Material Selection in Engineering Design Using Choquet Integral-Based Linguistic Operators under Hybrid Environment

Table 1

Criteria’s types, expressions, and requirements.

Criteria	Types	Expressions	Requirements
: economies	Cost	Linguistic terms	The less the ratings, the better the attributes. The ratings of material cost, subject to various factors, are hardly exactly identified and so expressed in linguistic terms according to the knowledge of experts.
: chemical stability	Beneficial	Linguistic terms	Materials with good chemical stability, though subject to repeated heat absorption and heat release, do not experience the problems of segregation, side reaction, and chemolysis and hence smaller attenuation in the heat storage capacity.
: phase change latent heat	Beneficial	Intervals	Under the same phase change temperature, the greater the phase change latent heat is, the more the energy can be stored.
: density	Beneficial	Exact values	For the materials with approximately equal phase change latent heat, the greater the density is, the greater the heat per volume can be stored, which lowers the cost of the heat storage equipment.
: thermal conductivity	Beneficial	Triangular values	Greater thermal conductivity implies quicker speed in the process of heat storage and extraction and better performance in conductivity, and that absorbing or releasing the same heat requires less temperature gradient.
: corrosivity	Cost	Linguistic terms	Materials with smaller high-temperature corrosivity are compatible with many other materials, which implies a wide range of material selection for the heat storage pieces of equipment, lowering their cost.