# Fault Coupling Analysis and Reliability Assessment of Actuation System Based on Bond Graph Model
## 1 Introduction
[13] combined the POF life model with statistics to propose a reliability assessment model and conducted a system-level reliability assessment on the aircraft's electric drive system. [PERSON] et al. [14] used EHA physical model and improved and extended Kalman filter technology based on excitation equivalent conversion to realize EHA multi-factor fault analysis and diagnosis. [PERSON] et al. [15] used AMESim to conduct fine modeling of the electromagnetic direct drive hydrostatic actuation system and build a system performance test platform to verify its effectiveness. [PERSON] et al. [16] used AMESim to build the electromechanical actuators (EMA) model and considered the uncertainty of its parameters to improve the model's accuracy and analyze the performance of the EMA. [PERSON] et al. [17] studied the influence of thermal energy on the operation of EHA. Based on the energy transfer, a dynamically coupled thermal model of the EHA was established to predict the temperature variations of its components during operation. Bond graph modeling was used by [PERSON] et al. [18] to develop a model of the piston pump in the flight brake, fault injection was used to monitor the change in the system's physical quantity, and the pump's fault identification and analysis were completed. In comparison to AMESim, Simulink, and mathematical models, the bond graph model has advantages in fault injection research because it makes it easier to inject the fault and observe the causal changes between various physical quantities in the system. It is suitable for the study of fault analysis of complex electromechanical systems. [PERSON] et al. [19] used bond graphs to build detailed models of the electromechanical hydrostatic actuator, laying the groundwork for subsequent studies. According to the above literature, the current physical mechanism model of the actuation system neglects the impact of the fault coupling phenomenon due to the accumulation of dissipative energy on the system. In addition, most studies focus on modeling individual actuators and their components but do not model or analyze the performance of the entire actuation system. The innovation of this paper is that it models the entire actuation system using the bond graph model, studies the physical degradation process of each actuation system component, and examines the mechanism of the fault coupling phenomenon caused by the accumulation of dissipated energy. By combining the bond graph model with the fault coupling mechanism, a fault coupling model for the actuation system with explicit mechanism support is developed. By analyzing the fault mechanism, single fault injection and multiple faults at the same time were carried out, respectively, which increased the nonlinearity of fault analysis. The influence of fault coupling propagation on the output energy change of simulation results was observed. The MEA actuation system has undergone a fault analysis and reliability assessment, and its weak points have been identified. As a result, a theoretical basis for the improvement of its reliability is provided and the safe operation of the MEA is guaranteed. The remainder of this article is organized as follows. The construction of the MEA actuation system model with the bond graph model is introduced in detail in Section 2. In Section 3, the analysis of the actuation system's fault coupling mechanism and the description of the degradation physical process are emphasized. Faults are injected into the model and simulation results for different faults are compared in Section 4 to enable fault analysis and system reliability assessment. In Section 5, the deficiencies of this study and future research perspectives are discussed. Finally, the work of this paper is summarized in Section 6. The flowchart studied in this paper is shown in Figure 1.