Damage analysis and fracture toughness evaluation in a thin woven composite laminate under static tension using infrared thermography

This work deals with the issue of damage growth in thin woven composite laminates subjected to tensile loading. The conducted tensile tests were monitored on-line with an infrared camera, and tested specimens were analysed using Scanning Electron Microscopy (SEM). Combined with SEM micrographs, observation of heat source fields enabled us to assess the damage sequence. Transverse weft cracking was confirmed to be the main damage mode and fiber breakage was the final damage leading to failure. For cracks which induce little variation of specimen stiffness, the classic “Compliance method” could not be used to compute energy release rate. Hence, we present here a new procedure based on the estimation of heat source fields to calculate the energy release rate associated with transverse weft cracking. The results are then compared to those computed with a simple 3D inverse model of the heat diffusion problem and those presented in the literature

Preliminary experimental study on the electrical impedance analysis for in-situ monitoring of the curing of carbon/epoxy composite material for aeronautical and aerospace structures

International audienceThis paper concerns the electrical characterization of T700/M21 unidirectional composite materials using sensors developed specifically for this study. It proposes a reliable and reproducible protocol for the characterization of the material during curing. Prior to the characterization, an analysis was carried out to assess the impact of parasitic access elements (resistance of the electrode/fibre interface or of the feed wire), which was reduced to a minimum by appropriate dimensioning of the electrodes. A study of the electrical conduction in relation to the direction of the fibres made it possible to establish a suitable approach to homogenized measurement of the material. Thermo-electric coupling by self-heating was also evaluated, with a view to obtaining measurements that were not influenced by this phenomenon. Finally, the use of electrical impedance spectral analysis allowed in-situ monitoring of the curing process. The results obtained are compared with those of a rheological analysis of the same material. These results highlight the value of the proposed protocol and demonstrate that, with the aid of these sensors, complete automation of the manufacturing process of composite structures is feasible (optimization of the cure cycle by real-time automatic control)