Assessment of the reference stress method for J-integral estimation of cracked riveted beams of an old wrought iron

This work deals with the application of the reference stress method to estimate the J-integral of cracked riveted beams of old puddle iron. The ductility of some of these materials makes it necessary to use elasto-plastic fracture criteria to assess damage tolerance. This requires a high computational effort, since it involves the determination of the J-integral in beams with plates and angles that interact by means of redundant forces dependent on crack size. The J-integral estimation method based on the reference stress could reduce this effort, provided it were shown to be valid for this type of beam. This work contributes to this end by comparing the J-integral values resultant from the reference stress method and a complete finite element modelling of a riveted beam consisting of two angles and a cracked plate made of actual puddle iron from a road bridge more than a century old but still in service. A number of samples removed from the bridge showed that this material failed in a ductile manner when it was fracture tested with fatigue precracked compact specimens, even at temperatures as low as −20 °C. The two types of J-integral values found are compared over the ranges of load and crack size explored.