4.3　Material properties of lamina and laminate

4.3.1　The mechanical properties of fibre reinforced plastic lamina for equipment and pipes should be determined by testing.When using the layering calculation method，the mechanical properties of the glass fibre reinforced plastic lamina shall be in accordance with the following requirements：

1　The mechanical properties of the lamina shall be in accordance with Table 4.3.1-1；

2　The winding angle and the unit tensile modulus of the circumferential and axial direction of the filament wound layer should be in accordance with Table 4.3.1-2；

3　The winding angle and the poisson ratio of the filament wound layer should be in accordance with Table 4.3.1-3；

4　The glass fibre content by mass of the lamina shall be in accordance with the following requirements：

1）For chopped strand mat，it should be 25％to 35％；

2）For woven roving，it should be 45％to 55％；

3）For winding roving，it should be 60％to 75％.

4.3.2　The mechanical properties of the fibre reinforced plastic laminates may be calculated according to the layering calculation based on the laminate theory or the testing results，and shall be in accordance with the following requirements：

1　When tested parameters or historical data are missing，the following layering calculation method shall be used；

1）The unit tensile stiffness and unit tensile strength of the laminate shall be calculated according to the following formulas：

where

X _lam —Unit tensile stiffness of laminate（N/mm）；

U _lam —Unit tensile strength of laminate（N/mm）；

n _i —Number of layers of the i -th lamina；

W _i — Fibre mass per unit area of the i -th lamina（kg/m ² ）；

X _i —Unit tensile modulus of the i -th lamina［N/（mm·kg/m ² ）］；for a filament wound layer，when the winding angle is less than 15°and the circumferential tensile modulus is calculated，the value shall be 0；when the winding angle is greater than 75°and the axial tensile modulus is calculated，the value shall be 0；

U _i —Unit tensile strength of the i -th lamina［N/（mm·kg/m ² ）］.

2）The tensile modulus of the laminate shall be calculated according to the following formulas：

where

E _lam —Tensile modulus of laminate（MPa）；

t _d —Calculated thickness of structural layer of laminate（mm）；

t _i —Structure calculation thickness of the i -th lamina（mm）；

m _g —Fibre mass percentage of the i -th lamina；

W _i — Fibre mass per unit area of the i -th lamina（kg/m ² ）；

ρ _r —Density of cured resin（kg/m ³ ）；

ρ _g —Density of fibre（kg/m ³ ）.

3）The flexural modulus of the laminate shall be calculated according to the following formulas：

where

E _b —Flexural modulus of laminate（MPa）；

W _i — Fibre mass per unit area of the i -th lamina（kg/m ² ）；

X _i —Unit tensile modulus of the i -th lamina ［N/（mm·kg/m ² ）］；

h _i —Distancebetweenthecenterofthe i -thlaminaandthecenterofthelaminate（mm）（Figure4.3.2）；

h ₀ —Distance between the neutral plane of the laminate and the center of the laminate（mm）.

2　When testing is used to determine the performance of lamina and laminate，it shall be in accordance with the following requirements：

1）The test specimens shall be made according to the designed layers，and the number of processed specimens for each test item shall not be less than 15；

2）Lamina and laminate performance testing items shall be in accordance with those specified in Table 4.3.2-1；

3）The confidence of the specimen data shall be calculated according to the following formulas：

where

J _lam —Typical values for preset layers performance；

—Average test results of measured performance of preset layup；

t — t -distribution threshold，which may be valued according to Table 4.3.2-2；

s —Standard deviation；

J —Actual test result；

N —Number of specimens.

Ⅰ　Equipment design factor and allowable strain

4.3.3　The design factor of the mechanical properties of the equipment shall be determined in accordance with the following requirements：

1　The design factor shall be calculated according to following formulas：

where

K —Design factor，shall not less than 6.0；

F —Buckling factor，shall not less than 4.0；

K ₁ —Partial design factor relating to test and verification of material properties；

K ₂ —Partial design factor relating to chemical environment；

K ₃ —Partial design factor relating to the influence of the design temperature and resin HDT ；

K ₄ —Partial design factor relating to long-term performance of laminate.

2　When the partial design factor cannot be determined，the design factor shall not be less than 10.0 and the buckling factor shall not be less than 5.0.

4.3.4　The test and verification partial design factor K ₁ shall be in accordance with the following requirements：

1　When the mechanical properties of the laminate used in the design are determined by the layering calculation method and the performance values of each lamina in Table 4.3.1 of this code are adopted， K ₁ shall be in accordance with the following requirements：

1）When there is a product performance of the same laminates manufactured within 18 months and there is acceptable historical test data of performance of the product， K ₁ shall be taken as 2.0；

2）When there is a product performance of the same laminates manufactured within 12 months and there is acceptable historical test data of performance of the product， K ₁ shall be taken as 1.5；

3）When there is a product performance of the same laminates manufactured within 12 months，and the performance of the lamina is verified by 5 data sets，get the average of 5 data and the average of 3 data excluding the maximum and minimum ones.The smaller of the two average values shall be greater than the performance value in Table 4.3.1 of this code， K ₁ shall be taken as 1.3；

4）When there is a product performance of the same laminates manufactured within 12 months，and the mechanical properties of the laminates used in the design are verified by a test of 5 data sets，get the average of 5 data and the average of 3 data excluding the maximum and minimum ones.The smaller of the two average values shall be greater than the mechanical properties of the laminate used in the design， K ₁ shall be taken as 1.2.

2　When the mechanical properties of the laminate used in the design are determined by the layering calculation，the performance of the lamina is determined by testing or by the original test results，and the performance of the lamina is verified by 5 data sets，get the average of 5 data and the average of 3 data excluding the maximum and minimum ones，the smaller of the two average values shall be greater than the performance value of the lamina， K ₁ shall be taken as 1.1.

3　When the mechanical properties of the laminates used in the design are measured and sampled from the simulated specimens of the laboratory，the performance test data shall not be less than 15 for the test verification， K ₁ shall be taken as 1.1.

4　When the mechanical properties of the laminate used in the design are measured and sampled from the equipment specimen，the performance test data shall not be less than 15 for the test verification，and K ₁ shall be taken as 1.0.

4.3.5　The value K ₂ of the partial design factor relating to the chemical environment shall meet the requirements of Appendix A of this code.

4.3.6　The partial design factor relating to the design temperature and the thermal deflection temperature（ HDT ）of the resin shall be calculated as follows，and the value K ₃ shall be in the range of 1.0—1.4.

where

T _d —Design temperature；

HDT —Heat deflection temperature of resin.

4.3.7　The partial design factor K ₄ relating to the long-term performance of the laminate shall be in accordance with Table 4.3.7 and the following requirements：

1　Where combination laminates of chopped strand mat，woven roving or winding roving，the value of K ₄ shall be taken for the major constituent；

2　For the calculation of the buckling factor F ，only the K ₄ value for flexural shall be used；

3　For the calculation of the overall design factor K ，where the loading is a combination of both tension and flexural，the K ₄ value for tension shall be used.

4.3.8　The allowable strain of laminates for equipment and the allowable unit load shall be in accordance with the following requirements：

1　The allowable strain value ε _ar of the resin shall be calculated according to the following formula，and shall not be greater than the value specified in Table 4.3.8-1；

where

ε _ar —Allowable strain value of resin（％）；

ε _r —Fracture elongation of resin casting body（％）.

2　The allowable strain value of the laminate shall be calculated according to the following formula：

where

ε _lam —Allowable strain value of laminate；

X _lam —Unittensilestiffness（N/mm）ofthelaminate，determinedinaccordancewithFormula（4.3.2-1）；

K —Design factor，determined in accordance with Formula（4.3.3-1）；

U _lam —Unit tensile strength（N/mm）of the laminate，determined in accordance with Formula（4.3.2-2）.

3　The allowable strain ε _d of the laminate for equipment shall be a small value in the calculated values of Formula（4.3.8-1）and Formula（4.3.8-2）.When the calculated values of Formula（4.3.8-1）and Formula（4.3.8-2）cannot be determined，the allowable strain shall be 0.001.

4　The maximum strain ε _test in the item when tested of the equipment shall not exceed the value specified in Table 4.3.8-2.

5　The allowable unit load of the equipment laminates shall be calculated according to the following formula：

where

［ q ］—Allowable unit load for equipment laminates（N/mm）.

6　The allowable shear stress of the equipment laminates shall be calculated according to the following formula：

where

［ τ ］—Allowable shear stress of equipment laminates（MPa）；

τ —The shear strength（MPa）of the equipment laminates，can be measured according to the current national standard GB/T 1450.2 Fibre-Reinforced Plastic Composites-Detemination of the Punch-Type Shear Strength ；when no detected value is available，50MPa is preferred；

K —The design factor，shall be in accordance with the requirements of Article 4.3.3 of this code.

Ⅱ　Allowable stress and allowable strain of pipe

4.3.9　The allowable stress of the pipe laminates shall be the elasticity modulus multiplied by the allowable strain.The elasticity modulus shall be determined in accordance with the requirements of Article 4.3.2 of this code.The allowable strain shall be determined by specified value method or longterm performance test method.The allowable stress shall be determined in accordance with the following requirements：

1　When the allowable strain is determined by Specified Value method，and the load conditions are occasional short-term loads not including the hydrostatic test load and Sustained loads including the thermal expansion load，the allowable stress shall be taken the value calculated in this article；

2　When the allowable strain is determined by Long-term Performance Test method，and the load conditions are Sustained loads not including the thermal expansion load，the allowable stress shall be taken the value calculated in this article；

3　When the allowable strain is determined by Long-term Performance Test method，and the load conditions are Sustained loads including the thermal expansion load，the allowable stress shall be the value calculated in this article times 125％；

4　When the allowable strain is determined by Long-term Performance Test method，and the load conditions are Occasional short-term loads and Sustained loads not including the thermal expansion load，the allowable stress shall be the value calculated in this article times 133％.

4.3.10　When using Specified Value method，the allowable strain of the laminate under chemical conditionsand temperatureconditionsshall bedetermined in accordancewith thefollowing requirements：

1　The classification of chemical conditions shall be determined according to the loss in flexural strength of the immersed non-stressed specimen under the set chemical environment，and shall be in accordance with the following requirements：

1）The thickness of the specimen shall be 4mm—6mm，it shall be subjected to a cure schedule simulating that to be used for the finished pipe，and shall be immersed for 6 months at the design temperature；

2）Chemical conditionsⅠ：this condition applies when the loss in flexural strength is less than 20％of the original value；

3）Chemical conditionsⅡ：this condition applies when the loss in flexural strength is more than 20％but less than 50％of the original value；

4）If the loss of flexural strength is greater than 50％of the original value，then the matrix fibre system shall be deemed unsuitable and not used.

2　The classification of temperature conditions shall be determined by the difference between the heat distortion temperature HDT of the resin and the design temperature and shall be in accordance with the following requirements：

1）Temperature condition Ⅰ，the design temperature shall be at least 40℃ below HDT ；

2）Temperature condition Ⅱ，the design temperature shall be at least 20℃ below but not more than 40℃below HDT .

3　When the chemical environment and temperature conditions are determined，in terms of temperature and chemical condition classifications，strain class ratings shall be selected according to those specified in Table 4.3.10-1.

4　When strain class ratings are determined，allowable strain shall be selected according to those specified in Table 4.3.10-2.

5　For pipes manufactured using filament wound at any angle between ±15°and ±75°，the anisotropic elastic analysis shall be carried out to confirm that the allowable strain is not exceeded.Without such an analysis the allowable strain shall be no greater than 0.0009.

4.3.11　When using the Long-term Performance Test method，the test shall comply with the relevant requirement of the current national standard GB/T 21238 Glass Fibre Reinforced Plastics Mortar Pipes ，the end of the specimen shall be a free end closure，and the allowable strain in circumferential direction shall be calculated according to the following formula：

where

ε _d —Allowable strain values at design life；

D _i —Pipe specimen internal diameter for long-term performance testing（mm）；

p _97.5 —The 97.5％lower confidence limit of the internal pressure to produce failure at the design life（MPa）；

X _lam —Laminate unit tensile stiffness of the specimen.When there is no such value，the specimen can be ablated according to the current national standard GB/T 2577 Test Method for Resin Content of Glass Fibre Reinforced Plastics ，and the fibre mass per unit area and the ply scheme of each specimen are obtained.The average value is then calculated according to the Formula（4.3.2-1）of this code；

K —Design factor，which shall not be less than 1.5.

4.3.12　When the number of cycles of fatigue load is greater than 1000 or the stress range of stress cycles is greater than 20％of the allowable stress，the allowable strain value either selected in Table 4.3.10-2 or calculated according to Formula（4.3.11）of this code shall also be divided by the fatigue correction factor K _n ， K _n shall be calculated according to the following formula：

where

K _n —Fatigue correction factor；

n —Number of stress cycles during design life；

A _σ —Stress range during a fatigue cycle；

σ _n —Maximum stress during a fatigue cycle.

4.3.13　The allowable strain of the pipe laminate shall less than 10％of the resin fracture strain.

4.3.14　When the long-term performance test method is used to determine the allowable strain value of the laminate，and then the allowable stress value is calculated，the simplified failure envelope calculation and failure determination of the pipeline and fittings shall be in accordance with the following requirements：

1　The short-term circumferential failure stress σ _sh and long-term regression ratio R can be obtained by the long-term performance test method ，and the axial tensile strength value σ _sa can be obtained according to the current national standard GB/T 5349 Fibre - Reinforced Thermosetting Plastic Composites Pipe - Determination of Longitudinal Tensile Properties ，and the biaxial stress ratio R shall be calculated according to the following formulas：

where

σ _sh —Short-term circumferential failure stress obtained by the long-term performance test method（MPa）；

σ _sa —Short-term axial tensile strength value（MPa），which can be measured according to the current national standard GB/T 5349 Fibre-Reinforced Thermosetting Plastic Composites Pipe-Determination of Longitudinal Tensile Properties ；

t — Pipe specimen structural wall thickness for the long-term performance testing（mm）；

R —Long-term regression ratio（％）；

p _{L，97.5％LCL} —97.5％lower confidence limit of the internal pressure to produce failure at the design life（MPa）；

p _{6，97.5％LCL} —97.5％lower confidence limit of the internal pressure to produce failure at 6min by the extrapolation curve（MPa）；

r —Biaxial stress ratio，which may be calculated according to Formula（4.3.14-3）.When no data，the default biaxial stress ratio of the component can be selected according to those specified in Table 4.3.14.

2　The calculation of the simplified failure envelope shall include the circumferential allowable stress and the allowable axial stress of the pure internal pressure state（2∶1），the allowable axial stress of the pure axial tensile state（0∶1），and they shall be calculated according to the following formulas：

where

σ _ah（2:1） —Circumferential allowable stress of the pure internal pressure state（2∶1）（MPa）；

σ _al （2:1）—Allowable axial stress of the pure internal pressure state（2∶1）（MPa）；

σ _al （0:1 ）—Allowable axial stress of the pure axial tensile state（0∶1）（MPa）；

K —Design factor，shall not be less than 1.5.

3　The three stress values calculated by the Formula（4.3.14-4）to Formula（4.3.14-6） shall be connected to the fold line which is the simplify the failure envelope（Figure 4.3.14）.The safety of the pipeline shall be determined by whether the calculated values of axial and circumferential stress are within the simplified failure envelope.