DFG project on phase-field modelling of fatigue cracks

Biaxversuch — Experimental setup of biax experiment at DLR.

The DFG project "Experimental analysis and phase-field modelling of interaction between plastic zone and fatigue crack growth in ductile materials under complex loads" is a cooperation project with Dr. Eric Breitbarth from Institute of Materials Research German Aerospace Center (DLR).

Airplane fuselages are loaded cyclically due to repeated take-off and landing, leading to fatigue cracks. The estimation of the crack growth rate is crucial for the design of the components. The project deals with both the numerical and the experimental analysis of fatigue cracks in aluminium sheets. The DLR studies the crack growth under multiaxial loading, e.g. with biax experiments as depicted in the photo above. In doing so, they record the crack growth rate and detect the plastic zone around the crack tip with the help of digital image correlation (DIC).

At our chair, the fatigue crack growth is simulated with the phase-field method. Thereby, we study under which loading conditions approximation methods based on brittle crack simulations can be used and when an expilicit modelling of the cyclic elastic-plastic material behaviour is necessary. To do so, an elastic-plastic phase-field model is implemented and parametrised. The cyclic crack closure is studied. Moreover, we develop techniques for saving computational time, which is crucial when dealing with cyclic loads. With the help of the model we want to study how fatigue cracks can be deflected deliberately.