Relationships between cohesion and tensile strength

Farley and Valentin (1967/68) were the first to correlate the bulk powder properties of cohesion C, and tensile strength T, for five different powders, containing a range of particle sizes. It has been shown for a range of powders (calcium carbonate, precipitated and mined, aluminium oxide and zinc dust) that cohesion appears to be approximately equivalent to 2T 

It is now believed, however, that more powder flow properties can be incorporated into this simple relationship of C = 2T. Incorporation of the parameters of particle size, bulk and powder densities leads to the relationship expressed as the Warren Spring equation 

The shear flowability index, n, was found, from past observations (Farley Valentin 1965, 67/68), to be independent of the bulk density of sheared compacted powder. Because of this independence of particle size from bulk density it is now realised that the shear flowability index, n, from the Warren Spring equation and the Jenike internal angle of friction may be the preferred parameters to eharacterise and quantify the flowability of powders. Jenike and others (Williams et al. 1970/71 Williams Birks 1965 Hill Wu 1996 Cox Hill 2004) selected the Jenike failure function to be one of the best indicators to predict the ease of powder movement and powder flowability. 

Rajendran Nair et al. (1990, 1993) examined the cohesiveness of mixtures of a coal and 10% clay mix, which had a residual moisture eontent of 0.15% moisture, with mixes having various amounts of added water. The parameter of cohesiveness (Cm) was derived from the yield loei measured in a Jenike shear cell tester and the tensile strength measured was from 

From the initial linear part of these series of yield loci, Rajendran Nair and co-workers calculated the internal friction, (/ rn, from the slope of the yield loci and also computed the tensile strength, Trn, from the extrapolated yield loci of the coal-clay-water mixtures, to arrive at the relationship  

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Figure 1.30 Relationship between cohesion and tensile strength for a range of industrial powders (Fadey Valentin 1967/68).

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