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♦ Difficult to assess materials after an accident. Possible dam‐
age (e.g. cracks) which is not visible to the human eye may
make it necessary to use thermal imaging, infrared and X-ray
methods.
♦ It is generally not permitted to repair structural CFRP compo‐
nents; these components must be renewed.
Important notes relating to the use of CFRP in series-production
vehicles:
For use in vehicles, its characteristics must be especially taken
into account with a view to more widespread servicing and repairs
in workshops. CFRP components are far less tolerant to damage
than metals. If a component is delaminated, it must be renewed.
Only apply the absolute minimum amount of force required in or‐
der to avoid damaging components remaining on the vehicle. Use
the specified tools only. Pay very careful attention to the descri‐
bed procedure and parameters; these will help to ensure that you
can work without causing any additional damage. It is very im‐
portant to perform this work very carefully and patiently.
CFRP components are all different
Unlike metals, the properties of CFRP are specific to individual
components and cannot be generalised. Each component has its
own individual characteristics, depending on the resin and fibres
used, the fibre orientation, the manufacturing method and many
other factors.
Deformation properties
CFRP components can be designed to dissipate energy by falling
apart, or to protect the safety cell in the event of an impact. Equal‐
ly, they can also be designed to deform. It is therefore important
to treat every component on its own merits and to follow the ap‐
propriate instructions.
Springback after load is applied
When load is applied, a CFRP component can deform, break or
suffer internal damage. After the load has been relieved, spring‐
back is possible for the component. In such cases, proper as‐
sessment of the component is critical to determine whether there
is any internal damage.
Detection of damage
Cracks, scratches and fibre breakage can be assessed from the
outside. If the back of the component is visible, it is possible to
detect impact damage in some cases. Any delamination caused
by an impact reduces the component's strength (including its
flexural strength) and therefore the laminate's strength and buck‐
ling resistance. As a visual inspection alone is not sufficient to
assess damage to CFRP components and as the characteristics
of the components are impaired dramatically by minor damage,
it is extremely important to carry out an inspection without causing
any irreparable damage before damage diagnosis is performed.
Overview of test methods which do not cause irreparable damage
♦ Radiographic method = computer tomography (CT)
♦ Acoustic method = ultrasound, knock test
♦ Optical method = shearography
♦ Thermal method = thermography
♦ Electric/magnetic method = eddy-current testing
General InformationBody Repairs, General Body Repairs - Edition 04.2018
18 5. Assessing damage
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