OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.6 Failure mechanisms and design criteria – Page 100
1.2 FRP laminates - failure mechanisms and failure type
1.2.1 A relationship between failure mechanisms and types according to the principles given in Sec.2 [3.4] is
given for FRP laminates in Table 6-2.
Table 6-2 Relationship between failure mechanism and failure type for FRP laminates
Failure Mechanisms Failure Type
Fibre Failure
Brittle
Matrix Cracking Brittle, if cracks are bridged by fibres: Plastic if only used as a criterion for leakage: Ductile
Delamination Brittle
Elastic buckling Brittle, plastic or ductile according to type of structure and loading.
1.2.2 In some cases a failure mechanisms is linked in a conservative way to a failure mode. If the failure
mechanisms is only linked to that failure mode in a conservative way, a different failure type than stated in
[1.2.1] may be used based on the criteria in Sec.2 [3.4].
Guidance note:
For example: onset of matrix cracking may be linked to leakage, even though it is known that a fairly large number
of matrix cracks must be present to cause leakage in most laminates. If matrix cracking is not linked to any other
failure modes than leakage, the failure type “ductile” may be chosen.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
Guidance note:
For elastic buckling the failure type is determined by the post-buckling behaviour. For elastic buckling of most simple,
symmetrical columns and struts the failure type may be considered plastic. For plates supported on all edges the
behaviour is often ductile. For some shell and optimised stiffened plate structures the behaviour may be brittle.
Note that deformations associated with elastic buckling may trigger other failure mechanisms such as fibre failure,
with consequent change of failure type.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
1.2.3 Failure mechanisms are often described in more detail for FRP laminates than the mechanisms given in
[1.2.1]. The Table 6-3 links the detailed failure mechanisms to the ones used in this standard.
Table 6-3 Mechanisms of failure for FRP laminates
Fibre Matrix Ply Inter-laminar Laminate
Fibre failure (tensile or Matrix cracking Fibre/matrix Delamination Rupture (1)
compressive)
debonding (2)
Fibre buckling (1) Matrix yielding Interlaminar tensile Global buckling
failure (3)
Interlaminar shear
failure (3)
Local buckling
Laminate creep
Laminate fatigue
described in this standard by
(1): fibre failure, (2): matrix cracking, (3): matrix cracking and or delamination.
1.2.4 Laminates typically show a sequence of failure mechanisms. These sequences should be considered. If
one failure mechanism cannot be well described it may be sufficient to design the component in a way that the
preceding failure mechanism will not occur.
Typical sequences are:
— matrix cracking => delamination => fibre failure
— debonding and matrix cracking => fibre buckling => fibre failure
— delamination => crack propagation due to fatigue => global buckling.
Unusual but possible sequence:
— wedge shaped matrix cracks => component failure in compression.
1.3 Sandwich structures - failure mechanisms and failure type
1.3.1 Sandwich structures are built of a light weight core embedded between two faces (or skins). Design
criteria are given for skins, cores and the core-skin interface.
DET NORSKE VERITAS AS