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DNV-OS-C501 Composite Components
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Sec.11
C. Processing steps
Sec.11
C 100 General
Sec.11 C
101 Bending of composites shall be avoided. A minimum bending
radius shall be defined if the process requires bending of materials.
Sec.11 C
102 Materials and components shall not be exposed to point-loads.
All possible point loads shall be evaluated and it shall be ensured
that they will not damage the material.
Sec.11 C
103 The working conditions are important when producing composite
parts. Ambient temperature ranges shall be defined and production
areas should be well ventilated. Dust, fumes, chemicals etc. may
influence curing conditions or may attack the material later during
service. The working conditions shall be defined.
Sec.11 C
104 Humidity shall be controlled at places where chemical reactions
occur. If humidity cannot be controlled its effect shall be evaluated.Sec.11
C 200 Raw materials
Sec.11 C
201 All raw materials shall be traceable for applications with normal
and high safety class.Sec.11
C 300 Storage of materials
Sec.11 C
301 The manufactures recommended storage conditions should be
followed. All materials shall be stored in clean and dry environments.
Sec.11 C
302 Fibres should be stored in a clean environment, preferably
wrapped up.
Sec.11 C
303 Resins and other chemicals should be stored in tight containers
or tanks.
Sec.11 C
304 All resins and chemicals shall not be used after their shelf
life has expired.
Sec.11 C
305 Some foam cores have internal gases from the production process
that diffuse out with time. Such cores shall be stored long enough
to allow the gases to diffuse out. Core skin delaminations may be
the result if the gases remain in the core.
Sec.11 C
306 When taking materials out of storage it is important that they
reach the same temperature as in the production facility while inside
their sealed storage bag or container. This step prevents the formation
of humidity on the materials.Sec.11
C 400 Mould construction
Sec.11 C
401 The word moulds is interpreted in this section in a wide sense,
covering many processes. Laying tables, mandrels and vacuum bags
are considered as moulds or parts of moulds.
Sec.11 C
402 Moulds should match all tolerances required by the design.
Sec.11 C
403 Sharp corners and discontinuities at joining points should
be avoided.
Sec.11 C
404 The surface finish shall be as specified. It shall be demonstrated
that the mould surface finish can produce components with the required
surface finish of the component.
Sec.11 C
405 Compatibility of mould release agents with the material and
further operations should be considered. Especially adhesive joining
or re-lamination may be effected by residues of mould release agents
on the surface of the component. This applies for mould release
agents that were applied to the mould and for mould release agents
that were added to the resin.
Sec.11 C
406 The structural stability of moulds or mandrels should be ensured.
Sec.11 C
407 Possible deformations of the moulds should be considered in
the design. The structure should be able to withstand all resulting
loads and strains.
Sec.11 C
408 If moulds are heated a controlled distribution of temperature
shall be ensured.
Sec.11 C
409 If a vacuum is applied inside the mould (or some bag), it shall
be ensured that no leaks exist. The vacuum shall be measured far
away from the point where the vacuum is pulled. Large moulds may
require more than one measurement point.
Sec.11 C
410 When removing the part from the mould large stresses and deformations
may be induced, especially if the component got stuck somewhere.
These effects should be avoided or at least carefully controlled.
Possible stresses or strains due to these operations should be considered
in the design. If such a situation occurs accidentally the loads
shall be estimated and the component shall be reanalysed.Sec.11
C 500 Resin
Sec.11 C
501 Two or more component resins shall be carefully mixed according
to manufacturers instructions, this is essential for a good cure.
Sec.11 C
502 The curing system shall be chosen in a way to prevent exothermic
overheating.
Sec.11 C
503 Changing accelerators or other ingredients that control the
speed of the cure are only permitted if they have no effect on the
mechanical properties. The resin supplier shall confirm this. In
addition, tensile tests according to section
4 H607 shall confirm no change in strength and stiffness
for components of normal and high safety class.
Sec.11 C
504 Barcol's hardness tests or other means should be
used to check the quality of the cure.
Sec.11 C
505 The viscosity of the resin and or the gel time should be measured
for all processes where the flow properties of the resin are important.
For details see D200.
Sec.11 C
506 It is recommended to take a sample from each batch of resin
used in components of normal or high safety class. The sample of
resin without fibres should be cured separately. A tensile or bending
test should be used to confirm that properties are within acceptable
tolerances. Sec.11
C 600 Producing laminates and sandwich
panels
Sec.11 C
601 Procedures to confirm the lay-up of fabrics shall be established.
A log shall be kept for components of normal or high safety class.
The accuracy of the lay-ups shall be verified independently during
production for high safety class components. Whether the verification
shall be done by the manufacturer himself, by the customer, or by
a third party should be decided by the project.
Sec.11 C
602 The accuracy of fibre orientations shall be specified for high
safety class components.
Sec.11 C
603 Fibres shall be well aligned showing no local distortions or
kinks.
Sec.11 C
604 Minimum and maximum overlap lengths of adjacent fabrics shall
be specified. The effect of overlaps may be similar to damage in
the laminate and shall be evaluated as described in section 4 A700.
Sec.11 C
605 The tolerances for gaps between cores shall be defined.
Sec.11 C
606 The surfaces of cores shall have smooth transitions across
the gaps. This is especially critical if cores are tapered.
Sec.11 C
607 Procedures shall be established to ensure a good bond between
skins and cores for all geometrical shapes in the component. The
quality of the interfacial bond shall be documented for all relevant
geometry, e.g., convex and concave surfaces.
Sec.11 C
608 Any gaps between cores shall be filled with the specified resin
or adhesives, unless it was specified that cores shall not be filled
and core properties were measured on cores with unfilled gaps, see section 5 F200.
Sec.11 C
609 Absorption of resin by the core shall be considered with respect
to weight of the total structure and the amount of resin needed
to obtain the desired fibre volume fraction in the laminates.
Sec.11 C
610 The curing temperature and pressure shall not effect the properties
of the core.
Sec.11 C
611 The temperature of all materials and the mould should be the
same during the lay-up, unless the process specifically requires
other conditions.Sec.11
C 700 Producing joints
Sec.11 C
701 The same requirements as for laminates and sandwich plates
in C500 apply.
Sec.11 C
702 Overlap lengths shall be clearly specified and tolerances shall
be given.
Sec.11 C
703 Surface preparations of adhesive or laminated joints shall
be clearly specified and shall be the same as for the specimens
that were tested to qualify the joint.
Sec.11 C
704 The application of adhesives shall follow well described procedures.
The procedures shall be exactly the same as for the specimens that
were tested to qualify the joint.
Sec.11 C
705 Surface preparation of adhesive or laminated joints and the
application of adhesives shall be verified independently during
production for normal and high safety class components. Whether
the verification shall be done by the manufacturer himself, by the
customer, or by a third party should be decided by the project.
Sec.11 C
706 The alignment of components and tolerances shall be specified.
Sec.11 C
707 Hole diameters positions and tolerances shall be specified
for bolted connections.
Sec.11 C
708 Washer sizes or other supports shall be specified.
Sec.11 C
709 Torque of the bolts shall be specified.
Sec.11 C
710 Bolted joints shall be verified independently during production
for high safety class components. Whether the verification shall
be done by the manufacturer himself, by the customer, or by a third
party should be decided by the project.Sec.11
C 800 Injection of resin and cure
Sec.11 C
801 The viscosity of the resin should be specified and controlled
for all processes where the flow is important (see also C505). As
a minimum the gel time should be checked.
Sec.11 C
802 The flow patterns of injection processes shall be documented.
Every part of the component shall be filled with resin. No paths
shall be blocked by resin that is already cured.
Sec.11 C
803 The curing schedule shall be specified and documented. A log
shall be kept for component of normal or high safety class. The
accuracy of the process shall be verified.Sec.11
C 900 Evaluation of the final product
Sec.11 C
901 A procedure should be given to describe the evaluation of
the finished product.
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