OS-C501

Recommendations

Info

Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 72 8.11.4 The relevance of competing failure mechanisms as described in Sec.7 [2.3] shall be evaluated. If competing failure mechanisms are present it may be necessary to measure material properties individually. 8.12 Comparing results from different processes and lay-ups 8.12.1 It is often not possible to measure ply properties from the actual laminate in the component. Special laminates should be produced. In some cases data are available for slightly different reinforcements. In some cases production processes are different. 8.12.2 This section shows how data can be converted between these different types of laminates. It is assumed here that the fibre volume fraction and the void content do not change. Further it is assumed that the same fibres matrix and sizing are used. If any of these items are changed in addition, they have to be accounted for by the methods described in the previous sections. If the laminate has a complicated lay-up, but a more simplified layup had to be used to obtain ply data, data are valid. 8.12.3 Compressive strength of UD laminates should be measured on UD laminates and not cross-plied laminates. Other properties can be treated as equivalent whether measured on UD or cross-plied laminates. 8.12.4 The normalised relations in Table 4-15 may be used to conservatively estimate the influence of reinforcements on ply properties. Properties should only be reduced, but never increased relative to measured values, unless experimental evidence can be provided. Table 4-15 Comparing results from different processes and lay-ups UD pre-preg Knitted fabric Twill Woven Roving Filament wound Short fibre Fibre dominated tensile strength 1 0.8 0.7 0.6 0.6 0.4 Fibre dominated compress. Strength 1 0.8 0.8 0.8 0.7 0.4 Matrix dominated strength (tensile and 0.9 1 1 1 1 0.5 compressive) Fibre dominated Modulus of elasticity 1 0.9 0.9 0.8 0.8 0.6 Matrix dominated Modulus of elasticity 0.9 1 1 1 1 0.5 8.12.5 The strains to failure can be calculated from Table 4-15 by the simple relationship ε = σ / E. 8.12.6 It is recommended to use direct measurements of the laminates made with the actual production process instead of using the procedures in [8.12.4] and [8.12.5]. 8.12.7 Different production methods may influence the characteristics of the laminate, due to for instance variations in fibre volume fraction, void content, and curing temperature. These aspects shall be considered as described in this section under [6]. 9 Properties with damaged or nonlinearly deformed matrix 9.1 Introduction 9.1.1 In most applications the matrix will crack or deform nonlinearly before the laminate fails. Describing this non-linear behaviour of the laminate properly requires a change of the matrix dominated ply properties to reflect the matrix damage in the laminate. 9.1.2 For some analysis methods (see Sec.9) the non-linear properties should be known. 9.2 Default values 9.2.1 Setting the matrix dominated Young's moduli of a damaged matrix to 0 is usually a conservative estimate. This approach is described here as a default. A better method that requires some testing is described in [9.3]. 9.2.2 If matrix failure occurs in a ply (according to the failure criteria in Sec.6 [4]), the ply properties should be locally degraded to the values given in Table 4-16. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.4 Materials - laminates – Page 73 Table 4-16 Default changes of ply properties with matrix damage Matrix cracking due to stress (see failure criteria in Sec.6 [4]) Change ply properties to (see also [9.2.3]) stress σ 2 transverse to the fibre direction E 2 = ν 12 = 0 shear stress σ 12 G 12 = ν 12 = 0 stress σ 3 transverse to the fibre direction E 3 = ν 31 = 0 shear stress σ 13 G 13 = ν 13 = 0 shear stress σ 23 G 23 = ν 23 = 0 9.2.3 In numerical calculations certain problems may arise, e.g. lack of ability to invert the structural stiffness matrix, when degraded material properties are set equal to 0. To overcome such problems, one may apply small values, e.g. 1% of the non-degraded values, instead of 0. Guidance note: Stiffness of a composite in compression will be similar to the linear (initial) value even under the presence of damage, since matrix cracks will close. In tension, the stiffness reduces gradually with the increase of damage. 9.3 Experimental approach ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 9.3.1 Instead of the default values given in [9.2], gradual degradation of the material properties at ply levels can be used, provided experiments document the validity of values larger than 0 for the type of laminate used. 9.3.2 The change of E 2 due to matrix cracking or non-linear deformation of the matrix may be determined from tests on 0/90 laminates. The Young's modulus of the laminate can be calculated with laminate theory from the ply properties. The initial modulus of the test E 0+90 should be consistent with the calculated modulus based on undamaged ply properties. The secant modulus at failure of the test E 0 + partially damaged 90 should be consistent with the calculated modulus based on an unchanged ply modulus in fibre direction and a modified modulus E 2 * representing the matrix with cracks. An example of experimental data is given in Figure 4-5. . 200 E II FAILURE E 0 + 90 E 0 + PARTIALLY DAMAGED 90 S T R E S S 100 E 0 + TOTALLY DAMAGED 90 STRAIN AT ONSETT OF MATRIX CRACKING 0 0.0 0.5 1.0 1.5 2.0 STRAIN Figure 4-5 Example of axial stress vs. strain curve of a 0/90 laminate to obtain magnitude of the matrix ply modulus of a laminate with matrix cracks. 9.3.3 The change of G 12 is usually due to a combination of non-linear behaviour at low strains and matrix cracking at higher strains. The change may be determined from axial tests on ±45 laminates. The shear modulus of the laminate can be calculated with laminate theory from the ply properties. The initial modulus of the test G 12 should be consistent with the calculated modulus based on undamaged ply properties (see [2.6]). The secant modulus at failure of the test G 12 at failure should be consistent with the calculated modulus based on an unchanged ply modulus in fibre direction and a modified modulus G 12 * representing non-linearity and the matrix with cracks. Instead of determining G 12 * at failure it may be taken at 90% of the failure load. An example of experimental data is given in Figure 4-6. DET NORSKE VERITAS AS
Page 1 and 2:
OFFSHORE STANDARD DNV-OS-C501 Compo
Page 3 and 4:
Offshore Standard DNV-OS-C501, Nove
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22: Offshore Standard DNV-OS-C501, Nove
Page 71: Offshore Standard DNV-OS-C501, Nove
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
show all

OS-C501

Create successful ePaper yourself

Delete template?

Save as template?