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Self-monitoring composites: visualisation of impacts

News International-French

22 Feb 2013

JEC Europe 2013 - Non-destructive testing methods for fibre-reinforced composites with an epoxy matrix are very costly and require complex equipment.

A bio-inspired sensitive composite layer based on a structural fabric containing microcapsules with a leuco dye, developer particles and a polymer matrix was developed for these substrate materials. Any mechanical action (indentation, impact, etc.) critical for the substrate material integrity causes mechanical overstrain of the microcapsules dispersed in the matrix, so that the capsules break and release the dye. The dye comes into chemical contact with the colour developer via microcracks. Upon chemical transformation, the dye changes colour, highlighting the area subjected to overstrains.

The composite layer gives a visual response in the form of a "bruise", indicating a place of possible damage of the substrate material. The construction elements or finished goods incorporating the bruisable composite layer can be inspected continuously. For example, a safety helmet with glued strips of bruisable layer is represented in the picture. The dark bruise is the response of the layer to a 5-kg beam dropped from a height of 0.5m.

Using this system, parts that have suffered critical mechanical action can be timely replaced or repaired. In some cases, this can reduce the necessary safety margin and save weight while improving the safety of existing structures. The use of a bruisable layer in structural health monitoring processes is a solution which will save time and money.

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