Philippe Marguerès

Space-resolved diffusing wave spectroscopy measurements of the macroscopic deformation and the microscopic dynamics in tensile strain tests

We couple a laser-based, space-resolved dynamic light scattering apparatus to a universal testing machine for mechanical extensional tests. We perform simultaneous optical and mechanical measurements on polyether ether ketone, a semi-crystalline polymer widely used in the industry. Due to the high turbidity of the sample, light is multiply scattered by the sample and the diffusing wave spectroscopy (DWS) formalism is used to interpret the data. Space-resolved DWS yields spatial maps of the sample strain and of the microscopic dynamics. An excellent agreement is found between the strain maps thus obtained and those measured by a conventional stereo-correlation bench. The microscopic dynamics reveals both affine motion and plastic rearrangements. Thanks to the extreme sensitivity of DWS to displacements as small as 1 nm, plastic activity and its spatial localization can be detected at an early stage of the sample deformation, making the technique presented here a valuable complement to existing material characterization methods.

Damage of woven composite under tensile and shear stress using infrared thermography and micrographic cuts

AbstractInfrared thermography was used to study damage developing in woven fabrics. Two different experiments were performed, a ±45° tensile test and a rail shear test. These two different types of tests show different damage scenarios, even if the shear stress/strain curves are similar. The ±45° tension test shows matrix hardening and matrix cracking whereas the rail shear test shows only matrix hardening. The infrared thermography was used to perform an energy balance, which enabled the visualization of the portion of dissipated energy caused by matrix cracking. The results showed that when the resin is subjected to pure shear, a larger amount of energy is stored by the material, whereas when the resin is subjected to hydrostatic pressure, the main part of mechanical energy is dissipated as heat.

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

This 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).

Combined Approach for the Characterization of Composites Manufactured by RFI and Industrial Application

A combined approach is proposed here to characterize composite structures made of a recent semi-preg called HexFIT® developed by Hexcel Composites® for resin film infusion (RFI). Physicochemical and mechanical tests were first carried out on specimens obtained by oven cured vacuum bag molding and then compared with autoclave cured specimens. Non-destructive evaluation techniques (US, IR, and RX) were used to sample specimens in manufactured plates for mechanical testing taking into account the effects of the process conditions. Multi-instrumented tensile tests undertaken on specimens with different widths allowed us to highlight limitations in classical tensile tests. The manufacture of a structural part called corner fitting is also presented taking into account the effects of the stacking sequence and the cure cycle. The preliminary results highlight the need to correctly define experimental protocols taking into account manufacture conditions and the inner architecture of the reinforcements.

Impédancemétrie électrique pour le monitoring de composites carbone/époxy

This article concerns the electrical characterization of T700/M21 unidirectional composite materials during the cure with sensors developed for the purpose. It proposes a reliable and reproducible protocol for the characterization of the material during curing. An analysis is carried out to assess the impact of parasitic access elements, which is 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. The use of electrical impedance spectral analysis allows in-situ monitoring of the curing process. The results obtained are compared with those of a rheological analysis of the same material and highlight the value of the proposed protocol.