was studied in a rotational rheometer with uniaxial compression (squeezing), as well as shearing superimposed on compression. At a high metal concentration, the elasticity of the material strongly increases under strain, compared with the plasticity. The elastic compression modulus increases with the growth of normal stress. Changes in the shear modulus depend on both normal and shear stresses. At a low compression force, the shear modulus is only slightly dependent on the shear stress. However, high compression stress leads to a decrease in the shear modulus by several orders with the growth of the shear stress. The decrease in the modulus seems to be rather unusual for compacted matter. This phenomenon could be explained by the rearrangement of the specific organization of the suspension under compression, leading to the creation of inhomogeneous structures and their displacement at flow, accompanied by wall slip. The obtained set of rheological characteristics of highly loaded metal-in-polymer suspensions is the basis for understanding the behavior of such systems in the powder injection molding process.
Highlights
Suspensions are permanent and important objects for rheological studies
High compression stress leads to a decrease in the shear modulus by several orders with the growth of the shear stress
Concentrated suspensions with solid phase contents of 55 and 60 vol.% are elastoplastic media that possess dominating plasticity. The latter is understood as the ability to undergo irreversible deformation under shearing and compression, which is limited, and the value depends on the stress
Summary
A diverse range of suspensions can be seen in nature, applied to various fields for technical and everyday use, and as a subject of scientific interest for exploring the fundamental relationships between the structure and properties of the matter. This is a topic of numerous research papers and comprehensive reviews, covering various aspects of the rheology of non-Brownian suspensions, including rather concentrated compositions [1,2]. We considered the rheological properties of similar suspensions covering the whole concentration range in shearing [3]. The concentration range between 55% and 65% is especially important for several applications of concentrated suspensions because a manufacturer desires to have as high a concentration of a solid component as possible, while maintaining the material integrity and plasticity
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