A test device for damage characterisation of composites based on in situ computed tomography

For engineering design of composites, suitable damage models are required which have to predict the onset of damage, the successive failure and the subsequent reduction of the mechanical properties. To verify existing modelling approaches, the clear experimental identification of the particular damage entities is an essential condition. However, due to the complexity of the failure mechanisms of novel materials like heterogeneous textile composites, a comprehensive damage analysis is still a challenging problem. Recent progress in the field of computed tomography enables in situ measurements to detect damage phenomena in composites under loading. The article describes such a novel test device that combines an integrated testing machine with a high precision computer tomograph. The in situ method was used to study the damage evolution in carbon fibre reinforced plastics (CFRPs) made of weft knitted and woven preforms. A special focus was set to damage processes under loading in thickness direction. For this purpose, cylindrical tensile specimens according to ASTM D 7291 were manufactured and tested. Compression specimens with different aspect ratios have been used to study the compressive failure of CFRP woven composites. The experimental results are discussed with respect to the possibilities and limitations of the in situ based test method.