OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.9 Structural analysis – Page 148
σ
σˆ
E lin
E nonlin
Figure 9-1
Typical stress-strain relation for a laminate containing 0, 45 and 90 layers
ε corr
Matrix cracking
in 90 layers
Matrix cracking
in 45 layers
εˆ
Fibre failure
in 0 layer.
Laminate
failure
ε
3.3 Creep, stress relaxation and stress rupture-stress relaxation
3.3.1 The presence of creep, stress relaxation and stress rupture-stress relaxation in composite structures
depends on the level of stresses and or strains and the condition of the constituent materials (intact, presence
of cracks or other failures).
3.3.2 Only analysis methods that provide conservative estimates of stresses/strains and material conditions
should be applied in predictions of phenomena like creep.
3.4 Fatigue
3.4.1 Failure due to fatigue may develop under long term cyclic loading conditions.
3.4.2 Development of fatigue failure depends on the maximum strains during each cycle, as well as the total
number of cycles with strains exceeding prescribed limits.
3.4.3 Thus, analysis methods providing conservative strain estimates may be applied in conjunction with
fatigue.
4 Analytical methods
4.1 General
4.1.1 Analytical methods can be divided into two classes: Analytical solutions of (differential) equations or
use of handbook formulae.
4.2 Assumptions and limitations
4.2.1 Analytical methods shall not be used outside their assumptions and limitations.
Guidance note:
The main disadvantage of available analytical solutions is that simplifications often put too many restrictions on
geometry, laminate build-up etc. and hence, are insufficient in the design of more complex composite structures.
Handbook formulae are usually too simple to cover all the design issues and are also in general not sufficient.
Simplified isotropic calculation methods should not be used, unless it can be demonstrated that these methods give
valid results.
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4.2.2 For analytical analysis of sandwich structures, special care shall be taken with assumptions in
approximate solutions that may be found in textbooks.
4.3 Link to numerical methods
4.3.1 Analytical solutions or handbook formulae used within their assumptions and limitations may be used to
validate finite element analysis results.
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