Definición de los Estilos de Enseñanza (EdE)

B.1 General

B.1.1 Tests. This appendix describes methods for the testing of resins, laminates and thermoplastics for pipes and fittings in reinforced plastics. Tests are specified for the determination of the following properties:

a) internal shear strength of bonding cement;

b) ultimate tensile unit strength of laminate and laminate layers;

c) unit modulus of laminate and laminate layers;

d) lap shear strength of laminate;

e) shear strength of bond between thermoplastics lining and laminate;

f) peel strength of bond between thermoplastics lining and laminate;

g) tensile strength of thermoplastics sheet and welds.

NOTE Recommended methods for tests to determine the following properties when required are as follows:

B.1.2 Accuracy of testing equipment. Testing machines shall be calibrated in accordance with BS 1610 and shall be maintained to grade A.

Extensometers, including ancillary or autographic equipment, shall be calibrated in accordance with BS 3846 and shall satisfy at least grade E requirements.

B.2 Internal shear strength of bonding cement

B.2.1 Test pieces. Lap joints shall be assembled from laminates, 100 mm min. × 25 ± 1 mm × 3 mm min.

thick, of equivalent resin reinforcement system to the socket and spigot materials and cement to give a minimum cement layer between laminates

of 25 ± 1 mm × 12.5 ± 0.5 mm × 1.5 mm max. thick. The assembly shall be carried out in accordance with the cement manufacturer’s instructions.

The ends of the laminates that are clamped to the tensile machine shall be built up to ensure the force is applied along the cemented joint.

Three test pieces shall be tested.

B.2.2 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.2.3 Procedure. Measure the cross-sectional area of the cemented part of the joint.

Clamp the test piece in the serrated jaws of a suitable tensile testing machine so that the jaws grip the built up faces of the end pieces and the test pieces are in axial alignment with the direction of pull.

Apply a force to the test piece by separating the jaws at a constant rate between 5.0 mm/min and 6.5 mm/min.

Record the maximum force at which the joint fails.

Test pieces which fail within the laminate or at the laminate/cement interface shall be disconnected and the test shall be repeated, unless the calculated shear strength is greater than that specified in clause 8.

B.2.4 Calculation. Calculate the internal shear strength, S_c, for each test piece from equation (22).

where

B.2.5 Report. The test report shall include the following:

a) identification of the laminate structure;

b) identification of the cement;

c) conditioning temperature of the test pieces;

d) individual test results;

e) date of the test.

B.3 Ultimate tensile unit strength of laminate and laminate layers

NOTE The tests for ultimate tensile unit strength and unit modulus (see B.4) may be combined using the same test pieces.

B.3.1 Test pieces. The form and number of test pieces shall be as described in BS 2782:Method 1003 for type II or type III specimens.

B.3.2 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.3.3 Procedure. Measure the mean width of the test piece to the nearest 0.05 mm and number of laminate layers.

water absorption: BS 2782:Method 430B electrical properties: BS 2044

cure of resin (Barcol hardness): BS 2782:Method 1001

(22)

F is the maximum force (in N);

A_c is the cross-sectional area of the cemented joint.

S_c F A_c

---=

Licensed copy: Mr. National University Singapore, National University of Singapore, Version correct as of 19/11/2012 08:31, (c) The British Standards Institution 2012

Clamp the test piece in the serrated jaws of a suitable tensile testing machine so that the jaws grip the entire faces of the end pieces and the test piece is in axial alignment with the direction of pull.

Apply a force to the test piece by separating the jaws at a constant rate such that fracture occurs in 0.5 min to 1.5 min. Report the maximum force applied.

Results obtained on test pieces that break within the area of the end pieces shall be disregarded and additional test pieces tested.

B.3.4 Calculation. Calculate the ultimate tensile unit strength u (in N/mm per kg/m² glass) from equation (23).

where

B.3.5 Report. The test report shall include the following:

a) identification of the laminate or laminate layers;

b) conditioning temperature of the test pieces;

c) when necessary, the direction of the major axes of the test specimens in relation to the direction of some feature of the material from which they were cut;

d) whether the faces of the test pieces where machined;

e) ultimate tensile unit strength of the material, reported as the arithmetic mean of the ultimate tensile unit strengths of the test pieces;

f) date of the test.

B.4 Unit modulus of laminate and laminate layers

B.4.1 Principle. The unit modulus shall be calculated from a determination of the tensile force necessary to produce in the test piece an extension of 0.10 mm on a length of 50 mm (0.2 % strain).

B.4.2 Test pieces. The form and number of test pieces shall be as described in BS 2782:Method 1003 for type II and type III specimens.

B.4.3 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing and the test carried out at 20 ± 5 °C.

B.4.4 Procedure. Measure the mean width of the test pieces to the nearest 0.01 mm and count the number of laminate layers.

Clamp the test piece in axial alignment with the direction of pull between the jaws of a suitable tensile testing machine.

Clamp an extensometer on the test piece. The extensometer shall be of a type that will measure extension over a length of 50 ± 1 mm of the test piece to an accuracy of at least 0.0025 mm. Apply a small initial tensioning force f to the test piece for the purpose of straightening it. (This force should be not

greater than 10 % of the expected force at 0.2 % strain.) With this initial force on the test piece, set the indicating device to zero. Increase the force steadily by separating the jaws at a rate of 1 mm/min ± 25 %, until the increase in extension indicated by the extensometer reaches 0.1 mm. Note the force, F, on the test piece at this extension. If the test is also to be used for the determination of ultimate tensile unit strength the extensometer should be removed as quickly as possible and the test continued as required by B.3.

(23)

F_max is the maximum force (in N);

b is the width of test piece (in mm);

n_x is the number of laminate layers in the test piece;

m_x is the mass of glass (in kg/m²) in one layer of laminate in the test piece.

u F_max b n_x m_x

---=

B.4.5 Calculation. Calculate the unit modulus X (in N/mm per kg/m² glass) from equation (24) or (25)

where

In cases where it is expected that 0.2 % strain may give rise to danger of fracture of the test piece, it is permissible to carry out the test at 0.1 % strain (corresponding to an extension of 0.05 mm over a 50 mm gauge length). The initial force shall be correspondingly smaller, and the unit modulus

(in N/mm per kg/m² glass) shall be calculated from equation (26) or (27).

B.4.6 Report. The test report shall include the following:

a) identification of the laminate;

b) conditioning temperature of the test pieces;

c) percentage strain at which the unit modulus was determined;

d) when necessary, the direction of the major axes of the test pieces in relation to the direction of some feature of the material from which they were cut;

e) unit modulus of the material, reported as the arithmetic mean of the unit modulus of the test pieces;

f) individual test results;

g) date of the test.

B.5 Lap shear strength of laminate

B.5.1 Test pieces.Test pieces shall conform to the dimensions and shape given in Figure 13. They shall have a minimum thickness of 3 mm and the overall length of the test pieces may be varied to accommodate the requirements of the available testing equipment. The edges of the test pieces shall be smooth but not rounded or bevelled.

Two parallel saw cuts, one in each opposite face of the test piece and 12.5 mm apart, shall be sawn across the entire width of the test piece and shall be parallel within 0.8 mm (see Figure 13). The depth of saw cuts shall be half laminate thickness plus the thickness of one layer, or half laminate thickness + 0.1, – 0 mm if the number of layers or the thickness per layer is unknown. Saw cuts shall be as narrow as possible.

If the laminate is made entirely from chopped strand mat or by spraying five test pieces shall be tested. If the laminate contains woven rovings or other directional reinforcement 10 test pieces, five parallel with each principal axis of anisotropy, shall be tested.

B.5.2 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.5.3 Procedure. Clamp the test piece in the jaws of the tensile testing machine and axially align the test piece with the direction of pull.

Apply a force to the test piece by separating the jaws at a constant rate of between 5.0 mm/min and 6.5 mm/min.

Record the maximum force at which separation of the layers occurs.

Test pieces that fail prematurely or at an obvious flaw shall be discarded and retests made.

(24)

or (25)

F is the force required to produce 0.2 % strain (in N);

f is the force applied to straighten the test piece initially (in N);

b is the test piece width (in mm);

n_x is the number of laminate layers in the test piece;

m_x is the mass of glass (in kg/m²) in one layer of laminate in the test piece.

(26)

or (27)

X_x F f– 0.002 b n _xm _x

---=

X_LAM F f– 0.002 b

---=

X_x F f– 0.001 b n _xm _x

---=

X_LAM F f– 0.001 b

---=

Licensed copy: Mr. National University Singapore, National University of Singapore, Version correct as of 19/11/2012 08:31, (c) The British Standards Institution 2012

NOTE A shear-type failure with some peeling at the interlaminar bond should result.

B.5.4 Calculation. Calculate the lap shear strength, S_s, for each test piece from equation (28).

where

B.5.5 Report. The test report shall include the following:

a) identification of the laminate;

b) conditioning temperature of the test pieces;

c) lap shear strength of the laminate reported as the arithmetic mean of the lap shear strengths of the test pieces;

d) individual test results;

e) date of the test.

B.6 Shear strength of bond between thermoplastics lining and laminate

B.6.1 Test pieces. The test piece shall be cut from the full thickness of the external laminate and lining and shall be of the form and dimensions shown in Figure 12.

Three test pieces shall be used.

B.6.2 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.6.3 Procedure. Make two thin saw cuts at right angles to the major axis 20 mm apart, symmetrically about the transverse centreline on the test piece. One cut shall be through the full thickness of the thermoplastics material but not into the laminate, the other shall be through the full thickness of the laminate but not into the thermoplastics material.

Measure the cross-sectional area between the saw cuts.

Clamp the test piece in the serrated jaws of a suitable tensile testing machine and axially align with the direction of pull.

Apply a force to the test piece by separating the jaws at a constant rate of 25 ± 6 mm/min.

Record the maximum force at which separation of the layers occurs.

If the test piece breaks other than at the interface and the calculated shear strength is less than that specified in clause 8 the test shall be repeated. If the repeat test fails the bond strength shall be recorded as failed.

B.6.4 Calculation. Calculate the shear strength of the bond from the maximum force and the area under shear and express in N/mm².

B.6.5 Report. The test report shall include the following:

a) identification of the liner/laminate;

b) conditioning temperature of the test pieces;

c) individual test results and the position of failure;

d) date of the test.

B.7 Peel strength of bond between thermoplastics lining and laminate

B.7.1 Test pieces. The test piece shall be cut from the full thickness of the laminate and lining and shall be of the form and dimensions shown in Figure 14.

Five test pieces shall be tested.

B.7.2 Conditioning and temperature of test. Test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.7.3 Procedure. Make a saw cut at one end of the test piece at the interface of the laminate and

thermoplastics material across the width of the test piece and for 20 mm along its length. The saw cut shall (28)

F is the maximum force (in N);

a is the distance between saw cuts (in mm);

b is the width of test piece (in mm).

S_s F ab

---=

Clamp the laminate horizontally in the jaws of a vice or clamp and apply a force to the thermoplastics lining by means of weights until the force is just sufficient to peel the lining from the laminate. During this operation ensure that the plane of the force remains normal to the laminate/thermoplastics interface (see Figure 14).

B.7.4 Calculation. Calculate the peel strength of the bond from the total force at peel and the measured width of the test piece, and express in newtons per millimetre width.

B.7.5 Report. The test report shall include the following:

a) identification of the lining/laminate;

b) conditioning of the test pieces;

c) bond peel strength of the thermoplastics lining/laminate combination reported as the arithmetic mean of the bond peel strengths of the test pieces;

d) individual test results;

e) date of the test.

B.8 Tensile strength of thermoplastics sheet and welds

B.8.1 Test pieces. The test piece from sheet shall be of the shape and dimensions shown in Figure 15 and the full thickness of the sheet.

The test piece of a weld shall be of the shape and dimensions shown in Figure 14.

Three test pieces shall be used for either test.

B.8.2 Conditioning and temperature of test. The test pieces shall be conditioned at 20 ± 5 °C for not less than 3 h immediately before testing. The test shall be carried out at 20 ± 5 °C.

B.8.3 Procedure. Measure the mean width and thickness to the nearest 0.02 mm.

Clamp the test piece at the widened ends or insert plugs if available and mount in the tensile testing machine in axial alignment with the direction of pull. Apply a force to the test piece by separating the grips at a constant rate of 25 ± 6 mm/min until it breaks, the range of the testing machine being such that the maximum force falls between 15 % and 85 % of the maximum scale reading.

B.8.4 Calculation. Calculate the tensile strength, B, for each test piece of the sheet and welded sheet from equation (29).

where

Calculate the arithmetic mean of the three results from each test and express the average value for the welded test pieces as a percentage of the average value for the sheet test pieces.

B.8.5 Report. The test report shall include the following:

a) identification of the thermoplastics sheet;

b) individual results and arithmetic mean of the tensile strength of the sheet;

c) individual results and arithmetic mean of the tensile strength of the weld;

d) percentage tensile strength of the weld compared with that of the sheet;

e) date of the test.

(29)

F is the maximum force (in N);

A is the original cross-sectional area (in mm²).

B F

A

----=

Licensed copy: Mr. National University Singapore, National University of Singapore, Version correct as of 19/11/2012 08:31, (c) The British Standards Institution 2012

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