OS-C501

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Offshore Standard DNV-OS-C501, November 2013 App.D Test methods for sandwich materials – Page 222 D.2.4.7 The recommended test method to determine shear modulus is ASTM C 273-00. D.2.5 Fracture toughness – Strain energy release rate D.2.5.1 This section covers the determination of fracture toughness K c , or strain energy release rate G c of core materials. D.2.5.2 For anisotropic material, tests should be carried in the direction parallel and normal to the direction of anisotropy. D.2.5.3 For mode-I fracture toughness measurement, two test specimen can be used: the single-edge-notch bending specimen (SENB) or the compact-tension specimen (CT). D.2.5.4 For mode-II fracture toughness measurement, the end-notch flexure specimen (ENF) or the compacttension-shear (CTS) specimen can be used. Guidance note: Fracture toughness represents the resistance of a material to fracture. Mode-I refers to tensile stress conditions at the crack tip, whereas mode-II refers to shear stress conditions. Mode-I and mode-II load cases are the principal load cases encountered when designing sandwich constructions. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- D.2.5.5 No specific standard test exist for core materials. D.2.6 Tests to obtain properties under long term static and cyclic loads D.2.6.1 The same tests as for measuring static properties can be used. D.2.6.2 Loads and test environments shall be carefully controlled over the entire test period. D.2.6.3 The strain rate should be kept constant for cyclic fatigue tests of visco elastic materials. This means the test frequency can be increased for lower strain (test) amplitudes. D.3 Adhesive materials - static tests D.3.1 General D.3.1.1 For testing of shear and flatwise tension, the test samples shall be made of two pieces of high density core material (preferably PVC foam) with the sandwich adhesive located in the midplane parallel to the steel supports. The adhesive should be thicker than 1mm thick and the core material shall be specified. D.3.2 Tensile tests D.3.2.1 The recommended test method is ISO-527-1997 to determine the strength and fracture elongation in tension of the adhesive. D.3.3 Flatwise tensile tests D.3.3.1 The recommended test method is ASTM C 297-61 to determine the strength in tension, flatwise, of the adhesive. D.3.4 Shear tests D.3.4.1 The recommended test method is ISO-1922-1981 to determine the strength of the adhesive. D.3.5 Tests to obtain properties under long term static and cyclic loads D.3.5.1 The same tests as for measuring static properties can be used. D.3.5.2 Loads and test environments shall be carefully controlled over the entire test period. D.3.5.3 The strain rate should be kept constant for cyclic fatigue tests of visco elastic materials. This means the test frequency can be increased for lower strain (test) amplitudes. D.4 Core skin interface properties D.4.1 Tensile tests D.4.1.1 The recommended test method is ASTM C 297-61 to determine the strength in tension, flatwise, of the core, or of the bond between the core and the faces, of an assembled sandwich beam or panel. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 App.D Test methods for sandwich materials – Page 223 D.4.2 Fracture toughness of the interface D.4.2.1 The test method covers the determination of the fracture toughness parameters occurring in an interfacial crack. Guidance note: At the cracked interface face/core of a transversely loaded sandwich structure, the crack tip is subjected to both mode- I and mode-II stress fields. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- D.4.2.2 For mode-I fracture toughness measurement, two test specimen can be used: the double-cantilever test specimen (DCB), or its modified version fitted with hinges. D.4.2.3 The interlaminar fracture toughness for isotropic materials is given by: K 2 Ic EG Ic P = ( d P) , c ∂ 1− ν D.4.2.4 For mode-I fracture toughness measurement, the 'Cracked-Sandwich-Beam' (CSB) test specimen can be used. D.4.2.5 Delamination strength of honeycomb type core material can be determined by carrying out the test ASTM C 363-57. D.4.3 Other tests 2 D.4.3.1 Sandwich peel tests are used to determine the peel resistance of adhesive bonds between facings and cores. Several tests methods exist; the climbing drum tests methods, ASTM D 1781; DCB-type peel test; peel tests using air pressure; the recommended test methods is ASTM D 1781-93. D.5 Tests for other properties D.5.1 Coefficient of thermal expansion D.5.1.1 The test covers the determination of the coefficient of linear thermal expansion of core materials. D.5.1.2 The recommended test methods are ASTM D 696-91 (within the range of +30 and -30ºC), ISO 4897:1985. D.5.2 Water absorption tests D.5.2.1 The test covers the determination of the relative rate of water absorption when immersed in a highly humid environment. D.5.2.2 The recommended test method is ASTM D 2842-6. Other test methods are available such as ASTM C 272-91, IDO 2896:1987. D.5.3 Diffusion and vapour transmission G = 2w D.5.3.1 The test aims to determine the permeability of water vapour through permeable or semi-permeable materials. D.5.3.2 The water vapour permeability (WVP) is calculated as: WVT = ∆W tA where - ∆W - is the weight change, - t - is time and - A - the test area. ∂a D.5.3.3 The recommended test method is SS 02 15 82. Other tests are available: ASTM E 96-94, ISO 1663:1981, ISO/DIS 1663. D.5.4 Tests for thermal conductivity measurements Ic D.5.4.1 The recommended test method is ASTM C 177-85. Other test methods can be used such as ASTM C 168-90, ASTM C 236-89, ASTM C 1045-90. The test covers the determination of the steady-state heat flux through flat specimens. DET NORSKE VERITAS AS
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OS-C501

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