Dynamic impulse and shock loads
Dynamic impulse or shock loads should not be exerted on forklift truck leaf chain as it can impose exceptionally high loads which are above the fatigue endurance limit of leaf chain.
These kinds of loads are induced in forklift truck leaf chain when high velocity movement of the load is followed by sudden abrupt stops. This adverse movement may simply be due to carrying the suspended load over uneven surfaces such as tracks, potholes and other rough ground. Trying to 'inch' loads beyond the rated capacity of leaf chain or lifting mechanism will also cause serious damage to forklift truck leaf chain.
If a leaf chain is often loaded above its fatigue endurance limit, it is more likely to experience premature fatigue cracking. It is not always easy to establish the fatigue endurance limit of forklift truck leaf chain but it will usually be lower than its certified SWL. Typically, forklift truck leaf chains will become worn (elongated) well before fatigue sets in and so it is only when a chain is subjected to continuous impulse loading that fatigue failure occurs.
Fatigue cracks will not necessarily be visible and are caused by periodic on-off loading above the endurance limit of the leaf chain. The factors that determine when fatigue failure will occur include the magnitude of the load, the frequency of its occurrence and the endurance limit of the forklift truck chain. These sorts of cycles and environments make it very difficult to predict forklift truck leaf chain life and it is, therefore, essential that regular inspections are conducted so that leaf chain replacement life can be adequately evaluated.