Abstract:
An analysis procedure is described which enables the strains and
stresses that develop during drying to be predicted from given material
properties of ceramic clays. The equations determining the drying
behaviour, which are developed in terms of the variables moisture stress,
effective stress, and total stress, define the material properties
required. Aqueous conductivity relates the water flow to the moisture
stress, and constitutive coefficients relate the clay deformation to the
effective stress. The moisture stress and effective stress are related
by the condition for total-stress equilibrium.
The finite-element method is used to establish a numerical-analysis
procedure for axially symmetric drying. Application of the procedure
to the radial drying of cylindrical shapes is described. Good correl
ation is obtained between predictions of circumferential tensile total-
stress development and the observed incidence of cracking in radial
drying of circular discs.
In a study of the relative significance of factors determining the
development of tensile stress in drying, a numerical factorial-experiment
is described. In the experiment some selected material-property and
drying-condition factors are systematically varied and the resulting
drying times and induced tensile stresses are obtained. Factor changes
that result in a reduction in the drying time, but no increase in the
tensile stress, are noted and their effects are quantified. The great
est effect is obtained from an increase in the aqueous conductivity, a
60% increase producing a 50^ reduction in drying time as well as a 1($
reduction in tensile stress. It is suggested that the factorial-
experiment procedure may be used to predict the factor changes that would
allow improvement of ’safe’ drying-rates, and maximum safe drying-rates
could be predicted, given maximum allowable tensile-stresses.