Purpose The purpose of this paper is to propose a set of constitutive functions for dried bodies for accurate prediction of the entire deformation process of ceramic products during firing and to present relevant methods for determining their coefficients from a series of respective thermo-mechanical analysis (TMA) tests. Design/methodology/approach The function forms of the sintering-induced strain rate, viscoplastic multiplier and elastic modulus are formulated in order with reference to empirical data of relative densities. Separate TMA tests are conducted to identify their coefficients, while a stairway thermal cycle test is carried out to identify the parameters in the densification rate. Then, various finite element analyses (FEA) are performed for accuracy confirmation. Findings The performances of the present constitutive functions along with the identified material parameters were validated in comparison with the relevant test results. It has then been confirmed that these functions enable us to some extent to accurately estimate the non-mechanical and mechanical deformations of dried bodies during firing. Also, by performing FEA of an actual sanitary ware product, the applicability and capability of the proposed set of constitutive functions could be demonstrated. Practical implications The present methodology with the proposed constitutive functions is a simple, but reliable and practical approach for simulating the deformation process of arbitrary ceramic products subjected to firing and applicable for practical applications in various engineering fields. Originality/value The constitutive functions of the viscoplastic multiplier and elastic modulus, which enable us to properly characterize the mechanical behavior of dried bodies subjected to firing, are originally formulated in analogy with that of the sintering-induced strain.

No abstract

We propose a set of constitutive equations of earthenware material subjected to the firing process and appropriate ways of determining their function forms and relevant material parameters from a series of respective experiments. The firing process under a specific heat curves is generally divided into three different phases; "thermal dilatation phase", "sintering phase" and "thermal contraction phase". These non-mechanical deformations are assumed not to be coincident, and the mechanical ones are assumed to be represented by viscoplastic constitutive model. Then, the key issue must be how to determine sintering strains by calibrating the employed function form of the densification rate with the data obtained from the stairway thermal cycle (STC) tests. Also, the presentations of the dependencies of the elastic and creep properties on both temperature and density are of particular importance to accurately predict the overall deformation of earthware.All the relevant material parameters as well as coefficients of thermal expansion and contraction are identified with the data obtained from respective mechanical experiments conducted in testing equipments for thermo-mechanical analysis (TMA) under several levels of termperature. The method of differential evolution, which is one of the metaheuristic optimization techniques, is employed to identify the creep parameters, since the mechanical responses to several levels of loading during firing processes involve all the non-mechanical and mechanical deformation of specimens simultaneously.The calculation results with the proposed constitutive equations are compared with the original experimental data to demonstrate the applicability for practical use of their function forms determined by the proposed strategy.