OS-C501
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Offshore Standard DNV-<strong>OS</strong>-<strong>C501</strong>, November 2013<br />
App.C Test methods for laminates – Page 217<br />
C.2.7 In-plane fracture toughness tests<br />
C.2.7.1 In-plane fracture toughness of laminates can be described by the point stress criterion, see Sec.6 [3.6].<br />
C.2.7.2 The point stress criterion needs a critical distance that is a material parameter. The critical distance can<br />
be measured on specimens with different crack length or hole sizes. At least three different crack or hole sizes<br />
should be measured.<br />
C.2.7.3 The critical distance for cracked specimens may differ from the critical distance for specimens with<br />
holes. The two tests should not be mixed.<br />
C.2.7.4 It is recommended to prepare specimens with cracks or holes that resemble closely the real application.<br />
C.2.7.5 The specimen width should be wider than the defect size, to avoid measuring edge effects.<br />
C.2.7.6 No standard tests are known for measuring fracture toughness.<br />
C.2.8 Interlaminar fracture toughness tests<br />
C.2.8.1 The Double Cantilever Beam (DCB) test is recommended to obtain the Mode I fracture toughness G IC .<br />
C.2.8.2 The End Notch Flexure (ENF) test is recommended to obtain the Mode I fracture toughness G IIC .<br />
C.2.8.3 No standards are developed for these tests.<br />
C.2.8.4 Both specimens use a starter crack to initiate crack growth.<br />
C.2.8.5 The starter crack should be introduced by placing a thin film between the two plies that shall<br />
delaminate. The film should not adhere to the matrix.<br />
C.2.8.6 It is best to grow a natural starter crack from the film by applying a few low amplitude fatigue cycles.<br />
Static testing can then be performed based on the crack length of the artificial crack and the naturally grown<br />
crack.<br />
C.2.8.7 If tests are performed based on the artificial crack only, the film should be very thin, less than 13 µm.<br />
C.3 Tests to obtain properties under long term static and cyclic loads<br />
C.3.1<br />
C.3.1.1 The same tests as for measuring static properties can be used.<br />
C.3.1.2 Loads and test environments shall be carefully controlled over the entire test period.<br />
C.3.1.3 The strain rate should be kept constant for cyclic fatigue tests of visco elastic materials. This means<br />
the test frequency can be increased for lower strain (test) amplitudes.<br />
C.3.1.4 The temperature of the specimens should be monitored to avoid heating of the specimen due to testing<br />
at too high frequencies.<br />
C.4 Tests to obtain the fibre fraction<br />
C.4.1<br />
C.4.1.1 The fibre volume fraction should be obtained using one of the following standards:<br />
— ASTM D3171 and ASTM D3553 Fibre volume fraction, digestion method.<br />
Guidance note:<br />
This method is used to find the fibre volume fraction by digestion of the matrix. The choice of chemical to digest the<br />
matrix depends on the matrix and fibres. Suggestions for chemicals are given in the standards. The composite weight<br />
is determined before and after the digestion of the matrix. The fibre volume fraction can be calculated from those<br />
measurements. Calculations are based on the density of the fibres. However, this density can vary, especially for<br />
carbon fibres. In this case only approximate values can be obtained.<br />
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— ASTM D3171 Fibre volume fraction, burnoff method<br />
— ISO 1172<br />
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