OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.6 Failure mechanisms and design criteria – Page 129
16.3.2 Ultimate failure of brittle and plastic core materials shall be checked with the design criterion for
orthotropic homogenous materials under [7].
16.3.3 In many cases the dominant stress in a core is shear, causing shear yield or failure or tensile failure in
45 o to the through thickness direction. This case is also covered by the criteria given under [6] and [7].
16.3.4 Core indentation due to local compressive stress shall be checked. The core will indent if the
compressive strength of the core is exceeded (see [16.3.1] and [16.3.2]).
16.4 Failure of the sandwich skin-core interface
16.4.1 Interface failure between the skin and core of a sandwich can be treated the same way as a delamination
([5]).
16.4.2 Care shall be taken to use proper material properties when applying the design criterion. Interface
properties may differ from the core or laminate properties.
16.4.3 Sandwich structures with PVC core show typically no failure directly in the interface, but they fail
inside the PVC core close to the interface. PVC core properties may be used in the design criteria.
16.4.4 Sandwich structures with Balsa core fail typically in the interface.
16.5 Buckling of sandwich structures
16.5.1 The same buckling criteria as for general structures apply, see under [8].
16.5.2 Sandwich structures show some special buckling modes. The following modes shall be considered:
16.5.3 Face wrinkling will occur when the compressive direct stress in the face will reach the local instability
(or wrinkling) stress, i.e.
σ ≥ ˆ
16.5.4 Global buckling will occur when the axial load will reach the critical buckling load, i.e.
16.5.5 Shear crimping will occur when the direct stress will reach the crimping stress, i.e.
16.5.6 Face dimpling or intercellular buckling occurs only in sandwich structures with honeycomb and
corrugated cores. Face dimpling will occur when the compressive stress in the cell wall reaches the buckling
stress of a honeycomb cell or a corrugated core, i.e.
17 Chemical decomposition / galvanic corrosion
17.1 General
σ
σ
face
σ wrinkling
P ≥ P cr.
face
σ crimping
17.1.1 A material may degrade due to chemical decomposition. This effect is covered in principle in this
standard by the time dependence of strength and stiffness values.
17.1.2 The extrapolation of long term data under environmental exposure describes usually the gradual effect
of environment or load on the properties. Chemical decomposition may act suddenly and rapidly and may not
be detected by mechanical long term tests.
17.1.3 If a material is exposed to chemicals, possible chemical decomposition should be considered.
≥
17.1.4 Possible galvanic corrosion should be considered when carbon fibre composites are in contact with
metal. Usually the metal degrades first, but in some cases also damage to the matrix and the fibres can happen.
Carbon composites should be electrically isolated from metal components.
ˆ
≥ ˆ
core
σ dinpling
DET NORSKE VERITAS AS