Study Of Effects Of Bolted Structure On The Tensile Stiffness Of Aero-engine Case

Aero-engine casing mainly connected by bolts, reach on the mechanical characteristics of bolted structure is vital for design and optimization of the whole casing. The discontinuity and nonlinear of the tensile stiffness caused by the multi-nonlinear of connective surface make it very difficult to research. The performance and reliability of aero-engine are influenced by bolted pretension, load, vibration, creep, fatigue, self-structure and so on. Generally, research of the contact pressure, friction condition and the changes of load transferring behavior of bolted structure under mechanical circumstance based on theory, finite element method and experiments. In order to provide a basis for damage identification and health monitoring in case of separation, seal failure and abrasion of bolted structure.This thesis mainly study with an object on bolted structure of longitudinal edge casing installation and establish the finite element model by ANSYS. Compare the error of calculated frequency of different finite element models with experimental measurements. Finally adopt the model which has friction coefficient setting of contact surface for performing numerical calculations, namely simulate the actual bolt pretension and contact through creating pretension element and contact pairs. Then study the influence of geometric parameters on the tensile stiffness of bolted structure under bolt pretension. A qualitative study which aimed to research of tensile stiffness changing with bolt pretension and axial load is done using the energy theory. To study of bolt pretension and external loads impact on dynamic characteristics of the bolted structure, instant hammering method is used for experimental modal analysis and obtain the natural frequency, mode of vibration and frequency response function. Due to machining errors and clamping conditions restrictions, the frequency error under the state of the cantilever is very large. Use parameter oriented model updating method to finish the model updating of geometrical dimension and boundary conditions. The revised frequency error are less than 5%, meeting the precision requirement. To reveal the tensile stiffness variations under the influence of bolt pretension and external loads, the equivalent model is proposed according to the mechanical characteristics and the tensile stiffness is formulated. There is a close correlation between numerical simulation and analytical solution of the tensile stiffness for both the single bolt and bolted structure. That is to say, the equivalent model which is used for solving bolt tensile stiffness has high precision. At the same time, the accuracy of the equivalent model is proved by the experimental modal analysis of bolted structure under the state of the cantilever.