Design against fatigue

Here is the number of cycles to fracture under the stress cycle in region i, and Nj/Nf is the fraction of the lifetime used up after N, cycles in that region. Failure occurs when the sum of the fractions is unity (eqn. (15.4)). This rule, too, is an empirical one. It is widely used in design against fatigue failure but if the component is a critical one. Miner s Rule should be checked by tests simulating service conditions. 

While laboratory measurements of growth rates of single delaminations firom starter defects are valuable to characterise intrinsic material behaviour under well-defined conditions, delamination growth from impact damage is a more realistic if a more complex situation and its characterisation is vital to design against fatigue in composite aircraft stmctures. 

Heywood, R.B. Designing against Fatigue. Chapman and Hall, London (1962)... 

Design against fatigue failure requires thorough education and experience in structural engineering, mechanical engineering, and materials science [21]. This subject is beyond the objectives of this book. To... 

Bonded-bolted joints have good load distribution and are generally designed so that the bolts take all the load. Then, the bolts would take all the load after the bond breaks (because the bolts do not receive load until the bond slips). The bond provides a change in failure mode and a sizable margin against fatigue failure. 

The damage-resistant structure designing against impact and fatigue... 

Face-centred cubic metals and hardened steels do not have a true fatigue limit S-N curve of type II, figure 10.19(b)). At a number of cycles beyond 10, the slope of the S-N curve is rather small and a limiting number of cycles of A b = 10 to 10 can be used to design safely against fatigue [130]. 

ESDU 86025 - Bonded Joints Considerations in design against acoustic fatigue. 

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