Helius:Fatigue
Fatigue failure of composite materials has long been a design obstacle in many energy, aerospace, and automotive applications. In many of these applications, the composite is subjected to a multiaxial load, while fatigue characterization is typically performed under simplified loading configurations. 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. To overcome these obstacles Helius:Fatigue combines multicontinuum theory (MCT) with the kinetic theory of fracture (KTF) for a physics-based prediction of composite fatigue life. This solution provides the following advantages:
- Computationally efficient
- Integrated with commercial finite element software
- Failure criteria applied at constituent level not the composite level
- Physics-based
- Easy material characterization
- Applicable to complex loading configurations
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. Until the release of Helius:MCT, no commercial finite element software was able to reliably extract constituent stresses and strains without substantial computational cost. Using Helius:MCT, we are able to extract constituent stresses from a routine structural analysis with negligible additional computational penalty. We apply the physics-based kinetic theory of fracture using constituent stresses to predict constituent fatigue failure, which leads to composite 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. The implication of this is that we can use simple creep tests to characterize the kinetic behavior of the constituent materials (usually a polymer). Moreover, once the material is characterized, we can use the theory to predict composite fatigue failure under any loading conditions.