OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.4 Materials - laminates – Page 41
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.
1.5 Mechanical properties
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
1.5.1 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.
1.5.2 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 Sec.4 [2].
1.5.3 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---of---G-u-i-d-a-n-c-e---n-o-t-e---
1.5.4 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.
1.5.5 If fibres of the same type are used in different layers in the laminate, one test series is sufficient to
determine their properties.
1.5.6 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.
1.5.7 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.
1.5.8 Properties can be established new or checked against typical values.
1.5.9 Mechanical properties depend on the load conditions and the environment.
1.5.10 For test data the condition parameters should be reported.
1.6 Characteristic values of mechanical properties
1.6.1 Characteristic values shall be used throughout this standard.
1.6.2 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.
1.6.3 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 Sec.4 [2.4]
and Sec.4 [3.11].
1.6.4 The characteristic value for stiffness shall be taken as the mean value in the distribution of the arbitrary
value of the stiffness property.
1.6.5 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.
DET NORSKE VERITAS AS