ANALYSIS OF ULTRA LOW CYCLE FATIGUE PROBLEMS WITH THE BARCELONA PLASTIC DAMAGE MODEL

X. MARTINEZ; S. OLLER; L. BARBU; A. BARBAT

Conferencia; XII International Conference on Computational Plasticity. Fundamentals and Applications COMPLAS XII; 2013

Ultra Low Cycle Fatigue (ULCF) takes place for a reduced number of cycles, usually lessthan 1000 and often less than 100. Contrary to what occurs with high cycle fatigue, in thisfailure mechanism plasticity plays an important role. The most common procedures used tosimulate ULCF are those based on counting the number of cycles that can be applied to thematerial for a given plastic strain. Examples of those approaches are the Coffin-Manson rule[3], the Basquin rule [3], or the enhanced rule proposed by Xue in [4]. However, one of themain drawbacks of these formulations is that they require of regular cycles to predict thematerial failure, and often this regularity does not exist. An example of an ULCF failure dueto an irregular cyclic load is found in the failure of large diameter pipes subjected to seismicloads, where the frequency varies along time and each cycle may have different amplitude.Current work proposes the use of a plastic damage model to simulate Ultra Low CycleFatigue. The model developed is based in the Barcelona model originally formulated byLubliner et al. [1]. Although this model was originally developed for concrete, here ispresented a new kinematic and isotropic hardening law specifically defined for the simulation of steel. One of the main characteristics of the model is that the hardening behaviour of the material is driven by the plastic energy dissipated. With this approach, it is possible to measure the energy required in each hysteresis cycle, as well as the available energy remaining on the material. Failure takes place when all the plastic fracture energy of the material has been dissipated.This paper shows that with the proposed model it is possible to simulate an ULCF failureby calibrating the available plastic energy of the material. One of the main advantages of theproposed procedure is that it is capable of predicting the material failure independently of the number of cycles applied to the structure, as well as the amplitude and frequency of those cycles. This is because the model is based on the actual loading history of the structure, being this loading history as random as needed. Therefore, it is possible to simulate the material failure produced by ULCF in a seismic event, or on any other cyclic load scenario. Besides, the formulation is capable of using any yield and potential surfaces to characterize the material, which increases its applicability to different steel alloys.