Computational Methods for Debonding in Composites

1 Computational Methods for Debonding in Composites 9
Fig. 1.7 COD vs axial stress
for the full T-bone specimen
and for an approximated 3D
solution using the rectangular
specimen of Fig. 1.8
5 mm
y
net stress unwidened part [MPa]
500.0
400.0
300.0
200.0
100.0
Elastic zones
2 mm 2 mm
10 mm
T-bone plate
rectangular plate
0.0
0.000 0.002 0.004 0.006 0.008
COD at free edge (x = 9 mm) [mm]
Fig. 1.8 Quarter of the rectangular specimen used in the approximate 3D solutions
small compared to data suggested in norms. The COD versus axial stress, measured
as the average stress in the narrow part of the strip, is shown in Fig. 1.7.
Numerical solutions of boundary-value problems involving materials that show
a descending branch after reaching a peak load level, can be highly mesh sensitive,
e.g. [7]. However, in the present situation, where the degrading phenomena are
limited to a discrete interface where the crack opening is controlled by a fracture
energy (cohesive-zone approach), the boundary value problem remains well-posed
and, consequently, no mesh sensitivity should be observed. This is confirmed in a
mesh refinement study of a three-dimensional rectangular plate, Fig. 1.8, which is
used to approximate the original T-bone specimen, but, because of its simpler geometry,
is less expensive in mesh refinement studies. The load-displacement curves for
the original T-bone specimen and the approximate 3D specimen are close, Fig. 1.7,
justifying the approximation for the purpose of a mesh refinement study.
Three different meshes have been used in the calculations. The coarse mesh consisted
of 20 elements over the width and 25 elements over the length of the plate.
x
Load