OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.7 Joints and interfaces – Page 133
2.4.3 Material properties of the joints to be compared should be similar. The analysis method should be able
to address all differences between the joints according to [2.1] and [2.2].
3 Specific joints
3.1 Laminated joints
3.1.1 Laminated joints rely on the strength of the interface for load transfer. The interface has resin dominated
strength properties. Defects in the interface tend to be more critical than defects in the interface of plies of
laminate, because the joint interface is the only and critical load path.
3.1.2 The strength of the joint may be different from the through thickness matrix properties of the laminate,
because the joint may be a resin rich layer and the joint may be applied to an already cured surface instead of
a wet on wet connection. (see manufacturing). The strength of the joint should be documented.
3.1.3 Laminated joints are very sensitive to peel conditions. Peel stresses should be avoided.
3.1.4 For the interface between the joining laminates the matrix design rules given in Sec.5 apply. The
resistance of the interface shall be determined with the same level of confidence as specified in Sec.4 [1.6]. It
shall be recognised that the resistance of the interface between the laminates may not be the same as the
corresponding resistance parameter of the joining laminates. Resin rich layers may even have to be analysed
by different failure criteria, e.g., the yield criterion in Sec.6 [6].
3.1.5 The laminates themselves, including possible over-laminations, shall be analysed like regular laminates.
3.2 Adhesive Joints
3.2.1 All issues related to laminated joints also apply to adhesive joints.
3.2.2 Geometrical details should be clearly specified, especially at points of stress concentrations like the
edges of the joints.
3.2.3 The relationship between all elastic constants of both substrates and the adhesive should be carefully
considered. Mismatches may introduce stresses or strains that can cause failure of the joint.
3.2.4 Thermal stresses should be considered.
3.2.5 Long term performance of adhesive should be established with great care. The long term performance is
not only influenced by properties of the substrate, the adhesive and the interface, but also by the surface
preparation and application method.
3.2.6 Relevant long term data shall be established exactly for the combination of materials, geometry, surface
preparation and fabrication procedures used in the joint.
3.2.7 An adhesive joint may also introduce local through thickness stresses in the composite laminate that can
lead to failure inside the laminate in the joint region.
3.3 Mechanical joints
3.3.1 Mechanical joints are often very sensitive to geometrical tolerances.
3.3.2 Creep of the materials shall be considered.
3.3.3 The pretension of bolted connections shall be chosen by considering possible creep of the material under
the bolt.
3.3.4 It is preferred to design the joint in a way that its performance is independent of the matrix. This way
matrix cracking or degradation of matrix properties are not important for the performance of the joint.
3.4 Joints in sandwich structures
3.4.1 All aspects related to laminated, adhesive and mechanical joint apply also to sandwich structures.
3.4.2 Sandwich structures have internal joints between core and skin and between cores. These joints are
usually evaluated independently, but their properties are treated as an internal part of the sandwich system.
Often the core properties are modified to incorporate the joint properties.
3.4.3 When two sandwich structures are joined complicated stress fields may result inside the sandwich
structure. Stresses inside the core can be very different near a joint compared to the typical shear stresses in a
panel.
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