OS-C501

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Offshore Standard DNV-OS-C501, November 2013 Sec.5 Materials – sandwich structures – Page 94 Table 5-10 Requirements for individual material to be part of representative data (Continued) Constituent core material(s): Requirements to group measurements from different sandwich cores Process parameters to be given with exposure time: Laminator (company) Processing method Processing temperature Processing pressure Process atmosphere (e.g. vacuum) Curing temperature Post curing (temperature and time) Density of sandwich structures Not relevant Same for all tests* Same for all tests* Same for all tests* Same for all tests* Same for all tests* Same for all tests* Same for all tests* Conditioning parameters: Temperature Water content of the core (wet, dry) Chemical environment Loading rate Same for all tests* Same for all tests* Same for all tests* Same for all tests* Number of specimens: * a wider range may be chosen if data are the minimum of a wide variety of products. 8.6 Qualification against representative data 8.6.1 A product may be qualified against representative data if certain requirements are met for cores and adhesives. 8.6.2 Similarity is described here for core materials and core adhesives. Skin laminates shall be treated like laminates described in Sec.4 [8]. For testing of core properties the skin properties are usually not relevant. 8.6.3 Cores may be considered to be similar, if: — the core is of the same generic type, e.g. cross-linked PVC, PUR, end-grained balsa, etc. — the cell structure is the same — the raw materials to produce the core are the same — manufacturer and trade name may be different σ ∧ — the shear strength xc core linear and compressive characteristic strength ( similarity requirements given in [8.7] 1t fibre and 1c fibre) fulfil the — the shear and compressive modulus is within 5% of the reference core. 8.6.4 Cores may be considered to be similar for a certain property, if: Reported individually for all properties — the core is of the same generic type, e.g. cross-linked PVC, PUR, end-grained balsa, etc. — the cell structure is similar — the raw materials to produce the core are the same — manufacturer and trade name may be different — the shear strength xc core linear and compressive characteristic strength ( 1t fibre and 1c fibre) fulfil the similarity requirements given in [8.7] after corrections for the density change have been made according to [6.3] — the shear and compressive modulus is within 5% of the reference core after corrections for the density change have been made according to [6.3]. σ ∧ 8.6.5 A core adhesive can be considered to be similar, if the adhesive is of the same generic type, e.g. vinylester, epoxy, and if its strain to failure is not less than the reference adhesive. 8.6.6 If the above basic similarity requirements are met, individual static sandwich structure properties shall be qualified as described in Table 5-11. Some properties can be based directly on represented data or an equation to modify them is given. Other properties shall be confirmed by experiment (see [8.7]-[8.9]). 8.6.7 Instead of confirming all material parameters individually component testing may be used to qualify an analysis, as described in Sec.4 [8.11]. ε ∧ ε ∧ ε ∧ ε ∧ DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.5 Materials – sandwich structures – Page 95 Table 5-11 Qualification against representative data Mechanical parameter 8.6.8 The entry “rep.” in Table 5-11 means that representative data may be used without testing. In some cases the representative data shall be multiplied by a factor as indicated in Table 5-11. 8.6.9 Confirm if critical for design means that the value or procedure of the lower safety class may be used if an additional safety factor of 2 can be applied in all relevant failure criteria. 8.6.10 The procedure of the higher safety class may always be used to obtain better values than can be obtained by using the procedure of the lower safety class. 8.6.11 If any of the confirmation tests show that the material is not similar to the representative material, all properties shall be re-qualified. 8.6.12 A full experimental determination of a property may always be used as an alternative to using representative data or confirmation testing. 8.6.13 For the qualification of adhesive materials data, see Sec.4. 8.7 Confirmation testing for static data 8.7.1 See Sec.4 [8.7]. 8.8 Confirmation testing for long term data 8.8.1 See Sec.4 [8.8] and [8.9]. 8.9 Use of manufacturers data or data from the literature as representative data 8.9.1 There is a vast amount of data available, but unfortunately data are often not well documented and essential information tends to be missing. 8.9.2 This section describes under which conditions such data may be used. Safety class Low Normal High Elastic constants All rep × 1 confirm E xt or E xc and G xc others: rep × 1 confirm Moduli, Poisson's ratios confirm if critical Strength and Strain to All rep × 0.9 confirm if critical confirm failure or yield Fracture Toughness Critical length In-plane rep × 0.8 confirm confirm G 1c Critical strain energy release rep × 0.8 confirm confirm rate in the fibre direction. G 2c Critical strain energy release rate in the fibre plane, normal rep × 0.8 confirm confirm to the fibre direction. Long Term Properties Creep / Stress relaxation rep. confirm if critical for design confirm Stress rupture rep. confirm if critical for design confirm Static strength reduction under permanent load rep. rep. confirm if critical for design Change of modulus under cyclic fatigue rep. rep. confirm if critical for design Cycles to failure rep. confirm if critical for design confirm Static strength reduction under fatigue load rep. rep. confirm if critical for design 8.9.3 It shall be documented that the data come from a reputable source. This can be done in the following way: — all data were taken from calibrated test equipment — data were witnessed by an independent third party or data were published and reviewed by at least two independent research teams. 8.9.4 If these requirements are not met data can still be used as representative data, but all new materials data have to be confirmed against these data, even if the requirements in [8.6] do not require a confirmation. DET NORSKE VERITAS AS
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