Fracture Mechanics

For structures that may have a discontinuity, fracture mechanics is used to evaluate the effect that is cause from the singularity created at the crack tip.  The method is also used for the assessment of whether a crack will initiate and whether and how much it may propagate as a load cycles.


Classical Fracture Mechanics

Classical fracture mechanics presumes the existence of a ‘flaw’ or a discontinuity in the material. This creates a singularity at the crack tip limiting the use of traditional stress analysis for material failure. We are experienced in both linear-elastic and elastic-plastic fracture mechanics approaches to determine the effect on structural integrity and damage tolerance. We have also developed failure assessment diagrams showing the transition from brittle fracture to plastic collapse of a structure and have been successfully used on aircraft on launch vehicle designs. We have used NASGRO as well as other fracture codes and a have a database of material parameters that are available as necessary.




XFEM Analysis

The use of XFEM (extended finite element method) in fracture mechanics has been successfully implemented to simulate crack initiation and propagation of non-standard flaws. This method adds additional degrees of freedom to the elements allowing an arbitrary crack to propagate along a solution-dependent path without requiring any re-meshing of the crack tip.



Ductile Fracture  

Prior to any existing flaw in the material, the initiation of a crack and the determination of fracture is dependent on all of the stress invariants. We have specified a series of tests to characterize a material over a range of the invariants and then successfully developed material failure models which simulate fracture. This is an active area of our research and development in order to provide greater model fidelity which in turn will assist in reducing potential over-design in a project which may include weight, cost, performance, or other factors.