Reliability analysis of kinetic accuracy considering hygrothermal deformation of composite cabin door

To address the problem that composite materials exhibit intensified swelling effect and increased dispersion degree under hygrothermal environment, which are prone to induce unexpected deformation of the cargo door structure, cause displacement of the connected mechanism fulcrums, and further directly lead to the inaccuracy of the Kinetic accuracy of the locking and unlocking mechanism as well as potential safety risks, a reliability analysis method for Kinetic accuracy under hygrothermal environment based on the second-moment implicit variance propagation is proposed. This method systematically reveals the uncertainty transfer mechanism through which hygrothermal environment affects the Kinetic accuracy of mechanisms via material properties. First, based on the mechanism kinetics principle and the hygrothermal constitutive relation of composite materials, an implicit function model of mechanism motion output considering hygrothermal deformation is established. Second, by introducing the second-moment implicit variance propagation method, a reliability analysis model is constructed to map the dispersion of composite material properties under hygrothermal conditions to the uncertainty of door structural deformation and finally to the deviation of mechanism motion output, realizing efficient analytical quantification of uncertainties. Finally, a case study is conducted on the ground unlocking process of the composite cargo door locking and latching mechanism of a civil aircraft. The results show that compared with the room-temperature dry condition, the insufficient motion of the locking mechanism leads to a 73.66% increase in the risk of unlocking failure due to incomplete actuation, while the excessive motion of the latching mechanism results in a slight decrease of approximately 12.53% in the failure probability. The proposed method can effectively evaluate the significant impact of hygrothermal environment on Kinetic accuracy reliability, providing a theoretical basis for reliability optimization and failure risk early warning of composite door mechanisms under hygrothermal environment.