OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.6 Failure mechanisms and design criteria – Page 108
∧
σ
∧
σ
∧
σ
12
13
23
in-plane shear strength, as defined in Sec.4.
through thickness shear strength, as defined in Sec.4.
through thickness shear strength, as defined in Sec.4.
3.3.6 If tensile and compressive fibre strength differ by more than 60% it should be checked that the individual
design criteria, i.e. fibre failure in [3.2] and matrix cracking in [4.2] or [4.3], do not give lower allowable
stresses than this criterion.
3.3.7 The characteristic strength σ nk for each of the stress components σ nk and the corresponding coefficients
of variation COV n are defined as specified in Sec.4 [1.6].
3.3.8 The combined COV comb of the characteristic strength
∧
σ nk is defined according to one of the following alternatives. The second alternative is conservative with
respect to the first.
or
where,
COV comb = max n (COV n )
n the co-ordinate system is the ply co-ordinate system, where n refers to the directions 11, 22, 33,
12, 13 and 23
COV n COV for stress component - n -
COV comb COV for the combined stress components
3.3.9 When two or more loads are combined, each stress component σ nk in direction n can be the result of
several combined loads. In that case each stress component σ nk j , which is the local load effect of the structure
in direction n due to load j, shall be considered separately as an individual stress component to determine the
COV.
or
∧
COV
COV
comb
comb
⎛
∧
⎞ ⎛
∧
= ⎜∑
σ nk . COVn
⎟ / ⎜∑
σ
⎝ n ⎠ ⎝ n
⎛ j ⎞ ⎛
= ⎜∑σ . COVn
⎟ / ⎜
nk ∑
⎝ n
⎠ ⎝ n
COV comb. = max n (COV n )
Guidance note:
This approach is conservative compared to the approach of Tukstra’s rule as used for the fibre design criteria. This
approach has been chosen for simplification. In the case of fibre failure, only the strains parallel to the fibre directions
have to be considered, whereas for matrix cracking all stress directions may interact.
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---
3.3.10 The choice of the partial safety factors shall be based on the most conservative partial safety factors
obtained when treating each stress component σ nk
j , which is the local load effect of the structure in direction
n due to load j, as a single load.
3.3.11 The partial safety factors γ F and γ M shall be chosen as described in Sec.8 with COVs equal to COV comb ,
as described in [3.3.8] and [3.3.9].
3.4 Special considerations for fibre failure under in-plane compressive loads
3.4.1 The orientation of matrix cracks shall be checked if the compressive strength of a laminate is important
([4.4]).
3.4.2 If matrix cracks with an orientation of 30 o -60 o relative to the plane of the laminate may be present, the
compressive strain to fibre failure used in the design criteria of this section shall be obtained from
measurements on laminates with the presence of matrix cracks with an orientation between 30 o and 60 o .
Alternatively, the compressive strain to failure may be reduced by 50%, or a component test shall be carried
out ([3.5]).
nk
⎞
⎟
⎠
j
σ
nk
⎞
⎟
⎠
DET NORSKE VERITAS AS