Study On Structural Integrity Assessment Methods Of Composite Fan Blade

Compared with traditional titanium alloy wide chord fan blade,carbon fiber reinforced resin matrix composite fan blade has more excellent performance.As the most front-end part,the fan blade is not only subjected to the centrifugal force produced by high-speed rotation and the unsteady aerodynamic force exerted by the surrounding air flow,but also the strong vibration of the blade caused by the external object impact,the unbalance of the fan rotor,and the rubbing with the casing,which makes a lot of provisions about the fan blade in the airworthiness certification of aeroengine.Among them,structural integrity is an important issue in engine airworthiness certification.Its airworthiness compliance ensures that there will be no permanent damage to the structure or negative effects on the operability and aerodynamic performance within the declared flight envelope.In this paper,the baseline composite fan blade is taken as the research object.Four common and important structural characteristics—static strength,vibration characteristics,high cycle fatigue and flutter stability are selected in the detailed verification stage,and the evaluation methods and realization methods of the above structural characteristics in laminated composite fan blades are studied:1.Aiming at the static strength,vibration characteristics,high cycle fatigue and flutter stability of laminated composite fan blades,a set of evaluation methods was explored and a calculation platform was built.2.Different failure criteria are used to calculate the reverse reserve factor and static strength failure location of each ply of the baseline blade.The results show that the Tsai-Wu failure criterion is conservative,the calculation time of secondary failure criterion and Hashin failure criterion is less,and the puck criterion is more close to the stacking form of composite blade internal ply.3.Using Campbell diagram,the resonance margin of the first six modes of the composite blade is analyzed.The strain energy density index is used to measure the concentration of vibration energy.Based on the constant life dirgram of each stress in the material principal coordinate system,the high cycle fatigue weak-link,vibration stress margin and initial failure stress direction of the blade under different vibration modes are evaluated.The results show that the resonance margin of the first two modes meets the requirements,the vibration energy of the second bending mode is the most concentrated,and the location of weak-link point is not more than 40% of spanwise.4.The application scope of the empirical and theoretical methods for predicting the flutter boundary of composite fan blades is summarized,and the flutter design requirements are pointed out.The flutter stability of the baseline blade was evaluated by three parameter method and empirical curve.