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Traditional metal fatigue analysis methods are not applicable to composites.
Composite analysis requires composite technology.
Composite Fatigue Simulation You Can Use
Fatigue failure of composite materials has long been a design obstacle in energy, aerospace, and automotive applications. In many of these applications, the composite is subjected to a multiaxial load, yet fatigue characterization testing is typically performed under simplified loading configurations. Furthermore, using homogenized composite stresses makes relating the characterization data to realistic load conditions difficult because physics-based theories cannot be easily applied at the composite level.
Helius:Fatigue™ overcomes these obstacles by combing the accuracy of Multicontinuum Technology (MCT) with the well established kinetic theory of fracture (KTF) for a composite-specific, physics-based prediction of composite fatigue life.
Accurate Fatigue Prediction Requires Constituent-Level Stress Analysis
In a large structural analysis, typically only homogenized composite stresses are computed. The problem with utilizing these stresses to predict fatigue behavior is that they do not represent the stresses in the individual constituent materials. But constituent stresses drive composite fatigue behavior. Helius:Fatigue uses the same MCT solution employed by Helius:MCT to access the stress and strain of the fiber and matrix, allowing fatigue damage to be modeled at the constituent level rather than for the homogenized composite. Using the efficient multiscale decomposition of MCT, Helius:Fatigue is able to reliably extract constituent stresses from a routine finite element analysis with negligible additional computational cost.
Read more about Multicontinuum Technology
A Physics-Based Approach Enables Broader Application
Most predictive theories pertain to a specific load history at a specific temperature and are not easily generalized to capture multi-axial load states, variable amplitude or spectral loading, temperature changes, or environmental effects. An efficient, general solution is unlikely to be achieved as long as composite fatigue predictions are based on purely empirical relationships. Physics-based concepts must be applied in order to use a minimal amount of characterization data to predict the fatigue life of a composite under a variety of loading and environmental conditions.
Helius:Fatigue applies the physics-based kinetic theory of fracture using constituent stresses to predict constituent fatigue failure, which leads to composite laminate failure and, ultimately, structural failure.
The kinetic theory of fracture uses two quantities, activation energy and activation volume, to relate the stress applied to a material to the rate of bond-breaking. Temperature is explicitly accounted for. The rate of bond breaking at a particular stress can be related to the fatigue life of the material under a cyclic stress load. Thus, simple creep tests can be used to characterize the kinetic behavior of the constituent materials (usually a polymer). Moreover, once the material is characterized, this method can be used to predict composite fatigue failure under any loading conditions.
Read the White Paper "Fatigue Life Prediction in Composite Materials"