Supervisors: Lars P. Mikkelsen, Bent F. Sørensen, Christian F. Niordson (DTU Mek)
External examiner: Henrik Myhre Jensen (Aarhus University).
Abstract: Finite element simulations of off-axis tunnel cracking in layered composite materials
The fatigue damage evolution in composite materials are typically initiated in polymer matrix composite by transverse tunnel cracking. Tunnel cracking which can occurs in layered composite such as in pre-pregs used in the aerospace industry or in backing bundles in non-crimp fabric used e.g. as the load carrying laminates in the wind turbine blades. Experimentally, this fatigue initiation process can be investigated and quantified using a [0/thetha/0/-theta]s material layup and therein keep track of the initiation and growth of the off-axis tunnel cracks. Nevertheless, in order to quantify the experimental measurements, a precise crack-tip simulation is necessary in order to couple the crack-growth measurements with the actually crack-tip loading.
During the thesis work the following task will be addressed:
- Building up and validate a tunnel crack tip model in the finite element code Abaqus
- Compare different ways to evaluate the available fracture energy (G) at the tunnel crack tip
- Investigate the convergence of the numerical predictions as a function of sample size and crack spacing
- Investigate the material properties influence on the crack tip loading
- Eventually expand the model addressing the individual bundle case in non-crimp fabric
- Relate the predictions to expected fatigue failure mechanism during fatigue loading of layered composite materials and eventually non-crimp fabrics.