OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.4 Materials - laminates – Page 62
6.2 Change of production method
6.2.1 A change in production method, e.g., going from hand lay-up to filament winding, is usually
accompanied by many other changes. Different resins are used, different fibres or sizings may be used, and the
fibre fraction and void content may change significantly.
6.2.2 A re-qualification of the materials data shall be done if the production process is not similar to the
original process - see [8.3]. A production process is similar as long as changes introduced by the new process
can be quantified as described in the following parts of [6] and the process group is not changed.
6.2.3 Examples of process groups are:
— hand-lay-up
— spray-lay-up
— pre-preg lay-up
— autoclave curing (in combination with one of the other processes
— resin injection processes
— resin transfer moulding
— centrifugal moulding
— filament winding
— tape winding.
6.3 Change of processing temperature and pressure
6.3.1 For simple processes of thermoset materials with only one cure temperature:
— curing temperature of the reference data was higher than in reality.
data shall be re-qualified
— curing temperature of the reference data was lower than in reality:
data are valid, as long as the temperature did not exceed the resin manufacturer's maximum curing
temperature.
6.3.2 For simple processes of thermoset materials with only one cure pressure:
— curing pressure of the reference data was higher than in reality:
data shall be re-qualified
— curing pressure of the reference data was lower than in reality:
data are valid, as long as the pressure did not exceed the resin manufacturer's maximum curing pressure.
6.3.3 For thermoplastic composites where the plies are welded or fused together, a processing window of
pressure and temperature should be established in which test data are applicable.
6.3.4 For complex curing cycles with varying temperature and pressure, any change to the process shall require
requalification of the data.
6.4 Change of post cure procedure
6.4.1 Post-curing has no influence on fibre dominated tensile properties.
6.4.2 Post curing may improve fibre dominated compressive properties and all matrix dominated properties.
6.4.3 For some matrix systems post curing accelerates some slow crosslinking reactions that would also take
place at room temperature. This is the case for many types of polyester. For these systems data obtained from
post cured specimens are also valid for materials that were not post cured.
6.4.4 For some matrix systems post curing creates a better crosslinked network that will never be achieved if
the laminate remains at room temperature. This is the case for many vinyl esters and epoxies. For these systems
data obtained from post cured specimens are not valid for materials that were not post cured.
6.5 Change of void content
6.5.1 If the void content of the reference data was higher than in reality, data are valid.
6.5.2 If the void content of the reference data was more than 10% (relative) lower than in reality, data shall be
re-qualified.
6.6 Correction for change in fibre volume fraction
6.6.1 For UD-plies:
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