LIOn Delamination of Laminated Composites (a) Fiber-Reinforced
Composites Considerable technological advances in the production of
high-strength fibers (graphite, boron, etc.) have led to a wide use of
light high-strength composite materials (graphite- epoxy, boron-epoxy,
etc.). It is expedient, to make thin- walled composite rods, plates, and
shells from such materials. Plates can be made by bonding a set of
unidirectional thin fiber layers, Fig.l.l. Such plates are orthotropic,
as a rule. A random short-fiber composite is shown in Fig. 1.2.
Fiber-reinforced composites are widely used in thin-walled aircraft
structures because of their specific high strength. For example, the
graphite-epoxy composite is characterized by a unidirectional tensile
strength of 1.4 GPa while the density is 1.6 Mg/rrt? . For comparison,
we may take a steel (steel 4340) whose corresponding properties are
identified by values like 1.2 GPa and 7.8 Mg/rrt? . 1. INTRODUCTION
Figure 1.1 2 1.1. On Delamination of Laminated Composites Figure 1.2
3 1. INTRODUCTION It is characteristic for laminated plastic material to
possess a fairly low bonding. Therefore, low-velocity impacts and
defects in manufacturing lead to local delamination. (b) Linear Problems
of Delamination Buckling Delamination can significantly reduce the
compressive strength and stiffness of the laminate. Local delamination
can be considered as a crack in the bond. Under buckling there appears a
high interlaminate stress at the crack edge that leads to a spreading of
the crack. Delamination growth can lead to structural instability.
