Research On Fatigue Progressive Damage Analysis Method For Composite Of Helicopter Blade

As the key component of helicopter, The rotor blades bear the complex cyclic load, which resultin serious fatigue problem, and directly affect the safety and reliability of the helicopter.At present,thefatigue life of the blades is vastly improved by introducing composite materials. But the compositematerials is limited to exert all strength to withstand fatigue loads, because of yet using safety lifedesign method which relying on limiting the work stress level and greatly reduced the S-N curve toensure the fatigue reliability. This thesis establish a new methods to improve the composite bladesfatigue life prediction reliability, and explore composite blade potential strength and life. It hastheoretical significance and engineering practical value.Firstly, starting from the mechanism of fatigue damage of the composite structure, this thesis,defining damage measures matrix in stress-strain relations, deducing the constitutive relation in theprogressive damage process, putting forward the material properties of degradation model based onthe static and fatigue test of the composite materials of helicopter blades, and using a Hashin failurecriteria to judge whether local materials failure, and finally establish the progressive damagesimulation model of composite structure.Secondly, based on the finite element stress calculation, this thesis code the progressive damageanalysis programs for composite blades, which using the fixed N-R method to buildup the incrementalcalculation procedure of nonlinear stress analysis, fatigue failure judgement and material performancedegradationWith regard to the experimental study, we completed the static and fatigue test of the compositematerials of helicopter blades, and based on experimental data, determined the parameters of thedamage and material performance degradation model; At the same time, using the developedprogressive damage analysis method to successfully predict the static strength and fatigue life of thecomposite laminates.Finally, the Z-9helicopter composite blade root segment is deeply investigatedby utilizing the progressive damage analysis method, and the fatigue progressive failure mode,flapping stiffness drop characteristics and fatigue life of the root segment are successfully obtained.The theoretical analysis results are got good agreement with the fatigue test data, which show thetheory model validity and analysis method validity.