Double Shear figures serve mainly to compare the relative strengths of different types of pin, or different diameters of the same type of pin. The conditions prevailing in a given application usually differ from test conditions. The test itself is carried out according to ISO 8749 and records the maximum load the pin will withstand before fracture. In practise, manufacturers’ figures provide the minimum load without any safety margin.
It is important to note that figures given based on testing to ISO 8749 do not allow for the effect of dynamic (shock) loads or bending moments. Specifically the test stipulates the following restrictions: -
- The clearance between the two pieces of the test block must not exceed 0.15 mm in order to maintain a straight line of shear. This is important in that in an assembly where the holes in the mating components are deeply countersunk, (even if the components themselves are flush) there will not be a straight line of shear and the resulting bending moment will reduce the shear strength.
- The shear planes must be at least one pin diameter from the end of the pin, and at least two diameters apart.
- The load must not be applied at a rate in excess of 13mm/min. In other words this is a test for static shear loads, not dynamic.
Consequently shear figures are a design guideline and not a guarantee of performance. The figures given elsewhere in this catalogue are for double shear applications. Where a pin is used in single shear, the values should be halved.
Where an engineering application includes conditions that are not covered by the ISO 8749 test, the following guidelines may be used.
- Where there are dynamic loads, a coiled pin will perform better due to its shock-absorbing features.
- Where there is a bending moment of some significance a hardened solid pin is preferable, either through hardened for maximum shear strength or case hardened where less shear strength but more resistance to bending moments is required.
- Where there is a high level of vibration, a grooved pin will have the maximum retention provided it is of the full-length parallel grooved type (DIN 1473).