Study On Thermal Adaptation Technology Of Composite Material Bolt Connection

Hypersonic vehicles use advanced composite materials for the load-carrying and heat-resistant structure.Since the expansion coefficient of the metal is much larger than that of the composite material,when the ordinary high-temperature alloy bolt is used to connect the composite structure,there is a problem that the bolt pre-tightening axial force will be reduced or even completely disappeared due to mismatch at high temperature.On the basis of the thermal adaptation technology,two kinds of new joint solution for thermal adaptative bolt are innovatively designed with a tapered surface matching interface using split structure,which can maintain much more residual axial force at 900 °C.The theoretical relationship formula between high temperature residual preload and various parameters is derived.The parameters include structural size,material elastic modulus,expansion coefficient,friction coefficient,etc.Finite element model is established according to the parameter conditions in the theoretical formula,which is compared with ordinary bolt model The change of axial force is simulated when the bolt temperature rises to verify the effectiveness for anti-loosening at high temperature of the scheme,the principle feasibility and the accuracy of the formula.The normal/high temperature static tensile test and vibration test of the thermal adaptative bolt and the ordinary bolt are performed,and the results show that the thermal adaptative bolt has good anti-loosening effect at high temperature.This paper deals with theoretical analysis,numerical simulation,and experimental verification.The specific work is as follows:(1)The thermal deformation coordination equation of bolt connection under temperature rising condition and the theoretical basis of thermal adaptation technology are given.Two kinds of new joint solution for thermal adaptative bolt which have split structure are proposed,and the structural design principle and material selection are analyzed.From the theoretical point of view,the rationality of anti-loosening performance at high temperature of the two schemes is analyzed and demonstrated.The theoretical relationship formula between the residual axial force at high temperature and the structural dimension,the friction coefficient of the interface and the material properties is deduced,which provides a theoretical basis for the subsequent finite element simulation results.(2)Theoretical formula method and finite element numerical simulation method are using to compare with ordinary flat-pad bolts to verify the anti-loosening performance at high temperature of thermal adaptive bolts;The accuracy of thermal deformation coordination equation is verified;The influence of various parameters on performance is explored It includes parameters such as the structure size parameter,the interface friction coefficient,the material expansion coefficient and its nonlinearity.And the numerical simulation method is used to reflect influence mode of the parameter revealed by the theoretical formula.(3)The constant/high temperature static tensile test of the thermal adaptive bolt and the ordinary bolt which is contrastive was carried out.The linear relationship between the inflection point load and the bolt axial force and tightening torque was analyzed.The ratio of the residual residual axial force at high temperature was discussed.Two data processing methods for evaluating anti-loosening effect at high temperature are discussed.From the view point of static test,it proves the good anti-loosening performance at high temperature of the thermal adaptive bolt.The high temperature vibration test is carried out,and the fundamental frequency of the contact method is compared with the non-contact method.The anti-loosening performance at high temperature of the thermal adaptive bolt is proved from the vibration test point.The expansion coefficient of the material selected by the scheme and the torque coefficient of the test piece were measured.