An experimental verification of numerical models for the fracture and fatigue of welded structures

Abstract

By allowing a more detailed analysis, numerical modelling has an important role to play in the development of structures. However, the results of a numerical model's analysis have to be verified with an experimental analysis for the application. Two full-scale welded-structure tests were used for the verification of the proposed numerical models. In the first case a pressure vessel pre-cracked in weld metal and instrumented for a J-integral measurement was tested. In this way the crack's driving force, expressed as the J integral, could be determined directly. The crack's driving force was calculated by applying the Ratwani-Erdogan-Irwin (REI) numerical model. The experimental results were compared to the values obtained with the REI model. In was shown that the application of the model produces conservative results and that the model can be applied for a structural integrity assessment of cracked pressure vessels. The second case was the welded structure of a rotor excavator. The critical welded components were modelled in full scale. The loading was recorded with strain gauges at critical locations, analyzed and elaborated in the form of the stress spectrum applied in the testing. The experimental results were compared to those obtained with numerical models. The comparison revealed that the model significantly overestimates the real cycle number for the fatigue limit. These two examples clearly demonstrated the complexity of the problem. In the case of the pressure vessel the model results are conservative, while those obtained for the fatigue are too optimistic.