Industrial Applications - The Boundary Element Method with Programming - page 445

elements and connection between surfaces had to be considered. Secondly, the task was
to determine surface stresses and then to investigate crack propagation. As outlined
previously, the BEM is well suited for this type of analysis.

Figure 17.3 Boundary element mesh viewed from one of the symmetry planes

Initially, an analysis with only one region was carried out without considering the
presence of cracks. This was done in order to check that the analysis was able to predict
crack initiation. The criteria chosen for this was the maximum tensile strength of the
material, taking into consideration the dynamic nature of the loading and the number of
cycles that the press had so far sustained (approx. 2 million cycles). This analysis was
also carried out to see if the model was adequate and to enable the client to get
confidence in the BEM analysis proposed. The contours of maximum stress obtained
from the single region analysis, shown in Figure 17.4, clearly indicate a stress
concentration at the locations where cracks were observed, of a magnitude which would
cause crack initiation there after a number of cycles.
After this verification of the model, a multi-region analysis was carried out. For this
each of the flanges where the crack was observed was divided into two regions. For
simplicity it was assumed that the crack path was known a priori and is in the diagonal
direction, as observed. Along this assumed crack path an interface was assumed between
regions and the interface was allowed to slip and separate.