Infrared thermography to evaluate impact damage in glass/epoxy with manufacturing defects

• Infrared thermography is used for monitoring impact events.
• Infrared detectors sense even slighter heat dissipated through low impact energy.
• Thermographic images allow for determination of damage extension.
• The visualized warm area matches the damaged area.
• A link between impact damage and manufacturing defects is established with lockin thermography.

The capability of an infrared imaging device to visualize the thermal effects, which develop in composites under low energy impact, was recently demonstrated by Meola and Carlomagno. The current aim is now to go on in the investigation of the behaviour of a glass fibre reinforced polymer under low energy impact with particular attention to the influence of fibres orientation and manufacturing defects. Several specimens are fabricated by the hand-layup technique and cured at ambient conditions to enable formation of porosity. Such specimens are impacted with a Charpy pendulum, which allows enough room for positioning of the infrared camera to see the specimen surface opposite to the impact and to record onset and evolution of thermal signatures. The material conditions before and after impact are non-destructively checked with lockin thermography. As a main finding, manufacturing defects, like porosity and fibres misalignment, seem to play a key role in the generation and evolution of thermal signatures, which bear witness for initiation and propagation of impact damage. The obtained results show how the use of an infrared imaging device may be useful in understanding impact damaging mechanisms and establishing the delamination threshold load.