  This paper aims to numerically study the pre-fatigue, low-velocity impact
(LVI) and fatigue progressive damage behaviours of a full-scale composite
helicopter tail structure under multipoint coordinated loading spectrum. First,
a fatigue progressive damage model (PDM) incorporating multiaxial fatigue
residual strength degradation rule, fatigue failure criteria based on fatigue
residual strength concept and sudden stiffness degradation rule was proposed.
Then, an LVI progressive damage model for plain-weave (PW) and unidirectional
(UD) composites was developed. Moreover, a full-process analysis algorithm with
a reasonable damage transfer strategy for pre-fatigue, LVI and fatigue
progressive damage analysis was proposed. Finally, a highly computational
efficient and accurate full-scale global-local finite element (FE) model of
helicopter tail structure was built to predict strain distribution under two
flight working conditions, to predict LVI damage under impact loading, and to
assess fatigue damage behaviours under multipoint coordinated loading spectrum.
The numerical predictions agree well with test results from this work and
literature data, indicating that the developed pre-fatigue, LVI, fatigue PDMs
and algorithms, as well as the global-local FE modelling based on
shell-to-solid coupling, can effectively analyse the impact damage tolerance of
full-scale aircraft structures.
