Section 4 Aluminium/steel transition joints

4.1.1 Provision is made in this Section for explosion bonded composite aluminium/steel transition joints used for connecting aluminium structures to steel plating.

4.1.2 Each individual application is to be separately approved as required by the relevant Rules dealing with design and construction.

4.2.1 Transition joints are to be manufactured by an approved producer in accordance with an approved specification which is to include the maximum temperature allowable at the interface during welding.

4.2.2 The aluminium material is to comply with the requirements of Ch 8, 1 Plates, bars and sections and the steel is to be of an appropriate grade complying with the requirements of Ch 3, 2 Normal strength steels for ship and other structural applications.

4.2.3 Alternative materials which comply with International, National or proprietary specifications may be accepted provided that they give reasonable equivalence to the requirements of Ch 8, 4.2 Manufacture 4.2.2 or are approved for a specific application.

4.2.4 Intermediate layers between the aluminium and steel may be used, in which case the material of any such layer is to be specified by the manufacturer and is to be recorded in the approval certificate. Any such intermediate layer is then to be used in all production transition joints.

4.3.1 Each composite plate is to be subjected to 100 per cent visual and ultrasonic examination in accordance with a relevant National Standard to determine the extent of any unbonded areas. Unbonded areas are unacceptable and any such area plus 25 mm of surrounding sound material is to be discarded.

4.4.1 Two shear test specimens and two tensile test specimens are to be taken from each end of each composite plate for tests to be made on the bond strength. One shear and one tensile test specimen from each end are to be tested at ambient temperature after heating to the maximum allowable interface temperature, see Ch 8, 4.2 Manufacture 4.2.1; the other two specimens are to be tested without heat treatment.

4.4.2 Shear tests may be made on a specimen as shown in Figure 8.4.1 Specimen and procedure for shear tests or an appropriate equivalent. Tensile tests may be made across the interface by welding extension pieces to each surface or by the ram method shown in Figure 8.4.2 Ram tensile test or by an appropriate alternative method.

Figure 8.4.1 Specimen and procedure for shear tests

4.4.3 The shear and tensile strengths of all the test specimens are to comply with the requirements of the manufacturing specification.

4.4.4 If either the shear or tensile strength of the bond is less than the specified minimum but not less than 70 per cent of the specified minimum, two additional shear and two tensile test specimens from each end of the composite plate are to be tested and, in addition, bend tests as described in Ch 8, 4.4 Mechanical tests 4.4.6 and Table 8.4.1 Bend tests on explosion bonded aluminium/steel composites are to be made.

Figure 8.4.2 Ram tensile test

4.4.5 If either the shear or tensile strength of the bond is less than 70 per cent of the specified minimum the cause is to be investigated. After evaluation of the results of this investigation, LR will consider the extent of composite plate which is to be rejected.

4.4.6 Bend tests, when required, are to be made under the following conditions, as listed in Table 8.4.1 Bend tests on explosion bonded aluminium/steel composites:

1. The aluminium plate is in tension.

2. The steel plate is in tension.

3. A side bend is applied.

4.5.1 Each acceptable transition strip is to be clearly marked with the following particulars:

1. LR or Clasifications Register and the abbreviated name of LR's local office.

2. Manufacturer's name or trade mark.

3. Identification mark for the grade of aluminium.

4. Identification mark for the grade of steel.

The particulars are to be stamped on the aluminium surface at one end of the strip.

4.6.1 A manufacturer’s certificate validated by LR is to be issued (see Ch 1, 3.1 General) and as a minimum is to include the following particulars:

1. Purchaser's name and order number.

2. The contract number for which the material is intended, if known.

3. Address to which the material is dispatched.

4. Description and dimensions of the material.

5. Specifications or grades of both the aluminium alloy and the steel and any intermediate layer.

6. Cast numbers of the steel and aluminium plates.

7. Identification number of the composite plate.

8. Mechanical test results (not required on shipping statement).