Composite Design, Analysis & Life Prediction
Simple stress analysis of composite laminates may be conducted using
classical lamination plate theory (CLPT) or anisotropic elasticity
solutions. These methods may be combined with other methods, such
as shear deformable plate theory and fracture analysis to determine
the performance of laminates and serve as a good first tool. However,
once the composite structure becomes more detailed with engineering
features, such as holes, cutouts, joints, etc. it is not possible
to use closed form solutions and reliance is often placed on finite
element analysis.
The modelling of composite laminates using FEA involves additional
steps to those for homogeneous materials. For example, the layered
and anisotropic nature of the composite needs to be modelled either
on a 'layer by layer' basis or using the aforementioned CLPT to determine
the composite performance of an element containing several plies.
The influence of bend twist couple in a laminate that is not symmetrical
about its mid-plane also needs to be modelled. Further the failure
of a composite material may included several mechanisms including
cracks, delaminations and fibre failure.
Life prediction of composite materials and components requires the
influence of combined service conditions on materials properties
to be studied as a function of severity and duration. No generalised
framework exists that can fully relate laboratory based property
data to component life in service. Specific techniques can be used
to overcome this shortcoming. For example, the application of probabilistic
strength theories can account for orders of magnitude difference
in stressed volume between coupons and engineering structures. Residual
strength tests can be related to fracture data under appropriately
defined conditions. Moisture permeability rates can be used to predict
reduction in matrix modulus, porosity or matrix cracks and hence
properties for a given material system. The reduction in stiffness
from fatigue
can
be estimated
from damage accumulation models. However, such theories cannot be
easily applied to real components which experience varying stresses,
temperatures and environments and are of a complex shape.
MERL provides an integrated approach to life prediction analysis,
studying the mechanism of degradation in the laboratory under accelerated
conditions, and then applies these under the defined conditions in
service. This work is supported by the appropriate numerical analysis.
Equipment exists at MERL for simulated service environments in the
following areas:
- Offshore oil & gas
- Aerospace
- Automotive
- Marine
- Renewable energies
- Medical applications
- Chemical processing
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