OS-C501

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Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 60 5.3 Effect of water Table 4-9 Effect of water on properties [listing typical property changes after long exposures of 10 6 cycles or 10 years] Property Qualitative Effect Quantitative effect orTest requirement Static elastic constants Slight reduction fibre dominated Static elastic constants matrix dominated Slight reduction Static Tensile strengths fibre dominated Static Tensile strengths matrix dominated Static Compressive strengths fibre dominated Static Compressive strengths matrix dominated Fracture toughness Creep / Stress relaxation fibre dominated Creep / Stress relaxation matrix dominated Time to stress rupture fibre dominated Time to stress rupture matrix dominated Change of static strength under permanent load fibre dominated Change of static strength under permanent load matrix dominated Change of modulus under fatigue - fibre dominated Change of modulus under fatigue - matrix dominated Time to fatigue failure fibre dominated Time to fatigue failure matrix dominated Change of static strength under fatigue load fibre dominated Change of static strength under fatigue load matrix dominated Glass: small reduction Hydrolysis may reduce strength at high temperatures. Carbon: slight reduction Aramid: slight reduction? some reduction Glass: small reduction Hydrolysis may reduce strength at high temperatures. Carbon: slight reduction Aramid: slight reduction? The combination of water and high temperature may give a severe strength reduction, because the supporting matrix can get weakened. some reduction The combination of water and high temperature may give a severe strength reduction, Unknown, may increase due to plastification effect. Accelerates in the presence of water Accelerates in the presence of water Gets shorter with the presence of water. The combination of water, high temperature and compressive load may give a severe reduction in time to failure, because the supporting matrix can get weakened. Gets shorter with the presence of water. The combination of water and high temperature may give a severe reduction of time to failure. Unknown, Probably the same as for static strength Unknown, Probably the same as for static strength Unknown, probably small effect Unknown Typically a slight reduction. If compressive loads are involved combined with water and high temperature fatigue lifetime may be severely reduced. Typically a slight reduction. If compressive loads are involved combined with water and high temperature fatigue lifetime may be severely reduced. Probably the same as for static strength Unknown Glass: reduce strength by 10% Carbon: measure Aramid: measure measure wet properties Glass: reduce strength by 10% Carbon: measure Aramid: measure measure wet properties can use the same reduction as for tensile strength test measure measure measure measure measure reduce stress level by 10% DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 61 5.3.1 The effect of seawater is generally less severe than the effect of fresh water. 5.3.2 The effect of distilled water is more severe than the effect of fresh water. 5.3.3 The combination of water and high temperature may be worse than the individual effects of temperature and water. 5.3.4 Aramid fibres shall not be exposed to the combination of water and temperature cycles above and below 0°C. 5.4 Effect of chemicals 5.4.1 The compatibility of a laminate to the exposure to chemicals shall be demonstrated. 5.4.2 In a qualitative way most chemicals tend to have similar effects as water on a composite. The degradation rates shall be obtained for the actual materials in question. In addition, chemicals may break down the matrix, attack the matrix / fibre interface or destroy the fibres. 5.5 Effect of UV radiation 5.5.1 UV radiation can break down the polymers and reduce their strength. The resistance of surface layers to UV radiation shall be documented and quantified if necessary. 5.5.2 Glass and carbon fibres are very resistant to UV radiation. 5.5.3 Aramid fibres are not resistant to UV radiation and shall be protected. 5.5.4 Polyesters tend to have a good UV resistance. 5.5.5 Epoxies tend to have a bad UV resistance. 5.5.6 Vinylester tend to have a variable UV resistance. 5.6 Electrolytic Corrosion 5.6.1 Carbon fibre laminates shall be isolated from direct contact with all metal parts to prevent electrolytic corrosion. 5.6.2 It is recommended to check the quality of the isolation by resistance measurements. Guidance note: Electrical connection between carbon fibres and steel in submerged conditions (with or without anodes) will cause cathodic protection of the carbon fibres where they are exposed to sea water (in cracks, cut surfaces etc.). When polarised the local pH at the fibre surface will be increased to ≈ 13 and salts from the sea water will precipitate on the fibres. The associated volume increase will force the crack to open more (“The wedging effect”). As a result, the mechanical properties of the laminate may be reduced, due to the gradually increasing loss of adhesion between the carbon fibres and the matrix. 5.7 Combination of environmental effects ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 5.7.1 The combination of environmental effects on materials, like combined humidity and heat, may be worse than the individual effects. 5.7.2 Test data should be obtained of the combined effect of environments on the material properties if relevant. The worst relevant combination of environments should be used for testing. 5.8 Blisters/osmosis 5.8.1 Some matrix systems develop blisters after some time of water exposure. Matrix systems should be chosen that have been proven to be blister resistant. A proper mixture of hardener and curing agent is also important to prevent blistering. Blistering can also be related to weak bonding between gelcoat and laminate. Blistering is also sometimes referred to as “Osmosis”. 6 Influence of process parameters 6.1 Introduction 6.1.1 Composite laminates can be produced in many ways. Changes to the process parameters may influence some or all-material parameters. 6.1.2 Process parameters are seen here in a wider sense. Change of void content or fibre fraction are part of this section, even though these changes are a results of other changes of more fundamental production parameters. DET NORSKE VERITAS AS
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OS-C501

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