Thermal-Mechanical Evolution Characteristics of Thermal Insulation Materials of Rock True Triaxial Testing Machines Under Complex Working Conditions
During the development of high-temperature true triaxial testing,the imposition of high-temperature environments,cyclic loading and unloading,cyclic thermal shocks,and other complex loading conditions necessitates stringent requirements for the thermal insulation performance of the test system.In oder to scientifically and rationally select appropriate thermal insulation materials for the high-temperature true triaxial test machines under such complex conditions,three kinds of high-temperature engineering thermal insulation materials(GX),glass fiber,and high-temperature resistant resin composite thermal insulation material(BX)and high temperature barrier composite mica material(YM)were prepared.A series of laboratory tests,including cyclic thermal shock,high-temperature exposure,and cyclic loading and unloading,were conducted to simulate the mechanical and thermal conditions representative of operational environments.These tests aimed to evaluate the thermal conductivity,elastic modulus,compressive strength,and microstructural evolution characteristics of the materials under complex working conditions.The results indicate that the thermal conductivity of the three insulation materials initially increases and subsequently decreases with rising temperature under high-temperature conditions,while the elastic modulus exhibits a certain degree of reduction.During cyclic thermal shock experiments,the thermal conductivity of the YM material demonstrated a consistent decline with an increasing number of heating and cooling cycles.In contrast,the thermal conductivity values of the other two materials initially increased and then decreased.The variation in the elastic modulus exhibited a pattern analogous to that observed under high-temperature conditions.Under cyclic loading and unloading conditions,the thermal conductivity of the insulation material initially increases and subsequently decreases as the number of cycles progresses.Notably,the first cycle of loading and unloading exerts the most significant influence on the thermal insulation and physical properties of the material.Scanning Electron Microscopy(SEM)results indicate that the pores within the laminated structure of the YM material remained small following thermal shock,with no significant crack formation observed after high-temperature treatment.The structure was both complete and stable.A comprehensive evaluation of the thermo-mechanical properties revealed that,after exposure to high-temperature environments and cyclic thermal shock,the structural integrity of the YM material was exceptionally stable.Consequently,YM material is deemed the optimal choice for insulation in rock true triaxial testing machines.This study establishes a foundational framework for the selection of thermal insulation materials in true triaxial test equipment and offers significant guidance for both the research and application of thermal insulation material sheets in true triaxial test machines.
thermal insulation materialscirculating heating and coolingcyclic loading and unloadingthermal conductivityphysical property
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