OS-C501

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Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 58 Wear rate proportional to (pv) Log p Figure 4-4 Wear rate (plotted against log pv) Log v ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 4.6.8 Wear properties usually degrade at elevated temperatures. The effects of ambient temperature and of frictional heating should be considered. 4.6.9 The presence of water between the two surfaces in contact usually has a lubricating effect, i.e. the wear properties of the wear system are better than those of the same system without presence of water. 4.6.10 Frictional coefficients and wear rates of materials are strongly influenced by the roughness of the counter-face against which they are sliding. In the steady state wear condition abrasive wear can become the dominant mechanism if the surface of the wearing material has been modified during previous passages. Typically, the wear mechanism changes from adhesion in the range of very smooth surfaces to abrasion for rough surfaces, leading to an increase of the wear rate. 4.6.11 The presence of fibres usually improves the wear resistance of a polymer matrix. The fibres are exposed at the sliding surface and support part of the applied loads. Moreover, the fibres smooth the surface of the counter-face to reduce the localised stresses at the asperity contacts. Guidance note: Carbon fibres are usually superior to glass fibres in reducing the wear rate and the frictional coefficient. Especially at high sliding speeds and high loads, they clearly improve the wear properties of the base polymer. For practical application of composites where friction becomes an important problem ,the use of a hybrid material (glass and carbon fibres) can be recommended. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 4.6.12 The orientation of the fibres in a polymer material with a given fibre content has also an influence on its wear properties: — for unidirectional laminates, the lowest wear rates are often obtained when the fibres are orientated perpendicular (normal) to the sliding surface — when the fibres are orientated parallel to the sliding surface, the differences between anti-parallel and parallel orientation are less clear. 4.6.13 The presence of fillers usually helps to reduce wear. However, the wear reducing action of fillers is dependent on factors such as shape and size, as well as the composition of the filler material. 4.6.14 Internal lubricant such as PTFE or silicone can be used to improve the wear resistance of a material. The two materials combine at the wear surface and form a high lubricate film, which acts in addition as a protecting layer for the fibres. 5 Influence of the environment on properties 5.1 Introduction 5.1.1 The environment can effect composites. Properties change usually gradually with time and long exposure times (a year and longer) are needed before properties change significantly. 5.1.2 Fibres and matrix are effected in different ways due to their different chemical nature. 5.1.3 The fibre matrix interface can have an important influence on the environmental resistance. The interface properties are influenced by the type of fibre, the sizing, the matrix, and the processing conditions. 5.1.4 Void content and the presence of matrix cracks can also influence the environmental resistance. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 59 5.1.5 The local environmental conditions shall be taken into account for the documentation of all properties under static and fatigue loads, see also [3]. 5.1.6 Possible degradation of unloaded structures shall also be documented, e.g. liners. 5.1.7 Cyclic environmental conditions shall be considered. 5.1.8 It shall be documented that the combined effects of cyclic loads, static load, and the environment are not worse than the separate effects considered in the sections above. 5.1.9 The following conditions are considered: — temperature — water — chemicals — UV radiation. 5.1.10 The tables in this section are ONLY valid for thermoset resins, like epoxy, polyester and vinyl ester with glass transition temperature below 150°C. Special resins for high temperature applications are not covered in the tables given here, data should be obtained experimentally. They are also ONLY valid for E-glass, Aramid, and carbon fibres, unless stated otherwise. Behaviour of other materials may be similar but shall be documented by test results. 5.2 Effect of temperature Table 4-8 Effect of temperature on short term properties [table listing typical instant (after one hour) property changes] Property Qualitative Effect Quantitative effect orTest requirement Static elastic constants fibre dominated none up to Tg - 20 °C of matrix Aramid below 60 °C no effect test if outside the range Static elastic constants matrix dominated none up to Tg - 20 °C no effect test if outside the range Static Tensile strengths fibre dominated None up to Tg - 20 °C of matrix Aramid below 60 °C no effect test if outside the range Static Tensile strengths matrix dominated None up to Tg - 20 °C no effect test if outside the range Static Compressive strengths fibre dominated None up to Tg - 20 °C of matrix Aramid below 60 °C no effect test if outside the range Static Compressive strengths matrix dominated None up to Tg - 20 °C of matrix no effect test if outside the range Fracture toughness Unknown test Creep / Stress relaxation fibre dominated Accelerates with increasing temperature Measure, may use time temperature superposition Creep / Stress relaxation matrix dominated Accelerates with increasing temperature Measure, may use time temperature superposition Time to stress rupture fibre dominated Gets shorter with increasing temperature Measure, may use time temperature superposition Time to stress rupture matrix dominated Gets shorter with increasing temperature Measure, may use time temperature superposition Change of static strength under permanent load fibre dominated Unknown, Probably the same as for static strength Change of static strength under permanent load May drop more quickly with increasing Adhesive type behaviour. matrix dominated temperature. Change of modulus under fatigue - fibre dominated May drop more quickly with increasing temperature. Change of modulus under fatigue - matrix dominated May drop more quickly with increasing temperature. Time to fatigue failure fibre dominated Gets slightly shorter with increasing temperature Time to fatigue failure Gets shorter with increasing temperature matrix dominated Change of static strength under fatigue load fibre dominated Unknown, Probably the same as for static strength Change of static strength under fatigue load matrix dominated Unknown DET NORSKE VERITAS AS
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