A Contribution to Time-Dependent Damage Modeling of Composite Structures
The paper presents a new damage model for predicting stiffness loss due to creep loading and cyclic fatigue. The model, developed within a continuum damage mechanics framework, is based on the idea of a time-dependent damage spectrum, some elements of which occur rapidly and others slowly. The use of this spectrum allows a single damage kinematic to model creep and fatigue damage and to take into account the effect of stress amplitude, R ratio, and frequency. The evolution equations are based on similar equation than the one describing the viscoelasticity model and are relatively easy to implement. The new model is compared to the experimental results on carbon fiber/epoxy tubes. Quasi-static, creep and fatigue tests are performed on filament-wound tubular specimens to characterize the elastic, viscoelastic and plastic behavior of the composite material. Varying amounts of damage are observed and discussed depending on stress level and R ratio. The experimental work aims to develop and validate the damage model for predicting stiffness loss due to creep loading and cyclic fatigue.
Fatigue damage modeling of fibre-reinforced composite materials: Review
This paper presents a review of the major fatigue models and life time prediction methodologies for fibrereinforced polymer composites, subjected to fatigue loadings. In this review, the fatigue models have been classified in three major categories: fatigue life models, which do not take into account the actual degradation mechanisms but use S-N curves or Goodman-type diagrams and introduce some sort of fatigue failure criterion; phenomenological models for residual stiffness/strength; and finally progressive damage models which use one or more damage variables related to measurable manifestations of damage (transverse matrix cracks, delamination size). Although this review does not pretend to be exhaustive, the most important models proposed during the last decades have been included, as well as the relevant equations upon which the respective models are based.
Cumulative damage theory for composite materials: Residual life and residual strength methods
Abstract The cumulative damage problem is formulated in terms of a damage function which must satisfy certain conditions. It is shown that such a damage function can be used with residual life theory as well as with residual strength theory, and that these two approaches are equivalent. Various assumptions regarding the dependence of the damage function on fatigue variables lead to both known and new results of life prediction. Comparison of analytical results with available test data did not reveal a best fit of any one prediction to the data.