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

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

Infrared 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

Electrochemically Triggered Pore Expansion in Nanoporous Gold Thin Films

Nanoporous electrode coatings have played a significant role in enhancing the performance of catalysts and sensors. For optimal performance in these applications, the fundamental requirement is a large effective surface area (site at which catalysis and sensing events occur) with unhindered transport of reactants and products to/from the active surface. This necessitates low-density porous electrodes with an interconnected 3D network of thin conductive ligaments to maintain high effective surface area. While the logical approach to create such electrodes is to etch the ligaments uniformly through the entire porous network, accomplishing this has not been trivial. Here, we use nanoporous gold (np-Au) as a model material system to demonstrate an electrochemically triggered etching method for restructuring sputter-deposited submicron np-Au thin films for enlarging the pores with minimal decrease in the effective surface area. We systematically employ time-varying potential waveforms to electrochemically modify morphologies and reveal underlying mechanisms of the etching process. The results suggest that the etch cycle at positive potentials plays a dual role of electrophoretic attraction of chloride ions and initiating the electrochemical etch. The final nanoporous morphology is dictated by a competition between ligament coarsening and ligament thinning, which provide a means to generate a wide range of electrode morphologies

Substrate Topography Guides Pore Morphology Evolution in Nanoporous Gold Thin Films.

This paper illustrates the effect of substrate topography on morphology evolution in nanoporous gold (np-Au) thin films. One micron-high silicon ridges with widths varying between 150 nm to 50 µm were fabricated and coated with 500 nm-thick np-Au films obtained by dealloying sputtered gold-silver alloy films. Analysis of scanning electron micrographs of the np-Au films following dealloying and thermal annealing revealed two distinct regimes where the ratio of film thickness to ridge width determines the morphological evolution of np-Au films

Substrate Topography Guides Pore Morphology Evolution in Nanoporous Gold Thin Films.

This paper illustrates the effect of substrate topography on morphology evolution in nanoporous gold (np-Au) thin films. One micron-high silicon ridges with widths varying between 150 nm to 50 µm were fabricated and coated with 500 nm-thick np-Au films obtained by dealloying sputtered gold-silver alloy films. Analysis of scanning electron micrographs of the np-Au films following dealloying and thermal annealing revealed two distinct regimes where the ratio of film thickness to ridge width determines the morphological evolution of np-Au films