Plastic failure risk of a metal matrix composite structure under variable thermal loads

In the heat sink components reinforced with fibrous metal matrix composites under cyclic heat flux loads; their structural reliability is frequently limited by the low cycle fatigue of the composites. The stress evolution in the composites becomes complex. In order to investigate the plastic failure risk of the composites, the stress evolution has to be tracked on different length scales. In addition, a proper criterion of plastic failure is needed for the relevant composite geometry and loads. In this work, a computational methodology is presented to estimate the plastic failure risk of a composite heat sink structure. This method was based on a triple scale non-linear finite element analysis and a shakedown theorem. Average lamina stresses were assessed using a micro-mechanics based constitutive law and compared with a shakedown boundary predicted by a direct shakedown analysis. By this comparison both the critical locations and the relative failure risk at each lamina could be identified. A remarkable merit of the current approach was that the computational costs could be enormously reduced by the two employed numerical techniques.