Robotic pre-drilled Z-pinning approach for enhancing the performance of composite fan blades in aircraft engines

Abstract

Composite fan blades serve as the primary barrier of protection in aircraft engines during the air intake process, and their mechanical properties play a significant role in aviation safety. The interlaminar performance of composite fan blades is relatively weak owing to the layered manufacturing process, rendering them susceptible to delamination under the application of external impact loads. Z-pin insertion is a technique that involves embedding an array of slender and rigid pins through the laminate to reinforce the composite materials by introducing an additional load-bearing medium through their thickness. However, the application of the Z-pin insertion technique presents significant challenges owing to their complex geometries and stringent performance requirements of the composite fan blades in aircraft engines. The intricate shapes of fan blades require the manual execution of the Z-pin insertion process, leading to low production efficiency and consistency. Moreover, the Z-pins that are not embedded along the normal direction of the curved surface can induce defects, such as matrix cracking or fiber misalignment, particularly on curved or irregular fan blade surfaces. Combined with the high stresses and dynamic loads experienced by fan blades during operation, the aforementioned factors complicate the selection of the optimal Z-pin insertion parameters in advanced aerospace applications. This paper presents a robotic pre-drilled Z-pinning (PDZP) approach for improving the performance of composite fan blades in aircraft engines. A series of experiments, including double cantilever beam and end-notched flexure tests, were conducted to obtain the optimal insertion parameters for the robotic PDZP process. Furthermore, a robotic PDZP posture model was developed to embed the Z-pins along the normal direction and to avoid matrix cracking or fiber misalignment in the curved or irregular regions of the fan blade. Additionally, a compensation method was proposed for the normal deviation during the PDZP process. Finally, a prototype of the robotic PDZP system was developed and subjected to impact tests, which demonstrated that the impact resistance of the composite fan blade satisfied the expected requirements.