OS-C501
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Offshore Standard DNV-<strong>OS</strong>-<strong>C501</strong>, November 2013<br />
Sec.6 Failure mechanisms and design criteria – Page 115<br />
4.3.7 The partial safety factors γ F and γ M shall be chosen as described in Sec.8 with a COV equal to COV comb ,<br />
for both the characteristic strengths and the local load effects (see [4.3.4]to [4.3.6]).<br />
4.3.8 The resistance model factor γ Rd shall be chosen to be 1.1. The model factor shall ensure a conservative<br />
result with respect to the simplifications made regarding the treatment of combined loads.<br />
4.3.9 Matrix failure cannot be checked on a laminate level, it shall always be checked on a ply level.<br />
4.4 Obtaining orientation of the failure surface<br />
4.4.1 The orientation of the fibre failure surface is critical if a structure is loaded in compression. Matrix crack<br />
failure surfaces with an orientation of 30 o to 60 o relative to the plane of the laminate can reduce compressive<br />
fibre strength and reduce the resistance to delamination.<br />
4.4.2 The orientation of the failure surface should be determined with the Puck design criterion by finding the<br />
angle q at which the matrix design criterion in [4.3.2] reaches its maximum.<br />
4.4.3 If the laminate may have matrix cracks with an orientation of 30 o to 60 o relative to the plane of the<br />
laminate the compressive fibre strength shall be measured on laminates with the presence of such cracks and<br />
this value shall be used in the fibre design criterion (see this section under [3]). In this case the tested laminate<br />
should be equal to the one used in the component.<br />
Guidance note:<br />
Matrix cracks with an orientation of 30 o to 60 o occur mainly when the ply is exposed to high in-plane shear stresses<br />
or compressive stresses normal to the fibre direction.<br />
4.5 Matrix cracking caused only by shear<br />
---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---<br />
4.5.1 Some laminates may fail (rupture) due to shear in the plies without fibre failure. This condition was<br />
described in [3.1.5]. In this case matrix cracking due to stresses transverse to the fibres is acceptable. To check<br />
for this condition the matrix failure design criteria described in [4.1]-[4.3] may be used by applying them just<br />
for shear stresses.<br />
4.5.2 For simple 2-D in-plane conditions the matrix cracking design criterion in [4.2] reduces to:<br />
where,<br />
σ 12<br />
∧<br />
matrix<br />
12<br />
σ<br />
γ F<br />
γ Sd<br />
γ M<br />
characteristic value of the local load effect of the structure (stress) in the in-plane shear direction<br />
12<br />
characteristic value of the stress components to matrix cracking in the in-plane shear direction 12<br />
partial load effect factor<br />
partial load-model factor<br />
partial resistance factor<br />
γ Rd partial resistance-model factor, γ Rd = 1.0<br />
The co-ordinate system is the ply co-ordinate system.<br />
4.6 Matrix failure checked by component testing<br />
4.6.1 Refer to section on component testing (Sec.10).<br />
5 Delamination<br />
5.1 General<br />
5.1.1 Delamination is a separation of plies. Delaminations are debonded areas that can grow gradually, once<br />
they are initiated.<br />
5.1.2 Delaminations can also be debonding between core materials and skins.<br />
5.2 Onset of delamination<br />
γ . γ . σ<br />
F<br />
Sd<br />
12<br />
∧<br />
matrix<br />
12<br />
σ<br />
<<br />
γ . γ<br />
5.2.1 The onset of delamination due to in-plane stresses or strains is difficult to predict. It is known that<br />
delaminations will not initiate before matrix cracks have formed. It is, therefore, a conservative choice to model<br />
the onset of delamination with the matrix cracking criteria from [4].<br />
M<br />
Rd<br />
DET NORSKE VERITAS AS