Computational Methods for Debonding in Composites

1 Computational Methods for Debonding in Composites 13
The displacement field φφφ is considered as a function of two kinds of variables; the
ordinary displacement field u, which will be split in a displacement of the top and
bottom surfaces ut and ub, respectively, and the internal stretch parameter w:
φφφ = φφφ(ut,ub,w) (1.24)
The derivation of the strains and the finite element formulation can be found in [15],
or in [17].
Using the solid-like shell element, the behaviour of a Glare panel with a circular
initial delamination and a sinusoidally shaped out-of-plane imperfection (with
an amplitude of 0.003 mm) subject to a compressive load has been examined. The
failure mechanism is slightly complicated, since the delaminated zone grows in a
direction perpendicular to the main loading direction. As a result, the delaminated
area transforms from a circular area into an ellipsoidal one. Consequently, the buckling
mode will change as well, and some parts of the top layer will tend to move
inwards. For this reason, the possibility of self-contact has been included and a
contact algorithm has been activated.
The specimen of Fig. 1.14 consists of an aluminium layer with thickness h1 = 0.2
mm and a Glare3 0/90 ◦ prepreg layer with a thickness h2 = 0.25 mm. An initially
circular delamination area with radius 8 mm is assumed. The layers are attached to
y
σy
x
σx 40 mm
R
σy
40 mm
delaminaton
=8mm
z
x
σx
Al 2024-T3, 0.2mm
Glare3 prepreg, 0.25 mm
Al 7075 backing plate
Fig. 1.14 Geometry of a Glare panel with a circular initial delamination