An Experimental and Numerical Investigation of the Mixed-mode Fracture Toughness and Lap Shear Strength of Aerospace Grade Composite Joints

The increasing use of composite materials in various
industries, such as aerospace, automotive and renewable
energy generation, has driven a need for a greater understanding
of the fracture behaviour of bonded composite
joints.
An important prerequisite for the adhesive bonding of
composites is the existence of a uniform surface free from
contaminants and mould release agents. While there are
several ways in which this may be achieved, the use of
peel plies has emerged as the preferred choice for many
industries due to the repeatable nature of the resulting surface,
particularly in the highly regulated aerospace industry.
However, the use of peel plies can present some problems.
It is possible that contamination from the peel ply
can be transferred to the composite substrate and adversely
affects the adhesive joint [1].
Composite joints are typically evaluated using lap
shear type tests. While these tests are relatively simple to
perform and post-process compared to their fracture mechanics
based counterparts, the results can often be misleading
and are greatly dependent on the overlap length,
the thickness of the substrate and the type of fillet employed
[2, 3].
The aim of this work is to show that composite joint
systems can be modelled using material properties determined
from fracture mechanics based tests. The fracture
parameters will be used to develop numerical models of the fracture tests that accurately predict the wide-area lapshear
test.