Probabilistic Assessment Methodology Ofimpact Damage Tolerance For Composite Aircraft Structures

Probabilistic assessment of damage tolerance for composite aircraft structure is an advanced technology for ensuring structures safety. In this thesis, the major problems exist in the assessment of failure probability of composite structures have been studied. The main features for this thesis are stated as follows:(1) Dent depth and damage area at a given impact energy, initial strength, temperature and moisture of composite structures are taken as random variables with general distributions. Based on semi-probabilistic compliance methods, an improved process for failure probability assessment has been proposed and the corresponding analysis software has been developed. In case there are only statistic data about damage type and size, part of the process should be changed. Based on the value of failure probability, the load level used for the certification of damge tolerance can be calculated.(2) According to the nondestructive testing method, there are two types of data, with or without signal value. The maximum likelihood method is used to calculate parameters of two models(the cumulative lognormal model and the log odds model) and the probability of detection at the 95% confidence level.(3) Based on the load superposition method and the principle of virtual work, approximate solutions are proposed for the bending of clamped symmetric angle-ply laminated rectangular thin and thick plates subjected to a central concentrated force.(4) The initial interlaminar shear strength, which determines the onset of delamination, has been defined and calculated based on Eshelby’s equivalent inclusion method. Combine the assumption that internal delamination is driven largely by interlaminar shear stresses resulted from bending of laminates, a simple and effective analytical method is presented to predict the damage area of composite laminates induced by low velocity impact.(5) According to methods of failure probability assessment of composite structures, the failure probability of composite laminates and composite portion of the fin of an aircraft have been calculated. The optimal detection interval of composite laminate has been estimated based on the safety condition.