Modelling Observed Crack Shapes

Zentech was involved in a project called “DISPLACE” between January 2009 and December 2011:
Developing Improved Service Propagation Lives in Arduous Cyclic Environments

This was a collaborative research programme led by Rolls-Royce (Derby) with partners:

• University of Birmingham
• University of Portsmouth
• Serco
• Zentech International Limited

The project was part funded by the UK Technology Strategy Board Project (reference TP/8/MAT/6/I/Q1525K). The total project cost was £1,692,589 with the TSB providing approximately half of that amount in funding.

As part of the project involvement, Zentech carried out simulations related to crack shape development in corner cracked test specimens. In particular, the investigations involved modelling of tunnelled crack shapes observed during high temperature dwell tests. The mechanism for shape development of these cracks is not properly understood [e.g. 1]. The simulations allow, for example, calculation of K distributions for crack shapes observed during testing.

The geometry used for the analysis is a corner crack specimen with a 7mm cross section as shown in Figure 1. Typical starter crack sizes introduced for testing are of the order 1mm.

A range of corner crack sizes were modelled. Idealised tunnelled crack sizes are modelled by offsetting a circular profile along the diagonal of the specimen cross-section. This is easily achieved with the user defined initial crack front option in Zencrack. Similarly, the user defined crack front option can be used to create a model with an observed non-symmetric crack shape. Typical meshes are shown in Figure 2.

Part of the investigation compared results from the Zencrack analyses with reference solutions [2]. Comparisons for stress intensity factor and T-stress for several idealised tunnelled cracks are shown in Figures 3 and 4.

Additional information about the analyses and details of further analyses carried out during this part of the DISPLACE project are shown in the video in Figure 5.