Thermostressed State of a Nozzle Vane from Max Phase Ceramics
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THERMOSTRESSED STATE OF A NOZZLE VANE FROM MAX PHASE CERAMICS B. S. Karpinos,a,1 V. M. Kulish,a and T. O. Prikhna
UDC 539.4
b
Numerical simulation results for the unsteady thermal and stressed states of a nozzle vane under unsteady operation conditions of the gas turbine are presented. The vane and nozzle block duct 3D computer model was constructed. The finite element mesh form, its sizes, and calculation time steps were optimized. The vane and duct contained 1.7 and 3.6 mln elements and 2.3 and 0.8 mln nodes, respectively. The mesh smoothing with corresponding nodal displacement near the transition zones and in the vicinity of curvilinear surfaces was used. The simulation consisted in successive numerical solutions of nonstationary flow problems for a moving medium and heat, transfer, thermal conductivity, and thermoelasticity problems for the vane. The parameters of unsteady thermal loading conditions were defined. The thermal properties of the moving medium and vane material were assumed to be time-dependent. For turbine power improvement conditions, time variations of duct flow parameters, temperatures, thermal stresses in different vane zones, their gradients and rates were analyzed. The essential nonuniformity of the thermostressed vane state and zones of thermal stresses, almost reaching the ultimate strength of the material, were noted. The effect of general heat flow components on the disturbance of thermal stresses was shown. Emphasis was placed upon the appearance of tensile stresses on a heated trailing edge of the vane (most critical zone). The conclusion was drawn regarding a potential application of a MAX phase Ti2ALC us a structural material for the vanes of short-life gas turbines. Keywords: thermal stresses, numerical simulation, nozzle vane, MAX phase Ti2AlC. Introduction. Recent investigations [1–4] are indicative of a lively interest of experts on materials science and deformable solid mechanics in the development and application of heat-resistant ceramic composites as structural and thermoinsulating materials. Particular emphasis has been placed to the class of thermodynamically equilibrium materials, the so-called MAX phases. The MAX phases are ternary lamellar chemical compounds with the formal stoichiometry Mn+1AXn (n =1, 2, 3, …), where M is the transition d-metal, A is the p-element (Si, Ge, Al, S, Sn, …), and X is carbon or nitrogen. These materials combine the properties of metals and ceramics. At high temperatures, they exhibit satisfactory static and thermocyclic strength, corrosive and chemical resistance. Research results [5, 6] show promise for increasing the operating temperatures of those materials to Tm =1800 K. The advancement of novel synthesis technologies gave impetus to the practical application of those materials. Progressive methods and technologies of pressure-assisted compaction (5–30 MPa), such as gas-shielded hot pressing, compression-aided sintering, and gas-shielded and vacuum spark plasma sintering could significantly improve the service properties and reduce t
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