Composite delamination in a double cantilever specimen
This example is based on a NAFEMS benchmark involving a double cantilever specimen (DCB) for measuring fracture toughness (see the References section below for full details).
The specimen is displacement loaded at the end. Since the model is displacement controlled, the energy release rate will decrease as the crack grows. Propagation occurs if the energy release rate is greater than the critical value GIC.
The aim of the benchmark is to determine the end load vs end displacement curve at which the critical energy release rate is achieved. Theoretical and experimental results are provided in the reference.
Since the specimen width is far greater than the thickness the problem can be analysed as a 2D plane strain problem. The Zencrack 3D model is constrained to behave as a 2D plane strain model - there is one layer of elements in the thickness direction.
The benchmark was modelled by:
- applying a known displacement to the model
- growing the crack until the crack length is achieved that gives the critical energy release rate
- the vertical force P for the critical energy release rate can then be determined at the end of the analysis.
This was repeated for the 10 displacement values given in the published reference i.e. 10 Zencrack analyses in total. Dummy crack growth data was used to ensure crack growth of 0.4mm between each finite element analysis. Each analysis was stopped by setting the critical GIC value as a threshold.
Figure 1 - Specimen with definition of end load, P, and displacement, delta, and delamination (or crack) length, a
Figure 2 - Typical cracked mesh (top) and deformed mesh (bottom)
Figure 3 - Comparison of Zencrack results with data from the reference
Benchmarks For Composite Delamination
G.A.O.Davies, published by NAFEMS Ltd, Ref. R0084, Issue 1, 2002.
(This example is benchmark 2, page 23).