OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.9 Structural analysis – Page 154
do not allow values for all three parameters to be specified, one should generally use the measured values for
G and ν, and let the E value be calculated (from the formula above) by the program. In that case the shear
response of the core will be described accurately. However, in particular applications, in which core shear
effects are negligible and axial stresses/strains are crucial, correct E values shall be applied.
Guidance note:
For many core materials experimentally measured values of E, G and ν are not in agreement with the isotropic
formula:
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
10.2.3 Anisotropic core shall be described with 4 elastic constants in a 2-D analysis, i.e. E x , E z , G xz, ν xz .
10.2.4 Anisotropic core shall be described with 9 elastic constants in a 3-D analysis, i.e. E x , E y , E z , G xy , G yz ,
G xz , ν xy , ν yz , ν xz .
10.3 2-D non-linear failure analysis
E
G =
2 (1 + ν )
10.3.1 If the through thickness stresses or the through width strains are insignificant, see [10.1.3], a 2-D
progressive analysis may be carried out.
10.3.2 At the beginning of the analysis, the analyst shall use non-degraded material properties.
10.3.3 All displacement calculations shall be based on time-dependent material properties related to, e.g.,
naturally or environmentally degradation during service life.
10.3.4 For an undamaged sandwich structure, the following stresses and load shall typically be calculated:
σ , , and .
face σ τ
core core Pcr
Guidance note:
Example: Transverse loading case for an open beam.
Stresses shall be calculated as follows:
σ
σ
Mz
=
D
face
E face
Mz
=
D
core
E core
Identically for a box beam:
τ
core
=
T
D
⎡
⎢ E
⎣
face
t
face
2
d
+
E
2
core
t
core
4
2
⎤
⎥
⎦
σ
Mz
=
D
face
E face
τ =
bd
4 I
2
N
in N-direction, and
τ
core
=
( 2 b + d )
8I
2
d
N
in direction perpendicular to
N.
10.3.5 For given loading conditions, stresses and strains shall be calculated and failure criteria shall be
checked.
10.3.6 Any failure of the face material shall be modelled the same way as for monolithic laminates according
to Sec.4 and Sec.9 [2].
10.3.7 If core failure of type ductile or plastic occurs due to core yielding (in tension or compression), E core *
shall be set equal to the secant modulus at the corresponding σ level; G core * shall be proportionally reduced by
the same amount. If σˆ is reached, E core and G core shall be reduced to 0 (default value) or to positive values
core
as described in [10.3.11].
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