| Aero-engine blade film cooling holes effectively reduce the operating temperature of the blade,but also destroy geometric continuity and reduce its lifetime in operation.The rupture mechanism of the film cooling holes is revealed by high-temperature rupture strength testing.The complex operating temperature field of film cooling holes,on the other hand,will have an effect on the rupture.In real complex environments,the coupling mechanism between temperature and stress fields,as well as the damage mechanism and life characteristics of film cooling holes under service circumstances,are not yet known.Therefore,studies on the mechanical performance of film cooling holes in complex temperature fields can provide a solid foundation for quality evaluation and optimization design of these structures.In this paper,creep damage and lifetime characteristics of nickel-based single crystal superalloy film cooling holes in complex environments were investigated based on conjugate heat transfer and the crystal plasticity finite element method.This study looked at how flow and aerodynamic characteristics affected the macroscopic performance,revealing how varied inclination angles affected the mechanical and cooling performance of film cooling holes as well as the thermalstress coupling mechanism.The study also clarified the interference effect of the temperature and stress field between multi-holes on the damage and rupture of the film cooling holes.The multiaxial creep life prediction method based on the geometric characteristics of film cooling holes was also investigated.The main research contents and conclusions are as follows:(1)During the film cooling,convective cooling in the inner wall contributes significantly more to the cooling function than external film cooling.Moreover,a decrease in inclination angle significantly improves overall cooling effectiveness while reducing mechanical performance.Among them,the 45° hole has a relatively better comprehensive performance.Additionally,stress concentration around the hole and relaxed distribution states are not sensitive to changes in the temperature field,but local temperature differences can cause additional stress concentration on the cold surface.Consequently,temperature field and stress field characteristics jointly determine different damage patterns in single crystal materials between hot and cold surfaces.On hot surfaces,high temperature induced low stress creep damage occurs.And on cold surfaces,low temperatures and additional stress concentrations induce high stress creep damage.(2)The temperature levels of the acute side of the cold surface and the hot surface of a film cooling hole are relatively close to one another under the interference of multi-hole temperature fields,but there are significant differences in temperature fields among multi-hole regions,leading to high-temperature holes around edges and low-temperature holes in central regions.As a result,the temperature and stress fields of several holes interact,causing additional tensile strains from high-temperature holes acting on low-temperature holes and increasing stress concentration.The rupture mechanism shifts from a center area holes-dominated rupture under a uniform temperature field to an edge high temperature holes-dominated rupture under the influence of the flow field temperature.As the blowing ratio rises,the rupture route leads to edge hole rupture progressively.(3)Based on continuum damage mechanics,an improved method for predicting multiaxial creep life is proposed by the existing skeletal point stress method.This method is efficient,accurate,and applicable to engineering applications.Compared with the traditional method,this new method can save up to 5/6 of the model quantities during the skeletal point position determination.The validated method is further tested using experiments,which analyze the multiaxial creep fracture characteristics of structures by combining the triaxiality factor and damage distribution analysis.A low triaxiality factor can significantly enhance creep ductility.As the notch acuity ratio increases,alloys tend to exhibit ductile creep fracture,and initial damage moves toward the center of the notch. |
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