Abstract
This paper discusses the prediction of fatigue response of composites using an empirical strength and stiffness degradation scheme coupled to a cumulative damage accumulation approach. The cumulative damage accumulation approach is needed to account for the non-constant stress levels that arise due to stress distributions from stiffness degradation during the fatigue loading. Degradation of strength and stiffness during fatigue loading of the composite was implemented by following the empirical model presented by Shokrieh and Lessard with some modification and correction to the non-dimensional load parameter definition. The fatigue analysis was performed using ABAQUS™ finite element software using a user-defined material subroutine UMAT developed for the material response. Implementation results were first verified for unidirectional laminate test cases and validated by predicting stress versus life (S-N) curves for several laminate coupons test simulations and residual strengths of Open Hole Tension (OHT) specimens subjected to constant amplitude fatigue loading.
Highlights
The Composite materials used in primary aircraft structures can experience fatigue damage and failure due to the repeated loads they experience
These models can be classified in the following categories [1]: fatigue life concepts [2,3], phenomenological models with stiffness [4,5], strength degradation models [6,7], continuum damage mechanics (CDM) based models [8,9,10] and micromechanics models [11,12] and uncertainty and Bayesian based probabilistic models [13,14,15]
Fatigue response of composite materials can be described by the stiffness and strength degradations they exhibit due to accumulation of damage
Summary
The Composite materials used in primary aircraft structures can experience fatigue damage and failure due to the repeated loads they experience. Fatigue response of composite materials can be described by the stiffness and strength degradations they exhibit due to accumulation of damage These are characterized by the residual stiffness and strength measurements of components tested at different stress levels and to varying fractions of their life (previously determined for life models). The material degradation model is based on life prediction models that use empirically fitted constant life curves [20] to determine the number of cycles to failure and a degradation model where the reductions in stiffness and strength occur as a function of the number of cycles of loading experienced as a fraction of the total life time
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