Engineering Critical Analyses (ECAs) use the principles of fracture mechanics to determine the defect tolerance of structures. ECA methods have been standardised in codes like BS 7910:2005. This code was based upon the expertise developed at TWI using wide plate and fatigue test results combined with analytical methods to define safe assessment procedures. BS 7910 is used widely, but modelling techniques are sometimes needed to augment the standardised methods. TWI uses Finite Element Analysis (FEA) to determine the crack loading and collapse loads of cracked structures undergoing complex modes of loading.
There are standardised methods for ECA and these are now used routinely by the petrochemical and power industries to determine the safety of their structures. Recent interest has been directed towards greater accuracy through the removal of the conservatisms in assumed toughnesses and in the distributions of residual stresses. TWI uses FEA to determine crack tip constraint in test specimens and for cracks in structures to determine whether lower constraint specimens can be used to measure toughness. FEA is also used to make predictions of welding residual stresses and to use the predicted distributions for assessment of their contributions to crack tip loading. There is also considerable interest from the Oil and Gas sector in Strain Based Design (SBD), where ECA is being used to assess structures where the nominal strains in some regions exceed the yield strain.
TWI has a unique combination of skills, facilities and corporate knowledge which means that a prompt and accurate response is given to fracture related problems. TWI fracture mechanics experts have both a working knowledge of the ECA codes and a considerable insight into the theoretical basis of the codes. This means that non-standard procedures based upon the methods of the codes are sometimes used. FEA can be done to provide additional analytical results for the development of advanced ECA techniques.
TWI regularly contributes to outcomes which provide customers with considerable cost savings based upon the ability to make accurate assessments of structural integrity. Customers can also be confident that remedial actions are needed when outcomes are less favourable.
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