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DNV-OS-C501 Composite Components
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Sec.4
A. General
Sec.4
A 100 Introduction
Sec.4 A
101 This section describes the mechanical material properties
needed for design. It describes how to obtain all strength properties
used in the failure criteria and all elastic properties needed for
stress calculations.
Sec.4 A
102 The basic material properties used in these rules are orthotropic
ply properties.
Sec.4 A
103 All properties shall be obtained directly by measurements
or shall be traced back to measurements. The qualification of material
properties is described in this section. Under certain conditions,
typical values from databases can be used. Strength and stiffness
values should be documented as characteristic values.
Sec.4 A
104 It is only necessary to obtain properties that are used in the
design calculations and failure criteria.Sec.4
A 200 Laminate specification
Sec.4 A
201 A composite laminate is made of many constituent materials
arranged and produced in a specific way. Laminates used in a component
shall be clearly specified and all materials shall be traceable.
Sec.4 A
202 A minimum set of process parameters and constituent material
characterisations is given in Table A1. All these items shall be
specified.Sec.4 A
| Table A1 Basic information to
identify a laminate |
| Constituent materials: |
| Generic
Fibre type |
| Type
of weave |
| Generic
resin type (e.g. epoxy, polyester) |
| Specific
resin type (trade name) |
| Process parameters: |
| Processing
method |
| Processing
temperature |
| Processing
pressure |
| Process
atmosphere (e.g. vacuum) |
| Post
curing (temperature and time) |
| Control
of fibre orientation |
| Fibre
volume fraction |
| Void
content |
| Conditioning parameters: |
| Temperature |
| Water
content of the laminate (wet, dry) |
| Chemical
environment |
| Loading
rate |
| Measure
values |
| Guaranteed
minimum value |
| Standard
deviation |
| Number
of specimens |
Sec.4
A 300 Lay-up specification
Sec.4 A
301 A laminate is made of a sequence of layers. All materials and
they stacking sequence shall be clearly identified.
Sec.4 A
302 The orientation of non-homogenous or anisotropic materials
shall be clearly specified on the materials level and the structural
level.
Sec.4 A
303 Laminates shall be specified in a way that they can be described
by a sequence of stacked orthotropic plies.
Sec.4 A
304 The procedures of Appendix B should
be followed to describe a lay-up.Sec.4
A 400 Orthotropic plies
Sec.4 A
401 An orthotropic ply is defined as a volume element with three
axis of symmetry with respect to mechanical properties. For this
standard the fibres should align with the symmetry axis.
Sec.4 A
402 There are three possible ply configurations:| — | unidirectional
(UD) ply.
In this ply all fibres run parallel
in the same direction (the 1 direction) |
| — | cross-ply.
In
this ply fibres run perpendicular to each other within one plane,
they run in the 1 and 2 direction. Typical reinforcement fabrics
are woven roving and twills |
| — | isotropic ply.
In
this ply fibres are randomly oriented without a preferred direction.
A typical reinforcement type of this class is chopped strand mat.
It could also be an injection moulded part as long as one can ensure
that the fibres are not aligned by the flow of the material into
the mould. |
Sec.4 A
403 The following is assumed in this standard:| — | the UD ply has linear elastic
properties |
| — | the cross-ply is bi-linear in tension and in compression. The
bi-linearity is caused by substantial matrix cracking |
| — | the isotropic ply is bi-linear like the cross-ply. |
Guidance note:
Bi-linear means that the stress strain curve of a cross plied
laminate can be roughly described by two linear lines.
Shear moduli and matrix moduli in compression are often non-linear.
A non-linear description may be used in the analysis if the non-linearity
is measured experimentally for the material. The assumptions in
403 can be used as a default.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.4 A
404 These simplifications are generally valid for thermoset plies.
However, their applicability shall always be checked.
Sec.4 A
405 Other modelling methods may be preferred for certain material
combinations.
Sec.4 A
406 Thermoplastic composites may show more non-linear characteristics.
Sec.4 A
407 Ply angles shall be specified between the laminate co-ordinate
system and the main fibre direction (1 direction). In addition,
it may be necessary to define an angle between the component co-ordinate
system and the laminate co-ordinate system.
Sec.4 A
408 Knitted fabrics shall be described as a sequence of UD-plies.
This is the best way to describe their bending characteristics properly.
If bending is not relevant for a specific application knitted fabrics
may also be described as a combination of 0/90 and UD-plies.
Sec.4 A
409 Quasi-isotropic laminate configurations, e.g. (0/90/±45)s or (0/±60) s , shall be described as a
sequence of UD-plies.
Sec.4 A
410 Filament wound materials shall be described as a sequence
of UD-plies, even though the filament wound fibres are interwoven.
One helical winding sequence shall be described by at least one
pair of UD-plies. The model should be built of symmetric UD-ply
sequences to represent helical winding sequences of the same fibre
angles in order to prevent unrealistic warping effects. If bending
of the laminate has to be described accurately the influence of
swapping the surface ply with the ply underneath shall be evaluated.
If more plies are needed to model the component probably should
be evaluated on an individual basis.Guidance note:
A pipe made of a ±55 filament wound material with
6 winding sequences and a total thickness of 6 mm shall be modelled.
If the pipe is just loaded under internal pressure it should
be described as a (+55/-55)3S laminate, i.e. a sequence
of 6 alternating UD-plies oriented in 55 and -55 direction. Each
ply has a thickness of 0.5 mm.
If the same pipe is exposed to bending loads it shall be evaluate whether
a (-55/+55)3S laminate
would give different results in the analysis compared to a (+55/-55)3S laminate. ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Guidance note:
A pipe is made of a ±80 filament wound material with
8 winding sequences and ±10 filament wound material with
4 winding sequences (from inside to outside). The thickness per
sequence is 1 mm, giving a total thickness of 12 mm. The pipe may
be modelled in the following way:
If the pipe is just loaded under internal pressure it may
be described as a (+80/-80)8S (+10/-10)4S laminate, i.e. a sequence of
16 alternating UD-plies oriented in 80 and -80 direction and 8 alternating
UD-plies oriented in 10 and -10 direction. Each ply has a thickness
of 0.5 mm. It may be possible to reduce the number of layers in
the analysis. As a minimum a laminate (+80/-80)2S (+10/-10)2S should be used for modelling
where the 80 and -80 plies are each 4mm thick and the 10 and -10
plies are each 2 mm thick.
If the same pipe is exposed to bending loads it shall be evaluate whether
a (+80/-80)8S (+10/-10)4S laminate would give different results
in the analysis compared to a (-80/+80)8S (-10/+10)4S laminate.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.4
A 500 Mechanical properties
Sec.4 A
501 This standard uses orthotropic ply properties for the mechanical
description of a composite laminate. A complete set of properties
for an orthotropic ply is given in the following sections.
Sec.4 A
502 All properties are dependent on the constituent materials and
the processing and conditioning conditions. It is convenient to
separate the properties into fibre and matrix dominated properties.
Which properties are fibre dominated and which are matrix dominated
are given in B.
Sec.4 A
503 It is possible that a structure is loaded in such a way that some
material properties are not relevant. In that case the non-relevant
properties do not have to be known, but it shall be documented that
the properties are not relevant for the application.Guidance note:
For example, in many cases a composite laminate is a shell
that is not loaded in the through thickness direction. In that case
all through thickness properties are not relevant. However, the
shell may be loaded in the through thickness direction at the load
introduction point (joint). In this case the through thickness properties shall
be known, unless the load introduction point is qualified by component
testing.
If a component is only loaded in tension, all compressive
properties are 'not relevant'.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.4 A
504 Fibre dominated properties shall be determined for all fibre
types in the laminate. Fibres processed by a different method, e.g.
woven, knitted, different sizing, different fibre material etc.
shall be treated as different types.
Sec.4 A
505 If fibres of the same type are used in different layers in the
laminate, one test series is sufficient to determine their properties.
Sec.4 A
506 Matrix dominated properties shall be determined for each ply.
Matrix dominated properties determined on the ply level are actually
a combination of the pure matrix properties and interaction effects
with the fibres and the matrix fibre interface. The properties of
each of these combinations shall be documented.
Sec.4 A
507 Matrix dominated properties can be measured just once if the
same matrix and same fibre types with the same sizing are used throughout
the laminate.
Sec.4 A
508 Properties can be established new or checked against typical
values.
Sec.4 A
509 Mechanical properties depend on the load conditions and the
environment.
Sec.4 A
510 For test data the condition parameters should be reported.Sec.4
A 600 Characteristic values of mechanical
properties
Sec.4 A
601 Characteristic values shall be used throughout this standard.
Sec.4 A
602 The characteristic value is a nominal value to characterise
a stochastic variable. The characteristic value of a mechanical
property is usually a value, which has a small probability of not
being exceeded in a hypothetically unlimited test series.
Sec.4 A
603 The characteristic value of a strength property is defined in
this standard as a low 2.5% quantile in the distribution
of the arbitrary strength. This is equivalent to the 97.5% tolerance. For
more details see B400 and C1100.
Sec.4 A
604 The characteristic value for stiffness shall be taken as the mean
value in the distribution of the arbitrary value of the stiffness
property.
Sec.4 A
605 All results shall be based on a 97.5% tolerance with
95% confidence. The confidence requirement is important
if only a limited number of test results is available.Sec.4
A 700 Properties of laminates with damage
Sec.4 A
701 In some cases a structure is expected to contain some damage,
e.g. impact damage, delaminations, cracks etc. If this is the case,
the laminate can be modelled with this damage as described in sections 9 and 6. Alternatively, the laminate can be
described with properties based on a laminate with damage.
Sec.4 A
702 Strength properties of a laminate with damage shall be measured
on laminates that contain the maximum expected damage. It shall
be carefully evaluated if the damage can be representative in small
test coupons. If there is any doubt about testing of laminates with
damage a conservative approach shall be chosen, that gives lower
than expected strength values.
Sec.4 A
703 Elastic constants like stiffness and Poisson's ratio
shall be measured on damaged and undamaged laminates. It shall be noticed
that modelling a structure with elastic properties based on a damaged
laminate may give wrong stress distributions (See section 9).
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