OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.4 Materials - laminates – Page 53
This geometrical description can be fairly easily put into a computer program.
R= -1
a
a
Sector 3
α
Q
b 1
b 2
µ
a 1 P
a 2
n 2
n 1
R=0.1
Enlargement of the region with the points P and Q.
R= -1
STRAIN AMPLITUDE [%]
2.00
1.00
R=10
Sector 1
Sector 2
Sector 3
b
a
b 1 b 2
Q
α P
a
a 1 n
n 1 2 2
R=0.1
Sector 4
0.00
-2.50 -1.50 -0.50 0.50 1.50 2.50
MEAN STRAIN [%]
Figure 4-3
Schematic of a constant amplitude life diagram. The drawing illustrates the description above how the
fatigue life for a strain amplitude α at mean µ (described by point P as an example) can be found
µ
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.7.14 Ideally fatigue should be measured on the actual laminate for the relevant loading condition and
environment.
3.7.15 For fibre dominated strength values, fatigue data from tests on the same fibre type may be used to
estimate fatigue.
3.7.16 For short fibre composites fatigue of the matrix due to shear in the matrix shall be considered in addition
to fatigue of the fibres.
3.7.17 S-N curves may also be measured for specific load sequences if relevant. This may be beneficial,
because Miner sum calculations would not be needed for that load sequence. The validity of the data for other
load sequences would have to be demonstrated.
3.8 Cycles to failure under fatigue loads for matrix dominated strengths
3.8.1 There is a considerable lack of data for the performance of composites under matrix dominated fatigue.
3.8.2 S-N curves for materials, whose fatigue behaviour is matrix-dominated, seem to be non-linear in a double
logarithmic representation. Fatigue lifetime calculations shall be made in a way to take account of this effect.
3.8.3 If the component is subjected to in-plane fatigue and matrix cracking can be accepted, and if it can fulfil
all static strength requirements with the reduced fatigue moduli given in this section [3.6], then matrix
dominated fatigue does not have to be considered.
3.8.4 If the component is subjected to in-plane fatigue and matrix cracking cannot be accepted, testing on the
actual laminate or component testing shall be carried out. The failure condition shall be a certain level of matrix
crack density or a relevant indirect criterion, like weepage of water through a pipe.
3.8.5 If the component cannot tolerate matrix cracking, effects of long term cyclic loads can be ignored if the
following three conditions are fulfilled:
— the stresses in the matrix are below the level of initiation of matrix cracking according to Sec.6 [3].
DET NORSKE VERITAS AS