ISO 18592:2009 specifies test specimens and procedures for performing constant load amplitude fatigue tests on multi-spot-welded and multi-axial specimens in the thickness range from 0,5 mm to 5 mm at room temperature and a relative humidity of max. 80 %. The applicability of ISO 18592:2009 to larger thicknesses can be limited by mechanical properties such as yield strength and formability of the specimen material. The thickness range for advanced high strength steels (AHSs) is generally below 3,0 mm. Greater thicknesses apply for aluminium alloys, for example.
Depending on the specimen used, it is possible from the results to evaluate the fatigue behaviour of: a) spot welds subjected to defined uniform load distribution; b) spot welds subjected to defined non-uniform load distribution; c) spot welds subjected to different defined combinations of shear-, peel-and normal-tension loads; and d) the tested specimen.
Multi-spot specimens with which the different load distributions can be realized are: 1) defined uniform load distribution; 2) defined non-uniform load distribution; 3) defined combinations of shear-, peel- and normal-tension loads; 4) spot welds subjected to undefined non-uniform load distribution.
The specimens and tests referred to under 4) are not dealt with further in ISO 18592:2009, because the results obtained with these specimens are specific to the components as tested and may not be generalized or used for deriving data pertaining to the load-carrying behaviour of the welds. Results obtained with such tests are suitable for comparing the mechanical properties of the tested components with those of similar components tested in the same manner. These tests are, however, not suitable for evaluating or comparing the load-carrying properties of the welds.
The test results of the fatigue tests obtained with component like specimens are suitable for deriving criteria for the selection of materials and thickness combinations for structures and components subjected to cyclic loading. This statement is especially relevant for results obtained with specimens with boundary conditions, i.e. a local stiffness similar to that of the structure in question. The results of a fatigue test are suitable for direct application to design only when the loading conditions in service and the stiffness of the design in the joint area are identical.