OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.6 Failure mechanisms and design criteria – Page 113
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.
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4.2.7 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.
4.2.8 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 [4.2.5] and [4.2.6].
4.2.9 Matrix failure cannot be checked on a laminate level, it shall always be checked on a ply level.
4.3 Matrix failure based on Puck's criterion
4.3.1 Matrix cracking can be predicted using the criterion from Puck. It is probably the design criterion that
describes the physics of the process the best.
4.3.2 The criterion evaluates the stress state over all possible failure surfaces. The orientation of the failure
surface is described by the angle θ. The stress state σ n , τ nt , τ nl in the co-ordinates of the failure surface described
by θ is obtained from the ply stresses by:
In addition, the stress component σ II in fibre direction is needed.
σ II = γ f · γ Sd · γ M · Rd σ 1
Failure is evaluated based on the stress state σ n , τ nt , τ nl for all angles q between - 90 and + 90 degrees. The
design criterion is:
if σ n (θ) ≤ 0
max
⎡
+ 2
2
2 +
F ( ( )) ( ( )) (
1(
)) ( )
⎤
f
σ
II
+ Fnnσ
n
θ + Fntτ
nt
θ + Fnlτ
n
θ + Fn
σ
n
θ < 1
⎢⎣
⎥⎦
for all θ with –90 ≤ θ ≤ 90,
if σ n (θ) < 0
⎧σ
n ⎫
⎪ ⎪
⎨τ
nt ⎬ = γ
F
. γ
⎪ ⎪
⎩τ
n ⎭
. γ
. γ
2
⎡ c
⎢
. ⎢ − sc
⎢
⎣ 0
2
( c
2 sc
− s
2
Sd M Rd
1
0 0
s
sc
( c = cosθ;
s = sin θ)
2
)
0
0
s
⎧σ
2
0 ⎤
⎪
⎪
σ
3
⎥
0 ⎥ ⎨τ
23
c ⎥ ⎪
⎦ τ
31
⎪
⎪⎩
τ
21
⎫
⎪
⎪
⎬
⎪
⎪
⎪⎭
max
⎡
Ff
σ
II
+
⎢⎣
− 2
2
2 −
( F σ ( θ)
) + ( F τ ( θ)
) + ( F τ ( θ)
) + F σ ( θ)
⎤
< 1
nn
n
nt
nt
nl n1
n
n
⎥⎦
for all θ with –90 ≤ θ ≤ 90,
where,
σ 1 , σ 2 , σ 3 , σ 12 , σ 13 , σ 23 characteristic values of the local load effect of the structure (stress) in the coordinates
of the ply.
γ F partial load effect factor (see [4.3.7])
γ Sd,
partial load-model factor (from structural analysis see Sec.9)
γ M partial resistance factor (see [4.3.7])
γ Rd partial resistance-model factor (see [4.3.8])
F ik strength factors (see [4.3.3]).
4.3.3 The strength factors F ik are functions of the ply strength
σ ∧
σ ∧
parameters matrix , matrix , shear , fibre , fibre
σ ∧
σ ∧ , and shape parameters of the failure surface.
2t
2c
12 1t
σ ∧
1c
The factors are defined as:
F
f
1
= , if σ ≥ 0 and
fibre
II
A
t
σ
1t
DET NORSKE VERITAS AS