Without prejudice to the prescript of can. 1643, a res iudicata occurs: 1/ if a second concordant sentence is rendered between the same parties over the same issue and on the same cause for petitioning; 2/ if an appeal against the sentence has not been introduced within the useful time; 3/ if at the appellate grade, the trial has been abated or renounced; 4/ if a definitive sentence has been rendered from which there is no appeal according to the norm of can. 1629.
Source: Code of Canon Law (Vatican.va)