JEC COMPOSITES MAGAZINE - Issue #80 - April 2013 - 53

The tooling has to be developed and manufactured in parallel to the development of the composite part. These steps
and the use of modern CAE/CAM tools are illustrated in
more detail below, focusing on the design and manufacturing
steps of the process.

Determination of required properties
The set of material properties required for the design of an
FRP structural part is wider than for a metallic part. Moreover – and again in contrast to metallic materials – not all of
the relevant material properties are readily available. Material properties often have to be determined before the design
process has kicked off. The following properties have to be
available for representative laminate samples:
- Static and dynamic tensile/compression/shear/torsion
strength
- Bearing strength
- Impact of environmental degradation
- Impact of preloading
- Thermal expansion
- Effect of physical impacts
- Drapability

Design
It is assumed that the part’s mould line is known at this stage
of development and that the design activity is limited to:
- the design of an FRP part respecting this mould line,
- any other geometrical constraints, and
- the ability to withstand the introduced loads.
The preliminary design step is strongly driven by considerations on the manufacturing process and results in a preliminary ply lay-up.
It is widely accepted that automated routines are applied at
this early stage of the design process where only interface
loads and geometric constraints are defined, so that a preliminary lay-up solution can be generated. However, in most
cases, the preliminary lay-up is the task of an experienced
composite designer.
As soon as the preliminary design iteration has been completed and the manufacturing process has been defined, the
development of the tooling can begin in parallel with the
detailed design of the part. The detailed part design and
tool design cannot be considered independently because the
position and orientation of the mould parting surfaces have
to be taken into consideration to define the contour of the
individual plies.
The development of the tooling is a crucial design task in
itself. Thermal characteristics, spring-in/-out, handling and
many other effects have to be considered. Tooling design
does have a significant impact on manufacturing costs, as
does the number of ship sets. The higher the number of ship
sets to be built, the higher the attention required for smart
tool design.
As part of the stress analysis, different failure criteria have to

Fig. 2: CAD screenshot of a laminate model showing lamina and ply
contours

be considered, depending on the applicable regulations and
stress methods. Modern CAE tools can be used to perform
anisotropic analysis directly on the DMU derived from the
preliminary design by considering the properties of the layup (i.e. local fibre orientation per lamina). This significantly
reduces the effort for establishing the finite element (FE)
model.
Potential critical stresses can be reduced by adapting the
lay-up. Different strategies are applicable, depending on
the specific situation. Critical stress is countered either by
introducing more fibres (or by adapting the fibre orientation
or the lay-up sequence) or by reducing the local stiffness in
order to attract less loads.
The design optimization is performed based on the stress
analysis results. The optimization includes an adaptation of
fibre orientation and stack-up sequence. Modern CAD tools

Fig. 3: Drapability analysis on a spherical surface (blue: ok, yellow: critical,
red: out of limit)

No80 April 2013 /

jec composites magazine 53

JEC COMPOSITES MAGAZINE - Issue #80 - April 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #80 - April 2013