# Fatigue Characteristics Analysis of Carbon Fiber Laminates with Multiple Initial Cracks
## 6 Conclusions  
Wind turbine blades serve as essential structural elements in wind energy systems, with their efficacy and dependability paramount for the overall system's security. As the trend towards larger and lighter blades continues to grow, carbon fiber composite materials, with their advantages of being lightweight, possessing high strength, and exhibiting corrosion resistance, have emerged as the material of choice for blade fabrication. Nonetheless, the manufacturing process of carbon fiber composites can easily introduce defects that, under adverse conditions and fluctuating loads, can cause cracks to propagate and interact, potentially leading to rapid blade fracture and jeopardizing operational safety. In light of this, the present study conducted static fatigue tests on carbon fiber laminates featuring multiple cracks of varying types and analyzed the fatigue life extension process of these multi-cracked plates through simulation. This research focused on the influence of material parameters, internal and edge cracks, crack angles, and the uncertainty associated with distances between cracks on fatigue life. Utilizing a PSO-BP neural network, a reliability model for carbon fiber plates was established, and sensitivity analysis of the physical uncertainty parameters was undertaken. The conclusions drawn are as follows:  
1. The results of static fatigue tests on carbon fiber laminates, which exhibit multiple cracks of varying configurations, reveal that variations in crack length are the predominant factor influencing the service life of carbon fiber laminates under fatigue conditions. Additionally, the dispersion of static fatigue data diminishes as the variables increase within the same level, whereas the dispersion in fatigue life data is significant and exhibits no clear pattern. At the specific condition where internal cracks measured L\({}_{1}\) = L\({}_{2}\) = 4 mm and the angle \(\theta\) was 90\({}^{\circ}\), the coefficient of variation peaked at 16.33%. This significant alteration highlights the considerable influence that uncertainties in physical parameters have on the service life of carbon fiber laminates when subjected to fatigue;
2. To efficiently overcome the challenges of high costs, extended timelines, and data limitations in fatigue testing, the XFEM method is employed for simulating the fatigue behavior of carbon fiber laminates containing multiple cracks. The comparison with experimental data shows a relative error within an acceptable 10% margin, satisfying practical engineering standards. The simulation captures the progression of fatigue crack growth at various stages of the material's lifespan, providing a means of ascertaining the physical parameters subject to uncertainty;
3. Utilizing the PSO-BP neural network, a fatigue life prediction model for carbon fiber laminates with multiple cracks is established, and based on this, a reliability function is constructed to assess its fatigue reliability. The Sobol method is then applied for sensitivity analysis on the 13 parameters that influence fatigue life, as identified through simulation. The analysis concludes that the most significant parameters affecting the fatigue life of the carbon fiber plate are the lengths of the edge and internal cracks and the angle between them, with the length of the edge crack having the greatest impact. Z.L. : Management and coordination of the planning and execution of research activities, with supervisory and leadership responsibility for the planning and execution of research activities; Y.Z. : Data curation, formal analysis, investigation, visualization, writing--original draft; H.L. : Provided experimental data, formal analysis, surveys, visualizations; X.L. : Provided experimental data, formal analysis, surveys, visualizations, supervisory responsibility, writing--review and editing; J.L. : Provided experimental data, formal analysis, surveys, visualizations; Z.S. : Provided experimental data, formal analysis, surveys, visualizations.