Design Of Insulation/Bearing Integrated Thermal Protection Connector And Failure Mechanism At High Temperature

In thermal protection system,the whole thermal protection system is constructed by splicing joints,in which the structural joints need to ensure their own strength to provide a safe and stable connection and prevent the thermal short circuit caused by the thermal protection structure without thermal insulation layer.The strength and reliability of connectors are related to the structural safety of aircraft,and their thermal insulation performance is related to the thermal protection effect of thermal protection system.Therefore,it is of great significance to design a kind of bolted connector with high strength and low thermal conductivity.Firstly,a kind of multi-layer gradient Ni/Y2SiO5 ceramic material with low porosity,low thermal conductivity and high strength was prepared.The thermal conductivity of porous Y2SiO5 ceramics(porosity is 30%)is 0.378W/m-K.The metal-ceramic composites formed by mixed Ni have high shear strength(62.12MPa,20%volNi/Y2SiO5)and small change of thermal conductivity(0.456W/m·K).For multi-layer functionally graded composites,ABAQUS finite element analysis software was used to simulate and verify the appropriate gradient composition and shear position.The simulation results show that the shear strength(57.41 MPa)of the multi-layer composites with 0%/10%/20%gradient is better than that with 0%/5%/10%gradient(49.78MPa),and the shear failure at the weak interface should be avoided.The main failure mode is brittle failure along the shear plane,which has the effect of slowing down brittle failure for the strengthening of Ni.When multilayer gradient materials are subjected to shear at high temperature,the shear strength decreased with the increase of temperature with the attenuation degree decreases.Secondly,the thermo-mechanical coupling behavior of typical multi-layer gradient Ni/Y2SiO5 composite bolts at high temperature was studied.The results show that the equivalent thermal conductivity of the bolt is 0.402 W/m K,which is mainly provided by porous ceramics in the middle layer.The thermal conductivity of the bolt has little change compared with that of porous ceramics(0.378W/m·K).However,the shear strength of the bolt structure(16.87MPa)is affected by the stress concentration caused by the setting of nuts and threads.Finally,considering the bearing capacity and thermal insulation performance of the bolt,the gradient composition and size are optimized.In the simulation,according to the structure which has the least residual thermal stress and the best relative thermal insulation performance,it is determined that the thickness of reinforced layer is 4mm,the thickness of transition layer is 6.5mm,and the thickness of insulation layer is 3mm.The effective thermal conductivity of the optimized structure is 0.435W/m·K,and the shear strength is 15.46MPa under thermo-mechanical coupling.