OS-C501

Offshore Standard DNV-OS-C501, November 2013
App.D Test methods for sandwich materials – Page 220
D.1 General
APPENDIX D TEST METHODS FOR SANDWICH MATERIALS
D.1.1 Introduction
D.1.1.1 This appendix describes recommended and preferred test methods for core materials alone and
sandwich components (including the face/core adhesive joints and the faces). Other test methods than the ones
described here may be used if they measure the same physical properties under the same conditions.
D.1.1.2 If no standard tests exist and no test methods are suggested, tests shall be chosen that measure the
desired properties with no or small side effects from specimen size and geometry. It shall be ensured that the
test results are correct or conservative with respect to the way they are used in the design.
D.1.1.3 The complete list of mechanical static properties (for core and adhesive materials) needed for
structural analysis in this standard is shown in Sec.5 [2] 'static properties'.
D.1.1.4 Guidelines for the testing of face materials alone are presented in App.C.
D.1.1.5 Health and safety shall be considered when performing tests. This standard does not address these
aspects and reference to applicable health and safety regulations shall be made.
D.1.2 General testing information
D.1.2.1 For anisotropic material, mechanical properties should be determined relative to the relevant direction
of anisotropy.
D.1.2.2 Tests should be carried at a loading rates corresponding to about 1% per minute, unless specified
differently in the standard.
D.1.2.3 For the preparation of test samples, curing conditions, surface treatment and application procedure
shall be according to the specifications as described in Sec.5 [1].
D.1.2.4 The evaluation of stress vs. strain curves is described in App.C, [C.3] for brittle, plastic and ductile
materials.
D.1.2.5 The use of strain gauges for the measurement of deformation in the core is difficult. Suitable adhesive
should be used to bond strain gauges to the core in order to avoid stress concentrations.
Guidance note:
If strain gauges are bonded with epoxy resin, for example, stress concentration will arise due to the difference of
between the adhesive stiffness and the (typically) low core stiffness. Alternatively, an extensometer could also be
used.
D.2 Core materials - static tests
D.2.1 Tensile tests
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D.2.1.1 The specimen dimensions should be sufficiently large to avoid end-effects.
D.2.1.2 For anisotropic material, test should be carried on specimen having their long axis parallel and normal
to the direction of anisotropy.
D.2.1.3 The entire stress-strain curve should be recorded.
D.2.1.4 The recommended test methods are ASTM D 1623-78(1995) for in-plane properties and ISO
1926:1979 for through-thickness properties. Other test methods are also available: ASTM D 638-93, ISO/DIS
1798, and ISO 527-2:1993.
D.2.2 Compressive tests
D.2.2.1 For anisotropic material, test should be carried on specimen having their long axis parallel and normal
to the direction of anisotropy.
D.2.2.2 The entire stress strain curve should be recorded.
D.2.2.3 A typical schematic of a stress-strain curve for a material exhibiting crushing behaviour, like foam
cores, is shown in Figure D-1. These materials have a compressive strength and a crushing strength (σ crush ).
The elastic parameters are the same as for a brittle material see App.C [C.3].
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