In this paper, the loading path effect on the elastic-plastic crack-front stress field in a thin plate is investigated. There different loading sequences include one proportional loading and two non-proportional loading paths are applied to the 3-D modified boundary layer (MBL) model under small-scale yielding conditions. For the same external displacement field applied at the outer boundary of the 3-D MBL model, the mode I K field and T-stress field combined as the different loading path is applied to investigate the influence of the nonproportional loading. The results show that for either the compressive or tensional T-stress, the loading path which applied K field followed by T field generates the lower crack-tip constraint. There is only slightly difference between the proportional loading path and the T-stress field following by K field loading path. The results show that it is very important to include the load sequence effects in fracture analysis when dealing with nonproportional loading conditions.

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