HEAT – High resolution detection of temperature distribution at cracktips of Amorphous Thermoplastics

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The influence of temperature plays an important role in thecharacterization of polymers and plastics. The intrinsic heating duringmechanical loading has not been considered yet. Knowing the precisethermal behaviour under loading enables to draw conclusions on themolecular processes and to formulate dependent fracture dynamics. Itis not unreasonable to believe that crack growth is inhibited bysoftening processes or supported by decomposition. For this, on onehand, the maximum temperature rise is of great importance and onthe other hand the temporal and spatial distribution of the heat plays asignificant role. Both can now be measured with state-of-the-artthermal imaging equipment and predicted with molecular dynamicstructural simulation. Energy release during fracture has been ofmuch interest in the past. However it was so far impossible todetermine satisfactorily. Microscopic softening or even meltingprocesses at the crack tip are realistic scenarios. They wouldinfluence the fracture properties and damage tolerance of plastics in away that has not been considered yet during part design. The relationof toughness, strain rate and crack growth would have to be revisitedcompletely and the material models would need to be updated. In thisproject this topic will be addressed and new approaches with temporalultrahigh resolution measurement and simulation tools are suggested.A temporal resolution that can resolve and relate the fracture processand the corresponding effects and mechanisms is needed for precisetemperature determination along a growing crack front. Therefore aspatial resolution in the lower μm range is necessary that visualizeselastic, plastic and open areas as well as different energy releasingfracture characteristics. With novel thermal imaging cameras this isnow possible. Simultaneously numerical investigations will beperformed, which on the one hand will reveal the mechanisms on the molecular level that are responsible for e.g. crack tip heating or acoustic emission. On the other hand by utilizing the well-establishedfinite element method real sized specimens will be simulated takinginto account experimental results as well as the nanoscalesimulations and thereby integrating thermal and acoustic effects intothe damage model. The knowledge acquired in this project can leadto a fundamental rethinking of previous fracture models and thusimproves the interpretation and prediction of damage of plastic parts.