PROBABILISTIC MODELING OF STRUCTURAL / AEROELASTIC LIFE CYCLE FOR RELIABILITY EVALUATION OF DAMAGE TOLERANT COMPOSITE STRUCTURES

摘要

Due to the large uncertainties related to material properties and damage of composites, current design practices require extra safety factors to cover such uncertainties, resulting in conservative designs and service guidelines for composite structures. In addition, current fatigue crack-growth-based structural maintenance methodology does not apply to composite aircraft.This paper presents a probabilistic model for estimating structural and aeroelastic reliability of damage-tolerant composite aircraft structures that enables damage tolerant design, damage tolerance and reliability substantiation, and optimal maintenance planning based on reliability. This development is motivated by the increasing use of composite materials in civil aircraft structures.The method is based on probabilistic structural lifecycle simulation with the consideration of all related parameters, such as material properties with their dispersions, material properties versus environmental variables, damage statistics (type, location, and size of damage), residual structural properties versus damage type and size, possible damage growth at high stress levels, probability of damage detection (POD), quality of repair, inspection intervals, etc.The new and significant aspects of the work is that the reliability of a damage-tolerant composite structure can be assessed on a quantitative basis, covering structural as well as aeroelastic failure modes, thus allowing aircraft manufacturers, operators and flight certification authorities to establish the maintenance service guidelines. Engineers will be able to use this methodology in the future as a guide, to establish design and inspection criteria while considering structural risk and maintenance cost at the same time.